Description
The Unified Data Management (UDM) function is a critical component of the 5G Core Network (5GC) based on the Service-Based Architecture (SBA). It serves as the centralized repository and management point for subscriber-related data. The UDM is responsible for storing and managing long-term subscription information, including user identities, security credentials, service profiles, and policy-related data. It interacts with other network functions through standardized service-based interfaces, primarily using HTTP/2 with JSON or CBOR encoding. The UDM's primary roles include authentication credential processing, user identification handling, access authorization, and subscription data management.
Architecturally, the UDM is a software-based network function that can be deployed in cloud environments. It often works in conjunction with the Unified Data Repository (UDR), which provides the actual persistent storage for the subscriber data. The UDM contains the application logic to process and manage this data, while the UDR acts as the database. Key internal components include the Authentication Credential Repository and Processing Function (ARPF), which stores long-term keys and runs authentication algorithms, and subscription data management logic. The UDM exposes its capabilities as services to other NFs, such as Nudm_UEAuthentication for authentication, Nudm_SubscriberDataManagement for subscription data, and Nudm_EventExposure for monitoring subscriber events.
How it works: When a user equipment (UE) attempts to register with the 5G network, the Access and Mobility Management Function (AMF) contacts the UDM. The UDM's ARPF generates authentication vectors (using the 5G Authentication and Key Agreement (5G-AKA) or EAP-AKA' procedures) and provides them to the AMF via the AUSF. For session establishment, the Session Management Function (SMF) retrieves the user's subscription data and policy profile from the UDM to determine allowed services, QoS parameters, and charging rules. The UDM also manages the binding between the user's permanent subscription identifier (SUPI) and the temporary identifier (SUCI) used for privacy, and it tracks the serving AMF for each subscriber to route signaling messages correctly.
Its role is central to network security, service personalization, and mobility management. By centralizing subscriber data, the UDM enables consistent policy enforcement across the network, supports seamless mobility and session continuity, and provides a single point of truth for user profiles. This is essential for advanced 5G features like network slicing, where the UDM provides the slice selection subscription information. Furthermore, its service-based design allows for flexible integration, scalability, and support for new services, forming the foundation for subscriber management in the 5G era.
Purpose & Motivation
The UDM was created to address the limitations of legacy subscriber data management in pre-5G networks, which was fragmented across different network elements. In 4G EPC, functions like the Home Subscriber Server (HSS) managed user profiles and authentication, but the architecture was node-based and less flexible. The proliferation of diverse 5G services, IoT, and network slicing demanded a more agile, scalable, and unified approach to data management.
The primary problem the UDM solves is the centralization and standardization of subscriber data handling. It consolidates functions previously spread across the HSS, Home Location Register (HLR), and other entities into a single, cloud-native network function. This unification simplifies operations, reduces data duplication, and provides a consistent view of the subscriber to all other core network functions. Its creation was motivated by the shift to the Service-Based Architecture (SBA), which requires network functions to expose capabilities as reusable services.
Historically, the UDM evolved from the HSS/HLR concepts but with a fundamental architectural redesign. It enables dynamic subscription management, real-time policy updates, and efficient support for massive numbers of IoT devices. By separating the application logic (UDM) from storage (UDR), it allows independent scaling and leverages modern cloud and software-defined networking principles. This addresses the need for a more programmable, automated, and service-aware core network capable of supporting the wide array of use cases envisioned for 5G and beyond.
Architecture
In the Network Map
- Mobile Network → 5G Core → UDM (Subscriber Management)
Evolution Lineage
- Evolved from: HSS (4G→5G)
- Network evolution overview →
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (122 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the UDM was introduced as a new, unified core network function, with key new capabilities including support for SUCI, UDM-triggered UE parameters update procedures, and enhanced discovery mechanisms. It also introduced specific services like Nudm_UEAuthentication and procedures for updating the STN-SR to the AMF for SRVCC support. Furthermore, Release 15 defined the UDM's role in EPS-5GS interworking without the N26 interface and its support for dynamic 5QIs.
