4 Functional Overview

4.1 General

This document defines the EPC LCS Protocol (ELP) used on the SLg interface between the GMLC and the MME and on the Lgd interface between the GMLC and the SGSN in the Evolved Packet Core (EPC).

The location of the SLg interface within the LCS logical architecture is shown in Figure 4.1-1.

Figure 4.1-1 SLg interface in the LCS Architecture

The location of the Lgd interface within the LCS logical architecture is shown in Figure 4.1-2.

Figure 4.1-2 Lgd interface in the LCS Architecture

The high level functions of the ELP protocol are described in 3GPP TS 23.271 [2].

The main functions of the protocol are:

– To allow the GMLC to request position estimates for a particular target UE from the MME or SGSN in order to support the EPC-MT-LR or PS-MT-LR positioning procedures. This is achieved using the Provide Subscriber Location message;

– To allow the MME or SGSN to return a position estimate or an error report to the GMLC in response to a Provide Subscriber Location request as part of an EPC-MT-LR or PS-MT-LR positioning procedure;

– To allow the MME to forward an unsolicited position estimate to the GMLC as part of the EPC-MO-LR or EPC-NI-LR procedures. This is achieved using the Subscriber Location Report message;

– To allow the SGSN to forward an unsolicited position estimate to the GMLC as part of the PS-MO-LR, PS-NI-LR or periodic MO-LR TTTP procedures. This is achieved using the Subscriber Location Report message;

– To allow the GMLC to acknowledge receipt of an unsolicited position estimate as part of the EPC-MO-LR, EPC-NI-LR, PS-MO-LR, PS-NI-LR or periodic MO-LR TTTP procedures;

– To allow the GMLC to request position estimates for a particular target UE from the SGSN or MME as part of the deferred MT-LR procedure. This is achieved using the Provide Subscriber Location message;

– To allow the SGSN or MME to acknowledge receipt of position estimate request to the GMLC as part of a deferred MT-LR procedure;

– To support the procedures for handover of an IMS emergency call with EPS/GPRS access.