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An introduction to GPRS

What to expect from this 'always on' wireless technology. Updated and reworked in December 2003 from my article in Palmtop User magazine, issue 3.

You'll have seen the claims of the mobile network providers (e.g. Vodafone) in adverts and on web sites. Upgrading your handheld hardware to use GPRS (General Packet Radio Service) is supposed to provide high-speed always-on Internet access wherever you are - and there's rarely much talk of the extra costs involved. There's no doubting that using GPRS can give you more or less instant Internet access, but in urban areas (I live in Reading, UK) 'high-speed' can in practice mean a bandwidth as low as 1K of data per second, less than for your standard dial-up GSM connection. And it's vital to watch your GPRS usage like a hawk and to match it to a suitable tariff or scheme to prevent yourself running up large bills.

What's different?

As with any technology, it's important to understand enough about it to be able to make wise buying decisions and to work round any limitations. When you dial up an Internet Service Provider (ISP) using your existing GSM mobile phone, a dedicated 'circuit' is set up for your sole use, just like when making a voice call. You pay for the duration of the call and for data it's usually limited to 9.6kbps or 14.4kbps, which equates to a download speed of just over 1K a second.

GPRS does things very differently, in theory making more efficient use of the mobile network's resources. Just as with the Internet itself, data is parcelled up into small packets, sent off across up to 8 'time slots' present on your provider's network, reassembled at the other end and finally passed on to the Internet at large via your provider's own gateway. In effect, then, your mobile network provider becomes your ISP. You also don't have sole use of their 8 GPRS slots, potentially sharing each slot in each mobile cell with hundreds of other GPRS users and their devices.

Speed issues

The theoretical maximum bandwidth for an imaginary GPRS device having sole use of all eight time slots on a network and without any error protection is 171.2kbps. This impressive number is cut down somewhat by a number of other 'bottleneck' factors. Firstly, as with any other computer data system, there's a significant degree of 'overhead' needed for error checking, to detect any scrambling of data in transit and then to automatically handle its resending.

P800 on the webSecondly, current GPRS-enabled phones and communicators are usually designed to only use a small number of slots. For example, the Sony Ericsson P800 is limited to using four GPRS network slots for download and one for upload. The Nokia 6310i and 7650 smartphones can make use of three slots for download, while the Handspring Treo 270 is restricted to just two slots for download, which works out as a theoretical maximum of 28.8kbps.

Thirdly, it's all very well having large amounts of Internet data flooding into a device but it has then got to be decoded and rendered. One reason for the modest GPRS specification of the Treo 270 is that its processor speed of only 33MHz, while fine for general Palm OS duties, would struggle to handle the data rates that (for example) the P800 is specified for.

Finally, having to share the GPRS network's bandwidth (within your local 'cells') with many other users can slow things up significantly. In mobile-saturated cities in office hours, you'll be lucky to get enough network time to achieve 1K of download per second, the same speed as for a standard dial-up data call over GSM. It all depends where you live and what you're using. A GPRS user in a semi-rural area with a P800 should get 5K per second easily.

Instant access

Of course, provisos over network and device bandwidth aside, GPRS's main advantage is that, once connected to your provider's network, you're always 'online'. Whereas a dial-up data session typically takes about 30 seconds before you're properly online, initial access to the Internet is virtually instantaneous. Removing the 30 second delay might seem a trivial improvement, but in reality it changes the whole way you use the Internet on your handheld or communicator.

Looking up an acronym or specification, or checking a stock price, or checking your POP3 mailbox can all be done on a whim. With a dial-up connection, the thought of staying still and unproductive for 30 seconds each time is usually enough to make you save the query for later.

Typical costs

Because there's no fixed call 'duration' with GPRS, a different way of charging had to be found by the mobile network providers, one based on the amount of data you send and receive. At the time of writing there are dozens of different tariffs and schemes, most based around a monthly charge for up to certain amount of bandwidth and then a surcharge per Megabyte thereafter. For example, Vodafone GPRS 15 costs £30 a month and covers you for up to 15MB of information. After that, it's around £2 per MB. Although quite expensive at the moment, these tariffs are sure to become cheaper as time goes on. And you can try out GPRS even on pay-as-you-go tariffs, without committing yourself financially. On Vodafone's PAYT scheme, GPRS/WAP access to their Vodafone Live! content is only 0.1p per kilobyte and general Internet browsing over GPRS is 1p per kilobyte.

Although GPRS charges are on top of your usual GSM mobile bill, don't forget that you won't be making any GSM data calls any more, so this component of your bill will be lower than usual.

Be wise!

Being charged by the byte means that it's essential to use some kind of strategy for keeping page download sizes down. It's quite practical to keep mainly within the so-called 'mobile web', where pages are designed for handheld or smartphone viewing and are very quick and cheap to download. A good place to start is www.google.com/palm, a generic PDA-optimised version of the famous search engine and an excellent candidate for your handheld or communicator's 'home' page. And of course, start with images turned off in your browser, perhaps just loading them on an as-needed basis. Working without images can reduce your GPRS traffic by a huge margin.

Things to note

Using Email over GPRS becomes slightly more immediate, in that you can check the contents of your POP3 mailbox fairly quickly and at fairly low cost.

Although the power requirements of being online all the time with GPRS are far, far lower than when making a dedicated dial-up GSM call, you will notice an impact on battery life.

Note that even though a smartphone or communicator can be 'online' all the time, voice calls can still be received as usual. Think of the GPRS connection as being a mass of SMS-like system messages flowing around the network and 'locked out' when a voice call is in progress. After answering (or making) a voice call, your GPRS connection resumes smoothly, starting with the packets of data your software requested (just before the call) finally being received and dealt with.

Do your homework!

The costs of upgrading to a GPRS-equipped communicator or smartphone and then using a GPRS connection day to day shouldn't be underestimated. If you can justify them, then go ahead, the always-on Internet awaits. For the rest of us, it should be borne in mind that even GPRS is a stop-gap solution ('2.5G') until proper high-speed wireless networks ('3G') become a reality. Consider your requirements and the platform and software you intend to use, and then compare the costs with those for standard dial-up access using a humble GSM data connection.

If you do decide to go for GPRS, note that setting up a communicator or phone manually can be tricky. Start off with your network provider's web site, where it's usually possible to get an OTA (Over The Air) configuration message sent out directly to your handset.

GPRS and Psion

A fairly brief footnote. Getting your Psion working online using a GPRS mobile phone is very practical and quite easy, but you might need some help setting it up for your particular phone and network provider combination.

As an example, my own setup, using a variety of GPRS mobile phones (I'm a journalist, remember!) on Vodafone, with my Series 5mx, is:

Psion : Control panel : Modems :
IR GPRS phone, 38400 baud, infrared, auto; init string ATZ, no data/fax init strings, Hardware flow control, Terminal Detect and Carrier Detect both ON, Fixed line.

Psion : Control panel : Internet :
Vodafone GPRS, dial-up, smart dialling NO, dial-up no. *99***1#, username 'wap', password 'wap'; IP and DNS addresses from server; plain text authentication ON.

For details on setting up a Psion palmtop with other networks, try the pages of settings at Mike McConnell's excellent web site. or Pete Sipple's FileSaveAs.