ETSI EN 300 188-4 English Printed Edition English PDF Integrated Services Digital Network (ISDN); Three-Party (3PTY) supplementary service; Digital Subscriber Signalling System No. one (DSS1) protocol; Part 4: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma specification for the user

standard published 05/01/2000 by European Telecommunications Standards Institute