Description
The Globally Unique Temporary UE Identity (GUTI) is a fundamental privacy and efficiency mechanism in 3GPP's Evolved Packet System (EPS) and 5G System (5GS). Its primary role is to replace the use of the permanent, subscriber-sensitive Superscript Permanent Identifier (SUPI) – which in 4G is the IMSI – in most radio signaling messages. The GUTI is assigned by the core network's Mobility Management Entity (MME) in EPS or the Access and Mobility Management Function (AMF) in 5GS during initial registration or attachment procedures. Once assigned, the UE uses the GUTI to identify itself in subsequent signaling interactions, such as during service requests, tracking area updates, or handovers.
The structure of the GUTI is hierarchical and contains information that allows the network to efficiently route signaling and locate the node managing the UE's mobility context. In EPS, the GUTI is composed of a Globally Unique MME Identifier (GUMMEI) and an MME-Temporary Mobile Subscriber Identity (M-TMSI). The GUMMEI uniquely identifies the MME that allocated the GUTI, and the M-TMSI is a unique identifier for the UE within that MME. In 5GS, the equivalent structure comprises a Globally Unique AMF Identifier (GUAMI) and a 5G-TMSI. This structure means that when a network entity receives a message with a GUTI, it can immediately determine which MME/AMF is responsible for the UE's context.
The operational lifecycle of a GUTI involves assignment, re-assignment, and usage. It is assigned during initial registration. The network may re-assign a new GUTI during certain procedures, like inter-MME/AMF handovers or for periodic privacy refresh. The UE stores its assigned GUTI in non-volatile memory to use it after power cycles. A key procedure involving the GUTI is identification. If a network node (like a new MME during inter-MME handover) receives a GUTI it does not recognize, it uses the embedded GUMMEI/GUAMI to query the old MME/AMF for the UE's context and permanent identity (IMSI/SUPI). This mechanism allows for seamless mobility and context transfer while still shielding the permanent identity on the radio link.
Purpose & Motivation
The GUTI was introduced primarily to address critical user privacy concerns associated with the permanent IMSI. In earlier 2G/3G systems, the IMSI was frequently sent in clear text over the radio interface, making it vulnerable to interception and tracking by passive eavesdroppers. An attacker could collect IMSIs to profile user locations, movements, and habits—a significant privacy breach. The GUTI solves this by acting as a pseudonym; the sensitive IMSI/SUPI is transmitted only during exceptional, secured initial procedures, and is otherwise replaced by the temporary GUTI.
Beyond privacy, the GUTI serves important network efficiency and operational purposes. The hierarchical structure of the GUTI (GUMMEI/GUAMI + TMSI) provides built-in routing information. This allows other network nodes, such as eNodeBs/gNBs or other MMEs/AMFs, to quickly determine the 'anchor' core network node managing the UE's session without needing complex lookups or broadcasting queries. This speeds up signaling procedures like handovers and paging.
The design of GUTI also supports scalability and network architecture evolution. By decoupling the temporary identity from the permanent one, operators can re-assign GUTIs independently (e.g., after a UE moves to a new MME/AMF area). This flexibility is crucial for load balancing, network optimization, and the distributed nature of 5G core networks. In essence, the GUTI is a cornerstone for enabling secure, efficient, and scalable mobility management in modern 3GPP systems.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (71 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the GUTI was fundamentally extended for 5G interworking by defining a new 5G-GUTI and specifying its use within procedures like the ATTACH REQUEST message for single-registered UEs. Furthermore, the release introduced detailed mapping rules between the 5G-GUTI and the EPS GUTI, including the derivation of a GUMMEI from a 5G GUTI with a specific interworking indication. It also clarified allocation procedures, such as assigning a new 5G-GUTI during the Mobile Originated (MO) service request procedure.
- EPS mobile identity and UE status in the ATTACH REQUEST message TS 24.301CR3028
- Update of UE identity used for attach in S1 mode for single-registered UE without N26 TS 24.301CR3070
- Clarification on eDRX handling with assigning a new GUTI TS 24.301CR2895
- Correction on transmission failure of IDENTITY RESPONSE message TS 24.301CR3078
- Correction on inclusion of GUTI for UE in single-registration mode TS 24.301CR3119
- GUMMEI mapped from 5G GUTI with indication at 5G interworking TS 24.301CR3108
+ 18 more changes
In Release 16, the GUTI's functionality was extended to support the management of the UE Radio Capability ID, enabling its assignment and deletion via the GUTI reallocation procedure. Furthermore, the release formally defined the Truncated 5G-S-TMSI, a shorter form of the temporary identity used for specific signalling scenarios. These additions provided new mechanisms for network efficiency and identity handling within the 5G system.
