In
telecommunicationTelecommunication is transmission over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, drums, semaphore, flags or heliograph. In modern times, telecommunication typically involves the use of electronic devices such as the telephone,...
s, a
circuit switching network is one that establishes a
circuitA 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...
(or
channelChannel, in communications , refers to the medium used to convey information from a sender to a receiver.- Overview :...
) between
nodesIn communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
and
terminalsIn the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers, work stations, routers in a VoIP network....
before the
usersIn telecommunications, a user is a person, organization, or other entity that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information....
may communicate, as if the nodes were physically connected with an electrical circuit.
The bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying
packet transfer delayPacket 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.
In
telecommunicationTelecommunication is transmission over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, drums, semaphore, flags or heliograph. In modern times, telecommunication typically involves the use of electronic devices such as the telephone,...
s, a
circuit switching network is one that establishes a
circuitA 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...
(or
channelChannel, in communications , refers to the medium used to convey information from a sender to a receiver.- Overview :...
) between
nodesIn communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
and
terminalsIn the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers, work stations, routers in a VoIP network....
before the
usersIn telecommunications, a user is a person, organization, or other entity that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information....
may communicate, as if the nodes were physically connected with an electrical circuit.
The bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying
packet transfer delayPacket 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 in a dedicated circuit that channel remains unavailable to other users. Channels that are available for new calls to be set up are said to be idle.
Virtual circuit switching is a
packet switchingPacket switching is a digital network communications method that groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all...
technology that may emulate circuit switching, in the sense that the connection is established before any packets are transferred, and that packets are delivered in order.
There is a common misunderstanding that circuit switching is used only for connecting voice circuits (analog or digital). 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 non-stop transfer without requiring packets and without most of the overhead traffic usually needed, making maximal and optimal use of available bandwidth. The disadvantage of inflexibility tends to reserve it for specialized applications, particularly with the overwhelming proliferation of internet-related technology.
The call
For
call setupIn 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 (
POTSPlain 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 most parts of the world. The name is a retronym, and is a reflection of the telephone service still available after the...
) does not.
The method of establishing the connection and monitoring its progress and termination through the network may also utilize a
separate control channelSeparate 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
CCS7Signaling System Number 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
TDMTime-division multiplexing is a type of digital or analog multiplexing in which two or more signals or bit streams 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...
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
Since the first days of the
telegraphThe electrical telegraph is a telegraph that uses electric signals. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages over wire...
it has been possible to
multiplexThe 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 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.
With circuit switching, and virtual circuit switching, a route is reserved from source to destination. The entire message is sent in order so that it does not have to be reassembled at the destination. Circuit switching can be relatively inefficient because capacity is wasted on connections which are set up but are not in continuous use (however momentarily). On the other hand, the connection is immediately available and capacity is guaranteed until the call is disconnected.
Circuit switching contrasts with
packet switchingPacket switching is a digital network communications method that groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all...
which splits traffic data (for instance, digital representation of sound, or computer data) into chunks, called packets, that are routed over a shared network.
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 the number of the packet, precluding the need for a dedicated path to help the packet find its way to its destination. Each is dispatched and many may go via different routes. 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 almost simultaneously over the same channel.
Examples of circuit switched networks
- Public Switched Telephone Network (PSTN)
The public switched telephone network is the network of the world's public circuit-switched telephone networks, in much the same way that the Internet is the network of the world's public IP-based packet-switched networks...
- ISDN B-channel
- Circuit Switched Data
Circuit 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 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. But actually on mobile the speed is less than 15kb/s.Like in circuit-switched...
(HSCSD) service in cellular systems such as GSM
- Datakit
Datakit is a virtual circuit-switched network layer computer networking protocol similar to X.25, developed at Bell Labs for both local-area and wide-area networks, and in widespread deployment by the Regional Bell Operating Companies . It supports file transfers, remote login, remote printing, and...
- X.21
X.21, sometimes referred to as X21, interface is a specification for differential communications introduced in the mid 1970’s by the ITU-T. X.21 was first introduced as a means to provide a digital signaling interface for telecommunications between carriers and customer’s equipment...
(Used in the German DATEX-L and Scandinavian DATEX circuit switched data network)
See also
- Packet switching
Packet switching is a digital network communications method that groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all...
- Message switching
In 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...
- Call (telecommunications)
In computer science and telecommunications a call is:* Any attempt to set up a telecommunication circuit* A unit of traffic measurement* The actions performed by a call originator* A telephone call...
- Clos network
In the field of telecommunications, a Clos network is a kind of multistage 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 switching...
- Time-Driven Switching
In 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...
External links