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 users 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.
The present document does not specify the additional requirements where the service is provided to the user via a
telecommunications network that is not an ISDN but does include interworking requirements of other networks with the
public ISDN.
Charging principles are outside the scope of the present document.
Interaction with supplementary services not listed in clause 7 is outside the scope of the present document.
The CFB supplementary service enables a served user to have the network redirect to another user calls which are
addressed to the served user s ISDN number and meet busy. The CFB supplementary service may operate on all calls,
or just those associated with specified basic services. The served user s ability to originate calls is unaffected by the
CFB supplementary service.
The CFB supplementary service is applicable to all circuit-switched telecommunication services.
The present document is applicable to the stage two and stage three documents for the ISDN CFB supplementary
service. The terms "stage two" and "stage three" are also defined in ITU-T Recommendation I.130 [1]. Where the text
indicates the status of a requirement, (i.e. as strict command or prohibition, as authorization leaving freedom, as a
capability or possibility), this shall be reflected in the text of (...abbreviated)