This fourth part of EN 301 060 is applicable to the Basic call control extensions at the "b" service entry point for VPN
applications for the pan-European Integrated Services Digital Network (ISDN) as provided by European public
telecommunications operators at the T reference point (as defined in ITU-T Recommendation I.411 [11]) by means of the
Digital Subscriber Signalling System No. one (DSS1) protocol. Stage three identifies the protocol procedures and
switching functions needed to support a telecommunications service (see ITU-T Recommendation I.130 [10]).
The present document specifies the Abstract Test Suite (ATS), and partial Protocol Implementation eXtra Information for
Testing (PIXIT) proforma for the user side of the T reference point or coincident S and T reference point of
implementation conforming to EN 301 060-1 [6] in compliance with the relevant requirements and in accordance with the
relevant guidance given in ISO/IEC 9646.