Switching Techniques

In large networks there might be multiple paths linking sender and receiver. Information may be switched as it travels through various communication channels. Hence for transmitting data across networks, Switching Techniques are used. These are:

1. Circuit Switching
2. Message Switching
3. Packet Switching

Hence lets study them in detail.

Circuit Switching

Circuit Switching diagrammatically explained. Image Courtesy: rfwireless-world.com

In this technique first the complete physical connection between the two computers is established and then data is transmitted from the source computer to the destination computer. Telephone switching equipment, for example, establishes a path that connects the caller's telephone to the receiver's telephone by making a physical connection. 

The important property of this switching technique is to set up an end-to-end path (connection) between computers before any data can be sent. Routing decisions must be made when the circuit is first established, but there are no decisions made after that time.

Message Switching

Message Switching diagrammatically explained. Image Courtesy: tutorialspoint.com

In this technique, the source computer sends data or the message to the switching office first, which stores the data in its buffer. It then looks for a free link to another switching office and then sends the data to this office. This process is continued until the data is delivered to the destination computers. Owing to this working principle, it is also known as Store and Forward. That is, Store first (in switching office), Forward later, one jump at a time.

Packet Switching

In packet switching, the analog signal from your phone is converted into a digital data stream. That series of digital bits is then divided into relatively tiny clusters of bits, called packets. Each packet has at its beginning the digital address -- a long number -- to which it is being sent. The system blasts out all those tiny packets, as fast as it can, and they travel across the nation's digital backbone systems to their destination: the telephone, or rather the telephone system, of the person you're calling. They do not necessarily travel together; they do not travel sequentially. They don't even all travel via the same route. But eventually they arrive at the right point -- that digital address added to the front of each string of digital data -- and at their destination are reassembled into the correct order, and then converted to analog form, so your friend can understand what you're saying.

With message switching, there is no limit on block size, in contrast to packet switching, which places a tight upper limit on block size. A fixed size of packet which can be transmitted across the network is specified. Another point of its difference from message switching is that data packets are stored on the disk in message switching, whereas in packet switching all the packets of fixed size are stored in the main memory. This improves the performance as the access time (time taken to access a data packet) is reduced, thus, the throughput (measure of performance) of the network is improved.