ent types of radio terminals are available depending of the scope of the use and nominal output: Handheld radio terminal Vehicular radio terminal Motorcycle radio terminal Aircraft radio terminal TETRA Network Elements Table D.1 Radio terminal power output classes Nominal output Class power (dBm) Direct Mode Standard PSTN/PABX Dispatcher TETRA TETRA Network A Network B Air Interface Standard Digital Switching Inter System Interface Standard Radio Terminal Hand Held Radio Base Station Peripheral Equipment Interface Standard Figure D.2 TETRA basic equipment and standard interface The radio terminal power output classes are specified by ETSI 392-2 (air interface) (Table D.1). The radio terminals have specific features for TETRA. For example, they usually have special buttons for emergency calls, for selecting the groups and push to talk and are also provided with a loudspeaker (Figure D.3). The SwIM is the heart of the system and contains the higher hierarchical layers in the network. It is mainly dedicated to the management of the overall network resources and to the system synchronisation. The most important functions of the digital switch are the following: TETRA Network Planning Figure D.3 Handheld radio terminal Call control functions Subscriber management Mobility management Management of the radio channel Management of the TETRA base station Management of the dispatcher workstation Signalling The functions of the TETRA base station are the following: Provides the air interface between the switching and management infrastructure and the radio terminals Conversion of the digital base band signal coming from the digital switch to the RF band Table D.2 shows the output power classes of the radio base station. The dispatcher workstation performs control and supervises the communication in the field and man- agement functions such as group management and subscriber administration. The most common dis- patcher communication function are the following: Receive calls and callback requests Make individual calls Make ca