This document specifies the PICS proforma, the Abstract test suite (ATS) and the partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma for the network side of the T reference point or coincident S and T reference point for the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecomunications operators by means of the Digital subscriber Signalling System No. one (DSS1) protocol, for Network Integration Testing (NIT) covering the end-to-end support of ISDN services. The pan-European ISDN is made up by connecting the different national networks and End-to-end NIT covers all the testing activities necessary to access the correct behaviour of the interconnected network from the point of view of access interfaces, network side. Both bearer services (and associated teleservices) and supplementary services are checked for interworking capability and compatibility, in the pan-European ISDN.