ETSI EN 300 188-4 English Printed Edition English PDF Final draft Version 1.4.1Integrated 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 specificat

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