International Mobile Equipment Identity

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The International Mobile Equipment Identity (IMEI) is a number unique to every GSM and UMTS mobile phone. It is usually found printed on the phone underneath the battery and can also be found by dialing the sequence *#06# into the phone.

The IMEI number is used by the GSM network to identify valid devices and therefore can be used to stop a stolen phone from accessing the network. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "ban" the phone using its IMEI number. This renders the phone useless, regardless of whether the phone's SIM is changed.

Unlike the Electronic Serial Number or MEID of CDMA and other wireless networks, the IMEI is only used to identify the device, and has no permanent or semi-permanent relation to the subscriber. Instead, the subscriber is identified by transmission of an IMSI number, which is stored on a SIM card which can (in theory) be transferred to any handset. However, many network and security features are enabled by knowing the current device being used by a subscriber.

Contents

[edit] Structure of the IMEI

The IMEI is a 15 or 17 digit number which includes information on the origin, model, and serial number of the device. The structure of the IMEI is specified in 3GPP TS 23.003. The model and origin comprise the initial 8-digit portion of the IMEI, known as the Type Allocation Code (TAC). The remainder of the IMEI is manufacturer-defined, with a Luhn check digit at the end (which is never transmitted).

As of 2004, the format of the IMEI is AA-BBBBBB-CCCCCC-D, although it may not always be displayed this way. This table explains what each part of the 15 digit IMEI is. Note that a 17 digit IMEI includes an additional 2 digits for the software revision in the format AA-BBBBBB-CCCCCC-D-EE

AA BBBBBB CCCCCC D
Reporting Body Identifier, indicating the GSMA-approved group that allocated the model TAC The remainder of the TAC Serial sequence of the model Luhn check digit of the entire number (or zero)

Prior to 2002, the TAC was 6 digits long and followed by a two-digit Final Assembly Code (FAC), which was a manufacturer-specific code indicating the location of the device's construction.

For example the code 35-209900-176148-1-23 tells us the following:
TAC: 352099 so it was issued by the BABT and has the allocation number 2099
FAC: 00 so it was numbered during the transition phase from the old format to the new format (described below)
SNR: 176148 - uniquely identifying a unit of this model
CD: 1 so it is a GSM Phase 2 or higher
SVN: 23 - The 'software version number' identifying the revision of the software installed on the phone.

The format changed from April 1, 2004 when the Final Assembly Code ceased to exist and the Type Approval Code increases to eight digits in length and became known as the Type Allocation Code. From January 1, 2003 until this time the FAC for all phones was 00.

The Reporting Body Identifier is allocated by the Global Decimal Administrator; the first two digits must be decimal (ie less than 0xA0) for it to be an IMEI and not an MEID.

The new CDMA Mobile Equipment Identifier (MEID) uses the same basic format as the IMEI.

[edit] Retrieving IMEI information from a GSM device

On many devices the IMEI number can be retrieved by entering *#06#. The IMEI number of a GSM device can be retrieved by sending the command AT+CGSN. For more information refer the 3GPP TS 27.007, Section 5.4 /2/ standards document.

Retrieving IMEI Information from a Sony Ericsson handset can be done by entering these keys: Right * Left Left * Left * Left (Other service menu items will be presented with this key combination.)

The IMEI can frequently be displayed through phone menus, under a section titled 'System Information', 'Device', 'Phone Info' or similar. Many phones also have the IMEI listed on a label in the battery compartment.

[edit] IMEI and the law

Many countries have acknowledged the use of the IMEI in reducing the effect of mobile phone theft, which has increased exponentially over the last few years[citation needed]. For example, in the United Kingdom under the Mobile Telephones (Re-programming) Act, changing the IMEI of a phone, or possessing equipment that can change it, is considered an offence under some circumstances.

There is a misunderstanding amongst some regulators that the existence of a formally allocated IMEI number range to a GSM terminal implies that the terminal is approved or complies with regulatory requirements. This is not the case. The linkage between regulatory approval and IMEI allocation was removed in April 2000 with the introduction of the European R&TTE Directive. Since that date, IMEIs have been allocated by BABT (acting on behalf of the GSM Association) to legitimate GSM terminal manufacturers without the need to provide evidence of approval.

[edit] Blacklist of stolen devices

When mobile equipment is stolen or lost, the operator or owner will typically contact the Central Equipment Identity Register (CEIR) which blacklists the device in all operator switches so that it will in effect become unusable, making theft of mobile equipment a useless business.

The IMEI number is not supposed to be easy to change, making the CEIR blacklisting effective. However this is not always the case: IMEI may be easy to change with special tools and operators may even flatly ignore the CEIR blacklist.

[edit] Difficulties

  • "New IMEIs can be programmed into stolen handsets and 10% of IMEIs are not unique." According to a BT-Cellnet spokesman quoted by the BBC. [1]
  • Facilities do not exist to unblock numbers listed in error on all networks. This is possible in the UK, however, where the user who initially blocked the IMEI must quote a password chosen at the time the block was applied.

[edit] See also

[edit] External links

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