Description
The Globally Unique AMF Identifier (GUAMI) is a structured identifier defined in 3GPP for the 5G System (5GS) that provides a globally unambiguous way to identify a specific instance of an Access and Mobility Management Function (AMF). An AMF is a core network function responsible for termination of NAS signaling, registration management, connection management, reachability management, and mobility management for User Equipment (UE). The GUAMI is constructed from three components: the Public Land Mobile Network (PLMN) Identifier (MCC and MNC), the AMF Region ID, the AMF Set ID, and the AMF Pointer. This hierarchical structure allows for efficient routing and scalability within and across PLMNs.
Architecturally, the GUAMI is assigned to each AMF instance by the network operator and is configured within the AMF's operational parameters. It is advertised by the AMF to other network functions, such as the Radio Access Network (RAN) nodes (gNBs) via the N2 interface and to other core functions like the Network Slice Selection Function (NSSF) via service-based interfaces. When a UE initiates registration to the 5G network, the RAN node uses the GUAMI, often derived from the Temporary Mobile Subscriber Identity (5G-S-TMSI) or provided in the initial NAS message, to select an appropriate AMF for the UE's request. The GUAMI enables the RAN to route the initial UE message to the correct AMF instance, even in deployments with multiple AMFs for load balancing and redundancy.
Operationally, the GUAMI plays a key role in several procedures. During registration, if the UE provides a GUAMI from a previous registration (within the 5G-GUTI), the network can use it to efficiently retrieve the UE's context. In mobility scenarios like handovers, the source AMF includes its GUAMI in the handover request to the target, ensuring the target system can identify and communicate with the correct AMF. For paging, the RAN uses the GUAMI to determine which AMF to contact when the network needs to reach an idle UE. The hierarchical nature of the GUAMI (Region ID, Set ID, Pointer) allows operators to organize AMFs into logical groups (Sets) within geographical regions, facilitating flexible deployment, disaster recovery, and efficient routing. The GUAMI is a fundamental element that underpins the stateless and service-based architecture of 5GC, enabling dynamic discovery and selection of AMF instances.
Purpose & Motivation
GUAMI was created to address the scalability, flexibility, and routing challenges inherent in the 5G Core's service-based architecture, which decouples software instances from hardware and allows for dynamic scaling of network functions. In previous generations like 4G EPS, the MME was identified by an MME Code and Group ID within a PLMN, but this lacked a globally unique scope and the granularity needed for cloud-native, distributed deployments. The motivation for GUAMI stemmed from the need to uniquely identify potentially thousands of AMF instances deployed across multiple data centers and geographical regions, supporting network slicing, edge computing, and high-availability requirements.
Historically, identifiers in mobile networks evolved from simple codes to more structured forms to support increasing network complexity. The introduction of 5G and its requirement for network slicing—where a single physical network hosts multiple logical networks—necessitated an identifier that could not only uniquely point to an AMF instance but also convey logical grouping information for efficient slice-aware routing. GUAMI solves this by incorporating PLMN ID, Region ID, Set ID, and Pointer, allowing operators to organize AMFs in a way that reflects their deployment topology and slice associations.
The technology solves critical problems in 5G operation: it enables the RAN to perform efficient AMF selection without requiring a central directory for every UE request, reducing signaling latency. It supports stateless operation, where an AMF instance can fail and another can take over, as the GUAMI provides a consistent handle for locating UE context. Furthermore, it facilitates inter-PLMN mobility and roaming by ensuring AMFs are globally addressable. By providing a structured, globally unique identifier, GUAMI is foundational to achieving the 5G vision of a flexible, scalable, and resilient core network that can support diverse services from massive IoT to ultra-reliable low-latency communications.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (377 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the GUAMI (Globally Unique AMF Identifier) was newly introduced as the 5G System's equivalent to the EPS GUMMEI, serving to uniquely identify the AMF that allocated a 5G-GUTI. A key definitional correction clarified its structure and ensured its inclusion within RRC messages for related procedures, such as during registration. This provided a foundational identifier for mobility management and context retrieval in the 5G core network.
- Storing Configured NSSAI when the PLMN is changed TS 24.501CR0203
- Introduction of PLMN Id in UECM & UE Authentication Services TS 29.503CR0026
- GUTI unique across AMFs in an AMF SET TS 23.501CR0089
- Use of identifiers for mobility between GERAN/UTRAN and 5GS TS 23.501CR0017
- Network sharing prioritised PLMN handling TS 23.501CR0056
- Inter-PLMN mobility when N26 is not used TS 23.501CR0070
+ 56 more changes
In Release 16, the key enhancement for the GUAMI function was its defined usage for EPS/5GS interworking, as explicitly called out in the Change Request titles. This provided specific guidance on how the Globally Unique AMF Identifier operates and is applied in scenarios involving mobility and session management between 4G EPS and 5GS networks.
