Who is Bluetooth
The Bluetooth Special Interest Group (SIG) is a privately held, not-for-profit trade association. The Special Interest Group was founded in September 1998. The Bluetooth SIG itself does not make, manufacture, or sell Bluetooth enabled products. The SIG has more than 9,000 member companies that are leaders in the telecommunications, computing, automotive, music, apparel, industrial automation, and network industries. SIG members drive development of Bluetooth wireless technology, and implement and market the technology in their products. The SIG has a small group of dedicated staff in Hong Kong, Sweden, and the USA.

The Bluetooth SIG global headquarters are in Bellevue, Washington, USA and has local offices in Hong Kong and Malmo, Sweden. The SIG staff is comprised of Executive Director Michael Foley, Ph.D., Marketing Director, Anders Edlund, and a small staff of marketing, engineering, and operations professionals.

In addition to the Bluetooth SIG staff, volunteers from member companies play key roles in furthering Bluetooth wireless technology and the organization behind it. Members support a number of working groups and committees that focus on specific areas, such as engineering, qualification, and marketing.

The Bluetooth SIG includes Promoter member companies Ericsson, Intel, Lenovo, Microsoft, Motorola, Nokia, and Toshiba, and thousands of Associate and Adopter member companies.

Bluetooth History
Initially (circa 1996-1997) the technology later known as Bluetooth was an Ericsson-internal project named multi-communicator link or short MC link. Cooperation with Intel was initiated in 1997. In 1998, Ericsson, IBM, Intel, Toshiba, and Nokia, formed a consortium and adopted the code name Bluetooth for their proposed open specification. In December 1999, 3Com, Lucent Technologies, Microsoft, and Motorola joined the initial founders as the promoter of Bluetooth Special Interest Group (SIG). Since that time, Lucent Technologies transferred their membership to their spinoff Agere Systems, and 3Com has left the promoter group. Agere Systems was later merged with LSI Corporation and left the Bluetooth promoters group in August 2007. The Bluetooth Special Interest Group (SIG) is a privately held, not-for-profit trade association with headquarters in Bellevue, Washington. As of January 2008, the SIG is composed of over 10,000 member companies that are leaders in the telecommunications, computing, automotive, music, apparel, industrial automation, and network industries, and a small group of dedicated staff in Hong Kong, Sweden, and the USA. SIG members drive the development of Bluetooth wireless technology, and implement and market the technology in their products varying from mobile phones to printers. The Bluetooth SIG itself does not make, manufacture, or sell Bluetooth enabled products. The executive director of the Bluetooth SIG is Michael W. Foley.

The Bluetooth Name
Bluetooth started as the code name for the association when it was first formed and the name stuck. The name "Bluetooth" is from the 10th century Danish King Harald Blatand - or Harold Bluetooth in English. King Blatand was instrumental in uniting warring factions in parts of what is now Norway, Sweden and Denmark - just as Bluetooth technology is designed to allow collaboration between differing industries such as the computing, mobile phone and automotive markets.

Mission Statement - Strengthen the Bluetooth brand by empowering SIG members to collaborate and innovate, creating the preferred wireless technology to connect diverse devices.

What is Bluetooth? Bluetooth is a wireless protocol utilizing short-range communications technology facilitating both voice and data transmissions over short distances from fixed and/or mobile devices, creating wireless personal area networks (PANs). The intent behind the development of Bluetooth was the creation of a single digital wireless protocol, capable of connecting multiple devices and overcoming issues arising from synchronization of these devices. Bluetooth provides a way to connect and exchange information between devices such as mobile phones, telephones, laptops, personal computers, printers, GPS receivers, digital cameras, and video game consoles over a secure, globally unlicensed Industrial, Scientific, and Medical (ISM) 2.4 GHz short-range radio frequency bandwidth. The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group. The Bluetooth SIG consists of companies in the areas of telecommunication, computing, networking, and consumer electronics.

Uses
Bluetooth is a standard and communications protocol primarily designed for low power consumption, with a short range (power-class-dependent: 1 meter, 10 meters, 100 meters) based on low-cost transceiver microchips in each device.[2] Bluetooth enables these devices to communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, as long as the received transmission is powerful enough. Bluetooth device class indicates the type of device and the supported services of which the information is transmitted during the discovery process

In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to pure class 2 network. This is accomplished by the higher sensitivity and transmission power of Class 1 devices.

