GSM - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 274

cell towers or to telephones. Although most people think of SMS messages as
“I will be 20 minutes late,” they are also an efi cient way of warning people in
case of an emergency, and for publicity, taxi reservations, payment systems,
or even for proprietary inter-application communication. The number of SMS
messages range in the billions per year, and although their use is slowly declin-
ing in favor of other messaging systems, in 2013, an estimated 145 billion SMS
messages were sent.
SMS is not the only data transfer technique used by the GSM network; two
other major systems exist.
GPRS
GPRS, short for General Packet Radio Service, is a packet-based data exchange
technique. Although most GSM connections were circuit-switched (meaning
that a connection was established and then terminated when the connection
was cut), GPRS introduced a packet-switching technique, allowing operators to
charge clients by the quantity of data used, and not the time spent transferring
data. GPRS is an extension to the GPS 2 G technology, and as such, is often known
as 2.5 G. This technology allows theoretical speeds of up to 50 Kbit/s, but true
throughput is often limited at 40 Kbit/s.
EDGE
EDGE, short for Enhanced Data rates for GSM Evolution, is an enhancement
over the previous GPRS data connection method. With a theoretical max speed
of 250 Kbit/s, this norm was soon called 2.75 G by mobile telephone owners. It is
still used today as a fallback when other high-speed networks are not available.
3 G
The third generation of mobile networks is a large change from the previous 2
G, and is not compatible with the older systems, but remains a fallback technol-
ogy for current telephones. 3 G allows for higher data speeds than previous
standards, ranging from 2 Mbit/s all the way to 28 Mbit/s.
The 3 G standard was created by the International Telecommunication Union,
which is not the same as the GSM committee. 3 G mobile devices can use the
2 G network, but 2 G devices cannot connect to 3 G networks. They must use
the older 2 G network, forcing operators to have several systems in place on
the same tower.