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Content for  TS 23.271  Word version:  17.0.0

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9.1.15  EPC Mobile Terminating Location Request (EPC-MT-LR) |R9|p. 108

Figure 9.18 illustrates the general network positioning for LCS clients external to the PLMN for EPC services. In this scenario, it is assumed that the target UE is identified using an MSISDN or IMSI. This procedure is applicable to a request from an LCS client for a current location, current or last known location or a deferred location for the UE availability event.
Reproduction of 3GPP TS 23.271, Fig. 9.18: General Network Positioning for EPC-MT-LR
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9.1.15.1  Location Preparation Procedurep. 108

Step 1.
For a request for a current location or a current or last known location the common PS and CS MT-LR procedure is performed as described in clause 9.1.1. For a request for a deferred location for the UE availability event, steps 1 and 2 of the deferred location request procedure are performed as described in clause 9.1.8.1.
Step 2.
GMLC sends a Provide Subscriber Location message to the MME indicated in step 1. This message carries the type of location information requested (e.g. current location and optionally, velocity), the UE subscriber's IMSI, LCS QoS information (e.g. accuracy, response time) and an indication of whether the LCS client has the override capability. For a session related location request, the message also carries the APN-NI to which the UE user has established the session. For a value added LCS client, the message shall carry the client name, the external identity of the LCS client and the Requestor Identity (if that is both supported and available), optionally the message may also carry the Service Type. Also the message may carry the type of the LCS client name and also the type of the Requestor identity if the requestor identity was included. If the result of the privacy check at H-GMLC/PPR indicated that the codeword shall be sent to the UE user, the message may carry also the codeword received from the LCS client. For a PLMN operator LCS client, the message shall carry the internal identity of the LCS client. If the Requestor Identity is provided, the GMLC shall send it as separate information. The message also shall carry the indicators of privacy related action which is described in clause 9.5.4, if it is provided by H-GMLC. If a deferred location was requested in step 1 for the UE availability event and if the GMLC supports delayed location reporting for UEs transiently not reachable ( i.e. because they are in extended idle mode DRX or PSM), the GMLC shall indicate support of delayed location reporting in this message.
2a) If the GMLC indicates support of delayed location reporting in step 2 and the MME supports delayed location reporting for UEs transiently not reachable, the MME sends a Provide Subscriber Location ack message with a "UE transiently not reachable" indication. In this case, steps 9a and 9b are executed instead of step 9. If the GMLC indicates support of delayed location reporting in step 2, and the MME does not support delayed location reporting and the UE is transiently not reachable, a Provide Subscriber Location return error shall be returned with a suitable cause.
Step 2b.
If step 2a occurs, the GMLC returns an LCS Service Response to the LCS Client by instigating steps 5, 6 and 7 of the procedure in clause 9.1.8.1.
Step 3.
If the GMLC is located in another PLMN or another country, the MME first authenticates that a location request is allowed from this PLMN or from this country. If not, an error response is returned. Secondly the MME checks if the UE is detached or suspended and in either such case an error response is returned. If the PSL message from the GMLC includes the indicators of privacy related action, the MME determines a required privacy related action as described in clause A.3.
If the UE is not using Control Plane CIoT EPS Optimisation and if the UE is in ECM-IDLE state and is not in power saving mode and is currently reachable, the MME performs a network triggered service request as defined in TS 23.401 in order to establish a signalling connection with the UE and assign a specific eNodeB. If step 2a was performed and the UE is transiently not reachable, the MME waits until the UE next becomes reachable and then performs a network triggered service request if needed to establish a signalling connection with the UE.
If the UE is using Control CIoT EPS Optimisation, procedures for Mobile Terminated Data Transport in Control Plane CIoT EPS optimisation as defined in TS 23.401 are performed by the MME to establish a signalling connection with the UE.
Step 4.
If the location request comes from a value added LCS client and the indicators of privacy related action indicates that the UE must either be notified or notified with privacy verification and the UE supports notification of LCS, a notification invoke message is sent to the target UE indicating the type of location request from the LCS Client (e.g. current location or "current or last known location") and the identity of the LCS client and the Requestor Identity (if that is both supported and available), whether privacy verification is required. Also the message may indicate the type of the LCS client name and also the type of the Requestor identity if the requestor identity was included. Moreover, the message may carry also the service type and the codeword. Optionally, the MME may after sending the NAS Location Notification Invoke message continue in parallel the location process, i.e. continue to step 6 without waiting for a LCS Location Notification Return Result message in step 5.
Step 5.
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 MME indicating, if privacy verification was requested, whether permission is granted or denied. Optionally, this message can be returned some time after step 4, but before step 9. If the UE user does not respond after a predetermined time period, the MME shall infer a "no response" condition. The MME shall return an error response to the GMLC if privacy verification was requested and either the UE user denies permission or there is no response with the UE privacy profile received from the GMLC indicating barring of the location request.
Step 6.
The MME selects a E-SMLC as described in clause 6.3.13 and sends a Location Request message to the selected E-SMLC. Once an MME has selected an E-SMLC it must continue to use that E-SMLC for the duration of the session. The Location Request includes the type of location information requested, the requested QoS, identity of serving cell, UE location capabilities and, if available, the Service Type. If the UE is in power saving mode, steps 4 and 5 do not apply, the location request specifies current or last known location and the MME has stored the last serving cell for the UE, this step may be performed to obtain the last known location. The location request also indicates RAT type and/or coverage level if applicable. If this step is performed after the MME receives the NAS Location Notification Return Result in step 5, the Location Request message contains the identity of the serving cell obtained from the S1-AP message that carries the NAS Location Notification Return Result.
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9.1.15.2  Positioning Measurement Establishment Procedurep. 110

