1

Last class Random Access Protocols

Slotted Aloha Aloha CSMACD ldquoTaking Turnsrdquo Protocols

Link-Layer Addressing

Today Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

2

Slotted ALOHA (Efficiency 036)

Pros single active node can

continuously transmit at full rate of channel

highly decentralized only slots in nodes need to be in sync

simple

Cons

collisions wasting slots

idle slots clock

synchronization

3

Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives

transmit immediately

collision probability increases frame sent at t0 collides with other frames sent in [t0-

1t0+1]

4

CSMACD collision detection

5

ldquoTaking Turnsrdquo MAC protocolsPolling master node

ldquoinvitesrdquo slave nodes to transmit in turn

concerns polling overhead latency single point of

failure (master)

Token passing control token passed

from one node to next sequentially

token message concerns

token overhead latency single point of failure

(token)

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

2

Slotted ALOHA (Efficiency 036)

Pros single active node can

continuously transmit at full rate of channel

highly decentralized only slots in nodes need to be in sync

simple

Cons

collisions wasting slots

idle slots clock

synchronization

3

Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives

transmit immediately

collision probability increases frame sent at t0 collides with other frames sent in [t0-

1t0+1]

4

CSMACD collision detection

5

ldquoTaking Turnsrdquo MAC protocolsPolling master node

ldquoinvitesrdquo slave nodes to transmit in turn

concerns polling overhead latency single point of

failure (master)

Token passing control token passed

from one node to next sequentially

token message concerns

token overhead latency single point of failure

(token)

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

3

Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives

transmit immediately

collision probability increases frame sent at t0 collides with other frames sent in [t0-

1t0+1]

4

CSMACD collision detection

5

ldquoTaking Turnsrdquo MAC protocolsPolling master node

ldquoinvitesrdquo slave nodes to transmit in turn

concerns polling overhead latency single point of

failure (master)

Token passing control token passed

from one node to next sequentially

token message concerns

token overhead latency single point of failure

(token)

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

4

CSMACD collision detection

5

ldquoTaking Turnsrdquo MAC protocolsPolling master node

ldquoinvitesrdquo slave nodes to transmit in turn

concerns polling overhead latency single point of

failure (master)

Token passing control token passed

from one node to next sequentially

token message concerns

token overhead latency single point of failure

(token)

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

5

ldquoTaking Turnsrdquo MAC protocolsPolling master node

ldquoinvitesrdquo slave nodes to transmit in turn

concerns polling overhead latency single point of

failure (master)

Token passing control token passed

from one node to next sequentially

token message concerns

token overhead latency single point of failure

(token)

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

6

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

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

58-23-D7-FA-20-B0

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

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

LAN

237196723

237196778

237196714

237196788

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

7

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

8

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

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

9

Ethernet uses CSMACD

No slots adapter doesnrsquot

transmit if it senses that some other adapter is transmitting that is carrier sense

transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection

Before attempting a retransmission adapter waits a random time that is random access

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

10

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

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

4 If adapter detects another transmission while transmitting aborts and sends jam signal (48 bits)

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

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

11

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

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

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

12

CSMACD efficiency Tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

13

10BaseT and 100BaseT 10100 Mbps rate latter called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub ldquostar topologyrdquo 100

m max distance between nodes and hub

twisted pair

hub

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

14

Gbit Ethernet

uses standard Ethernet frame format allows for point-to-point links and shared

broadcast channels in shared mode CSMACD is used short

distances between nodes required for efficiency

uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

15

Overview

Ethernet Hubs and Switches Wireless links characteristics CDMA IEEE 80211 wireless LANs

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

16

HubsHubs are essentially physical-layer repeaters

bits coming from one link go out all other links at the same rate no frame buffering no CSMACD at hub adapters detect collisions provides net management functionality

bull can disconnect a malfunctioning adapter

twisted pair

hub

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

17

Interconnecting with hubs

Pros Enables

interdepartmental communication

Extends max distance btw nodes

If a hub malfunctions the backbone hub can disconnect it

Cons Collision domains are

transferred into one large common domain

Cannot interconnect 10BaseT and 100BaseT hubs

hub

hubhub

hub

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

18

Switch Link layer device

stores and forwards Ethernet frames examines frame header and selectively forwards

frame based on MAC dest address 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

