3. Interfaces & Protocols

The GMLC supports a number of standardized interfaces (reference points) defined by 3GPP for LCS. Each interface corresponds to a specific peer entity in the location architecture and has defined protocols/messages. Below we detail each interface and the protocols in use:

3.1 Le – External LCS Client ↔ GMLC

Le is the interface between an external LCS client (an application or value-added service provider) and the GMLC. It is an application-layer interface, often IP-based, and is not fully specified by 3GPP in terms of protocol (3GPP refers to OMA for this). In practice, Le is implemented using the OMA Mobile Location Protocol (MLP) or a RESTful API in modern systems. The OMA MLP (for example LIF TS 101 and OMA-TS-MLP) is an XML over HTTP protocol that supports location requests and responses. 3GPP acknowledges MLP as the exemplar for Le: “Signalling on this interface may use the OMA Mobile Location Protocol (MLP)”. In MLP, the external client sends a request like StandardLocationImmediateRequest with the target’s ID and requested QoS, and the GMLC responds with StandardLocationImmediateAnswer containing the position or an error.