Description
The 4G-GUTI is a critical identifier in 5G System (5GS) architecture that serves UEs that have performed inter-Radio Access Technology (inter-RAT) mobility from 4G Evolved Packet System (EPS) to 5GS. It is constructed by the Access and Mobility Management Function (AMF) when a UE registers with the 5G core network (5GC) using 4G credentials and procedures, specifically during an Attach procedure with EPS to 5GS mobility. The identifier consists of two main components: the Globally Unique AMF Identifier (GUAMI) and the 5G-Temporary Mobile Subscriber Identity (5G-TMSI). The GUAMI portion identifies the specific AMF that allocated the 4G-GUTI, while the 5G-TMSI is a unique identifier within that AMF's context.
When a UE initially accesses the 5GS via E-UTRAN (4G radio), it provides its 4G-based credentials, typically including the 4G GUTI from the EPS. The AMF then allocates a 4G-GUTI to this UE, which serves as its temporary identity within the 5GS. This allocation occurs during the registration procedure and is communicated to the UE in the Registration Accept message. The 4G-GUTI is stored in the UE's non-volatile memory alongside its 5G-GUTI, allowing the UE to use either identifier depending on the access network and registration context.
The primary technical function of the 4G-GUTI is to enable the AMF to uniquely identify UEs that have performed EPS to 5GS mobility without requiring them to obtain a native 5G-GUTI. When such a UE initiates communication in 5GS, it includes the 4G-GUTI in the initial NAS message, allowing the AMF to retrieve the UE's context from its database. The AMF maintains a mapping between the 4G-GUTI and the UE's full subscription data, including security context and mobility parameters. This mechanism is particularly important during handovers between 4G and 5G networks, as it allows for seamless continuity of service without requiring re-authentication or complete re-registration.
From a security perspective, the 4G-GUTI serves the same fundamental purpose as other temporary identifiers in mobile networks: it protects the user's permanent subscription identifier (SUPI) from being transmitted over the air interface, thereby enhancing privacy and security. The 4G-GUTI can be reallocated periodically or during specific events (such as inter-AMF handovers) to further enhance security through identifier freshness. The AMF manages the lifecycle of 4G-GUTIs, including allocation, reallocation, and invalidation, ensuring that each identifier remains unique within its operational context and time window.
Purpose & Motivation
The 4G-GUTI was created to address the specific requirements of inter-RAT mobility between 4G EPS and 5GS, particularly during the transition period when many UEs would initially access 5G networks using 4G-based credentials and procedures. As 5G networks were deployed, there was a need to support UEs that could connect to 5GC via both 4G radio (E-UTRAN) and 5G radio (NG-RAN), requiring a consistent identification mechanism that worked across both access types. The 4G-GUTI enables this by providing a temporary identifier that bridges the 4G and 5G identity systems.
Prior to 5G, temporary identifiers were specific to each generation (e.g., 4G GUTI for EPS, 3G P-TMSI for UMTS). This approach created challenges for inter-generation mobility, as UEs moving between systems often needed to obtain new temporary identifiers through complete registration procedures. The 4G-GUTI solves this by allowing UEs that registered via 4G procedures to maintain a consistent temporary identity when operating in 5GS, reducing signaling overhead and improving mobility performance. This was particularly important for early 5G deployments where many UEs supported 5G core network capabilities but accessed via 4G radio infrastructure.
The creation of 4G-GUTI also addressed privacy and security concerns specific to inter-RAT scenarios. By allowing UEs to use a temporary identifier derived from their 4G registration context, the system prevents the need to transmit 5G-specific permanent identifiers over 4G radio links, maintaining the privacy protections established in both systems. This approach also enables more efficient handovers between 4G and 5G, as the network can quickly identify and authenticate UEs based on their 4G-GUTI without requiring full 5G authentication procedures every time they move between the systems.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (60 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the primary new function for the 4G-GUTI was the introduction of a "mapped 5G-GUTI," which is a 5G-GUTI derived from a previously allocated 4G-GUTI to facilitate interworking between E-UTRAN/EPC and 5GCN. This mechanism supports inter-system changes for UEs operating in single-registration mode, enabling a mapped 5G NAS security context to be established during the transition. Furthermore, the release specified procedures for using this mapped identity during initial registration and network-triggered service requests, though it clarified that including a 5G-GUTI mapped from a valid 4G-GUTI in a REGISTRATION REQUEST message during an initial registration is not available in Rel-15.
