A method of multiplexing several communication channels on one higher bandwidth channel. It works by quickly cycling around each of the smaller channels in a round-robin fashion, taking a sample from each and putting it out over the larger channel. By staying synchronized with the multiplexer, the demultiplexer can read the samples off the higher bandwidth channel and place them, round-robin, back onto lower bandwidth channels at the receiving end.

In addition to the transmitted data, synchronization information is sent, sometimes on an alternate signalling channel. If the mux and demux get out of sync, the information will end up on the wrong channels at the receiving end, and all hell will break loose.