7.6.2 HLR Failure

23.1193GPPGateway Location Register (GLR)Release 17Stage 2TS

In the case of HLR restart when the GLR receives a reset message from a HLR, it marks all subscriber records for which the HLR number matches the HLR number received in the reset message. This indicates that when the MS next makes radio contact the GLR needs to initiate a location registration procedure to the HLR. If the HLR included an HLR-ID list in the reset message, then only those subscriber records for which the leading digits of the IMSI match one of the HLR-IDs in the HLR-ID list will be marked.

Then the GLR sends a RESET message, which includes the GLR number as the HLR number and HLR-ID list if the GLR received it from the HLR, to the serving node (i.e. VLR or SGSN). The receiving serving node may use the HLR number or HLR-ID list (if present) to identify the affected users. In the case that the serving node uses the HLR number, it regards the users as affected, whose subscriber record stores the number as HLR number equal to the received GLR number. On the other hand in the case that the serving node uses the HLR-ID list, it regards the users as affected, whose IMSI has the leading digits equal to one of HLR-IDs. After that when the affected user accesses the network, the serving node initiates a location registration procedure to the GLR. When the GLR receives an Update Location message from the serving node and identifies that the subscriber record in the GLR is marked as needing to notify the HLR when the MS makes radio contact then the GLR sends the Update Location message to the HLR.

The recovery procedure of HLR Failure is illustrated in Figure 7.6/2. Each step is explained in the following list.

Figure 7.6/2: Recovery procedure of HLR Failure

Procedure:

1. When the HLR restart occurs and the GLR receives a RESET message, the GLR identifies affected users by received HLR number and sets the indicator ("LSIC") "not confirmed" for the users. If the HLR included an HLR –ID list in the reset message, then only those subscriber records for which the leading digits of the IMSI match one of the HLR-IDs in the HLR-ID list will be marked.

2. The GLR sends reset messages to the serving node where the affected users are roaming. The reset message includes the GLR number as HLR number and HLR-ID list if the GLR receives it from the HLR. Receiving serving node may regard the users as affected by HLR number or HLR-ID list (if present).

3. When the affected user accesses the network, the serving node initiates an update location procedure to the GLR. If the GLR identifies that the indicator ("LSIC") set to "not confirmed" for the user, it relays the message to the HLR.

4. When the HLR receives the Update Location message, it initiates the insert subscriber data procedure. During the procedure the GLR relays the messages between the serving node and HLR transparently.

5. If the HLR implements Forward Check SS indication, it sends the Forward Check SS ind message to the GLR and the GLR relays the message to the VLR. (implemented only for CS domain).

6. When the serving node receives the Update Location ack message, the restoration procedure is completed.

7.6.2.1 Suppression of Intra-PLMN signalling

During the HLR restoration procedure involving the GLR, the GLR notifies the GLR number as the HLR number to the serving node in a Reset message. Therefore, in case the serving node does not use the HLR-ID list (i.e. the case that HLR did not send the HLR-ID list to the serving node via GLR or the case that the serving node does not support the usage of the HLR-ID list), the serving node regards all users accommodated into the GLR as affected. This leads to the unnecessary location updates for the restoration of the users not from the restarting HLR. To suppress this unnecessary signalling within VPLMN some mechanism as shown in following subsections may be used.

7.6.2.1.1 Usage of the HLR id List (Tool 1)

In this tool the GLR generates HLR-ID list, which is composed of MCC+MNC, by translating the CC and NDC of the HLR and sends it to the serving node in the Reset message. On receiving the HLR-ID list the serving node may or may not use this. If the serving node uses the HLR-ID list and identifies HPLMN where the restarting HLR exists, no unnecessary signaling traffic for the users from the other PLMNs occurs.

7.6.2.1.2 Multiple GLR number allocation (Tool 2)

In this tool the GLR has multiple GLR numbers corresponding to each HLR. The numbers, which can be routed to the GLR, are allocated as multiple GLR numbers. The correspondence between HLR numbers and GLR numbers is statistically kept in the non-volatile memory. See Figure 7.6/3.

Figure 7.6/3: Multiple GLR number allocation

Possible scenarios for GLR number allocation are as follows.

In this tool, if one GLR number is allocated for one HLR and VPLMN has the roaming agreements with many PLMNs, many GLR numbers are needed.

As possible variation of scenario, a GLR number may be assigned to a group of HLRs. This group can be grouped by, for instance, country code or network destination code and so on. If one GLR number is assigned for many HLRs, the occupied address space is small, however the unnecessary signalling traffic for the users not associated to restarting HLR increases. On the other hand, if one GLR number is assigned for few HLRs, the unnecessary signalling traffic is small, however the occupied address space is larger.

How many HLRs are grouped is operator dependent.