Description
The SEAL Location Management Server (SLM-S) is a service capability server within the 3GPP's Service Enabler Architecture Layer (SEAL) for vertical applications. SEAL provides a standardized set of common service enablers (like location, group management, configuration) to facilitate application development for 3GPP networks. The SLM-S acts as the central entity that exposes network-based location services to authorized Application Clients (ACs). It receives location requests, orchestrates the positioning process with the underlying network (e.g., 5GC, EPC), and returns the location results.
Architecturally, the SLM-S interfaces with two main entities. First, it exposes a northbound API (based on RESTful principles) to the Application Client, defined in 3GPP TS 24.545. This API allows the AC to request location fixes for a target User Equipment (UE) using various request types: Immediate (single fix), Periodic (fixes at intervals), or Triggered (fix when UE enters/leaves an area). Second, on the southbound side, the SLM-S interfaces with the core network's location retrieval mechanisms. In a 5G system, this is typically the Gateway Mobile Location Centre (GMLC) and Location Management Function (LMF) via standardized interfaces (e.g., Nlg, NLs). The SLM-S translates the application's service-level location request into the appropriate network-level procedures, such as initiating a Mobile Terminated Location Request (MT-LR).
Its operation involves session management, policy enforcement, and privacy handling. When an AC sends a request, the SLM-S validates it against the subscriber's privacy settings (stored in a Privacy Profile Register) and the AC's authorization. If permitted, it establishes a location session, interacts with the network to obtain the UE's location (using methods like GNSS, OTDOA, or cell-ID), and streams the results back to the AC. It can also support deferred reporting, storing locations if the AC is temporarily unavailable. By acting as an abstraction layer, the SLM-S shields application developers from the complexities of direct interaction with 3GPP network elements like the GMLC or LMF.
Purpose & Motivation
The SLM-S was created to streamline and standardize how vertical industry applications (e.g., logistics, emergency services, IoT asset tracking) request and consume location information from 3GPP networks. Before SEAL, each vertical often developed custom, non-interoperable integrations with network location services like the GMLC, leading to fragmentation, high development costs, and inconsistent privacy/security handling. The SLM-S provides a unified, application-friendly API that is consistent across different operators and network generations (4G, 5G).
Its development was motivated by the 5G vision of network exposure and vertical enablement. 3GPP recognized that location is a fundamental enabler for countless services, but the existing mechanisms (e.g., LCS APIs) needed modernization for cloud-native, API-driven ecosystems. The SLM-S, as part of SEAL, addresses the limitations of previous approaches by offering a service-based architecture that aligns with 5G principles. It solves the problem of access complexity by providing a single, well-defined endpoint for all location service types. Furthermore, it centralizes critical functions like privacy authorization and policy control, ensuring regulatory compliance (e.g., GDPR) is handled consistently by the network rather than being delegated to each individual application developer.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (89 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 16, the SLM-S (SEAL Location Management Server) function was introduced with new XML schemas and updated procedures to support location-based services for vertical applications. Specifically, it introduced XML schemas for location information reporting, subscription, notification, request, and location-based query, along with procedures for querying a list of users based on location. The release also defined updates to HTTP-based location information subscription and client-triggered or VAL server-triggered location reporting procedures.
- IANA registration template of SEAL location management TS 24.545CR0001
- Structure and data semantics for query list of users based on location procedure TS 24.545CR0004
- XML scheme for location reporting configuration procedure for SEAL location management TS 24.545CR0005
- Timers used in location management TS 24.545CR0018
- Updates to HTTP based location information subscription procedure TS 24.545CR0020
- Updates to XML schema of configuration for SEAL location management TS 24.545CR0021
+ 8 more changes
In Release 17, the SLM-S (SEAL Location Management Server) function was enhanced to support off-network location management, introducing new procedures for event-triggered and on-demand location reporting as well as location area monitoring. The protocol was expanded to support the Constrained Application Protocol (CoAP) for these new reporting and configuration procedures. Furthermore, the location data model was enriched with the addition of altitude within location coordinates.
- Off network Location Management - Basic Message Control and Message Format TS 24.545CR0034
- Off network Location Management - Event-triggered location reporting procedure TS 24.545CR0035
- Off network Location Management - On-demand location reporting TS 24.545CR0036
- Location area monitoring information procedure TS 24.545CR0041
- Addition of CoAP for Event-triggered location reporting procedure TS 24.545CR0044
- Addition of CoAP for On-demand location reporting procedure TS 24.545CR0045
+ 7 more changes
In Release 18, the SLM-S (SEAL Location Management Server) function introduced several new procedures and enhancements, including a location service registration update and deregistration procedure, a location reporting configuration notification, and the addition of location QoS and supplementary location information. It also added support for tracking dynamic UAVs and defined a location client initiated cancel trigger procedure. Furthermore, the release resolved the editor's note on the UDP port number for the SEAL off-network location management protocol (SLMP).
- Multi-USS management procedures TS 24.257CR0010
- Tracking dynamic UAVs - server procedure TS 24.257CR0026
- Add Location QoS in the related information TS 24.545CR0068
- Coding aspect of the location service registration procedure TS 24.545CR0070
- Add the procedure of location profiling for supporting location service enablement TS 24.545CR0071
- Add the location service registration update procedure TS 24.545CR0078
+ 17 more changes
In Release 19, the SEAL Location Management Server (SLM-S) introduced new capabilities including adaptive location configuration and reporting, velocity reporting in location procedures, and support for sidelink positioning management. It also added procedures for confirming location service subscriptions and notifications, optimized services for multiple UEs sharing the same location, and introduced new HTTP and CoAP procedures for location positioning configuration and history reporting. Furthermore, enhancements were made for reusing stored UE location information and enforcing No-Transmit Zone (NTZ) assistance.
- UAE-layer/SEAL/LMS assisted NTZ enforcement TS 24.257CR0054
- Support for adaptive location configuration and reporting TS 24.545CR0108
- Exposure of value-added UE location information TS 24.545CR0109
- LMS reuse the stored UE location information TS 24.545CR0111
- Clarification on Location area monitoring information procedure TS 24.545CR0112
- Add failure case in the on-demand location reporting procedure TS 24.545CR0125
+ 33 more changes
Explore further
Broader topics and technologies where SLM-S plays a role.
Defining Specifications
3GPP specifications that define or reference SLM-S, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.257 vj40 | UAS Application Enabler (UAE) Layer | Rel-19 |
| TS 24.545 vj40 | SEAL Location Management Protocol Specification | Rel-19 |