The International Mobile Equipment Identity (IMEI) is a number, usually unique, to identify 3GPP and iDEN mobile phones, as well as some satellite phones. The IMEI consists of 15 decimal digits: 14 digits plus a check digit while the IMEISV consists of 16 decimal digits: 14 digits plus two software version digits. These numbers includes information on the origin, model, and serial number of the device. The structure of the IMEI/SV is 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.