TETRA communication system is a mobile communication system based on the technique of Time Division Multiple Access (TDMA). In order to satisfy the requirements of mobile communication of special departments in European countries, ETSI combined with users, manufacturers, testing departments and even government to design and establish the unite, standard and open system. The system can provide commands scheduling, data transmission and telephone services based on one platform. It not only provides multiple group Dispatch function, short data message service, packet data services and full duplex mobile telephone services but also supports powerful DMO mode realizing rights judging, air interface encryption and point to point encryption.