Mobile and personnel location systems are becoming more and more common and important. Except in the security area, many applications have been discovered and will have a greater development boost in the LBS (Location Based Services) area. An architecture of LoCation Service (LCS) is designed by 3GPP in technical specification TS 23.271[2]. It is used in GSM, UMTS and EPS. Figure 2.1 shows its general arrangement.
- Gb: Interface between 2G-SGSN and GERAN
- Lc: Interface between gateway MLC and gsmSCF (CAMEL interface)
- Le: Interface between External User and MLC (external interface)
- Lg: Interface between Gateway MLC-VMSC, GMLC-MSC Server, GMLC-SGSN (gateway MLC interface)
- Lh: Interface between Gateway MLC and HLR (HLR interface)
- Lid: Interface between GMLC and PMD
- Lpp: Interface between GMLC (H-GMLC) and PPR entity
- Lr: Interface between gateway MLCs
- Lu: Interface between 3G-SGSN or MSC and GERAN or UTRAN
- SLg: Interface between GMLC and MME
- SLs: Interface between MME and E-SMLC
Central point of whole achitecture is GMLC (Gateway Mobile Location Center). It contains functionality required to support LCS. GMLC is the first node an external LCS client accesses in a GSM or UMTS network. The GMLC may request routing information from the HLR (Home Location register) or HSS (Home Subscriber Server). After performing registration authorization, it sends positioning requests to either the VMSC (Visited Mobile Switching Centre), SGSN (Serving GPRS Support Node) or MSC (Mobile Switching Centre) Server and receives final location estimates from the corresponding entity.The VMSC, SGSN or MSC connect to the corresponding Access Network. And the Access Network will provide the positioning of the UE.
Communication between the GMLC and Exernal LCS Client is performed by Mobile Location Protocol (MLP).