9.1.17 EPC Network Induced Location Request (EPC-NI-LR)

23.2713GPPFunctional stage 2 description of Location Services (LCS)Release 17TS

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 [41]). The procedure is illustrated in figure 9.20.

Figure 9.20: Network Induced Location Request for EPC

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.

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.

NOTE: If the UE is in connected mode and step 2 was not performed immediately after step 1, the MME may not have the most current serving cell identity if there was an intra-eNodeB handover.

9.1.17.1 Positioning Measurement Establishment Procedure

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.

9.1.17.2 Location Calculation and Release Procedure

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.

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.

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.

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.

8) At some point, MME determines that emergency service is no longer active (e.g. EPS bearer for emergency service is deactivated).

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).

10) The GMLC shall acknowledge receipt of the location report from MME.

NOTE: Determination of the GMLC in step 5 must ensure a match with any LRF/GMLC used by the IMS Core to assist with location retrieval for, and/or routing of, the IMS Emergency call as described in clause 9.8.4.