IMSI stands for International Mobile Subscriber Identity. This refers to a unique number consisting of 15 digits on the SIM card, which is used to identify a mobile subscriber.
The International Mobile Subscriber Identity (IMSI) is a globally unique number that is stored on a special chip on the SIM card. It is assigned to every user of a mobile network and is therefore crucial for authentication: if a device attempts to establish a connection to the mobile network, the IMSI is used by the mobile network operator to enable unique identification.
In most cases, the IMSI number comprises 15 digits. These are made up of three different parts:
The first three digits of the number represent the MCC and indicate the country in which the SIM user is registered.
The MNC usually consists of two digits and stands for the mobile network or network operator on which the SIM is active.
Together with the MNC, the MCC forms the IMSI block identifier.
The last group of digits is the MSIN, which usually consists of nine to ten digits. These are unique to each SIM card and can therefore be clearly assigned to a mobile subscriber. In Germany, for example, the number is assigned by the Federal Network Agency.
The IMSI number 262 04 5678910111 thus consists of
The IMSI is not the same as an ICCID (Integrated Circuit Card Identification) number. Both are part of the SIM profile and thus a key element of mobile data transmission. However, the IMSI identifies the subscriber of the mobile network, whereas the ICCID identifies the SIM card itself.
For example, multiple SIM cards can have the same IMSI if they are associated with the same subscriber. The ICCID, however, is unique to each card and is thus responsible for the physical identification of the card within the network.
A stable cellular connection is crucial for IoT applications. That is why they must be able to use multiple cellular networks—both within a country and across national borders. There are various technical approaches to achieving this.
In addition to M2M SIM cards that can connect to different mobile networks based on roaming agreements, there are also multi-IMSI SIM cards. With a multi-IMSI SIM, multiple IMSIs are stored on the same M2M SIM. If only one IMSI is stored on a SIM card, it is a single-IMSI SIM.
If multiple IMSIs are stored on an M2M SIM, the SIM can switch between these identities depending on the country, network availability, and configuration. If the default IMSI cannot establish a connection with any provider in the area, one of the other IMSIs stored on the SIM takes over. This switch is referred to as an IMSI switch.
There is no one-size-fits-all answer to this question. Both approaches share the same goal: to provide IoT devices with the most stable connection possible. Multi-IMSI SIMs and M2M SIM cards both achieve this; the only difference is in their technical implementation.
Which approach makes more sense depends, among other things, on the following factors:
- the country of use,
- the available roaming agreements,
- local network coverage, and
- regulatory requirements in individual countries.
In many IoT projects, a single IMSI and extensive roaming agreements already provide reliable network coverage. However, a Multi-IMSI can offer additional flexibility in certain scenarios.
Do you have any further questions about IMSI or would you like to find out more about its possible applications? Our team of M2M experts will be happy to answer your questions and support you with your IoT project.
