Circuit switching is defined as a mechanism applied in telecommunications (mainly in PSTN) whereby the user is allocated the full use of the communication channel for the duration of the call.
That is if two parties wish to communicate, the calling party has to first dial the numbers of the called party. Once those numbers are dialed, the originating exchange will find a path to the terminating exchange, which will in turn find the called party.
After the circuit or channel has been set up, then communication will take place, then once they are through the channel will be cleared. This mechanism is referred to as being connection-oriented.
Advantages of Circuit Switching:
• Once the circuit has been set up, communication is fast and without error.
• It is highly reliable
Disadvantages:
• Involves a lot of overhead, during channel set up.
• Waists a lot of bandwidth, especial in speech whereby a user is sometimes listening, and not talking.
• Channel set up may take longer.
To overcome the disadvantages of circuit switching, packet switching was introduced, and instead of dedicating a channel to only two parties for the duration of the call it routes packets individually as they are available. This mechanism is referred to as being connectionless.
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