9.1.6A PS-MT-LR without HLR Query

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

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 [36a] 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 [36a].

Figure 9.5A: Positioning for a Emergency Services PS-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 V‑GMLC by previously supplied correlation information for the emergency call.

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.

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.

4) RAN performs positioning as for a normal PS‑MT‑LR.

5) RAN returns a location estimate to the SGSN as for a normal PS‑MT‑LR.

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.

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

NOTE: The SGSN determined by the GMLC in step 2 must be the current SGSN for the UE. In the event of handover to a new SGSN, this may require updating of the GMLC using the PS‑NI‑LR procedure in clause 9.1.7. Before any handover has occurred, this may require using the cell ID or SAI for the UE provided by the IMS Core.