local area netowrks 1

8/7/2019 Local Area Netowrks 1

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Medium Access Control

Protocols and Local AreaNetworks

Part I: Medium Access Control


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Chapter Overview

Broadcast Networks All information sent to all

users

No routing

Shared media Radio

Cellular telephony

Wireless LANs

Copper & Optical

Ethernet LANs

Cable Modem Access

Medium Access Control To coordinate access to

shared medium

Data link layer since directtransfer of frames

Local Area Networks

High-speed, low-costcommunications betweenco-located computers

Typically based onbroadcast networks

Simple & cheap

Limited number of users


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Multiple Access Communications

Shared media basis for broadcast networks Inexpensive: radio over air; copper or coaxial cable

M users communicate by broadcasting into medium

Key issue: How to share the medium?

12

3

4

5M

Shared multipleaccess medium


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Medium sharing techniques

Static

channelization

Dynamic medium

access control

Scheduling Random access

Approaches to Media Sharing

Partition medium

Dedicatedallocation to users

Satellitetransmission

Cellular Telephone

Polling: take turns

Request for slot intransmissionschedule

Token ring

Wireless LANs

Loosecoordination

Send, wait, retry ifnecessary

Aloha

Ethernet


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Satellite Channel

uplink fin downlink fout

Channelization: Satellite


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Inbound line

Outbound lineHost

computer

Stations

Scheduling: Polling

1 2 3M

Poll 1

Data from 1

Poll 2

Data from 2

Data to M


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Ring networks

Scheduling: Token-Passing

token

Station that holds token transmits into ring

tokenData to M


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Multitapped Bus

Random Access

Transmit when ready

Crash!!

Transmissions can occur; need retransmission strategy


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Two stations are trying to share a common medium

Two-Station MAC Example

Atransmitsat t= 0

Distance dmeterstprop= d / seconds

A B

A B

B does nottransmit beforet= tprop& Acaptureschannel

Case 1

B transmitsbefore t= tpropand detectscollision soonthereafter

A B

A B

A detectscollision at

t= 2 tprop

Case 2


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Efficiency of Two-Station Example

Each frame transmission requires 2tpropof quiet time Station B needs to be quiet tprop before andafter time when

Station A transmits

Rtransmission bit rate

L bits/frame

aLRtRtL

L

propprop 21

1

/21

1

2max

+=

+=

+==Efficiency

RL

ta

prop

/

=

NormalizedDelay-Bandwidth

Product

dbits/secon21

1

2/R

atRL

LR

propeff +

=

+

==putMaxThrough

Propagation delay

Time to transmit a frame


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Typical MAC Efficiencies

CSMA-CD (Ethernet) protocol:

Token-ring network

a= latency of the ring (bits)/average frame length

Two-Station Example:

a21

1

+=Efficiency

a44.61

1

+

=Efficiency

a+=1

1Efficiency

If a


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MAC protocol features

Delay-bandwidth product

Efficiency

Transfer delay

Fairness

Reliability

Capability to carry different types of traffic

Quality of service

Cost


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Random Access


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ALOHA

Wireless link to provide data transfer between maincampus & remote campuses of University of Hawaii Simplest solution: just do it

A station transmits whenever it has data to transmit If more than one frames are transmitted, they interfere with

each other (collide) and are lost If ACK not received within timeout, then a station picks random

backoff time (to avoid repeated collision)

Station retransmits frame after backoff time

tt0t0-X t0+X t0+X+2tprop t0+X+2tprop + B

Vulnerableperiod

Time-out

Backoff period B

First transmission Retransmission


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ALOHA Model

Definitions and assumptions Xframe transmission time (assume constant)

S: throughput (average # successful frame transmissions perXseconds)

G: load (average # transmission attempts per X sec.)

