Chapter 5Link Layer

slides are modified from J Kurose amp K Ross

CPE 400 600Computer Communication Networks

Lecture 23

DataLink Layer 2

Ethernet bus topology popular through mid 90s

all nodes in same collision domain (can collide with each other)

today star topology prevails active switch in center each ldquospokerdquo runs a (separate) Ethernet protocol (nodes

do not collide with each other)

bus coaxial cable

switch

star

DataLink Layer 3

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock

rates

DataLink Layer 4

Ethernet Frame Structure (more) Addresses 6 bytes

if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol

otherwise adapter discards frame

Type indicates higher layer protocol (mostly IP but others possible eg Novell IPX AppleTalk)

CRC checked at receiver if error is detected frame is dropped

DataLink Layer 5

Ethernet CSMACD algorithm1 NIC receives datagram from network layer creates

frame

2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 2

Ethernet bus topology popular through mid 90s

all nodes in same collision domain (can collide with each other)

today star topology prevails active switch in center each ldquospokerdquo runs a (separate) Ethernet protocol (nodes

do not collide with each other)

bus coaxial cable

switch

star

DataLink Layer 3

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock

rates

DataLink Layer 4

Ethernet Frame Structure (more) Addresses 6 bytes

if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol

otherwise adapter discards frame

Type indicates higher layer protocol (mostly IP but others possible eg Novell IPX AppleTalk)

CRC checked at receiver if error is detected frame is dropped

DataLink Layer 5

Ethernet CSMACD algorithm1 NIC receives datagram from network layer creates

frame

2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 3

Ethernet Frame Structure

Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame

Preamble 7 bytes with pattern 10101010 followed by one

byte with pattern 10101011 used to synchronize receiver sender clock

rates

DataLink Layer 4

Ethernet Frame Structure (more) Addresses 6 bytes

if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol

otherwise adapter discards frame

Type indicates higher layer protocol (mostly IP but others possible eg Novell IPX AppleTalk)

CRC checked at receiver if error is detected frame is dropped

DataLink Layer 5

Ethernet CSMACD algorithm1 NIC receives datagram from network layer creates

frame

2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 4

Ethernet Frame Structure (more) Addresses 6 bytes

if adapter receives frame with matching destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol

otherwise adapter discards frame

Type indicates higher layer protocol (mostly IP but others possible eg Novell IPX AppleTalk)

CRC checked at receiver if error is detected frame is dropped

DataLink Layer 5

Ethernet CSMACD algorithm1 NIC receives datagram from network layer creates

frame

2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 5

Ethernet CSMACD algorithm1 NIC receives datagram from network layer creates

frame

2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 6

CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN

ttrans = time to transmit max-size frame

efficiency goes to 1 as tprop goes to 0

as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

transprop ttefficiency

51

1

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 7

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standards common MAC protocol and frame format

different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bps

different physical layer media fiber cable

application

transport

network

link

physical

MAC protocoland frame format

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 8

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rate all nodes connected to hub can collide with one another no frame buffering no CSMACD at hub host NICs detect collisions

twisted pair

hub

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 9

Switch link-layer device smarter than hubs take active

role store forward Ethernet frames examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

transparent hosts are unaware of presence of switches

plug-and-play self-learning switches do not need to be configured

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 10

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

switches buffer packets Ethernet protocol used on

each incoming link but no collisions full duplex each link is its own collision

domain

switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions not possible with dumb hub

A

Arsquo

B

Brsquo

C

Crsquo

switch with six interfaces(123456)

1 23

45

6

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 11

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host

2 index switch table using MAC dest address

3 if entry found for destination then

if dest on segment from which frame arrived then drop the frame

else forward the frame on interface indicated

else floodforward on all but the interface on which the frame arrived

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 12

Self-learning forwarding example A

Arsquo

B

Brsquo

C

Crsquo

1 23

45

6

A Arsquo

Source ADest Arsquo

MAC addr interface TTL

Switch table (initially empty)

