ETS 300 137 : integrated services digital network (ISDN): closed user group (CUG) supplementary service: functional capabilities and information flows / European Telecommunications Standards Institute
ETS 300 153 : integrated services digital network (ISDN): attachment requirements for terminal equipment to connect to an ISDN using ISDN basic access: (candidate NET3 part 1) / European Telecommunications Standards Institute
ETS 300 245 : integrated services digital network (ISDN): technical characteristics of telephony terminals / European Telecommunications Standards Institute
ETS 300 281 : integrated services digital network (ISDN): telephony 7 kHz teleservice terminal requirements necessary for end-to-end compatibility / European Telecommunications Standards Institute