On the face of it, there’s a lot of technology choice in the wireless market right now. The technologies available are wide and varied, and people are often confused about which is the right one to use – yet in reality, each technology has its own purpose and there’s really not a great deal of overlap. In this RTFM, we’ll explain how it all works.
GPRS is the General Packet Radio System, an extension to the data services provided by mobile phone providers. Traditional cellphone data services worked just like modems – you had a fixed data rate (9,600bit/s with early GSM phones, 19,200bit/s later on) and you paid based on the time you were connected. GPRS works differently – you’re permanently connected and you pay for the volume of data you send and receive.
The GPRS service implemented by most UK providers can run up to four 9,600bit/s channels at once, which gives a maximum data rate of up to 38Kbit/s. You don’t necessarily get this rate all the time – the number of channels you can grab depends on how busy the cell transmitter you happen to be near actually is.
In order to use a GPRS service, you either need a GPRS-capable GSM modem card for your PC/PDA, or you need to link the latter to a mobile phone that can do GPRS. By far the most common approach is to connect the computer and a phone, and Bluetooth is the newest way to do it. Previously you’re been stuck with having to have a USB or serial cable between the two devices, or to use an infra-red connection (which relies on carefully positioning the phone near the laptop’s IR port) but Bluetooth allows you to have the two devices out of sight of each other and up to about 10 metres apart – so you can surf the net without taking the phone out of your pocket. Although its 1Mbit/s limit sounds puny (and wouldn’t be at all suitable for LAN operation) it’s more than enough when you consider that it’s about 25 times faster than the GSM connection the phone’s talking down.
In addition to connecting computing devices together, Bluetooth has other uses. Although there’s talk of all your domestic appliances talking to each other, this hasn’t yet happened on any scale, mainly because nobody’s really figured out exactly why the fridge would need to talk to the TV. It is, however, very useful for eliminating bits of wire in medium-bandwidth applications – the most obvious being to provide wire-free hands-free kits for cellphones.
Wi-Fi is another name for the IEEE802.10 wireless LAN range of standards (though it’s generally regarded as synonymous with the entry-level 802.11b – see below), and its intended application is firmly in the camp of allowing computers to intercommunicate as if they were connected to a LAN, but without the wires. The first incarnation, and thus the one that is (a) popular and (b) cheap enough to be used in the home is IEEE802.10b, which runs at 11Mbit/sec (though as the signal gets weaker between endpoints it’ll trade off speed for error-correction, down to 1Mbit/s) in the 2.4GHz frequency band.
Two further variants of the IEEE802.10 standard are now seeing the light: the “a” and “g” flavours. The “g” flavour is merely a high-speed (54Mbit/s) development of “b”, which means that “b” and “g” can coexist in the same network. The “a” standard departs from the basis of “g” and “b”, mainly due to a desire to move out of the increasingly-crowded 2.4GHz band (it runs at an underlying 5GHz). This frequency increase, combined with a change in the way the signal is modulated, gives “a” a potential higher speed than “g” in the future, though current implementations run at 54Mbit/s.
In summary, then: “b” is cheap but slow, “g” is the obvious migration path which means you don’t have to chuck away your “b” kit, and “a” is more scaleable but isn’t compatible with existing “b” or “g” kit.
It should be obvious by now, then, that these three wireless communication standards are different horses for different courses. GPRS is slow and specific to communications over a packet radio network (the GSM mobile phone standard, in reality); Bluetooth is medium-speed and short distance but isn’t designed to be a LAN protocol (and indeed, no hardware vendor we know supports Bluetooth-based LANs); Wi-Fi is another name for IEEE802.10, which is currently a range of three LAN-oriented protocols which compromise neatly between slow-and-cheap, fast-and-expensive, speed-capped-but-migrateable and scaleable-speed-but-chuck-away-the-old-kit.