Trunked Mode Operation (TMO) and Direct Mode Operation (DMO)

Trunked Mode Operation means using TETRA mobile radios in combination with network infrastructure while Direct Mode Operation is TETRA radio  communication between mobile radios without using a TETRA network infrastructure.

Trunked Mode Operation (TMO)

When a TETRA mobile radio starts a groupcall by pressing the "Push To Talk" (PTT) audio will be transmitted to the selected TETRA basestation. The other radios that have the same talkgroup selected and are located in a different geographical area and are being served by a different TETRA basestation receive the audio via their basestation. In TMO mode the network intelligence is used to assign a channels and transport the audio from sender to receiver. The audio is transported by the TETRA network or infrastructure.

Direct Mode Operation (DMO)

In DMO mode the TETRA mobile stations communicate directly with each other without using the TETRA infrastructure. The radio need to stay withing coverage of each other. DMO is often used in situation were coverage of TETRA network infrastructure is not available.