B.2 Busy condition (NDUB) detected by terminating AS

24.6283GPPCommon Basic Communication procedures using IP Multimedia (IM) Core Network (CN) subsystemProtocol specificationRelease 17TS

This subclause shows an example of a signalling flow when a terminating network determines the user to be busy i.e. the NDUB case.

Figure B.2 shows the signalling flow for the scenario.

NOTE: The signalling flow is simplified for readability reasons.

Figure B.2: Busy condition (NDUB) detected by terminating AS

This signalling flow assumes the following:

– the user in the terminating network needs the involvement of AS for NDUB or other busy condition activated services like CCBS or CFBS; and

– that the filter criteria are set for basic communication accordingly.

The steps of the flow are as follows:

1) The S-CSCF serving the terminating user receives an INVITE request from the originating network. The originating network may be an IMS network, a PSTN/ISDN Emulation network, another SIP based network or a MGCF interworking with PSTN/ISDN.

2) The S-CSCF checks the IFC and finds that a trigger fires and sends the INVITE request to the AS. The address to the AS is obtained from the IFC.

3) The AS checks the busy condition and detects that it is NDUB and sends a 486 (Busy here) response to the

4) The AS sends the 486 (Busy here) response to the originating network via the S-CSCF.

5) The S-CSCF sends the 486 (Busy here) response to the originating network.

Annex C (normative):

Annex D (normative):
AS establishing multiple dialogs with originating UE