ETSI TS 100 600 Digital cellular telecommunications system (Phase 2+) (GSM); Signalling requirements on interworking between the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN) and the Public Land Mobile Network (PLMN) (GSM 09.03 version 6.0.0 Release 1997)

standard by European Telecommunications Standards Institute, 04/01/1999