The loss or corruption of subscriber data in the HLR has an impact not only in the HLR’s own PLMN but also on the service for its mobiles in other PLMNs. Restoration of the data in the HLR requires co-operation from all the VLRs to which its mobiles have roamed.
5.1 Restart of the HLR
When an HLR restarts after failure it performs the following actions for the subscriber data records that have been affected by the HLR fault:
– reload all data from the non-volatile back-up;
– reset all "MS Purged" flags;
– mark each subscriber record "SS Check Required" by setting the "Check SS" indicator if the "Forward Check SS Indication" service is implemented;
– send a "Reset" message to each VLR where one or more of its MSs are registered. This causes each VLR concerned to mark each relevant subscriber record "Location Information Not Confirmed in HLR"; and
– send a “Reset” message to each SGSN where one or more of its MSs are registered. This causes each SGSN to mark each relevant MM context "Location Information Not Confirmed in HLR".
5.2 Procedures During Restoration
5.2.1 Mobile terminated call
If the VLR receives a "Process Access Request" request in response to a "Page" or "Search for MS" operation, after successful authentication, if required, it checks the indicator "Location Information Confirmed in HLR". If this indicates "Not Confirmed" the VLR triggers an "Update Location" to the HLR as described in subclause 4.2.1.d).
When the HLR receives the "Update Location" request it stores the VLR number, MSC number and LMSI in the subscriber record as for normal operation.
If the "Forward Check SS Indication" service is implemented, the HLR checks the indicator "Check SS". If this indicates "Check Required", after successful completion of the subscriber data retrieval procedure that ran embedded in the "Update Location" procedure the HLR sends a "Forward Check SS Indication" to the VLR and marks the subscriber record "Check Not Required. When the VLR receives the "Forward Check SS Indication" request it forwards an indication to the MS to alert the user that supplementary service parameters should be checked.
5.2.2 Mobile Originated Activity
When the VLR receives a request from an MS (MS originated call, mobile originated Short Message, call-independent supplementary service activity or location registration request) whose IMSI record is marked "Location Information Not Confirmed in HLR", it will perform an "Update Location" to the HLR as described in subclauses 4.2.3 and 4.2.4 above.
When the HLR receives an "Update Location" request from the VLR, it proceeds as described in subclause 5.2.1.