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