scope:

This ETS specifies the stage 3 description of the Supplementary Service Call Waiting (SS-CW) for the Terrestrial Trunked Radio (TETRA). SS-CW permits a called user to acknowledge an incoming individual call while he is already busy. Subsequently that user shall have the choice to accept, reject or ignore that incoming call. Man-Machine Interface (MMI) and charging principles are outside the scope of this ETS. Supplementary service specifications are produced in three stages according to the method defined in ITU-T Recommendation I.130 [1]. The stage 1 description specifies the service from the user's point of view (see ETS 300 392-10-11 [7]). The stage 2 description identifies the functional capabilities and the information flows needed to support the service as specified in its stage 1 description (see ETS 300 392-11-11 [8]). The present stage 3 description specifies the protocols at the air interface and at the various Inter-System Interfaces (ISI) to support SS-CW.