CHAPTER CHAPTER

MultiplexingMultiplexing

Chapter Objectives

• Describe direct and inverse multiplexing

• List and explain the different types of multiplexing techniques used in electronic and optical transmission

• Give illustrative examples of the use of multiplexers in the field

Chapter Modules

• Direct and inverse multiplexing• Listing of multiplexing techniques

and Frequency Division Multiplexing

• Time Division and Wave Division Multiplexing

• Practical multiplexer connections

MODULE 1

Direct and Inverse Multiplexing

Overview Of Direct Multiplexing

• Direct multiplexing or multiplexing is the same as channel splitting

• It means the splitting of one physical line into multiple communication channels

• A communication channel is one that engages in a communication session

• The usage of the term multiplexing in general means direct multiplexing

Direct Multiplexing Example

Session 1

Session 3

Session 2

Session 1

Session 3

Session 2 Mux Mux

One physical line carryingmultiple channels.A B

Sample Application Areas

• Mainframe-based communication• Long-distance links• Fiber-optic communication

– A relatively new introduction

• Digital lines such as DSL

Overview Of Inverse Multiplexing

• Combination of multiple transmission lines or multiple communication channels to support a single communication session

• Binding of multiple transmission lines for the purpose of engaging in a single communication session

Inverse Multiplexing

Session 1 Session 1Inv..Mux

Inv..Mux

Multiple Transmission Lines

One communication channel

A B

Bonding

• Inverse multiplexing is also known as bonding when it is done dynamically– For example, this can be achieved in

modem and ISDN transmission

• Bonding is normally carried out dynamically

Sample application Areas

• Video conferencing– Conducted over ISDN lines

• T-1 line inverse multiplexing• ATM inverse multiplexing

Inverse Multiplexing with Analog Lines

• The primary purpose is to increase the speed of Internet connection made over regular analog telephone lines

• Modems are being introduced to combine analog telephone lines

• Combination of two lines operating at 56K bps each results in an effective communication speed of 112K bps

In Summary

• Direct multiplexing– Maximize the economical use of

cables

• Inverse multiplexing– Increase the communication speed of

a single communication session

END OF MODULEEND OF MODULE

MODULE 2

Communication Lines, Channels and Sessions

Lines, Channels and Sessions

• A transmission line is a physical medium that carries the information– Coaxial cable

• A communication channel is a conduit for the flow of information– Multiple channels in physical medium

• A communication session is the actual process of engaging in a communication task

One Transmission Line and Multiple Communication

Channels

Line

Channels

Mainframe Coaxial cable

Terminals

Multiple Transmission Lines and One

Communication Session

Micro

Multiple ISDN lines (multiple B channels).

Single Session

Combined speed = 6 X 64 = 384K bps

2 B Channels eachoperating at 64K bps

Micro

One Transmission Line, One Channel and Multiple

Sessions

Internet

Internet client engaged in multiple communication sessions.

Data Packets

END OF MODULEEND OF MODULE

MODULE 3

Frequency Division Multiplexing (FDM)

Multiplexing Techniques

• Frequency Division Multiplexing• Time Division Multiplexing• Statistical Time Division

Multiplexing • Wave Division Multiplexing

Direct Multiplexing Techniques

• Frequency Division Multiplexing– Channel division is based on frequency

• Time Division Multiplexing– Time slots are assigned for each channel

• Statistical Time Division Multiplexing– A variation of Time Division Multiplexing concept

that optimizes on the concept of Time Division multiplexing

• Wave Division Multiplexing, the multiplexing is based on different wavelengths of light

Frequency Division Multiplexing (FDM)

MUX MUX

F1F2

F3

F1

F2

F3

Each channel is assignedA different frequency (Half-duplex Example)

Analog

A B

Computer Communication Using FDM

MUX

One or Modems May Be Incorporated Within the Multiplexer As Well.

Analog

Modem

Mic

ro

Digital Analog

END OF MODULEEND OF MODULE

MODULE 4

Time Division and Wave Division Multiplexing

Time Division Multiplexing in a Nutshell

• Time division simply allows a fixed period of time for communication for each channel

Time Division Multiplexing (TDM)

MUX

T1

T2

T3

T1 T2 T3 T1 T2 T3

Time slots are equally divided among channels.

Modem

AnalogDigital

Salient Features of Time Division Multiplexing • Each channel is assigned a fixed period

of time for transmission• The opportunity to transmit is given on

a round-robin basis• Time division multiplexers can

therefore processes the information in digital form

• A modem is only required to connect a multiplexer to an analog line

Drawback with Time Division Multiplexing

• TDM assigns a fixed period of time for each channel

• When a channel does not have any information to transmit during the allocated time period, it still remains connected– Either part or the entire portion of the

allocated time period is wasted

Statistical Time Division Multiplexing

MUX

T1

T2

T3

T1 T2 T3 T2 T3

Time slots are not equally divided among channels.

Modem

AnalogDigital

Statistical Time Division Multiplexing Properties

• STDM is similar to TDM except for one difference– A time slice may be shortened due to the

absence of data for transmission

• Each channel is initially assigned a fixed period of time– The time period is forfeited in part or in full if

there is no data to be transmitted

• Obviously, STDM is more efficient than TDM

END OF MODULEEND OF MODULE

MODULE 5

Wave Division Multiplexing

Wave Division Multiplexing (WDM)

• Similar to FDM– Light waves are involved in place of

electronic signals

• The term wave length is used instead of the term frequency– Note that the wave length is inversely

proportional to frequency

• Used in fiber optics transmission

Wave Division Multiplexing Connection

Detect and differentiate light rays of different wave lengths at the receiving end.

W1

W2

W3

W1

W2

W3

Light rays of different wave lengths (frequencies) are assigned for different channels.

END OF MODULEEND OF MODULE

MODULE 6

Practical Multiplexer Connections

Module Objectives

• Provide practical examples in the use of multiplexers– Use of multiplexers in a mainframe

environment– Use of multiplexers in Wide Area

Networks (WAN)

Use Of Multiplexers in a Mainframe Environment

MUX

MUX

Modem Modem

Terminal

Clu

ster

Con

trolle

r

Terminal Terminal

Wide Area Multiplexing

FEP

MUX

MUX

MUX

Modem

Main

fram

e

112 kbps

San Francisco

56 kbps

56 Kbps

Wide Area Multiplexing Cont.

Term. Term.Term. Term. Term.

112

56

56

28 2818.618.6 18.6

Los Angeles Long Beach

Mod. Mod.

Wide Area Multiplexing Observation

• Multiple channels are multiplexed and de-multiplexed

• A combination of multiplexers can be used in combining faster and slower channels

END OF MODULE END OF MODULE

END OF CHAPTEREND OF CHAPTER