Description
Mobile Terminated Location Request (MT-LR) is a standardized procedure within the 3GPP Location Services (LCS) architecture. It allows an external LCS Client (e.g., an emergency call center, a logistics application, or a lawful interception entity) to request and receive the location of a target User Equipment (UE). The architecture involves several key entities: the LCS Client, the Gateway Mobile Location Center (GMLC), the Home Subscriber Server (HSS), the Mobility Management Entity (MME) in LTE, the Serving GPRS Support Node (SGSN) in UMTS, or the Access and Mobility Management Function (AMF) in 5GC, and the location determination functions within the Radio Access Network (RAN) and core network (e.g., Enhanced Serving Mobile Location Center - E-SMLC in LTE, Location Management Function - LMF in 5G). The procedure is initiated by the LCS Client sending a location request to the GMLC. The GMLC acts as the gateway, performing authorization and privacy checks based on the client's identity and the subscriber's privacy profile stored in the HSS. If authorized, the GMLC queries the HSS to find the serving node (MME/SGSN/AMF) for the target UE. The request is then forwarded to this serving node. The serving node, in coordination with the RAN and the specific location server (E-SMLC/LMF), triggers the location determination process. This can involve various positioning methods such as Observed Time Difference of Arrival (OTDOA), Uplink Time Difference of Arrival (UTDOA), Assisted GNSS (A-GNSS), or Enhanced Cell ID (E-CID). The calculated location estimate is then routed back through the chain (serving node -> GMLC) to the requesting LCS Client. The entire process adheres to strict privacy regulations, requiring subscriber consent (either pre-provisioned or real-time) unless overridden by legal authority (e.g., for emergency services). The MT-LR procedure is defined across multiple protocol layers and network generations, ensuring consistent service delivery from GSM to 5G.
Purpose & Motivation
MT-LR exists to provide a standardized, secure, and privacy-compliant mechanism for authorized external entities to locate mobile subscribers. It solves the problem of enabling valuable location-based services (e.g., navigation, friend-finder, asset tracking) and critical services (like Enhanced 911/E112 emergency location) without exposing subscriber location arbitrarily. Before its standardization, proprietary solutions or limited network capabilities made widespread, interoperable location services difficult. The creation of MT-LR was motivated by regulatory requirements (e.g., emergency caller location), commercial opportunities for Location-Based Services (LBS), and operational needs (e.g., fleet management). It addressed the limitations of earlier, non-standardized methods by defining clear architectural roles, interfaces (e.g., Le, Lg, SLg, NLs), and privacy control procedures. This allows network operators to offer location as a controlled service to third-party providers while protecting subscriber privacy. The procedure ensures that location retrieval can be performed regardless of the UE's state (idle or connected) and across different radio access technologies.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (198 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the MT-LR function was enhanced with the addition of High Accuracy location estimates and the capability to request OTDOA assistance data specifically for NR (New Radio). Furthermore, updates were made to distinguish the location source when a sensor-based positioning method is utilized.
- Enhance location information in trusted and untrusted WLAN TS 32.251CR0503
- OpenAPI updates for MSISDN-less Mobile Originated SMS TS 29.122CR0027
- Enhancement of LocationArea TS 29.122CR0053
- Location header TS 29.122CR0117
- Addition of High Accuracy location estimates TS 29.171CR0051
- OTDOA Assistance Data Request for NR TS 36.355CR0222
+ 1 more changes
In Release 16, key enhancements for the MT-LR function included the completion and clarification of the 5GC-MT-LR procedure for commercial location services, alongside specific corrections to the MT-LR procedure for both 3GPP and non-3GPP access. The release also introduced support for Location Services via the NEF (Network Exposure Function) and completed the procedures for deferred and bulk operation MT-LR requests.
