What is IMEI?
IMEI (International Mobile Equipment Identity) is a unique 15-digit number assigned to every 3GPP mobile device (smartphone, tablet, IoT module) that identifies the hardware equipment itself — distinct from the SIM/USIM which identifies the subscriber. The IMEI is used by mobile networks to identify valid devices, block stolen equipment, and track device types for network management. It is stored in the device’s firmware and is checked by the network during registration procedures.
How Does IMEI Work?
The IMEI consists of a Type Allocation Code (TAC, 8 digits) identifying the device manufacturer and model, a Serial Number (SNR, 6 digits) uniquely identifying the individual device, and a Check Digit (1 digit, Luhn algorithm). When a UE attaches to the network, the AMF (in 5G) or MME (in 4G) can request the IMEI via an Identity Request message. The network checks the IMEI against the EIR (Equipment Identity Register) which maintains whitelists, blacklists, and greylists. Blacklisted IMEIs (reported as stolen) are denied service. The IMEISV (IMEI Software Version) variant adds two software version digits, replacing the check digit.
Use Cases
Stolen device blocking and tracking, device type identification for network optimization, regulatory device certification tracking, operator device whitelisting and policy enforcement, and IoT device fleet management.
3GPP / Standards Reference
3GPP TS 23.003 (Numbering, addressing and identification — IMEI structure), 3GPP TS 22.016 (International Mobile Equipment Identities), GSMA IMEI Allocation Guidelines
Related Terms
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
