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.

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 the relevant stage two and stage three documents.

Furthermore, conformance to the present document is met by conforming to the stage three documents with the field of application appropriate to the equipment being implemented. Therefore, no method of testing is provided for the present document.