GPRS technology tutorial [1]

- 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 telecommunications system, 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 the system enables much higher data rates to be achieved.

GPRS became the first stepping-stone on the path between the second-generation GSM cell phone system and the 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.

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.

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.

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.

Further pages of this tutorial
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