Step 7.
If the requested location information and the location accuracy within the QoS can be satisfied based on parameters received from the MME, e.g. cell identity, the E-SMLC may send a Location Response immediately. If the requested location information indicates a last known location, the E-SMLC shall determine a last known location based on the cell identity and send a Location Response immediately. Otherwise, the E-SMLC determines the positioning method and instigates the particular message sequence for this method as described in clause 9.3a. If the position method returns position measurements, the E-SMLC uses them to compute a location estimate. If there has been a failure to obtain position measurements, the E-SMLC may use the current cell identity to derive an approximate location estimate. If an already computed location estimate is returned for an UE based position method, the E-SMLC may verify consistency with the current cell. If the location estimate so obtained does not satisfy the requested accuracy and sufficient response time still remains, the E-SMLC may instigate a further location attempt using the same or a different position method. If a vertical location co ordinate is requested but the E-SMLC can only obtain horizontal co-ordinates, these may be returned.
NB-IoT UEs may perform measurements for some positioning methods only when in ECM-IDLE state. An E-SMLC that is aware of this (e.g. from an indication sent by the UE) may allow additional response time to the UE (e.g. in the QoS) to obtain the measurements. An MME that is aware of this (e.g. from the UE access type) may also allow additional time for a location session to complete.
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9.1.15.3  Location Calculation and Release Procedurep. 110

