Switching: Explained with its types

Definition of Switching:

Switching is important technique that determines how connections are made and how data move over WAN. Switching sends data along different in the same way as train can be sending or switched on multiple tracks.

Types of Switching:

1.     Packet Switching

2.     Circuit Switching

3.     Message Switching

Circuit Switching :

In circuit Switching, a dedicated physical connection is established b/w the sender and the receiver and maintain for the entire conversation, for example the PSTN ( Public switch telephone network) uses a circuit switching system.

When you make a call a physical link b/w the two phones is dedicated during the entire conversation when one hangs up, the connection is terminated and the circuit is released.

Routing Methods in circuit switched networks:

Before any two computers can transfer data, a dedicated circuit must be established b/w the two. The sending machine requests a connections to the destination, after which the destination machine signals that it is ready to accept data, the data in then sent the source to the destination, and the destination sends acknowledgement back to the source.

When the conversation is finished the source sends a signal to the destination, indicating that the connection is no longer needed, and disconnects itself.

Advantages:

Ø  This is important for time critical application such as audio and video.

Ø  The communication channel (once established) is dedicated.

Ø  Also once  the circuit a established , there is virtually no channel access delay; since the channel is always available, it does not need to be requested again.

Disadvantages:

Ø  Circuit switching does have its disadvantages. One is that it is often an inefficient use of the transmission media.

Ø  Possible long wait to establish a connection, (10 seconds,   more on long- distance or international calls.) during which  no data can be transmitted.

Ø  More expensive than any other switching techniques, because a dedicated path is required for each connection.

Ø  Because the connection is dedicated even when it is idle, no other devices can use the channel.

Message Switching:

Message switching is unlike circuit switching in that it does not establish dedicated path b/w two communication devices; instead, each message treated as an independent unit and includes its own destination and source address. Each complete message is then transmitted from device to device through the inter-network. Each intermediate device receives the message, stores it until the next device is ready to receive it and then forwards it to the next device. For this reason a message-switching network is sometimes referred to as a store and forward network.

Packet switching:

In packet switching messages are  broken up into packets, each of which includes a header with source, destination and intermediate node address information. Individual packets don’t always follow the same route, the is called independent routing, from source to destination and can follow multiple routes to reach to the destination unlike message switching, packet switching restrict packets maximum length packet switching work more quickly and efficiency than message switching. There are two method of packet switching.

I.        Data Grame packet switching

    II.       2. Virtual circuit packet switching

Data gram packet switching:

Datagram packet switching is similar to message switching in that each packet is a self-contained unit with complete  addressing information attached.

In it a message is divided into a stream of packet, each packet is separating address and independent.

It is possible for a packet to be destroyed if one of the nodes on  its way is crashed momentarily. Thus all its queued packets may lost.

Virtual packet switching:

•          In the virtual circuit approach, a preplanned route is established  before any data packets are sent.

•            A logical connection is established when

Ø        a sender send a "call  request packet" to the receiver and

Ø        the receiver send back an acknowledge packet "call accepted

         packet" to the sender if the  receiver agrees on conversational parameters.

Advantages of packet switching:

v  Packet switching is cost effective, because switching  devices do not need massivamountof secondary   storage.

v  Packet can be rerouted if there is any problem, such as,  busy or  disabled links.

v  The advantage of packet switching is that many  network users can share the samechannel at the same   time. Packet switching can maximize link efficiency by  making optimal use of link bandwidth.

 Disadvantages:

v     Protocols for packet switching are typically more complex.

v     It can add some initial costs in implementation.

v     If packet is lost, sender needs to retransmit the data