Multiplexing: Sharing a medium

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Multiplexing Sharing a medium

• Prepared by
• Kam Wai Leong GS12951
• Lee Chyng Wei GS13106
• Loh Chan Yuang GS12952
• Tan Kok Jin GS12592
• Tung Kok Kong GS12953

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Content

• Introduction
• Multiplexer
• Techniques used for Multiplexing
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Synchronous Time Division Multiplexing
• Statistical Time Division Multiplexing
• Wavelength division multiplexing (WDM)

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Introduction

• What is multiplexing?
• Multiplexing is the transmission of multiple data
  communication sessions over a common wire or
  medium.
• It reduces the number of wires or cable required
  to connect multiple sessions.
• What is session?
• A session is considered to be data communication
  between two devices computer to computer,
  terminal to computer, etc.

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Why Multiplexing?

• For an individual lines running from 3 terminals
  to one mainframe is not a problem.
• But if the numbers of terminals increase to 10
  and above?

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Example

• Imagine a mainframe computer with 1200 terminals
  connected, and each terminal running its own wire
  to the mainframe.
• If each wire was 1/4" in diameter (typical Cat 5
  cable), you would have a wiring bundle going into
  the computer that is roughly 2 feet in diameter
  !!!

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Multiplexer
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Multiplexer

• A multiplexer allows sharing of a common line to
  transmit the many terminal communications (as in
  the above example).
• The connection between the multiplexer and the
  mainframe is normally a high speed data link, and
  is not usually divided into separate lines.
• The operation of multiplexers (abbreviated MUXs)
  is transparent to the sending and receiving
  computers.
• Transparent means that, as far as everyone is
  concerned, they appear to be directly connected
  to the mainframe with individual wires.

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Multiplexer

• The multiplexer does not interfere with the
  normal flow of data and it can allow a
  significant reduction in the overall cost of
  connecting to remote sites (through the reduced
  cost of cable and telephone line charges).
• Multiplexers are used to connect terminals
  located throughout a building to a central
  mainframe.
• They are also used to connect terminals located
  at remote locations to a central mainframe
  through the phone lines (refer figure below).

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Terminal and central mainframe is connected
through phone line
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Techniques used for Multiplexing

• Under the simplest conditions, a medium can carry
  only one signal at any moment in time.
• For multiple signals to share one medium, the
  medium must somehow be divided, giving each
  signal a portion of the total bandwidth.

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Techniques used for Multiplexing

• There are 3 basic techniques that are used for
• multiplexing
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Wavelength division multiplexing (WDM)

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Frequency Division Multiplexing (FDM)

• Analog signaling is used to transmit the signals.
• Broadcast radio and television, cable television,
  and the AMPS cellular phone systems use frequency
  division multiplexing.
• This technique is the oldest multiplexing
  technique.
• Since it involves analog signaling, it is more
  susceptible to noise.

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Frequency Division Multiplexing (FDM)

• Is an analog technique where each communications
  channel is assigned a carrier frequency.
• A guard band is used to separate the channels to
  ensure that the channels do not interfere with
  each other (see figure below)

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T3
T2
T1
Guard Band
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Frequency Division Multiplexing (FDM)

• FDM does not require all channels to terminate at
  a single location.
• Channels can be extracted using a multi-drop
  technique, terminals can be stationed at
  different locations within a building or a city.
  (see figure below)

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Frequency Division Multiplexing (FDM)
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Time Division Multiplexing (TDM)

• Sharing of the signal is accomplished by dividing
  available transmission time on a medium among
  users.
• Digital signaling is used exclusively.
• Time division multiplexing comes in two basic
  forms
• 1. Synchronous time division multiplexing, and
• 2. Statistical, or asynchronous time division
• multiplexing.

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Synchronous Time Division Multiplexing

• The original time division multiplexing.
• The multiplexor accepts input from attached
  devices in a round-robin fashion and transmit the
  data in a never ending pattern.
• T1 and ISDN telephone lines are common examples
  of synchronous time division multiplexing.

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Synchronous Time Division Multiplexing
Sample output stream generated by a synchronous
time division multiplexing
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Synchronous Time Division Multiplexing

• If one device generates data at a faster rate
  than other devices, then the multiplexor must
  either sample the incoming data stream from that
  device more often than it samples the other
  devices, or buffer the faster incoming stream.
• If a device has nothing to transmit, the
  multiplexor must still insert a piece of data
  from that device into the multiplexed stream.

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Synchronous Time Division Multiplexing
A synchronous time division multiplexing system
that samples device A twice as fast as the other
devices
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Synchronous Time Division Multiplexing
Multiplexor transmission stream with only one
input device transmitting data
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Synchronous Time Division Multiplexing
Transmitted frame with added synchronizations bits

• So that the receiver may stay synchronized with
  the incoming data stream, the transmitting
  multiplexor can insert alternating 1s and 0s
  into the data stream.

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Synchronous Time Division Multiplexing
T-1 multiplexed data stream

• The T-1 multiplexor stream is a continuous series
  of frames.

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Synchronous Time Division Multiplexing
ISDN frame layout showing B channel bits and
signaling control information bits

• The ISDN multiplexor stream is also a continuous
  stream of frames. Each frame contains various
  control and sync info.

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Statistical Time Division Multiplexing

• A statistical multiplexor transmits only the data
  from active workstations.
• If a workstation is not active, no space is
  wasted on the multiplexed stream.
• A statistical multiplexor accepts the incoming
  data streams and creates a frame containing only
  the data to be transmitted.

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Statistical Time Division Multiplexing
Two stations out of four transmitting via a
statistical multiplexor
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Statistical Time Division Multiplexing
Sample address and data in a statistical
multiplexor output stream

• To identify each piece of data, an address is
  included.

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Statistical Time Division Multiplexing
Packets of address length, and data fields in a
statistical multiplexor data stream

• If the data is of variable size, a length is also
  included.

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Statistical Time Division Multiplexing
Frame layout for the information packet
transferred between statistical multiplexor

• More precisely, the transmitted frame contains a
  collection of data groups.

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Dense Wavelength Division Multiplexing

• Dense wavelength division multiplexing
  multiplexes multiple data streams onto a single
  fiber optic line.
• Different wavelength lasers transmit the multiple
  signals.
• Each signal carried on the fiber can be
  transmitted at a different rate from the other
  signals.

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Dense Wavelength Division Multiplexing
Fiber optic line using dense wavelength division
multiplexing and supporting multiple-speed
transmissions
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Dense Wavelength Division Multiplexing

• Also known as code division multiple access
• An advanced technique that allows multiple
  devices to transmit on the same frequencies at
  the same time.
• Each mobile device is assigned a unique 64-bit
  code
• To send a binary 1, mobile device transmits the
  unique code
• To send a binary 0, mobile device transmits the
  inverse of code

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Conclusion
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The End

• Thank for your precious time!!