A Bluetooth profile is a wireless interface specification for Bluetooth-based communication between devices. In order to use Bluetooth technology, a device must be compatible with the subset of Bluetooth profiles necessary to use the desired services. A Bluetooth profile resides on top of the Bluetooth Core Specification and (optionally) additional protocols. While the profile may use certain features of the core specification, specific versions of profiles are rarely tied to specific versions of the core specification. For example, there are HFP 1.5 implementations using both Bluetooth 2.0 and Bluetooth 1.2 core specifications.

Hands-Free Profile (HFP) This is commonly used to allow car hands-free kits to communicate with mobile phones in the car. It uses SCO (see Synchronous Connection Oriented link) to carry a mono, Continuously variable slope delta modulation or Pulse-code modulation with logarithmic a-law or ?-law quantization audio channel. Currently in version 1.5. In 2002 Audi, with the Audi A8, was the first motor vehicle manufacturer to install Bluetooth technology in a car, enabling the passenger to use a wireless in-car phone. The following year DaimlerChrysler and Acura introduced Bluetooth technology integration with the audio system as a standard feature in the third generation Acura TL in a system dubbed HandsFree Link (HFL). Later, BMW added it as an option on its 1 Series, 3 Series, 5 Series, 7 Series and X5 vehicles. Since then, other manufacturers have followed suit, with many vehicles, including the Toyota Prius (Since 2004), 2007 Toyota Camry, 2007 Infiniti G35, and the Lexus LS 430 (Since 2004). The Bluetooth car kits allow users with Bluetooth-equipped cell phones to make use of some of the phone's features, such as making calls, while the phone itself can be left in a suitcase or in the boot/trunk, for instance. Companies like Nokia, Johnson Controls, RAYTEL, Parrot and Motorola manufacture Bluetooth hands-free car kits for well-known brand car manufacturers.

List of applications

A typical Bluetooth mobile phone headset More prevalent applications of Bluetooth include:

* Wireless control of and communication between a mobile phone and a hands-free headset. This was one of the earliest applications to become popular.
* Wireless networking between PCs in a confined space and where little bandwidth is required.
* Wireless communications with PC input and output devices, the most common being the mouse, keyboard and printer.
* Transfer of files between devices with OBEX.
* Transfer of contact details, calendar appointments, and reminders between devices with OBEX.
* Replacement of traditional wired serial communications in test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices.
* For controls where infrared was traditionally used.
* Sending small advertisements from Bluetooth enabled advertising hoardings to other, discoverable, Bluetooth devices.
* Two seventh-generation game consoles, Nintendo's Wii and Sony's PlayStation 3 use Bluetooth for their respective wireless controllers.
* Dial-up internet access on personal computer or PDA using a data-capable mobile phone as a modem.

Bluetooth vs. Wi-Fi in networking
Bluetooth and Wi-Fi have different applications in today's offices, homes, and on the move: setting up networks, printing, or transferring presentations and files from PDAs to computers. Both are versions of unlicensed spread spectrum technology. Bluetooth differs from Wi-Fi in that the latter provides higher throughput and covers greater distances, but requires more expensive hardware and higher power consumption. They use the same frequency range, but employ different modulation techniques. While Bluetooth is a replacement for a variety of applications, Wi-Fi is a replacement only for local area network access. Bluetooth can be thought of as wireless USB[citation needed], whereas Wi-Fi is wireless Ethernet[citation needed], both operating at much lower bandwidth[citation needed] than cable networking systems. However, this analogy is not entirely accurate since any Bluetooth device can, in theory, host any other Bluetooth device—something that is not universal to USB devices, therefore it would resemble more a wireless FireWire.

Bluetooth Devices
Bluetooth exists in many products, such as telephones, printers, modems and headsets. The technology is useful when transferring information between two or more devices that are near each other in low-bandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e. with a Bluetooth headset) or byte data with hand-held computers (transferring files). Bluetooth simplifies the discovery and setup of services between devices. Bluetooth devices advertise all of the services they provide. This makes using services easier because there is no longer a need to set up network addresses or permissions as in many other network.

