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communications channelAlso called a "circuit" or "line," it is a pathway over which data are transferred between remote devices. It may refer to the entire physical medium, such as a telephone line, optical fiber, coaxial cable or twisted wire pair, or, it may refer to one of several carrier frequencies transmitted simultaneously within the line.
the engineering devices and communications circuit in which signals containing data propagate from a transmitter to a receiver. The engineering devices (electrical signal amplifiers and devices for encoding and decoding the signals) are located at intermediate (repeater) stations and the terminal stations of the channel. The communications circuit may be various kinds of lines such as aerial and cable wires, radio and radio-relay links, and wave guides. The transmitter converts the messages into signals, which are fed to the input of the communications circuit; from the signal received at the channel’s output, the receiver reproduces the transmitted messages. The transmitter, communications circuit, and receiver constitute a communications system, or a data-transmission system.
A distinction is made among telephone, sound-broadcasting, television, facsimile, telegraph, telemetry, remote-control, and digital data-transmission channels, depending on the purpose of the system of which the communications channel is a part; depending on the type of signals transmitted by the channels, they may be classified as continuous or discrete with respect to both values and time. A communications channel usually has a large number of inputs and outputs and is called a multiplexed channel; it can provide two-way signal transmission.