Understanding Bluetooth

Throughout this chapter we have discussed various wireless communication protocols. These technologies range in scope from long distance WLANs to one-meter IrDA devices. Each of these technologies has its niche, as well as its attendant strengths and weaknesses. For example, WLANs enable the transmission of data up to several hundred feet, but often require manual configuration changes that are difficult to implement. On the other hand, IrDA permits a seamless connection between devices without the need for extra configuration. However, their usability is dependent upon a direct line of sight no more than one meter away.

Although each technology discussed so far has its use, there is still a gap between WLANs and PANs. This is where the Bluetooth market steps in. For example, if you are in a conference room and want to share a file from your PDA, you would have several options. One option is to get everyone connected to a LAN, set up shares, configure IP addresses and more. Another option is to manually copy the file to each person in the room using a floppy disk or CD-ROM. The third option is to set up a wireless LAN which, like the hardwired LAN, still requires configuration and setup time. The last option is to use Bluetooth. This option does not require individual configuration, and is often included with many of the devices sold on the market today.

Bluetooth is the result of more than 1,000 companies working together for a common cause. The name actually originates from Danish history, which indicates how culturally widespread this technology is. The design goals of Bluetooth are that it should be inexpensive, easy to use, and of course, wireless. As a result, you can now find everything from keyboards to operating systems supporting Bluetooth. Users can simply walk into a room and be connected ”without wires, configuration changes, or troubleshooting.

Like 802.11b, Bluetooth also operates in the 2.4GHz ISM range. Although this adds more traffic to that particularly well-used chunk of frequency, its impact is minimal because of the low range the devices tend to have (10 meters ). In addition, Bluetooth uses the previously mentioned Frequency Hopping Spread Spectrum (FHSS). However, Bluetooth takes the use of this frequency to the next level by spreading the hops out over 79 channels and hopping up to 1600 times per second. The combination of FHSS and reduced wattage provides a relatively interference-free operation for Bluetooth.

In addition to the preceding specs , Bluetooth also supports rather large packet sizes, and can transfer data upwards of 64Kbps for two-way data flow, or 730Kbps for one-way communication. This essentially means Bluetooth can send large packages of data at a speed comparable to a typical Internet connection.

As previously mentioned, Bluetooth devices do not need to be manually configured. This is the true strength of this technology. For example, a group of users could walk into a room, turn on their laptops, and be able to instantly share files.

When one Bluetooth device requests a file or service from another Bluetooth device, the first becomes a "master" device. This is important in the communication process, because the master device controls how the Bluetooth data is passed. As you learned, Bluetooth is an FHSS-type of communication. This means that the frequency changes rapidly while devices are communicating. Each frequency change represents a different channel. Using such modulation, it is possible to have several Bluetooth devices communicating with each other in a small area. The master device determines what frequencies are used and in what order they are used. It accomplishes this using an identification number known as the BD_ADDR, or Bluetooth Device Address. Because each and every Bluetooth device has a unique BD_ADDR, it is unlikely that any two Bluetooth sessions will share the same frequency-hopping scheme.

Another advantage of Bluetooth is its capability to relay messages from one device to another, forming what is known as a piconet . A piconet also uses the master device's BD_ADDR feature to control the "slave" devices' data transmissions. This is possible because Bluetooth devices relay the data from one device to another. Figure 2.8 illustrates this concept.

Figure 2.8. Bluetooth communications.

In Figure 2.8, you can see that not all the devices communicate directly with each other. Instead, they relay the data on to adjacent Bluetooth devices that are outside of the master device's range. This "daisy-chain" design greatly increases the effective range of the piconet, and offers a unique form of networking.

In addition to the operational features, Bluetooth has several security features built into it that provide authentication, authorization, and encryption. It does this through two security options. The first is the use of a PIN similar to that of a voice-mail system. If the PIN option is enabled, the slave device and master device compare PINs, and if they match, the session is opened. If not, no communication will be granted. This ensures that your device will not randomly connect to other Bluetooth devices, which could result in accidentally updating the wrong Outlook task list or worse .

Although this is one measure of protection, it still does not address encryption. Although the SSFH scheme is derived by the BD_ADDR, there is some safety in the fact that it would take a very advanced sniffer to capture the PIN, as it would have to determine the master device's BD_ADDR and be prepared to change channels and monitor traffic on the various frequencies.

If encryption is required, Bluetooth will combine the BD_ADDR, PIN, and an embedded key in the master device to set up the encrypted session. This feature offers a fairly secure means of data transfer.

In addition to the security options that are built into Bluetooth, a user can set up additional encryption, authentication, or authorization options into the additional protocols that use Bluetooth, such as TCP/IP. This could include SSL or application-based security features. Bluetooth data protection is similar to that of WEP. Bluetooth defines only the bottom-most layer of data transfer, just like Ethernet.

Although Bluetooth can facilitate data transfer, it is still limited because of its minimal range and reduced speed. Bluetooth is useful for office environments, where a local group of people need to share information. Because Bluetooth is inexpensive and automatic, its use will proliferate in certain localized scenarios, including office meeting rooms or public meeting areas like airport lounges.