| Bluetooth is an omnidirectional wireless | | | | traffic flow as demand warrants. For example, |
| technology that provides limited-range voice | | | | if the user wants to download a large data |
| and data transmission over the unlicensed | | | | file, as much bandwidth as is needed will be |
| 2.4-GHz frequency band, allowing connections | | | | allocated to the transfer. Then, at the next |
| with a wide variety of fixed and portable | | | | moment, if a file is being uploaded, that |
| devices that normally would have to be cabled | | | | same amount of bandwidth can be allocated to |
| together. Up to eight devices—one | | | | that transfer. |
| master and seven slaves—can | | | | |
| communicate with one another in a socalled | | | | No matter what the application—voice |
| piconet at distances of up to 30 feet. | | | | or data—making connections between |
| | | | Bluetooth devices is as easy as powering them |
| Applications | | | | up. In fact, one advantage of Bluetooth is |
| | | | that it does not need to be set up—it |
| Among the many things users can do with | | | | is always on, running in the background, and |
| Bluetooth is swap data and synchronize files | | | | looking for other devices that it can |
| merely by having the devices come within | | | | communicate with. |
| range of one another. Images captured with a | | | | |
| digital camera, for example, can be dropped | | | | When Bluetooth devices come within range of |
| off at a personal computer (PC) for editing | | | | one another, they engage in a service |
| or a color printer for output on | | | | discovery procedure, which entails the |
| photo-quality paper—all without having | | | | exchange of messages to become aware of each |
| to connect cables, load files, open | | | | other’s service and feature |
| applications, or click buttons. The | | | | capabilities. Having located available |
| technology is a combination of circuit | | | | services within the vicinity, the user may |
| switching and packet switching, making it | | | | select from any of them. After that, a |
| suitable for voice as well as data. Instead | | | | connection between two or more Bluetooth |
| of fumbling with a cell phone while driving, | | | | devices can be established. |
| for example, the user can wear a lightweight | | | | |
| headset to answer a call and engage in a | | | | The radio link itself is very robust, using |
| conversation even if the phone is tucked away | | | | frequencyhopping spread-spectrum technology |
| in a briefcase or purse. While useful in | | | | to overcome interference and fading. Spread |
| minimizing the need for cables, wireless | | | | spectrum is a digital coding technique in |
| local area networks (LANs) are not intended | | | | which the signal is taken apart or |
| for interconnecting the range of mobile | | | | “spread†so that packets are sent |
| devices people carry around everyday between | | | | over time slots of 625 microseconds (ìs) |
| home and office. For this, Bluetooth is | | | | in length between the master and slave units |
| needed. And in the office, a Bluetooth | | | | within a piconet. It sounds more like noise |
| portable device can be TABLE B-1 Performance | | | | as it is sent through the air. With the |
| Characteristics of Bluetooth Products Feature | | | | addition of frequency hopping—having |
| Function Performance Connection type Spread | | | | the signals skip from one frequency to |
| spectrum (frequency hopping) Spectrum 2.4-GHz | | | | another—wireless transmissions are |
| ISM (industrial, scientific, and medical) | | | | made even more secure. Bluetooth specifies a |
| band Transmission power 1 milliwatt (mW) | | | | rate of 1600 hops per second among 79 |
| Aggregate data rate 1 Mbps using frequency | | | | frequencies. Since only the sender and |
| hopping Range Up to 30 feet (9 meters) | | | | receiver know the hopping sequence for coding |
| Supported stations Up to eight devices per | | | | and decoding the signal, eavesdropping is |
| piconet Voice channels Up to three | | | | virtually impossible. For enhanced security, |
| synchronous channels Data security For | | | | Bluetooth also supports device authentication |
| authentication, a 128-bit key; for | | | | and encryption. |
| encryption, the key size is configurable | | | | |
| between 8 and 128 bits Addressing Each device | | | | Other frequency-hopping transmitters in the |
| has a 48-bit Media Access Control (MAC) | | | | vicinity will be using different hopping |
| address that is used to establish a | | | | patterns and much slower hop rates than |
| connection with another device in motion | | | | Bluetooth devices. Although the chance of |
| while connected to the LAN access point as | | | | Bluetooth devices interfering with |
| long as the user stays within the 30-foot | | | | non-Bluetooth devices that share the same |
| range. Bluetooth can be combined with other | | | | 2.4-GHz band is minimal, should non- |
| technologies to offer wholly new | | | | Bluetooth transmitters and Bluetooth |
| capabilities, such as automatically lowering | | | | transmitters coincidentally attempt to use |
| the ring volume of cell phones or shutting | | | | the same frequency at the same moment, the |
