Advanced Networks Lectur 5.Pptx

8/9/2019 Advanced Networks Lectur 5.Pptx

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AdvancedComputerNetworks

Lecture #5

Instructor: Dr. Niamat Ullah


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- 1DirectLinkNetworks

1. PhysicalConnectingHosts

2. ( )HardwareBuildingBlocks Nodesand Links

3. ( , , , 4 /5 )Encoding NRZ NRZ !anchester B B4. "raming


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DataLinkLayer

Di#erent$unctionsatthelinklevel

Encoding

"raming

/Errordetection correctionRelia%ledelivery

!ediaaccesscontrol

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-Directly Connected Networks

oi t to poi t li ks: Eachnodeisdirectly

connectedtoallothersviaalink

ultiple ccess

:Allnodessharethesamephysical

medium

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- -point to point

multipleaccess


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Physical!edium

&ignalstravelthroughthemediumandrepresent%its

&hannon'sCapacity(heorem

C=Blog2(1+S/N)

De)nesthe upper%ound onthelinkcapacityCinH*

-Can %eusedtoevaluatethe +error $ree,%andwidth o$a line

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:&hannon's(heorem E-ample

- :.oice grade phoneline B=3,300 -300 = 3H* /H*

= 30(ypical&NR d ,B where

d = 10B - log10(S/N)

30"or d%S/N=1,000

C= 3,000 -log2(1+1,000) 300 /%ps

Higher%andwidthB( ),inH* highercapacity

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:Encoding !ore&chemes ( )NRZ nverted NRZ : 1&witch$romcurrentstatetorepresenta

1 ,(hissolves thepro%lemo$consecutive s %uto%viouslydoes nothing $or0 .consecutive s

!anchesterEncoding: 12Rthe%itstreamwiththeclock

0 1 ,Because %oth s and s result ina transitiontothe signal the clock can %e

.e#ectivelyrecoveredatthereceiver

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(he pro%lem withthe !anchesterencodingschemeisthatitdou%lestherateatwhichsignal

,transitionsaremadeonthelink whichmeansthatthereceiverhashal$thetimetodetecteachpulseo$

.the signal (he rateatwhich the signalchanges iscalledthelink's baudrate.

,nthecaseo$the!anchesterencoding the%itrate ,ishal$the%audrate sotheencodingisconsidered

50% .only e3cient

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4 /5B B Encoding &cheme'ncode ()it s"mols into 5)it codes

* &nal encoding that !e consider, called 4B/5B, attemptsto address the ine%cienc" of the +anchester encoding!ithout suering from the prolem of having e-tendeddurations of high or lo! signals.

'ach code!ord has no more than one starting ero, and

no more than t!o trailing erosNo more than /)conse0utive eros

The idea of (1251 is to insert e-tra its into the itstreamso as to reak up long se0uences of $s or s.

Then use N34I to solve the consecutive s prolem

$6 e%cienc" 7 it is overhead8

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4 /5E-ample o$ B B Encoding4-bit data

symbol

5-bit code 4-bit data

symbol

5-bit code

$$$$ $ $$$ $$$

$$$ $$$ $$ $$

$$$ $$$ $$ $$

$$ $$ $ $

$$$ $$$ $$ $$

$$ $$ $ $

$$ $$ $ $$

$ $ $

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Thus, when sent back-to-back, no pair of 5-bit codes results in more than three

consecutive 0s being transmitted. The resulting 5-bit codes are then transmitted

using the NR! encoding, which e"plains wh# the code is onl# concerned about

consecutive 0s$NR! alread# solves the problem of consecutive %s.

The &'(5' encoding results in )0* efficienc#.


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"raming

( )(heprocess o$grouping%itsinto$rames messages orpackets

(ypicallyimplemented%ythenetworkadaptor

?4hy$rames

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-Byte 2riented"raming

:B&5NC Binarysynchronouscommunication

"rameisacollectiono$%ytesNeedtoindicatethe%eginningandendo$a$rame

&entinelcharactersareused

:&5N &ynchroni*ationcharacter

:&2H &tarto$header

, : ,&(1 E(1 &tarto$te-t Endo$te-t

:CRC Cyclicredundancycheck

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-Pro%lem withByte oriented"raming

'T9 ma" occur in the pa"load

recede it !ith a DL' 7data)link)escape8 character

rolem propagates, precede DL' !ith anotherDL' 7e-tra overhead8

oint)to)oint 78 protocol used " I

;T9: $$

a"load: ,5$$ "tes


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-Byte counting"raming

#nclude the o$ %ytesin the $rame asa )eld intheheader

( )DigitalData CommunicationsProtocol DDC!P

: #Count &peci)es o$%ytesinthe %ody

CRCensuresthatcount)eldisnotcorrupted

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-Bit oriented"raming

- ( )High Level DataLinkControl HDLC

/ , : 01111110Beginning end o$$rame 6ag

nsteado$inserting%ytesdo%itstu3ng

0 1&enderaddsa a$ter )veconsecutive s

1Receiverremoves*eroa$ter)ve s

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-E-ample o$ Bit stu3ng;ender

$ $ $

3eceiver $ $ $ $ $ $$

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$ $ $ $

- - - -


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11DirectLinkNetworks7

1. ErrorDetection

2. ( 802.3)Ethernet EEE


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Single bit errorsare the leastlikelyt"pe of errors in serial data

transmission ecause the noisemust have a ver" short duration!hich is ver" rare.

