link layeruserspages.uob.edu.bh/mangoud/mohab/eeg555_files/… · · 2016-02-1612 slotted aloha...

1

Link Layer

51 Introduction and services

56 Link-layer switchesservices52 Error detection and correction 53Multiple access protocols54 Link-layer Addressing

5 DataLink Layer 5-1

Addressing55 Ethernet

Link Layer IntroductionSome terminology

hosts and routers are nodescommunication channels that communication channels that connect adjacent nodes along communication path are links

wired linkswireless linksLANs

layer-2 packet is a frameencapsulates datagram


ncapsu at s atagram

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

2

Link layer contextdatagram transferred by different link protocols over different links

transportation analogytrip from Princeton to Lausanneover different links

eg Ethernet on first link frame relay on intermediate links 80211 on last link

each link protocol provides different

i

limo Princeton to JFKplane JFK to Genevatrain Geneva to Lausanne

tourist = datagramtransport segment = communication link


serviceseg may or may not provide rdt over link

transportation mode = link layer protocoltravel agent = routing algorithm

Link Layer Servicesframing link access

encapsulate datagram into frame adding header trailerchannel access if shared mediumldquoMACrdquo addresses used in frame headers to identify source dest

bull different from IP addressreliable delivery between adjacent nodes

we learned how to do this already (chapter 3)ld d l b l k (f b d


seldom used on low bit-error link (fiber some twisted pair)wireless links high error rates

bull Q why both link-level and end-end reliability

3

Link Layer Services (more)

flow controlpacing between adjacent sending and receiving nodespacing between adjacent sending and receiving nodes

error detectionerrors caused by signal attenuation noise receiver detects presence of errors

bull signals sender for retransmission or drops frame

error correction


receiver identifies and corrects bit error(s) without resorting to retransmission

half-duplex and full-duplexwith half duplex nodes at both ends of link can transmit but not at same time

Where is the link layer implemented

in each and every hostlink layer implemented in y pldquoadaptorrdquo (aka network interface card NIC)

Ethernet card PCMCI card 80211 cardimplements link physical layer

tt h i t h trsquo controller

cpu memory

host bus (eg PCI)

host schematic

applicationtransportnetwork

link

linkphysical


attaches into hostrsquos system busescombination of hardware software firmware

physicaltransmission

network adaptercard

physical

4

Adaptors Communicating

datagram datagram

sending side receiving side

controller controller

sending host receiving hostdatagram

frame


sending sideencapsulates datagram in frameadds error checking bits rdt flow control etc

receiving sidelooks for errors rdt flow control etcextracts datagram passes to upper layer at receiving side

Link Layer


56 Link-layer switches5 7 PPPservices

52 Error detection and correction53Multiple access protocols54 Link-layer Addressing

57 PPP58 Link virtualization MPLS59 A day in the life of a web request



5

Error DetectionEDC= Error Detection and Correction bits (redundancy)D = Data protected by error checking may include header fields

bull Error detection not 100 reliablebull protocol may miss some errors but rarelybull larger EDC field yields better detection and correction

otherwise


Parity CheckingSingle Bit ParityDetect single bit errors

Two Dimensional Bit ParityDetect and correct single bit errors


0 0

6

Internet checksum (review)

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted packet (note used at transport layer only)

Sendertreat segment contents as sequence of 16-bit integerschecksum addition (1rsquos complement sum) of

Receivercompute checksum of received segmentcheck if computed checksum equals checksum field value

NO - error detected


complement sum) of segment contentssender puts checksum value into UDP checksum field

YES - no error detected But maybe errors nonetheless

Checksumming Cyclic Redundancy Checkview data bits D as a binary numberchoose r+1 bit pattern (generator) Ggoal choose r CRC bits R such thatgoal choose r CRC bits R such that

ltDRgt exactly divisible by G (modulo 2) receiver knows G divides ltDRgt by G If non-zero remainder error detectedcan detect all burst errors less than r+1 bits

widely used in practice (Ethernet 80211 WiFi ATM)