- UE radio capability ID assignment via GUTI reallocation procedure TS 24.301CR3328
- SUCI computation: implementers' test data for network specific identifier-based SUPI TS 33.501CR0847
- Signalling UE capability Identity TS 36.300CR1294
- Deletion of UE Radio Capability ID using GUTI reallocation TS 23.401CR3587
- Global uniqueness of NID TS 23.003CR0553
- SUPI definition for 5G-RG and FN-RG TS 23.003CR0567
+ 3 more changes
In Release 17, key enhancements to the GUTI function focused on supporting MUSIM devices and improving identity handling procedures. This specifically introduced the concept of an IMSI Offset for EPS attach and Tracking Area Update procedures, along with the storage of an Alternative IMSI in the MME's MM context. Furthermore, the release provided clarifications on the mapped GUTI terminology and aligned GUTI allocation with best practices for generating unpredictable identifiers.
- Introducing IMSI Offset to Attach and TAU procedures for MUSIM handling in EPS TS 24.301CR3527
- Negotiated IMSI offset and TAU COMPLETE TS 24.301CR3614
- Negotiated IMSI offset when TAU COMPLETE is not received by network TS 24.301CR3625
- Storing of alternative IMSI TS 24.301CR3679
- Clarification on removing condition of paging restriction and IMSI Offset TS 23.401CR3652
- Adding Alternative IMSI to the MM Context in the MME TS 23.401CR3677
+ 16 more changes
In Release 18, specific clarifications and updates were made to the handling of temporary identifiers, including the removal of the GUTI from the Registration Reject message. Furthermore, editor's notes related to the temporary identifier used during trusted non-3GPP access were resolved, and work was done to ensure a consistent value name for the GUTI type.
- Decorated NAI format for 5G-NSWO for SUPI TS 23.003CR0696
- Include DN-specific identity in PDN CONNECTIVITY REQUEST TS 24.301CR3861
- Resolution of editor notes related to the temporary identifier used during trusted non-3GPP access. TS 33.501CR1766
- Clarification on NAI format for Anonymous SUPI in 5G-NSWO in SNPN access mode. TS 23.003CR0698
- Indicating the SDNAEPC DN-specific identity in the protocol configuration options TS 24.301CR3886
- Abnormal case for SDNAEPC related to DN-specific identity TS 24.301CR4011
+ 5 more changes
In Release 19, the GUTI function was enhanced with the capability for RAT utilization control in GUTI reallocation and specific UE actions were defined upon GUTI deletion. The release also included a correction on the term "4G-GUTI." Furthermore, procedures were updated to handle an invalid EPS bearer identity within the Data container IE of the EMM TRANSPORT message.
- Invalid EPS bearer identity in the Data container IE in the EMM TRANSPORT message TS 24.301CR4494
- LCS Session Identity and LCS User Plane Connection/Binding ID TS 23.003CR0719
- Correction on term 4G-GUTI TS 24.301CR4180
- RAT utilization control in GUTI reallocation TS 24.301CR4124
- UE actions upon GUTI deletion TS 24.301CR4442
Explore further
Broader topics and technologies where GUTI plays a role.
Defining Specifications
3GPP specifications that define or reference GUTI, 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 23.251 vj00 | Network Sharing Stage 2 Specification | Rel-19 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.801 v810 | CT1 SAE NAS Aspects for EPC | Rel-8 |
| TS 29.303 vj10 | DNS Procedures for Evolved Packet System | Rel-19 |
| TS 31.117 vj10 | USIM Application Toolkit Test for Non-Removable UICC | Rel-19 |
| TS 31.127 vi40 | UICC-terminal interaction testing specification | Rel-18 |
| TS 33.126 vj30 | Lawful Interception Requirements | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.835 vg10 | Study on authentication and key management for apps | Rel-16 |
| TS 33.843 vf10 | Security Study for ProSe UE-to-Network Relay | Rel-15 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |