What is IMEI? (International Mobile Station Equipment Identity)

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What is IMEI?

The International Mobile Station Equipment Identity or IMEI is a number, usually unique,to identify 3GPP (i.e., GSM, UMTS and LTE) and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone, but can also be displayed on-screen on most phones by entering *#06# on the dial-pad, or alongside other system information in the settings menu on smartphone operating systems.

 

The IMEI number is used by a GSM network to identify valid devices and therefore can be used for stopping a stolen phone from accessing that network. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "blacklist" the phone using its IMEI number. This renders the phone useless on that network and sometimes other networks too, whether or not the phone's SIM is changed.

 

The IMEI is only used for identifying 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 that 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.

 

Korean) 
쉽게 이야기 하자면, 핸드폰 기계 자체를 구분짓기 위해 부여하는 ID이다.
Network에서는 초기 Network Attach 시 IMEI를 확인 후 망 접속을 허용할지 거부 할지 결정을 한다.
또한, 기기 ID이기 때문에, 분실 시에도 해당 ID를 확용하여 분실/도난 신고를 할 수 있고, 
기지국에서는 해당 ID 값을 가지고, 해당 폰을 망에 절대 붙일 수 없게 할 수도 있다.
이전에는 SKT 폰에 KT USIM을 넣으면 절대 망에 접속이 되지 않았으나, 현재에는 통신사 기기에 상관없이 USIM만 넣고 몇번 껐다 켜면 핸드폰 터진다.
이게 IMEI를 활용하여, 망에서 구분짓는 것의 하나의 예라고 할 수 있겠다.

 

Structure of the IMEI and IMEISV (IMEI Software Version)

The IMEI (15 decimal digits: 14 digits plus a check digit) or IMEISV (16 digits) includes information on the origin, model, and serial number of the device. The structure of the IMEI/SV are specified in 3GPP TS 23.003. The model and origin comprise the initial 8-digit portion of the IMEI/SV, known as the Type Allocation Code (TAC). The remainder of the IMEI is manufacturer-defined, with a Luhn check digit at the end. For the IMEI format prior to 2003, the GSMA guideline was to have this Check Digit always transmitted to the network as zero. This guideline seems to have disappeared for the format valid from 2003 and onwards.

As of 2004, the format of the IMEI is AA-BBBBBB-CCCCCC-D, although it may not always be displayed this way. The IMEISV drops the Luhn check digit in favour of an additional two digits for the Software Version Number (SVN), making the format AA-BBBBBB-CCCCCC-EE

For example, the old style IMEI code 35-209900-176148-1 or IMEISV code 35-209900-176148-23 tells us the following:
TAC : 35-2099 - issued by the BABT (code 35) with the allocation number 2099
FAC : 00 - indicating the phone was made during the transition period when FACs were being removed.
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. 99 is reserved.

By contrast, the new style IMEI code 49-015420-323751 has a 8-digit TAC of 49-015420.

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

You can check this easier at the below path.

http://www.imei.info/

 

Korea) 
IMEI의 구조는 위에서 보는 것과 같이, TAC + Serial Number + Checksum으로 구성되어 있다.
TAC / Serial Number / Check Sum에 대해서는 위의 정보를 활용하기 바란다.

 

Check digit computation

The last number of the IMEI is a check digit calculated using the Luhn algorithm.

 

According to the IMEI Allocation and Approval Guidelines,

 

The Check Digit shall be calculated according to Luhn formula (ISO/IEC 7812). (See GSM 02.16 / 3GPP 22.016). The Check Digit is a function of all other digits in the IMEI. The Software Version Number (SVN) of a mobile is not included in the calculation.

 

The purpose of the Check Digit is to help guard against the possibility of incorrect entries to the CEIR and EIR equipment.

 

The presentation of the Check Digit both electronically and in printed form on the label and packaging is very important. Logistics (using bar-code reader) and EIR/CEIR administration cannot use the Check Digit unless it is printed outside of the packaging, and on the ME IMEI/Type Accreditation label.

 

The check digit is not transmitted over the radio interface, nor is it stored in the EIR database at any point. Therefore, all references to the last three or six digits of an IMEI refer to the actual IMEI number, to which the check digit does not belong.

 

The check digit is validated in three steps:

 

Starting from the right, double every other digit (e.g., 7 → 14).

Sum the digits (e.g., 14 → 1 + 4).

Check if the sum is divisible by 10.

Conversely, one can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. For the example IMEI 49015420323751?,

 

 

You can calculate it easier at the below path.

http://www.imei.info/calc

Korea )

위의 설명을 보면 어떠한 방식으로 Check Sum을 계산하는지 한눈에 알 수 있다.

근데, 솔직히 누가 일일이 계산하고 있겠나?

위의 사이트에 들어가면 자동으로 계산을 해주고 있다.

사용자가 할 일은 거의 없을거 같지만,,,, 개발자라면 필요한 내용 중에 하나이다.

 

 

 

Refer : http://en.wikipedia.org/wiki/International_Mobile_Station_Equipment_Identity