duplex

communications Used to describe a communications channel

that can carry signals in both directions, in contrast to a

simplex channel which only ever carries a signal in one

direction.

If signals can only flow in one direction at a time the

communications is "half-duplex", like a single-lane road with

traffic lights at each end. Walkie-talkies with a

"press-to-talk" button provide half-duplex communications.

If signals can flow in both directions simultaneously the

communications is "full-duplex", like a normal two-lane

road. Telephones provide full-duplex communications.

The term "duplex" was first used in wireless, telegraph, and

telephone communications. Nearly all communications circuits

used by computers are two-way, so the term is seldom used.

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(2001-07-21)