7

CRC ExampleWant

D2r XOR R = nGi l lequivalentlyD2r = nG XOR R

equivalentlyif we divide D2r by G want remainder R


R = remainder[ ]D2r

G

Link Layer



52 Error detection and correction 53Multiple access protocols54 Link-layer Addressing




8

Multiple Access Links and ProtocolsTwo types of ldquolinksrdquo

point-to-pointPPP for dial-up accessf ppoint-to-point link between Ethernet switch and host

broadcast (shared wire or medium)old-fashioned Ethernetupstream HFC80211 wireless LAN


shared wire (eg cabled Ethernet)

shared RF(eg 80211 WiFi)

shared RF(satellite)

humans at acocktail party

(shared air acoustical)

Multiple Access protocolssingle shared broadcast channel two or more simultaneous transmissions by nodes interference

collision if node receives two or more signals at the same timemultiple access protocol

distributed algorithm that determines how nodes share channel ie determine when node can transmitcommunication about channel sharing must use channel


communication about channel sharing must use channel itself

no out-of-band channel for coordination

9

Ideal Multiple Access Protocol

Broadcast channel of rate R bps1 when one node wants to transmit it can send at 1 when one node wants to transmit it can send at

rate R2 when M nodes want to transmit each can send at

average rate RM3 fully decentralized

no special node to coordinate transmissions h i ti f l k l t


no synchronization of clocks slots4 simple

MAC Protocols a taxonomyThree broad classes

Channel Partitioningdi id h l i t sm ll ldquo i srdquo (tim sl ts divide channel into smaller ldquopiecesrdquo (time slots frequency code)allocate piece to node for exclusive use

Random Accesschannel not divided allow collisionsldquorecoverrdquo from collisions

ldquoTaking turnsrdquo


Taking turnsnodes take turns but nodes with more to send can take longer turns

10

Channel Partitioning MAC protocols TDMA

TDMA time division multiple accessaccess to channel in rounds each station gets fixed length slot (length = pkt trans time) in each round unused slots go idle example 6-station LAN 134 have pkt slots 256 idle


1 3 4 1 3 4

6-slotframe

Channel Partitioning MAC protocols FDMA

FDMA frequency division multiple accesschannel spectrum divided into frequency bandsp q yeach station assigned fixed frequency bandunused transmission time in frequency bands go idle example 6-station LAN 134 have pkt frequency bands 256 idle

nds


freq

uenc

y ba

n

FDM cable

11

Random Access Protocols

When node has packet to sendtransmit at full channel data rate Rtransmit at full channel data rate Rno a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquorandom access MAC protocol specifies

how to detect collisionshow to recover from collisions (eg via delayed retransmissions)


retransmissions)Examples of random access MAC protocols

slotted ALOHAALOHACSMA CSMACD CSMACA

Slotted ALOHA

Assumptionsall frames same size

Operationwhen node obtains fresh all frames same size

time divided into equal size slots (time to transmit 1 frame)nodes start to transmit only slot beginning nodes are synchronized

when node obtains fresh frame transmits in next slot

if no collision node can send new frame in next slotif collision node

t it f i


yif 2 or more nodes transmit in slot all nodes detect collision

retransmits frame in each subsequent slot with prob p until success

12

Slotted ALOHA

Prossingle active node can continuously transmit t f ll t f h l

Conscollisions wasting slotsidle slots

d b bl t


at full rate of channelhighly decentralized only slots in nodes need to be in syncsimple

nodes may be able to detect collision in less than time to transmit packetclock synchronization

