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Content for  TS 23.271  Word version:  17.0.0

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9  General Network Positioning Proceduresp. 56

The generic network positioning procedure of providing the location information of an UE subscriber can be partitioned into the following procedures.
Location Preparation Procedure
This generic procedure is concerned with verifying the privacy restrictions of the UE subscriber, reserving network resources, communicating with the UE to be located and determining the positioning method to be used for locating the UE subscriber based on the requested QoS and the UE and network capabilities.
Positioning Measurement Establishment Procedure
This procedure is concerned with performing measurements by involving the necessary network and/or UE resources. Depending on the positioning method to be used for locating the UE the internals of this procedure can be positioning method dependent. The procedure is completed with the end of the positioning measurements.
Location Calculation and Release Procedure
This generic procedure is initiated after the measurements are completed and is concerned with calculating the location and optionally, velocity of the UE and releasing all network and/or UE resources involved in the positioning.
Each of the following procedures defines the support of a single location request (MT LR, MO LR or NI LR) that may be immediate or deferred. Treatment alternatives for a new location request when other concurrent locations requests are already ongoing for the same target UE is not generally defined in these procedures except in certain specific cases. For such general treatment alternatives, refer to clause 4.5.
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9.1  Mobile Terminating Location Requestp. 57

The MT-LR procedures for the location request from the LCS client which does not have the privacy override capability are described in the clause 9.1.1.
The MT-LR procedures for the location request from the LCS client which has the privacy override capability (e.g. the request is come from the emergency service provider) are described in the clause 9.1.1A. In this case the H-GMLC is not involved to the location procedures and the privacy check procedures in H-GMLC/PPR are skipped.
It is noted that R-GMLC or the UE may handle the periodicity of location requests as requested by the LCS client both in CS and PS domain.
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9.1.1  Common MT-LR procedure in PS and CS domainp. 58

Reproduction of 3GPP TS 23.271, Fig. 9.1: General Network Positioning for a MT-LR
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Step 1.
An external LCS client requests the current location and optionally, velocity of a target UE from a GMLC. The LCS Client may also request a deferred location request, i.e. based on event. The R-GMLC verifies the identity of the LCS client and its subscription to the LCS service requested and derives the MSISDN or IMSI or pseudonym of the target UE to be located and the LCS QoS from either subscription data or data supplied by the LCS client. For a call related location request, the LCS client includes the LCS client's called party number, as dialled by the target mobile user, in the LCS service request. For a session related location request, the LCS client includes the APN-NI of the LCS client, as used by the target UE, in the LCS service request. For a call/session related request the R-GMLC may verify that the called party number or APN-NI is correct for the LCS client in question. The LCS client's dialled number or APN-NI are checked in step 9 for the call/session related class.
The LCS request may carry also the Service Identity and the Codeword and the service coverage information. The R-GMLC may verify that the Service Identity received in the LCS request matches one of the service identities allowed for the LCS client. If the service identity does not match one of the service identities for the LCS client, the R-GMLC shall reject the LCS request. Otherwise, the R-GMLC can map the received service identity in a corresponding service type.
If the location request is originated by a Requestor, the Requestor Identity may be added to the LCS service request. The LCS client should authenticate the Requestor Identity but this is outside the scope of this specification. The LCS service request may also contain the type of the Requestor identity if the requestor identity was included.
If the H-GMLC address is not contained in the pseudonym or cannot deduced from the pseudonym, the R-GMLC shall determine the verinym for the pseudonym. In this case the R-GMLC may access to its associated PMD as described in clause 9.1.1.3.
The R-GMLC verifies whether it stores the privacy profile of the target UE. If the R-GMLC stores the UE's privacy profile, (this means the R-GMLC is the H-GMLC of the target UE), then step 2, 3, 4 and 12 are skipped.
If location is required for more than one UE, the steps following below may be repeated and in that case the R-GMLC should verify whether the number of Target UEs in the LCS request is equal or less than the Maximum Target UE Number of the LCS client. If the Maximum Target UE Number is exceeded, the R-GMLC should respond to the client with proper error cause. If periodic location is requested, the steps following below may be repeated or the R GMLC may forward the periodic location request to the UE, see clause 9.1.12.
Step 2.
If the R-GMLC already knows, (e.g. from a previous location request or an internal lookup table), or is able to determine, (e.g. it is possible to use a DNS lookup mechanism similar to IETF RFC 2916), the network address of H-GMLC of the target UE, or in case the location service request contains the target UE's pseudonym, which includes the target UE's Home-GMLC address, or a pseudonym from which the target UE's Home-GMLC address can be deduced, then this step and step 3 may be skipped.
