lls to and receive calls from PABX/PSTN and other external systems Handle emergency calls Communicate with one or several groups Send and receive status and short data messages The most common management functions performed by the dispatcher are the following: Add and remove radio users from groups Create new groups and temporary groups TETRA Main Features Table D.2 Base station power classes Nominal output Class power (dBm) Add new radio users to the system or modify communication rights and other attributes of existing radio users Manage groups and group areas Manage organisations Manage workstations and client applications Manage parameters, connection groups and circuit groups Figure D.2 shows the interfaces that the TETRA standard specifies: Air interface (between the radio base station and the radio terminal) Peripheral equipment interface (between the radio terminal and peripheral equipment such as the computer) Intersystem interface (between the TETRA network of different manufacturers) Direct mode operation (between radio terminals for direct communication) Each of these interfaces is described in detail in the relevant ETSI recommendation. The manufacturers can freely design the other interfaces (e.g. the interface between the radio base station and the digital switch). D.4 TETRA Main Features The TETRA standard introduces very interesting features for the emergency and safety networks and most of them are innovative for existing analogue systems and nonstandard networks. Each user, depending by his/her rights, can perform individual or group communication. Individual communication can be full duplex or half duplex. This type of call is point-to-point, i.e. between two users. On the contrary, in a group call different users can be involved in the same time (point-to-multipoint). However, only one user can speak at a time according to the priority. The creation of this group of users is not restricted to an area or number of channels; furthermore, with additional features the group calls allocate traffic