Integrated Services Digital Network (ISDN); Closed User Group (CUG) supplementary service; functional capabilities and information flows; english version ETS 300137:1992
Integrated Services Digital Network (ISDN) - Signalling System No.7 (SS7) - ISDN User Part (ISUP) version 4 for the international interface - Part 9: Closed User Group (CUG) supplementary service [ITU-T Recommendation Q.735, clause 1 (1993), modified]
