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The Truth About Bluetooth

The Truth About Bluetooth

Bluetooth and Wireless Ethernet can happily coexist, at the same time, in the same space, and sharing the same frequency.

"XTC versus Adam Ant,
Only one will survive,
Beatle-based pop versus new romantic,
History will decide"
- "XTC vs Adam Ant,"
They Might Be Giants, 1996

It's strange, but until I heard that song, I had never considered Adam Ant to be in any kind of competition with XTC. After all, you can hardly compare Adam Ant enticing you to "Beat My Guest" with the somewhat lighter "This Is Pop," and while They Might Be Giants were probably trying to make a point with the song, the argument reminded me of that which seems to be surrounding Wireless Ethernet and Bluetooth. Adam Ant and XTC happily coexist on my CD shelf, as long as Holst isn't stirring up trouble between them, and Bluetooth devices happily share the air around them with Wireless Ethernet signals. Actually, that's a point worth making, because no matter how often I say it, people don't seem to understand:

Bluetooth and Wireless Ethernet can happily coexist, at the same time, in the same space, and sharing the same frequency.

Actually, as both technologies are constantly changing frequencies (or "hopping") they are never on the same frequency for very long, if ever, and no user (or application) would ever notice even if a clash was to occur. If anyone ever tells you they interfere with each other, send them my way and I'll knock some sense into them (or, if they are bigger than me, I might just demonstrate both technologies working at the same time).

It's Not About Networks
While accessing the Internet is a very worthy thing, it's not what Bluetooth is about; the ambition of Bluetooth was never to allow users to read Slashdot in the bath, but to provide a mechanism for peer-to-peer communications, something most people seem to have forgotten.

Chief among those with amnesia seems to be Microsoft, whose next version of the PocketPC operating environment proudly claimed to offer a standard Bluetooth API to application developers. Having received the latest beta, it's clear that the API is there, as long as your only intention is to use Bluetooth to connect to your network or the Internet; connections to other Bluetooth devices are not catered to in this version!

Of course, much useful work can be done with a TCP/IP connection to a network and the servers there. Company intranets can provide a wide range of applications, which will only increase with Microsoft's .NET initiative. Network resources can be made available to wireless users, and the simple fact that cables don't have to be connected can be enough to convince people to use the technology. But that's only the very beginning of what Bluetooth can, and will, do.

Bluetooth is sometimes called a PAN (Personal Area Network) technology, but this is something of a misnomer. While other technologies connect to networks, Bluetooth connects devices to other devices. While it is certainly possible to use Bluetooth to connect to a device that can offer network access as a ser-vice, it's not what Bluetooth is for and, as a result, it's not what Bluetooth is good at. When people want to connect to networks, then Wi-Fi is an obvious technology, but for talking to actual things, nothing compares to Bluetooth.

Because Bluetooth is a peer-to-peer technology, there's no need for servers or networks; connections can be made from device to device. When we're accessing a network, we are interested in the resources available on that network, so with peer-to-peer technologies we need to think about what resources are available on other Bluetooth devices, and what we could do if we had access to them.

Some examples are very obvious. A Bluetooth printer offers a printing service. Devices can connect to it and print documents, which is nice, but when we're talking about handheld devices, such as mobile phones and PDAs, the resources available may be harder to see.

There have been several attempts to provide browsable catalogs of services available on a network. Most notably there has been Jini from Sun, now in its much-reduced JXTA form. The ability for a user to dynamically join a network and see what's available has long been the dream, but no attempt has come close to what Bluetooth now offers.

By using a radio interface, Bluetooth is able to bypass many of the problems other service discovery protocols have encountered, and because it's not just one standard, but mandates within itself the use of other detailed standards, it can enable complex interactions between devices even if they have never been formally introduced. This is probably best explained with an example. Once I've described what happened as a user, I'll go through the process from the Bluetooth protocol point of view.

Personal Experience
I recently purchased a Nokia 7650 mobile phone (and actually reviewed it in WBT, Vol. 2, issue 8; it's lovely). It's got a built-in camera and Bluetooth connectivity among other things. After unpacking it (Nokia is kind enough to provide charged batteries, so no waiting to play, er..., sorry, work), I started playing with the features, including the camera. I took a photograph of my wife (looking stern at more money spent on mobile phones) and then pressed "Option" to see what I could do with my snap. The options proved to include "Send," which, when selected, was then split into three (see Figure 1), one of the choices being Bluetooth.

Selecting Bluetooth shows, after a few seconds, a list of Bluetooth devices found nearby, one of which is called "Bell" and is my printer.

