The present document specifies the stage 3 description of the Supplementary Services CFU Call Forwarding Unconditional@ CFB Call Forwarding on Busy@ CFNRy Call Forwarding on No Reply and CFNRc Call Forwarding on Not Reachable for the Terrestrial Trunked Radio (TETRA). SS-CFU@ SS-CFB@ SS-CFNRy and SS-CFNRc are supplementary services which allow a served user to have a TETRA network send all or specific incoming calls addressed to the served user's TETRA number to another number. Man-Machine Interface and charging principles are outside the scope of the present document. The present document is applicable to Voice plus Data individual call or group call; some parts of the present document are applicable to SDS (Short Data Service); more specifically to the following entities: - the MS of either the calling user or the called user during an individual call or a group call; - the originating Switching and Management Infrastructure (SwMI) in an individual call or a group call; - the group controlling SwMI for a group call; - the terminating SwMI in an individual call; - the interworking SwMI for an individual call. The present document is based on the latest version of ECMA-174 [i.1]. Contrary to ECMA-174 [i.1]@ the present document does not define Call Deflection supplementary service and the present document distinguishes between the case of No Reply and the case of Not Reachable. Moreover@ the present document defines the protocol in cases of group calls and of mobility not covered by ECMA-174 [i.1]. The present document also specifies additional signalling protocol requirements for the support of interactions at the ISI reference point@ other supplementary services and ANFs. The present document is applicable to SwMIs that can interconnect to form a TETRA network.