Otherwise, the R-GMLC sends a SEND_ROUTING_INFO_FOR_LCS message to the home HLR/HSS of the target UE to be located with the IMSI or MSISDN of the UE.
The details of the alternative methods of retrieving H-GMLC address other than the sending SEND_ROUTING_INFO_FOR_LCS message to the HLR/HSS, (e.g. internal lookup table, DNS lookup mechanism), are not in the scope of this specification.
Step 3.
The HLR/HSS verifies whether the R-GMLC is authorized to request UE location information. If not, an error response is returned.
Otherwise the HLR/HSS returns one or several of the network addresses of the current SGSN and/or VMSC/MSC server and/or current MME, the LCS capabilities of the serving nodes if available , the V-GMLC address associated with the serving nodes, if available and whichever of the IMSI and MSISDN that was not provided in step 2. The HLR/HSS returns the address of the H-GMLC. The HLR/HSS also returns the address of the PPR, if available.
Step 4.
If R-GMLC finds out that it is the H-GMLC, the signalling steps 4 and 15 are skipped.
If the R-GMLC did not receive the H-GMLC address in step 3 and can not retrieve the H-GMLC address in some other way (e.g. DNS lookup), then steps 4, 5, 6, 7, 8, 10, 11, 12, 14 and 15 are skipped and the R-GMLC directly sends the PSL message to the serving node.
Otherwise, the R-GMLC sends the location request to the H-GMLC. If one or several of the network addresses of the current SGSN and/or VMSC/MSC server and/or current MME, the LCS core network signalling capabilities of the serving nodes, IMSI and MSISDN for the target UE and the address of the V-GMLC and the PPR have been retrieved in Step 3, the R-GMLC shall pass the information with the location request to the H-GMLC. The R-GMLC shall also send the service coverage information to the H-GMLC, if the information is available.
Step 5.
The H-GMLC verifies whether the R-GMLC is authorized to request UE location information. If the R-GMLC is not authorized, an error response is returned.
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 (MSISDN or IMSI) of the target UE. If the H-GMLC can resolve the address of PMD from the pseudonym, the H-GMLC requests the verinym from its associated PMD, see clause 9.1.1.3. In case H-GMLC knows that the PMD functionality is integrated in PPR, it can include the information from the LCS Identity Request in the LCS authorisation request to the PPR, see clause 9.1.1.1. In this case, if H-GMLC is not able to obtain the verinym of the target UE, the H-GMLC shall cancel the location request.
The H-GMLC performs privacy check on the basis of the UE user's privacy profile stored in the H-GMLC and the capabilities of the serving nodes (MSC/VLR and/or SGSN and/or MME), if available. If the privacy profile of the target UE is stored in a PPR and the H-GMLC received the network address of the PPR from R-GMLC or is able to determine the PPR address (e.g. from a previous location request or an internal lookup table), the H-GMLC shall ask the PPR to perform the privacy check as described in the clause 9.1.1.1. If the privacy profile is stored in a PPR but the network address of the PPR is not available, the H-GMLC shall send SRI for LCS message to HLR/HSS in step 6 in order to get the PPR address and the privacy check in this step shall be performed after step 7. Also if the key of the UE user's privacy profile (i.e. MSISDN or IMSI) is not available, the privacy check in this step shall be performed after step 7. The H-GMLC/PPR verifies LCS barring restrictions in the UE user's privacy profile in the H-GMLC/PPR. In verifying the barring restrictions, barring of the whole location request is assumed if any part of it is barred or any requisite condition is not satisfied. If the location service request is to be barred, GMLC shall terminate the request towards the R-GMLC or the LCS client with the appropriate error code. As a result of the privacy check, the H-GMLC/PPR selects one or two indicators of the privacy check related action and/or a pseudo-external identity in the case of interaction with a pre Rel-6 serving node. (The details of the indicator of the privacy check related action and the pseudo-external identity are described in clause 9.5.4 and Annex C). If 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 H-GMLC stores the location estimate 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. In case the result of the privacy check for call/session unrelated class is "Location allowed without notification" then steps 6, 7, 8, 9 and 10 may be skipped.
Step 6.
