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