Switching

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Chapter 14
Switching
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Figure 14-1
Switched Network
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Figure 14-2
Switching Methods
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Figure 14-3
Circuit-Switched Network
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Figure 14-4
A Circuit Switch

• n inputs m outputs
• The number of inputs does not have to match the
  number o outputs.

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Figure 14-5
A Folded Switch

• n x n folded switch
• n lines in full-duplex mode

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Figure 14-6
Circuit Switching
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Figure 14-7
Crossbar Switch

• N inputs m outputs n x m cross-points.
• Major limitation Number of cross-points.

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Figure 14-8
Multistage Switch

• 2 x 2 crossbar switch

• 15 x 15 crossbar switch 15 x 15 cross-points

• 5 x 2 crossbar switch 5 x 2 cross-points

• Number of cross-points
• - First stage 3 x 5 x 2, Second stage 2 x 2 x
  2, Third stage 3 x 5 x 2

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Figure 14-9
Switching Path Multi Paths

• Blocking
• - The reduction cross-points results in a
  phenomenon called blocking.
• - As the number of stages increases, possible
  blocking increases.

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Figure 14-10
TDM with and without a TSI (Time-Slot Interchange)
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Figure 14-11
Time Slot Interchange
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Figure 14-12
TDM Bus
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Figure 14-13
TST (Time-Space-Time) Switch

• Advantages
• - Space Switch Instantaneous
• - Time Switch No cross-points
• Disadvantages
• - Space Switch Number of cross-points
• - Time Switch Delay (Time-Slot Interchange)

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Figure 14-14
PSTN (Public Switched Telephone Network) Hierarchy
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Figure 14-15
Touch-Tone Dialing

• Dual-tone multi-frequency

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Figure 14-16
Packet Switching Approaches

• Datagram approach
• - Each packet is treated independently from all
  others.
• - Datagram sequence is out of order.
• - Reorder datagrams in transport layer.
• Virtual circuit approach
• - A single route is chosen between sender and
  receiver at the beginning of the session.

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Figure 14-17
Datagram Approach
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Figure 14-18
Multiple Channels in Datagram Approach
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Figure 14-19
Switched Virtual Circuit (SVC)

• Switched Virtual Circuit (SVC)
• - A virtual circuit is created whenever it is
  needed and exists only for the duration of the
  specific exchange.

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Figure 14-20
Permanent Virtual Circuit (PVC)

• Permanent Virtual Circuit (PVC)
• - The circuit is dedicated to the specific
  users.
• - No one else can use it because it is always
  in place.

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Figure 14-21
Path versus Route
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Figure 14-22
Dedicated versus Shared
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Figure 14-23
Message Switching

• The delays inherent in the process, as well as
  the requirements for large-capacity storage media
  at each node.

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Summary

• Circuit Switching
• Space- and time-division switches
• Packet Switching
• Datagram/SVC/PVC approach
• Message Switching