TETRA is an acronym for TErrestrial Trunked RAdio. Tetra is an open voice standard developed by the European Telecom Standards Institute (ETSI) and is in use primarally overseas and in Europe. The first users to implement TETRA are the European public safety and emergency services, i.e. Police, Fire, EMS, border control officials, etc.
The existing public safety networks are coming to the end of their economic lifetime and TETRA provides the key features like equiment standardisation, direct mode, encryption and last call set-up time for these services.
TETRA uses a 4-slot TDMA channel, allowing for both Voice and Control channels. It can use strong encryption on the air interface, and this is usually used on sensitive traffic, but commercial networks are often unencrypted.
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