Slotted Aloha efficiencymax efficiency find p that maximizes Np(1-p)N-1

Efficiency long-run fraction of successful slots (many nodes all with many

suppose N nodes with many frames to send each transmits in slot with probability p

for many nodes take limit of Np(1-p)N-1

as N goes to infinity gives

Max efficiency = 1e = 37

y yframes to send)


prob that given node has success in a slot = p(1-p)N-1

prob that any node has a success = Np(1-p)N-1

At best channelused for useful transmissions 37of time

13

Pure (unslotted) ALOHAunslotted Aloha simpler no synchronizationwhen frame first arrives

transmit immediately collision probability increases

frame sent at t0 collides with other frames sent in [t0-1t0+1]


Pure Aloha efficiencyP(success by given node) = P(node transmits)

P(no other node transmits in [p0-1p0] p0 p0

P(no other node transmits in [p0-1p0] = p (1-p)N-1 (1-p)N-1

= p (1-p)2(N-1)

hellip choosing optimum p and then letting n -gt infty


= 1(2e) = 18

even worse than slotted Aloha

14

CSMA (Carrier Sense Multiple Access)

CSMA listen before transmitIf channel sensed idle transmit entire frame

If channel sensed busy defer transmission

human analogy donrsquot interrupt others


CSMA collisionscollisions can still occurpropagation delay means

spatial layout of nodes

two nodes may not heareach otherrsquos transmission

collisionentire packet transmission time wastednote


role of distance amp propagation delay in determining collision probability

15

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in CSMA

collisions detected within short timemcolliding transmissions aborted reducing channel wastage

collision detectioneasy in wired LANs measure signal strengths compare transmitted received signals


difficult in wireless LANs received signal strength overwhelmed by local transmission strength

human analogy the polite conversationalist

CSMACD collision detection


16

ldquoTaking Turnsrdquo MAC protocols

channel partitioning MAC protocolsshare channel efficiently and fairly at high loadshare channel efficiently and fairly at high loadinefficient at low load delay in channel access 1N bandwidth allocated even if only 1 active node

Random access MAC protocolsefficient at low load single node can fully

ili h l


utilize channelhigh load collision overhead

ldquotaking turnsrdquo protocolslook for best of both worlds

ldquoTaking Turnsrdquo MAC protocolsPolling

master node ldquoinvitesrdquo slave nodes to transmit in turntypically used with ldquodumbrdquo slave devicesconcerns

polling overhead

master

poll

data

data


polling overhead latencysingle point of failure (master)

slaves

17

ldquoTaking Turnsrdquo MAC protocolsToken passing

control token passed f d

T

from one node to next sequentiallytoken messageconcerns

token overhead latency

(nothingto send)

T


ysingle point of failure (token)

data

Summary of MAC protocols

channel partitioning by time frequency or codeTime Division Frequency DivisionTime Division Frequency Division

random access (dynamic) ALOHA S-ALOHA CSMA CSMACDcarrier sensing easy in some technologies (wire) hard in others (wireless)CSMACD used in EthernetCSMACA used in 80211


taking turnspolling from central site token passingBluetooth FDDI IBM Token Ring

18

Link Layer


56 Link-layer switchesservices52 Error detection and correction 53Multiple access protocols54 Link-Layer Addressing



MAC Addresses and ARP

32-bit IP address k l ddnetwork-layer address

used to get datagram to destination IP subnet

MAC (or LAN or physical or Ethernet) address

function get frame from one interface to another


physically-connected interface (same network)48 bit MAC address (for most LANs)

bull burned in NIC ROM also sometimes software settable

19

LAN Addresses and ARPEach adapter on LAN has unique LAN address

Broadcast address =FF-FF-FF-FF-FF-FF

= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53

LAN(wired orwireless)


58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)

MAC address allocation administered by IEEEmanufacturer buys portion of MAC address space manufacturer buys portion of MAC address space (to assure uniqueness)analogy

(a) MAC address like Social Security Number(b) IP address like postal address

MAC flat address portability


p ycan move LAN card from one LAN to another

IP hierarchical address NOT portableaddress depends on IP subnet to which node is attached

