The transmission of data in both directions, but only one direction at a time. For example, two-way radio (push-to-talk phones) use half-duplex communications. When one party speaks, the other party listens. Contrast with full-duplex.Are Cellphones Half-Duplex?No, but they often sound as if they are. The cellular system generally uses separate transmit and receive channels for a two-way conversation. However, the GSM system switches back and forth between transmit and receive, and it often does not sound like a two-channel, full-duplex system. No digital cellular system is quite like the good old analog days when each phone call had two dedicated channels the entire session. See push-to-talk and GSM.