This first part of EN 301 065 specifies the stage three of the Completion of Calls on No Reply (CCNR) 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
ITU-T Recommendation I.411 [6]) by means of the Digital Subscriber Signalling System No. one (DSS1) protocol.
Stage three identifies the protocol procedures and switching functions needed to support a telecommunication service
(see CCITT Recommendation I.130 [3]).
In addition, the present document specifies the protocol requirements at the T reference point where the service is
provided to the user via an intermediate private ISDN.
The present document does not specify the additional protocol requirements where the service is provided to the user via
a telecommunications network that is not an ISDN.
The CCNR supplementary service enables user A, encountering a destination B, which does not answer the call, to have
the call completed without having to make a new call attempt when the destination B becomes not busy after having
initiated an activity .
The CCNR supplementary service is applicable to all circuit-switched telecommunication services with the following
exceptions:
a) call 2 of the videotelephony teleservice;
b) call 2 of the audiographic conference teleservice;
c) call 2 and subsequent calls of videoconference teleservice;
d) all other circuit-switched telecommunication services requiring the use of more than one B-channel.
Further parts of EN 301 065 specify the method of testing required to identify conformance to the present document.
The present document is applicable to equipment supporting the CCNR supplementary service, to be attached at either
side of a T reference point or coincident S and T reference point when used as an access to the public ISDN.