7.1 Logical Functions

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

This clause gives the logical functions performed within the GLR.

7.1.1 Message Relay Function

This function is used for the exchange of MAP operation between HLR and VLR/SGSN via GLR. When a message is received from VLR or SGSN, the GLR identifies the relevant HLR using appropriate logic, and vice versa.

7.1.2 Address Conversion Function

The Address Conversion function in the GLR is performed when the GLR receives the Update Location message from the VLR or the Update GPRS Location message from the SGSN, and the HLR updating is required. The GLR will convert visited node addresses as follows:

– VLR Number converts to the GLR Number.

– MSC Number converts to the IM-MSC Number.

– SGSN Number converts to the GLR Number.

– SGSN Address converts to the IM-GSN Address.

The converted numbers are sent to the HLR with the Update Location message or Update GPRS message. The HLR stores these addresses as the location information. The HLR uses the GLR Number as the destination address of the messages to VLR and SGSN (e.g., Insert Subscriber Data) and the messages are actually routed to the GLR. The IM-MSC Number is sent to e.g., the SMS-GMSC with a Send Routing Info for Short Message ack message as a destination address to the MSC and the SMS-GMSC uses the IM-MSC Number as the destination address of a Forward Short Message. The IM-GSN Address is sent to the GGSN with Send Routing Info for GPRS ack message and used as the destination address of PDU Notification message.

According to this scheme, the actual visited node addresses would be stored only in the GLR. The GLR can hide second and further UL messages towards the HLR. Consequently inter-PLMN signalling will be reduced.

The address conversion function in the GLR is performed also when the GLR receives any messages that include the HLR Number from the HLR. The GLR will modify the HLR Number as follows.

– HLR Number converts to the GLR Number.

The GLR Number is sent to the VLR or SGSN with the same message received from HLR. The VLR or SGSN stores the GLR Number as the HLR number.

7.1.3 Subscriber Information Caching Function

This function is to store the subscriber’s information, which is obtained from HLR during location updating procedure. When the HLR send Insert Subscriber Data message to VLR and/or SGSN via GLR for the location update, the subscriber information is also stored in the GLR and kept until it receives Cancel Location message from HLR. The stored information is used for HLR emulation Function.

7.1.4 Subscriber Information Cancellation Function

This function is to delete subscriber information stored in GLR and also in VLR and SGSN as requested from HLR or from Location Updating Screening Function in the GLR.

7.1.5 HLR emulation Function

This function is to handle the location management procedure only within the visited network. When it is decided that the request of location update can be handled at the GLR without involving HLR by Location Updating Screening Function, this function is invoked and GLR acts like the HLR of the subscriber.

7.1.6 Location Updating Screening Function

This function is used to judge, whether requested location updating is necessary to be indicated to HLR or not. When the GLR has the IMSI record, the GLR may not indicate the location updating to HLR and HLR emulation function is invoked. However, even though the GLR stores the IMSI record, the update location has to be indicated to HLR in some cases. The detail procedures of the cases are shown below.

7.1.7 Routeing Information Providing Function

This function is used to provide routeing information to the Intermediate MSC and the Intermediate GSN.

An Address Interrogation function is located within the IM-MSC, IM-GSN and GLR. The IM-MSC, IM-GSN and GLR need the actual visited node address when they need to forward messages to the actual visited node. The IM-MSC and IM-GSN interrogate the GLR to obtain these actual visited node addresses. The GLR holds the actual visited node address internally.

7.1.8 Regional Restriction and Unsupported Services handling Function

This function is used to handle the regional restriction indication or unsupported service indication in Insert Subscriber Data ack message. When the GLR receives the indication, the GLR initiates the location updating procedure toward the HLR. And later, when the user returns to an MSC/SGSN area that is not restricted due to regional subscription or an area that supports the services subscribed, the GLR identifies the need to notify the HLR of the return. Therefore the location updating procedure is initiated toward the HLR for this handling.

7.1.9 Super Charger function

This function is used handle the location management procedure from the serving node (i.e. VLR or SGSN) which supports the Super-Charger features. This is basically the same as the Super-Charged HLR. (Refer to 3G TS 23.116 [9]) Followings are supplementary explanation for the GLR behaviour as Super-Charged HLR:

– When the subscription data is updated by insert subscriber data procedure from the HLR, the GLR shall update the age indicator to reflect the change of the subscription data and sends the subscription data to the serving node identified by the GLR.

If the GLR receives location registration request from the Super-Charged serving node and has no subscription data for the user, whatever the content of the age indicator in the request is, when the GLR receives the subscription data from the HLR, it relays the data to the serving node.