IMSI
The IMSI is the subscription identifier on a SIM: up to 15 digits of MCC, MNC and MSIN that the network uses to authenticate and locate a device.
Definitions only — a term explained here is not a service we sell.
The international mobile subscriber identity (IMSI) names one subscription to the network. It is up to 15 digits: a 3-digit MCC, a 2- or 3-digit MNC and an MSIN, stored on the SIM or eUICC.
The network uses the IMSI to authenticate the device and to update its location. Over the radio interface it normally uses a temporary identifier such as a TMSI or GUTI.
Structure
The MNC is 2 or 3 digits depending on the network, so a fixed character split misreads the MSIN. Confirm the MNC length per network and validate the IMSI against the MCC-MNC range.
IMSI structure
Decoded in your browser. Nothing is uploaded.
- MCC
- 274
- MNC
- 01
- MSIN
- 1234567890
Text description
The example is synthetic. The first three digits are the MCC; the figure reads the next two as the MNC and the rest as the MSIN. Type another value and the figure decodes it in the browser.
Privacy and multi-IMSI
Treat the IMSI as privacy-sensitive: keep it out of customer-facing logs and do not use it as a primary key without controls. A multi-IMSI SIM changes the active IMSI to present a local identity in each market. Ask what triggers the switch and what happens to an active session. The four numbers explainer shows how the identifiers relate.