scope:

The present document defines the stage 3 specifications of the Supplementary Service Priority Call (SS-PC) for the Terrestrial Trunked RAdio (TETRA).

The SS-PC enables a user to have preferential access to the network resources in the TETRA system in times of congestion. The SS-PC applies for the basic services: circuit mode calls (speech or data). The SS-PC specifies the definition, activation, deactivation and interrogation for the usage of low and high call priorities in the TETRA system. The operations are defined for the Switching and Management Infrastructure (SwMI), for the Mobile Station (MS) and for the Line Station (LS). SS-PC can be defined to subscribers of one TETRA system, but the subscribers can be located in several TETRA systems and the information flows can be delivered over the Inter System Interface (ISI). SS-PC can also be invoked for basic services within one TETRA system or for basic services that extend over ISI to several TETRA systems.

The pre-emptive priorities are outside of the scope of the present document.

Man-Machine Interface (MMI) and Charging principles are outside the scope of the present document.

Supplementary Service stage 3 specification is preceded by the stage 1 and the stage 2 specifications of the service. Stage 1 describes the functional capabilities from the user's point of view. Stage 2 defines the functional behaviour in terms of Functional Entities (FEs) and information flows. Stage 3 gives a precise description of the Supplementary Service from the implementation point of view. It defines the protocol for the service and the encoding rules for the information flows. It defines the processes for the functional entities and their behaviour. The described protocols and behaviour apply to the SwMI, for the MS and for the LS and can be applied over the ISI between TETRA systems. Aspects relating to all supplementary services are detailed in EN 300 392-9 [2].