ETSI EN 301 001-4 English Printed Edition English PDF Integrated Services Digital Network (ISDN); Outgoing Call Barring (OCB) supplementary services; 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 use

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