Frequently Asked Questions
An International Mobile Subscriber Identity (IMSI) is used in any mobile network that interconnects with other networks. It is a unique, international identifies that allows for roaming on mobile service provider networks.
The IMSI is a fixed 15-digit length. It consists of a three-digit Mobile Country Code (MCC), a three-digit Mobile Network Code (MNC), and a nine-digit Mobile Station Identification Number (MSIN). The MSIN can now be used for Shared HNI assignments. In those instances, the first four digits are used as the IMSI Block Number (IBN), the remaining five digits are used for the User Identification Number (UIN)
ATIS is responsible for the assignment and administration of the first six digits, the MCC and MNC, to network operators. The network operator to which the digits are assigned, is responsible for the assignment and administration of the MSIN, the last nine digits.
A Home Network Identifier (HNI) identifies a mobile subscriber’s home network. It is comprised of the first six digits of the IMSI – the MCC and MNC. An HNI is unique to a country with multiple assigned MCCs. Since there are multiple assigned MCCs, the HNI must both be used to determine the Home Location Register (HLR).
Within the United States, a Shared HNI is used to identify a Citizens Broadband Radio Service (CBRS) operation. The overall IMSI format remains the same; however; for the purposes of defining an HNI for the CBRS range, the MSIN is divided into two components:
- The first four digits are used as the IMSI Block Number (IBN)
- The last five digits are used for the User Identification Number (UIN).
Canadian IMSIs are assigned by the Canadian Numbering Administrator (CNA). Call +1 613-683-3285 for questions concerning IMSI administration in Canada.
There is a $325 non-refundable fee which is charged during the application process. Once a code is assigned, the Alliance for Telecommunications Industry Solutions (ATIS) charges an annual maintenance fee per assignment.
ATIS will issue the HNI within 10 business days of receipt of a properly completed application, including receipt of the application fee and any required supporting documentation.
To return an HNI or to have the assignee information changed, please complete the appropriate modification form at https://imsiadmin.com/forms/.
More information can be found in the IMSI Assignment Guidelines and Procedures, which are maintained by the ATIS – IMSI Oversight Council (IOC) or by calling ATIS at +1 202-662-2540.