Multiplexing

• Many to one/one to many

• Types of multiplexing

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Multiplexing

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link i.e. Dividing link into channels

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Multiplexing vs. No Multiplexing

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FDM

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FDM

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FDM

• FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidth of the signals to be transmitted.

• Channels can be separated by strips of unused bandwidth guard bands to prevent signals from overlapping.

• Applications: Telephone System, AM& FM radio broadcasting, TV Broadcasting

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Multiplexing process

• Each source generates a signal of a similar frequency range.

• Inside a MUX, these similar signals modulates different carrier frequencies

• The resulting modulated signals are the combined into a single composite signals that is sent over a media link

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FDM, Time Domain

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Multiplexing, Frequency Domain

Demultiplexing process

• The demultiplexer uses a series of filters to decompose the multiplexed signals into its constituent signals.

• The individual signals are then passed to a demodulator that separates them from their carriers and passes them to the output lines

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Demultiplexing, Time Domain

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Demultiplexing, Frequency Domain

TDM

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TDM

• TDM is a digital multiplexing technique for combining several low rate channels into one high rate one.

• It is a digital process which allows several connections to share the high bandwidth of a link.

• Instead of sharing a portion of the BW as in FDM, time is shared

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Synchronous TDM• In this the data flow is divided into units where each input connection is divided into

units where each input occupies one input time slot. A unit can be 1 bit, I character or 1 block of data

• If the input time slot is Ts then o/p time slot will be T/n where n is no of connections• TDM can be visualized as two fast rotating switches, one on the multiplexing side

another on demultiplexing side

Synchronous TDM

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

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TDM, Multiplexing

Figure 8-11

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TDM, Demultiplexing

Framing Bits

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Asynchronous TDM• In this TDM slots are dynamically allotted to improve bandwidth efficiency.• Multiplexer checks each input in round robin fashion. It allocates a slot for input line if the line

has data to send, otherwise it skip the data and check the next time.• Addressing: In asynchronous multiplexing there is no fixed relationship between input & output.• We need to include the address of the receiver inside each slot to show where it is to be delivered.

• The addressing can be n bits to define N different output lines with n =log2 N

Asynchronous TDM

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Frames and Addresses

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a. Only three lines sending data

Frames and Addresses

b. Only four lines sending data

Frames and Addresses

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c. All five lines sending data