Physical Layer Multiplexing - Slides

Physical Layer - CSCI 232 CSCI 232 Computer Networking Physical Layer Multiplexing George Blankenship Blankenship Physical Layer Multiplexing

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SCI 232 CSCI 232 Computer Networking: Physical Layer Multiplexing eorge Blankenship George Blankenship Physical Layer Multiplexing George Blankenship 1
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Lecture Outline • Sharing a medium – Multiple dialogs irtual concurrency Virtual concurrency •F D M – Copper medium iber medium Fiber medium •T D M – Digital carrier SONET – Statistical multiplexing • Cable modem •D S L • Spread Spectrum Physical Layer Multiplexing George Blankenship 2
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Multiplexing Physical Layer Multiplexing George Blankenship 3
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Frequency Division Multiplexing • Useful bandwidth of medium exceeds required bandwidth of individual channels • Each signal is modulated to a different carrier frequency arrier frequencies separated so signals do Carrier frequencies separated so signals do not overlap (guard bands) hannel allocated even if no data • Channel allocated even if no data • Model is broadcast radio Physical Layer Multiplexing George Blankenship 4
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Three Voice Band Signals Physical Layer Multiplexing George Blankenship 5
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Time Division Multiplexing • Synchronous – Transmission period divided into discrete time slots – Channel assigned to a time slot – Data demand cannot exceed capacity • Statistical – Data is divided into discrete packages – Package contains channel identity – Data demand can exceed capacity Physical Layer Multiplexing George Blankenship 6
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Synchronous TDM • Data rate of medium exceeds data rate of digital signal to be transmitted • Multiple digital signals interleaved in time • May be at bit level of blocks ime slots preassigned to sources and fixed • Time slots preassigned to sources and fixed • Time slots allocated even if no data • Time slots do not have to be evenly distributed amongst sources Physical Layer Multiplexing George Blankenship 7
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TDM Link Control • No headers and trailers ata link control protocols not needed • Data link control protocols not needed • Flow control t t f lti l d li i fi d – Data rate of multiplexed line is fixed – If one channel receiver can not receive data, the others must carry on – The corresponding source must be quenched – This leaves empty slots • Error control – Errors are detected and handled by individual channel systems Physical Layer Multiplexing George Blankenship 8
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Data Link Control on TDM Physical Layer Multiplexing George Blankenship 9
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This note was uploaded on 09/03/2010 for the course CS 232 taught by Professor Susan during the Summer '09 term at GWU.

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Physical Layer - CSCI 232 CSCI 232 Computer Networking Physical Layer Multiplexing George Blankenship Blankenship Physical Layer Multiplexing

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