If the H-GMLC does not know IMSI for the particular MSISDN (e.g. from a previous location request), and the VMSC/MSC server address, SGSN address or MME address, the H-GMLC shall send a SEND_ROUTING_INFO_FOR_LCS message to the home HLR/HSS of the target UE to be located with the IMSI or MSISDN of this UE. Also if the privacy profile is stored in a PPR but the network address of the PPR was not available in the step 5, the H-GMLC shall send the SRI for LCS message to HLR/HSS. Otherwise, this step and step 7 may be skipped.
Step 7.
The HLR/HSS then returns one or several of the network addresses of the current SGSN and/or VMSC/MSC server and/or current MME, the LCS core network signalling capabilities of the serving nodes , the V-GMLC address associated with the serving nodes, if available, "Optimized Lgd" indicator if enabled according to the criteria in clause 5.7 and whichever of the IMSI and MSISDN that was not provided in step (6) for the particular UE. The HLR/HSS may also return the address of the PPR, if available.
Step 8.
If step 6 and step 7 were performed, the H-GMLC/PPR may do a new privacy check, or if the privacy profile is stored in a PPR but the network address of the PPR was not available in step 5 and the PPR address is obtained in step 7, the H-GMLC shall ask the PPR to perform the privacy check as described in the clause 9.1.1.1.
If the location request is an immediate location request and the service coverage information was sent from R-GMLC, the H-GMLC checks the country codes of the serving node addresses. If the H-GMLC finds out the current SGSN and/or VMSC/MSC server and/or current MME locates out of the service coverage, the H-GMLC returns an appropriate error message to the R-GMLC or the LCS client.
In the cases when the H-GMLC did not receive the address of the V-GMLC, or when the V-GMLC address is the same as the H-GMLC address, or when both PLMN operators agree not to use the Lr interface, the H-GMLC does not send the location request to the V-GMLC and step 10 is skipped. In this case, the H-GMLC sends the location service request message to the serving node.
If the H-GMLC received the address of the V-GMLC from the HLR/HSS and the V-GMLC address is different from the H-GMLC address, the H-GMLC may send the location request to the V-GMLC. The location request shall contain one or several of the network addresses of the current SGSN and/or MSC/VLR and/or current MME, and the IMSI and MSISDN of the target UE. The location request may also carry the requested action of the VPLMN as the result of the privacy check in the H-GMLC (i.e. by using the indicator of the privacy check related action as described in clause 9.5.4 or by using the pseudo-external identity as described in Annex C in the case of query to a pre Rel-6 serving node). If the result of privacy check indicates that the notification (and verification) based on current location is needed, the H-GMLC shall send a location request to the V-GMLC indicating "positioning allowed without notification" or, for backwards compatibility with a pre Rel-6 serving node, a pseudo external identity representing the same privacy notification and verification action required as for the "positioning allowed without notification" procedure as described in Annex C and V-GMLC shall send a Provide Subscriber Location message to the MSC/SGSN/MME indicating "positioning allowed without notification" or, for backwards compatibility with a pre Rel-6 serving node, a pseudo external identity representing the same privacy notification and verification action required as for the "positioning allowed without notification" procedure as described in Annex C. The V-GMLC first authenticates that the location request is allowed from this GMLC, PLMN or from this country. If not, an error response is returned.
Step 9.
If the GMLC (H-GMLC, R-GMLC or V-GMLC) receives only the MSC/VLR address, the MT LR proceeds as the CS-MT-LR procedure described in clause 9.1.2. If the GMLC receives only the SGSN address, the MT LR proceeds as the PS-MT-LR procedure described in clause 9.1.6. If the GMLC receives only the MME address, the MT LR proceeds as the EPC-MT-LR procedure described in clause 9.1.15. If the GMLC receives several of the following addresses, SGSN, VMSC, MSC Server and/or MME, it has to decide where to send the location request. If the requested MT-LR is known to be associated with a CS call, the CS-MT-LR procedure shall be invoked. If the requested MT-LR is associated with a PS session in UTRAN, the PS-MT-LR procedure shall be invoked. If the requested MT-LR is associated with a PS session in E-UTRAN, the EPC-MT-LR procedure shall be invoked. Otherwise, two or more of CS-MT-LR, PS-MT-LR and EPC-MT-LR are applicable. If the GMLC has determined that PS-MT-LR and/or EPC-MT-LR procedures are to be executed then according to the criteria in clause 5.7 the GMLC shall set the "Optimized Lgd" indicator in the Provide Subscriber Location request procedure for either EPC-MT-LR or PS-MT-LR. In this case, GMLC shall only execute either EPC-MT-LR or PS-MT-LR procedure. If LCS Client indicated deferred location request, GMLC shall indicate this together with applicable event type (e.g. UE available) in the requested EPC/PS/CS-MT-LR, see clauses 9.1.8 and clause 9.1.15.
