what is esn

Electronic serial number - Wikipedia, the free encyclopedia


** Electronic serial number **

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*Electronic serial numbers* (*ESNs*) were created by the U.S. Federal
Communications Commission (FCC) to uniquely identify mobile devices, from
the days of AMPS in the United States starting in the early 1980s. The
administrative role was taken over by the Telecommunications Industry
Association in 1997 and is still maintained by them. ESNs are currently
mainly used with CDMA phones (and were previously used by AMPS and TDMA
phones), compared to International Mobile Equipment Identity (IMEI) numbers
used by all GSM phones.^[1]

The first 8 bits of the ESN was originally the manufacturer code, leaving
24 bits for the manufacturer to assign up to 16,777,215 codes to mobiles.
To allow more than 256 manufacturers to be identified the manufacturer code
was extended to 14 bits, leaving 18 bits for the manufacturer to assign up
to 262,144 codes. Manufacturer code 0x80 is reserved from assignment and is
used instead as an 8-bit prefix for pseudo-ESNs (pESN). The remaining 24
bits are the least significant bits of the SHA-1 hash of a mobile equipment
identifier (MEID). Pseudo-ESNs are not guaranteed to be unique (the MEID is
the unique identifier if the phone has a pseudo-ESN).

ESNs are often represented as either 11-digit decimal numbers or 8 digit
hexadecimal numbers. For the decimal format the first three digits are the
decimal representation of the first 8 bits (between 000 and 255 inclusive)
and the next 8 digits are derived from the remaining 24 bits and will be
between 00000000 and 16777215 inclusive. The decimal format of pseudo ESNs
will therefore begin with 128. The decimal format separately displays 8 bit
manufacturer codes in the first 3


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