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Content for  TS 23.273  Word version:  18.4.0

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6.1.2  5GC-MT-LR Procedure for the commercial location servicep. 49

Figure 6.1.2-1 illustrates the general network positioning requested by the LCS clients, the AF or the NF (e.g. NWDAF). In this scenario, it is assumed that the target UE may be identified using an SUPI or GPSI. This procedure is applicable to a request from an LCS client, an NF or an AF for a current location of the target UE, and it is assumed that
  • Privacy verification may be required for the location service request;
  • The LCS client, or the AF or NF needs to be authorised to use the location service.
Reproduction of 3GPP TS 23.273, Fig. 6.1.2-1: 5GC-MT-LR Procedure for the commercial location services
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Step 1.
The LCS Client, the NF or the AF (via NEF) sends a request to the (H)GMLC for a location and optionally a velocity for the target UE which may be identified by an GPSI or an SUPI. The request may include the required QoS, supported GAD shapes and other attributes. (H)GMLC (for 1a, 1c) or NEF (for 1b) authorizes the LCS Client, the NF or the AF for the usage of the LCS service. If the authorization fails, step 2-23 are skipped and (H)GMLC (for 1a, 1c) or NEF (for 1b) responds to the LCS Client, the NF or the AF the failure of the service authorization in step 24. In some cases, the (H)GMLC derives the GPSI or SUPI of the target UE and possibly the QoS from either subscription data or other data supplied by the LCS Client, the NF or the AF.
The LCS request may carry also the Service Identity (see TS 22.071) and the Codeword and the service coverage information. The (H)GMLC may verify that the Service Identity received in the LCS request matches one of the service identities allowed for the LCS client or AF. If the service identity does not match one of the service identities for the LCS client or AF, the (H)GMLC shall reject the LCS request. Otherwise, the (H)GMLC can map the received service identity in a corresponding service type.
The LCS service request may include a scheduled location time if a current location of the UE is required at a specific time in the future.
The LCS service request may include integrity requirements including Time-to-Alert (TTA), Target Integrity Risk (TIR) and Alert Limit(AL). Definitions of these parameters are specified in TS 38.305.
If the LCS service request contains the pseudonym of the target UE and the (H)GMLC cannot resolve the PMD address from the pseudonym, the (H)GMLC itself determines the verinym (GPSI or SUPI) of the target UE. If the (H)GMLC can resolve the address of PMD from the pseudonym, the HGMLC requests the verinym from its associated PMD. If (H)GMLC is not able to obtain the verinym of the target UE, the (H)GMLC shall cancel the location request.
If a scheduled location time is not included and the requested type of location is "current or last known location" and the requested maximum age of location information is available, the (H)GMLC verifies whether it stores the previously obtained location estimate of the target UE. If the HGMLC stores the location estimate and timestamp of the location estimate (if available) and the location estimate satisfies the requested accuracy and the requested maximum age of location, the (H)GMLC checks the result of the privacy check at step 2. If the result of the privacy check for call/session unrelated class is "Location allowed without notification" then steps 3-23 may be skipped.
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Step 1b-1.
AF sends the Nnef_EventExposure_Subscribe to the NEF.
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Step 1b-2.
The NEF identifies based on the QoS attribute received from the location request that higher than cell-ID level location accuracy is required and invokes the Ngmlc_Location_ProvideLocation_Request service operation to the (H)GMLC, which contains the attributes received from the AF request. The NEF may also invoke the Ngmlc_Location_ProvideLocation_Request service operation to the (H)GMLC for lower than cell-ID location accuracy as an implementation option or if a scheduled location time is included.
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Step 1c.
The NF (e.g. NWDAF) invokes the Ngmlc_Location_ProvideLocation service operation to the (H)GMLC.
If location is required for more than one UE, the steps following below may be repeated and in that case the NEF or HGMLC receiving location request, shall verify whether the number of Target UEs in the Nnef_EventExposure_Subscribe, Ngmlc_Location_ProvideLocation or LCS request is equal to or less than the Maximum Target UE Number of the LCS client. If Maximum Target UE Number is exceeded, the NEF or HGMLC shall reject the Nnef_EventExposure_Subscribe, Ngmlc_Location_ProviceLocation or LCS request, the steps 2-23 are skipped, and then GMLC respond to the client with proper error cause in the step 24.
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Step 2.
The (H)GMLC invokes a Nudm_SDM_Get service operation towards the UDM of the target UE to get the privacy settings of the UE identified by its GPSI or SUPI. The UDM returns the target UE Privacy setting of the UE. The (H)GMLC checks the UE LCS privacy profile. If the target UE is not allowed to be located, steps 3-23 are skipped. The UDM may also reply (H)GMLC with an LPHAP indication, if stored in the UE LCS subscriber data.
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Step 3.
