ITWALES.COM - First experiences of Bluetooth

Posted: Mon, June 16, 2003

First experiences of Bluetooth

By Dafydd Rees

How Bluetooth works
The pairing process
The acid test
Conclusion

Most notebook users have from time to time found that they have to attach many different cables to their computer. Apart from the physical wear and tear, continually attaching and disconnecting external devices is annoying. Bluetooth is a 'wire replacement technology' for establishing data connections between small, electronic devices such as mobile phones, portable computers, digital cameras, mobile headsets and MP3 players.

This connection technology fits very well with the new digital hub vision being evangelized by Apple Computers, where the computer becomes the centre of a range of single-purpose digital devices. Each device is supposed to be easy to use, because it's specialized (like a camera or a phone), although these devices require connection to a computer to provide common storage and management of the digital content that they process ( http://www.apple.com/bluetooth/ ).

How Bluetooth works

Bluetooth is designed to be a cheap, low power, standard wireless technology for connecting devices. The technology is named "Bluetooth" after King Harald Blatand II of Denmark, in tribute apparently to his diplomatic skills uniting Scandinavia.

Unlike wired connections, each Bluetooth-enabled device contains a short-range radio transceiver to broadcast and receive Bluetooth signals. Many mobile phones, PDAs and notebooks have infrared connections that allow file transfer, printing and transfer of electronic business cards. Unfortunately, these infrared connections require a clear, line-of-sight between device ports. Some printers for example have infrared ports, but it's hardly a convenient feature when you're balancing your notebook with one hand, in front of the printer while you select "print" with the other hand! Since Bluetooth is a radio-based technology, there's no need to establish line-of-sight connections. Bluetooth radio signals generally have a range of 10cm to 10m, although some sophisticated Bluetooth LAN access points claim considerably larger ranges.

Although traditional, wireless infrared connections are typically configured as serial ports, Bluetooth can be considered more like a USB connection, where many different types of device can be connected, and the presence of particular devices and their capabilities are discovered dynamically. Of course, radio signals are broadcast, therefore the Bluetooth set of standards includes authentication and encryption features.

These allow users, software developers and manufacturers to use a common framework of standards to ensure that only authorized devices are granted access to remote services, and that no intermediary can intercept Bluetooth radio packets and reconstruct sensitive data. (Although the Bluetooth framework of standards includes these security facilities, several notebook and desktop computer software packages allow users to use unencrypted and unauthenticated Bluetooth connections). In practical terms, devices are secured by configuring them to refuse service to all devices except those that are explicitly registered using through a process called "pairing".

The pairing process

In order to replace a physical connection between your mobile phone and your notebook, typically you'd establish a pairing between your mobile phone and your notebook. For example, I can set my phone to "discoverable". In this state, my mobile is advertising itself to nearby devices for a limited period of time. I can then tell my computer to search for local Bluetooth devices. The name of my phone appears in a list. From this list, I choose to browse the services available on my phone, and select one of these. Browsing my SonyEricsson T68i mobile reveals, "dial-up networking", "fax", "synchronization", "inbox" and two "serial port replacement" services.

Although I can see these services from my notebook, selecting one brings up a prompt on my phone, asking me whether I should grant service to my notebook. One of the options presented is "add to paired". Selecting "add to paired" triggers a negotiation between my notebook and phone to establish a trusted connection. I'm prompted to type in a pass code on the phone. The computer is then notified that the phone is trying to establish a pairing, and I have to re-type the pass code on the computer to ensure that I'm connecting the right devices together. This "pairing" between devices need only happen on the first connection. After that, each device has a record of the other, and can securely establish that future connections come from the registered device.

