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Content for  TS 23.271  Word version:  17.0.0

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9.1.6  Packet Switched Mobile Terminating Location Request (PS-MT-LR)p. 76

Figure 9.5 illustrates the general network positioning for LCS clients external to the PLMN for packet switched services. In this scenario, it is assumed that the target UE is identified using an MSISDN or IMSI.
Reproduction of 3GPP TS 23.271, Fig. 9.5: General Network Positioning for Packet Switched MT-LR
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9.1.6.1  Location Preparation Procedurep. 77

Step 1.
Common PS and CS MT-LR procedure as described in clause 9.1.1.
Step 2.
GMLC sends a Provide Subscriber Location message to the SGSN indicated by the HLR/HSS. 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 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 (or the pseudo external identity) 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. In addition, in order to display the requestor identity in case of pre rel-5 network elements (i.e. SGSN and/or UE), the requestor identity may be also added to the LCS client name by the GMLC. When the Requestor identity is added to the LCS client name the practise described in the Annex D should be followed. 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 the GMLC supports delayed location reporting for UEs transiently not reachable (i.e because they are in extended idle mode DRX or PSM), this shall be indicated in this message.
Step 2a.
If the UE for which the request in step 2 is related is transiently not reachable and the GMLC supports delayed location reporting for UEs transiently not reachable as indicated in step 2, the SGSN sends a Provide Subscriber Location ack and a "UE transiently not reachable" indication. In this case step 10a and 10b are executed instead of step 10.
Step 3.
If the GMLC is located in another PLMN or another country, the SGSN first authenticates that a location request is allowed from this PLMN or from this country. If not, an error response is returned. If the PSL message from the GMLC includes the indicators of privacy related action, the SGSN determines a required privacy related action as described in Annex A.3. If the PSL message from the GMLC does not include the indicators of privacy related action, the SGSN then verifies LCS barring restrictions in the UE user's subscription profile in the SGSN. 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 LCS is to be barred without notifying the target UE and a LCS client accessing a GMLC in the same country does not have the override capability, an error response is returned to the GMLC.
Otherwise, if the UE is in idle mode, the SGSN performs paging. The paging procedure is defined in TS 23.060.
Step 4.
Security functions may be executed. These procedures are defined in TS 23.060.
Step 5.
If the location request comes from a value added LCS client and the indicators of privacy related action or the UE subscription profile 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 SGSN may after sending the LCS Location Notification Invoke message continue in parallel the location process, i.e. continue to step 7 without waiting for a LCS Location Notification Return Result message in step 6.
Step 6.
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 SGSN indicating, if privacy verification was requested, whether permission is granted or denied. Optionally, this message can be returned some time after step 5, but before step 10. If the UE user does not respond after a predetermined time period, the SGSN shall infer a "no response" condition. The SGSN 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 7.
The SGSN sends a Location Request message to the RAN. This message includes the type of location information requested, the requested QoS and any other location information received in paging response.
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9.1.6.2  Positioning Measurement Establishment Procedurep. 78

Step 8.
If the requested location information and the location accuracy within the QoS can be satisfied based on parameters received from the SGSN and the parameters obtained by the RAN e.g. cell coverage and timing information (i.e. RTT or TA), the RAN may send a Location Report immediately. Otherwise, the RAN determines the positioning method and instigates the particular message sequence for this method in UTRAN Stage 2 TS 25.305 and in GERAN Stage 2 TS 43.059. If the position method returns position measurements, the RAN uses them to compute a location estimate. If there has been a failure to obtain position measurements, the RAN may use the current cell information and, if available, RTT or TA value to derive an approximate location estimate. If an already computed location estimate is returned for an UE based position method, the RAN may verify consistency with the current cell and, if available, RTT or TA. If the location estimate so obtained does not satisfy the requested accuracy and sufficient response time still remains, the RAN may instigate a further location attempt using the same or a different position method. If a vertical location co ordinate is requested but the RAN can only obtain horizontal co-ordinates, these may be returned.
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9.1.6.3  Location Calculation and Release Procedurep. 79

Step 9.
When location information best satisfying the requested location type and QoS has been obtained, the RAN returns it to the SGSN in a Location Report message. RAN 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 RAN returns a Location Report message containing a failure cause and no location estimate.
Step 10.
This step is executed only if Step 2a was not executed. The SGSN returns the location information, its age and obtained accuracy indication to the GMLC, if the SGSN has not initiated the Privacy Verification process in step 5. If step 5 has been performed for privacy verification, the SGSN returns the location information only, if it has received a LCS 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 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 SGSN shall return an error response to the GMLC. If the SGSN did not return a successful location estimate, but the privacy checks were successfully executed, the SGSN 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 SGSN may record charging information.
Step 10a.
This step is executed only if Step 2a was executed. The SGSN shall send a Subscriber Location Report to the GMLC, and, if these were obtained in steps 7 to 9, the location information, its age and obtained accuracy indication to the GMLC, if the SGSN has not initiated the Privacy Verification process in step 5. If step 5 has been performed for privacy verification, the SGSN returns the location information only, if it has received a LCS 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 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 SGSN shall send an error indication to the GMLC. If the SGSN did not return a successful location estimate, but the privacy checks were successfully executed, the SGSN 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 SGSN may record charging information. If SGSN relocation happens before location information can be reported, the old SGSN includes an error cause code indicating that it cannot proceed with the request as a result of UE mobility. The GMLC may reiterate then its request towards the new SGSN.
Step 10b.
If step 10a was executed, the GMLC shall acknowledge receipt of the Subscriber Location Report.
Step 11.
Common MT-LR procedure in PS and CS domain as described in clause 9.1.1.
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9.1.6A  PS-MT-LR without HLR Query |R7|p. 79