Psuccess: probability a frame transmission is successful

successGPS =

XX

frame

transmission

Prior interval

Any transmission thatbegins duringvulnerable periodleads to collision

Success if no arrivalsduring 2X seconds


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Abramsons Assumption

What is probability of no arrivals in vulnerable period? Abramson assumption: Effect of backoff algorithm is that

frame arrivals are equally likely to occur at any time interval

Gis avg. # arrivals per Xseconds (1 frame transmission time)

Divide Xinto nintervals of duration =X/n p =probability of arrival in interval, then

G = n p since there are nintervals in Xseconds

==

=

==

nas)1(p)-(1

intervals]2ninarrivals0[seconds]2Xinarrivals0[

222n Gn

success

e

n

G

PPP


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Throughput of ALOHA

Gsuccess GeGPS

2

==

0

0.020.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0

0.00

7812

5

0.01

5625

0.03

125

0.06

25

0.12

50.

25 0.5 1 2 4

G

S

Collisions are meansfor coordinating

access Max throughput ismax= 1/2e (18.4%)

Bimodal behavior:

Small G, SG

Large G, S0

Collisions cansnowball and dropthroughput to zero

e-2= 0.184


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Slotted ALOHA

Time is slotted in X seconds slots Stations synchronized to frame times Stations transmit frames in first slot after frame arrival Backoff intervals in multiples of slots

t(k+1)XkX

t0+X+2tprop+ BVulnerable

period

Time-out

Backoff period B

t0+X+2tprop

Only frames that arrive during prior X seconds collide


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Throughput of Slotted ALOHA

Gnn

success

Gen

GGpG

GPGPGPS

==

=

==

)1()1(

intervals]ninarrivalsno[seconds]Xinarrivalsno[

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.

01563

0.

03125

0.

0625

0.

125

0.

25

0.

5 1 2 4 8

Ge-G

Ge-2G

G

S0.184

0.368


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Carrier Sensing Multiple Access (CSMA)

A

Station A beginstransmission at

t= 0

A

Station A captureschannel at t= tprop

A station senses the channel before it starts transmission If busy, either wait or schedule backoff (different options)

If idle, start transmission

Vulnerable period is reduced to tprop(due to channel captureeffect)

When collisions occur they involve entire frame transmission times

If tprop>X (or if a>1), no gain compared to ALOHA or slottedALOHA


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Transmitter behavior when busy channel is sensed 1-persistent CSMA (most greedy)

Start transmission as soon as the channel becomes idle

Low delay and low efficiency

Non-persistent CSMA (least greedy) Wait a backoff period, then sense carrier again

High delay and high efficiency

p-persistent CSMA (adjustable greedy)

Wait till channel becomes idle, transmit with prob. p; orwait one mini-slot time & re-sense with probability 1-p

Delay and efficiency can be balanced

CSMA Options

Sensing


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.0

2

0.0

3

0.0

6

0.1

3

0.2

5

0. 5 1 2 4 8

16

32

64

0.53

0.45

0.16

S

G

a =0.01

a =0.1

a = 1

1-Persistent CSMA Throughput

Better than Aloha& slotted Aloha

for small a

Worse than Alohafor a > 1

a = tprop/ X

CSMA ith C lli i D t ti


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CSMA with Collision Detection(CSMA/CD)

Monitor for collisions & abort transmission Stations with frames to send, first do carrier sensing

After beginning transmissions, stations continuelistening to the medium to detect collisions

If collisions detected, all stations involved stoptransmission, reschedule random backoff times, andtry again at scheduled times

In CSMA collisions result in wastage of X seconds spent

transmitting an entire frame CSMA-CD reduces wastage to time to detect collision

and abort transmission


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CSMA/CD reaction time

It takes2 tpropto find out if channel has been captured

A begins totransmit at

t= 0

A B B begins totransmit att= tprop-;

B detectscollision att= tprop

A B

A B

A detectscollision att= 2 tprop-


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CSMA-CD Application: Ethernet

First Ethernet LAN standard used CSMA-CD 1-persistent Carrier Sensing

R = 10 Mbps

tprop = 51.2 microseconds 512 bits = 64 byte slot

accommodates 2.5 km + 4 repeaters

Truncated Binary Exponential Backoff

After nth collision, select backoff from {0, 1,, 2k 1},where k=min(n, 10)

M i Th h t f R d


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Maximum Throughput for RandomAccess MACs