20

ARP Address Resolution Protocol

Each IP node (host router) on LAN has

Question how to determineMAC address of B

ARP tableARP table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgtTTL (Time To Live) time ft hi h dd

knowing Brsquos IP address

1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714


after which address mapping will be forgotten (typically 20 min)58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788

ARP protocol Same LAN (network)

A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table

A caches (saves) IP-to-MAC address pair in its

A broadcasts ARP query packet containing Bs IP address

dest MAC address = FF-FF-FF-FF-FF-FFall machines on LAN receive ARP query

ARP table until information becomes old (times out)

soft state information that times out (goes away) unless refreshed

ARP is ldquoplug-and-playrdquonodes create their ARP


B receives ARP packet replies to A with its (Bs) MAC address

frame sent to Arsquos MAC address (unicast)

nodes create their ARP tables without intervention from net administrator

21

Addressing routing to another LAN

74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F

walkthrough send datagram from A to B via Rassume A knows Brsquos IP address

R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D

two ARP tables in router R one for each IP network (LAN)

A creates IP datagram with source A destination B A uses ARP to get Rrsquos MAC address for 111111111110A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagramArsquos NIC sends frame Rrsquos NIC receives frame

This is a really importantexample ndash make sure youunderstandR s NIC receives frame

R removes IP datagram from Ethernet frame sees its destined to BR uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram sends to B

E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer





Ethernetldquodominantrdquo wired LAN technology

cheap $20 for NICfi t id l d LAN t h lfirst widely used LAN technologysimpler cheaper than token LANs and ATMkept up with speed race 10 Mbps ndash 10 Gbps

lf E h


Metcalfersquos Ethernetsketch

23

Star topologybus topology popular through mid 90s

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

today star topology prevailstoday star topology prevailsactive switch in centereach ldquospokerdquo runs a (separate) Ethernet protocol (nodes do not collide with each other)


switch

bus coaxial cable star

Ethernet Frame StructureSending adapter encapsulates IP datagram (or other

network layer protocol packet) in Ethernet frame

Preamble7 bytes with pattern 10101010 followed by one byte with pattern 10101011


byte with pattern 10101011used to synchronize receiver sender clock rates

24

Ethernet Frame Structure (more)Addresses 6 bytes

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


frame is dropped

Ethernet Unreliable connectionless

connectionless No handshaking between sending and receiving NICs receiving NICs unreliable receiving NIC doesnrsquot send acks or nacksto sending NIC

stream of datagrams passed to network layer can have gaps (missing datagrams)gaps will be filled if app is using TCPotherwise app will see gaps


pp g pEthernetrsquos MAC protocol unslotted CSMACD

25

Ethernet CSMACD algorithm1 NIC receives datagram

from network layer creates frame

4 If NIC detects another transmission while transmitting aborts and 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

transmitting aborts and sends jam signal

5 After aborting NIC enters exponential backoff after mth collision NIC chooses K at random from


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

random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2

Ethernetrsquos CSMACD (more)Jam Signal make sure all

other transmitters are aware of collision 48 bits

Exponential BackoffGoal adapt retransmission attempts to estimated f

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

attempts to estimated current load

heavy load random wait will be longer

first collision choose K from 01 delay is K 512 bit transmission timesafter second collision choose


after second collision choose K from 0123hellipafter ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

26

CSMACD efficiency

Tprop = max prop delay between 2 nodes in LANt = time to transmit max-size framettrans = time to transmit max-size frame

efficiency goes to 1 t t 0

transprop ttefficiency

511

+=


as tprop goes to 0as ttrans goes to infinity

better performance than ALOHA and simple cheap decentralized

8023 Ethernet Standards Link amp Physical Layers

many different Ethernet standardscommon MAC protocol and frame formatdiff t s ds 2 Mb s 10 Mb s 100 Mb s different speeds 2 Mbps 10 Mbps 100 Mbps 1Gbps 10G bpsdifferent physical layer media fiber cable

application MAC protocoland frame format


transportnetwork

linkphysical

100BASE-TX

100BASE-T4

100BASE-FX100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layercopper (twisterpair) physical layer

