two way

A two-way radio is a radio that can both transmit and receive a signal (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, designed for bidirectional person-to-person voice communication with other users with similar radios. Two-way radios are available in mobile, stationary base and hand-held portable configurations. Hand-held two-way radios are often called walkie-talkies, handie-talkies or hand-helds.
Two-way radio systems usually use a single radio channel and operate in a half-duplex mode: the user can talk, or he can listen, but not at the same time. The radio is normally in receive mode so the user can hear all other transmissions on the channel. When the user wants to talk he presses a "push-to-talk" button, which turns off the receiver and turns on the transmitter; when he releases the button the receiver is activated again. Multiple users on the channel must take turns talking. Other two-way radio systems operate in full-duplex mode, in which both parties can talk simultaneously. This requires either two separate radio channels or channel sharing methods such as time division duplex (TDD) to carry the two directions of the conversation simultaneously on a single radio frequency. A cell phone is an example of a full-duplex two-way radio. During a phone call, the phone communicates with the cell tower over two radio channels; an incoming one to carry the remote party's voice to the user, and an outgoing one to carry the user's voice to the remote party.

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