OENORM EN 300356-8 V 4.1.2
Integrated Services Digital Network (ISDN) - Signalling System No.7 (SS7) - ISDN User Part (ISUP) version 4 for the international interface - Part 8: User-to-User Signalling (UUS) supplementary service [ITU-T Recommendation Q.737, clause 1 (1997), modified]