ETS 300 136 : integrated services digital network (ISDN): closed user group (CUG) supplementary service: service description / European Telecommunications Standards Institute
ETS 300 137 : integrated services digital network (ISDN): closed user group (CUG) supplementary service: functional capabilities and information flows / European Telecommunications Standards Institute
ETS 300 156 : integrated services digital network (ISDN): attachment requirements for terminal equipment to connect to an ISDN using ISDN primary rate access: (candidate NET 5) / European Telecommunications Standards Institute
ETS 300 245 : integrated services digital network (ISDN): technical characteristics of telephony terminals / European Telecommunications Standards Institute