ETSI TS 101 818-4 English Printed Edition English PDF Integrated Services Digital Network (ISDN); Digital Subscriber Signalling System No. one (DSS1) protocol; Trunk Hunting (TH) supplementary service; Part 4: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma specification for the user

standard published 11/01/2001 by European Telecommunications Standards Institute