TAC (Terminal Access Controller)

In the IMEI, the Type Allocation Code is the first eight digits identifying the manufacturer and model of a mobile device. Operators and the GSMA TAC database use it to enforce equipment policies, detect cloned or non-type-approved handsets, and block stolen devices via the EIR. TAC is also reused in some contexts as a Tracking Area Code in LTE and 5G, identifying a group of cells for mobility management. Both meanings are common in telecom security work and should be disambiguated by context.

Categories: Radio Access NetworkIdentity and SubscriberProtocols and Standards

TAC in context

The radio access network is the layer where mobile devices attach to the operator's infrastructure. Attacks in this layer include IMSI catching, rogue base stations, downgrade attacks and jamming, and defenses hinge on mutual authentication, integrity-protected signaling and Open RAN supply-chain hygiene.

Subscriber identifiers (IMSI, SUPI, MSISDN, IMEI) are the anchor for authentication, charging, lawful interception and fraud analytics. Any protocol or interface that leaks a permanent identifier is treated as a serious privacy defect, which is why 5G introduced SUCI concealment on the air interface.

To place TAC in the wider telecom-security picture, review EIR, IMEI, NB-IoT, LA, MCC and 2G.

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