Step 10.
The V-GMLC sends the location service response to the H-GMLC in accordance with the requested LCS QoS Class. If the requested LCS QoS class was Assured, V-GMLC sends the result only if the result has been indicated to fulfil the requested accuracy, otherwise V-GMLC sends a LCS service response with a suitable error cause. If the UE requested LCS QoS class was Best Effort, V-GMLC sends whatever result it received with an appropriate indication if the requested accuracy was not met. The location service response may contain the information about the positioning method used. The V-GMLC may record charging information.
Step 11.
If the privacy check in step 5 indicates that further privacy checks are needed, or on the basis of the privacy profile, the H-GMLC shall perform an additional privacy check or the H-GMLC may ask the PPR to perform the privacy check as described in the clause 9.1.1.1 in order to decide whether the H-GMLC can forward the location information to the LCS client or send a notification if the result of the privacy check requires the notification and verification based on current location. If the location request from the R-GMLC or the LCS client contained the pseudonym, the H-GMLC shall use the pseudonym of the target UE in the location response to the R-GMLC or the LCS client. One example when this additional privacy check is needed is when the target UE user has defined different privacy settings for different geographical locations.
Step 12.
If the result of privacy checks in step 11 indicates that the notification (and verification) based on current location is needed, the HGMLC shall send a location request to the V-GMLC indicating "notification only" or, for backwards compatibility with a pre Rel-6 serving node, a pseudo external identity representing the same privacy notification and verification action required as for the "notification only" procedure as described in Annex C. Otherwise this step and steps 13, 14 may be skipped. If the H-GMLC received the address of the V-GMLC from the HLR/HSS and the V-GMLC address is different from the H-GMLC address in step 8, the H-GMLC may send the location request to the V-GMLC. The location request shall contain one or several of the network addresses of the current SGSN and/or MSC/VLR and/or current MME, and the IMSI and MSISDN of the target UE.
Step 13.
If the GMLC (H-GMLC, R-GMLC or V-GMLC) received only the MSC/VLR address in step 9, the MT LR proceeds as the CS post positioning notification and verification procedure described in clause 9.1.10 or clause 9.1.2 if pseudo external identity is used. If the GMLC receives only the SGSN address in step 9, the MT LR proceeds as the PS post positioning notification and verification procedure described in clause 9.1.11 or clause 9.1.6 if pseudo external identity is used. If the GMLC receives only the MME address in step 9, the MT LR proceeds as the EPC post positioning notification and verification procedure described in clause 9.1.18. If the GMLC receives several of the following addresses, SGSN, VMSC, MSC Server and/or MME, it has to decide where to send the location request. If the requested MT-LR is known to be associated with a CS call, the CS post positioning notification and verification procedure shall be invoked. If the requested MT-LR is associated with a PS session in UTRAN, the PS post positioning notification and verification procedure shall be invoked. If the requested MT-LR is associated with a PS session in E-UTRAN, the EPC post positioning notification and verification procedure shall be invoked. Otherwise, CS and/or PS and/or EPC post positioning notification and verification procedure are applicable.
Step 14.
The V-GMLC sends the location service response with an indication of the result of notification and verification procedure performed in step 13 to the H-GMLC.
Step 15.
The H-GMLC sends the location service response to the R-GMLC. The H-GMLC may store the location information and its age. The location service response may contain the information about the positioning method used and the indication whether the obtained location estimate satisfies the requested accuracy or not. The H-GMLC may record charging information.
Step 16.
R-GMLC sends the location service response to the LCS client. If the location request from the LCS client contained the pseudonym and the R-GMLC resolved the verinym from the pseudonym in the step 1, the R-GMLC shall use the pseudonym of the target UE in the location response to the LCS client. If the LCS client requires it, the R-GMLC may first transform the universal location co-ordinates provided by the SGSN or MSC/MSC server or MME into some local geographic system. The R-GMLC may record charging information both for the LCS client and inter-network revenue charges from the SGSN or MSC/MSC server or MME's network. The location service response from the R-GMLC to the LCS client may contain the information about the positioning method used and the indication whether the obtained location estimate satisfies the requested accuracy or not.
The detailed CS-MT-LR, PS-MT-LR and EPC-MT-LR procedures in step 9 of Figure 9.1 are described in clauses 9.1.2, 9.1.6 and 9.1.15. The detailed procedure for deferred PS/CS-MT-LR is described in clause 9.1.8.
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