What is an IMSI? Definition of multi and single IMSI

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.

IMSI briefly explained:

  • IMSI stands for International Mobile Subscriber Identity.
  • The IMSI is a unique identifier that is assigned to every mobile phone user worldwide.
  • It usually comprises 15 digits.
  • The IMSI has nothing to do with the mobile phone number.

IMSI: International Mobile Subscriber Identity

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.

Structure of the IMSI number:

In most cases, the IMSI number comprises 15 digits. These are made up of three different parts:

  • MCC (Mobile Country Code)
  • MNC (Mobile Network Code)
  • MSIN (Mobile Subscriber Identification Number)

The first three digits of the number represent the MCC and indicate the country in which the user of the SIM is registered. The MNC usually consists of two digits and stands for the mobile network or the network operator in 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 individual for 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 therefore consists of

  • 262: Identification number for Germany
  • 04: Code mobile network, here Vodafone
  • 5678919111: individual number of the user

IMSI vs. ICCID: What is the difference?

The IMSI is not the same as an ICCID number (Integrated Circuit Card Identification). Both are part of the SIM profile and therefore 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, several SIM cards can have the same IMSI if they are connected to the same subscriber. However, the ICCID is different in each case and is therefore responsible for the physical identification of the card in the network.

IMSI and roaming: single and multi-IMSI

For many IoT applications, it is important that the device can connect to different networks. Although an IMSI originates from a specific mobile subscriber, it still allows connection to different mobile networks.

With our M2M SIM card, devices can connect to different mobile networks worldwide. To do this, they are constantly in roaming mode, both at home and abroad. Thanks to uncontrolled roaming, a device can then automatically select the network with the best signal.

We can offer even more connection options and therefore better coverage if we have several IMSIs on the same M2M SIM. In this case, we speak of a multi-IMSI. For example, it is always possible to decide which IMSI is to be used in any given country. If only one IMSI is stored on a SIM card, this is a single IMSI.

Multi-IMSI M2M SIM cards

In the unlikely event that the default IMSI cannot establish a connection to any provider, the other IMSIs serve as a backup to connect to. If the first IMSI set up cannot find a roaming partner, a so-called IMSI switch takes place. The second IMSI then attempts to connect to one of the available network providers. Particularly for IoT devices that are on the move, such as in the transport or logistics industry, good network coverage is necessary even across national borders and is guaranteed thanks to the multi-IMSI.

The advantages of the multi-IMSI SIM are therefore obvious:

Open questions?

Do you have any further questions about IMSI or would you like to find out more about its possible applications? Our team will be happy to answer your questions and support you with your IoT project.

Laura Gaber
Laura Gaber
Laura Gaber, M.Sc., is the longest-serving of our two Marketing Lauras. The Cologne native worked for several years as a communications all-rounder at EU level for the renewable energy sector. In 2016, Laura's curiosity drove her further afield - straight into the north and our arms. Since then, she has been dealing with the latest developments in digitalization, M2M communication and the IoT on a daily basis.