The Bluetooth standards establish a set of profiles that support different wireless services. These include dial-up networking, file transfer, synchronization, serial port replacement, "object push", headset, human interface (keyboard and mouse), high-level printing service, low-level (cable-replacement) printing, and local area network access. Shopping for a PCIMCIA card for my notebook and a USB dongle for my desktop made it quite apparent that although many manufacturers sell Bluetooth hardware, few seem willing to list exactly which profiles their hardware and software will support. Reports of difficulties installing Bluetooth drivers and software seem to be borne out, both with my PCIMCIA card and my USB dongle.

Two things became clear from my shopping experience:

Just because a device carries the Bluetooth logo doesn't mean it'll support the profile that you require.
Manufacturers aren't publishing clear lists of profiles supported by their products. (In some cases it was easier to discover the size, weight and appearance of a device, than the services it provides!)

The acid test

The installation process for my PCIMCIA card and the USB dongle proved to be a minor ordeal. Driver files were misplaced, security warnings explained how uncertified drivers could destabilize the system, but since Microsoft didn't have a certification process for Bluetooth devices yet, it'd probably be all right. Some of these problems may be attributable to the vendor but I think it's fair to say that for the casual user and for the home market generally, they were showstoppers. Its tempting to blame Microsoft for their reluctant adoption of Bluetooth support in Windows, although even Apple's leadership has encountered serious problems with synchronization software.

With the PCIMCIA card on my laptop I found that I could connect to an ISP using the dial-up networking profile and then with the serial port profile through my mobile phone. The dial-up networking profile appeared like an ordinary Windows XP dial-up connection, whereas the (virtual) serial port profile made my phone appear as an ordinary serial port, requiring a phone-specific modem driver before a connection could be established. In terms of outgoing services, it turned out to be relatively easy to configure my desktop to share out its internal modem as a dial-up networking service. I found that I could provide "borrow" this desktop internal modem from inside my notebook, just as I'd done with the modem inside my mobile phone.

The file transfer service (between my notebook and my desktop) proved to be very slow compared with Ethernet and wireless LAN. (Wireless LAN has a theoretical maximum speed of 50Mbps, whereas Bluetooth can reach a maximum overall speed of 721 kbps.) Another limitation appeared in the windows software support where a designated folder had to be set aside for file transfer, suggesting that files would need to be copied between this "swap" directory and their real location, causing people to use this file transfer service more like a serial cable connection than a networked directory share.

I had more luck with small electronic devices, having succeeded transferring pictures from my mobile phone to a model 3970 iPAQ PocketPC. Transferring business cards from my phone to the Pocket PC also worked well. Pairing a headset with a phone also proved to be simple. The headset came with a four-digit pass code number. Holding a button on the headset made it "discoverable". I then set about pairing with it from the phone. This wireless headset seems to provide better quality audio than the built-in speaker and microphone in the phone itself, and only seems to drop connections when the headset battery becomes too low to operate. Normally, the headset is kept switched on, "listening" for a connection request from the paired phone.

Conclusion

Although I use Bluetooth to connect computers, phones and headsets, I wouldn't recommend it at the moment for casual users looking to connect a computer to any other device. You need to be fairly tolerant and tenacious to reach a working configuration that involves computers, although it seems to work quite well with mobile phones, headsets and PDA devices.

Since Bluetooth has a typical range of ten meters and a maximum speed of under 1Mbps, it's obviously not positioned to compete with wireless Ethernet (802.11b technology). Perhaps the most promising application of Bluetooth is the replacement of the tangle of cables that need to be repeatedly attached, and disconnected from notebook computers, and the expensive docking stations that provide wired connections by locking your portable down to a desk. There certainly is a case for Bluetooth adoption amongst technical professionals who travel frequently, although it remains to be seen if manufacturers and software vendors improve the situation to the point where non-technical people can easily use this technology.

Resources

http://www.bluetooth.com
http://www.apple.com/bluetooth/
http://www.theregister.co.uk/content/39/31065.html

About the Author

Dafydd Rees is a software developer specializing in object-technology, and a graduate of the University of Wales Swansea. He welcomes feedback at http://www.dafydd.net/feedback.html .

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