27

Manchester encoding

used in 10BaseTeach bit has a transition


each bit has a transitionallows clocks in sending and receiving nodes to synchronize to each other

no need for a centralized global clock among nodesHey this is physical-layer stuff

Link Layer


56 Link-layer switches LANsservices

52 Error detection and correction 53 Multiple access protocols54 Link-layer Addressing

LANs



28

Hubshellip physical-layer (ldquodumbrdquo) repeaters

bits coming in one link go out all other links at same rateall nodes connected to hub can collide with one anotherno frame bufferingno CSMACD at hub host NICs detect collisions

d


twisted pair

hub

Switchlink-layer device smarter than hubs take active role

t f d Eth t fstore forward Ethernet framesexamine 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


phosts are unaware of presence of switches

plug-and-play self-learningswitches do not need to be configured

29

Switch allows multiple simultaneous transmissions

hosts have dedicated direct connection to switch

A

BCrsquodirect connection to switchswitches buffer packetsEthernet protocol used on each incoming link but no collisions full duplex

each link is its own collision domain Brsquo

C

1 2 345

6


switching A-to-Arsquo and B-to-Brsquo simultaneously without collisions

not possible with dumb hub

ArsquoB

switch with six interfaces(123456)

Switch Table

Q how does switch know that Arsquo reachable via interface 4

A

BCrsquoBrsquo reachable via interface 5A each switch has a switch table each entry

(MAC address of host interface to reach host time stamp)

looks like a routing table Brsquo

C

1 2 345

6


gQ how are entries created maintained in switch table

something like a routing protocol

ArsquoB


30

Switch self-learning

switch learns which hosts can be reached through

A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces

when frame received switch ldquolearnsrdquo location of sender incoming LAN segmentrecords senderlocation pair in switch table Brsquo

C

1 2 345

6


pair in switch tableArsquoB

MAC addr interface TTLSwitch table

(initially empty)A 1 60

Switch frame filteringforwardingWhen frame received

1 record link associated with sending host1 record link associated with sending host2 index switch table using MAC dest address3 if entry found for destination

then if dest on segment from which frame arrived

then drop the framel f d th f i t f i di t d


else forward the frame on interface indicated

else flood forward on all but the interface on which the frame arrived

31

Self-learning forwarding example

A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345

6A ArsquoA ArsquoA ArsquoA ArsquoA Arsquoframe destination unknown flood

Arsquo A

destination A location knownselective send


ArsquoB


(initially empty)A 1 60Arsquo 4 60

Interconnecting switches

switches can be connected together

S4

A

B

S1

C D

E

FS2

4

S3

HI

G


Q sending from A to G - how does S1 know to forward frame destined to F via S4 and S3A self learning (works exactly the same as in single-switch case)

32

Self-learning multi-switch exampleSuppose C sends frame to I I responds to C

S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12


Q show switch tables and packet forwarding in S1 S2 S3 S4

Institutional network

to externalmail server

to externalnetwork

router

IP subnet

web server


33

Switches vs Routersboth store-and-forward devices

routers network layer devices (examine network layer headers))switches are link layer devices

routers maintain routing tables implement routing algorithmsswitches maintain switch tables implement filtering learning algorithms


