Integrated Services Digital Network (ISDN); Direct Dialling in (DDI) Supplementary Service Digital Subscriber Signalling System No. One (DSS1) Protocol
This standard specifies the stage three of the Direct Dialling in (DDI) supplementary service for the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators at the T reference point or coincident S and T reference point (as defined in CCITT Recommendation I.411 [1]) by means of the Digital Subscriber Signalling System No. one (DSS1). Stage three identifies the protocol procedures and switching functions needed to support a telecommunications service (see CCITT Recommendation I.130 [2]). The DDI supplementary service enables a user to call directly via a public ISDN a user on a private ISDN by using the public ISDN numbering plan. The DDI supplementary service is applicable to all telecommunications services. Further part(s) of this standard specify the method of testing required to Identify conformance to this standard. This standard is applicable to equipment supporting the DDI supplementary service@ to be attached at either side of a T reference point or coincident S and T reference points when used as an access to the public ISDN.