IMSI – International Mobile Subscriber Identity [Explained]


IMSI means international mobile subscriber identity which is a 15 digits long unique number, associated with Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) network mobile phone users.

The IMSI number would be a unique identification number for a GSM subscriber. If we talk about IMSI format then it will have two parts as shown below:

  • First part is comprised of 6 digits in the North American standard and 5 digits in the European standard.
  • Second part is allocated by the network operator to uniquely identify the subscriber.

The IMSI is stored in the mobile SIM and is sent by the phone to an appropriate network which later used to acquire the details of the mobile in the Visitor Location Register (VLR) or the Home Location Register (HLR).

IMSI Number, Format, and Catcher

International Mobile Subscriber Identity – IMSI Format, Catcher Explained by FunTecho

When a phone is affiliated, a temporary IMSI is generated and allocated to identify the subscriber in future exchanges. This all embedded in the SIM and is provided anytime the network is accessed. It is transmitted during initialization.

Now to prevent the subscriber from being identified and tracked by mediator on a radio interface, the IMSI is rarely transmitted. A randomly generated temporary mobile subscriber identity (TMSI) is sent instead of the IMSI, to ensure that the identity of the mobile subscriber remains confidential and eliminate the need to transfer it in an unspecified form over radio links.

Generally, IMSI is stored as a 64-bit field in the phone’s SIM. It is associated with a mobile network interconnecting with other mobile networks, especially EVDO, GSM and CDMA networks. The number is directly provisioned in the phone or in the R-UIM card.

IMSI Format

The 3 components within International Mobile Subscriber Identity are mobile country code, mobile network code, and mobile subscriber identification number.

  • The mobile country code has a similar meaning and format to the location area identifier.
  • The mobile network code is assigned by the government of each country.
  • The mobile subscriber identification number identifies the mobile subscriber and is assigned by the operator.

IMSI Catcher

At the point when versatile stations are fueled on, they play out an area update method by demonstrating their IMSI to the organization. The main area update strategy is alluded to as the IMSI join technique. The versatile station likewise performs area refreshing to demonstrate the current area when it moves to another area region.

The area refreshing message is shipped off the new VLR, giving the area data to the endorser’s HLR. Area refreshing is occasionally performed. The versatile station isn’t de registered if after the refreshing time span the portable station isn’t enlisted. The IMSI confine methodology is performed when a versatile station is controlled off to advise the organization that it is not, at this point associated.

So that’s all about International Mobile Subscriber Identity. If you have any question or doubt regarding this, the please let us know in the comment section below and don’t forget to share it with others on social sites.