Download Multiplexer - dhimas ruswanto

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Multiplexer
Multiplexing
FDM
TDM
WDM
Front-End Processor
Controllers
• A device that combines data from several
devices into a single stream
• Multiplexers are used in pairs (multiplexer and
demultiplexer)
• Increases efficiency, reduces cost
• Idle time is reduced
Network using multiplexers
• Used in WANS, LANs, wireless networks
– In WANs, used on point-to-point, multipoint
lines
– Connection multiplexer in LANs
– Multiple radio signals combined on wireless
networks
Corporate Network using multiplexers
• Connect communications lines to another
multiplexer
• Using several levels of multiplexers at
several sites
• Reduces costs
• Many types of multiplexing techniques
employed:
– Frequency Division Multiplexing
– Time Division Multiplexing
• Synchronous Time Division Multiplexing
• Statistical Time Division Multiplexing
– Wave Division Multiplexing
• FDM is used with analog signals.
• Used in television and radio transmission.
• Bandwidth divided into narrow bandwidths
• How it works?
– A multiplexer accepts analog signals from multiple
sources, each of which has a specified bandwidth.
– Guard bands (unused parts of the frequency range It acts as a buffer between adjacent channels to
avoid one channel’s data from crossing over into
another channel) used to separate the signals.
– The signals then are combined in to another, more
complex signal with a much larger bandwidth.
– The resulting signal is transmitted over some
medium to its destination, where demultiplexer
extracts and separates the individual components
Frequency Division Multiplexing
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TDM is used with digital signals.
Many input signals are combined and
transmitted together.
The technique interleaves more than one
individual digital signal into another channel
by giving each original signal time a slot in the
multiplexed channel.
TDM has split into two separate technologies;
- synchronous time division multiplexing
- statistical time division multiplexing
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Each incoming source gets a turn to transmit,
proceeding through the sources in roundrobin fashion
The demultiplexor on the receiver end of the
high speed link must disassemble the
incoming bit stream and deliver each bit (or
byte) to the appropriate destination
A precise order must be maintained so that
the demultiplexor can disassemble and
deliver the bits to the respective owners
Must maintaining synchronization between
the receiver and transmitter
Must transmit empty slot and cannot take
advantage of the empty slot.
• Transmit data only from active users i.e. no
empty time slots
• Multiplexer scan the buffers and create a
variable-size frame depending on how
many buffers contain data.
• Frame is created that contains data and
address of data to identify who sent the
data and for whom it is intended
• Examples - data entry systems, point of
sale systems
• Advantage :
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Does not need a line as high speed as
synchronous time division multiplexing for
transferring the same amount of data
Good for connecting a number of lower speed
devices that do not transmit data on a
continuous basis to a remote computer system
• Disadvantage:
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increased level of complexity.
• Used for analog and digital transmission over
fiber optic cables
• Optical signals from light sources consists of
different wavelengths
• The simultaneous transmission of these
light sources over a single fiber-optic
channel
• Light sources of different wavelengths are
combined by a WDM multiplexor before
transmission
• A WDM demultiplexor separates them and
Beneficial from cost and performance
– it increases bandwidth without requiring the installation of additional
fiber, (cost)
– WDM consolidates data from separate channels onto a single line
(performance)
Multiplexing Technique
Advantages
Disadvantages
Frequency Division
Multiplexing
-Simple
-Popular with Radio, TV, cable TV,
local telephone exchange
-Analog signals only
-Limited by frequency ranges
Synchronous Time Division
Multiplexing
-Digital Signals
-Wastes bandwidth
-Relatively simple
-Commonly used with T1 and
ISDN
Statistical Time Divison
Multiplexing
-More efficient use of bandwidth
-Packets can be various sizes
-Frame can contain control and
error information
-More complex than
synchronous time division
multiplexing
Wavelength Divison
Multiplexing
-Very high capacities over fiber
-Scalable
-Signals can have varying speeds
-Cost
-Complexity
• FEP is a small-sized computer which interfaces to
the host computer a number of networks, such as
peripheral devices (terminals, disk units, printers
and tape units)
• Data is transferred between the host computer and
the FEP using a high-speed parallel interface.
• The FEP communicates with peripheral devices
using slower serial interfaces.
• The purpose is to off-load from the host computer
the work of managing the peripheral devices,
transmitting and receiving messages, packet
assembly and disassembly, error detection and
error correction
FEP in communications network
• Scaled-down version of an FEP
– Handles up to 64 devices
– Cluster controller
• Specifically used with IBM servers
– Remote controller
• Located a distance from the server
– Local controller
• Located near the server
Controller in data communications network