ETSI EN 300 138-6 English Printed Edition English PDF Integrated 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 specification for the network

standard published 11/01/1999 by European Telecommunications Standards Institute