Circuit switching
Encyclopedia
Circuit switching is a methodology of implementing a telecommunications network
in which two network nodes establish a dedicated communications channel (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.
Circuit switching contrasts with packet switching
which divides the data to be transmitted into packets transmitted through the network independently. Packet switching shares available network bandwidth between multiple communication sessions.
In circuit switching, the bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying packet transfer delay
. Each circuit cannot be used 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 unavailable to other users. Channels that are available for new calls are said to be idle.
Virtual circuit switching is a 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.
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. Its advantage is that it provides for continuous transfer without the overhead associated with packets making maximal use of available bandwidth for that communication. The disadvantage is inflexibility; the connection and the bandwidth associated with it are reserved and unavailable for other uses.
and control (and other administrative purposes), it is possible to use a separate dedicated signalling channel from the end node to the network. ISDN is one such service that uses a separate signalling channel while plain old telephone service
(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
to transport the actual circuit data.
Early telephone exchanges are 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. 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.
which divides the data to be transmitted into small units, called packets, transmitted through the network independently. Packet switching shares available network bandwidth between multiple communication sessions.
Multiplexing
multiple telecommunications connections over the same physical conductor has been possible for a long time, but nonetheless each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls.
In circuit switching, and virtual circuit switching, a route and bandwidth is reserved from source to destination. Circuit switching can be relatively inefficient because capacity is guaranteed on connections which are set up but are not in continuous use, but rather momentarily. However, the connection is immediately available while established.
Packet switching is the process of segmenting a message/data to be transmitted into several smaller packets. Each packet 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 packet is dispatched independently and each may be routed via a different path. At the destination, the original message is reassembled in the correct order, based on the packet number. 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.
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
in which two network nodes establish a dedicated communications channel (circuit
Telecommunication circuit
A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...
) 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.
Circuit switching contrasts with packet switching
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
which divides the data to be transmitted into packets transmitted through the network independently. Packet switching shares available network bandwidth between multiple communication sessions.
In circuit switching, the bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying packet transfer delay
Packet transfer delay
Packet transfer delay is a concept in packet switching technology.The sum of store-and-forward delay that a packet experiences in each router gives the transfer or queuing delay of that packet across the network...
. Each circuit cannot be used 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 unavailable to other users. Channels that are available for new calls are said to be idle.
Virtual circuit switching is a packet switching
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
technology that emulates circuit switching, in the sense that the connection is established before any packets are transferred, and packets are delivered in order.
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. Its advantage is that it provides for continuous transfer without the overhead associated with packets making maximal use of available bandwidth for that communication. The disadvantage is inflexibility; the connection and the bandwidth associated with it are reserved and unavailable for other uses.
The call
For call setupCall processing
In telecommunication, the term call processing has the following meanings:# The sequence of operations performed by a switching system from the acceptance of an incoming call through the final disposition of the call...
and control (and other administrative purposes), it is possible to use a separate dedicated signalling channel from the end node to the network. ISDN is one such service that uses a separate signalling channel while plain old telephone service
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
(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
Separate channel signaling
Separate channel signaling is a form of signaling in which the whole or a part of one or more channels in a multichannel system is used to provide for supervisory and control signals for the message traffic channels....
as in the case of links between telephone exchanges which use CCS7
Signalling System 7
Signalling System No. 7 is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls...
packet-switched signalling protocol to communicate the call setup and control information and use TDM
Time-division multiplexing
Time-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
to transport the actual circuit data.
Early telephone exchanges are 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. 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.
Compared to datagram packet switching
Circuit switching contrasts with packet switchingPacket switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
which divides the data to be transmitted into small units, called packets, transmitted through the network independently. Packet switching shares available network bandwidth between multiple communication sessions.
Multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
multiple telecommunications connections over the same physical conductor has been possible for a long time, but nonetheless each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls.
In circuit switching, and virtual circuit switching, a route and bandwidth is reserved from source to destination. Circuit switching can be relatively inefficient because capacity is guaranteed on connections which are set up but are not in continuous use, but rather momentarily. However, the connection is immediately available while established.
Packet switching is the process of segmenting a message/data to be transmitted into several smaller packets. Each packet 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 packet is dispatched independently and each may be routed via a different path. At the destination, the original message is reassembled in the correct order, based on the packet number. 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.
Examples of circuit-switched networks
- public switched telephone networkPublic switched telephone networkThe public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
(PSTN) - ISDN B-channel
- Circuit Switched DataCircuit Switched DataCircuit Switched Data is the original form of data transmission developed for the time division multiple access -based mobile phone systems like Global System for Mobile Communications...
(CSD) and High-Speed Circuit-Switched DataHigh-Speed Circuit-Switched DataHigh-speed circuit-switched data , is an enhancement to Circuit Switched Data , the original data transmission mechanism of the GSM mobile phone system, four times faster than GSM, with data rates up to 38.4 kbit/s....
(HSCSD) service in cellular systems such as GSM - DatakitDatakitDatakit is a virtual circuit switch which was developed at Bell Labs for both local-area and wide-area networks, and in widespread deployment by the Regional Bell Operating Companies ....
- X.21X.21X.21 is an interface specification for differential communications introduced in the mid 1970s by the ITU-T. X.21 was first introduced as a means to provide a digital signaling interface for telecommunications between carriers and customers' equipment...
(Used in the German DATEX-L and Scandinavian DATEX circuit switched data network)
See also
- Packet switchingPacket switchingPacket switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
- Message switchingMessage switchingIn telecommunications, message switching was the precursor of packet switching, where messages were routed in their entirety, one hop at a time. It was first introduced by Leonard Kleinrock in 1961. Message switching systems are nowadays mostly implemented over packet-switched or circuit-switched...
- Call (telecommunications)
- Clos networkClos networkIn the field of telecommunications, a Clos network is a kind of multistage circuit switching network, first formalized by Charles Clos in 1953, which represents a theoretical idealization of practical multi-stage telephone switching systems. Clos networks are required when the physical circuit...
- Time-Driven SwitchingTime-driven switchingIn Telecommunication and Computer networking, Time-Driven Switching is a node by node time variant implementation of Circuit switching, where the propagating datagram is shorter in space than the distance between source and destination...
- Connection-orientedConnection-orientedConnection-oriented communication is a data communication mode in telecommunications whereby the devices at the end points use a protocol to establish an end-to-end logical or physical connection before any data may be sent. In case of digital transmission, in-order delivery of a bit stream or...