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Content for  TS 23.273  Word version:  17.4.0

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6.3  Deferred 5GC-MT-LR Procedure for Periodic, Triggered and UE Available Location EventsWord‑p. 44

6.3.1  Initiation and Reporting of Location EventsWord‑p. 44

Figure 6.3.1-1 summarizes the initiation and reporting of location events for a deferred 5GC-MT-LR procedure for Periodic, Triggered and UE Available Location Events. The procedure supports mobility of a UE within a VPLMN 5GCN and from a 5GCN to an EPC.
Reproduction of 3GPP TS 23.273, Fig. 6.3.1-1: Deferred 5GC-MT-LR for periodic, triggered and UE available location events
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Step 1.
The external location services client or the AF (via NEF) sends a request to the (H)GMLC for location reporting for periodic, triggered or UE available location events. The request is sent as described for step 1 in clause 6.1.2 with the differences described here. The LCS Service Request provides the type of periodic or triggered location reporting being requested and associated parameters. For periodic location, the LCS Service Request includes the time interval between successive location reports, the total number of reports and may include location QoS. For periodic location reporting, the LCS Service Request may include a scheduled location time for the first periodic location report. For area event reporting, the LCS Service Request includes details of the target geographical area, whether the event to be reported is the UE being inside, entering into or leaving the target area, the duration of event reporting, the minimum and maximum time intervals between successive event reports, the maximum event sampling interval, whether location estimates shall be included in event reports (and associated location QoS), and whether only one location report is required or more than one. If the target area is expressed by a local coordinate system or a geopolitical name, the (H)GMLC shall convert the target area to a geographical area expressed by a shape as defined in TS 23.032. For motion event reporting, the LCS Service Request includes the threshold linear distance, the duration of event reporting, the minimum and maximum time intervals between successive event reports, the maximum event sampling interval, whether location estimates shall be included in event reports (and associated location QoS), and whether only one location report is required or more than one.
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Step 1b-1.
AF invokes the Nnef_EventExposure_Subscribe service operation to the NEF.
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Step 1b-2.
The NEF forwards the request to the (H)GMLC. The NEF assigns a LDR refence number locally and sends it to (H-)GMLC,
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Step 2.
The (H)GMLC may verify UE privacy requirements as for step 2 in clause 6.1.2. The (H)GMLC may also subscribe to and receive notification of UE privacy profile updates according to steps 0 and 4 of clause 6.12.1.
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Step 3.
The (H)GMLC queries the UDM for the AMF address and, in the case of roaming, a VGMLC address as for step 3 in clause 6.1.2.
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Step 4.
This step is skipped for a non-roaming UE. For a roaming UE, the HGMLC obtains a VGMLC address if not received at step 3 and invokes the Ngmlc_Location_Provide Location Request service operation to forward the location request to the VGMLC as described for step 4 of in clause 6.1.2. The (H)GMLC also includes a contact address for the (H)GMLC (Notification Target Address, e.g. a URI) and an LDR reference number (Notification correlation ID) to be used for event reporting at steps 20 and 29. The LDR reference number is either allocated by (H-)GMLC based on predefined rule, e.g. operator's policy if the location request is received in step 1a, or allocated by NEF, if the location request is received in step 1b.
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Step 5.
The (H)GMLC or VGMLC invokes the Namf_Location_ProvidePositioningInfo Request service operation to forward the location request to the serving AMF as described for step 5 in clause 6.1.2 and includes the (H)GMLC contact address and LDR reference number. The LDR reference number is either allocated by (H-)GMLC based on predefined rule, e.g. operator's policy if the location request is received in step 1a, or allocated by NEF, if the location request is received in step 1b. For area event reporting, the target geographical area is converted into a corresponding list of cell and/or tracking area identities.
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Step 6-8.
If the AMF supports a deferred location request, the AMF returns an acknowledgment to the external LCS client, via the (H)GMLC and, in the case of roaming, the VGMLC, indicating that the request for deferred location was accepted. The VGMLC, when used, may optionally release resources for the deferred location request at this point.
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Step 9.
If the UE is not currently reachable (e.g. is using eDRX or PSM), the AMF waits for the UE to become reachable.
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Step 10.
Once the UE is reachable, if the UE is then in CM IDLE state, the AMF initiates a network triggered Service Request procedure as defined in clause 4.2.3.3 of TS 23.502 to establish a signalling connection with the UE.
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Step 11-12.
The AMF performs steps 7-8 in clause 6.1.2 to notify the UE of the location request and verify privacy requirements if required by the location request received at step 5 and supported by the UE. The AMF includes in the notification to the UE the type of deferred location request in the case of periodic or triggered location.
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Step 13.
The AMF selects an LMF as described for step 6 in clause 6.1.1. The selection may take into account the type of deferred location request (e.g. whether periodic or triggered) and any parameters for the deferred location request (e.g. the number of event reports required and/or the duration).
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Step 14.
