An initiative from the European Telecommunications Standards Institute (ETSI) for a single standard for digital mobile radio services. Terrestrial Trunked Radio (Tetra) is defined in a memorandum of understanding between a number of different equipment vendors, service providers, testing bodies, and regulatory agencies that was laid out in 1994.
Tetra consists of two complementary standards:
Tetra includes support for security features such as multilevel authentication and encryption, allows voice and data communication to be combined using the same equipment, and supports multiplexing of up to four channels to provide data rates of up to 144 Kbps. Tetra is complementary to the Global System for Mobile Communications (GSM) cellular communication standard: GSM can be considered an extension of the Integrated Services Digital Network (ISDN) to the wireless domain, while Tetra is an extension of ISDN Private Branch Exchange (PBX) systems to the same domain. Tetra thus provides additional communication functionality not built into GSM, such as direct mobile-to-mobile communication that bypasses the communication infrastructure, support for broadcast and group call features, fast call setup, priority call, and so on.
Because of the recent growth of the Internet and wide demand for high-speed wireless mobile data services, a new high-speed wireless mobile packet-switching system called the Digital Advanced Wireless System (DAWS) is currently being developed by the ETSI to supersede the Tetra PDO standard.