The (H)GMLC invokes a Nudm_UECM_Get service operation towards the UDM of the target UE with GPSI or SUPI of this UE. The UDM returns the network addresses of the current serving AMF and additionally the address of a VGMLC (for roaming case). If the location request is an immediate location request, the (H)GMLC checks the country codes of the serving node addresses. If the (H)GMLC finds the current AMF is out of the service coverage of the (H)GMLC, the (H)GMLC returns an appropriate error message to the LCS client, the NF or the AF (via NEF).
GMLC may determine the LMF ID based on the LCS data for an LCS Client/AF. In case a group ID is provided or derived from the location request, GMLC determines the LMF ID based on the provisioned Group ID.
GMLC may be configured with an LMF ID, irrelevant to any LCS client/AF. When the GMLC receives a MT location request from LCS client/AF, GMLC determines the LMF ID for all LCS client/AF.
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Step 4.
For a non-roaming case, this step is skipped. In the case of roaming, the HGMLC may receive an address of a VGMLC (together with the network address of the current serving AMF) from the UDM in step 3, otherwise, the HGMLC may use the NRF service in the HPLMN to select an available VGMLC in the VPLMN, based on the VPLMN identification contained in the AMF address received in step 3. The HGMLC then sends the location request to the VGMLC by invoking the Ngmlc_Location_ProvideLocation service operation towards the VGMLC. In the cases when the HGMLC did not receive the address of the VGMLC, or when the VGMLC address is the same as the HGMLC address, or when both PLMN operators agree, the HGMLC sends the location service request message to the serving AMF. In this case, step 4 is skipped. If the result of privacy check indicates that the verification based on current location is needed, the HGMLC shall send a location request to the VGMLC (in the case of roaming) or to the AMF (in the case of non-roaming) indicating "positioning allowed without notification" and VGMLC shall invoke an Namf_Location_ProvidePositioningInfo Request service operation towards the AMF at step 5. H-GMLC also provides the LCS client type of AF, if received in step 41b-2, or LCS client type of LCS client and other attributes to be sent to AMF in step 5.
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Step 5.
In the case of roaming, the VGMLC first authorizes that the location request is allowed from this HGMLC, PLMN or from this country. If not, an error response is returned. The (H)GMLC or VGMLC invokes the Namf_Location_ProvidePositioningInfo service operation towards the AMF to request the current location of the UE. The service operation includes the SUPI, the client type and may include the required LCS QoS, supported GAD shapes, scheduled location time, service type and other attributes as received or determined in step 1. If received in step 2, the (H)GMLC or VGMLC provides the LPHAP indication to the AMF.
To support location service in PNI-NPN with signalling optimisation, the H-GMLC also includes a contact address (Notification Target Address, e.g. a URI) and a Notification Correlation ID, which is used by LMF to provide location determination to H-GMLC directly.
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Step 6.
If the UE is 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.
If signalling connection establishment fails, step 7-13 are skipped and the AMF answers to the GMLC in step 14 with the last known location of the UE (i.e. Cell ID) together with the age of this location.
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Step 7.
If the indicator of privacy check related action indicates that the UE must either be notified or notified with privacy verification and if the UE supports LCS notification (according to the UE capability information), a notification invoke message is sent to the target UE, indicating the identity of the LCS client and the , service type (if that is both supported and available) and whether privacy verification is required.
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Step 8.
The target UE notifies the UE user of the location request and, if privacy verification was requested, waits for the user to grant or withhold permission. The UE then returns a notification result to the AMF indicating, if privacy verification was requested, whether permission is granted or denied for the current LCS request. If the UE user does not respond after a predetermined time period, the AMF shall infer a "no response" condition. The AMF shall return an error response in step 14 and if roaming VGMLC in step 15 to the HGMLC if privacy verification was requested and either the UE user denies permission or there is no response with the indication received from the (H)GMLC indicating barring of the location request and steps 10~13 are skipped.
The notification result may also indicate the Location Privacy Indication setting for subsequent LCS requests; i.e whether subsequent LCS requests, if generated, will be allowed or disallowed by the UE. The Location Privacy Indication may also indicate a time for disallowing the subsequent LCS requests.
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Step 9.
The AMF invokes the Nudm_ParameterProvision_Update (LCS privacy) service operation to store in the UDM the Location Privacy Indication information received from the UE. The UDM may then store the updated UE privacy setting information into the UDR as the "LCS privacy" Data Subset of the Subscription Data.
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Step 10-13.
Step 10-13 are the same as steps 6-9 defined in clause 6.1.1 with the addition that LMF can also perform 6.11.4 as positioning procedure and service type may be indicated towards the LMF and the exception that the LMF may determine the UE location in local coordinates or geographical co-ordinates or both. If the supported GAD shapes is not received in step 11 or Local Co-ordinates is not included in the supported GAD shapes, the LMF shall determine a geographical location. If a scheduled location time is provided at step 5, steps 11 and 12 include the following additional differences..
