In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used for other users until the circuit is released and a new connection is set up. Even if no actual communication is taking place in a dedicated circuit then, that channel still remains unavailable to other users. Channels that are available for new calls to be set up are said to be idle.

In contrast, packet switching networks do not require a circuit to be established and allow many pairs of nodes to communicate almost simultaneously over the same "wire" channel. Time-division multiplexing could be seen as a compromise between circuit switching and packet switching by giving exclusive control to different nodes for each specific time slot.

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

The method of establishing the connection and monitoring its progress and termination may utilize a separate control channel as in the case of links between telephone exchanges which use TDM and CCS7.

Early telephone systems are a suitable example of circuit switching. 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 two subscribers' 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 either dedicated to one call at a time, or it was idle between calls. Circuit switching can be relatively inefficient because capacity is wasted on connections which are set up but are not in continuous use (however momentarily).

Circuit switching contrasts with packet switching which splits traffic data (for instance, digital representation of sound, or computer network data) into chunks, called packets, that are individually addressed and routed over a shared network.

See also

• Packet switching

External links

• Netheads vs Bellheads by Steve Steinberg
• Out of Sight, Out of Mind, Big Old Stupid Telephone Companies Are Throwing Away Their Only Real Asset Opinion piece on packet switching vs circuit switching

Telecommunications | Network architecture

Leitungsvermittlung | Piirikytkentä | Commutation de circuits | מיתוג מעגלים | Multiplazione#Multiplazione deterministica | 回線交換 | 회선 교환 | Circuit-switching | Comutação de circuitos | Мережа з комутацією каналів