Wi-Fi
Wi-Fi is more like a traditional Ethernet network, and requires configuration to set up shared resources, transmit files, and to set up audio links (for example, headsets and hands-free devices). It uses the same radio frequencies as Bluetooth, but with higher power resulting in a stronger connection. Wi-Fi is sometimes called "wireless Ethernet." This description is accurate as it also provides an indication of its relative strengths and weaknesses. Wi-Fi requires more setup, but is better suited for operating full-scale networks because it enables a faster connection, better range from the base station, and better security than Bluetooths.

Specifications and features
The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were working for Ericsson Mobile Platforms in Lund, Sweden. The specification is based on frequency-hopping spread spectrum technology. The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May 20, 1998. Today it has a membership of over 7000 companies worldwide. It was established by Ericsson, IBM, Intel, Toshiba, and Nokia, and later joined by many other companies.

Bluetooth 1.0 and 1.0B
Versions 1.0 and 1.0B had many problems, and manufacturers had difficulty making their products interoperable. Versions 1.0 and 1.0B also included mandatory Bluetooth hardware device address (BD_ADDR) transmission in the Connecting process (rendering anonymity impossible at the protocol level), which was a major setback for certain services planned for use in Bluetooth environment

Bluetooth 1.1
* Ratified as IEEE Standard 802.15.1-2002.
* Many errors found in the 1.0B specifications were fixed.
* Added support for non-encrypted channels.
* Received Signal Strength Indicator (RSSI).

Bluetooth 1.2
This version is backward-compatible with 1.1 and the major enhancements include the following:
* Faster Connection and Discovery
* Adaptive frequency-hopping spread spectrum (AFH), which improves resistance to radio frequency interference by avoiding the use of crowded frequencies in the hopping sequence.
* Higher transmission speeds in practice, up to 721 kbit/s, as in 1.1.
* Extended Synchronous Connections (eSCO), which improve voice quality of audio links by allowing retransmissions of corrupted packets, and may optionally increase audio latency to provide better support for concurrent data transfer.
* Host Controller Interface (HCI) support for three-wire UART.
* Ratified as IEEE Standard 802.15.1-2005.

Bluetooth 2.0
This version, specified on November 10, 2004, is backward-compatible with 1.1. The main enhancement is the introduction of an Enhanced Data Rate (EDR) of 3.0 Mbit/s for both data (ACL) and voice (eSCO) packets. This has the following effects:
* Three times faster transmission speed—up to 10 times in certain cases (up to 2.1 Mbit/s).
* Lower power consumption through a reduced duty cycle.
* Simplification of multi-link scenarios due to more available bandwidth.

The practical data transfer rate is 2.1 megabits per second and the basic signalling rate is about 3 megabits per second. The "Bluetooth 2.0 + EDR" specification given at the Bluetooth Special Interest Group (SIG) includes EDR and there is no specification "Bluetooth 2.0" as used by many vendors. The HTC TyTN pocket PC phone, shows "Bluetooth 2.0 without EDR" on its data sheet. In many cases it is not clear whether a product claiming to support "Bluetooth 2.0" actually supports the EDR higher transfer rate.

Bluetooth 2.1
Bluetooth Core Specification Version 2.1 is fully backward-compatible with 1.1, and was adopted by the Bluetooth SIG on July 26, 2007. This specification includes the following features:

* Extended inquiry response: provides more information during the inquiry procedure to allow better filtering of devices before connection. This information includes the name of the device, a list of services the device supports, as well as other information like the time of day, and pairing information.

* Sniff subrating: reduces the power consumption when devices are in the sniff low-power mode, especially on links with asymmetric data flows. Human interface devices (HID) are expected to benefit the most, with mouse and keyboard devices increasing the battery life by a factor of 3 to 10. It lets devices decide how long they will wait before sending keepalive messages to one another. Previous Bluetooth implementations featured keep alive message frequencies of up to several times per second. In contrast, the 2.1 specification allows pairs of devices to negotiate this value between them to as infrequently as once every 5 or 10 seconds.

* Encryption Pause Resume: enables an encryption key to be refreshed, enabling much stronger encryption for connections that stay up for longer than 23.3 hours (one Bluetooth day). * Secure Simple Pairing: radically improves the pairing experience for Bluetooth devices, while increasing the use and strength of security. It is expected that this feature will significantly increase the use of Bluetooth.

