GPRS technology tutorial
a summary or tutorial describing GPRS, the General Packet Radio Service,
the technology used to provide higher speed data over the GSM cellular
telecommunications network.
GSM was the most successful second generation cellular
technology, but the need for higher data rates spawned new developments to
enable data to be transferred at much higher rates. The first system to make an
impact on the market was GPRS. The letters GPRS stand for General Packet Radio
System, and this cellular technology enables much higher data rates to be
achieved.
GPRS became the first stepping-stone on the path between the
second-generation GSM cellular technology and the 3G W-CDMA / UMTS system. With
GPRS offering data services with data rates up to 115 kbps, facilities such as
web browsing and other services requiring data transfer became possible.
Although some data could be transferred using GSM, the rate was too slow for
real data applications.
GPRS and packet switching
The key element of GPRS is that it uses packet switched data
rather than circuit switched data, and this technique makes much more efficient
use of the available capacity. This is because most data transfer occurs in what
is often termed a "bursty" fashion. The transfer occurs in short peaks, followed
by breaks when there is little or no activity.
Using a traditional approach a circuit is switched
permanently to a particular user. This is known as a circuit switched mode. In
view of the bursty nature of data transfer it means that there are periods when
it will not be carrying data.
To improve the situation the overall capacity can be shared
between several users. To achieve this the data is split into packets and tags
inserted into the packet to provide the destination address. Packets from
several sources can then be transmitted over the link. As it is unlikely that
the data burst for different users will occur all at the same time, by sharing
the overall resource in this fashion, the channel, or combined channels can be
used far more efficiently. This approach is known as packet switching, and it is
at the core of many cellular data systems, and in this case GPRS.
GPRS network
GPRS and GSM are able to operate alongside one another on the
same network, and using the same base stations. However upgrades are needed. The
network upgrades reflect many of those needed for 3G, and in this way the
investment in converting a network for GPRS prepares the core infrastructure for
later evolution to a 3G W-CDMA / UMTS.
The upgraded network, as described in later pages of this
tutorial, has both the elements used for GSM as well as new entities that are
used for the GPRS packet data service.
GPRS mobiles
Not only does the network need to be upgraded for GPRS, but
new GPRS mobiles are also required. It is not possible to upgrade an existing
GSM mobile for use as a GPRS mobile, although GSM mobiles can be used for GSM
speech on a network that also carries GPRS. To utilise GPRS new modes are
required to enable it to transmit the data in the required format.
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