Step 8.
When location information best satisfying the requested location type and QoS has been obtained, the E-SMLC returns it to the MME in a Location Response message. E-SMLC shall in its response include an indication whether the obtained location estimate satisfies the requested accuracy or not. The information of the positioning method used may be returned with the location information. If a location estimate could not be obtained, the E-SMLC returns a Location Response message containing a failure cause and no location estimate.
Step 9.
This step is executed only if step 2a was not executed. The MME returns the location information, its age and obtained accuracy indication to the GMLC, if the MME has not initiated the Privacy Verification process in step 4. If step 4 has been performed for privacy verification, the MME returns the location information only, if it has received a NAS Location Notification Return Result indicating that permission is granted. In these cases, the information about the positioning method used may be sent with the location information. If a NAS Location Notification Return Result message indicating that permission is not granted is received, or there is no response, with the requested privacy action or the UE subscription profile indicating barring of location, the MME shall return an error response to the GMLC. If the MME did not return a successful location estimate, but the privacy checks were successfully executed, the MME may return the last known location of the target UE if this is known and the LCS client is requesting the current or last known location. The MME may record charging information.
Step 9a.
This step is executed only if step 2a was executed. The MME shall send a Subscriber Location Report to the GMLC, and, if these were obtained in steps 6 to 8, the location information, its age and obtained accuracy indication to the GMLC, if the MME has not initiated the Privacy Verification process in step 4. If step 4 has been performed for privacy verification, the MME sends the location information only, if it has received a NAS Location Notification Return Result indicating that permission is granted. In these cases, the information about the positioning method used may be sent with the location information. If a NAS Location Notification Return Result message indicating that permission is not granted is received, or there is no response, with the requested privacy action or the UE subscription profile indicating barring of location, the MME shall send an error indication to the GMLC. The MME shall include in the Subscriber Location Report any identities for the UE received in step 2. The MME may record charging information. If MME relocation or change of MME happens before location information can be obtained or reported, the old MME includes an error cause code indicating that it cannot proceed with the request and includes the address of the new MME if available. The GMLC may reiterate then its request towards the new MME.
Step 9b.
If step 9a was executed, the GMLC shall acknowledge receipt of the Subscriber Location Report.
Step 10.
For a request for a current location or a current or last known location in step 1, the common MT-LR procedure in PS and CS domain as described in clause 9.1.1 is performed. For a request for a deferred location for the UE availability event in step 1, steps 11, 13, 14 and 15 of the procedure in clause 9.1.8.2 are performed.
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9.1.16  EPC-MT-LR without HLR Query |R9|p. 111

Figure 9.19 illustrates current or last known location requests for an emergency services call, where an emergency services client (i.e., a Public Safety Answering Point) identifies the target UE and the serving LRF using correlation information that was previously provided to it by the IMS Core. The signalling used to provide the correlation information to the PSAP is defined in TS 23.167. The correlation information may be used by the LRF to retrieve other information previously provided to it by the IMS Core as per TS 23.167 and/or MME as described in clause 9.1.17. This allows the V GMLC associated with the LRF to request location from the MME without first querying the home HLR of the target UE. This scenario therefore supports location of emergency calls from roamers or SIM-less emergency calls, or non-registered (U)SIM emergency calls, and requires that the initial location, as well as UE and MME identifying information had been pushed to the GMLC/LRF as per clause 9.1.17 or as per TS 23.167.
Reproduction of 3GPP TS 23.271, Fig. 9.19: Positioning for a Emergency Services EPC-MT-LR without HLR Query
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Step 1.
Same as step 1 in Figure 9.1 but with the LCS client (PSAP) identifying first the target UE and the serving LRF by previously supplied correlation information for the emergency call.
Step 2.
The LRF/GMLC may determine the MME by associating the correlation information received from the PSAP with other information received previously from the MME using an EPC NI LR as in clause 9.1.17 and/or from the IMS core as in TS 23.167. The Provide Subscriber Location message sent to the MME carries, if available, the MSISDN or the IMSI and, if available, the IMEI for the target UE, as well as the required QoS and an indication of a location request from an emergency services client. The MME identifies the target UE using the IMSI, MSISDN and/or the IMEI. In case of a SIM-less emergency call, or non-registered (U)SIM emergency call, the IMEI shall be always sent.
Step 3.
The MME sends a Location Request to the E-SMLC, as for a normal EPC MT LR.
Step 4.
E-SMLC performs positioning as for a normal EPC MT LR.
Step 5.
E-SMLC returns a location estimate to the MME as for a normal EPC MT LR.
Step 6.
The MME returns the location information, its age and obtained accuracy indication to the LRF/GMLC. The information about the positioning method used may be sent with the location information. If the E-SMLC did not return a successful location estimate, the MME may return the last known location of the target UE if this is known and the LCS client is requesting the current or last known location.
Step 7.
The LRF sends the location service response to the LCS client (PSAP).
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9.1.17  EPC Network Induced Location Request (EPC-NI-LR) |R9|p. 112

