duplex
Communications with one channel in each
direction. If data can flow in both directions simultaneously
the communications is "{full-duplex}" else it is
"{half-duplex}".
A {simplex} channel can only carry one message at a time,
though it does not imply the channel is unidirectional.
The term "duplex" was first used in wireless, telegraph, and
telephone communications, where "duplex" circuits between
communicating terminals were capable of transmission in both
directions, and "simplex" indicated transmission from a sender
to a reciever, or broadcast to several potential receivers.
Nearly all communications circuits used by computers are
two-way, so the distinction between simplex and duplex is
seldom made.
(2000-03-30)