2

Link layer contextdatagram transferred by different link protocols over different links

transportation analogytrip from Princeton to Lausanneover different links

eg Ethernet on first link frame relay on intermediate links 80211 on last link

each link protocol provides different

i

limo Princeton to JFKplane JFK to Genevatrain Geneva to Lausanne

tourist = datagramtransport segment = communication link


serviceseg may or may not provide rdt over link

transportation mode = link layer protocoltravel agent = routing algorithm

Link Layer Servicesframing link access

encapsulate datagram into frame adding header trailerchannel access if shared mediumldquoMACrdquo addresses used in frame headers to identify source dest

bull different from IP addressreliable delivery between adjacent nodes

we learned how to do this already (chapter 3)ld d l b l k (f b d


seldom used on low bit-error link (fiber some twisted pair)wireless links high error rates

bull Q why both link-level and end-end reliability

3





error correction








cpu memory

host bus (eg PCI)

host schematic


link

linkphysical




network adaptercard

physical

4


datagram datagram




frame




Link Layer







5



otherwise





0 0

6





NO - error detected








7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





3





error correction








cpu memory

host bus (eg PCI)

host schematic


link

linkphysical




network adaptercard

physical

4


datagram datagram




frame




Link Layer







5



otherwise





0 0

6





NO - error detected








7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





4


datagram datagram




frame




Link Layer







5



otherwise





0 0

6





NO - error detected








7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





5



otherwise





0 0

6





NO - error detected








7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





6





NO - error detected








7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





7

CRC ExampleWant




R = remainder[ ]D2r

G

Link Layer







8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





8
















9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





9














10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





10




1 3 4 1 3 4

6-slotframe



nds


freq

uenc

y ba

n

FDM cable

11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





11








Slotted ALOHA






t it f i




12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





12

Slotted ALOHA



d b bl t










y yframes to send)





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





13








= p (1-p)2(N-1)



= 1(2e) = 18


14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





14












15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





15









16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





16




ili h l






polling overhead

master

poll

data

data



slaves

17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





17



T



(nothingto send)

T



data






18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





18

Link Layer













19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





19



= adapter

1A-2F-BB-76-09-AD

71 65 F7 2B 08 53



58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN Address (more)







20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





20







1A-2F-BB-76-09-AD

LAN

137196723

137196778

137196714



0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137196788













21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





21


74-29-9C-E8-FF-55 88-B2-2F-54-1A-0F


R

1A-23-F9-CD-06-9B

222222222220111111111110

E6-E9-00-17-BB-4B

111111111112

111111111111

A222222222221

B222222222222

49-BD-D2-C7-56-2A


CC-49-DE-D0-AB-7D





E6-E9-00-17-BB-4BA

74-29-9C-E8-FF-55

222 222 222 221

88-B2-2F-54-1A-0F

understand


R

1A-23-F9-CD-06-9B

222222222220111111111110

6 9 00

CC-49-DE-D0-AB-7D

111111111112

111111111111

222222222221

B222222222222

49-BD-D2-C7-56-2A

22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

Source ADest Arsquo

gwhich interfaces


C

1 2 345

6












31


A

BCrsquo

A Arsquo

Source ADest Arsquo

Brsquo

C

1 2 345


Arsquo A



ArsquoB





S4

A

B

S1

C D

E

FS2

4

S3

HI

G



32


S41

A

B

S1

C D

E

FS2

4

S3

HI

G

12





to externalnetwork

router

IP subnet

web server


33





22

Link Layer







lf E h



23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

+=








transportnetwork

linkphysical

100BASE-TX

100BASE-T4




27

Manchester encoding





Link Layer




LANs



28



d


twisted pair

hub



transparent




29



A



C

1 2 345

6




ArsquoB


Switch Table


A




C

1 2 345

6




ArsquoB


30



A

BCrsquo

A Arsquo

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32


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to externalnetwork

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33





23





switch







24





frame is dropped






25





















26

CSMACD efficiency




511

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transportnetwork

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27

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28



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29



A



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12





to externalnetwork

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33





24





frame is dropped






25





















26

CSMACD efficiency




511

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27

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Link Layer




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28



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29



A



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4

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12





to externalnetwork

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33





25





















26

CSMACD efficiency




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27

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28



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A



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4

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12





to externalnetwork

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33





26

CSMACD efficiency




511

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27

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33





27

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33





28



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29



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30



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to externalnetwork

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31


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32


S41

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to externalnetwork

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33





33





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