9.1.9 Deferred Location Request Procedure for the change of area event

23.2713GPPFunctional stage 2 description of Location Services (LCS)Release 17TS

Figure 9-6d illustrates the procedures for a Deferred Location Request where the Location Report is returned to the network by the UE following a change of area event. An area event occurs when the UE leaves, enters or is within a target area as defined by geographical area, PLMN identity, country code or geopolitical name of the area. Details of the target area are contained in the LCS Service Request message, see clause 5.5.1.

The PLMN operator may choose to use another mechanism (such as SIM Application Toolkit) for the transfer and detection mechanism of the Area Definition and change of area event information to the UE. In this case, the GMLCs handle steps 2 to 7 and 11 to 14 differently from that shown below. An alternative mechanism is detailed in Annex F

Figure 9.6d: Deferred MT-LR procedure for the Area event

1) The LCS Service Request contains the change of area type deferred location request information, i.e. details of the target area and the nature of the event, whether the event to be reported is the UE being inside, entering into or leaving the target area. The LCS service request may specify the validity time, i.e. start time and stop time, for the deferred location request and R-GMLC may cancel the deferred location request as described in clause 9.1.9.1. In addition, when validity time of a pending area event request in the target UE expires, the UE shall delete the pending deferred location request. The LCS Service Request shall contain an indication of the minimum interval time between area event reports, if applicable. The LCS service request shall contain the information whether the deferred area event may be reported one time only, or several times. If the change of area event is reported one time only, the Location Service request shall be completed after the first area event has occurred. If the target area is expressed by local coordinate system or geopolitical name, the R-GMLC shall convert the target area to geographical area expressed by a shape defined in TS 23.032 [11]. In addition to the target area definition, the LCS Client may include the country code of the target area in the area event request.

2) LCS service request handling between GMLCs as described in clause 9.1.1. The information received by the R-GMLC is transferred to the H-GMLC. If indication of the requested location estimate is included in the area event request, the H-GMLC should record this indication and any relevant parameters such as QoS. The H-GMLC assigns a LDR reference number to this LCS Service request then transfers the information to the V-GMLC, including the LDR reference number and the H-GMLC address.

If the H-GMLC notices that the current visited PLMN does not serve the target area, it may generate a modified deferred LCS service request in order to get notified when the target UE enters a PLMN that serves the target area. The modified target area event is that the target UE enters one of the PLMNs that serve the original target area. Note that the new area event may include multiple PLMNs (identified by PLMN IDs) if there are more than one PLMN that serves the original target area, based on the stored PLMN list and the corresponding estimated coverage. The H-GMLC then generates a new location request with the new defined area event and the same rest of the information in the original request.

The new location request is sent to the target UE via the current V-GMLC. The H-GMLC keeps the original area event location service request pending for as long as determined by the validity time of the request. When the UE enters one of the pre-defined PLMNs, it sends an area event location report to H-GMLC. The H-GMLC then sends the original area event location service request to the UE via the new V-GMLC. If the H-GMLC cannot derive a list of PLMNs that may cover the target area, and the current visited network does not cover the target area, the H-GMLC may reject the request.

3) If the received target area is expressed by a shape defined in TS 23.032 [11], V-GMLC converts the target area into an Area Definition consisting of the corresponding list of cell identities, location areas or routing area. If the V-GMLC is not able to translate the target area into network identities, it shall reject the request and send an LCS service response to H-GMLC with the appropriate error cause.
If the received target area is expressed by country code or PLMN identity, the V-GMLC shall use the country code or PLMN identity as the Area Definition.
The V-GMLC sends the Area Definition to MSC/SGSN in the Provide Subscriber Location request (deferred) and includes the LDR reference number and the H-GMLC address in the request.
The message shall define whether the event to be reported is the UE being inside, entering into or leaving the area. The message shall also include the validity period of the location request, the minimum interval time between area event reports, the information whether the deferred area event may be reported one time only or several times, if applicable.

4) The MSC/SGSN verifies the UE capabilities with regard to the change of area event. If either the MSC/ SGSN or the UE does not support the deferred location request for the change of area event (for temporary or permanent reasons), a Provide Subscriber Location return error shall be returned with a suitable cause in step 7.
If the UE is in idle mode, the core network performs paging, authentication and ciphering. If privacy notification/verification is requested, the MSC/SGSN sends an LCS Location Notification Invoke message to the target UE with a location type indicating activation of a deferred location request, a deferred location event type containing the change of area types requested and an indication as to whether privacy verification is required. LCS Location Notification is further specified in clauses 9.1.2 and 9.1.6. If privacy verification was requested, the UE returns an LCS Location Notification Return Result to the MSC/SGSN indicating whether permission is granted or denied. If a previous deferred location request is ongoing in the UE and the MSC/SGSN proceeds with the current deferred request, the UE may return an LCS Location Notification Return Error response to the MSC/SGSN indicating that the new request cannot be supported.

