Terrestrial Trunked Radio (TETRA) - Voice plus Data (V+D) - Part 11: Supplementary services stage 2 - Sub-part 13: Call Completion to Busy Subscriber (CCBS)
Digital cellular telecommunications system (Phase 2) - General requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN) - (GSM 09.07 version 4.13.1)
Digital cellular telecommunications system (Phase 2+) - Specification of the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface (GSM 11.11 version 5.10.1 Release 1996)
Digital cellular telecommunications system (Phase 2) - Base Station System (BSS) equipment specification - Part 2: Signalling aspects (GSM 11.23 version 4.9.1)
Digital cellular telecommunications system (Phase 2) - Radio Link Protocol (RLP) for data and telematic services on the Mobile Station-Base Station System (MS-BSS) interface and the Base Station System-Mobile-services Switching Centre (BSS-MSC) interface (GSM 04.22 version 4.5.1)
Digital cellular telecommunications system (Phase 2+) - General on Terminal Adaptation Functions (TAF) for Mobile Stations (MS) (GSM 07.01 version 5.9.1 Release 1996)