Bluetooth explained How the short-range wireless networking specification works. By Alan Zeichick From May 2000 issue The typical workspace or home office is awash in cables. Cables between computers, keyboards, mice, and speakers. Cables between computers, scanners, Zip drives, and digital cameras. Cables between different computers. Enough already! Wouldn't it be great if the wires would just go away? That's the premise behind Bluetooth , a short-range wireless networking specification being developed by the Bluetooth Special Interest Group (SIG), a wide-reaching vendor alliance that includes the likes of 3Com , Ericsson , Lucent Technologies , Microsoft , Motorola , and Nokia , among others. Using radio waves, Bluetooth-based PCs will be able to communicate with each other, as well as with peripherals, handheld computers, smart telephones, and other devices. Each device will still need electricity, so that might mean a power cord when batteries can't provide the needed juice. But one cord is still far better than the confusion of wires now crisscrossing the space under or behind many desks. LOOK, MA, NO WIRES Bluetooth promises not only an end to cable hell, but also the beginning of seamless compatibility. Just place the printer near the computer, and print to it. Place the cellular telephone near the laptop, and use the laptop's keyboard to update the phone's speed-dial directories. Carry the laptop into the kitchen, and still have faster-than-modem access to the local area network (LAN) and Internet via a Bluetooth-enabled Ethernet hub. Like the popular universal serial bus (USB), the Bluetooth specification allows devices to be connected ad hoc to other devices, without rebooting or complex software installation and configuration procedures. There are two main technologies within the Bluetooth specification, which is distributed freely to any SIG member company wishing to build compatible devices: the radio transmitter/receiver, which allows the devices to talk to each other, and the underlying networking logic, which allows that radio communication to be meaningful. The radio specification calls for a versatile transceiver design that normally works within a ten-meter radius. Bluetooth specifies 79 different frequencies within the 2.4-GHz radio band -- the same band that high-end cordless telephones use. Because it's unlicensed, no special permits are required to build, sell, or operate Bluetooth radios. The radios operate in a mode known as frequency hopping, which involves rapidly shifting between different radio channels within the band range to find the frequency with the least interference and noise. In especially noisy conditions, the radios switch frequencies up to 1,600 times per second and use spread spectrum technology, which means they simultaneously transmit on as many as five frequencies at a time. A group of devices actively communicating within a ten-meter range of each other is called a piconet. All of the devices can support either one data channel or three voice channels. The voice channels operate at 64 Kbps, the same as conventional telephones. Bluetooth's data bandwidth is therefore much better than telephone modems (which now typically have speeds of about 56 Kbps), but slower than a conventional Ethernet (10 Mbps) or even modern high-speed infrared links (4 Mbps). Multiple piconets can operate in the same area, because each piconet can have its own frequency-hopping sequence. As many as ten overlapping piconets can be merged into a single entity called a scatternet, using a single Bluetooth device as a bridge between the networks (see "Scatternet Shot"). Under the Bluetooth specification, portable devices are limited to about ten meters, using a minute antenna with about one milliwatt of power. However, the specification allows for higher-powered base stations with larger antennas, which would have a range of up to 100 meters. Whole-home Internet routers or telephone base stations would use the higher-powered base stations. SLAVE DRIVER A Bluetooth piconet starts with two connected devices, such as a portable PC and a cellular phone, and may grow to include up to eight connected devices. A Bluetooth system acts as the master device, controlling the frequency-hopping sequence and allocating the data and voice channels for the duration of the piconet connection. All other devices are designated as slaves, controlled by the master. The portion of the Bluetooth implementation that handles not only the master/slave relationship, but also the process of converting voice to digital data, splitting it into packets, and performing error correction is known as the link processor. The link processor, which must be functionally identical on all Bluetooth-compliant devices, also allows the devices to identify themselves to each other, describing not only the type of device they are, but also which functions they support and which other devices are authorized to access those functions. All of this data processing and master/slave synchronization happens behind the scenes, much the same way that a modern digital cell phone transparently identifies itself to the local cellular network whenever the phone is turned on. Bluetooth radios and link processors have no intrinsic value of their own; they exist merely to allow application software to communicate with peripheral devices. Built into the link processor are the application programming interfaces, or APIs, that allow device drivers or custom-written software to operate over Bluetooth radio links as if they were ordinary Ethernet or telephone connections. Since portability and ubiquity are design goals for Bluetooth-compliant devices, the hardware must be small in size and draw only small amounts of electrical current. Original equipment manufacturers are now designing and building Bluetooth-compliant modules, which are self-contained units that include the radio transceiver and antenna, digital signal processors to filter out noise, a microprocessor with the Bluetooth link-processing firmware and memory, and connectors for power and interfacing with the rest of the portable device's electronics. Early implementation of Bluetooth electronics used multichip modules, or MCMs, which were comprised of chips and other discrete components mounted onto a tiny circuit board. Some providers are trying to reduce the number of components in the module to two -- one for the radio and one for the microprocessor -- so that all the components can fit onto a single chip as small as half a square inch in size. Bringing the number of chips down from five or six to just one will reduce size, cut manufacturing and assembly costs, and improve reliability. As for power consumption, when not connected to a piconet, a 2.7-volt Bluetooth module will draw less than 30 microamps of power. When serving as part of a piconet, but not transmitting data, the module draws about ten times that amount. Only when it is transmitting data does a Bluetooth system begin draining the battery, and even then, it draws only 33 milliamps for a fraction of a second. LET THE TOOTH BE KNOWN Beyond the technology, a key aspect of Bluetooth is compatibility. A few bad apples could ruin the spec for everyone. Part of the official Bluetooth specification, therefore, describes a qualification program. Aspects of the program are still being worked out, but the goal is for Bluetooth SIG member companies to appoint members to a Bluetooth qualification review board, which will develop a test procedure and authorize test facilities. Only when a product has been tested and approved by the review board's qualification body can it officially use the Bluetooth logo and other branding paraphernalia. When Bluetooth-based products become widely available, they should prove to be popular because of their small size, flexibility, and ease of use. It may take several years, however, before there's a sufficient base of devices, including desktop computers, printers, and LAN gear. Only when manufacturers begin including the technology as part of their base offerings -- the same way that USB ports are included on all computers and many peripherals these days -- will Bluetooth's real impact be felt. Once you get a few Bluetooth devices, don't be too quick to throw away your Fast Ethernet cables. Bluetooth still has low data-transfer rates -- faster than a standard data modem, but slower than a LAN or USB -- so it will primarily remain a technology of convenience aimed at handheld and portable devices. Even so, that's a huge market that's eager to escape from cable hell. Alan Zeichick is principal technology analyst with Camden Associates and editor in chief of BZ Media's SD Times. Write to alan@bzmedia.com.