The AMF invokes the Nlmf_Location_DetermineLocation Request service operation towards the LMF to initiate a request for deferred UE location. For a request for periodic or triggered location, the service operation includes all the information received in step 4 or step 5 including the (H)GMLC contact address, LDR reference number, UE Positioning Capability if available and any scheduled location time and may include a list of allowed access types for event reporting at step 22. For a request for the UE available location event, the (H)GMLC contact address and LDR reference number are not included. In all cases, the service operation includes an LCS Correlation identifier, the AMF identifier, the serving cell identity, the client type and may include an indication if UE supports LPP, the required QoS and Supported GAD shapes.
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Step 15.
The LMF performs one or more of the positioning procedures described in clause 6.11.1, 6.11.2 and 6.11.3 and as described for step 8 in clause 6.1.1. During this step, the LMF may request and obtain the UE positioning capabilities (e.g. which may indicate the type(s) of periodic and triggered location supported by the UE and the access types supported by the UE for event reporting). The LMF may also obtain the UE location - e.g. for a request for the UE available location event or when an initial location is requested for periodic or triggered UE location. For a request for the UE available location event, the LMF skips steps 16 and 17.
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Step 16.
If periodic or triggered location was requested, the LMF sends a supplementary services LCS Periodic-Triggered Invoke Request to the UE via the serving AMF by invoking the Namf_Communication_N1N2MessageTransfer service operation. The LCS Periodic-Triggered Location Invoke carries the location request information received from the AMF at step 14, including the (H)GMLC contact address, LDR reference number and any scheduled location time. The LCS Periodic-Triggered Location Invoke also includes a deferred routing identifier, which can be the identification of the LMF when the LMF will act as a serving LMF or a default LMF identification otherwise. The LCS Periodic-Triggered Location Invoke may indicate the allowed access types for event reporting at step 25 (e.g. one or more of NR, E-UTRA connected to 5GC, non-3GPP access connected to 5GC, any of the RAT Types specified for NR satellite access) and may include embedded positioning message(s) which indicates certain allowed or required location measurements (or a location estimate and the timestamp of the location estimate if available) at step 24 for each location event reported (e.g. based on the positioning capabilities of the UE obtained in step 14 and the allowed access types). As part of NAS transport of the LCS Periodic-Triggered Location Invoke from the serving AMF to the UE, the serving AMF includes an immediate routing identifier in the NAS transport message containing an LCS Correlation identifier - e.g. according to clause 6.11.1.
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Step 17.
If the request in step 16 can be supported, the UE returns a supplementary services acknowledgment to the LMF, which is transferred via the serving AMF using the immediate routing identifier and delivered to the LMF using an Namf_Communication_N1MessageNotify service operation.
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Step 18.
The LMF invokes the Nlmf_Location_DetermineLocation Response service operation towards the AMF to respond to the request at step 14. For a request for the UE available location event, the response includes any UE location obtained at step 15 and the LMF then releases all resources. For a periodic or triggered location request, the response includes any location obtained at step 15, a confirmation of whether periodic or triggered location was successfully activated in the UE according to steps 16 and 17 and the identification of the LMF in the case of successful activation with a serving LMF; the LMF also retains state information and resources for later steps if the LMF acts a serving LMF. If the multiple QoS class was used in the location request, the LMF provides the achieved Location QoS Accuracy in step 15. If the UE cannot support the periodic and triggered location request, the service operation returned to the AMF shall include a suitable error cause. The service operation also includes the UE Positioning Capability if the UE Positioning Capability is received in step 15 including an indication that the capabilities are non-variable and not received from AMF in step 14.
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Step 19.
The AMF invokes the Namf_Location_EventNotify service operation towards the VGMLC for roaming, or (H)GMLC for non-roaming, and includes any location received at step 18 and, for periodic or triggered location, a confirmation of whether or not periodic or triggered location was successfully activated in the target UE. The VGMLC, if used, may be the same VGMLC used in steps 5 and 6 or may be a different VGMLC. In the case of a different VGMLC, the AMF includes the HGMLC contact address and LDR reference number. The AMF also includes the LMF identification and the achieved Location QoS Accuracy if received at step 18. The AMF may then release all resources for the location request and cease support for the procedure.
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Step 20.
This step is skipped for a non-roaming UE. For a roaming UE, The VGMLC forwards the response received at step 19 to the HGMLC using the HGMLC contact address received at step 19 (for a different VGMLC) or received and stored at step 4 (for the same VGMLC) and includes the LDR reference number and any LMF identification that was received. The VGMLC may then release all resources for the location request and cease support for the procedure.
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Step 21.
The (H)GMLC forwards the response to the external LCS client or AF (via the NEF). If the location request at step 1 was for the UE available location event, the procedure terminates here and further steps 22-31 are not performed.
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Step 22.
