The present document defines principles and requirements generally applicable to the stage 2 and 3 descriptions of supplementary services for the Terrestrial Trunked Radio (TETRA). The present document is applicable to any TETRA terminal equipment (Mobile Station (MS) or Line Station (LS)) and to any TETRA network (Switching and Management Infrastructure - SwMI) which support at least one TETRA Supplementary Service (SS). In addition, its routeing requirements of supplementary service information are applicable to any TETRA network with a Voice plus Data (V+D) Inter-System Interface (ISI) to another TETRA network which supports at least one TETRA SS.