Carrier System

In telecommunication, a carrier system (loosely, a synonym with carrier) is a multichannel telecommunications system in which a number of individual channels (e.g. data, audio, video or combination thereof) are multiplexed for transmission. The transmission occurs between nodes of a network.

In carrier systems, many different forms of multiplexing may be used, such as time-division multiplexing and frequency-division multiplexing. A cable television system is an example of a carrier system that uses frequency-division multiplexing. Many different television programs are carried simultaneously on the same coaxial cable by sending each at a different frequency. Multiple layers of multiplexing may ultimately be performed upon a given input signal; i.e., the output resulting from one stage of modulation may in turn be modulated. For example, in the public telephone network, many telephone calls are sent over shared trunklines by time-division multiplexing; then for long distance calls several of these channels may be sent over a communications satellite link by frequency-division multiplexing. At a given node, specified channels, groups, supergroups, etc. may be demultiplexed by add-drop multiplexers without demultiplexing the others.