Lesson 8

Switching Techniques in a computer Network

Objectives:

1. Understand switching techniques

2. Understand various switching techniques such as circuit switching, message switching and packet switching

Switching

• Switching in a computer network helps in deciding the best route for data transmission if there are multiple paths in a larger network.

Circuit Switching

• A dedicated path is established between the sender and a receiver.

• Before data transfer, connection will be established first.

• Example: Telephone network

  • 3 Phase of circuit switching

    • Connection establishment

    • Data transfer

    • Connection Disconnection

Message Switching

• Store forward mechanism

• Message is transferred as a complete unit and forwarded using store and forward mechanism at the intermediary node.

• Not suited for streaming media and real-time applications.

Note:

Not applicable for streaming or live data transfer

Packet Switching

• The message is broken into individual chunks called packets.

• Each packet is sent individually

• Each packet will have a source and destination IP address with sequence number

• Sequence number will help the receiver to

  • reorder the packets

  • detect missing packets and

  • send acknowledgements (will wait for missing packets)

Two approaches to packet switching

1. Datagram Approach

• connectionless switching

• each independent entity is called as datagram

• datagrams contain destination information and the intermediary devices uses this information to forward datagrams to right destination.

• In datagram packet switching approach, thepath is fized.

• Intermediate nodes take the routing decision to forward the packets.

2. Virtual Circuit Approach

• connection-oriented switching

• a preplanned route is established before the message are sent

• call request and call accept packets (special packets) are used to established the connection between sender and receiver.

• path is fixed for the duration of logical connection.

Note: the route is being decided based on availability of routes.