At any time after detecting an emergency situation (i.e. after emergency Attach, UE requested emergency PDN Connectivity), the MME may initiate the EPC Network Induced Location Request (EPC NI LR) procedure. The procedure can also be used to verify a UE location (country or international area) for NB-IoT, LTE-M and WB EUTRAN satellite access (see TS 23.401). The procedure is illustrated in Figure 9.20.
Reproduction of 3GPP TS 23.271, Fig. 9.20: Network Induced Location Request for EPC
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Step 1.
A trigger to initiate the EPC-NI-LR procedure happens, e.g. when an emergency attach or emergency PDN connection establishment is detected, or when the MME decides to verify the UE location (country or international area) via LCS service for a UE registering or registered for NB-IoT, LTE-M or WB-EUTRAN satellite access. For the emergency call invocation from the user, the UE performs emergency attach if not attached or requests emergency PDN connection if already normal attached. As part of the Attach procedure, the UE support of LPP indication is provided by the UE to the MME.
Step 2.
The MME selects a E-SMLC as described in clause 6.3.13 and sends a Location Request message to the selected E-SMLC. Once an MME has selected an E-SMLC it must continue to use that E-SMLC for the duration of the session. The Location Request includes the type of location information requested, the requested QoS, identity of serving cell and UE capability to support LPP. When MME needs to know the country of the UE, an indication of this is included.
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9.1.17.1  Positioning Measurement Establishment Procedurep. 113

Step 3.
If the requested location information and the location accuracy within the QoS can be satisfied based on parameters received from the MME, e.g. cell identity, the E-SMLC may send a Location Response immediately. Otherwise, the E-SMLC determines the positioning method and instigates the particular message sequence for this method as described in clause 9.3a. If the position method returns position measurements, the E-SMLC uses them to compute a location estimate. If there has been a failure to obtain position measurements, the E-SMLC may use the current cell identity to derive an approximate location estimate. If an already computed location estimate is returned for an UE based position method, the E-SMLC may verify consistency with the current cell identity. If the location estimate so obtained does not satisfy the requested accuracy and sufficient response time still remains, the E-SMLC may instigate a further location attempt using the same or a different position method. If a vertical location co-ordinate is requested but the E-SMLC can only obtain horizontal co-ordinates, these may be returned. If the MME included an indication of UE country determination at step 2, the E-SMLC maps the location estimate to a country or an international area.
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9.1.17.2  Location Calculation and Release Procedurep. 113

Step 4.
When a location estimate best satisfying the requested QoS has been obtained, the E-SMLC returns a Location Response to the MME with an indication whether the obtained location estimate satisfies the requested accuracy or not. This message carries the location estimate that was obtained. If a location estimate was not successfully obtained, a failure cause is included in the Location Response. When UE country determination is indicated at step 2, E-SMLC also returns an indication of the country or international area determined at step 3. If in step 1 the MME decided to verify the UE location (country or international area) via LCS service for a UE registering or registered for NB-IoT, LTE-M or WB-EUTRAN satellite access, the remaining steps are skipped.
Step 5.
The MME may determine the GMLC and emergency services client using the cell identity or the location estimate or according to some fixed association for the MME. The MME shall send a Subscriber Location Report to the GMLC carrying the IMEI and if available the IMSI and MSISDN of the UE, the event causing the message (EMERGENCY_CALL_ORIGINATION), and, if these were obtained in steps 2 to 4, the location estimate and its age and the indication received from E-SMLC whether the obtained location estimate satisfies the requested accuracy or not. The serving cell identity of the UE may also be sent if available. The MME shall include its own address. The MME may record charging information.
Step 6.
The GMLC shall acknowledge receipt of the location estimate provided that the associated LRF serves the emergency services LCS client and the client is accessible. These conditions would normally be fulfilled if the LRF either already has created, or expects to later create, a record for the UE for the emergency services session as described in clause 9.8.4.
Step 7.
The LRF associated with the GMLC treats the received location estimate as described in clause 9.8.4: e.g. may use the location information to assist routing of the emergency session to the PSAP/emergency centre and/or may transfer the location information to the emergency services LCS client immediately or upon request from the client. The LRF/GMLC may store the information received in step 5: e.g. may store the UE identity and the address of the MME. The LRF/GMLC may record charging information.
Step 8.
At some point, MME determines that emergency service is no longer active (e.g. EPS bearer for emergency service is deactivated).
Step 9.
The MME may send a Subscriber Location Report to the GMLC carrying the same UE's information as in step 5 and the event causing the message (EMERGENCY_CALL_RELEASE).
Step 10.
The GMLC shall acknowledge receipt of the location report from MME.
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9.1.18  EPC Post Positioning Notification and Verification Procedure |R9|p. 113

