Circuit switching

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In telecommunications, a circuit switching network is a network that established a circuit (or channel) between nodes before they may communicate. This circuit is dedicated and cannot be used for other means until the circuit is cancelled/closed and a new one created. If no actual communication is taking place in this circuit then the channel remains idle. This lead to packet switching networks that do not require a circuit to be established and allows many pairs of nodes to communicate over the same "wire" while others are idle. Time-division multiplexing could be seen as a compromise between circuit and packet switched by giving exclusive control to different nodes for a specific time slot.

For connection control (and other administrative purposes), it is possible to use a separate channel. ISDN is one such protocol that uses a separate channel while the Public Switched Telephone Network is not.

The method of establishing the connection and monitoring its progress and availability may utilize a separate control channel as in the case of .

Early telephone systems are a suitable example. The subscriber would ask the operator to connect them to another subscriber, whether on the same exchange or via an inter-exchange link and another operator. In any case, the end result was a physical electrical connection between the subscriber's telephones for the duration of the call. The copper wire used for the connection could not be used to carry other calls at the same time — even if the subscribers were in fact not talking and the line was silent.

In later years it became possible to multiplex multiple connections over the same physical conductor, but nonetheless each channel on the multiplexed link was dedicated to one call at a time. Circuit switching can be relatively inefficient because capacity is wasted on connections which are set up but (however momentarily) not in use.

Circuit switching contrasts with packet switching which splits data (for instance, digital representation of sound, or computer network data) into chunks which are separately routed over a shared network.

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