scope:

The present document defines the stage one of the Call Forwarding Busy (CFB) supplementary service for the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators. Stage one is an overall service description from the user' s point of view (see ITU-T Recommendation I.130 [1]), but does not deal with the details of the human interface itself. The present document defines the interworking requirements of private ISDNs with the public ISDN. In addition the present document specifies the base functionality where the service is provided to the user via a private ISDN.