Description
The Type Allocation Code (TAC) is the foundational component of both the IMEI and IMEI-SV. It constitutes the first eight digits of these identifiers. The TAC itself is not a random number; it is a code officially allocated by a central body (historously by BABT, now by the Global System for Mobile Communications Association's GSMA-led IMEI Allocation Board) to a device manufacturer for a specific device model or a range of models. Therefore, the TAC uniquely identifies the device's brand, model, and often specific variant (e.g., different colors or regional versions).
Operationally, the TAC is the most frequently used part of the IMEI for high-level device identification. When a network receives a full IMEI, it can immediately extract the TAC to determine the device type without needing the unique serial number. This is leveraged in numerous network functions. For instance, radio access network algorithms might apply specific optimization parameters based on the device model identified by the TAC. Core network policy functions can use the TAC to apply device-specific QoS policies or restrictions. It is also the primary key used in device databases and analytics platforms to categorize device populations.
From a regulatory and standards perspective, the TAC is crucial for device type approval. Regulatory bodies use the TAC to track which device models have been certified for operation in their jurisdictions. The TAC is also integral to the IMEI-based device blocking ecosystem. While a full IMEI is needed to block a specific stolen device, a TAC can be used in more broad actions. For example, if a particular device model is found to have a critical, un-patchable radio flaw, regulators or operators could potentially block all devices with that TAC from accessing the network, a process that would utilize the Equipment Identity Register's (EIR) capabilities. The TAC's structure ensures global uniqueness and prevents collisions between different manufacturers' device codes.
Purpose & Motivation
The TAC was established to provide a standardized, hierarchical structure within the IMEI, enabling efficient categorization and identification of device models at scale. Before its formal definition, identifying a device model from its serial number required proprietary manufacturer databases, which was inefficient for network operators and regulators. The TAC solves this by encoding the model information directly into the identifier's structure, allowing for instant recognition.
Its creation was motivated by the needs of regulatory type-approval processes, device market analytics, and network optimization. Regulators needed a reliable code to associate with a device's certification documents. Network operators needed to quickly identify device capabilities (e.g., supported frequency bands, maximum data rates) to optimize radio resource allocation and troubleshoot device-specific issues. The TAC, introduced as a core part of the IMEI and later refined, met these needs by providing a globally unique, operator-readable 'model number' that is consistently reported by every device. This allows for automated systems to apply model-specific configurations and policies across the entire mobile network.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (27 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, a new permanent identifier format, the IMEISV (International Mobile Equipment Identity and Software Version number), was formally introduced for use in NAS procedures. This allows the network to identify a UE and its software version for functions like the UE identity check procedure between the MME and EIR over the S13 interface. The introduction provides a standardized method for equipment identification and verification within the 5G system architecture.
- Mobile Terminated SMS over NAS: 5GS Access Selection TS 23.501CR0201
- Coordination of reference point allocation TS 23.501CR0356
- Clarification on Registration with AMF re-allocation TS 23.501CR0719
- Permanent identifier with IMEISV format TS 23.501CR0875
- Adding a new 5G-GUTI allocation condition TS 23.501CR0958
In Release 16, a key change for the IMEI/TAC function was the correction of its use specifically for non-3GPP only UEs, ensuring proper identity handling for these devices. This built upon the existing framework where the S13 interface enables UE identity check procedures between the MME and EIR. The update provided necessary clarifications to align identity management procedures across different access types.
- UPF Selection influenced by the indication of the identity/identities of 5G AN N3 User Plane capability TS 23.501CR0862
- UE IP address Allocation by UPF: N4 impacts TS 23.501CR0931
- Addition of UE IP address Allocation by UPF TS 23.501CR0954
- UE IP address Allocation by AAA/DHCP TS 23.501CR1180
- UE Radio Capability ID allocation in EPS TS 23.401CR3527
- Correction of use of PEI/IMEI for non-3GPP only UEs TS 23.501CR1390
+ 4 more changes
In Release 17, there were no specific changes to the IMEI/TAC function documented in the provided grounding context or listed Change Request titles. The CR titles and technical excerpts focus on other areas like UPF resource allocation, user identity mapping, and AMF re-allocation, without mentioning updates to the EIR, S13 interface, or the UE identity check procedure related to IMEI. Therefore, based solely on the given materials, Release 17 introduced no new features for IMEI/TAC.
In Release 18, the key update for the IMEI/TAC function was the introduction of specific provisioning and indication procedures for mobile Integrated Access and Backhaul (IAB) nodes. This included corrections to the provisioning of the Type Allocation Code (TAC) for a mobile IAB-Donor Unit (IAB-DU). Furthermore, the release clarified the requirement for a mobile IAB node to indicate its IAB capability when establishing a Radio Resource Control (RRC) connection.
- Introduction of Mobile Base Station Relay TS 23.501CR3813
- Support of Group AF Sessions for QoS Resource Allocation and QoS monitoring operation TS 23.501CR4128
- Update for the support of mobile IAB TS 23.501CR3850
- Corrections on mobile IAB-DU's TAC provisioning TS 23.501CR5250
- Clarification on mobile IAB indication when establishing RRC connection TS 23.501CR5302
In Release 19, the IMEI/TAC function was updated to enhance the UE identity check procedure between the MME and EIR over the S13 interface. The release also introduced improvements to Tracking Area list management, ensuring the allocation of a Tracking Area Identity list that provides homogenous support for EPS bearers. Furthermore, specific considerations were added for PDN GW selection and APN usage during congestion control procedures.
In Release 20, the primary update for the IMEI/TAC function was the introduction of support for a Dynamic Network Identity. This enhancement is reflected in the UE identity check procedure between the MME and the EIR over the S13 interface, which verifies the International Mobile Equipment Identity.
- Support for Dynamic Network Identity TS 23.501CR6483
Explore further
Broader topics and technologies where IMEI-TAC plays a role.
Defining Specifications
3GPP specifications that define or reference IMEI-TAC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 29.122 vj40 | T8 Reference Point for Northbound APIs | Rel-19 |
| TS 29.675 vj10 | UE Radio Capability Provisioning Service | Rel-19 |
| TS 32.422 vk00 | Telecom Management: Trace Control & Configuration | Rel-20 |