Electronic Serial Number

Electronic Serial Numbers (ESNs) were created by the FCC to uniquely identify mobile devices from the days of AMPS in the United States from the early 1980s. The administrative role was taken over by the Telecommunications Industry Association in 1997. ESNs are mainly used with AMPS, TDMA and CDMA phones in the United States, compared to IMEI numbers used by all GSM phones. [ [http://www.tiaonline.org/standards/resources/esn/index.cfm Electronic Serial Numbers (ESN)] ]

An ESN is 32 bits long. It consists of three fields, including an 8-bit manufacturer code, an 18-bit unique serial number, and 6 bits that were reserved for later use, although in practice these 6 bits have long been combined into a 24-bit serial number field. This format only allowed 256 different manufacturers to be distinguished. Therefore, when it became clear that this would not suffice, a new format was created, with a 14 bit manufacturer code and 18 bit serial number. All recently assigned ESN codes (and all UIMID codes) use this format.

Manufacturer code 0x80 was reserved and now is used to represent pseudo ESNs (pESN) which are calculated from an MEID or EUIMID. Pseudo-ESNs are not guaranteed to be unique.

ESNs are often represented as 11 digit decimal numbers or 8 digit hex numbers. The first three digits are the decimal representation of the first 8 bits (between 000 and 255 inclusive) and the next 8 are derived from the remaining 24 bits and will be between 00000000 and 16777215 inclusive. The decimal format of pseudo ESN's will therefore begin with 128. The decimal format separately displays 8 bit manufacturer codes, but not 14 bit codes.

As ESNs are running out, a new serial number format named Mobile Equipment ID (MEID) has been created. MEIDs are 56 bits long, which is the same length as IMEI and, in fact, MEID was created to be compatible with IMEI. The main difference between MEID and IMEI is that the MEID allows hexadecimal digits while IMEI allows only decimal digits.

The last of the virgin (never before used) ESN codes is expected to be allocated in 2008. Allocation will continue for a short time (likely through 2009) with reclaimed ESN codes, those previously assigned to AMPS or TDMA phones and therefore not present on cdma2000 systems. Reclaimed codes have been used for UIMID assignments for some time. Codes are assigned according to industry guidelines. [ESN Assignment Guidelines and Procedures, Version 1.9c. May 2007. [http://tiaonline.org/standards/resources/esn/documents/ESN_Guidelines_v1.9c.pdf]

Uses for the ESN

Some of the uses for the ESN require uniqueness. With MEID phones this longer identifier should be used instead of the non-unique pseudo-ESN.

# A unique identifier for a cellular phone. It is useful in this role as it is designed to be unchangeable, unlike subscription identifiers which may change. Uses for this include:
## Identifying stolen mobiles even if provisioned with a new subscription identifier.
## For lawful intercept to prove that a particular physical device was used for a call.
## For inventory control.
## For warranty purposes.
## To identify devices with malfunctioning radios.
## For initial provisioning.
# The source for the cdma2000 PLCM (public long code mask) that separates communications.
# Radio interface addressing for a mobile, particularly when a subscription identifier is not available.
# Access probe timing (pseudo-randomly spreads out the delay between access attempts to avoid deadlock under heavy load).
# An input to CAVE authentication.
# Registration timing.
# A unique key for many 'back office' systems.
# ANSI-41 validation (along with MIN or IMSI).

References

External links

* [http://www.tiaonline.org/standards/resources/esn/ Official TIA Resource Page for ESN and UIMID]