- Support of Concurrent Location Request TS 23.273CR0006
- Adding Location Privacy Setting operation TS 24.571CR0001
- Removal of a BDT warning notification request TS 29.122CR0189
- Supporting the Location Services via NEF TS 29.122CR0228
- Clarification on positioning access selection in the 5GC-MO-LR procedure TS 23.273CR0008
- Correction and Improvement of Low Power Periodic and Triggered Location TS 23.273CR0011
+ 40 more changes
In Release 17, key enhancements for the MT-LR function included the introduction of a **Scheduled Location Time** for deferred and bulk location requests, support for **periodic and triggered location procedures while the UE is in RRC INACTIVE state**, and the ability to handle **Multiple QoS Classes** within a single deferred location request. Furthermore, the release added capabilities for providing location estimates in **Local Coordinates** and delivering **higher resolution timestamps** for improved accuracy.
- Introduction of the Scheduled Location Time TS 23.273CR0187
- Addition of a Scheduled Location Time TS 23.273CR0151
- Periodic and Triggered 5GC-MT-LR Procedure in RRC INACTIVE state TS 23.273CR0228
- Additional of Scheduled Location Time TS 24.571CR0012
- Support for Multiple QoS Class in deferred location request TS 29.122CR0491
- Higher Resolution Timestamp for Location Estimates TS 29.515CR0059
+ 31 more changes
In Release 18, the MT-LR function was enhanced to support new scenarios including Mobile Base Station Relay (MBSR) involvement and ranging and sidelink positioning procedures. It also introduced the capability for a UE to establish a user plane connection to an LCS Client or AF for periodic or triggered 5GC-MT-LR event reporting. Furthermore, enhancements were made for UE power saving in triggered location and for location service continuity between EPS and 5GS for deferred MT-LR.
- 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
+ 75 more changes
In Release 19, the MT-LR function was enhanced with a new deferred procedure for periodic location events based on NRPPa periodic measurement reports. It also introduced support for location services involving WAB-Nodes and MWAB-gNBs, requiring specific procedural corrections for these nodes. Furthermore, the release added support for reporting AF request rate limitation information and introduced control parameters for on-demand positioning system information block requests.
- 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
- Support of AF request rate limitation information reporting TS 29.122CR0903
- Support request authorization with the resource owner TS 29.122CR0960
- Add message flow of converged charging for 5GC-MT-LR TS 32.271CR0031
- Add message flow of converged charging for 5GC-MO-LR TS 32.271CR0032
+ 21 more changes
Explore further
Broader topics and technologies where MT-LR plays a role.
Defining Specifications
3GPP specifications that define or reference MT-LR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 03.071 v7b0 | Location Services (LCS) Stage 2 Description | Rel-7 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.171 v1300 | LCS Stage 2 Specification for UMTS | Rel-4 |
| TS 23.271 vj00 | LCS Stage 2 Specification | Rel-19 |
| TS 23.273 vj50 | 5G Location Services Stage 2 Architecture | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.730 ve00 | Study on extended CIoT architecture | Rel-14 |
| TS 24.171 vj00 | NAS Protocol for LCS in E-UTRAN | Rel-19 |
| TS 24.514 vj30 | Ranging & Sidelink Positioning in 5GS | Rel-19 |
| TS 24.571 vj20 | Control Plane LCS Procedures | Rel-19 |
| TS 29.122 vj40 | T8 Reference Point for Northbound APIs | Rel-19 |
| TS 29.171 vj00 | LCS Application Protocol (LCS-AP) Specification | Rel-19 |
| TS 29.515 vj50 | Ngmlc Service Based Interface Protocol | Rel-19 |
| TS 32.250 vj00 | Circuit Switched Offline Charging | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.271 vj20 | 3GPP LCS Charging Management Spec | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.293 vj00 | Proxy Function in Domestic Service Provider | Rel-19 |
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.856 vg00 | Study on local NR positioning in NG-RAN | Rel-16 |
| TR 38.857 vh00 | Study on NR Positioning Enhancements | Rel-17 |