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C-MSISDN (Correlation mobile subscriber international ISDN)

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C-MSISDN stands for Correlation mobile subscriber international ISDN. It is a concept used in the telecommunications industry to identify a mobile subscriber's device and map it to its SIM card. In this article, we will discuss what C-MSISDN is, how it works, and its importance in the telecommunications industry.

Mobile Network Operators (MNOs) assign a unique identification number to every mobile subscriber who uses their network. This identification number is called the International Mobile Subscriber Identity (IMSI). It is a 15-digit number that is stored on the Subscriber Identity Module (SIM) card of the mobile device. The IMSI is used by the MNO to identify the subscriber and provide services to them.

However, there are situations where the MNO needs to correlate the mobile subscriber's device with the phone number that they are using. For example, when a subscriber calls customer support, the MNO needs to know which device they are calling from to provide appropriate assistance. This is where the C-MSISDN comes in.

The C-MSISDN is a unique number that is assigned to each mobile device that is registered on an MNO's network. It is a 14-digit number that is derived from the mobile subscriber's phone number and the IMSI of their SIM card. The C-MSISDN is used by the MNO to identify the mobile subscriber's device and map it to their phone number.

The C-MSISDN is composed of the following elements:

  1. Mobile Country Code (MCC): A three-digit number that identifies the country where the mobile network is located.
  2. Mobile Network Code (MNC): A two or three-digit number that identifies the MNO that the mobile device is registered on.
  3. MSISDN: The phone number of the mobile subscriber, which can be up to 15 digits long.
  4. Check Digit: A single digit that is used to validate the C-MSISDN.

To generate a C-MSISDN, the MNO concatenates the MCC, MNC, IMSI, and MSISDN of the mobile subscriber's device. Then, it calculates the check digit using the Luhn algorithm, which is a simple checksum formula that is used to validate credit card numbers, IMEI numbers, and other identification numbers.

The Luhn algorithm works as follows:

  1. Starting from the rightmost digit and moving left, double every second digit. If the result is greater than 9, add the two digits together.
  2. Sum all of the resulting digits.
  3. If the total sum is divisible by 10, then the number is valid.

Once the MNO has generated the C-MSISDN, it stores it in its database along with the mobile subscriber's phone number and IMSI. The C-MSISDN is used by the MNO to identify the mobile subscriber's device and map it to their phone number.

The C-MSISDN is important in the telecommunications industry because it enables MNOs to correlate a mobile subscriber's device with their phone number. This is necessary for providing services such as call forwarding, call barring, and roaming. For example, if a subscriber activates call forwarding, the MNO needs to know which device to forward the calls to. Without the C-MSISDN, the MNO would not be able to identify the subscriber's device and provide this service.

In addition to call forwarding and call barring, the C-MSISDN is also important for mobile number portability (MNP). MNP is the process of transferring a mobile subscriber's phone number from one MNO to another. The C-MSISDN is used to ensure that the subscriber's device is correctly mapped to their phone number during the transfer process.

The C-MSISDN is also used in fraud prevention and detection. For example, if a subscriber reports that their mobile device has been lost or stolen, the MNO can use the C-MSISDN to block the device from accessing the network. This prevents unauthorized use of the subscriber's phone number and helps to prevent fraud.

Another use case for the C-MSISDN is in the implementation of Value-Added Services (VAS). VAS are additional services that are offered by MNOs to mobile subscribers. These services can include things like mobile banking, mobile payments, and mobile advertising. The C-MSISDN is used to identify the subscriber's device and provide access to the appropriate VAS.

Overall, the C-MSISDN is a critical component of the telecommunications industry. It enables MNOs to identify and correlate a mobile subscriber's device with their phone number, which is necessary for providing services such as call forwarding, call barring, and roaming. It is also important for mobile number portability, fraud prevention and detection, and the implementation of Value-Added Services. Without the C-MSISDN, MNOs would not be able to provide these services to their subscribers.

In conclusion, the C-MSISDN is a complex but essential concept in the telecommunications industry. It allows MNOs to identify and correlate a mobile subscriber's device with their phone number, which is necessary for providing services to their subscribers. The C-MSISDN has many use cases, including call forwarding, call barring, roaming, mobile number portability, fraud prevention and detection, and the implementation of Value-Added Services. It is a critical component of the telecommunications infrastructure, and its importance will only continue to grow as mobile technology evolves.