The Access Assignment Channel (AACH) is a radio channel in Terrestrial TrunkedRadio
(TETRA). The AACH radio channel is generated in the Medium Access Control (MAC). It is a unidirectional radio channel for the downlink over which the access rights to the control channels and the slots for the uplink and downlink instructions from each physical channel are indicated. The AACH information is mapped in the broadcast block and is present on each downlink slot.