Location Information Server

Description

The Location Information Server (LIS) is a core network functional entity within the 3GPP architecture for providing Location Services (LCS). Defined across specifications such as TS 23.868 (for service requirements), TS 25.414 (for UTRAN Iu interface), and TS 36.855 (for LTE positioning), it is responsible for managing location requests, determining the geographical position of a UE, and delivering that information to authorized clients, known as LCS Clients. These clients can be internal network entities (e.g., for lawful interception) or external third-party application servers (e.g., for navigation services).

Architecturally, the LIS is often realized through components like the Gateway Mobile Location Centre (GMLC) and the Serving Mobile Location Centre (SMLC). The GMLC acts as the gateway, handling authentication, authorization, and privacy checks for location requests from external clients, and routing requests to the appropriate network node. The SMLC (or Evolved SMLC - E-SMLC in LTE) is the entity that actually performs or coordinates the position calculation. It selects the positioning method (e.g., A-GNSS, OTDOA, E-CID), communicates with the UE and radio access network to obtain measurements, and computes the final location estimate.

The LIS operates through a standardized sequence. An LCS Client sends a location request to the GMLC. The GMLC authenticates the client and determines the UE's serving network node (e.g., MSC or MME). It then forwards the request to this node, which engages the SMLC/E-SMLC. The SMLC initiates the positioning procedure with the UE via the radio access network (e.g., through the LIRF in UTRAN or directly via LPP in LTE). The UE may provide measurements (for network-based calculation) or even a computed position (for terminal-based calculation). The SMLC formats the location estimate (e.g., latitude, longitude, uncertainty) and sends it back through the chain to the GMLC, which finally delivers it to the requesting LCS Client, often using the Open Mobile Alliance (OMA) Mobile Location Protocol (MLP).

Its role is critical for a wide range of services. For emergency services, it must provide rapid and accurate location to Public Safety Answering Points (PSAPs). For commercial services, it enables applications like fleet tracking, location-based advertising, and social networking features. The LIS architecture ensures privacy controls are enforced, so a user's location is only disclosed with consent or under legal mandate, and it supports various quality of service parameters like response time and accuracy required by different applications.

Purpose & Motivation

The Location Information Server was developed to provide a standardized, scalable, and secure platform for delivering location information in cellular networks. Before its formalization in 3GPP, location services were often proprietary or limited in scope. The LIS architecture created a unified framework that separated the location determination function from the applications that consume it, enabling a wide ecosystem of location-based services.

It solves the problem of how to efficiently and reliably determine a mobile device's position and make it available to authorized entities. This addresses both regulatory drivers, such as Enhanced 911 (E-911) in the US and E-112 in Europe, which mandate the provision of caller location for emergency services, and commercial opportunities in the growing LBS market. The LIS provides the necessary interfaces, privacy mechanisms, and service logic to support these diverse use cases.

The motivation for its creation stemmed from the convergence of mobile communication and positioning technologies (like GPS) in the late 1990s and early 2000s. 3GPP recognized the need for an architectural framework that could support multiple positioning technologies (network-based, handset-based), integrate with core network elements for subscriber management, and expose location via standard protocols to foster application development. The LIS, through components like the GMLC and SMLC, fulfilled this need, establishing the foundation for all subsequent 3GPP location services.

Key Features

• Provides geographical location of UEs to authorized LCS Clients via standardized interfaces (e.g., OMA MLP)
• Supports multiple positioning methods including A-GNSS, OTDOA, and Enhanced Cell ID
• Enforces privacy and authorization policies for location access
• Architecturally composed of gateway (GMLC) and calculation (SMLC/E-SMLC) functions
• Integrates with core network (HLR/HSS, MME) for subscriber and session information
• Delivers location with specified Quality of Service (QoS) parameters like accuracy and response time

Evolution Across Releases

Defining Specifications