Physical Layer Multiplexing

Physical Layer Multiplexing - CSCI - Computer Networking...

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CSCI - Computer Networking Physical Layer Multiplexing George Blankenship 1 Physical Layer Multiplexing George Blankenship 1 CSCI 232 Computer Networking: Physical Layer Multiplexing George Blankenship Physical Layer Multiplexing George Blankenship 2 Lecture Outline • Sharing a medium – Multiple dialogs – Virtual concurrency •F DM – Copper medium – Fiber medium •T DM – Digital carrier – SONET – Statistical multiplexing • Cable modem •D S L • Spread Spectrum Physical Layer
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CSCI - Computer Networking Physical Layer Multiplexing George Blankenship 2 Physical Layer Multiplexing George Blankenship 4 Frequency Division Multiplexing • Useful bandwidth of medium exceeds required bandwidth of individual channels • Each signal is modulated to a different carrier frequency • Carrier frequencies separated so signals do not overlap (guard bands) • Channel allocated even if no data • Model is broadcast radio Physical Layer Multiplexing George Blankenship 5 Three Voice Band Signals Physical Layer Multiplexing George Blankenship 6 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
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CSCI - Computer Networking Physical Layer Multiplexing George Blankenship 3 Physical Layer Multiplexing George Blankenship 7 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 • 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 8 TDM Link Control • No headers and trailers • Data link control protocols not needed • Flow control – 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
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Physical Layer Multiplexing - CSCI - Computer Networking...

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