Communications Circuit

(Russian trakt sviazi), a complex of equipment and communication lines designed to establish specialized channels for the transmission of information. Communications circuits are characterized by specific, standard criteria, such as the frequency bandwidth and information transmission rate.

In Russian the concept of a communications circuit is often used in describing multichannel communications systems. For example, in multichannel systems with frequency-division multiplexing, standard voice-frequency channels are combined by means of carrier terminal equipment into standard 12-channel groups that occupy a standard frequency band of 60–108 kilo-hertz (the primary group circuit). The standard secondary group of channels occupies the frequency band 312–552 kilohertz (the secondary group circuit) and is formed by combining five standard primary groups. Additional groups of channels are formed in the same way. The set of all channel groups in a multichannel system constitutes a group, or multichannel, communications circuit, which may be characterized by the system’s total frequency bandwidth.

The standard criterion used for data-transmission systems is the information transmission rate. Data-transmission circuits are classified as low-speed (50 to 200–300 bits/sec), medium-speed (600–10,000 bits/sec), and high-speed (48,000 bits/sec and higher) circuits. A data-transmission circuit consists of several standard channels, data-transmission equipment, including such signal-conversion equipment as modulators and demodulators (modems), channel-monitoring equipment, and error-protection equipment. In addition to their use in multichannel communication and data transmission, standard communications circuits are also found in television, audio-broadcasting, broadband, and video-telephone communications.

In Russian the concept of a communications circuit is sometimes used in a narrower sense to designate the antenna/waveguide channel of a radio-relay link, a group channel in pulse-code modulation equipment, or the linear channel of multiplexing systems.