The present document defines the stage 2 specification of the Supplementary Service Ambience Listening (SS-AL) for
the Terrestrial Trunked Radio (TETRA). Stage 2 identifies the functional entities involved in the supplementary service
and the information flows between them. Aspects relating to all supplementary services are detailed in
EN 300 392-9 [2].
NOTE: The stage 2 description is followed by the stage 3 description, which specifies the encoding rules for the
information flows and process behaviour for the different entities in the SwMI and in the MS.
Charging principles and Man-Machine Interface (MMI) are outside the scope of the present document.
The SS-AL enables a served user to place a TETRA Mobile Station (MS) into a special type of voice call whereby the
called MS transmits without any action from, or indication to, the affected user. The ambience listening call may
include a second listening party.