multiplexing

multiplexing in communication, technique whereby two or more independent messages, or information-bearing signals, are carried by a single common medium, or channel. When multiplexing is performed, two or more channels are combined into a single channel, or, in a process often called demultiplexing, a single channel is divided into several subchannels. Many different types of multiplexing are possible. One type is frequency-division multiplexing, in which a single frequency channel is subdivided into two or more subchannels, each of which can then carry a smaller range of frequencies than could the original channel. Frequency-division multiplexing is used in television broadcasting, when audio and video signals share a single channel; in stereophonic FM radio broadcasting, when two audio signals share a single channel; and in microwave transmission of long-distance telephone calls, when 60 or more conversations are carried by a single microwave beam. A second type of multiplexing is time-division multiplexing, in which successive small time intervals are used for the transmission of messages over a single channel. Time-division multiplexing is often used in the construction of digital computers. When information can be stored into or retrieved from the computer's memory at a much greater rate than it can be supplied or used by an external device such as a card reader, printer, or teletype terminal, several such low-speed devices can share a single multiplexed data channel.

multiplexing The process of combining multiple messages simultaneously on the same physical or logical transmission medium. There are two main types: time division multiplexing (TDM) and frequency division multiplexing (FDM). In TDM a device is allocated specific time slots in which to use the transmission medium. FDM divides the transmission medium into channels of smaller bandwidth to which the user has exclusive rights. FDM and TDM can be combined to provide devices with time slots of logical channels.