In addition to direct mode operation ( DMO), in which the end users can communicate directly with each other, terrestrial trunked radio ( TETRA) also has trunked mode operation (TMO). This is the standard operation via the Tetra network.
In TMO operation, communication between two or more terminals takes place via the radio network. The subscriber who has a connection request dials into the Tetra network, which connects him to the desired subscriber or subscribers via the various switching stations.
In TMO mode, there is the single connection between two communication partners, the direct call, and the connection with a group, the group call. The single call operates in duplex, so that everyone can talk and receive at the same time, whereas the group call operates in half-duplex. In this mode, specific groups can be addressed, for example, for use in fire or emergency situations.