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TETRA is an open standard first developed by the ETSI in the early 1990's.

Some unique PMR services of TETRA are:

  • Wide area fast call set-up "all informed net" group calls 
  • Direct Mode Operation (DMO) allowing "back to back" communications between radio terminals independent of the network 
  • High level voice encryption to meet the security needs of public safety organisations 
  • An Emergency Call facility that gets through even if the system is busy 
  • Full duplex voice for PABX and PSTN telephony communications
  • SwMI (Switching and Management Infrastructure)

The abbreviation SwMI is used to classify all of the equipment and sub-systems that comprise a TETRA network, including base stations.

  • 1 - Air Interface

The most important and complex interfaces are considered to be the air interfaces' between the base station and radio terminals (1) and the Direct Mode Operation (DMO) interface (2).

  • 2 - DMO Interface

DMO is a facility that allows terminals to operate in local radio nets independent of the main TETRA network infrastructure.

  • 3 - MMI (Man Machine Interface)

This is the interface that sits between the system and the user. This includes the hardware buttons, menu system and, in a way, the programming software.

  • 4 - Peripheral Equipment Interface

This interface standardises the connection of the radio terminal to an external device, and supports data transmission between applications in the device and the connected TETRA radio terminal. The PEI also supports certain elements of control within the radio terminal from the external device and/or application.

  • 5 - Local Dispatcher Interface

This interface was intended to allow connection to remote wire line dispatcher consoles like those located in major control rooms.  Work on this interface was dropped in ETSI TC TETRA as it was considered too complex to implement without degrading performance.This was because the PMR industry had specialist manufacturers of control room equipment, the majority of which differed in the way they interfaced to PMR networks.  Similarly, the TETRA network architecture of manufacturers also differed.

  • 6 - PSTN/ISDN/PABX Gateway

This standardised interface enables TETRA to interface with the PSTN, the ISDN and/or a PABX.

  • 7 - Inter-System Interface

This standardised Inter-System Interface (ISI) allows infrastructures supplied by different TETRA manufacturers to inter-operate with each other allowing interoperability between two or more networks.

  • 8 - Network Management Interface

Like the local dispatcher interface, it was recognised during standardisation activities that a common network management interface was impractical. Fortunately, this early standardisation was not wasted as it was later turned into a comprehensive guide to assist users in defining network management requirements.