Bluetooth, the wireless cable replacement technology, is at that troubled phase that many technologies go through, when it's not quite come into use but there are already contenders to replace it.

The problem Bluetooth is designed to address is still very much with us: it is the tangle of cables we have on our desks, and in the pouch pockets of our laptop bags, taking data from phones to PDAs, from PCs to printers. The solution it offers is a simple one: put a cheap radio in every device we own and they can send the data without wires.

The concept, of a wireless personal area network (WPAN) is simple. The complication is in the context.

The basics
Bluetooth was proposed by Ericsson (and named after Harald Bluetooth, a Christian Viking king, who ruled Denmark from 940 to 985 AD) and taken up by Nokia, IBM, Toshiba and Intel in 1998.

The Bluetooth specification version 1 was published in 2000 and a version was adopted by the IEEE in 2002 as IEEE 802.15.1. The SIG is till the place where Bluetooth evolves and it recently approved Version 1.2.

In order to have a standard that works without any complication the SIG defined the "application layer", as well as the underlying protocol, so users can simply set a particular kind of Bluetooth behaviour and make two devices work together. These applications include voice (for telephone headsets) and data. The standard transmits data at 723 kbit/s, has a range of a couple of metres, operates in the licence-exempt 2.4GHZ band and hops 1600 times a second between 79 different frequencies.

The context and competition
The chips are cheap enough to put in all manner of places and they are starting to appear in phones and other places (one million Bluetooth phones ship each week according to the Bluetooth SIG). However, there is more to getting a standard used than getting it built in. It has to meet a need better than other standards and not clash with them.

Despite a comparatively rapid path to standardisation, and a steady flow of new Bluetooth products, there is still a frequent feeling that not enough people actually use the standard. This is partly because it is still fiddly to get working and really for leading edge users. The SIG has been criticised for creating too many profiles within the technology, for slightly-different applications, causing complication. The most common places to see Bluetooth in action are linking a laptop to a phone to use as a GPRS modem and linking a headset to a phone for cordless hands-free operation.

Security worries have dogged Bluetooth but as with any networking, good practice (checking the security settings are turned on, for instance) is enough to make it secure enough to use. For one thing, the short range means you can most likely see anyone trying to link to your device.

While some wonder if the standard will be a minority interest, much like the very widely implemented 4 kbit/s IrDA infra-red technology (which is comparatively rarely used), it seems clear that it will have distinct jobs to do, although other technologies overlap to some extent.

It is ideal for synchronising PDAs and router-like software that can share an Internet connection could make a very useful personal area network amongst a user's mobile devices, or the clutter on his or her desk.

Wi-Fi and Bluetooth
During its lifetime, Wi-Fi has been the biggest cloud over Bluetooth's future (and, at times, vice versa). Both operate in the same 2.4GHz band (though 802.11a shuffles up to the 5GHz band) and Bluetooth's frequent hopping has been felt to be a danger of conflict.

These fears have been exaggerated.

Practical experience so far has been that Bluetooth's range is small and the devices are portable: if they cause a problem, then they can be moved. In future there are expected to be many more Bluetooth devices (five times as many as Wi-Fi, at 286 million in 2008, according to a recent Forrester Report, so this process will become harder, say such reports, along with our own prophet of Wi-Fi doom.

This overplays the conflict, as Wi-Fi and Bluetooth can be combined in the same device, even on the same radio chip, with intelligence to avoid conflicts within the WPAN of that device. The Bluetooth standard has been developed in version 1.2 to avoid conflict with other standards.

Other competitors
Further in the future, Ultra-Wide Band (UWB) radio promises a technology that could completely displace Bluetooth but is a way off. Under current licencing it is not usable in Europe, even if there were products available. However, it will offer connections at 400 Mbit/s over the same distance as Bluetooth, using similar power or less, so must be a potential replacement. The data rate for UWB means it can actually go after cables that Bluetooth doesn't touch, such as USB.

Another contender is Zigbee (IEEE 802.15.4), yet another cable replacement technology in the 2.4GHz band. However, Bluetooth need not worry. ZigBee is slower, at 250 kbit/s, as it is designed for very low power consumption and long battery life, in devices such as monitors that can be left operating for a couple of years.

The standard is complete, and the technology is sponsored by Honeywell, Invensys, Mitsubishi, Motorola and Philips.

Conclusion
Bluetooth is a successful standard but don't expect it to solve every problem, or be here for ever. If you have not already, you will probably find it in your phone or PDA in the next year or two. You will also find there are times when it can actually help.