Cell phones get a bigger ID space
Industry shifting to 56-bit identifiers as ESN pool runs out of numbers
- By William Jackson
- May 29, 2008
SERVICE PROVIDERS and
manufacturers of wireless phones
are in the middle of their own
version of the data world's move
from IPv4 to IPv6.
Since the 1980s, a 32-bit electronic
serial number (ESN)
has been a unique hardware
identifier in U.S. Code
Division Multiple Access
(CDMA) cell phones, and a
similar User Identity Module ID
(UIM-ID) has identified phones
using Removal User Identity
Modules. But decades of explosive
growth in mobile telephony
have eaten away at the 4 billionnumber
reservoir of ESNs.
'CDMA started early with a relatively
small numbering space,'
said Andrew Kurtzman, corporate
counsel at the Telecommunications
(TIA), which has administered
ESNs since 1997. 'It was doomed
to run out, as all numbering systems
Efforts by TIA to recover unused
numbers and dole them out
to manufacturers has postponed
the inevitable for several years,
but the ESN pool is expected to
be exhausted sometime this year.
To replace it, the industry is
shifting to a 56-bit Mobile
Equipment Identifier (MEID)
and a similar Expanded UIM-ID.
The 56-bit numbering space is
dramatically larger, Kurtzman
said. It is 62,500 times larger
than the ESN space, enough to
provide 256 trillion unique IDs
for mobile wireless telephone
Industry has been phasing in
the new numbering scheme since
2006, but network equipment
vendors and service providers
must upgrade networks and back
offices to use the new MEID before
ESN is exhausted.
'Unfortunately, the progress
of migration to MEID and
E-UIM-ID has been slower than
expected,' said the CDMA Development
Group, an industry
organization spearheading the
transition. 'At the current rate, it
is likely that ESNs and UIM-IDs
will be completely depleted during
2008, possibly before all networks
are capable of fully supporting
MEID and E-UIM-ID
The problem is not critical in
the United States, where the
major wireless carriers have made
the transition, Kurtzman said. 'In
the [United States], Verizon and
Sprint are done. There is no issue
The Federal Communications
Commission administered global
ESN pool assignments until turning
the task over to TIA in 1997.
The numbers are intended to
be difficult to change in the field
and are transmitted when a call
is made from a cell phone so it
can be identified by the network
and the service provider for
billing and service provisioning.
'It makes the handset unique
on the network," Kurtzman said.
'They can say, 'We know who
owns it, and we will allow it to
Cloning a cell phone ' reprogramming
it to transmit the ESN
and carrier's identification number
of another phone to steal
service from another account '
is fraud under the Communications
Telephone Protection acts.
The MEID is burned into
a chip, making it more difficult
TIA has been working to recover
unused ESNs from manufacturers
so they can be reissued, but
the task is tedious and relatively
unproductive. 'The successful efforts
yield minimal unused code,'
the organization said. At the
same time, the number of new
phones and subscribers is growing
by hundreds of millions each
During the transition from ESN
to MEID, a pseudo-ESN can be
used to provide service to an
MEID phone on a network not
yet equipped to handle MEID.
Pseudo-ESNs are produced by
using a hashing algorithm to reduce
the 56-bit MEID to a 24-bit
ESN, to which the first 8 bits of
the MEID are added. This produces
a 32-bit number that can
be processed by an ESN network
for backward compatibility, but
the pseudo-ESN is not unique.
Although collisions are unlikely,
they could occur.
William Jackson is freelance writer and the author of the CyberEye blog.