| them off as users enter quiet zones such as | | | | data packets transmitted by one or both |
| churches, restaurants, theaters, and | | | | devices will become garbled in the collision, |
| classrooms. On leaving the quiet zone, the | | | | and a retransmission of the affected data |
| cell phones are returned to their original | | | | packets will be required. Anew data packet |
| settings. | | | | will be sent again on the next hopping cycle |
| | | | of each transmitter. Voice packets, because |
| Topology | | | | of their sensitivity to delay, are never |
| | | | retransmitted. |
| The devices within a piconet play one of two | | | | |
| roles: that of master or slave. The master is | | | | Points of Convergence |
| the device in a piconet whose clock and | | | | |
| hopping sequence are used to synchronize all | | | | In some ways, Bluetooth competes with |
| other devices (i.e., slaves) in the piconet. | | | | infrared, and in other ways, the two |
| The unit that carries out the paging | | | | technologies are complementary. With both |
| procedure and establishes a connection is by | | | | infrared and Bluetooth, data exchange is |
| default the master of the connection. The | | | | considered to be a fundamental function. Data |
| slaves are the units within a piconet that | | | | exchange can be as simple as transferring |
| are synchronized to the master via its clock | | | | business card information from a mobile phone |
| and hopping sequence. | | | | to a palmtop or as sophisticated as |
| | | | synchronizing personal information between a |
| The Bluetooth topology is best described as a | | | | palmtop and desktop PC. In fact, both |
| multiplepiconet structure. Since Bluetooth | | | | technologies can support many of the same |
| supports both point-topoint and | | | | applications, raising the question: Why would |
| point-to-multipoint connections, several | | | | users need both technologies? |
| piconets can be established and linked | | | | |
| together in a topology called a | | | | The answer lies in the fact that each |
| “scatternet†whenever the need | | | | technology has its advantages and |
| arises. | | | | disadvantages. The very scenarios that leave |
| | | | infrared falling short are the ones where |
| Piconets are uncoordinated, with frequency | | | | Bluetooth excels, and vice versa. Take the |
| hopping occurring independently. Several | | | | electronic exchange of business card |
| piconets can be established and linked | | | | information between two devices. This |
| together ad hoc, where each piconet is | | | | application usually will take place in a |
| identified by a different frequency-hopping | | | | conference room or exhibit floor where a |
| sequence. All users participating on the same | | | | number of other devices may be attempting to |
| piconet are synchronized to this hopping | | | | do the same thing. This is the situation |
| sequence. Although synchronization of | | | | where infrared excels. The shortrange and |
| different piconets is not permitted in the | | | | narrow angle of infrared—30 degrees or |
| unlicensed ISM band, Bluetooth units may | | | | less— allow each user to aim his or |
| participate in different piconets through | | | | her device at the intended recipient with |
| Time Division Multiplexing (TDM). This | | | | point-and-shoot ease. Close proximity to |
| enables a unit to sequentially participate in | | | | another person is natural in a business card |
| different piconets by being active in only | | | | exchange situation, as is pointing one device |
| one piconet at a time. | | | | at another. The limited range and angle of |
| | | | infrared allow other users to perform a |
| With its service discovery protocol, | | | | similar activity with ample security and no |
| Bluetooth enables a much broader vision of | | | | interference. In the same situation, a |
| networking, including the creation of | | | | Bluetooth device would not perform as well as |
| personal area networks, where all the devices | | | | an infrared device. With its omnidirectional |
| in a person’s life can communicate and | | | | capability, the Bluetooth device must first |
| work together. Technical safeguards ensure | | | | discover the intended recipient. The user |
| that a cluster of Bluetooth devices in public | | | | cannot simply point at the intended |
| places, such as an airport lounge or train | | | | recipient—a Bluetooth device must |
| terminal, would not suddenly start talking to | | | | perform a discovery operation that probably |
| one another. | | | | will reveal several other Bluetooth devices |
| | | | within range, so close proximity offers no |
| Technology | | | | advantage here. The user will be forced to |
| | | | select from a list of discovered devices and |
| Two types of links have been defined for | | | | apply a security mechanism to prevent |
| Bluetooth in support of voice and data | | | | unauthorized access. All this makes the use |
| applications: an asynchronous connectionless | | | | of Bluetooth for business card exchange an |
| (ACL) link and a synchronous | | | | awkward and needlessly time-consuming |
| connection-oriented (SCO) link. ACL links | | | | process. |
| support data traffic on a best-effort basis. | | | | |