Example:Example:

If data is sent at +ps then eachit lasts onl" 2,$$$,$$$ sec. or >s.

?or a single)it error to occur, thenoise must have a duration of onl" >s, !hich is ver" rare.


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The term burst errorburst errormeans thatt!o or more its in the data unit

have changed from to $ or from $to .

Burst errorsdoes notnecessaril"mean that the errors occur inconsecutive bits, the length of theurst is measured from the &rst

corrupted it to the last corruptedit. ;ome its in et!een ma" nothave een corrupted.


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Burst error is most likely to happenin serial transmissionsince the

duration of noise is normall" longer thanthe duration of a it.

The numer of its aected depends onthe data rate and duration of noise.

Example:Example:If data is sent at rate @ Aps then a noise of

2$$ sec can aect $ its.72$$B$$$8

If same data is sent at rate @ +ps then a noiseof 2$$ sec can aect $,$$$ its.72$$B$C8


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Checksum


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802.3 Ethernet

Carrier-sense multiple access with collision detection(CSMA/C!.

CS = carrier sense

MA = multiple access

CD = collision detection"ase Ethernet standard is #0 M$ps.

100Mbps, 1Gbps, 10Gbps standards came later


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Ethernet CSMA/C

CSMA/C (carrier sense multiple access with collisiondetection! media access protocol is used.

Data is transmitted in the form of packets.

Sense channel prior to actual packet transmission.

Transmit packet onl if channel is sensed idle! else,defer the transmission until channel becomes idle.

After packet transmission is started, the node monitorsits o"n transmission to see if the packet has

e#perienced a collision.$f the packet is obser%ed to be under&oin& a collision,the transmission is aborted and the packet isretransmitted after a random inter%al of time usin&'inar (#ponential 'ackoff al&orithm.


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CSMA/C (Ctnd..!

After first collision, each station "aits for 0 or 1 slot beforetrin& a&ain.

After second collision, the pick either 0, 1, ), or * slots atrandom to "ait.

After *rd. collision, number of slots to "ait is bet"een 0 and )*+1.

$n &eneral, after $ collisions, "ait is bet"een 0 and ) i 1.

After 10 collisions, randomi-ation inter%al fro-en at 10)*slots.

After 1 collisions, error/


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Ethernet %rame Structure

&ream$le'

btes "ith pattern 10101010 follo"ed b one bte "ithpattern 10101011

sed to snchroni-e recei%er, sender clock rates

Addresses' btes, frame is recei%ed b all adapters on a2A3 and dropped if address does not match

en)th') btes, len&th of Data field

C*C'4 btes &enerated usin& C5+*), checked at recei%er, iferror is detected, the frame is simpl dropped

ata &a+load'Ma#imum 1600 btes, minimum 4 btes$f data is less than 4 btes, pad "ith -eros to 4 btes

2en&th


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Ethernet&h+sical Media '-

10 'ase6 + Thick Co+a#ial Cable "ith 'us Topolo&

10 'ase) + Thin Co+a#ial Cable "ith 'us Topolo&

10 'aseT + T7 Cat *86 "ith Tree Topolo&

10 'ase92 + Multimode8Sin&lemode 9iber "ith Tree

Topolo&

Ma,imum Se)ment en)th

10 'ase6 + 600 m "ith at most 4 repeaters :se 'rid&e to e#tend the net"ork;

10 'ase) + 1


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%ast Ethernet

#00 M$ps $andwidth

ses same CSMA/C media access protocol and packetormat as in Ethernet.

#00"ase (&! and #00"ase% (%i$er! standards

&h+sical media '-

100 'aseT + T7 Cat 6e

100 'ase9 + Multimode 8 Sin&lemode 9iber

%ull uple,/1al uple, operations.


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%ast Ethernet

&roision or Auto-e)otiation o media speed'#0 M$ps or #00M$ps (popularl+ aaila$le or coppermedia onl+!.

Ma,imum Se)ment en)th#00 "ase - #00 m

#00 "ase % - 2 4m (Multimode %i$er!

#00 "ase % - 20 km (Sin)lemode %i$er!


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5i)a$it Ethernet

# 5$ps $andwidth.

ses same CSMA/C media access protocol as in Ethernetand is $ackward compati$le (#0/#00/#00 modules areaaila$le!.

#000"ase (&!6 #000"aseS (Multimode %i$er! and#000"ase (Multimode/Sin)lemode %i$er! standards.


1000 'ase T + 100m :Cat 6e8;

1000 'ase S + )6 m :Multimode 9iber;1000 'ase 2 + 61) m :Multimode 9iber;

1000 'ase 2 + )0 >m :Sin&lemode 9iber;

1000 'ase 2? + m :Sin&lemode 9iber;


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#0 5i) Ethernet

#0 5$ps $andwidth.

ses same CSMA/C media access protocol as in

Ethernet.

&ropositioned or Metro-Ethernet


10G'ase+25 + 10 >m :Sin&lemode 9iber;

10G'ase+(5 + 40 >m :Sin&lemode 9iber;

Advanced Networks Lectur 5.Pptx

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