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
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (38 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 16, the MT-LR function was enhanced with new procedures for the 5G Core network (5GC), including the completion and cancellation of a deferred 5GC-MT-LR process. The release also introduced corrections and clarifications for bulk operation MT-LR procedures and for scenarios involving both 3GPP and Non-3GPP access types. These updates provided a more complete and robust framework for commercial and emergency location services within the 5G system.
- Clarification of 5GC-MT-LR procedure for the commercial location service TS 23.273CR0024
- Corrections to bulk operation MT-LR procedure TS 23.273CR0046
- Corrections to MT-LR procedure for 3GPP and Non-3GPP access TS 23.273CR0047
- Completion of Deferred 5GC-MT-LR procedure for TS 23.273 TS 23.273CR0055
- Completion of 5GC-MT-LR Procedure for TS 23.273 TS 23.273CR0056
- Completion of Cancellation of a Deferred 5GC-MT-LR procedure for TS 23.273 TS 23.273CR0074
+ 2 more changes
In Release 17, key enhancements for the MT-LR function included the introduction of the Periodic and Triggered 5GC-MT-LR procedure for UEs in RRC INACTIVE state. Furthermore, improvements were made to the deferred MT-LR mechanism by adding the time of position determination to its periodic reporting. The release also contained corrections to the 5GC-MT-LR procedure for commercial location services and to the overall description of deferred MT-LR.
- Periodic and Triggered 5GC-MT-LR Procedure in RRC INACTIVE state TS 23.273CR0228
- Add time of position determination to Deferred MT-LR periodic TS 23.273CR0147
- Correction to the 5GC-MT-LR Procedure for the commercial location service TS 23.273CR0230
- Correction on the description of deferred MT-LR TS 38.305CR0102
In Release 18, the MT-LR function was enhanced to support periodic and triggered location event reporting over a user plane connection to an LCS Client or Application Function. It also introduced explicit support for MT-LR procedures involving Sidelink Positioning (SL-MT-LR) and Mobile Base Station Relays (MBSR), and expanded identifier support to include GPSI and Application Layer IDs.
- Multiple location report for MT-LR Immediate Location Request for the regulatory service TS 23.273CR0237
- Support of a UE user plane connection to an LCS Client or AF for periodic or triggered 5GC-MT-LR event reporting TS 23.273CR0264
- MT-LR procedure for when a MBSR is involved in the location of a UE. TS 23.273CR0288
- Support of MT-LR for Ranging and Sidelink Positioning TS 23.273CR0321
- Location service continuity between EPS and 5GS (bi-direction) for deferred MT-LR TS 23.273CR0349
- Signalling support to enable a periodic or triggered 5GC-MT-LR event reporting over user plane connection TS 24.571CR0015
+ 12 more changes
In Release 19, the MT-LR function was enhanced with a new deferred procedure for the 5G Core (5GC-MT-LR) to handle periodic location events based on NRPPa periodic measurement reports. The release also introduced support for the 5GC-MT-LR procedure involving the Mobile Wireless Anchor Box (MWAB) and provided updates for the Service Layer MT-LR (SL-MT-LR) for periodic and triggered events. Furthermore, the specifications were updated to include the message flow for converged charging for 5GC-MT-LR and to correct information elements in the SL-MT-LR response.
- Adding Deferred 5GC-MT-LR Procedure for Periodic Location Events based NRPPa Periodic Measurement Reports TS 23.273CR0589
- Add message flow of converged charging for 5GC-MT-LR TS 32.271CR0031
- Correction of the 5GC-MT-LR procedure involving MWAB TS 23.273CR0730
- Update on SL-MT-LR for periodic, triggered Location Events TS 24.514CR0050
- Update on SL-MT-LR for periodic, triggered Location Events TS 24.571CR0090
- Support of 5GC-MT-LR procedure involving MWAB TS 29.515CR0198
+ 2 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 |
