Transcript Slides of Basic Switching

Summary
what is switching ? Types of switching?
 circuit switching, message switching,
packet switching
 Two approaches in packet switching
(Datagram approach, Virtual circuit
Approach)
 Circuit switching technologies
(Space Division SW, Time Division SW)

What is Switching ?
To connect party A with party B is called
switching, three necessary part of
switching
1.
2.
3.
Terminal
Central Node
Media
Types OF Switching
1.
2.
3.
Circuit Switching
Message Switching
Packet Switching
1. Circuit Switching
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In circuit switching the data is sent as a continuous stream of
bits
B.W is guaranteed ( because dedicated links) and delay is
essentially limited to propagation time
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Physical connection b/w party A and party B

PSTN is an example of circuit Switching
Three steps involves
1. Circuit / Call Establishment
2. Data Transfer
3. Circuit / Call Disconnect
2. Message Switching
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
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When terminal user type a message that is sent for some
other terminal, system stores the message and delivers it to
the required terminal at some later time
The reason is the system is designed to maximize the
utilization of transmission links
Not use for real time Application
3. Packet switching

PS n/w is designed for data communication

Data are packetize and sent packet by packet

Advantage is that use multiple links to transfer data across
network while circuit switching use one dedicated link
1.
2.
Packet switching uses two approaches:
Datagram Approach
( used in n/w layer)
Virtual Circuit Approach ( used in data link layer)
Two main technologies of Switches
Circuit switching today can use either of two technologies
1.
Space Division switch
2.
Time Division Switch
1. Space Division switch


1.
2.
Signal paths are physically separate from one an
other
Originally designed for analog n/w but now using
in both
Crossbar Switch (M*N)
Multistage Switch
2. Time Division Switch

CS technique in which time division multiplexing
is used to achieve switching
Two methods:
1.
Time slot interchange
2.
TDM Bus
Centralized switching
1.
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Simple switching Structure
Accommodate limited terminal practically
Number of terminals increases the links become
more complex
To connect N terminal the formula is ((N^2)-N)/2
Form the mesh topology
Continue….
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Idea of “Centralized Switching”, all the terminal with
one central node
Central node reduce the average length of
transmission link as compare to simple switching
structure
Star Topology
Continue…
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Central node performs all switching operation using
any one of techniques: Space Division Switching or
Time Division Switching or some time both