0

0.2

0.4

0.6

0.8

1

0.01 0.1 1

ALOHA

Slotted ALOHA

1-P CSMA

Non-P CSMA

CSMA/CD

a

max

For small a: CSMA-CD has best throughput

For larger a: Aloha & slotted Aloha better throughput


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Scheduling




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Scheduling for Medium Access Control

Schedule frame transmissions to avoid collision inshared medium

More efficient channel utilization

Less variability in delays

Can provide fairness to stations

Increased computational or procedural complexity

Two main approaches

Reservation

Polling


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Reservations Systems

Centralized systems: A central controller acceptsrequests from stations and issues grants to transmit

Frequency Division Duplex (FDD): Separate frequency bandsfor uplink & downlink

Time-Division Duplex (TDD): Uplink & downlink time-share the

same channel

Distributed systems: Stations implement a decentralizedalgorithm to determine transmission order

Central

Controller


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tr 3 5 r 3 5 r 3 5 8 r 3 5 8 r 3

8

Example

Initially stations 3 & 5 have reservations to transmit frames

Station 8 becomes active and makes reservation

Cycle now also includes frame transmissions from station 8


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Polling Systems

Centralized polling systems: A central controllertransmits polling messages to stations according to acertain order

Distributed polling systems: A permit for frametransmission is passed from station to station accordingto a certain order

A signaling procedure exists for setting up order

Central

Controller


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Application: Token-Passing Rings

Free Token = Poll

Listen mode

Delay

Input

fromring

Output

toring

Ready station looks for free token

Flips bit to change free token to busy

Transmit mode

Delay

To device From device

Ready station inserts its frames

Reinserts free token when done

token

Frame Delimiter is TokenFree = 01111110Busy = 01111111


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Methods of Token Reinsertion

Ring latency: number of bits that canbe simultaneously in transit on ring

Multi-token operation

Free token transmitted immediatelyafter last bit of data frame

Single-token operation

Free token inserted after last bit of thebusy token is received back

Transmission time at least ring latency

If frame is longer than ring latency,equivalent to multi-token operation

Single-Frame operation Free token inserted after transmitting

station has received last bit of its frame

Equivalent to attaching trailer equal toring latency

Busy tokenFree token

Frame

Idle Fill


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Application Examples

Single-frame reinsertion IEEE 802.5 Token Ring LAN @ 4 Mbps

Single token reinsertion

IBM Token Ring @ 4 Mbps

Multitoken reinsertion

IEEE 802.5 and IBM Ring LANs @ 16 Mbps

FDDI Ring @ 50 Mbps

All of these LANs incorporate token priority mechanisms


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Comparison of MAC approaches

Aloha & Slotted Aloha Simple & quick transfer at very low load

Accommodates large number of low-traffic bursty users

Highly variable delay at moderate loads

Efficiency does not depend on a

CSMA-CD

Quick transfer and high efficiency for low delay-bandwidthproduct

Can accommodate large number of bursty users

Variable and unpredictable delay


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Comparison of MAC approaches

Reservation On-demand transmission of bursty or steady streams

Accommodates large number of low-traffic users withslotted Aloha reservations

Can incorporate QoS Handles large delay-bandwidth product via delayed grants

Polling

Generalization of time-division multiplexing

Provides fairness through regular access opportunities

Can provide bounds on access delay

Performance deteriorates with large delay-bandwidthproduct


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Part II: Local Area Networks


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What is a LAN?

Local area means: Private ownership

freedom from regulatory constraints of WANs

Short distance (~1km) between computers

low cost very high-speed, relatively error-free communication complex error control unnecessary

Machines are constantly moved Keeping track of location of computers a chore

Simply give each machine a unique address Broadcastall messages to all machines in the LAN

Need a medium access control protocol


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Typical LAN Structure

RAM

RAMROM

EthernetProcessor

TransmissionMedium

Network InterfaceCard (NIC)

