DL - 4G Americas

Figure B.2. LCS Control Plane Architecture in EPS (Based on 3GPP TS 23.271).
The LCS architecture follows a client/server model with the Gateway Mobile Location Center (GMLC)
acting as the location server providing location information to LCS clients. The GMLC sends location
requests to the Enhanced Serving Mobile Location Center (E-SMLC) through the MME to retrieve this
location information. The E-SMLC is responsible for interaction with the UE through E-UTRAN to obtain
the UE position estimate or get position measurements that helps the E-SMLC estimate the UE position
(see section B.2.3.1 UE Positioning for more detail). Note that the GMLC interaction over the interfaces
connecting to it other than SLg in Figure B.2 was already available before Rel-9 for GSM and UMTS
access.
The LCS clients may either be part of the core network or external to the core network and can also
reside in the UE or be attached to the UE. Depending on the location of the LCS client the Location
Request initiated by the LCS client may either be a Mobile Originated Location Request (MO-LR), Mobile
Terminated Location Request (MT-LR) or Network Induced Location Request (NI-LR). Also, immediate
location requests are supported where the LCS client expects the location information interactively.
There are various possible uses for the location information, but they are broadly categorized in to four
areas viz:
1. Commercial LCS (or Value-Added Services)
2. Internal LCS
3. Emergency LCS
4. Lawful Intercept LCS
Emergency location service is possible even if the UE does not have a valid service subscription due to
regulatory mandates. Support of location service related functionality in the E-UTRAN, MME and UE are
optional. LCS is applicable to any target UE whether or not the UE supports LCS.
The following outline provides the functions of various LCS architectural elements:
www.4gamericas.org February 2011 Page 120