ETSI EN 300 356-21 English Printed Edition English PDF Integrated Services Digital Network (ISDN); Signalling System No.7 (SS7); ISDN User Part (ISUP) version 4 for the international interface; Part 21: Anonymous Call Rejection (ACR) supplementary service [ITU-T Recommendation Q.731, clause 4 (1993)]

standard published 07/01/2001 by European Telecommunications Standards Institute