9.1.7 Packet Switched Network Induced Location Request (PS-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 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.

Figure 9.6: Network Induced Location Request for the PS Domain

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 Procedure

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.

9.1.7.2 Location Calculation and Release Procedure

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.

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.

5) The GMLC shall acknowledge receipt of the location estimate provided that it serves the identified LCS client and the client is accessible.

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.

NOTE: Determination of the GMLC in step 4 must ensure a match with any GMLC used by the IMS Core to assist with location retrieval for, and/or routing of, the IMS Emergency call.