MSIN

MSIN stands for Mobile Subscriber Identification Number, and is the portion of the International Mobile Subscriber Identity (IMSI) that uniquely identifies a subscriber within a mobile network's home Public Land Mobile Network (PLMN). The IMSI also contains the Mobile Country Code (MCC) and Mobile Network Code (MNC); together these elements enable networks to identify and authenticate subscribers on a global scale, with MCC and MNC identifying the operator and country, and MSIN identifying the subscriber within that operator.

The MSIN is assigned by the mobile operator and is of variable length. The total IMSI length is up to 15 digits, with MCC usually 3 digits and MNC either 2 or 3 digits; as a result, the MSIN can range in length accordingly, typically making the MSIN 7–10 digits in common setups. The MSIN by itself is not globally unique; uniqueness is achieved only when combined with MCC and MNC.

In practice, networks use the IMSI for subscriber authentication and location tracking during attach, call setup, and data sessions. On the radio interface, the IMSI is often not transmitted; temporary identifiers like TMSI (temporary mobile subscriber identity) or GUTI are used to protect privacy. The MSIN remains sensitive information; operators and standards emphasize secure handling and minimization of IMSI exposure, especially for roaming and inter-network procedures.