MESSAGE SWITCHING:

1   A message is a logical unit of information and can be of any length.

2. In message switching, if a station wishes to send a message to another

station, it first adds the destination address to the message.

3. Message switching does not establish a dedicated path between the two

communicating devices i.e. no direct link is established between sender and

receiver.

3. Each message is treated as an independent unit.

4. In message switching, each complete message is then transmitted from

device to device through the internetwork i.e. message is transmitted from

the source node to intermediate node.

5. The intermediate node stores the complete message temporarily, inspects it

for errors and transmits the message to the next node based on an available

free channel and its routing information. Because of this reason message

switched networks are called store and forward network as shown in fig.

6. The actual path taken by the message to its destination is dynamic as the

path is established as it travels along.

7. When the message reaches a node, the channel on which it came is released

for use by another message.

8. As shown in Figure message Ml is transmitted from A to D and M2 is

transmitted C to B. Message Ml follows the route A --> I --> II --> III --> D

and M2 follows the route C --> IV --> II --> B depending upon the

availability of free path at that particular moment.

9. The first electromechanical telecommunication system used message

switching for telegrams. The message was punched on paper tape off-line at

the sending office and then read in and transmitted over a communication

line to the next office along the way, where it was punched out on paper

tape. An operator there tore the tape off and read it in on tape readers.

                        

Advantages of Message Switching

 

The various advantages of message switching are:

 

1. It provides efficient traffic management by assigning priorities to the

messages to be switched.

2. No physical connection is required between the source & destination as it

is in circuit switching.

3. It reduces the traffic congestion on network because of store & forward

facility. Each node can store the message until communication channel

becomes available.

4. Channels are used effectively and network devices share the data

channels.

5. It supports the message length of unlimited size.

 

Disadvantages of Message Switching

 

The various disadvantages of message switching are:

 

1. As message length is unlimited, each switching node must have sufficient

storage to buffer message.

2. Storing & forwarding facility introduces delay thus making message

switching unsuitable for real time applications like voice and video.