Aduplexcommunication systemis apoint-to-pointsystem composed of two connected parties or devices that can communicate with one another in both directions, simultaneously. An example of a duplex device is atelephone. The people at both ends of a telephone call can speak at the same time and simultaneously each be heard by the other at the same time. The earphone reproduces the speech of the other person as the microphone transmits the speech of the local person, because there is a two-way communication channel between them.
Duplex systems are employed in many communications networks, either to allow for a communication "two-way street" between two connected parties or to provide a "reverse path" for the monitoring and remote adjustment of equipment in the field.
Systems that do not need the duplex capability use insteadsimplex communicationin which one device transmits and the others can only "listen" and can not be heard while in the moment of "listening" (one transmits/talks and the other can only receive/listen at a time). Examples arebroadcastradio and television,garage door openers,baby monitors,wireless microphones,radio controlled models,surveillance cameras, and missiletelemetry.
