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In cellular service there are two main
competing network technologies: Global
System for Mobile Communications (GSM)
and Code Division Multiple Access (CDMA).
Cellular carriers including Sprint PCS,
AT&T Wireless, Verizon and T-Mobile
use one or the other. Understanding the
difference between GSM and CDMA will
allow you to choose a carrier that uses
the preferable network technology for
your needs.
The GSM Association is an international
organization founded in 1987, dedicated
to providing, developing, and overseeing
the worldwide wireless standard of GSM.
CDMA, a proprietary standard designed by
Qualcomm in the United States, has been
the dominant network standard for North
America and parts of Asia. However, GSM
networks continue to make inroads in the
United States, as CDMA networks make
progress in other parts of the world.
There are camps on both sides that
firmly believe either GSM or CDMA
architecture is superior to the other.
That said, to the non-invested consumer
who simply wants bottom line information
to make a choice, the following
considerations may be helpful.
Coverage: The most important factor is
getting service in the areas you will be
using your phone. Upon viewing
competitors' coverage maps you may
discover that only GSM or CDMA carriers
offer cellular service in your area. If
so, there is no decision to be made, but
most people will find that they do have
a choice.
Data Transfer Speed: With the advent of
cellular phones doing double and triple
duty as streaming video devices, podcast
receivers and email devices, speed is
important to those who use the phone for
more than making calls. CDMA has been
traditionally faster than GSM, though
both technologies continue to rapidly
leapfrog along this path. Both boast
"3G" standards, or 3rd generation
technologies.
EVDO, also known as CDMA2000, is CDMA's
answer to the need for speed with a
downstream rate of about 2 megabits per
second, though some reports suggest real
world speeds are closer to 300-700
kilobits per second (kbps). This is
comparable to basic DSL. As of fall
2005, EVDO is in the process of being
deployed. It is not available everywhere
and requires a phone that is CDMA2000
ready.
GSM's answer is EDGE (Enhanced Data
Rates for GSM Evolution), which boasts
data rates of up to 384 kbps with real
world speeds reported closer to 70-140
kbps. With added technologies still in
the works that include UMTS (Universal
Mobile Telephone Standard) and HSDPA
(High Speed Downlink Packet Access),
speeds reportedly increase to about
275—380 kbps. This technology is also
known as W-CDMA, but is incompatible
with CDMA networks. An EDGE-ready phone
is required.
In the case of EVDO, theoretical high
traffic can degrade speed and
performance, while the EDGE network is
more susceptible to interference. Both
require being within close range of a
cell to get the best speeds, while
performance decreases with distance.
Subscriber Identity Module (SIM) cards:
In the United States only GSM phones use
SIM cards. The removable SIM card allows
phones to be instantly activated,
interchanged, swapped out and upgraded,
all without carrier intervention. The
SIM itself is tied to the network,
rather than the actual phone. Phones
that are card-enabled can be used with
any GSM carrier.
The CDMA equivalent, a R-UIM card, is
only available in parts of Asia but
remains on the horizon for the U.S.
market. CDMA carriers in the U.S.
require proprietary handsets that are
linked to one carrier only and are not
card-enabled. To upgrade a CDMA phone,
the carrier must deactivate the old
phone then activate the new one. The old
phone becomes useless.
Roaming: For the most part, both
networks have fairly concentrated
coverage in major cities and along major
highways. GSM carriers, however, have
roaming contracts with other GSM
carriers, allowing wider coverage of
more rural areas, generally speaking,
often without roaming charges to the
customer. CDMA networks may not cover
rural areas as well as GSM carriers, and
though they may contract with GSM cells
for roaming in more rural areas, the
charge to the customer will generally be
significantly higher.
International Roaming: If you need to
make calls to other countries, a GSM
carrier can offer international roaming,
as GSM networks dominate the world
market. If you travel to other countries
you can even use your GSM cell phone
abroad, providing it is a quad-band
phone (850/900/1800/1900 MHz). By
purchasing a SIM card with minutes and a
local number in the country you are
visiting, you can make calls against the
card to save yourself international
roaming charges from your carrier back
home. CDMA phones that are not
card-enabled do not have this
capability.
According CDG.org, CDMA networks support
over 270 million subscribers worldwide,
while GSM.org tallies up their score at
over 1 billion. As CDMA phones become R-UIM
enabled and roaming contracts between
networks improve, integration of the
standards might eventually make
differences all but transparent to the
consumer.
The chief GSM carriers in the United
States are AT&T Wireless, recently
merged with AT&T Wireless, and T-Mobile
USA. Major CDMA carriers are Sprint PCS,
Verizon and Virgin Mobile. There are
also several smaller cellular companies
on both networks.
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