Komunkasi Data Dalam Jaringan

8/21/2019 Komunkasi Data Dalam Jaringan

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William Stallings

Data and ComputerCommunications

7th Edition

Chapter 8

Multiplexing


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Multiplexing


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Frequency Division Multiplexing

• FDM• Useful bandwidth of medium exceeds

required bandwidth of channel

• Each signal is modulated to a dierentcarrier frequency

• Carrier frequencies separated so signalsdo not oerlap !guard bands"

• e#g# broadcast radio

• Channel allocated een if no data


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Frequency Division Multiplexing

Diagram


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FDM System


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FDM of hree !oice"and Signals


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#nalog Carrier Systems

• $%&% !U'$"• (ierarchy of FDM schemes

• )roup*+, oice channels !-.(/ each" 0 -1.(/

*2ange 34.(/ to +41.(/

• 'upergroup*34 channel

*FDM of 5 group signals on carriers between -,4.(/ and

3+, .(/• Mastergroup

*+4 supergroups


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Wavelength Division

Multiplexing

• Multiple beams of light at dierent frequency• Carried by optical 6ber

• $ form of FDM

• Each color of light !waelength" carries separate datachannel

• +778 9ell :abs*+44 beams

*Each at +4 )bps

*)iing + terabit per second !%bps"

• Commercial systems of +34 channels of +4 )bps now

aailable• :ab systems !$lcatel" ,53 channels at ;7#1 )bps each

*+4#+ %bps

*


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WDM $peration

• 'ame general architecture as other FDM• =umber of sources generating laser beams at

dierent frequencies

• Multiplexer consolidates sources for transmission

oer single 6ber• as ,44M(/ per channel

• =ow 54)(/


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Dense Wavelength Division

Multiplexing

• D>DM• =o o?cial or standard de6nition

• @mplies more channels more closely

spaced that >DM• ,44)(/ or less


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Synchronous ime Division

Multiplexing

• Data rate of medium exceeds data rate ofdigital signal to be transmitted

• Multiple digital signals interleaed in time

• May be at bit leel of bloc.s• %ime slots preassigned to sources and

6xed

• %ime slots allocated een if no data

• %ime slots do not hae to be eenlydistributed amongst sources


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ime Division Multiplexing


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DM System


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DM %in& Control

• =o headers and trailers• Data lin. control protocols not needed

• Flow control*Data rate of multiplexed line is 6xed

*@f one channel receier can not receie dataAthe others must carry on

* %he corresponding source must be quenched

* %his leaes empty slots

• Error control*Errors are detected and handled by indiidual

channel systems


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Data %in& Control on DM


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Framing

• =o Bag or '=C characters brac.eting %DMframes

• Must proide synchroni/ing mechanism

• $dded digit framing

*


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'ulse Stuffing

• Hroblem 'ynchroni/ing data sources• Cloc.s in dierent sources drifting

• Data rates from dierent sources notrelated by simple rational number

• 'olution Hulse 'tu?ng*


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DM of #nalog and Digital

Sources


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Digital Carrier Systems

• (ierarchy of %DM• U'$ICanadaIJapan use one system

• @%U% use a similar !but dierent" system

• U' system based on D'+ format• Multiplexes ,- channels

• Each frame has 1 bits per channel plus

one framing bit• +7; bits per frame


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Digital Carrier Systems ()*

• For oice each channel contains one word ofdigiti/ed data !HCMA 1444 samples per sec"*Data rate 1444x+7; 0 +#5--Mbps

*Fie out of six frames hae 1 bit HCM samples

*'ixth frame is 8 bit HCM word plus signaling bit*'ignaling bits form stream for each channel

containing control and routing info

• 'ame format for digital data

*,; channels of data• 8 bits per frame plus indicator bit for data or systemscontrol

*,-th channel is sync


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Mixed Data

• D'+ can carry mixed oice and datasignals

• ,- channels used

• =o sync byte• Can also interleae D'+ channels

*Ds, is four D'+ giing 3#;+,Mbps


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DS+, ransmission Format


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S$-E.SD/

• 'ynchronous


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S$-E Frame Format


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S$-E SS+, $verhead $ctets


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Statistical DM

• @n 'ynchronous %DM many slots arewasted

• 'tatistical %DM allocates time slotsdynamically based on demand

• Multiplexer scans input lines and collectsdata until frame full

• Data rate on line lower than aggregate

rates of input lines


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Statistical DM Frame Formats


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'erformance

•


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0uffer Si1e

and Delay


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Ca"le Modem $utline

• %wo channels from cable %L proider dedicated todata transfer*


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Ca"le Modem $peration

• Downstream*Cable scheduler deliers data in small pac.ets

*@f more than one subscriber actieA each gets fraction ofdownstream capacity

• May get 544.bps to +#5Mbps

*$lso used to allocate upstream time slots to subscribers

• Upstream*User requests timeslots on shared upstream channel

• Dedicated slots for this

*(eadend scheduler sends bac. assignment of futuretme slots to subscriber


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Ca"le Modem Scheme


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#symmetrical Digital

Su"scri"er %ine

• $D':• :in. between subscriber and networ.

*:ocal loop

• Uses currently installed twisted pair cable*Can carry broader spectrum*+ M(/ or more


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#DS% Design

• $symmetric*)reater capacity downstream than upstream

• Frequency diision multiplexing

*:owest ,5.(/ for oice• Hlain old telephone serice !H


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#DS% Channel Configuration


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Discrete Multitone

• DM%• Multiple carrier signals at dierent frequencies

• 'ome bits on each channel

• -.(/ subchannels

• 'end test signal and use subchannels withbetter signal to noise ratio

• ,53 downstream subchannels at -.(/ !34.bps"

*+5#;3M(/*@mpairments bring this down to +#5Mbps to 7Mbps


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DM 0its 'er Channel

#llocation


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DM ransmitter


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xDS%

• (igh data rate D':• 'ingle line D':

• Lery high data rate D':


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2equired 2eading

• 'tallings chapter 1• >eb sites on

*$D':

*'

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