9.1.16 EPC-MT-LR without HLR Query

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

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 [36a]. 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 [36a] 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 [36a].

Figure 9.19: Positioning for a Emergency Services EPC-MT-LR without HLR Query

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.

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 [36a]. 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.

3) The MME sends a Location Request to the E-SMLC, as for a normal EPC MT LR.

4) E-SMLC performs positioning as for a normal EPC MT LR.

5) E-SMLC returns a location estimate to the MME as for a normal EPC MT LR.

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.

7) The LRF sends the location service response to the LCS client (PSAP).

NOTE: The MME determined by the LRF/GMLC in step 2 must be the current MME for the UE. In the event of handover to a new MME, this may require updating of the GMLC using the EPC NI LR procedure in clause 9.1.17.