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Step 11.
The AMF includes the scheduled location time in the Nlmf_Location_DetermineLocation service operation sent towards the LMF. If received in step 5, the AMF provides the LPHAP indication to the LMF.
If H-GMLC contact address is received in step 5, AMF also includes the H-GMLC contact address and the Notification Correlation ID in the Nlmf_Location_DetermineLocation service operation and sends towards the LMF.
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Step 12.
If received in step 11 of the LPHAP indication, the LMF may determine an appropriate positioning method by taking into account the LPHAP indication. When sending a location request to the UE, the LMF may include the scheduled location time.
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If H-GMLC contact address and the Notification Correlation ID is received in step 11, the LMF responds to AMF in the Nlmf_location_determineLocation Response to indicate that the location determination will be sent directly to GMLC. In this case, the LMF determines to use local AMF for obtaining Non-UE Associated Network Assistance Data, as described in clause 6.11.3.
When LMF determines the UE location, it executes the step 28 as described in clause 6.3.1.
Step 14.
The AMF returns the Namf_Location_ProvidePositioningInfo Response towards the (V)GMLC (or HGMLC for roaming when the NL3 reference point is not supported) to return the current location of the UE. The service operation includes the location estimate, its age and accuracy and may include information about the positioning method and the timestamp of the location estimate.
If indicated in step 13 that the location determination will be sent directly to GMLC, AMF responds to GMLC with Namf_location_providePositioningInfo Response to indicate that GMLC will receive the location from LMF directly.
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Step 15.
In the case of roaming, the VGMLC forwards the location estimation of the target UE, its age, its accuracy and optionally the information about the positioning method received at step 14 to the HGMLC. For non-roaming scenario, this step is skipped.
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Step 16.
If the privacy check in step 2 indicates that further privacy checks are needed, the (H)GMLC shall perform an additional privacy check in order to decide whether the (H)GMLC can forward the location information to the LCS client or AF or send a notification if the result of the privacy check requires the notification and verification based on current location. One example when this additional privacy check is needed is when the target UE user has defined different privacy settings for different geographical locations. When an additional privacy check is not needed, the (H)GMLC skips steps 17-23.
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Step 17.
If the result of privacy checks in step 16 indicates that the notification (and verification) based on current location is needed, and in the case of roaming, the (H)GMLC shall send a location request to the VGMLC with location type indicating "notification only".
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Step 18.
The (H)GMLC or VGMLC invokes the Namf_Location_ProvidePositioningInfo service operation towards the AMF to request notification (and verification) based on current location.
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Step 19.
If the UE is 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 20.
If the indicator of privacy check related action indicates that the UE must either be notified or notified with privacy verification and if the UE supports LCS notification, the AMF sends a notification invoke message to the target UE, indicating the identity of the LCS client and the service type (if that is both supported and available) and whether privacy verification is required.
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Step 21.
Step 21 is the same as step 8.
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Step 22.
The AMF returns the Namf_Location_ProvidePositioningInfo Response towards the (V)GMLC (or HGMLC for roaming when the NL3 reference point is not supported) with an indication of the result of notification and verification procedure performed in steps 20-21.
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Step 23.
In the case of roaming, the VGMLC forwards an indication of the result of notification and verification procedure to the HGMLC. For non-roaming scenario, this step is skipped.
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Step 24.
The (H)GMLC sends the location service response to the LCS Client, the NF or the AF (via the NEF) if the target UE is allowed to be located by the LCS Client, the NF or the AF. Accordingly, NEF invokes Nnef_EventExposure_Notify or sends Nnef_EventExposure_Subscribe Response to the AF. If the location request from the LCS Client contained the pseudonym and the (H)GMLC resolved the verinym from the pseudonym in step 1, the (H)GMLC shall use the pseudonym of the target UE in the location response to the external LCS client. If the external LCS client or AF requires it, the (H)GMLC may first transform the universal location co-ordinates provided by the AMF into some local geographic reference system. The (H)GMLC may record charging information both for the LCS Client or AF and inter-network revenue charges from the AMF's network. The location service response from the (H)GMLC to the LCS Client, the NF or the AF may contain the information about the positioning method used and the indication whether the obtained location estimate satisfies the requested accuracy or not. If in step 2, step 15, step 16 or step 23 the (H)GMLC identifies that the target UE is not allowed to be located by the LCS Client, the NF or the AF, it rejects the LCS service request, and optionally indicate in the response the reason of the rejection, i.e. the target UE is not allowed to be located. If the LCS QoS Class is Assured and (H)GMLC detects that requested accuracy is not achieved, the (H)GMLC sends error response including failure cause.
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