* NFC cooperation: automatic creation of secure Bluetooth connections when NFC radio interface is also available. For example, a headset should be paired with a Bluetooth 2.1 phone including NFC just by bringing the two devices close to each other (a few centimeters). Another example is automatic uploading of photos from a mobile phone or camera to a digital picture frame just by bringing the phone or camera close to the frame

Future of Bluetooth

* Broadcast Channel: enables Bluetooth information points. This will drive the adoption of Bluetooth into mobile phones, and enable advertising models based around users pulling information from the information points, and not based around the object push model that is used in a limited way today.

* Topology Management: enables the automatic configuration of the piconet topologies especially in scatternet situations that are becoming more common today. This should all be invisible to the users of the technology, while also making the technology just work.

* Alternate MAC PHY: enables the use of alternative MAC and PHY's for transporting Bluetooth profile data. The Bluetooth Radio will still be used for device discovery, initial connection and profile configuration, however when lots of data needs to be sent, the high speed alternate MAC PHY's will be used to transport the data. This means that the proven low power connection models of Bluetooth are used when the system is idle, and the low power per bit radios are used when lots of data needs to be sent.

* QoS improvements: enable audio and video data to be transmitted at a higher quality, especially when best effort traffic is being transmitted in the same piconet.

High-speed Bluetooth
On 28 March 2006, the Bluetooth Special Interest Group announced its selection of the WiMedia Alliance Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) version of UWB for integration with current Bluetooth wireless technology. UWB integration will create a version of Bluetooth wireless technology with a high-speed/high-data-rate option. This new version of Bluetooth technology will meet the high-speed demands of synchronizing and transferring large amounts of data, as well as enabling high-quality video and audio applications for portable devices, multi-media projectors and television sets, and wireless VOIP. At the same time, Bluetooth technology will continue catering to the needs of very low power applications such as mouse, keyboards, and mono headsets, enabling devices to select the most appropriate physical radio for the application requirements, thereby offering the best of both worlds.

Bluetooth 3.0
The next version of Bluetooth after v2.1, code-named Seattle (the version number of which is TBD) has many of the same features, but is most notable for plans to adopt ultra-wideband (UWB) radio technology. This will allow Bluetooth use over UWB radio, enabling very fast data transfers of up to 480 Mbit/s, while building on the very low-power idle modes of Bluetooth.

Bluetooth Low Energy
On June 12, 2007, Nokia and Bluetooth SIG announced that Wibree will be a part of the Bluetooth specification as an ultra low power Bluetooth technology. Expected use cases include watches displaying Caller ID information, sports sensors monitoring your heart rate during exercise, as well as medical devices. The Medical Devices Working Group is also creating a medical devices profile and associated protocols to enable this market. Battery life for devices using Bluetooth low energy technology is designed to be up to one year.

Technical Information

Bluetooth Protocol Stack
" Bluetooth is defined as a layer protocol architecture consisting of core protocols, cable replacement protocols, telephony control protocols, and adopted protocols”

Core Protocols
Bluetooth’s core protocols form a five-layer stack, consisting of the following:

Bluetooth Radio – specifics details of the air interface, including frequency, frequency hopping, modulation scheme, and transmission power.

Baseband – concerned with connection establishment within a piconet, addressing, packet format, timing, and power control.

Link Manager Protocol (LMP) – establishes the link setup between Bluetooth devices and manages ongoing links, including security aspects (e.g. authentication and encryption), and control and negotiation of baseband packet size Logical

Link Control and Adaptation Protocol (L2CAP) – adapts the upper-layer protocols to the baseband layer, providing both connectionless and connection-oriented services.

Service Discovery Protocol (SDP) – handles device information, services, and queries for service characteristics between two or more Bluetooth devices.

Cable Replacement Protocol
Radio frequency communications (RFCOMM) is the cable replacement protocol used to create a virtual serial port used to make replacement of cable technologies transparent through minimal modification of existing devices. RFCOMM provides for binary data transport and emulates EIA-232 (formerly RS-232) control signals over the Bluetooth baseband layer.

Telephony Control Protocol
Telephony control protocol-binary (TCS BIN) is the bit-oriented protocol that defines the call control signaling for the establishment of voice and data calls between Bluetooth devices. Additionally, “TCS BIN defines mobility management procedures for handling groups of Bluetooth TCS devices”

Adopted Protocols
Adapted protocols are defined by other standards-making organizations and incorporated into Bluetooth’s protocol stack., allowing Bluetooth to create protocols only when necessary. The adopted protocols include:

Point-to-Point Protocol (PPP) – Internet standard protocol for transporting IP datagrams over a point-to-point link TCP/IP/UDP – Foundation Protocols for TCP/IP protocol suite

Object Exchange Protocol (OBEX) – Session-layer protocol for the exchange of objects, providing a model for object and operation representation

Wireless Application Environment / Wireless Application Protocol (WAE/WAP) – WAE specifies an application framework for wireless devices and WAP is an open standard to provide mobile users access to telephony and information services.

