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IntroductionIntroduction
Used in long distance transmission.
Chapter 6 Multiplexers and Switching Concepts
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Multiplexer and DemultiplexerMultiplexer and Demultiplexer
MUX: combines several low-speed data channels and transmits all of the data on a single high-speed channel
DMUX: the opposite of a multiplexer.
Introduction
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6.1 Types of Multiplexers6.1 Types of Multiplexers
TDM (SPM, FPM) FDM WDM CDM.
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TDMTDM Each input is assigned equal time to
transmit its information have idle time.
6.1 Types of Multiplexers
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SPMSPM
The bandwidth is dynamically allocated to active users.
6.1 Types of Multiplexers
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FPMFPM
Use the same method as SPM SPM: use store-and-forward
technology, perform error detection FPM: does not use store-and-forward
technology , faster than SPM, can’t perform error detection.
6.1 Types of Multiplexers
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FDMFDM
Used for analog transmission , several signals transmit on a single line.
6.1 Types of Multiplexers
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6.2 Telephone System Operation 6.2 Telephone System Operation
Telephone system transmits information in analog signal from a telephone set to the Central Office
PCM method is used in the central switch to convert the human voice to digital signals (Fig 6.7).
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6.3 Digitizing the Voice 6.3 Digitizing the Voice
PAM: the human voice is sampled at the rate of 8000 samples per second
PCM: each PAM sample is represented by eight bits (digital signal DS-0)
DS-0: the rate is 8000*8=64Kbps .
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6.4 T1 Link 6.4 T1 Link
Long distance carriers use TDM to transmit voice signals over high-speed digital lines
One of the application of TDM is the T1 link
A T1 link carries a level-1 digital signal (DS-1) .
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DS-1 DS-1
A DS-1 is generated by multiplexing 24 voice digital signals (DS-0) .
6.4 T1 Link
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DS-2 and T2 Link DS-2 and T2 Link
The rate of T1 link: 24 DS-0 + 8k overhead = 24*64k+8k=1.544Mbps
A DS-2 is generated by multiplexing 4 DS-1
The rate of T2 link: (24*4=96 DS-0, 168 overhead) 96*64k+168k=6.312M .
6.4 T1 Link
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6.5 Switching Concepts6.5 Switching Concepts
To overcome the disadvantage of a fully-connected network, a device called a switch is used to connect stations.
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Type of switchingType of switching
Circuit Switching Message Switching Packet Switching (Virtual Circuit) Cell Switching.
6.5 Switching Concepts
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Circuit SwitchingCircuit Switching
A physical connection must be established between the source and the destination before transmission of data begins
Only two stations use a communication link at the same time.
6.5 Switching Concepts
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Message SwitchingMessage Switching
The entire message is transmitted to the switch
The switch stores the message, then retransmits it to the next switch or destination
The switch needs to have a large buffer.
6.5 Switching Concepts
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Packet switchingPacket switching
Source divides the message into packets, each packet has a sequence number
Each packet send by a different route and may be out of order at the destination
The destination uses the sequence numbers of the packets to put them in proper order.
6.5 Switching Concepts
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Virtual circuitVirtual circuit
A type of packet switching The routing of the packets is specified
before transmission All packets will be received at the
destination in the proper order.
6.5 Switching Concepts
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Packet switching and Virtual circuit
Packet switching and Virtual circuit
6.5 Switching Concepts
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Short answer questionsShort answer questions
17, 20
Chapter 6 Multiplexers and Switching Concepts