- UDM receives notification of target/new AMF after AMF planned removal TS 29.503CR0001
- Security mechanism for UE Parameters Update via UDM Control Plane Procedure TS 33.501CR0484
- Procedure for UDM-triggered UE parameters update TS 24.501CR0594
- UDM discovery clarifications TS 23.501CR0041
- UDM Discovery with SUPI as input TS 23.501CR0091
- UDM services - addition to Nudm_UEAuthentication TS 23.501CR0224
+ 20 more changes
In Release 16, the UDM was enhanced to support 5G Single Radio Voice Call Continuity (SRVCC) by updating the AMF with the Session Transfer Number for SRVCC (STN-SR) received from the network, using the Nudm_SDM_Notification service. Furthermore, the release introduced capabilities for the UDM to report UE SRVCC capability to service layer functions and to retrieve the subscribed Network Slice Selection Assistance Information (NSSAI).
- Adding UDM update the STN-SR to AMF TS 23.237CR0507
- eSBA communication schemas related to UDM and UDR discovery and selection TS 23.501CR0800
- Report 5G SRVCC Capability to UDM TS 29.503CR0215
- Subscribed NSSAI from the UDM TS 29.503CR0247
- UDM Authn. Vector Generation for HSS TS 29.503CR0389
- UDM Discovery by Internal Group ID TS 23.501CR1737
+ 13 more changes
In Release 17, the UDM saw enhancements for network data analytics by enabling the NWDAF to register with and be discovered by the UDM for UE-related analytics. It also introduced new capabilities for managing IP indexes and supporting persistent data collection. Furthermore, the release expanded UDM functionality for standalone non-public networks (SNPN), including impacts on onboarding and provisioning, and refined procedures for services like Steering of Roaming (SoR) and Lawful Interception.
- Discover NWDAF for UE related Analytics using UDM TS 23.501CR2702
- AUSF/UDM discovery based SUCI information TS 23.501CR3170
- IP Index in UDM TS 29.503CR0610
- NWDAF register into UDM TS 29.503CR0649
- Persistent Data Collection via UDM TS 29.503CR0705
- Provisioning Session Authorization Information in UDM TS 29.503CR0733
+ 29 more changes
In Release 18, the UDM saw enhancements for procedures like UDM-triggered PDU Session deregistration and UDM-initiated SMF deregistration. New capabilities were added, including support for NSWO in SNPNs, ProSe LI reporting, and the determination of Internal Group ID values for 5G VN group management. The release also introduced updates for AKMA-related services and improvements to the robustness of defined interfaces and protocols.
- Compatibility of UDM not supporting SMS SBI TS 23.540CR0013
- Improvement to UDM-triggered PDU Session deregistration procedure TS 29.503CR0959
- UDM initiated SMF Deregistration and Implicit Unsubsribe for SMF Events TS 29.503CR1190
- Procedures update for checking mechanism of clock quality information received from UDM and AF TS 29.513CR0536
- Addition of UDM Start of Intercept and De-Reg Records Stage 2 TS 33.127CR0185
- HSS-UDM Interworking LI Stage 2 TS 33.127CR0191
+ 20 more changes
In Release 19, the UDM function introduced several new capabilities including support for translating multiple SUPIs to GPSIs, provisioning 5G femto cell information, and selecting AF-specific identifiers during multiple identifier translation. Furthermore, the release enhanced UDM procedures for SRVCC by specifying that the UDM updates the AMF with the received STN-SR using the Nudm_SDM_Notification service operation, based on interactions with the SCC AS.
- Support for Multiple SUPI to GPSI Conversion in UDM TS 29.503CR1305
- Provision of 5G Femto Information to UDM TS 29.503CR1322
- Support for AF Specific Identifier Selection in Multiple Identifiers Translation in UDM TS 29.503CR1341
- MPS for Messaging Indicator in UDM TS 29.503CR1361
- EIF Interaction with UDM TS 29.503CR1445
- UDM AnyUe selection for Nudm_EE exposure service TS 29.503CR1498
+ 9 more changes
In Release 20, a specific enhancement for the UDM was the capability to provide per-subscriber Allowed MAC addresses from UDM. Furthermore, the release detailed procedures for the UDM to update the AMF with a received STN-SR for SRVCC, using the Nudm_SDM_Notification service operation as specified in TS 23.502.
