ETSI EN 300 210-4 English Printed Edition English PDF Integrated Services Digital Network (ISDN); Freephone (FPH) 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 12/01/1998 by European Telecommunications Standards Institute