A 1 60

A ArsquoA ArsquoA ArsquoA ArsquoA Arsquo

frame destination unknown flood

Arsquo A

destination A location known

Arsquo 4 60

selective send

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 13

Interconnecting switches

switches can be connected together

A

B

Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3

A self learning (works exactly the same as in single-switch case)

S1

C D

E

FS2

S4

S3

H

I

G

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 14

Switches vs Routers both store-and-forward devices

routers network layer devices (examine network layer headers)

switches are link layer devices

routers maintain routing tables implement routing algorithms

switches maintain switch tables implement filtering learning algorithms

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 15

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 16

Point to Point Data Link Control one sender one receiver one link easier than

broadcast link no Media Access Control no need for explicit MAC addressing eg dialup link ISDN line

popular point-to-point DLC protocols PPP (point-to-point protocol) HDLC High level data link control (Data link

used to be considered ldquohigh layerrdquo in protocol stack)

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 17

PPP Design Requirements [RFC 1557] packet framing encapsulation of network-layer

datagram in data link frame carry network layer data of any network layer

protocol (not just IP) at same time ability to demultiplex upwards

bit transparency must carry any bit pattern in the data field

error detection (no correction)

connection liveness detect signal link failure to network layer

network layer address negotiation endpoint can learnconfigure each otherrsquos network address

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 18

PPP non-requirements

no error correctionrecovery

no flow control

out of order delivery OK

no need to support multipoint links (eg polling)

Error recovery flow control data re-ordering all relegated to higher layers

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 19

PPP Data Frame Flag delimiter (framing)

Address does nothing (only one option)

Control does nothing in the future possible multiple control fields

Protocol upper layer protocol to which frame delivered (eg IP PPP-LCP IPCP etc)

info upper layer data being carried

check cyclic redundancy check for error detection

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 20

Byte Stuffing ldquodata transparencyrdquo requirement data field must

be allowed to include flag pattern lt01111110gt

Q is received lt01111110gt data or flag

Sender adds (ldquostuffsrdquo) special control escape lt01111101gt byte before each lt01111110gt data byte

Receiver 01111101 discard control escape byte continue data reception

Q what if data contains lt01111101gt add extra lt01111101gt byte before each

lt01111101gt data byte

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 21

Byte Stuffing

flag bytepatternin datato send

flag byte pattern plusstuffed byte in transmitted data

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 22

PPP Data Control ProtocolBefore exchanging network-

layer data data link peers must

configure PPP link (max frame length authentication)

learnconfigure network layer information for IP carry IP Control

Protocol (IPCP) msgs (protocol field 8021) to configurelearn IP address

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 23

Lecture 23 Outline

55 Ethernet

56 Link-layer switches

57 Point to Point Protocol

58 Link Virtualization ATM MPLS

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 24

Virtualization of networks

Virtualization of resources powerful abstraction in systems engineering

computing examples virtual memory virtual devices Virtual machines eg java IBM VM os from 1960rsquos70rsquos

layering of abstractions donrsquot sweat the details of the lower layer only deal with lower layers abstractly

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 25

The Internet virtualizing networks

1974 multiple unconnected nets ARPAnet data-over-cable networks packet satellite network (Aloha) packet radio network

hellip differing in addressing conventions packet formats error recovery routing

ARPAnet satellite net

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 26

The Internet virtualizing networks

ARPAnet satellite net

gateway

Internetwork layer (IP) addressing internetwork

appears as single uniform entity despite underlying local network heterogeneity

network of networks

Gateway ldquoembed internetwork

packets in local packet format or extract themrdquo

route (at internetwork level) to next gateway

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 27

Cerf amp Kahnrsquos Internetwork ArchitectureWhat is virtualized two layers of addressing internetwork and local

network new layer (IP) makes everything homogeneous at

internetwork layer underlying local network technology

cable satellite telephone modem today ATM MPLS

hellip ldquoinvisiblerdquo at internetwork layer Looks like a link layer technology to IP

