Historically data speeds on mobile phones has been very very slow, in fact when modems were @ 56kbps (dial up) the mobile was still at 9.6kbps and it stayed there for quite some time, in fact if you don't have GPRS or a high speed data service and use wap you'll be using a 9,6k dial up connection.
The arrival of GSM technology gave the chance for a different type of data connection one where data is moved in packets, IP data is already packetised and bytes of info are sent all round the world in this form everyday
GSM networks are made up of a number of transmitters or cells each of these can have a range of a few kilometres or just a few hundred meters depending on their proximity to each other, the range of frequencies used by each transmitter cannot overlap with its neighbour. In the UK 2 main GSM frequency sets are used GSM 900 and 1800 (1900) is used in the USA, a transmitter will work within a 200mhz band and split this up into a number of radio channels or time slots.
The GPRS system may not be allowed to use them all, but dependant on the class of GPRS network the operator is running the mobile device may connect to multiple channels to achieve a greater bandwidth. Also the coding schemes shown below can effect the bandwidth systems will drop to a lower coding system (CS-1) if the radio reception is poor as it includes higher error correction much like an FM radio might switch to mono if the stereo signal get too weak.
GPRS sits on top of this GSM technology and mobile service providers can offer the general packet radio service to its subscribers as an always on connection rather than the traditional dial up data connections.
Cells that have been upgraded to GPRS add a packet control unit that distributes data over one of the radio channels to your device and also GPRS gateways or nodes these bridge the data between the mobiles network and the outside world or internet. The packetsied nature of GPRS data allows networks to dynamically fill the unused voice channels with GPRS data, providers normally allocate a minimum bandwidth to GPRS data but at off peak times you can get much more throughput perhaps 4 times as much. Lets not forget this is a far more efficient way of delivering data from the network providers as they no longer need to use a whole voice channel to deliver data GPRS users effectively buy the left overs from voice users.
So what are the benefits of GPRS to the user?
For a start its always on, the mobile device will gain an IP address from the DHCP pool available at each cell, the network will then allow you to exchange data whenever you need to without having to dial up an authenticate. Practical uses of this allow for swift recovery of email with frequent pop3 checks of your mailbox and messenger style applications can work on GPRS too so having MSN on your mobile is possible, although Symbian messenger and other 3rd party applications are far more common.
Of course there is the much vaunted benefit of speed, while GPRS theoretically could deliver 172.2kbps by using all 8 timeslots without any error correction in practice network configurations will allow up to 40kbps which is a 4 fold increase on the 9.6kbps still offered as a data service.
Then there are the rich media applications which while publicised by 3G providers are equally at home on a 2 or 2.5g GPRS enabled platform, very little content on the 3G networks is streamed it is far more likely to be downloaded to the phone and then viewed.
So despite the higher speeds of 3G the current GPRS services are enabling video to mobile application to operate successfully at least once you get past the fact that each network has differing video standards!
Applications that work well on GPRS are those that fall into the category "I want it now" that can quite easily be email or the latest goal scored by your team, but this can also extend to web browsing on a long train journey or Navigation applications. In fact a real life example is the ability of LP to manage the technical parameters of this site and view live statistics via his GPRS enabled P800.
GPRS technology will continue to evolve, but now it is driven by users rather than a government frequency auction so we should see more and more useable applications and cheaper access packages.
source : http://www.lordpercy.com
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