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full Contents for  TS 23.273  Word version:   16.3.0

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1…   4…   4.2a…   4.3…   5…   6…   6.1.2   6.2   6.3…   6.3.2…   6.4   6.5…   6.7…   6.8   6.9…   6.10…   6.11…   6.12…   6.13…   6.14…   7…   8…   A…   B…

 

6.3  Deferred 5GC-MT-LR Procedure for Periodic, Triggered and UE Available Location EventsWord-p. 42
6.3.1  Initiation and Reporting of Location Events
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.
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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 area event reporting, the LCS Service Request includes details of the target 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.
NOTE 1:
The HGMLC may also query the HSS of the target UE for a serving MME address as described in clause 9.1.1 of TS 23.271. The deferred EPC-MT-LR procedure for Periodic and Triggered Location described in clause 9.1.19 of TS 23.271 or the EPC-MT-LR procedure for the UE availability event described in clause 9.1.15 of TS 23.271 may then be performed instead of steps 4-31 - e.g. if the HSS returns an MME address but the UDM does not return an AMF address.
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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.
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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.
NOTE 2:
In the event of mobility of the UE to another AMF or to EPC when the UE becomes reachable, the old AMF can return an event indication to the (H)GMLC as at steps 19 and 20 and may include the address of the new serving AMF or MME if known. If a new serving AMF or MME is not known, the (H)GMLC can repeat step 3 to query the UDM and HSS for the new AMF or MME address. If a new AMF address is received, the (H)GMLC can restart the procedure from step 4.
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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.
NOTE 3:
The AMF may decide to cancel the location request before the UE becomes reachable (e.g. due to lack of resources or due to a timeout on the UE becoming reachable) or when the UE becomes reachable (e.g. if the AMF executes NAS level congestion control on the UE, or for other reasons). The AMF then skips steps 10-18 and proceeds to step 19 to return an indication of location cancelation to the VGMLC or (H)GMLC.
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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 and LDR reference number 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 and LDR reference number. 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, E-UTRA connected to EPC, non-3GPP access connected to 5GC) and may include an embedded positioning message which indicates certain allowed or required location measurements (or a location estimate) 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.
NOTE 4:
The deferred routing identifier may be global (e.g. an IP address, UUID or URI) or may be local. The deferred routing identifier is used for routing in step 25. However, the immediate routing identifier included by the AMF in step 15 is used for routing in step 17.
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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 UE cannot support the periodic and triggered location request, the service operation returned to the AMF shall include a suitable error cause.
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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 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.
NOTE 5:
As an optional optimization for a roaming UE, instead of performing steps 19 and 20, the AMF may invoke the Namf_Location_EventNotify service operation directly towards the HGMLC (e.g. if a VGMLC is not used or if the VGMLC ceases support after step 8).
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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.
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Step 23.
The UE obtains any location measurements or a location estimate that were requested or allowed at step 16.
NOTE 6:
Obtaining a location estimate when requested also applies to the trigger event corresponding to expiration of the maximum reporting interval for an area event or motion event.
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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 an embedded positioning message which includes any location measurements or location estimate 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.
NOTE 7:
When forwarding the event report message to the LMF in step 25, the AMF includes the deferred routing identifier received in step 25 as the LCS Correlation Identifier. The deferred routing identifier can assist a serving LMF in identifying the periodic or triggered location session if the same serving LMF had assigned the deferred routing identifier at step 16 or can indicate to the LMF that it is acting as a default LMF.
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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.
NOTE 8:
Inclusion of a new deferred routing identifier in the event report acknowledgment at step 26 may be used to change the serving LMF (e.g. if a UE moves into an area or to an access type that is better supported by a different LMF or if the serving LMF is overloaded) or to enable a default LMF to become a serving LMF.
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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. 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.
NOTE 9:
A precondition for the procedure in clause 6.11.1 is that an LCS Correlation identifier assigned by the serving AMF has been previously passed to the LMF. The LCS Correlation identifier is used in steps 1, 3, 6 and 7 in clause 6.11.1 to ensure that during a positioning session between the LMF and UE, positioning response messages from the UE are returned by the AMF to the correct LMF and carrying an indication (the LCS Correlation identifier) which can be recognized by the LMF. To retain this capability in step 27, the LMF shall assign a Correlation identifier indicating the LMF (and optionally a positioning session) for use at step 1 in clause 6.11.1. To enable an AMF to distinguish a Correlation identifier assigned by an LMF (used in this procedure) from a Correlation identifier assigned by the AMF (used otherwise for clause 6.11.1), the two types of Correlation identifier could be selected from different ranges, with or without a flag.
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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 obtained at step 27.
NOTE 10:
In the case of roaming, the LMF may select the VGMLC for step 28 using the NRF service or using configuration information in the LMF or may use the same VGMLC as for steps 3-8 (e.g. if the LMF acts as a serving LMF and received the VGMLC address from the AMF as part of step 14).
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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.
NOTE 11:
As an optional optimization for a roaming UE, instead of performing steps 28 and 29, the LMF may invoke the Nlmf_Location_EventNotify service operation directly towards the HGMLC.
NOTE 12:
In the event of mobility of the UE to an access network for which event reporting at step 22 is not allowed (e.g. an access network in EPS) or if the UE is otherwise unable to send event reports (e.g. due to being powered off), the (H)GMLC may not receive event reports at step 28 or step 29 at fixed intervals for periodic location or at intervals equal to or less than the maximum reporting interval for triggered location. In such a case, the (H)GMLC may cancel the periodic or triggered location reporting using the procedures defined in clause 6.3.3. The UE may also cancel the periodic or triggered location reporting either locally or using the procedure defined in clause 6.3.2 once the UE can access an access network that is allowed for event reporting.
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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 to the external LCS client or AF (via the NEF), and 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.
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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.
NOTE 13:
Service continuity for reporting of periodic or trigger events when a UE moves between 5GS and EPS is not supported in this release of the specification.
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