The document discusses packet switching and different types of packet switching networks. It describes how in a packet switching network, data is broken into packets that can take different paths to the destination. There are two main types of packet switching - connectionless datagram switching, where each packet is routed independently, and connection-oriented virtual circuit switching, which establishes connections between nodes like circuit switching but allocates resources dynamically like packet switching. Virtual circuit switching uses two addressing schemes - global addresses and local virtual circuit identifiers assigned within the network. The document provides examples and diagrams to illustrate these different types of packet switched networks.

1. SNS COLLEGE OF ENGINEERING
Kurumbapalayam(Po), Coimbatore – 641 107
Accredited by NAAC-UGC with ‘A’ Grade
Approved by AICTE, Recognized by UGC & Affiliated to Anna University, Chennai
SNSCE / IT/ Sem V / S Rijutha / AP / IT
Department of Information Technology
Course Name : CS8591 Computer Networks
III Year / V Sem
Unit 1: Introduction and Physical Layer
Topic 9: Switching II - Packet Switch

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Introduction
➢Connected via many routers
➢Data broken into packets
➢Packet - IP Address and Sequence information

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Introduction
➢Packet travel any path in the network to reach destination
➢Find the fast channel
➢They don't need to arrive in sequence
➢Reassemble at the destination
➢Internet - Packet Switching

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Packet Switching
⮚ Transferring the data to a network in
form of packets.
⮚ The data is broken into small pieces of
fixed or variable length, called Packet.
⮚ Size determined by the network or the
governing protocol.
⮚ Ex: if one of the network's routers fails,
packets can be automatically re-routed
to avoid that device.
Packet Switching

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Packet Switching and its Types
⮚ Principle, Store and Forward
⮚ There is no resource allocation for a packet
⮚ No reserve bandwidth
⮚ No scheduled processing time
⮚ Resource are allocated on demand, FCFS
⮚Other packet being processed, packet wait, delay
➢Types
○ Connectionless (datagram switching)
○ Connection-oriented (virtual circuit switching)

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Datagram Switching
➢Each packet, called a datagram
➢Separate entity
➢Each packet is routed independently through the network
➢Packey may arrive out of order
➢Packey may go missing
➢Datagram switching - network layer

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Datagram Switching
A datagram network with four switches (routers)

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Datagram Networks
⮚ It is a connectionless service
⮚ No call setup or teardown phases
⮚ No connection state information in routers
⮚ Packets forward using destination address

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Routing Table
Routing Table in Datagram
networks
⮚ Routing table dynamic and updated periodically.
⮚ Destination addresses and corresponding forwarding
output ports are recorded in the tables
⮚Destination Address, remain same
⮚Switch receive the packet, destination address examined
⮚Routing table, identify the corresponding output port
⮚Better efficiency, resource allocated only when packet is
transferred .

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Efficiency and Delay
⮚ Efficiency
○ Better than circuit switching
○ Resource allocated only when packet is transferred
○ Traffic, change the path
⮚Delay
○ High delay than in virtual circuit network
○ No setup and teardown phases
○ Delay is not uniform, packet not travel in same switch

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⮚Virtual circuit switching is a hybrid technology combining features of both circuit switching
and packet switching
⮚Provide connection-oriented service
⮚Setup, Teardown and data transfer phase
⮚Resource allocated, setup phase, circuit switch network, follow same path
⮚Resource allocated on demand, datagram network
⮚Virtual circuit network, data link layer
Virtual Circuit Networks

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Virtual Circuit Networks
⮚ Network has switches that allow data from source to destination
Virtual CircuitNetwork

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Virtual Circuit Networks
⮚Two Addressing
○ Global
○ Local (VCI)
➢ Global Addressing
○ Network address
○ Used as a common address by all the users of the network
○ A source or a destination needs to have a global address
➢ Local Addressing
○ Virtual circuit Identifier - VCI
○ Used for data transfer
○ A address used by frame between two nodes

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Virtual Circuit Identifier
⮚ Used for data transfer
⮚ Frame arrive switch, it has VCI
⮚Frame leaves, it has different VCI
⮚Delay, for setup and teardown respectively are 1

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Switch and Table
⮚ Frame arrive at port 1, VCI of 14
⮚Frame leaves from port3, VCI to 22

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Source to Destination Data
Transfer
⮚Frame from source A reaches destination B.]
⮚VCI change during the trip.
⮚Each switch changes the VCI and route the frame
⮚ Data transfer phrase is active until source sends all its frame

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Setup Request and Acknowledgement
⮚Setup request in a virtual circuit network
⮚Setup request frame is sent from the source to the
destination
⮚ Special frame called the acknowledgment frame
⮚ Completes the entries in the switching tables

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Virtual Circuit vs Datagram

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Puzzle
1. Most packet switches use this principle ____________?
a) Stop and wait b) Store and forward c) Store and wait d) Stop and
forward
2. In _________ systems, resources are allocated on demand.
a) packet switching b) circuit switching c) line switching d) frequency
switching
3. A switch in the datagram network uses __________
a) Destination address b) Sender address c) Routing table d) Header

20. THANK YOU !
SNSCE / IT/ Sem V / S Rijutha / AP / IT
SNSCE / IT/ Sem V / S Rijutha / AP / IT