A CUG is a group of users that can be members of one or other public authorities; Every RDSI member of a CUG is identified by an RDSI number. The additional user group service (CUG) allows a group of users to communicate only between them or, if necessary, only one or more users may have access to the group.
ITU-T Q.735.1 SPANISH-1993 history
1993ITU-T Q.735.1 SPANISH-1993 Stage 3 Description for Community of Interest Supplementary Services Using SS No. 7 Clause 1 - Closed User Group (CUG)