Integrated Services Digital Network (ISDN) - Signalling System No. 7 - ISDN User Part (ISUP) version 2 for the international interface - Part 33: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma specification for basic services [ITU-T Recommendation Q.784.2 (1997), clauses 2 to 5 and annex B to C, modified]; English version ETS 300356-33:1997