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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.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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