ETSI EN 301 141-6 Integrated Services Digital Network (ISDN); Narrowband Multi-service Delivery System (NMDS); Part 6: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) specification for the NMDS Layer 2 PSTN-GW function (NTN side)

standard by European Telecommunications Standards Institute, 02/01/2002