Integrated Services Digital Network (ISDN) - Digital Subscriber Signalling System No. one (DSS1) protocol; Signalling network layer for circuit-mode basic call control - Part 1: Protocol specification [ITU-T-Recommendation Q.931 (1993), modified] (Endorsement of the English version EN 300403-1 V 1.3.2 (1999-11) as German standard)
Edition 2000-10

Information Technology - Telecommunications and Information Exchange Between Systems - Private Integrated Services Network - Circuit Mode Bearer Services - Inter-Exchange Signalling Procedures and Protocol
Edition 2001-02-01

Information Technology - Telecommunications and Information Exchange Between Systems - Private Integrated Services Network - Mapping Functions for the Employment of Virtual Private Network Scenarios
Edition 2004-01-01

Integrated Services Digital Network (ISDN) - Digital Subscriber Signalling System No. one (DSS1) protocol - Signalling network layer for circuit-mode basic call control - Part 1: Protocol specification [ITU-T Recommendation Q.931 (1993), modified]
Edition 2000-02-01