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 28

ATM and MPLS

ATM MPLS separate networks in their own right different service models addressing routing

from Internet

viewed by Internet as logical link connecting IP routers just like dialup link is really part of separate

network (telephone network)

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 29

Asynchronous Transfer Mode ATM 1990rsquos00 standard for high-speed (155Mbps

to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture

Goal integrated end-end transport of carry voice video data meeting timingQoS requirements of voice

video (versus Internet best-effort model) ldquonext generationrdquo telephony technical roots in

telephone world packet-switching (fixed length packets called

ldquocellsrdquo) using virtual circuits

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 30

ATM architecture

adaptation layer only at edge of ATM network data segmentationreassembly roughly analagous to Internet transport layer

ATM layer ldquonetworkrdquo layer cell switching routing

physical layer

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 31

ATM network or link layerVision end-to-end

transport ldquoATM from desktop to desktoprdquo ATM is a network

technology

Reality used to connect IP backbone routers ldquoIP over ATMrdquo ATM as switched link

layer connecting IP routers

ATMnetwork

IPnetwork

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 32

ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL) ldquoadaptsrdquo upper

layers (IP or native ATM applications) to ATM layer below

AAL present only in end systems not in switches

AAL layer segment (headertrailer fields data) fragmented across multiple ATM cells analogy TCP segment in many IP packets

physical

ATM

AAL

physical

ATM

AAL

physical

ATM

physical

ATM

end system end systemswitch switch

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 33

ATM Adaptation Layer (AAL) [more] Different versions of AAL layers depending on ATM

service class AAL1 for CBR (Constant Bit Rate) services eg circuit

emulation

AAL2 for VBR (Variable Bit Rate) services eg MPEG video

AAL5 for data (eg IP datagrams)

AAL PDU

ATM cell

User data

small payload -gt short cell-creation delay for digitized

voice

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 34

ATM LayerService transport cells across ATM network

analogous to IP network layer

very different services than IP network layer

NetworkArchitecture

Internet

ATM

ATM

ATM

ATM

ServiceModel

best effort

CBR

VBR

ABR

UBR

Bandwidth

none

constantrateguaranteedrateguaranteed minimumnone

Loss

no

yes

yes

no

no

Order

no

yes

yes

yes

yes

Timing

no

yes

yes

no

no

Congestionfeedback

no (inferredvia loss)nocongestionnocongestionyes

no

Guarantees

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 35

ATM Layer Virtual Circuits VC transport cells carried on VC from source to

dest call setup teardown for each call before data can flow each packet carries VC identifier (not destination ID) every switch on source-dest path maintain ldquostaterdquo for

each passing connection linkswitch resources (bandwidth buffers) may be

allocated to VC to get circuit-like perf

Permanent VCs (PVCs) long lasting connections typically ldquopermanentrdquo route between to IP routers

Switched VCs (SVC) dynamically set up on per-call basis

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 36

ATM VCs

Advantages of ATM VC approach

QoS performance guarantee for connection mapped to VC (bandwidth delay delay jitter)

Drawbacks of ATM VC approach

Inefficient support of datagram traffic

one PVC between each sourcedest pair) does not scale (N2 connections needed)

SVC introduces call setup latency processing overhead for short lived connections

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 37

ATM cell header

5-byte ATM cell header

VCI virtual channel ID will change from link to link thru net

PT Payload type (eg RM cell versus data cell)

CLP Cell Loss Priority bit CLP = 1 implies low priority cell can be discarded if

congestion

HEC Header Error Checksum cyclic redundancy check

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 38

ATM Physical Layer Transmission Convergence Sublayer (TCS) adapts

ATM layer above to PMD sublayer below Header checksum generation 8 bits CRC Cell delineation With ldquounstructuredrdquo PMD sublayer transmission of idle

cells when no data cells to send

Physical Medium Dependent depends on physical medium being used SONETSDH (like a container carrying bits) TDM

