What is the IMEI Number? Learn about IMEISV and IMEI Check.

The IMEI number is a globally unique identifier used by the device manufacturer and network operators. This is useful for updating software, tracking, and blocking or allowing a phone.

Know all about the IMEI number.

The IMEI number is a 15-digit unique identifier assigned to each device by its manufacturer. Its full form is International Mobile Equipment Identity. At any time, a device manufacturer can obtain information about the device by looking at the IMEI number, such as the year, model number, and so on.

What is an IMEI Number
What is an IMEI Number

IMEI number and SIM card:

A cellphone is also an electronic device that has an IMEI number. A phone requires a SIM card to get voice, data, and SMS services.

An IMSI number uniquely identifies each sim card in cellular communication, while the mobile device into which the sim is inserted is uniquely identified by an IMEI number.

When a mobile subscriber replaces a sim card, only the IMSI changes and the device’s IMEI remains unchanged. This tutorial will discuss the IMEI and how a cellular network uses this unique Identity in 3G and 4G.

How to get IMEI information?

There are various ways to get IMI details. In a basic way, the number can be obtained from the device itself. E.g., for a smartphone (Android), in the settings of the mobile phone (Samsung Galaxy S8 Settings->About phone->Status->IMEI Information) or by dialing a code (e.g., *#06#). The code works on all devices.

Why IMEI is important?

A mobile device can only communicate with a mobile operator with a valid hardware identity. It is used to allow or disallow devices in the event of theft or for technical reasons. The information on the device is not supposed to change once it is embedded.

What is the structure of an IMEI number?

It is fifteen digit long value. The digits are segmented. Each group of digits in the IMEI structure represents unique information. The structure is constructed in such a way that the manufacturer of the device and other details can be determined by looking at the number.

IMEI Structure Format

The number is divided into the following parts:

What is a Type Allocation Code (TAC code)?

This is a unique eight-digit code. The manufacturer requests a TAC code for a new device model from the international GSM standard body. The TAC code is divided into two sub-sections, one is two digits long, and another is six digits.  AA BBBBBB is the format,

  1. AA –  Allocation Body
  2. BBBBBB – Manufacture’s code e.g Apple Company for iPhone has its own code.

What is Serial Number (SNR)?

This is a six-digit number. Within a TAC, each serial number uniquely identifies a device. The manufacturer controls the serial number range. When a new IMEI needs to assign a device, the manufacturer allocates and reserves a new serial number from the range. As an outcome, each device will get a unique identity globally.

What is the Check Digit for the IMEI number verification?

This is the final component of the IMEI with a single-digit value. A check digit is calculated from the values of other (TAC and SNR) digits using a formula. An IMEI number check process utilizes the check digit to ensure that the IMEI has not been altered in any way.

The Luhn Algorithm verifies the IMEI’s integrity on the network. The receiving entity recalculates the check digit and compares it against the check digit received. The check is critical because it verifies that the IMEI number is valid and that the device has not been tampered with.

What is IMEIsv Meaning?

It is similar to the IMEI but contains additional information. With a 16-bit value, the first 14 digits are identical to those in the IMEI. The last two digits correspond to the software version. The first 14 digits contain information about the device, while the remaining two contain information about the software version.

How IMEIsv is advantageous over IMEI?

A device requires regular manufacturer and application provider updates to function correctly. One should know the device’s current hardware version to ensure software updates are applied correctly. Version information is required to set up the application and firmware accurately.

What are the possible uses for the IMEI number?

Tracing of a lost phone.

Following a report of a lost mobile device. The police provide the IMEI number to all mobile operators in a country/area to track the phone. Each mobile operator places the device under surveillance by using the IMEI number.

When a new or older SIM card is inserted into a mobile phone, the phone attempts to connect to the roaming network. The roaming network transmits IMEI, IMSI, and MSISDN information to the operator’s backend servers to trace the location.

With MSISDN, location and other activities (voice calls, SMS, etc.) can be traced for a SIM card.

Over the Air(OTA) updates for a device:

Updates by manufacturer:

Occasionally, a manufacturer may require to send firmware and other updates. While sending, device information is necessary to ensure the device receives the correct updates. The IMEI is a unique identifier for each device from which the sender gets the information (type, brand, model, and so on).

Updates by mobile network operator:

While roaming, the carrier may send an update to alter the phone’s settings. IMSI, APN, and other parameters can be modified as a part of the process. The most common example is an OTA update allowing users to switch the IMSI on a multi-IMSI sim card to save money on roaming charges.

An OTA may be triggered to update the IMSI based on the location of a subscriber roaming to ensure that the subscriber uses the most appropriate IMSI for that area. The device receives the appropriate settings or updates if the mobile operator knows the IMEI.

How does a mobile operator allow and disallow a device?

EIR is the central mobile phone database, which has IMEI number status along with IMEI. There may be a central EIR in a country where all roaming mobile operators query a device’s legality. When a call starts, the serving MSC or SGSN sends an IMEI check operation to the EIR, which responds to the MSC. If the response is successful, then the call is completed else. The call is dropped.

IMEI-Check over network:

In 2G or 3G network:

IMEI checks whether a device can register for data or voice calls. This is achieved by using a gsm network node named  Equipment Identity Register (EIR). Represents is a central database of IMEIs in the roaming network. Upon receiving a check request, EIR may return any of the following.

  • Unknown Equipment, When the device is not registered in EIR.
  • White List, When Equipment number is allowed to operate.
  • Blocklist, When the Equipment number is not allowed to operate.
  • Grey List, When the Equipment number is allowed to operate with observation.

When a call is initiated, the MSC does the ss7 signaling using a gsm map protocol to check IMEI.

In the 4G network :

In a 4G network, the Diameter protocol is the underlying protocol. The S13 and S13′ are used in the 4G network over diameter signaling. S13 is used between MME and EIR, and S13 is used between SGSN and EIR. The 3GPP application id is 16777252. 3GPP Spec for S13/S13′
ME identity check procedure is used for identity verification. ME-Identity-Check-Request/Answer (ECR/ECA),  Commands, or messages are used. When a mobile phone tries to register on the network, a ME identity check procedure is used between MME/SGSN and EIR.

< ME-Identity-Check-Request > ::= < Diameter Header: 324, REQ, PXY, 16777252 >
< Session-Id >
[ Vendor-Specific-Application-Id ]
{ Auth-Session-State }
{ Origin-Host }
{ Origin-Realm }
[ Destination-Host ]
{ Destination-Realm }
{ Terminal-Information }
[ User-Name ]
*[ AVP ]
*[ Proxy-Info ]
*[ Route-Record ]

The Terminal Information AVP has ME Identity, and the User name (optional) has IMSI.

< ME-Identity-Check-Answer> ::= < Diameter Header: 324, PXY, 16777252 >
< Session-Id >
[ Vendor-Specific-Application-Id ]
[ Result-Code ]
[ Experimental-Result ]
{ Auth-Session-State }
{ Origin-Host }
{ Origin-Realm }
[ Equipment-Status ]
*[ AVP ]
*[ Failed-AVP ]
*[ Proxy-Info ]
*[ Route-Record ]

If the result code received DIAMETER SUCCESS (2001) from EIR, then Equipment Status AVP has the status (whitelisted, blacklisted, or greylisted) of ME identity status.

Device lock from a mobile operator:

There are phones which mobile operators provide along with their sim cards. These phones work only when a sim card from that mobile operator is used. This check is done by using hardware information obtained from the IMEI number. When a device switches on, the mobile network checks if the IMSI is the device given with the subscription. Then only the device is allowed to register on the network.