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Channel

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A channel is essentially a communication circuit between two or more devices. You can think of a channel as a pipe for sending data between two systems. In a computer system, a channel provides an input/output interface between the processor and some peripheral device. In telecommunication, a channel may take one of the forms described below and pictured in Figure C-10. Keep in mind that a channel may be one of many channels that run over the same physical circuit. These channels are called virtual channels or virtual circuits.

  • One channel carried on a physical wire or wireless medium between two systems. The twisted-pair copper wire in the local loop between your phone and the local central office is a dedicated channel that forms its own circuit.

  • Time-division multiplexed channels, in which signals from several sources such as telephones and computers are merged into a single stream of data and separated by intervals of time.

  • Frequency-division multiplexed channels, in which signals from many sources are transmitted over a single wire or wireless medium by modulating each signal on carriers at different frequencies.

  • Packet or cell switching, in which packets from many sources are multiplexed and transmitted from endpoint to endpoint over a switched network.

[Figure 10: See book]

For applications that use TCP, a virtual circuit is set up as a logical link between applications and processes running on different systems. A system may have several TCP connections set up between multiple systems at any one time. When connected to the Internet, you can simultaneously obtain your mail and connect with a server to check stocks or news. Packets flow into your system across virtual connections that cross the Internet. Each connection is managed as a socket, which is essentially an IP address and a port number. See "Ports" and "Sockets API" for more information. Also see TCP (Transmission Control Protocol).

The topics "Bandwidth" and "Delay, Latency, and Jitter" discuss channel capacities and delay problems. A related topic is "Throughput." The topic "Cable and Wiring" discusses cabling systems and things that affect transmissions, including interference, cable distance, and so on.




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