The International Mobile Subscriber Identity (IMSI) number is central to identifying users on a carrier network. It is a unique number that is assigned to a cell phone or mobile device to identify it on the GSM, UMTS, or LTE network.
Typical the IMSI number is stored on the SIM card of the mobile device and is sent to the network as required.
An IMSI number is 15 digits long, and includes the Mobile Country Code (MCC), Mobile Network Code (MNC), and Mobile Station Identification Number (MSIN).
The Home Network Identity (HNI) is made up of the MCC and MNC. The HNI is used to fully identify a user’s home network. This is important because some large countries have more than one country code for a single carrier. For example a customer with a mobile carrier on the East Coast of the United States would have a different MCC than a customer on the West Coast with the same carrier because even through the MNC would be the same the MCC would be different — the United States uses MCCs 310 to 316 due to its size.
If an IMSI number is not from the local carrier’s network, IMSI analysis is performed to resolve the number into a Global Title which is used to access the user’s information remotely on their home carrier’s network for things like billing and international roaming.