Stage 3 Description for Community of Interest Supplementary Services Using SS No. 7 Clause 1 - Closed User Group (CUG) Clause 3 - Multilevel Precedence and Preemption - Specifications of Signalling System No. 7 (Study Group XI) 71 pp (ETSI ETS 300 356-9:
The supplementary service Closed User Group (CUG) enables users to form groups, to and from which access is restricted.A specific user may be a member of one or more CUGs.Members of a specificCUG can communicate among themselves but not with users outside the group.SpecificCUG members can have additional capabilitiesthat allow them to originate calls outside the group,and/or to receive calls from outside the group.Specific CUG members can have additional restrictions that prevent them from originating calls to other members of the CUG, or from receiving calls from other members of the CUG.