The equipment identity register( EIR) is a component of the switching subsystem( SSS) in GSM networks. The International Mobile Equipment Identities( IMEI) of the mobile stations are registered in this database, and in the event of defective devices, or devices that have been reported stolen or lost, the connection to and from these devices is prevented.
Each GSM terminal has its own device number, which is fixed by hardware and cannot be changed. When requested, the terminal sends the device number to the network; the network compares it with the number stored in the device database (EIR). If the two numbers do not match, network access can be blocked.
Three different lists are maintained in the device database: a white list for approved terminal devices, a gray list for faulty obsolete devices, and a black list for lost and blocked terminal devices.