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