OC3 = 15552 Mbps OC12 = 62208 Mbps OC48 = 245 Gbps OC192 = 96 Gbps

T1T3 (old telephone hierarchy) 15 Mbps 45 Mbps unstructured just cells (busyidle)

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 39

IP-Over-ATMClassic IP only 3 ldquonetworksrdquo (eg LAN

segments) MAC and IP addresses

IP over ATM replace ldquonetworkrdquo (eg LAN

segment) with ATM network ATM addresses IP

addresses

EthernetLANs

ATMnetwork

EthernetLANs

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 40

IP-Over-ATM

AALATMphyphy

Eth

IP

ATMphy

ATMphy

apptransport

IPAALATMphy

apptransport

IPEthphy

IP datagrams into ATM AAL5

PDUs

IP addresses to ATM addresses

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 41

Datagram Journey in IP-over-ATM Network

at Source Host IP layer maps between IP ATM dest address (using ARP) passes datagram to AAL5 AAL5 encapsulates data segments cells passes to ATM

layer

ATM network moves cell along VC to destination

at Destination Host AAL5 reassembles cells into original datagram if CRC OK datagram is passed to IP

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 42

Multiprotocol label switching (MPLS)

initial goal speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding borrowing ideas from Virtual Circuit (VC) approach

but IP datagram still keeps IP address

PPP or Ethernet header

IP header remainder of link-layer frameMPLS header

label Exp S TTL

20 3 1 5

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 43

MPLS capable routers

aka label-switched router

forwards packets to outgoing interface based only on label value (donrsquot inspect IP address) MPLS forwarding table distinct from IP forwarding tables

signaling protocol needed to set up forwarding RSVP-TE forwarding possible along paths that IP alone would not

allow (eg source-specific routing) use MPLS for traffic engineering

must co-exist with IP-only routers

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 44

R1R2

D

R3R4

R50

1

00

A

R6

in out outlabel label dest interface 6 - A 0

in out outlabel label dest interface10 6 A 1

12 9 D 0

1

in out outlabel label dest interface 8 6 A 0

0

in out outlabel label dest interface 10 A 0

12 D 0 8 A 1

MPLS forwarding tables

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary

DataLink Layer 45

Chapter 5 Summary principles behind data link layer services

error detection correction sharing a broadcast channel multiple access link layer addressing

instantiation and implementation of various link layer technologies Ethernet switched LANS PPP virtualized networks as a link layer ATM MPLS

• Slide 1
• Ethernet
• Ethernet Frame Structure
• Ethernet Frame Structure (more)
• Ethernet CSMACD algorithm
• CSMACD efficiency
• 8023 Ethernet Standards Link amp Physical Layers
• Hubs
• Switch
• Switch allows multiple simultaneous transmissions
• Switch frame filteringforwarding
• Self-learning forwarding example
• Interconnecting switches
• Switches vs Routers
• Lecture 23 Outline
• Point to Point Data Link Control
• PPP Design Requirements [RFC 1557]
• PPP non-requirements
• PPP Data Frame
• Byte Stuffing
• Slide 21
• PPP Data Control Protocol
• Slide 23
• Virtualization of networks
• The Internet virtualizing networks
• Slide 26
• Cerf amp Kahnrsquos Internetwork Architecture
• ATM and MPLS
• Asynchronous Transfer Mode ATM
• ATM architecture
• ATM network or link layer
• ATM Adaptation Layer (AAL)
• ATM Adaptation Layer (AAL) [more]
• ATM Layer
• ATM Layer Virtual Circuits
• ATM VCs
• ATM cell header
• ATM Physical Layer
• IP-Over-ATM
• Slide 40
• Datagram Journey in IP-over-ATM Network
• Multiprotocol label switching (MPLS)
• MPLS capable routers
• MPLS forwarding tables
• Chapter 5 Summary