7.6.3 VLR Failure

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

In the case of VLR restart, the VLR retrieves subscriber data from the GLR to recover its database. The required capability of the GLR to support this procedure is the same as that of the HLR in the case of VLR restart without GLR. The procedure is described in 3G TS 23.007 [2].

Basically, data recovery is achieved through the restore procedure requested from the VLR in the case of mobile terminating call, or normal location updating in the case where there is radio contact (for example on location updating and call originating from the user).

The restoration procedure of VLR Failure is illustrated in Figure 7.6/4 and 7.6/5. Each step is explained in the following list.

Figure 7.6/4: Restoration of the VLR by Mobile Terminated call

Procedure:

1) When the VLR receives Provide Roaming Number message, it identifies that no IMSI record exists and creates a skeleton IMSI record and returns the Provide Roaming Number ack message with MSRN to the HLR via the GLR. The GLR only relays these messages.

2) The VLR also sends the Restore Data message to the GLR when it identifies that no IMSI record exists in order to recover subscriber record for the IMSI.

3) The GLR that receives the message initiates insert subscriber procedure to the VLR.

4) The recovery of IMSI record in the VLR is completed after it receives Restore Data ack message.

Figure 7.6/5: Restoration of the VLR by Mobile Originated activity and Update Location

Procedure:

1) (Mobile Originated case).
When the VLR receives MO activity request and identifies that no IMSI record exists, it returns negative response with cause (Unidentified Subscriber). The user who receives the negative response initiates update location procedure and then the VLR creates a skeleton IMSI record.
(Update Location case).
When the user initiates location update procedure and the VLR identifies that no IMSI record exists, the VLR creates a skeleton IMSI record.

2) After successful authentication the VLR sends Update Location message to the GLR.

3) When the GLR receives the Update Location message from the VLR, it initiates insert subscriber procedure normally.

4) After insert subscriber procedure completed the GLR sends Update Location ack message to the VLR.

5) When the VLR receives the Update Location ack message, it confirms the registration for the user. At this time the recovery of IMSI record in the VLR is completed.