The present document specifies the stage 3 description of the Supplementary Service Include Call (SS-IC) for the Terrestrial Trunked Radio (TETRA). SS-IC permits the served user participating a call to include other participant to that call. Man-Machine Interface (MMI) and charging principles are outside the scope of the present document. 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 300 392-10-17 [7]). The stage 2 description identifies the functional capabilities and the information flo