The present document defines the stage 2 specification of the Supplementary Service Barring of Outgoing Calls (SS-BOC) for the Terrestrial Trunked Radio (TETRA) as provided by European operators. SS-BOC enables barring restriction for outgoing calls to be set. SS-BOC specifies the definition, interrogation and operation of the supplementary service. The Switching and Management Infrastructure (SwMI) applies the SS-BOC definitions when the restricted user requests an outgoing service.