5) The MSC/SGSN sends the LCS Area Event Invoke to the UE carrying the Area Definition, other area event information, the LDR reference number and the H-GMLC address. The message shall also define whether the event to be reported is the UE being inside, entering into, leaving the area. The message shall also include the validity period of the location request, the minimum interval time between area event reports and the information whether the deferred area event may be reported one time only, or several times, if applicable.

6) If the LCS Area Event Invoke is successfully received by the UE and the UE supports the change of area type deferred location request, the UE sends acknowledgement to MSC/SGSN and begins monitoring for the change of area event. The UE shall determine whether it is inside, entering into or leaving the target area by comparing the current serving cell identity, location area, routing area, PLMN identity or country code to the Area Definition received from the MSC/SGSN. In case of soft handover, it is sufficient if one of the cells belongs to the target area. In case the Area Definition consists of a location or routing area, PLMN or country identity the UE shall check for the area event during the normal location or routing area update procedure. The change of area event detection mechanism must not influence on the normal UE cell selection and reselection procedures.
If the UE does not support the deferred location request (for temporary or permanent reasons), it shall send the LCS Area Event Invoke ack. with the appropriate error cause. If a previous deferred location request is still ongoing in the UE, the UE may return an LCS Area Event Return Error response to the MSC/SGSN indicating that the new request cannot be supported.

7) If either the MSC/ SGSN or the UE does not support the deferred location request for the change of area event (for temporary or permanent reasons), a Provide Subscriber Location return error shall be returned to the V-GMLC with a suitable cause. If both of the SGSN/MSC and UE supports the deferred location request for the change of area event, a Provide Subscriber Location ack. shall be returned to the V-GMLC without a location estimate. MSC/SGSN shall include the result of the notification/verification in the response to the V-GMLC, if the notification/verification is needed. The response message shall include the LDR reference number and the H-GMLC address. The change of area event invoke result shall be also included, if necessary. After sending the Provide Subscriber Location ack to the V-GMLC, the deferred location request shall be completed in the MSC/SGSN. The SGSN/MSC may record charging information for an accepted area event request.

8) to 10) V-GMLC returns the LCS Service Response via H-GMLC and R-GMLC to the LCS Client to notify whether the request was successfully accepted or not. When the H-GMLC returns the LCS Service Response to the R-GMLC, the LDR reference number assigned by the H-GMLC shall be included, then the R‑GMLC shall transfer the LDR reference number to the LCS Client in the LCS Service Response. After sending the LCS Service Response to the H-GMLC, the deferred location request shall be completed in the V-GMLC. The V-GMLC or R-GMLC may record charging information for an accepted area event request.

11) UE detects that the requested area event has occurred.

12) Before sending the LCS Area Event Report the UE shall establish either a CS radio connection or PS signalling connection as specified in clauses 9.2.1 and 9.2.2. The UE sends the LCS Area Event Report to the VMSC/SGSN including the original LDR reference number and the H-GMLC address. The report shall also include the result of the notification/verification procedure, if the notification/verification is needed.

When the MSC/SGSN receives the report and it can handle this report, an acknowledgement as a response should be sent to the UE. If the UE does not receive any response from the MSC/SGSN after sending the report, i.e. the current MSC/SGSN does not support the deferred location request for the area event (for temporary or permanent reasons), the UE may re-send the report more times. If the UE always does not receive the response, the UE shall stop sending the report, then record a corresponding flag to indicate that a report has been sent unsuccessfully. When the UE performs location update and detects the LAI or RA is changed, if the flag has been set, the UE shall send the report to the corresponding MSC/SGSN, and the flag will be cleared upon a success of the sending.
If the UE was requested to report the change of area event one time only, the deferred location request shall be completed. In case multiple reports were requested, the UE must not send a repeated LCS Area Event Report more often than the requested minimum interval indicated in the LCS Area Event Invoke.

Editor’s Note: It could be useful to have MSC/SGSN repeat the notification procedure with the target UE after the UE has reported the change of area event, but this is for further study.

13) The MSC/SGSN sends the subscriber location report to its associated V-GMLC with an indication of the event occurrence, the LDR reference number, the H-GMLC address and may also include the indication whether the obtained location estimate satisfies the requested accuracy or not (provided that this indication is obtained from RAN with the location estimate). V-GMLC sends an acknowledgement to MSC/SGSN in step 13b and the MSC/SGSN may record charging information.

14) The V-GMLC sends the LCS Service Response to the H-GMLC with an indication of the event occurrence, the LDR reference number and the H-GMLC address. The LCS Service Response is sent in accordance with the requested QoS Class, as described in clause 9.1.1 for common MT-LR. The LDR reference number and the H-GMLC address will be used to identify the source of the original deferred location request in the case that the UE has relocated before the area event occurred. The V-GMLC may record charging information.