Unique MACphysical address


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MAC Sub-layer

Data linklayer

802.3CSMA-CD

802.5Token Ring

802.2 Logical link control

Physicallayer

MAC

LLC

802.11Wireless

LAN

Network layer Network layer

Physicallayer

OSIIEEE 802

Various physical layers

OtherLANs


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Logical Link Control Layer

PHY

MAC

PHY

MAC

PHY

MAC

Unreliable Datagram Service

PHY

MAC

PHY

MAC

PHY

MAC

Reliable frame service

LLCLLC LLC

A C

A C

IEEE 802.2: LLC enhances service provided by MAC


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Logical Link Control Services

Type 1: Unacknowledged connectionless service Unnumbered frame mode of HDLC

Type 2: Reliable connection-oriented service

Asynchronous balanced mode of HDLC

Type 3: Acknowledged connectionless service

Additional addressing

A workstation has a single MAC physical address Can handle several logical connections, distinguished by

their SAP (service access points).


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43

Layer 2 addressing


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44

LAN Addresses and ARP

Each adapter on LAN has unique LAN address

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

= adapter

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(wired orwireless)


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LAN Address (more)

MAC address allocation administered by IEEE manufacturer buys portion of MAC address space (to

assure uniqueness)

analogy:

(a) MAC address: like Social Security Number

(b) IP address: like postal address

MAC flat address portability

can move LAN card from one LAN to another

IP hierarchical address NOT portable

address depends on IP subnet to which node is attached


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46

ARP: Address Resolution Protocol

Each IP node (host,router) on LAN has ARPtable

ARP table: IP/MAC

address mappings forsome LAN nodes

< IP address; MAC address; TTL>

TTL (Time To Live): timeafter which address

mapping will be forgotten(typically 20 min)

Question:how to determineMAC address of B

knowing Bs 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

137.196.7.23

137.196.7.78

137.196.7.14

137.196.7.88


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47

ARP protocol: Same LAN A wants to send datagram to

B, and Bs MAC address notin As ARP table.

A broadcasts ARP querypacket, containing B's IPaddress

dest MAC address = FF-FF-FF-FF-FF-FF

all machines on LANreceive ARP query

B receives ARP packet,replies to A with its (B's)MAC address

frame sent to As MACaddress (unicast)

A caches (saves) IP-to-MACaddress pair in its ARP tableuntil information becomes old(times out)

soft state: information that

times out (goes away)unless refreshed

ARP is plug-and-play:

nodes create their ARPtables without intervention

from net administrator


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Ethernet


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A bit of history

1970 ALOHAnet radio network deployed in Hawaiian islands 1973 Metcalf and Boggs invent Ethernet, random access in wired net 1979 DIX Ethernet II Standard 1985 IEEE 802.3 LAN Standard (10 Mbps) 1995 Fast Ethernet (100 Mbps) 1998 Gigabit Ethernet

2002 10 Gigabit Ethernet Ethernet is the dominant LAN standard

Metcalfs Sketch


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IEEE 802.3 MAC: Ethernet

MAC Protocol: CSMA/CD

Slot Timeis the critical system parameter upper bound on time to detect collision

upper bound on time to acquire channel upper bound on length of frame segment generated by

collision

quantum for retransmission scheduling

max{round-trip propagation, MAC jam time}

Truncated binary exponential backoff for retransmission n: 0 < r < 2k, where k=min(n,10)

Give up after 16 retransmissions


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IEEE 802.3 Original Parameters

Transmission Rate: 10 Mbps Min Frame: 512 bits = 64 bytes

Slot time: 512 bits/10 Mbps = 51.2 sec

51.2 sec x 2x105 km/sec =10.24 km, 1 way

5.12 km round trip distance Max Length: 2500 meters + 4 repeaters

Each x10 increase in bit rate, must be accompanied by

x10 decrease in distance


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IEEE 802.3 MAC Frame

Preamble SDDestination

addressSourceaddress

Length Information Pad FCS

7 1 6 6 2 4

64 - 1518 bytesSynch Startframe

802.3 MAC Frame

Every frame transmission begins from scratch

Preamble helps receivers synchronize their clocksto transmitter clock

7 bytes of 10101010 generate a square wave

Start frame byte changes to 10101011

Receivers look for change in 10 pattern


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7 1 6 6 2 4


MAC address: Six bytes (48 bits) single address (unicast)

first 24 bits assigned to manufacturer (OUI);next 24 bits assigned by manufacturer

