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Terrestrial Trunked Radio〔ETSI EN 300 392-2 v3.2.1〕 (TETRA) (formerly known as Trans-European Trunked Radio) is a professional mobile radio and two-way transceiver (colloquially known as a walkie talkie) specification. TETRA was specifically designed for use by government agencies, emergency services, (police forces, fire departments, ambulance) for public safety networks, rail transport staff for train radios, transport services and the military. TETRA is a European Telecommunications Standards Institute (ETSI) standard, first version published 1995; it is mentioned by the European Radiocommunications Committee (ERC).〔(【引用サイトリンク】url=http://www.ero.dk/B8FF1CC0-8C6C-4C8C-9019-7EB21FCABBD6?frames=no& )〕 == Description == TETRA uses Time Division Multiple Access (TDMA) with four user channels on one radio carrier and 25 kHz spacing between carriers. Both point-to-point and point-to-multipoint transfer can be used. Digital data transmission is also included in the standard though at a low data rate. TETRA Mobile Stations (MS) can communicate direct-mode operation (DMO) or using trunked-mode operation (TMO) using switching and management infrastructure (SwMI) made of TETRA base stations (TBS). As well as allowing direct communications in situations where network coverage is not available, DMO also includes the possibility of using a sequence of one or more TETRA terminals as relays. This functionality is called DMO gateway (from DMO to TMO) or DMO repeater (from DMO to DMO). In emergency situations this feature allows direct communications underground or in areas of bad coverage. In addition to voice and dispatch services, the TETRA system supports several types of data communication. Status messages and ''short data services'' (SDS) are provided over the system's main control channel, while packet-switched data or circuit-switched data communication uses specifically assigned channels. TETRA provides for authentication of terminals towards infrastructure and vice versa. For protection against eavesdropping; air interface encryption and end-to-end encryption is available. The common mode of operation is in a group calling mode in which a single button push will connect the user to the users in a selected call group and/or a dispatcher. It is also possible for the terminal to act as a one-to-one walkie talkie but without the normal range limitation since the call still uses the network. TETRA terminals can act as mobile phones (cell phones), with a full-duplex direct connection to other TETRA Users or the PSTN. Emergency buttons, provided on the terminals, enable the users to transmit emergency signals, to the dispatcher, overriding any other activity taking place at the same time. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Terrestrial Trunked Radio」の詳細全文を読む スポンサード リンク
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