half duplex (HDx)
Half-duplex operation (HDx) is a type of data transmission in which the data stations can transmit and receive over the same channel, but not simultaneously.
Half-duplex allows the alternate use of a transmission line in both directions and is therefore also referred to as alternating operation. With half-duplex, only transmission or reception is possible at the interfaces at any one time. The signal direction is reversed. It corresponds to non-simultaneous two-way communication. Examples of half-duplex transmissions are professional radio, trunked radio such as Chekker and walkie-talkies.
If the two data stations can transmit and receive at the same time, it is duplex or full duplex; if only one station can transmit data and the other receive data at a time, it is simplex.