15) In case the UE moves to another PLMN of the PLMN identities list, according to the PLMN identity the UE shall determine whether the Area Definition of the target area is available. If it is not available, the UE shall report that it has roamed into a new PLMN, including the new PLMN identity and the LDR reference number. The H-GMLC shall transfer the original area event request to the V-GMLC of the new PLMN. The procedure should be continued as described in step 2 and onwards where the Area Definition of the new PLMN shall be downloaded to the UE. Otherwise, the UE monitors the area event in the new PLMN, does not inform the H-GMLC that it has entered into a new PLMN.

16) The H-GMLC performs the privacy check as described in clause 9.1.1.

17) If the H-GMLC finds the indication of the requested location estimate is stored, the H-GMLC should generate a new immediate LCS Service Request with the QoS specified in the original request. Then the H-GMLC sends the new request as described in clause 9.1.1 to the V-GMLC and waits the result the location request, the subsequent procedures in clause 9.1.1 are continued.

The H-GMLC sends the LCS Service Response to R-GMLC with the LDR reference number. If the location estimate of the target UE is requested in the request and the location estimate was successfully obtained, the H-GMLC shall put the obtained location estimate into the LCS Service Response. If the location estimate of the target UE is requested in the request but the location estimate could not be obtained, the H-GMLC sends the LCS Service Response without the location estimate. Unless multiple reports were requested, the deferred location request shall be completed in the H-GMLC after sending the LCS Service Response to the R-GMLC. The H-GMLC may record charging information.

18) The R-GMLC sends the LCS Service Response to the LCS client. Unless multiple reports were requested, the deferred location request shall be completed in the R-GMLC after sending the LCS Service Response to the LCS client. The R-GMLC may record charging information.

9.1.9.1 Cancellation of a Deferred Location Request – Change of Area event

Figure 9-7b illustrates the procedure for cancelling the Deferred Location Request for the change of area event.

Figure 9.7b: Cancellation of a Deferred MT-LR with change of area event procedure

1) The LCS Client requests the cancellation of a previously requested Deferred Location Request. The LDR reference number that was included in the previous LCS Service Response sent by the GMLC shall be included in the request to indicate which outstanding LDR should be cancelled.

2) The R-GMLC sends the cancellation request to H-GMLC, including the LDR reference number. R-GMLC may itself initiate the cancellation for some other reason, e.g. the expiry of the validity timer specified by the start time and stop time; or the expiry of an implementation dependent timer specified by the Operator as a default value in the R-GMLC when the stop time is undefined or exceeds the maximum allowed value.

3) The H-GMLC forwards the LCS Cancel Service Request to V-GMLC with the LDR reference number which is received from the R-GMLC, and the H-GMLC address. The H-GMLC may itself initiate the cancellation procedure, when the UE’s privacy profile stored in the H-GMLC or in the PPR was changed. For every outstanding Deferred Location Request against that UE, the H-GMLC shall perform or ask the PPR to perform a new privacy check based on the updated privacy profile. If the privacy check passes, i.e. the LCS Client is still allowed to position the target UE, the handling of the outstanding Deferred Location Request should be continued. Otherwise, if the privacy check does not pass, i.e. the Location estimate of the target UE is not allowed to be provided to the LCS Client, the H-GMLC shall initiate a cancellation procedure.

NOTE: The H-GMLC shall know that the UE subscriber’s privacy profile has been changed in the PPR when the LCS Privacy Profile Update has been sent from PPR to H-GMLC as described in clause 9.1.1.2.

4) The V-GMLC sends the Provide Subscriber Location request to SGSN/MSC, indicating a cancellation of a deferred location request and including the LDR reference number specified by the LCS Client in the LCS Cancel Service Request and the H-GMLC address received from the H-GMLC.

5) The SGSN/MSC sends the LCS Area Event Cancellation, including the LDR reference number and the H-GMLC address, request to UE.

6a) The UE cancels the Area event deferred location request and sends the LCS Area Event cancellation ack., with no area event information included to VMSC/SGSN.

6b) While the UE is monitoring for the area event to occur, the UE may cancel or terminate the deferred location request for the change of area on its own behalf by sending the LCS Area Event report with the LDR reference number, an indication of the cancellation and an appropriate error cause.

7) The SGSN/MSC sends the cancellation acknowledgement to the V-GMLC in the Provide Subscriber Location Ack, with the LDR reference number and the H-GMLC address.

8) The V-GMLC sends the LCS Cancel Service Response to H-GMLC with the LDR reference number and the H-GMLC address.

9) H-GMLC sends the LCS Cancel Service Response to R-GMLC with the LDR reference number. H-GMLC may send the LCS Cancel Service Response to R-GMLC, even if the R-GMLC/LCS client has not requested the cancellation, see step 3.

10) R-GMLC sends the LCS Cancel Service Response to the LCS Client.