- Interworking between E-UTRAN/EPC and N3IWF/5GCN TS 24.501CR0176
- Remove the remaining instance of SUPI paging TS 24.501CR0055
- Interworking with E-UTRAN connected to EPC of a UE registered to 5GC via non-3GPP access TS 24.501CR0311
- Correction on 5G-GUTI type encoding TS 24.501CR0329
- Clarification on the temporary identity in the service request procedure TS 24.501CR0352
- Alignment of 5G-GUTI assignment with SA3 TS 24.501CR0470
+ 9 more changes
In Release 16, a key enhancement for the 4G-GUTI function was the defined procedure for its inclusion during initial registration in N1 mode. Specifically, the UE is now required to include the ATTACH REQUEST message within the REGISTRATION REQUEST message when using a 5G-GUTI that was mapped from a 4G-GUTI. This supports interworking between E-UTRAN connected to EPC and 5G core network access.
- 5G-GUTI as additional guti in initial registration and UE holds 4G-GUTI TS 24.501CR0782
- 5G-GUTI not globally unique in an SNPN TS 24.501CR1458
- Octet alignment for 5G-GUTI in 5GS mobile identity IE TS 24.501CR1583
- 5GMM cause value #74 in an SNPN with a globally-unique SNPN identity TS 24.501CR2019
- Inclusion of ATTACH REQUEST message in REGISTRATION REQUEST message during initial registration when 5G-GUTI mapped from 4G-GUTI is used TS 24.501CR0793
- Correction of certain erroneous Information Element Identifiers TS 24.501CR2033
+ 5 more changes
In Release 17, specific clarifications and procedures were introduced for the handling of a mapped 5G-GUTI, which is a 5G-GUTI mapped from a previously allocated 4G-GUTI. The release added details for 5G-GUTI reallocation procedures, including scenarios like after resuming from 5GMM-IDLE mode with a suspend indication and during mobility registration updates for SNPNs. Furthermore, it provided clarifications on maintaining the 5G-GUTI in abnormal cases and on the associated terminology.
- Avoid including both PAP/CHAP and EAP identifiers in PDU session establishment request TS 24.501CR2941
- Reference to UCU procedure is missing for a 5G-GUTI reallocation variant TS 24.501CR2979
- Clarification of maintaining 5G-GUTI in an abnormal case TS 24.501CR3016
- Clarification on the setting of packet filter identifier value TS 24.501CR3300
- UE identity when onboarding in SNPN for which the UE has 5G-GUTI TS 24.501CR3392
- Network identifier is not specified TS 24.501CR3389
+ 12 more changes
In Release 18, the 4G-GUTI function was updated to clarify its role in interworking procedures, specifically regarding the handling of the N3IWF/TNGF identifier information within the REGISTRATION REJECT message. The changes included corrections for the transmission and reception of the N3IWF identifier information element during these interworking scenarios between non-3GPP access and 5G core networks. Furthermore, the release introduced considerations for equivalent SNPNs, which influence the selection of a 5G-GUTI that may be mapped from a previously allocated 4G-GUTI.
- Protecting the N3IWF/TNGF identifier information in the REGISTRATION REJECT message TS 24.501CR5932
- Correction for N3IWF identifier IE TS 24.501CR5120
- Equivalent SNPNs: 5G-GUTI selection TS 24.501CR4997
- Correction related to receiving N3IWF identifier IE in the REGISTRATION REJECT TS 24.501CR5322
- Custom throttling to temporary failed 5GSM procedure TS 24.501CR6245
In Release 19, the primary update for the 4G-GUTI function was the formal specification for the "Use of native 4G-GUTI." This introduces the distinct concept of a native 4G-GUTI, defined separately from a mapped 5G-GUTI, to be used within procedures for interworking between E-UTRAN/EPC and 5G core networks, particularly when a UE operates in single-registration or dual-registration mode.
- Support of reject QoS differentiation for non-3GPP device identifier(s) TS 24.501CR6926
- Procedure update for QoS differentiation of non-3GPP device identifiers TS 24.501CR6994
- Suspending QoS differentiation for non-3GPP device identifier TS 24.501CR7087
- Correction to the inconsistent LCS correlation identifier TS 24.501CR6380
- Use of native 4G-GUTI TS 24.501CR6417
- Support of multiple Non-3GPP device identifiers for QoS differentiation TS 24.501CR6925
+ 5 more changes
Explore further
Broader topics and technologies where 4G-GUTI plays a role.
Defining Specifications
3GPP specifications that define or reference 4G-GUTI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |