direct mode operation (TETRA) (DMO)
Terrestrial Trunked Radio(TETRA) knows different Tetra services with which the communication of the participants is supported. In direct mode operation (DMO), two devices in direct call or several Tetra terminals in group call can communicate with each other directly, i.e. without using the Tetra network, via their air interface.
In this mode of operation, a single terminal performs the switching functions between the subscribers. In the switching function, the mobile switching node acts as a gateway via which the connection to the Tetra network can also be established.
Communication is initiated by the subscriber who presses the talk button first. The corresponding mobile device then forms the master, the other devices are the slaves. To ensure that the radio traffic of DMO operation does not interfere with trunked mode operation( TMO) via the exchanges, DMO operation is assigned its own radio frequencies, which are set in the radios beforehand. The frequency band between 406.1 MHz and 410 MHz has also been released for direct mode. This means that additional transmission channels are available for DMO operation.