Communication and connection
A master Bluetooth device can communicate with up to seven devices. This network group of up to eight devices is called a piconet. A piconet is an ad-hoc computer network, using Bluetooth technology protocols to allow one master device to interconnect with up to seven active devices. Up to 255 further devices can be inactive, or parked, which the master device can bring into active status at any time. At any given time, data can be transferred between the master and one other device, however, the devices can switch roles and the slave can become the master at any time. The master switches rapidly from one device to another in a round-robin fashion. (Simultaneous transmission from the master to multiple other devices is possible, but not used much.) Bluetooth specification allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role and the slave role in one piconet. Many USB Bluetooth adapters are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth adapters, however, have limited services, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth, but they do not offer much in the way of services that modern adapters do.

Setting up connections
Any Bluetooth device will transmit the following information on demand:

* Device name.
* Device class.
* List of services.
* Technical information, for example, device features, manufacturer, Bluetooth specification used, clock offset.

Any device may perform an inquiry to find other devices to connect to, and any device can be configured to respond to such inquiries. However, if the device trying to connect knows the address of the device, it always responds to direct connection requests and transmits the information shown in the list above if requested. Use of device services may require pairing or acceptance by its owner, but the connection itself can be initiated by any device and held until it goes out of range. Some devices can be connected to only one device at a time, and connecting to them prevents them from connecting to other devices and appearing in inquiries until they disconnect from the other device. Every device has a unique 48-bit address. However these addresses are generally not shown in inquiries. Instead, friendly Bluetooth names are used, which can be set by the user. This name appears when another user scans for devices and in lists of paired devices. Most phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most phones and laptops show only the Bluetooth names and special programs that are required to get additional information about remote devices. This can be confusing as, for example, there could be several phones in range named T610

Pairing
Pairs of devices may establish a trusted relationship by learning (by user input) a shared secret known as a passkey. A device that wants to communicate only with a trusted device can cryptographically authenticate the identity of the other device. Trusted devices may also encrypt the data that they exchange over the airwaves so that no one can listen in. The encryption can, however, be turned off, and passkeys are stored on the device file system, not on the Bluetooth chip itself. Since the Bluetooth address is permanent, a pairing is preserved, even if the Bluetooth name is changed. Pairs can be deleted at any time by either device. Devices generally require pairing or prompt the owner before they allow a remote device to use any or most of their services. Some devices, such as mobile phones, usually accept OBEX business cards and notes without any pairing or prompts. Certain printers and access points allow any device to use its services by default, much like unsecured Wi-Fi networks. Pairing algorithms are sometimes manufacturer-specific for transmitters and receivers used in applications such as music and entertainment. Bluetooth 2.1 has an optional "touch-to-pair" feature based on NFC. By simply bringing two devices into close range (around 10cm), pairing can securely take place without entering a passkey or manual configuration.

Air interface
The protocol operates in the license-free ISM band at 2.4-2.4835 GHz. To avoid interfering with other protocols that use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR) and reach 2.1 Mbit/s. Technically, version 2.0 devices have a higher power consumption, but the three times faster rate reduces the transmission times, effectively reducing power consumption to half that of 1.x devices (assuming equal traffic load)

Security
Overview Bluetooth implements confidentiality, authentication and key derivation with custom algorithms based on the SAFER+ block cipher. In Bluetooth, key generation is generally based on a Bluetooth PIN, which must be entered into both devices. This procedure might be modified if one of the devices has a fixed PIN, e.g. for headsets or similar devices with a restricted user interface. During pairing, an initialization key or master key is generated, using the E22 algorithm. The E0 stream cipher is used for encrypting packets, granting confidentiality and is based on a shared cryptographic secret, namely a previously generated link key or master key. Those keys, used for subsequent encryption of data sent via the air interface, rely on the Bluetooth PIN, which has been entered into one or both devices. An overview of Bluetooth vulnerabilities exploits has been published by Andreas Becker.