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

19

Forwarding

bull How to determine onto which LAN segment to forward framebull Looks like a routing problem

hub

hubhub

switch1

2 3

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

20

Self learning

A switch has a switch table entry in switch table

(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be 60

min) switch learns which hosts can be reached through

which interfaces when frame received switch ldquolearnsrdquo location

of sender incoming LAN segment records senderlocation pair in switch table

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

21

FilteringForwardingWhen switch receives a frame

index switch table using MAC dest addressif 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 flood

forward on all but the interface on which the frame arrived

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

22

Switch example

Suppose C sends frame to D

Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into

interfaces 2 and 3

frame received by D

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEG

1123

12 3

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

23

Switch example

Suppose D replies back with frame to C

Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to

interface 1

frame received by C

hub

hub hub

switch

A

B CD

EF

G H

I

address interface

ABEGC

11231

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

24

Switch traffic isolation switch installation breaks subnet into LAN

segments switch filters packets

same-LAN-segment frames not usually forwarded onto other LAN segments

segments become separate collision domains

hub hub hub

switch

collision domain collision domain

collision domain

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

25

Switches dedicated access Switch with many

interfaces Hosts have direct

connection to switch No collisions full duplex

Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions

switch

A

Arsquo

B

Brsquo

C

Crsquo

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

26

More on Switches

cut-through switching frame forwarded from input to output port without first collecting entire frameslight reduction in latency

combinations of shareddedicated 101001000 Mbps interfaces

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

27

Institutional network

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

28

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

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

29

Overview

Ethernet Hubs and Switches Mobile and wireless networks CDMA IEEE 80211 wireless LANs

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

30

Wireless and Mobile Networks

Background wireless (mobile) phone subscribers now

exceeds wired phone subscribers

computer nets laptops palmtops PDAs

two important (but different) challenges communication over wireless link handling mobile user who changes point of

attachment to network

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

31

Elements of a wireless network

network infrastructure

wireless hosts laptop PDA IP phone run applications may be stationary

(non-mobile) or mobile wireless does not

always mean mobility

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

32

Elements of a wireless network

network infrastructure

base station typically connected to

wired network relay - responsible for

sending packets between wired network and wireless host(s) in its ldquoareardquo eg cell towers

80211 access points

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

33

Elements of a wireless network

network infrastructure

wireless link typically used to

connect mobile(s) to base station

multiple access protocol coordinates link access

various data rates transmission distance

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

34

Elements of a wireless network

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

35

Elements of a wireless network

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

36

Wireless Link CharacteristicsDifferences from wired link hellip

decreased signal strength radio signal attenuates as it propagates through matter (path loss)

interference from other sources standardized wireless network frequencies (eg 24 GHz) shared by other devices (eg phone)

multipath propagation radio signal reflects off objects ground arriving ad destination at slightly different times

hellip make communication across (even a point to point) wireless link much more ldquodifficultrdquo

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics

37

Wireless network characteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interferring at B

• Last class
• Slotted ALOHA (Efficiency 036)
• Pure (unslotted) ALOHA
• CSMACD collision detection
• ldquoTaking Turnsrdquo MAC protocols
• ARP Address Resolution Protocol
• Overview
• Ethernet Frame Structure
• Ethernet uses CSMACD
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• 10BaseT and 100BaseT
• Gbit Ethernet
• Slide 15
• Hubs
• Interconnecting with hubs
• Switch
• Forwarding
• Self learning
• FilteringForwarding
• Switch example
• Slide 23
• Switch traffic isolation
• Switches dedicated access
• More on Switches
• Institutional network
• Switches vs Routers
• Slide 29
• Wireless and Mobile Networks
• Elements of a wireless network
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Wireless Link Characteristics
• Wireless network characteristics