Integrated Services Digital Network (ISDN) - Signalling System No. 7; ISDN User Part (ISUP) version 2 for the international interface - Part 1: Basic services (ITU-T Recommendations Q.761 to Q.764 (1993), modified) (Endorsement of the English version EN 300356-1 V 3.2.2 (1998-08) as German standard)