18-03-2011, 06:28 PM
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 | M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
 Switching
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.
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