What Is IMEI Number Used For: New IMEI Structure

05.10.2015

What is IMEI number today? We told you about the historical structure of IMEI numbers used as unique identifiers for mobile devices from across the world. The whole history of these codes can be divided into two main periods: before 2002 and from 2003. Let’s continue our story devoted to ‘Everything about IMEI’ that will help you to learn more about your smartphone identifier valid nowadays.

A lot of Apple fans are asking ‘What is IMEI iPhone number?’ – when it comes to unlocking or checking information about the smartphone. Every mobile device in the world has this number. IMEI stands for International Mobile Equipment Identify code. Every Mobile Equipment [ME] has its unique IMEI. Through them it is possible to control your access to networks, block access etc. So what is IMEI number used for? It identifies your device in the huge system with millions and millions of other gadgets. This code is controlled by Type Allocation Holder and Reporting Body [we talked about these terms in our previous post about IMEI TAC and FAC components].

IMEI Details FAC TAC Code

Modern IMEI Structure

IMEI-Structure-New

TAC Type Allocation Code, formerly known as Type Approval Code
NN Reporting Body Identifier
XXXXYY ME Type Identifier defined by the Reporting Body
ZZZZZZ Allocated by the Reporting Body but assigned per ME by the manufacturer
A Check digit, defined as a function of all other IMEI digits


Each modern IMEI has a 15-digit number with digits ranging from 0 to 9 that are coded as binary coded decimal. Our current IMEI format is used from January 1st, 2003. This is the date when the older format was changed to the following formula: NN XXXXYY ZZZZZZ A What do parts of this new IMEI structure mean to ordinary users? Everything is not that complicated.

8-digit TAC Code

TAC Code standedfor Type Approval Code however beginning from 2003 it is called Type Allocation Code. This is the 8-digit number.

It is worth to note that there are some allocation principles that always refer to any IMEI number:

  • One ME Type can get several TACs allocated to it. This happens when the company needs the permission to produce more than one million devices. It can also be done to help distinguish between different market versions of gadgets.
  • When the ME Type has more than one Type Allocation Holder – its TAC code must be different.
  • Every ME Type has either one unique TAC code or a set of unique TAC codes.
  • Each TAC code has to be unique and indentify the ME Type.

TAC’s first part is a 2-digit acronym NN that is now a part of IMEI TAC number. NN or Reporting Body Indentifiers is a 2-digit part of the TAC code. It identifies the Reporting Body that issued the IMEI number. The allocation of the NN part that is issued by Reporting Bodies is coordinated by the GSM Association.

Here are the main allocation principles that refer to IMEI numbers:

  • The Reporting Body Identifier has to be unique and uniquely identify the Reporting Body.
  • The allocation of the Reporting Body identifier is coordinated by the GSM Association.
  • Sometimes it is necessary to use the same Reporting Body Identifier and when it happens it is important that the ME Type Identifier also defines the Reporting Body. It is better to avoide such approach but when for any resons it must be used – the GSM Association has to coordinate how the Reporting Body is allocated and use the range of values of the first digit of the ME Type Identifier.

TAC’s second part XXXXYY is used to define the ME Type. XXXXYY is the ME Type Identifier that consists of 6 digits. This part of the TAC code is controlled by the Reporting Body.

The Reporting body 2-digit identifier (NN) + the ME Type 6-digit Identifier (XXXXYY) are both used to identify each ME Type.

Here are the main allocation principles that are used for ME Type:

  • Each ME Type has set of TACs or one unique TAC code. While one ME Type can get more than one TAC, one TAC code must not be related to more than one ME Type.
  • If it is possible, each ME Type Identifier has to be allocated sequentially. It is necessary to avoid gaps in the ME Type range [if this is possible].
  • The new ME Type Indetifier or TAC code is required for each ME Build Level with major changes. This can include new major options and features added to the ME Build Level. It can also include the big changes that actually modify the ME Type performance. If the changes added to the ME Build Level are not major and don’t change the ME performance – it doesn’t need a new ME Type Identifier (TAC code). It is the responsibility of the Reporting Body to determine the minor / major changes added to the ME Build Level.
  • The two digits (YY) were changed to 00 between 01/01/03 and 31/03/04 which was the changeover period.
  • The four-digit part (XXXX) was allocated sequentially by Reporting Bodies between 01/01/03 and 31/03/04 [thus the TAC number that was allocated after NN123400 was NN 123500 etc.]. Starting from April 1st, 2004 the two-digits YY are incremented sequentially.
  • Multimode / Multiband ME is required to have one TAC code and one IMEI number. If the IMEI is allocated by more than one Reporting Body, the Reporting Bodies have to coordinate their actions and make sure that the IMEI allocated by them meets all the requirements.

The SNR or Serial Number is the 6-digit ZZZZZZ number that indentifies every ME or a particular ME Type and is unique.

While the device manufacturer can assign the number range to its individual mobile stations, this number range must be allocated by the Reporting Body. Here are the main allocation principles:

  • Every ME of each METype has a unique Serial Number for its TAC code.
  • It is necessary to allocate Serial Numbers sequentially (if possible).
  • The Reporting Body can allocate a partial range for the Serial Number in special situations, for example, when the product has low volume.

Check Digit A is 1-digit number. It is calculated using the Luhn formula (ISO / IEC 7812). It’s a function of all the digits used in the IMEI number. It is worth to note that SVN [or Software Version Number] doesn’t participate in the calculation.

The Check Digit is created to help avoid using incorrect entries to the EIR and CEIR equipment. It is highly important to use the CheckDigit in the product label, packaging and electronically. EIR and CEIR administration and logistics (that use the bar-code reader) must not use the Check Digit number if it is not printed outside of the packaging and on the ME IMEI / Type Accreditation label.

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