What on earth is? GPRS

If you go down to the mobile phone shop today you're in for a big surprise. No sooner has the Wap bubble deflated (it never really got big enough to burst) than retailers are preparing an onslaught of hype for the latest, this-time-it-really-is-the-greatest technology, GPRS.

Short for General Packet Radio Service, GPRS is just one of many fancy-sounding abbreviations that mobile phone buyers will have to contend with over the coming months and years, but will it be another much-hyped flop?

GPRS is a data-transport technology. If that's got you befuddled already, then simply know that a GPRS-enabled mobile phone won't give you clearer voice calls reception or wider network coverage.

In fact, all things being equal, the only advantage GPRS phones have over current mobile handsets is an ability to receive electronic information like emails and access Wap sites much more quickly.

While it might take a traditional mobile, say, 10 seconds to download and display a Wap site, a GPRS handset will finish the same job in a fraction of the time.

The upshot is that, unless you become a regular user of mobile data services, GPRS is unlikely to hold much appeal. Even so, you can bet the value of your monthly statements that network operators - the BT Cellnets and Vodafones of this world - will work hand-in-hand with retailers to extol the technology's limited virtues to all and indifferent sundry.

The reason behind the big GPRS push is, almost inevitably, financial: there's money to be made in the provision of data services. However, airtime providers have to think creatively when it comes to billing.

GPRS is an 'always-on' technology, meaning that the network is ready to deliver data to your phone at any time, without delay. In order to profit from this, companies charge for each byte of data downloaded, on top of existing tariffs, like monthly or pay-as-you-go plans. BT Cellnet, for example, charges 2p for each kilobyte of data delivered to a GPRS handset, plus a monthly fee for the service.

The science

To upgrade existing GSM networks to cope with GPRS requires hardware and software additions. Base-station controllers (computers that handle the workings of every antenna making up the network) are given new software to enable them to detect whether a mobile device is GSM or GPRS.

Serving GPRS Support Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs) are also installed. Again, these are powerful computers and they work together to provide mobile devices with a gateway to the internet. SGSNs track the movement of the connected mobile phone across the network while GGSNs deal with data requests and delivery.

A GGSN's specific job is to prepare electronic information for transport over GPRS. The data for a requested web page, for example, is received first by a GGSN computer. Here, it is broken up into pieces (packets) before being broadcast over the mobile airwaves.

Elsewhere, a technique known as time-division duplexing effectively allows GPRS-enabled phones to send and receive data at the same time.

The basics

Although GPRS uses existing mobile telephone networks, it handles data in a different way to GSM. Traditionally, GSM phone connections are made using 'circuit switching'. When a person places a mobile call, a very small part of the network's available capacity is reserved solely for the duration of that call.

If you've ever received a "network busy" message when trying to dial a number, it's because there are no free 'slots' available - the network's caller allocation is full at this time.

Rather than block off chunks of the network capacity, information destined for a GPRS mobile phone is chopped up into packets. Each packet is given electronic directions for its journey and travels independently of others across any available part of the network (the internet also uses packet switching, incidentally). The phone then collects pieces of the incoming data puzzle, reassembling them when the final packet arrives.

Since the packets are broadcast over a wide range of radio frequencies, as opposed to the tiny fraction that current mobile phone circuit-switching technology uses, much more data can be sent and subsequently received. The upshot is that much faster data transfer rates are achievable - up to a theoretical maximum of 171Kbit/s.

Why you need to know about it

It's important to understand that everyone in the industry, from the networks down to the High Street retailers, views GPRS as a technological halfway house. Existing GSM data-transfer rates of up to 14.4Kbit/s are simply too slow for the provision of useful information services, but so-called third-generation (3G) phone-mast networks, which will deliver vastly improved connection speeds, are still years away from completion.

GPRS is a stopgap for 3G. Indeed, industry types often refer it to as '2.5G'. The technology piggybacks on existing networks and provides much faster data delivery, and most major networks around the globe are being upgraded to offer GPRS-delivered services.

However, if you're buying a new phone soon, ignore the sales pitch and ask yourself whether you really need a GPRS handset. Are you a Wap user? Do you use a phone to get your notebook PC hooked up to the internet when you're out and about? If you answer positively then GPRS could well be of benefit. Otherwise, don't bother.

JARGONBUSTER

Byte: A measurement of computer data, equivalent to eight binary bits (ones and zeros). In a text file, for example, each alphanumeric character takes up one byte of storage.

GSM: Global System for Mobile communications. The digital mobile phone system used in the UK.

Kbit/s: Kilobits per second. A measure of data transfer or modem speed. A kilobit is 1,000 individual bits of computer data. Most modems download information at up to 56Kbps.