- Serving PLMN rate control, general description TS 24.501CR0972
- Serving PLMN rate control, activation TS 24.501CR0973
- PLMN ID and NID provided to the lower layers TS 24.501CR1055
- Abnormal case handling for receipt of 5GMM cause value #11 from a PLMN TS 24.501CR1229
- "S-NSSAI not available in the current PLMN" when non NSSAA supported UE requesting the S-NSSAI subjects to NSSAA TS 24.501CR1598
- Alternative 2: Handling of a UE not allowed to access SNPN services via a PLMN by subscription with 5GMM cause value #72 TS 24.501CR2252
+ 93 more changes
In Release 17, updates to the GUAMI function primarily enhanced support for mobility and service continuity between SNPNs and PLMNs, as indicated by CRs focusing on inter-PLMN mobility of PDU sessions and mobility support between SNPNs and between SNPN and PLMN. This included mechanisms to handle network selection and identifier translation in these scenarios. Furthermore, specific enhancements addressed the handling of session management policy data on a per-PLMN basis and the provisioning of user plane services when a PLMN is operating as an onboarding network.
- Informative guideline on supporting session/service continuity between SNPN and PLMN when using N3IWF TS 23.501CR2563
- User Plane Remote Provisioning of UEs if PLMN as ON TS 23.501CR2802
- Mobility support between SNPNs and between SNPN and PLMN TS 23.501CR2826
- PLMN with disaster condition TS 24.501CR3585
- Enabling update of SOR-SNPN-SI in a PLMN TS 24.501CR3839
- PLMN with disaster condition IE as cleartext TS 24.501CR3970
+ 95 more changes
In Release 18, the GUAMI function was enhanced to ensure the uniqueness of the PLMN-assigned Network Slice Instance (NSI) Identifier, which is a component used within the GUAMI construct. This update specifically mandated that a PLMN must make a Provisioned NSSAI Instance Identifier (PIN ID) unique within that PLMN, as indicated by the CR title "Make PIN ID unique in PLMN". Furthermore, the release included alignment and corrections on the use of PLMN IDs in application function requests, which supports the consistent identification and routing of network functions associated with a GUAMI.
- SNPN Identifier based N3IWF FQDN TS 23.003CR0687
- Edge Relocation within the same hosting PLMN's EHEs TS 23.501CR3820
- KI#4: Support for Centralized NSACF in a PLMN with multi-service areas TS 23.501CR3822
- PIN identifiers TS 23.501CR4287
- Protecting the N3IWF/TNGF identifier information in the REGISTRATION REJECT message TS 24.501CR5932
- Add new types for PLMN Operator Class TS 29.503CR1047
+ 47 more changes
In Release 19, the enhancements for GUAMI primarily involved the integration of new non-3GPP device identifiers and the support for their handling within the 5G system, as indicated by the addition of these identifiers to the Namf_AIoT_MessageDelivery service operation. This included defining specific identifiers for non-3GPP devices connecting behind a UE or 5G-RG and enhancing procedures for their QoS differentiation and management. Furthermore, corrections and cleanup were applied to the definitions of related identifiers, such as those for Ambient IoT, to ensure consistency within the framework.
- Non-3GPP Device Identifier TS 23.003CR0708
- Definition of AIoT Device Permanent Identifier TS 23.003CR0713
- NF discovery and selection by target PLMN TS 23.501CR5399
- UDR enhancement supporting Device Identifier of non-3GPP Devices connecting behind a UE/5G-RG TS 23.501CR5547
- Definition of identifiers of N3GPP device behind UE/5G-RG TS 23.501CR5749
- Storage and replacement of RAT utilization control information associated to the current PLMN TS 24.501CR6460
+ 56 more changes
Explore further
Broader topics and technologies where GUAMI plays a role.
Defining Specifications
3GPP specifications that define or reference GUAMI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.003 vj50 | Numbering, addressing and identification in 3GPP | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 29.503 vj50 | UDM Service Based Interface Stage 3 | 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 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.571 vj50 | Common Data Types for 5G Service Based Interfaces | Rel-19 |
| 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 32.291 vj40 | Charging Management: Service-Based Interface Protocol | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |