Mobile Location Protocol

Description

The Mobile Location Protocol (MLP) is an XML-based application-layer protocol used for requesting and delivering location information of a Mobile Station (MS). It operates between a Location Service (LCS) Client and a Location Server, such as a Gateway Mobile Location Center (GMLC) in a 3GPP network. MLP provides a standardized interface that abstracts the underlying network-specific positioning technologies (e.g., Cell-ID, OTDOA, A-GPS), allowing service applications to request location in a uniform manner. The protocol defines a set of service primitives for different location request types, including immediate location, triggered location reporting, and standard location reporting.

The core of MLP is its request-response model using XML documents over HTTP/HTTPS or other transport. A typical MLP exchange involves the LCS Client sending a standardized MLP Service Request (e.g., a Standard Location Immediate Request - SLIR) to the Location Server. This request contains parameters such as the target MSISDN or IMSI, the required quality of service (QoS) like accuracy and response time, and the type of location estimate (e.g., latitude/longitude). The Location Server authenticates and authorizes the request, interacts with the mobile network's positioning subsystems (like the Serving Mobile Location Center - SMLC) to obtain the location fix, and then formulates an MLP Service Answer (e.g., Standard Location Immediate Answer - SLIA) back to the client, containing the location estimate or an error code.

MLP supports multiple service types to cater to different application needs. The Immediate Service is for one-time location retrieval. The Triggered Service allows a client to set up a subscription for periodic or event-driven location reports (e.g., when a device enters a defined area). The Reporting Service is used by the network to push location information to a client, often following a triggered event. MLP also defines elements for privacy and security, ensuring that location requests comply with the user's privacy settings and that communication between client and server is secure. Within 3GPP, MLP is specified as a key external interface (Le interface) for the Gateway Mobile Location Center (GMLC), enabling lawful intercept, emergency services (E911/E112), and commercial location-based services (LBS) like navigation, friend-finder, and asset tracking.

Purpose & Motivation

MLP was developed to solve the problem of proprietary and fragmented interfaces for accessing mobile device location. In the early days of location-based services, network equipment vendors and service providers often used bespoke protocols, hindering interoperability and slowing the development of a broad ecosystem of LBS applications. The creation of a standardized, application-level protocol was motivated by the need to provide a single, consistent way for authorized external applications to request location information, regardless of the underlying network technology (GSM, UMTS, LTE) or the positioning method used.

Its adoption by 3GPP and standardization by the Open Mobile Alliance (OMA) provided the necessary common language between service providers and mobile operators. This enabled the scalable deployment of commercial LBS, emergency services (where standardized interfaces are critical for connecting PSAPs), and value-added services. MLP abstracts the complexities of the radio access network, allowing application developers to focus on service logic rather than network integration, thereby fostering innovation in the location services market.

Key Features

• XML-based protocol for structured location request and response messages
• Support for immediate, triggered, and reporting location service types
• Definition of standardized QoS parameters for location accuracy and response time
• Transport over HTTP/HTTPS for web-friendly integration
• Built-in mechanisms for privacy and authorization handling
• Standardized error codes and reporting for robust service operation

Evolution Across Releases

Defining Specifications