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Switching

* Switching is a method in which communication devices are connected to one another efficiently.
* A switch is intermediary hardware or software that links devices together temporarily.
* There are three fundamental switching methods: circuit switching, packet switching, and message switching.
* In circuit switching, a direct physical connection between two devices is created by space-division switches, time-division switches, or both.
* In a space-division switch, the path from one device to another is spatially separate from other paths.
* A crossbar is the most common space-division switch. It connects n inputs to m outputs via n × m crosspoints.
* Multistage switches can reduce the number of crosspoints needed, but blocking may result.
* Blocking occurs when not every input has its own unique path to every output.
* In a time-division switch, the inputs are divided in time, using TDM. A control unit sends the input to the correct output device.
* The time-slot interchange and the TDM bus are two types of time-division switches.
* Space- and time-division switches may be combined.
* A telephone network is an example of a circuit-switched network.
* A telephone system has three major components: local loops, trunks, and switching offices.
* The United States is divided into more than 200 local exchange carriers (ILECs) and competitive local exchange carriers (CLECs). Inter-LATA services are handled by interexchange carriers (IXCs).
* Telephone companies provide digital services such as switched/56 services and digital data services.
* The AT&T monopoly was broken in 1984 through a government suit.