Cisco: 00-00-0C3COM: 02-60-8C

multicast address = 01 00 5e broadcast = 111...111 (FF:FF:FF:FF:FF:FF)

802.3 MAC Frame


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7 1 6 6 2 4


802.3 MAC Frame

Length: # bytes in information field

Max frame 1518 bytes, excluding preamble & SD

Max information 1500 bytes: 05DC

Pad: ensures min frame of 64 bytes

FCS: CCITT-32 CRC, covers addresses, length,information, pad fields

NIC discards frames with improper lengths or failed CRC


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IEEE 802.3 Physical Layer

(a) transceivers (b)

10base5 10base2 10baseT 10baseFX

Medium Thick coax Thin coax Twisted pair Optical fiber

Max. Segment Length 500 m 200 m 100 m 2 km

Topology Bus Bus StarPoint-to-

point link

Table 6.2 IEEE 802.3 10 Mbps medium alternatives

Thick Coax: Stiff, hard to work with

Thin Coax: T connectors flaky


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Fast Ethernet

100baseT4 100baseT 100baseFX

MediumTwisted pair category 3

UTP 4 pairs

Twisted pair category 5

UTP two pairs

Optical fiber multimode

Two strands

Max. Segment

Length

100 m 100 m 2 km

Topology Star Star Star

Table 6.4 IEEE 802.3 100 Mbps Ethernet medium alternatives

To preserve compatibility with 10 Mbps Ethernet:

Same frame format, same interfaces, same protocols

Hub topology only with twisted pair & fiber

Bus topology & coaxial cable abandoned

Category 3 twisted pair (ordinary telephone grade) requires 4 pairs

Category 5 twisted pair requires 2 pairs (most popular)

Most prevalent LAN today


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Gigabit EthernetTable 6.3 IEEE 802.3 1 Gbps Fast Ethernet medium alternatives

1000baseSX 1000baseLX 1000baseCX 1000baseT

Medium

Optical fiber

multimode

Two strands

Optical fiber

single mode

Two strands

Shieldedcopper cable

Twisted paircategory 5

UTP

Max. SegmentLength

550 m 5 km 25 m 100 m

Topology Star Star Star Star

Slot time increased to 512 bytes

Small frames need to be extended to 512 B

Frame bursting to allow stations to transmit burst of short frames

Frame structure preserved but CSMA-CD essentially abandoned

Extensive deployment in backbone of enterprise data networks andin server farms


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10 Gigabit Ethernet

Table 6.5 IEEE 802.3 10 Gbps Ethernet medium alternatives

10GbaseSR 10GBaseLR 10GbaseEW 10GbaseLX4

Medium

Two opticalfibersMultimode at850 nm

64B66B code

Two optical fibers

Single-mode at1310 nm

64B66B

Two optical fibers

Single-mode at1550 nmSONET

compatibility

Two optical fibersmultimode/single-mode with fourwavelengths at1310 nm band

8B10B code

Max. SegmentLength

300 m 10 km 40 km 300 m 10 km

Frame structure preserved

CSMA-CD protocol officially abandoned LAN PHY for local network applications

WAN PHY for wide area interconnection using SONET OC-192c

Extensive deployment in metro networks anticipated


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LAN Bridges and Switches


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Hub

Station StationStation

Two TwistedPairs

Hubs, Bridges & Routers

Interconnecting Hubs Repeater: Signal regeneration

All traffic appears in both LANs

Bridge/Switch: MAC address filtering

Local traffic stays in own LAN

Routers: Internet routing All traffic stays in own LAN

Hub

Station Station Station

Two TwistedPairs

?

