Circuit switching is a method of implementing a

telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, message ...

in which two

network nodes In telecommunications networks, a node (, ‘knot’) is either a redistribution point or a communication endpoint. The definition of a node depends on the network and protocol layer referred to. A physical network node is an electronic device ...

establish a dedicated

communications channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informat ...

( circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an

electrical circuit An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources, ...

. Circuit switching originated in analog

telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and internet. The idea was revolutionized in the 1920s, as more and more ...

s where the network created a dedicated circuit between two telephones for the duration of a

telephone call A telephone call is a connection over a telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and interne ...

. It contrasts with

message switching In telecommunications, message switching involves messages routed in their entirety, one hop at a time. It evolved from circuit switching and was the precursor of packet switching. History Western Union operated a message switching system, Plan ...

and

packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into ''network packet, packets'' that are transmitted over a digital Telecommunications network, network. Packets are made of a header (computing), header and ...

used in modern digital networks in which the trunklines between switching centers carry data between many different nodes in the form of

data packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control informa ...

s without dedicated circuits.

Description

The defining example of a circuit-switched network is the early analog

. When a

call Call or Calls may refer to: Arts, entertainment, and media Games * Call, a type of betting in poker * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from Lahore, Paki ...

is made from one telephone to another, switches within the

telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...

s create a continuous wire circuit between the two telephones, for as long as the call lasts. In circuit switching, the bit delay is constant during a connection (as opposed to packet switching, where packet queues may cause varying and potentially indefinitely long packet transfer delays). No circuit can be degraded by competing users because it is protected from use by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains reserved and protected from competing users. While circuit switching is commonly used for connecting voice circuits, the concept of a dedicated path persisting between two communicating parties or nodes can be extended to signal content other than voice. The advantage of using circuit switching is that it provides for continuous transfer without the overhead associated with packets, making maximal use of available bandwidth for that communication. One disadvantage is that it can be relatively inefficient because unused capacity guaranteed to a connection cannot be used by other connections on the same network. In addition, calls cannot be established or will be dropped if the circuit is broken.

The call

For

call setup In telecommunication, call setup is the process of establishing a virtual circuit across a telecommunications network. Call setup is typically accomplished using a signaling protocol. The term call set-up time has the following meanings: # The ...

and control (and other administrative purposes), it is possible to use a separate dedicated

signalling In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

channel from the end node to the network.

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wo ...

is one such service that uses a separate signalling channel while

plain old telephone service Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...

(POTS) does not. The method of establishing the connection and monitoring its progress and termination through the network may also utilize a separate control channel as in the case of links between telephone exchanges which use CCS7 packet-switched signalling protocol to communicate the call setup and control information and use

TDM TDM may refer to: * ''TDM (film), TDM'', a 2023 Indian Marathi language, Marathi comedy film * TDM (Macau) (), a Macanese radio and television network * The Yamaha TDM, a motorcycle model * Target Disk Mode, a boot mode on certain Macintosh compute ...

to transport the actual circuit data. Early

telephone exchanges telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

were a suitable example of circuit switching. The subscriber would ask the operator to connect to another subscriber, whether on the same exchange or via an inter-exchange link and another operator. The 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.

Alternatives

In circuit switching, a route and its associated bandwidth is reserved from source to destination, making circuit switching relatively inefficient since capacity is reserved whether or not the connection is in continuous use. Circuit switching contrasts with

and

. Both of these methods can make better use of available network bandwidth between multiple communication sessions under typical conditions in data communication networks. Message switching routes messages in their entirety, one hop at a time, that is,

store and forward Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in ...

of the entire message. Packet switching divides the data to be transmitted into packets transmitted through the network independently. Instead of being dedicated to one communication session at a time, network links are shared by packets from multiple competing communication sessions, resulting in the loss of the quality of service guarantees that are provided by circuit switching. Packet switching can be based on

connection-oriented communication Connection-oriented communication is a network communication mode in telecommunications and computer networking, where a communication session or a semi-permanent connection is established before any useful data can be transferred. The establish ...

or connection-less communication. That is, based on virtual circuits or datagrams. Virtual circuits use packet switching technology that emulates circuit switching, in the sense that the connection is established before any packets are transferred, and packets are delivered in order. Connection-less packet switching divides the data to be transmitted into packets, called

datagrams A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The deliv ...

, transmitted through the network independently. Each datagram is labeled with its destination and a sequence number for ordering related packets, precluding the need for a dedicated path to help the packet find its way to its destination. Each datagram is dispatched independently and each may be routed via a different path. At the destination, the original message is reordered based on the packet number to reproduce the original message. As a result, datagram packet switching networks do not require a circuit to be established and allow many pairs of nodes to communicate concurrently over the same channel.

Multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...

multiple telecommunications connections over the same physical conductor has been possible for a long time, but each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls.

Examples of circuit-switched networks

Public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

(PSTN) *

B channel {{for, Indonesian television network formerly known as B-Channel, RTV (Indonesian TV network) B channel (bearer) is a telecommunications term which refers to the ISDN channel in which the primary data or voice communication is carried. It ha ...

Circuit Switched Data In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM). After 2010 many teleco ...

(CSD) and

High-Speed Circuit-Switched Data In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM). After 2010 many teleco ...

(HSCSD) service in cellular systems such as

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...

Datakit Datakit is a virtual circuit switch which was developed by Sandy Fraser at Bell Labs for both local-area and wide-area networks, and in widespread deployment by the Regional Bell Operating Companies (RBOCs). Datakit uses a cell relay protocol simi ...

* X.21 (Used in the German DATEX-L and Scandinavian DATEX circuit switched data network) *

Optical mesh network An optical mesh network is a type of optical telecommunications network employing wired fiber-optic communication or wireless free-space optical communication in a mesh network architecture. Most optical mesh networks use fiber-optic communicatio ...

References

External links