- Providing per-subscriber Allowed MAC addresses from UDM TS 23.501CR6395
Explore further
Broader topics and technologies where UDM plays a role.
Defining Specifications
3GPP specifications that define or reference UDM, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.237 vj00 | IMS Service Continuity (ISC) Stage 2 | Rel-19 |
| TS 23.292 vj00 | IMS Centralized Services (ICS) Architecture | Rel-19 |
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.540 vj20 | 5G Service Based SMS Stage 2 | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.732 vg00 | User Data Interworking, Coexistence, Migration Study | Rel-16 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TR 23.973 vj00 | Separate HSS/UDM Deployment Scenarios & Solutions | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TR 26.919 vj00 | Study on 5G Conversational Media Handling | Rel-19 |
| TR 26.942 vj00 | Study on Media Energy Consumption Exposure & Evaluation | Rel-19 |
| TS 28.540 vk10 | 5G Network Resource Model (NRM) Management | Rel-20 |
| TS 28.561 vk00 | Management and Orchestration; Network Digital Twin | Rel-20 |
| TS 28.802 vf00 | Management Study for 5G Network Architecture | Rel-15 |
| TR 28.833 vi01 | Technical Report on 5G LAN-type Service Management | Rel-18 |
| TR 28.837 vi00 | Technical Report on Trace/MDT Management | Rel-18 |
| TR 28.840 vi10 | Technical Report | Rel-18 |
| TS 29.165 vj10 | Inter-IMS Network to Network Interface (NNI) | Rel-19 |
| TS 29.337 vj00 | Diameter T4 Interface for MTC Device Triggering | Rel-19 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | Rel-19 |
| TS 29.504 vj50 | Nudr Service Based Interface Stage 3 Protocol | Rel-19 |
| TS 29.505 vj50 | UDR Service for Subscription Data Usage | Rel-19 |
| TS 29.507 vj40 | 5G Access & Mobility Policy Control Service | Rel-19 |
| TS 29.508 vj40 | 5G Session Management Event Exposure Service | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.523 vj20 | 5G Policy Control Event Exposure Service | Rel-19 |
| TS 29.524 vj00 | 5G Cause Code Mapping Specification | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.544 vj30 | Nspaf Service Based Interface (SP-AF) Stage 3 | Rel-19 |
| TS 29.550 vj20 | 5G Steering of Roaming Service Based Interface | Rel-19 |
| TS 29.552 vj40 | 5G Network Data Analytics Signalling Flows | Rel-19 |
| TS 29.563 vj30 | TS 29563: Nhss services for HSS-UDM interworking | Rel-19 |
| TS 29.574 vj40 | 5G Data Collection Coordination Services Stage 3 | Rel-19 |
| TS 29.575 vj40 | 5G Analytics Data Repository Services Stage 3 | Rel-19 |
| TS 29.576 vj40 | 5G Messaging Framework Adaptor Services Stage 3 | Rel-19 |
| TR 29.829 vh10 | SMS Service-Based Interfaces for 5G Core | Rel-17 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.256 vj40 | 5G Connection & Mobility Charging Spec | Rel-19 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.514 vk00 | 5G Security Assurance for UDM | Rel-20 |
| TS 33.515 vk00 | 5G SMF Security Assurance Specification | Rel-20 |
| TS 33.529 vj10 | SCAS for SMSF Security Assurance | Rel-19 |
| TS 33.535 vj00 | 5G AKMA: Authentication and Key Management for Apps | Rel-19 |
| TS 33.545 vj20 | Security for NR Femto Subsystem | Rel-19 |
| TS 33.701 vj00 | Study on mitigations against bidding down attacks | Rel-19 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 33.749 vj00 | Study on security aspects of edge computing enhancement | Rel-19 |
| TS 33.835 vg10 | Study on authentication and key management for apps | Rel-16 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TR 33.847 vh10 | 5G Proximity Services Security Study | Rel-17 |
| TS 35.234 vj00 | MILENAGE-256 Algorithm Set Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