HigherScalability


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Switch vs. Hub

Hub

All Stations share thebandwidth

Collision happens

Half Duplex Operation

Used for packetsniffing today

Switch

Each station has thefull bandwidth

No collision

Full Duplex Operation

Used widely today


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Bridge

Network

Physical

Network

LLC

PhysicalPhysicalPhysical

LLC

MAC MACMAC MAC

Bridge Operation

Common case involves LANs of same type

Bridging is done at MAC level


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Interconnection of IEEE LANs withcomplete transparency

Use table lookup, and

discard frame, if source &destination in same LAN

forward frame, if source &destination in different LAN

use flooding, if destinationunknown

Use backward learning to build table

observe source address of arrivingLANs

handle topology changes byremoving old entries

Transparent Bridges

Bridge

S1 S2

S4

S3

S5 S6

LAN1

LAN2


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B1

S1 S2

B2

S3 S4 S5

Port 1 Port 2 Port 1 Port 2

LAN1 LAN2 LAN3

Address Port Address Port


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1

Address Port

S1 1

S1S5

S1 to S5 S1 to S5 S1 to S5 S1 to S5


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1

S3 1

Address Port

S1 1

S3 1

S3S2

S3S2

S3S2 S3S2S3S2 S3S2


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

S4 S3

Address Port

S1 1

S3 2

S4 2

Address Port

S1 1

S3 1

S4 2

S4S3

S4

S3

S4S3S4S3


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B1

S1 S2

B2

S3 S4 S5


LAN1 LAN2 LAN3

Address Port

S1 1

S3 2

S4 2

S2 1

Address Port

S1 1

S3 1

S4 2

S2S1

S2S1

S2S1


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Adaptive Learning

In a static network, tables eventually store alladdresses & learning stops

In practice, stations are added & moved all

the time Introduce timer (minutes) to age each entry &

force it to be relearned periodically

If frame arrives on port that differs from frame

address & port in table, update immediately


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Avoiding Loops

LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)


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Spanning Tree Algorithm1. Select a root bridgeamong all the bridges.

root bridge = the lowest bridge ID.2. Determine the root portfor each bridge except the

root bridge root port = port with the least-cost path to the root bridge

3. Select a designated bridgefor each LAN designated bridge = bridge has least-cost path from the

LAN to the root bridge. designated portconnects the LAN and the designated

bridge

4. All root ports and all designated ports are placedinto a forwarding state. These are the only portsthat are allowed to forward frames. The other portsare placed into a blocking state.


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Bridge 1 selected as root bridge


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Root port selected for everybridge except root port

R

R

R

R


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LAN1

LAN2

LAN3

B1 B2

B3

B4

B5

LAN4

(1)

(2)

(1)

(1)

(1)

(1)

(2)

(2)

(2)

(2)

(3)

Select designated bridgefor each LAN

R

R

R

R

D

D

D D


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S R i B id


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Source Routing Bridges

To interconnect IEEE 802.5 token rings Each source station determines route to destination

Routing information inserted in frame

Routingcontrol

Route 1designator

Route 2designator

Route mdesignator

Destinationaddress

Sourceaddress

Routinginformation

Data FCS

2 bytes 2 bytes 2 bytes 2 bytes

Vi t l LAN


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Physical

partition

Logical partition

Bridge

or

switch

VLAN 1 VLAN 2 VLAN 3

S17

2 3 4 5 61

8

9 Floor n 1

Floor n

Floor n+ 1

S2

S3

S4

S5

S6

S7

S8

S9

Virtual LAN Partitioning a local area network into smaller layer-2 subnets

Devices on two different VLANs operate as if they are on twoseparate LANs.

o You will need alayer 3 device (e.g.router) tocommunicatebetween twoVLANs.

P P t VLAN


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Logical partition

Bridge

or

switch

VLAN 1 VLAN 2 VLAN 3

S17

2 3 4 5 61

8

9 Floor n 1

Floor n

Floor n+ 1

S2

S3

S4

S5

S6

S7

S8

S9

Per-Port VLANs

Bridge only forwards frames to outgoing ports associated with same VLAN

T d VLAN


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Tagged VLANs

More flexible than Port-based VLANs Insert VLAN tag after source MAC address in each

frame

VLAN protocol ID + tag

VLAN-aware bridge forwards frames to outgoing portsaccording to VLAN ID

VLAN ID can be associated with a port statically throughconfiguration or dynamically through bridge learning

IEEE 802.1q

local area netowrks 1

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