Figure 9.21 illustrates the post positioning notification and verification procedure.
Reproduction of 3GPP TS 23.271, Fig. 9.21: EPC Post Positioning Notification and Verification Procedure
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Step 1.
Common PS and CS MT-LR procedure as described in clause 9.1.1.
Step 2.
The GMLC sends a Provide Subscriber Location message to the MME with an indication of "notification only". This message carries the UE subscriber's IMSI. For a session related location request, the message also carries the APN-NI to which the user has established the session. For a value added LCS client, the message shall carry the client name, the external identity of the LCS client and the Requestor Identity (if that is both supported and available), optionally the message may also carry the Service Type. Also the message may carry the type of the LCS client name and also the type of the Requestor identity if the requestor identity was included. If the result of the privacy check at H-GMLC/PPR indicated that the codeword shall be sent to the UE user, the message may carry also the codeword received from the LCS client. For a PLMN operator LCS client, the message shall carry the internal identity of the LCS client. If the Requestor Identity is provided, the GMLC shall send it as separate information.
Step 3.
The MME first checks if the UE is detached or suspended. If this is the case, an error response is returned. The MME determines a required privacy related action as described in Annex A.3 based on the indicators of privacy related action in the PSL message from the GMLC.
If the UE is not using Control Plane CIoT EPS Optimisation and if the UE is in ECM-IDLE state, the MME performs a network triggered service request as defined in TS 23.401 in order to establish a signalling connection with the UE and assign a specific eNodeB.
If the UE is using Control Plane CIoT EPS Optimisation, procedures for Mobile Terminated Data Transport in Control Plane CIoT EPS optimisation as defined in TS 23.401 are performed by the MME to establish a signalling connection with the UE.
Step 4.
A notification invoke message is sent to the target UE indicating a location type of notification and verification only, the identity of the LCS client and the Requestor Identity (if that is both supported and available), whether privacy verification is required. Also the message may indicate the type of the LCS client name and also the type of the Requestor identity if the requestor identity was included. Moreover, the message may carry also the service type and the codeword.
Step 5.
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 MME indicating, if privacy verification was requested, whether permission is granted or denied. If the UE user does not respond after a predetermined time period, the MME shall infer a "no response" condition. The MME shall return an error response to the GMLC if privacy verification was requested and either the UE user denies permission or there is no response with the UE subscription profile indicating barring of the location request.
Step 6.
The MME returns the indication of successful notification and verification result, if it has received a NAS Location Notification Return Result indicating that permission is granted. If a LCS Location Notification Return Result message indicating that permission is not granted is received, or there is no response, with the requested privacy action or the UE subscription profile indicating barring of location, the MME shall return an error response to the GMLC.
Step 7.
Common MT-LR procedure in PS and CS domain as described in clause 9.1.1.
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