IMSI: The central subscriber identification explained

IMSI: The central subscriber identification in mobile networks explained

The IMSI number uniquely identifies every mobile subscriber within a network. Companies offering mobile services and IoT applications need the IMSI to ensure secure and reliable communication between devices and networks. In this article, you’ll learn everything essential – from its function to security aspects.

What is IMSI?

IMSI stands for ‘International Mobile Subscriber Identity’ and works similarly to a fingerprint for mobile subscribers. It is a globally unique identification number assigned to each SIM which, within a mobile network, identifies mobile users. The IMSI SIM number contains information about the country, the network operator and the individual subscriber identification, allowing the user to be clearly assigned to a mobile provider, which allocates network settings such as tariff plans and permissions.

For IoT and M2M, the IMSI number plays a crucial role. Thanks to its seamless integration into global mobile standards, the number offers flexibility and security, meaning IoT devices can operate worldwide in mobile networks without requiring local adjustments.

The role of the International Mobile Subscriber Identity in mobile networks

The IMSI uniquely identifies mobile subscribers. As soon as a subscriber connects to a mobile network, the device sends the IMSI SIM number to the network operator, who confirms the identity. This step then grants access to network resources and assigns the correct tariff.

Another critical application is authentication. The IMSI number ensures that only authorized users can access the mobile network, protecting both the subscriber and the operator from unauthorized access. After authentication, the IMSI correctly assigns mobile usage and ensures accurate billing.

The role of the IMSI SIM Number on the Internet of Things

In connected environments, it’s crucial that each device is reliably and uniquely identified, and can communicate with multiple devices. IMSI ensures that IoT devices receive unique identification and secure access to network resources.

For M2M (Machine-to-Machine), the IMSI supports automated communication between machines. Sensors, vehicles, or industrial systems can exchange data via mobile networks, which are processed by central platforms. The IMSI SIM number enables global connectivity, allowing devices to communicate worldwide, regardless of their location.

The authentication process ensures that only authorized devices access the network and that data is transmitted securely. This security is especially important in critical infrastructures such as energy supply or logistics.

The structure of the IMSI code explained

The length of the IMSI consists of up to 15 digits and is composed of three main components: the Mobile Country Code (MCC), the Mobile Network Code (MNC), and the Mobile Subscriber Identification Number (MSIN).

• Mobile Country Code (MCC): The MCC is made up of three digits and specifies the country where the mobile subscriber is registered. For example, 232 represents Austria.

• Mobile Network Code (MNC): After the MCC comes the MNC, typically consisting of two digits. This code identifies the specific mobile operator within the country. In Austria, the code 02 represents A1 Telekom Austria.

• Mobile Subscriber Identification Number (MSIN): The last and largest section of the IMSI number is the MSIN, which has a total of nine or ten digits and uniquely identifies the subscriber within a network. This allows millions of mobile subscribers to be individually recognized within a network.

Together, they complete the full form of the IMSI SIM number, which is globally unique for each subscriber. It enables not only the individual assignment of mobile devices but also seamless access to various networks across multiple countries, which is particularly important for international IoT and M2M applications.

Single IMSI or Multi IMSI: The right roaming solution

When using a Single IMSI, a SIM card is equipped with one IMSI number, which remains unchanged throughout its use, providing access to a specific mobile network. It is suitable for applications where the device primarily stays within one country. However, high roaming costs may occur if the device is used internationally.

A Multi IMSI, on the other hand, is able to store multiple IMSI numbers on a single SIM card, allowing it to switch between various mobile networks when necessary. Once a network change is required, the Multi IMSI SIM automatically activates a new number to connect with a local network, therefore reducing roaming costs and improving network coverage. The IMSI switch occurs automatically based on network availability and conditions stored on the SIM card.

Multi IMSI is especially beneficial for global M2M and IoT applications, where companies require high flexibility. The automatic switch between different IMSI SIM numbers makes seamless communication across borders possible, meaning companies save costs and improve the reliability and efficiency of their IoT applications.

Differences between IMSI, IMEI and ICCID

Besides the IMSI code, there are two other key identification numbers in mobile communication: IMEI and ICCID. While the IMSI number identifies the mobile subscriber, the other codes serve different specific functions.

• IMEI (International Mobile Equipment Identity): The IMEI number identifies the mobile device itself, such as a smartphone or an IoT device. It is unique to each device and remains unchanged even when the SIM card is swapped. Mobile operators can use the IMEI to block lost or stolen devices or check device status.

• ICCID (Integrated Circuit Card Identifier): The ICCID is the unique identification number of the SIM card. It is printed on the card and includes information about the SIM card issuer. When the SIM card is changed, the ICCID number changes accordingly.

IMSI identifies the user, IMEI indicates the device, and ICCID specifies the SIM card. Together, the three numbers enable comprehensive management and control of mobile connections, particularly for IoT applications with many connected devices.

Security concerns about the International Mobile Subscriber Identity

Exposing the IMSI code can pose a security risk, as attackers are able to track a device’s location or monitor the user’s activities. To counter this, mobile operators encrypt the IMSI during communication, meaning once a device connects to the mobile network, a temporary key replaces the IMSI number, called TMSI (Temporary Mobile Subscriber Identity). This temporary code changes regularly, ensuring that the actual IMSI SIM number is not revealed in every communication process.

Conclusion: The central role of IMSI in connectivity

The IMSI number is indispensable for identifying mobile subscribers, as it enables secure communication and seamless connections in global networks. Especially on the Internet of Things, companies use the IMSI to manage and protect a variety of connected devices. It will continue to be an essential element for mobile communication.

FAQ about IMSI

What is the IMSI number?
The IMSI (International Mobile Subscriber Identity) is a unique code assigned to each mobile subscriber. It is used to identify users in the mobile network and control network access.

What information does the IMSI code contain?
The IMSI contains information about the country, the network operator and the individual subscriber identification.

Where can I find the IMSI SIM number?
The IMSI number is stored on the SIM card and used by the mobile device in the background, although it is generally not visible directly on the SIM card.

Is IMEI the same as IMSI?
No, the IMEI identifies the mobile device, while the IMSI identifies the mobile subscriber device within the network. Both numbers serve different purposes.

What is the IMSI format?
The 15-digit IMSI number is divided into three parts: the Mobile Country Code (MCC), the Mobile Network Code (MNC) and the Mobile Subscriber Identification Number (MSIN).