1 Introduction 4 Used in long distance transmission. Chapter 6 Multiplexers and Switching Concepts.

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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.


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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.


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FDMFDM

Used for analog transmission , several signals transmit on a single line.


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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.


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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.


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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.


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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.


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Packet switching and Virtual circuit

Packet switching and Virtual circuit


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Short answer questionsShort answer questions

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1 Introduction 4 Used in long distance transmission. Chapter 6 Multiplexers and Switching Concepts.

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Transcript of 1 Introduction 4 Used in long distance transmission. Chapter 6 Multiplexers and Switching Concepts.