I simply selected the printer, and to my immense surprise the printer upstairs rendered my photograph in glorious color. Notice that no configuration was needed, no drivers loaded, no setup required. I tried more options and discovered that I could print contact details and Calendar appointments, all without ever telling the phone what sort of printer I owned.

So, what actually happens during that process? It starts with the picture being taken and Bluetooth being selected as a transport mechanism. The phone then starts looking for Bluetooth devices. Any Bluetooth device may advertise its presence by listening to see if anyone is asking, and responding with its name.

Devices don't have to advertise all the time. Users are at liberty to switch off advertising and it does use some power, but mains powered devices have no particular reason not to. Each device responds with its name, as shown in Figure 2. Any device can then be polled to see what services it supports; a number identifies each service, with common services being standard, and developers able to define their own for bespoke applications.

It would be nice to say that when I selected Bell, the phone polled to see if that device supported "Printing" and it said yes. Unfortunately "Printing" is not yet a standardized service; the details of what drivers should be available are still under discussion, so it's currently not possible for a device to say it's a printer.

But there are other ways of receiving information for printing, and HP has worked hard to make their printer work with Bluetooth devices. Part of the Bluetooth standard mandates the use of other formats, and for image transfer, JPEG is always used.

So the phone simply asks if the printer is a device that can accept image information; the printer responds yes, and then prints the image. In the same way, Bluetooth mandates the use of the vCard and vCalendar formats for exchanging contact information and appointments, respectively. So when the phone tries to send some contact details, the printer accepts the vCard format data and prints it out.

The same system is used when two people swap details using Bluetooth. By making use of the vCard format, Bluetooth users can be sure that not only can they communicate with each other, but their respective devices can also understand what's being said.

A Whole New Range of Possibilities
This is proper science-fiction stuff! Ask an application to print out and it looks around to see if there's a printer handy. If so, it asks the printer if it minds being used, and assuming that's okay, it starts printing. Ask your PDA for Internet access and things might even go further. Perhaps it will look around to see who's offering an Internet access service, but before leaping to connect, it might interrogate each to see who's offering the best service. My mobile phone might offer Internet access, but at slow speeds and high costs, while my office LAN is cheap and fast, when available.

There's also no reason to assume communications would always be user-interaction driven. There's nothing to stop my desktop PC from constantly looking to see if my mobile phone is around (say, every five minutes) and synchronizing my data if the phone turns up. It could even block use of my computer if my phone wasn't around! The ability for applications to communicate when they feel like it opens up a whole host of possibilities, from interactive displays to automatic doors.

There are obviously security considerations, but Bluetooth communications can easily be encrypted and generally are. While the range of the devices lends itself to a level of security (you might notice a hacker listening in on your communication when he's within 10 meters of you; in fact, from what I know of hackers, you'll probably be able to smell him), for many applications it's important to know your communications will be secure. Again, simplicity for the end user has been paramount in the design, and deployment, of Bluetooth.

When Bluetooth requests a secure link between two devices, they will both display a dialog to their users asking for a four-digit number to be used as an encryption key. This number is agreed on between the users and entered on both devices. As the users are only 10 meters apart, it's relatively easy for them to communicate the key between them. We find that shouting works well, but the truly paranoid might like to use hand signals or nods of the head. In this way, the key is exchanged over a secure medium, enabling very secure cryptography.

Hopefully I've demonstrated that Bluetooth is unique in the marketplace, not only as a communications standard for devices, but also as a set of data formats and ways of behaving that guarantee the user simplicity of use through complexity of design. While technologies like Wireless Ethernet provide workers with access to their corporate networks, Bluetooth allows devices to talk directly to each other - not so much a Personal Area Network as a babble of conversations. So we don't have to choose between technologies. Indeed the new HP iPaq now has both Wi-Fi and Bluetooth built in. After all, as the song says:

"Even the singer from Bow Wow Wow,
Can't make up her mind"
- "XTC vs Adam Ant,"
They Might Be Giants, 1996

More Stories By Bill Ray

Bill Ray, former editor-in-chief (and continuing distinguished contributor to) Wireless Business & Technology magazine, has been developing wireless applications for over 20 ears on just about every platform available. Heavily involved in Java since its release, he developed some of the first cryptography applications for Java and was a founder of JCP Computer Services, a company later sold to Sun Microsystems. At Swisscom he was responsible for the first Java-capable DTV set-top box, and currently holds the position of head of Enabling Software at 02, a UK network operator.

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