Figure 9.5A 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 GMLC 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 out of scope of this TS, but is presumed to occur on the signalling for the call. The correlation information may be used by the GMLC to retrieve other information previously provided to it by the IMS Core as per TS 23.167 and/or SGSN as described in clause 9.1.7. This allows the requesting V GMLC to request location from the SGSN 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 SGSN identifying information had been pushed to the GMLC as per clause 9.1.7 or as per TS 23.167.
Reproduction of 3GPP TS 23.271, Fig. 9.5A: Positioning for a Emergency Services PS-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 V GMLC by previously supplied correlation information for the emergency call.
Step 2.
The GMLC may determine the SGSN by associating the correlation information received from the PSAP with other information received previously from the SGSN using a PS NI LR and/or from the IMS core. The Provide Subscriber Location request sent to the SGSN 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 SGSN 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 SGSN verifies that UE privacy is overridden by the emergency services provider and that positioning is not prevented for other reasons (e.g. unreachable UE). The SGSN then sends a Location Request to the RAN, as for a normal PS MT LR.
Step 4.
RAN performs positioning as for a normal PS MT LR.
Step 5.
RAN returns a location estimate to the SGSN as for a normal PS MT LR.
Step 6.
The SGSN returns the location information, its age and obtained accuracy indication to the GMLC. The information about the positioning method used may be sent with the location information. If the RAN did not return a successful location estimate, the SGSN 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 GMLC sends the location service response to the LCS client (PSAP).
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9.1.7  Packet Switched Network Induced Location Request (PS-NI-LR)p. 80

At any time after detecting an emergency situation (i.e. after emergency Attach or Service Request for emergency, PDP context activation towards emergency APN), the SGSN may initiate the Packet Switched Network Induced Location Request (PS NI LR) procedure. At any time after the handover or relocation of an emergency PDP context from an old to a new SGSN, where the old SGSN indicates that a PS NI LR is still needed, the new SGSN may initiate a PS NI LR to the GMLC indicated by the old SGSN. At any time after the handover or relocation of an emergency PDP context from an old to a new SGSN, where the old SGSN indicates that a PS NI LR is not needed but provides a GMLC address, the new SGSN may initiate a PS NI LR procedure to transfer its address to the GMLC indicated by the old SGSN in order to support a later PS MT LR. The procedure is illustrated in Figure 9.6.
Reproduction of 3GPP TS 23.271, Fig. 9.6: Network Induced Location Request for the PS Domain
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Step 1.
The SGSN sends a Location Request message to the RAN. This message indicates the type of location information requested and requested QoS. If the location of the UE is not required (e.g. the SGSN is only sending its address to the GMLC), the SGSN skips both this step and steps 2 and 3.

9.1.7.1  Positioning Measurement Establishment Procedurep. 81

Step 2.
If the requested location information and the location accuracy within the QoS can be satisfied based on parameters received from the SGSN and the parameters obtained by the RAN e.g. cell coverage and timing information (i.e. RTT or TA), the RAN may send a Location Report immediately. Otherwise, the RAN determines the positioning method and instigates the particular message sequence for this method. If the position method returns position measurements, the RAN uses them to compute a location estimate. If there has been a failure to obtain position measurements, the RAN may use the current cell information and, if available, RTT or TA value to derive an approximate location estimate. If an already computed location estimate is returned for an UE based position method, the RAN may verify consistency with the current cell and, if available, RTT or TA value. If the location estimate so obtained does not satisfy the requested accuracy and sufficient response time still remains, the RAN may instigate a further location attempt using the same or a different position method. If a vertical location co-ordinate is requested but the RAN can only obtain horizontal co-ordinates, these may be returned.
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9.1.7.2  Location Calculation and Release Procedurep. 81

Step 3.
When a location estimate best satisfying the requested QoS has been obtained, the RAN returns a Location Report to the SGSN 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 Report.
Step 4.
The SGSN may determine the GMLC and emergency services client using the SAI or cell identity, the location estimate if obtained or information received from a previous SGSN in the case of SRNS relocation, RAU or handover. The SGSN shall send a Subscriber Location Report to the GMLC carrying the MSISDN of the UE, the identity of the LCS client, the event causing the message (PS NI LR), and, if these were obtained in steps 1 to 3, the location estimate and its age and the indication received from RAN whether the obtained location estimate satisfies the requested accuracy or not. The serving cell identity or SAI of the UE may also be sent. The SGSN may include its own address. If the UE was not authenticated, the IMEI shall be included. The SGSN may record charging information.
Step 5.
The GMLC shall acknowledge receipt of the location estimate provided that it serves the identified LCS client and the client is accessible.
Step 6.
The GMLC may transfer the location information to the LCS client either immediately or upon request from the client. The GMLC may store the information received in step 4: e.g. may store the UE identity and the address of the SGSN. The GMLC may record charging information.
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