The DMR standard allows for the ability to use the second time-slot for reverse-channel signalling – that is, instructions in the form of signalling being sent to the radio on the second time slot channel while the first channel is in a call. This enables priority call control, remote control of the transmitting radio, or emergency call pre-emption and gives precise control and flexibility to the operator of a radio system. FDMA systems cannot deliver similar functionality because they are limited to one path only per spectrum channel.
