Description
The Home Gateway Mobile Location Centre (HGMLC) is a central component of the 3GPP Location Services (LCS) architecture, defined as part of the control plane. It resides within the subscriber's Home Public Land Mobile Network (HPLMN). The HGMLC serves as the primary entry point for external Location Service Clients (LCS clients) requesting the location of a User Equipment (UE). Its fundamental role is to authorize and authenticate these external requests based on the client's identity and the subscriber's privacy settings, ensuring compliance with regulatory requirements like those for emergency services (e.g., E911) and lawful intercept.
Architecturally, the HGMLC interfaces with several network entities. It communicates with the Visited Gateway Mobile Location Centre (VGMLC) in a visited network when the target UE is roaming, using the Lh interface. For subscribers within its home network, it interacts with the Mobile Switching Centre (MSC) or Mobility Management Entity (MME)/Access and Mobility Management Function (AMF) via the Lg interface. The HGMLC also interfaces with the Home Subscriber Server (HSS) to retrieve subscriber data and routing information. The core protocol for these communications is the Mobile Application Part (MAP) for circuit-switched networks or Diameter for packet-switched networks, as specified in 3GPP TS 29.503.
The HGMLC's operation involves several key steps. Upon receiving a location request from an LCS client, it verifies the client's service authorization. It then checks the target subscriber's privacy profile, which defines who is permitted to locate the UE and under what conditions. If authorized, the HGMLC determines the UE's current serving node (e.g., MSC, SGSN, MME, AMF). If the UE is in its home network, the HGMLC forwards the location request directly to the appropriate node. If the UE is roaming, it routes the request to the VGMLC in the visited network. The HGMLC subsequently receives the location estimate (e.g., geographic coordinates) from the network and returns it to the requesting LCS client.
Its role extends beyond simple request routing. The HGMLC is responsible for billing correlation for location transactions, maintaining logs for auditing, and supporting deferred location requests (e.g., periodic or triggered location reporting). In the context of 5G, the HGMLC's functions are integrated into the Location Management Function (LMF) and Network Exposure Function (NEF) architecture, but the logical separation between home and visited network responsibilities remains a key concept for inter-operator and roaming scenarios.
Purpose & Motivation
The HGMLC was introduced to provide a standardized, secure, and scalable architecture for providing location services in mobile networks. Prior to its standardization, location services were often proprietary, limiting interoperability between network equipment vendors and between different operators' networks. The HGMLC addresses the need for a centralized, home-network-controlled entity to manage external access to subscriber location data, which is a highly sensitive resource.
The primary problems it solves are privacy, security, and inter-operator coordination. It enforces subscriber privacy policies, preventing unauthorized tracking. It provides a single, secure gateway for third-party LCS clients, simplifying network security policies. For roaming subscribers, it enables the home network to maintain control over location service authorization and billing, while delegating the location determination itself to the visited network's infrastructure via the VGMLC. This model is crucial for global roaming agreements.
Its creation was motivated by the growing demand for commercial location-based services (e.g., navigation, friend-finders) and stringent regulatory mandates for emergency caller location (E-911 in the US, E-112 in Europe). The HGMLC architecture allows operators to offer these services in a controlled, billable manner while protecting subscriber rights and meeting legal obligations for emergency service provisioning.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (88 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the HGMLC function was newly introduced to support deferred location requests with event reporting, specifically for area events and periodic location. This enables the HGMLC to remain aware of continuing support by the UE for an area event, such as when a maximum reporting time expires. The release also defined procedures for Mobile Terminated Location Requests (MT-LR) where an external LCS client or AF can request location, subject to UE privacy verification.
In Release 16, the HGMLC function was enhanced to support Mobile Originated Location Requests (MO-LR) initiated by the UE itself, allowing it to request location-related information from the network. It also introduced the ability to provide location reports for UEs connected via non-3GPP access types, expanding location service coverage. Furthermore, improvements were made for periodic and triggered location reporting, including exception handling for delayed reports, and procedures were clarified for commercial Mobile Terminated Location Request (MT-LR) services and UE location privacy profile updates.
- Support of Concurrent Location Request TS 23.273CR0006
- Mobile Originated Data TS 29.503CR0254
- Location report for non-3GPP access TS 29.503CR0266
- UE Location Privacy Profile Update TS 29.503CR0360
- Location information retrieval for GMLC TS 29.503CR0363
- VGMLC address registration TS 29.503CR0368
+ 22 more changes
In Release 17, the HGMLC function was enhanced with new capabilities including support for location estimates in Local Coordinates, the addition of a Scheduled Location Time for deferred requests, and explicit support for Location Services applicable to SNPNs. The release also introduced a new procedure for unified location service exposure for NFs in the serving PLMN and added support for an indication of reliable UE location information requirement. Furthermore, it provided clarifications and corrections to existing procedures like the 5GC-MT-LR and area event reporting.
- Introduction of the Scheduled Location Time TS 23.273CR0187
- Addition of a Scheduled Location Time TS 23.273CR0151
- Location estimate in Local Coordinates TS 23.273CR0144
- Clarification on requesting current location from AMF. TS 23.273CR0146
- Support for Multiple QoS Class in deferred location requests TS 23.273CR0150
- Add a new procedure for unified location service exposure for NF in serving PLMN TS 23.273CR0163
+ 13 more changes
In Release 18, the Home Gateway Mobile Location Centre (HGMLC) saw enhancements for location service continuity and new operational scenarios. Key additions included bi-directional service continuity between EPS and 5GS for both immediate and deferred Mobile Terminated Location Requests (MT-LR), and support for location services when a Mobile Base Station Relay (MBSR) is involved. The release also introduced capabilities for a local LMF and GMLC selection, and enabled UE location reporting with finer granularity for target area events.
- Multiple location report for MT-LR Immediate Location Request for the regulatory service TS 23.273CR0237
- Support of Mobile Base Station Relay for Location Service TS 23.273CR0240
- UE location reporting only when the UE locates in the target area defined with finer granularity TS 23.273CR0242
- Privacy Check for NWDAF requesting UE location from GMLC TS 23.273CR0249
- Introduce new feature: local LMF and GMLC selection TS 23.273CR0254
- Verification of location for NTN access TS 23.273CR0258
+ 25 more changes
In Release 19, the HGMLC function was enhanced with a new deferred location procedure for 5GC-MT-LR based on NRPPa periodic measurement reports. It also introduced support for multiple location reports for next-generation emergency routing and clarified location services for UEs served by an MWAB-gNB. Furthermore, the release removed the inter-PLMN GMLC communication via NEF and added PLMN-level accuracy as a configurable parameter for location reporting events.
- Adding Deferred 5GC-MT-LR Procedure for Periodic Location Events based NRPPa Periodic Measurement Reports TS 23.273CR0589
- Multiple Location Report for Next Generation Emergency Routing TS 23.273CR0608
- Clarification of location services when a UE is served by a MWAB-gNB TS 23.273CR0670
- Inter PLMN GMLC communication via NEF removal TS 23.273CR0736
- PLMN level accuracy in "Location Reporting" event type TS 29.503CR1522
Explore further
Broader topics and technologies where HGMLC plays a role.
Defining Specifications
3GPP specifications that define or reference HGMLC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.273 vj50 | 5G Location Services Stage 2 Architecture | Rel-19 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | Rel-19 |