Recommendation Q.931 (03/93)
DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 (DSS 1) - ISDN
USER-NETWORK INTERFACE LAYER 3 SPECIFICATION
FOR BASIC CALL CONTROL
(Malaga-Torremolinos, 1984; modified at Helsinki, 1993)
This Recommendation specifies the procedures for the establishing, maintaining, and clearing of network connections at the ISDN user-network interface. These procedures are defined in terms of messages exchanged over the D-channel of basic and primary rate interface structures. The functions and procedures of this protocol, and the relationship with other layers, are described in general terms in Recommendation Q.930 (I.450) [1].
This Recommendation is intended to specify the essential features, procedures, and messages required for call control in the D-channel. However, there are some details of procedure which have not yet been specified, and which will be the subject of further study.