8 Impact of supplementary services

03.043GPPSignalling Requirements Relating to Routing of Calls to Mobile SubscribersTS

8.1 Call Forwarding

If Call Forwarding Unconditional is active, the HLR returns the forwarded-to number in response to the interrogation. The exchange which interrogated the HLR routes the call to the forwarded-to number; if the forwarded-to number identifies a mobile subscriber then the call will be routed from the interrogating exchange as described above.

If the called MS is marked as detached, the VLR returns an ‘absent subscriber’ error in response to the request for an MSRN. If Call Forwarding on Mobile Subscriber Not Reachable is active, the HLR returns the forwarded-to number in response to the interrogation. The exchange which interrogated the HLR routes the call to the forwarded-to number; if the forwarded-to number identifies a mobile subscriber then the call will be routed from the interrogating exchange as described above.

In other cases where a conditional Call Forwarding service (on MS busy, on no reply or on MS not reachable) is active, the call forwarding is invoked at the VMSC as a result of the call setup attempt there after the call has been routed to the VMSC as described above.

8.2 Closed User Group

If the called MS is a member of a Closed User Group (CUG) the CUG parameters are stored in the HLR. When the HLR receives an interrogation to route a call to the MS, it checks the CUG parameters. If the call is authorised, the HLR returns an MSRN in the response to the interrogation; if the call is not authorised the HLR returns an appropriate error.

8.3 Barring of Incoming Calls

If Barring of Incoming Calls is active, the HLR returns an error response to the interrogation; this causes the interrogating exchange to return an appropriate indication to the calling subscriber to discourage repeated attempts to call the barred MS.

8.4 Supplementary Service Incompatibility

If the interrogation message to the HLR contains information which shows that the call would be incompatible with one of the supplementary services active for the called MS, the HLR returns an error response to the interrogation; this causes the interrogating exchange to return an appropriate indication to the calling subscriber to discourage repeated attempts to call the MS under the same conditions.