| The information carried can be user data or | | | | However, in other data-exchange situations, |
| control data. SCO links support real-time | | | | Bluetooth might be the preferred choice. |
| voice and multimedia traffic using reserved | | | | Bluetooth’s ability to penetrate solid |
| bandwidth. Both data and voice are carried in | | | | objects and its ability to communicate with |
| the form of packets, and Bluetooth devices | | | | other devices in a piconet allow for |
| can support active ACL and SCO links at the | | | | data-exchange opportunities that are very |
| same time. ACL links support symmetric or | | | | difficult or impossible with infrared. For |
| asymmetric packetswitched point-to-multipoint | | | | example, Bluetooth allows a user to |
| connections used for data. For symmetric | | | | synchronize a mobile phone with a notebook |
| connections, the maximum data rate is 433.9 | | | | computer without taking the phone out of a |
| kbps in both directions, send and receive. | | | | jacket pocket or purse. This would allow the |
| For asymmetric connections, the maximum data | | | | user to type a new address at the computer |
| rate is 723.2 kbps in one direction and 57.6 | | | | and move it to the mobile phone’s |
| kbps in the reverse direction. If errors are | | | | directory without unpacking the phone and |
| detected at the receiving device, a | | | | setting up a cable connection between the two |
| notification is sent in the header of the | | | | devices. The omnidirectional capability of |
| return packet so that only lost or corrupt | | | | Bluetooth allows synchronization to occur |
| packets need to be retransmitted. | | | | instantly, assuming that the phone and |
| | | | computer are within 30 feet of each other. |
| SCO links provide symmetric circuit-switched | | | | |
| point-topoint connections, which are | | | | Using Bluetooth for synchronization does not |
| typically used for voice. Three synchronous | | | | require that the phone remain in a fixed |
| channels of 64 kbps each are available for | | | | location. If a phone is carried about in a |
| voice. The channels are derived through the | | | | briefcase, the synchronization can occur |
| use of either Pulse Code Modulation (PCM) or | | | | while the user moves around. This is not |
| Continuous Variable Slope Delta (CVSD) | | | | possible with infrared because the signal is |
| Modulation. PCM is the standard for encoding | | | | not able to penetrate solid objects, and the |
| speech in analog form into the digital format | | | | devices must be within a few feet of each |
| of ones and zeros. CVSD is another standard | | | | other. Furthermore, the use of infrared |
| for analog-to-digital encoding but offers | | | | requires that both devices remain stationary |
| more immunity to interference and therefore | | | | while the synchronization occurs. |
| is better suited than PCM for voice | | | | |
| communication over a wireless link. Bluetooth | | | | When it comes to data transfers, infrared |
| supports both PCM and CVSD; the appropriate | | | | does offer a big speed advantage over |
| voice-coding scheme is selected after | | | | Bluetooth. While Bluetooth moves data between |
| negotiations between the link managers of | | | | devices at an aggregate rate of 1 Mbps, |
| each Bluetooth device before the call takes | | | | infrared offers 4 Mbps of data throughput. |
| place. | | | | Ahigher -speed version of infrared is now |
| | | | available that can transmit data between |
| Voice and data are sent as packets. | | | | devices at up to 16 Mbps—a four times |
| Communication is handled with Time Division | | | | improvement over the previous version. The |
| Duplexing (TDD), which divides the channel | | | | higher speed is achieved with the Very Fast |
| into time slots, each 625 microseconds | | | | Infrared (VFIR) Protocol, which is designed |
| (ìs) in length. The time slots are | | | | to address the new demands of transferring |
| numbered according to the clock of the | | | | large image files between digital cameras, |
| piconet master. In the time slots, master and | | | | scanners, and PCs. Even when Bluetooth is |
| slave can transmit packets. In the TDD | | | | enhanced for higher data rates in the future, |
| scheme, master and slave alternatively | | | | infrared is likely to maintain its speed |
| transmit. The master starts its transmission | | | | advantage for many years to come. Bluetooth |
| in even-numbered time slots only, and the | | | | complements infrared’s point-and-shoot |
| slave starts its transmission in odd-numbered | | | | ease of use with omnidirectional signaling, |
| time slots only. The start of the packet is | | | | longer-distance communications, and capacity |
| aligned with the slot start. Packets | | | | to penetrate walls. For some users, having |
| transmitted by the master or the slave may | | | | both Bluetooth and infrared will provide the |
| extend over as many as five time slots. | | | | optimal short-range wireless solution. For |
| | | | others, the choice of adding Bluetooth or |
| With TDD, bandwidth can be allocated on an | | | | infrared will be based on the applications |
| as-needed basis, changing the makeup of the | | | | and intended usage. |