Integrated Services Digital Network (ISDN); Signalling System No. 7 (SS7) - ISDN User Part (ISUP) version 3 for the International interface - Part 36: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma specification for supplementary services (Endorsement of the English version EN 300356-36 V 3.3.1 (2003-01) as German standard)