The present document defines the stage 1 specification of the Barring of Outgoing Call (BOC) supplementary service for the Trans-European Trunked Radio (TETRA). Stage 1 is an overall service description from the users point of view but does not deal with the details of the human interface itself. The present document specifies the service description of the supplementary service and the procedures to be expected with successful and unsuccessful outcomes. In addition, the present document specifies the interactions with other TETRA supplementary services and interworking considerations. Charging principles are outside the scope of the present document. The B