ch08 1
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Multiplexing
• Many to one/one to many
• Types of multiplexing
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Multiplexing vs. No Multiplexing
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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FDM
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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FDM
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
FDM, Time Domain
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Multiplexing, Frequency Domain
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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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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Demultiplexing, Time Domain
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WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
Demultiplexing, Frequency Domain
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TDM
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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
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Synchronous TDM
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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TDM, Multiplexing
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Figure 8-11
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
TDM, Demultiplexing
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Framing Bits
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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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
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Asynchronous TDM
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
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Frames and Addresses
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
a. Only three lines sending data
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Frames and Addresses
b. Only four lines sending data
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Frames and Addresses
WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
c. All five lines sending data