Transcript cis 484 communication systems - California State University, Los

CHAPTER
Multiplexing
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 2
Session 3
A
Session 1
Mux
Mux
Session 2
Session 3
One physical line carrying
multiple channels.
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
One communication channel
Session 1
A
Inv..
Mux
Inv..
Mux
Session 1
Multiple Transmission Lines
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 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
2 B Channels each
operating at 64K bps
Micro
Single Session
Multiple ISDN lines (multiple
B channels).
Combined speed = 6 X 64 = 384K bps
One Transmission Line, One
Channel and Multiple Sessions
Internet
Micro
Data Packets
Internet client engaged in multiple communication sessions.
END 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)
Analog
F1
F1
F2
MUX
MUX
F2
F3
F3
A
Each channel is assigned
A different frequency
(Half-duplex Example)
B
Computer Communication Using
FDM
Digital
Analog
Analog
Micro
Modem
MUX
One or Modems May Be Incorporated
Within the Multiplexer As Well.
END 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)
Digital
Analog
T1
T2
MUX
Modem
T3
T1
T2
T3
T1
T2
T3
Time slots are equally divided among channels.
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
Digital
Analog
T1
T2
MUX
Modem
T3
T1
T2 T3 T2
T3
Time slots are not equally divided among channels.
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 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
Light rays of different wave lengths (frequencies)
are assigned for different channels.
W1
W1
W2
W2
W3
W3
Detect and differentiate light rays
of different wave lengths at the
receiving end.
END 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)
Cluster
Controller
Use Of Multiplexers in a
Mainframe Environment
MUX
Modem
Modem
MUX
Terminal
Terminal
Terminal
Wide Area Multiplexing
San Francisco
Mainframe
56 kbps
MUX
MUX
FEP
MUX
56 Kbps
Modem
112 kbps
Wide Area Multiplexing Cont.
Los Angeles
112
Long Beach
56
Mod.
Mod.
56
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Term.
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18.6
Term.
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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 CHAPTER