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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.
 Secondly, 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. |