Bluejacking
Bluejacking is the sending of either a picture or a message from one user to an unsuspecting user through Bluetooth wireless technology. Common applications are short messages (e.g. you’ve just been bluejacked!), advertisements (e.g. eat at Joe’s). and business information. Bluejacking does NOT involve the removal or alteration of any data from the device. These business cards often have a clever or flirtatious message rather than the typical name and phone number.[citation needed] Bluejackers often look for the receiving phone to ping or the user to react. They then send another, more personal message to that device. Once again, in order to carry out a bluejacking, the sending and receiving devices must be within range of each other, which is typically 10 meters for most mobile devices. Devices that are set in non-discoverable mode are not susceptible to bluejacking. However, the Linux application Redfang claims to find non-discoverable Bluetooth devices.

Health concerns
Bluetooth uses the microwave radio frequency spectrum in the 2.4 GHz to 2.4835 GHz range. Maximum power output from a Bluetooth radio is 100 mW, 2.5 mW, and 1 mW for Class 1, Class 2, and Class 3 devices respectively, which puts Class 1 at roughly the same level as mobile phones, and the other two classes much lower. Accordingly, Class 2 and Class 3 Bluetooth devices are considered less of a potential hazard than mobile phones, and Class 1 may be comparable to that of mobile phones.

How Bluetooth Works
The technology of Bluetooth wireless is a short range communications method intended to replace the cables that connect portable or fixed devices while maintaining the highest levels of security. The key features offered by Bluetooth include low power and low cost. The specification in Bluetooth defines a uniform structure for a wide range of devices to communicate and connect with one another. The technology behind Bluetooth has achieved global satisfaction such as enabled devices, almost everywhere in the world. Bluetooth devices will connect and communicate without wires through short range and networks known as piconets.

Each device will simultaneously communicate with up to seven other devices within a single piconet, meaning that each device can also belong to several piconets simultaneously. The piconets are dynamically established as Bluetooth enabled devices enter and leave the proximity of radio. A fundamental to Bluetooth strength is the ability to handle both data and voice transmissions simultaneously. This will enable users to enjoy varieties of innovative solutions such as hands free talking, printing and fax capabilities, and other applications.

Bluetooth devices will normally operate at 2.4 GHZ in the license free, globally available ISM radio band. The advantage to this band includes worldwide availability and compatibility. A disadvantage to this however, is that the devices must share this band with other RF emitters. This includes automobile security systems, other wireless devices, and other noise sources, such as microwaves. To overcome this challenge, Bluetooth employs a fast frequency hopping scheme and therefore uses shorter packets than other standards within the ISM band. This scheme helps to make Bluetooth communication more robust and more secure.

Frequency hopping
Frequency hopping is basically jumping from frequency to frequency within the ISM radio band. After a bluetooth device sends or receives a packet, it and the device (or devices) it's communicating with hop to another frequency before the next packet is sent. This scheme offers three advantages:

1. Allows Bluetooth devices to use the entirety of the available ISM band, while never transmitting from a fixed frequency for more than a short period of time. This helps insure that Bluetooth conforms to the ISM restrictions on the transmission quantity per frequency.

2. Ensures that any interference won't last long. Any packet that doesn't arrive safely to its destination can be resent to the next frequency.

3. Provides a base level of security as it's very hard for an eavesdropping device to predict which frequency the Bluetooth devices will use next.

The connected devices however, must agree upon the frequency they will use next. The specification in Bluetooth ensures this in two ways. First, it defines a master and slave type relationship between bluetooth devices. Next, it specifies an algorithm that uses device specific information when calculating the frequency hop sequences.

A Bluetooth device that operates in master mode can communicate with up to seven devices that are set in slave mode. To each of the slaves, the master. Bluetooth device will send its own unique address and the value of its own internal clock. The information sent is then used to calculate the frequency hop sequences. Because the master device and each of the slave devices use the same algorithm with the same initial input, the connected devices will always arrive together at the next frequency that they have agreed upon.

As a replacement for cable technology, it's no wonder that Bluetooth devices are usually battery powered, such as wireless mice and battery powered cell phones. To conserve the power, most devices operate in low power. This helps to give Bluetooth devices a range of around 5 - 10 meters.This range is far enough for wireless communication but close enough to avoid drawing too much power from the power source of the device.