ETSI EN 300 138-6 English Printed Edition English PDF Final draft Version 1.5.1Integrated Services Digital Network (ISDN); Closed User Group (CUG) supplementary service; Digital Subscriber Signalling System No. one (DSS1) protocol; Part 6: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma speci

standard published 12/01/2001 by European Telecommunications Standards Institute