7.6.1 GLR Failure

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

A consequence of GLR restart is that an Update Location has to be performed for all roaming subscribers within the VPLMN.

The GLR will keep a part of the IMSI record in non-volatile memory by periodical backup. If the IMSI record in main memory is lost or broken by restart, it is retrieved from non-volatile backup memory as in HLR. This backup data would contain enough information to send "Provide Roaming Number" message to the VLR when it is requested by the HLR. The data which shall be stored in backed-up would be "VLR number", "SGSN number", "IMSI".

In case of GLR restart, it sends "Reset" message including the GLR number as the HLR number to VLR/SGSN where one or more of its mobile terminals are registered to prompt location updating attempt from VLR/SGSN. On receiving the location updating request, the GLR relays it to the HLR to restore its location and subscriber data. The restoration trigger can be the normal location updating from mobile terminal, call origination and call termination and so on.

The assumption in the case of terminating call in circuit switched service is that GLR would have VLR number in non-volatile memory so that it could know the exact VLR mobile terminal registered. If GLR loses VLR number or has only old VLR number, it loses the opportunity to restore its data at the timing of terminating call. This situation is the same as the case of HLR that loses VLR number after restart.

Also in this case, GLR shall have an indicator representing restart of GLR. This indicator is set "Not Confirmed" when GLR restarts, and kept the status until subscriber profile is successfully downloaded from HLR. This shall be triggered by radio contact of the mobile terminal.

The restoration indicator is called the "Location and Subscriber information Confirmed by HLR" (LSIC) and defined as follows:

If the LSIC is set to "Not confirmed," the GLR send Update Location message to HLR.

"Location and Subscriber information confirmed by HLR" is set to "Not Confirmed" at any of following events:

– The GLR receives an "Update Location" request for an MS for which the GLR has no IMSI records.

– The GLR receives a "Reset" message from the HLR with which the MS is registered.

– The GLR detects the restart of itself and the IMSI record does not seem to be guaranteed (e.g. data retrieved from backup non-volatile memory).

"Location and Subscriber information confirmed by HLR" is set to "Confirmed" at any of following events:

– The GLR successfully performs an "Update Location" to the HLR.

The recovery procedure of GLR Failure is illustrated in Figure 7.6/1. Each step is explained in the following list.

Figure 7.6/1: Recovery of the GLR


1. After restart of the GLR it sets the "LSIC" "not confirmed" and sends the Reset message to the VLR and/or SGSN. The VLR sets the indicator "Location Information Confirmed in HLR" of affected user "not confirmed" and waits for access from/to the user.

2. After identifying access from the user and successful authentication the VLR or SGSN sends Update Location message to the GLR. After identifying access to the user and successful authentication the VLR or SGSN sends Restore data message to the GLR. If the GLR identifies the "LSIC" set in "Not Confirmed", it relays the message to the HLR.

3. When the HLR receives the Update Location or Restore Data message from the GLR, it initiates insert subscriber procedure. During the procedure the GLR relay messages.

4. After the insert subscriber procedure, the HLR returns Update Location ack or Restore Data ack message to the VLR via the GLR. When the VLR and the GLR receives the message, each indicator in both nodes is set "confirmed".