A networking technology that provides a temporary physical, dedicated connection between two end systems / nodes guaranteeing a fixed transmission capacity. Voice calls on the telephone networks are the best example. As this transmission takes place along a complex network, important things to consider are the nodes which make up the path for this connection.
This path is decided before the data transmission and the system helps in selecting which route to follow based on some routing algorithms. In circuit Switching, the end to end resources are dedicated once the connection is established and no sharing of resources take place.
Circuit Switching technique offers a circuit like guaranteed performance if a call is setup before the data transmission takes place.This dedicated circuit cannot be used until it is released and a new caller asks for setting up a connection on this path.The channel remains unavailable to other users even if no actual communication is taking place in a dedicated circuit. Channels that are available for new calls to be set up are said to be idle.
Techniques of Circuit Switching
Two techniques are used for the implementation of a circuit in a link.
- Frequency Division Multiplexing (FDM)
- Time-Division Multiplexing (TDM).
Frequency Division Multiplexing (FDM):
In FDM technique, the connections established across the link shares the frequency band of a link among themselves. Specifically, a frequency band is dedicated by the link to each connection for the duration of the connection. In telephone networks, this frequency band typically has a width of 4 kHz. The width of the band is called the bandwidth. FM radio stations also use FDM to share microwave frequency spectrum.
Time Division Multiplexing:
The trend in modern telephony is to replace FDM with TDM. For using a TDM link, time is divided into frames.These frames are of fixed duration and each frame is divided into a fixed number of time slots. Whenever the network wants to establish a connection across a link,one time slot in every frame is reserved for the connection. These slots are reserved for the exclusive use of that connection, with a time slot available for use (in every frame) to transmit the connection's data.
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