For a periodic or triggered location request where steps 16 and 17 were successfully performed, the UE monitors for occurrence of the trigger or periodic event requested in step 16. For the area event or motion event, the UE monitors the requested event at intervals equal to or less than the maximum event sampling interval. An event trigger is detected by the UE when any of the following occur: (i) a requested area event or motion event has been detected and the minimum reporting time interval has elapsed since the last report (if this is not the first event report); (ii) a requested periodic location event has occurred; or (iii) the maximum reporting time for an area event or motion event has expired. When a trigger or periodic event is detected and if the UE is camped on or connected to (or can otherwise access) an access type allowed by the LMF at step 16, the UE proceeds to step 23. If the UE cannot access an allowed access type, the UE may skip reporting the trigger event or may report the trigger event at a later time when an allowed access type becomes available, according to requirements received from the LMF at step 16. When a scheduled location time is provided for periodic location request at step 16, a UE should perform steps 23-25 some time in advance of the scheduled location time for the first periodic event report or some time in advance of the periodic interval expiration for each succeeding periodic event report in order to enable location measurements at step 23 or step 27 to occur near to each of these times, respectively.
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Step 23.
The UE obtains any location measurements or a location estimate that were requested or allowed at step 16.
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Step 24.
The UE performs a UE triggered service request as defined in clause 4.2.3.2 of TS 23.502 if in CM-IDLE state in order to establish a signalling connection with the AMF.
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Step 25.
The UE sends a supplementary services event report message to the LMF which is transferred via the serving AMF (which may be different to the original serving AMF for steps 14-16) and is delivered to the LMF using an Namf_Communication_N1MessageNotify service operation. The event report may indicate the type of event being reported (e.g. whether a normal event or expiration of the maximum reporting interval) and may include embedded positioning message(s) which includes any location measurements or location estimate and the timestamp of the location estimate if available obtained at step 23. The UE also includes the deferred routing identifier received in step 16 in the NAS Transport message used to transfer the event report from the UE to the AMF. The AMF then forwards the event report to either the serving LMF or any suitable LMF based on whether the deferred routing identifier indicates a particular LMF or any (default) LMF. If a different LMF than the serving LMF is used, procedure in clause 6.4 is used. The UE also includes the (H)GMLC contact address, the LDR reference number, whether location estimates are to be reported and if so the location QoS in the event report and any scheduled location time indicated at step 16 for periodic reporting.
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Step 26.
When the LMF receives the event report and if it can handle this event report, the LMF updates the status of event reporting(e.g. the number of event reports so far received from the UE and/or the duration of event reporting so far) and returns a supplementary services acknowledgment for the event report to the UE. The acknowledgment may optionally include a new deferred routing identifier indicating a new serving LMF or a default (any) LMF. If the UE does not receive any response from the LMF after a predefined time, i.e. the current LMF does not support the deferred location request (for temporary or permanent reasons) or due to some radio access failures, the UE may re-send the report one or more times. If the UE sends the repeated event report more than the predefined maximum resending time and the UE still does not receive any response from AMF, the UE shall stop resending the report and reserve the event report, then record a corresponding flag to indicate that a report has been sent unsuccessfully. When the UE performs location update and detects the PLMN is changed, if the flag has been set, the UE shall send the report to the corresponding AMF, and the flag will be cleared upon a success of the sending.
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Step 27.
If a location estimate is needed for event reporting, the LMF may perform one or more of the positioning procedures described in clause 6.11.1, 6.11.2 and 6.11.3 and as described for step 8 in clause 6.1.1 and step 12 in clause 6.1.2. The LMF then determines the UE location using the location measurements and/or location estimate(s) obtained at this step and/or received at step 25. The LMF may also determine the timestamp of the location estimate.
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Step 28.
In the case of roaming, the LMF selects a VGMLC (which may be different to the VGMLC for steps 3-8 and steps 19-21), The LMF then invokes an Nlmf_Location_EventNotify service operation towards the selected VGMLC or (H)GMLC with an indication of the type of event being reported, the (H)GMLC contact address and LDR reference number, the identification of the LMF if this is a serving LMF, and any location estimate and the timestamp of the location estimate (if available) obtained at step 27. If multiple QoS class was used in the initial location request, the LMF provides the achieved Location QoS Accuracy in step 27.
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Step 29.
This step is skipped for a non-roaming UE. For a roaming UE, the VGMLC invokes an Ngmlc_Location_EventNotify service operation to forward the information received in step 28 (e.g. including the type of event being reported, the LDR reference number and possibly the LMF identification) to the HGMLC which identifies the periodic and triggered location request from the LDR reference number.
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Step 30.
The (H)GMLC uses the LDR reference number received in step 28 or step 29 to identify the periodic and triggered location request received in step 1 and then sends the type of event being reported and any location estimate and the timestamp of the location estimate (if available) and used positioning methods to the external LCS client or AF (via the NEF), and sends the LDR reference number to LCS client. The (H)GMLC may also verify UE privacy requirements before reporting the event and any location to the external LCS client or AF. If multiple QoS class was used in the initial location request, the LMF provides the achieved Location QoS Accuracy in step 27.
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Step 31.
The UE continues to monitor for further periodic or trigger events as in step 22 and instigates steps 23-30 each time a trigger event is detected.
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