What is bluetooth

Bluetooth is an omnidirectional wireless technologymuch bandwidth as is needed will be allocated to
that provides limited-range voice and datathe transfer. Then, at the next moment, if a file
transmission over the unlicensed 2.4-GHzis being uploaded, that same amount of bandwidth
frequency band, allowing connections with a widecan be allocated to that transfer.
variety of fixed and portable devices thatNo matter what the application—voice
normally would have to be cabled together. Up toor data—making connections between
eight devices—one master and sevenBluetooth devices is as easy as powering them
slaves—can communicate with oneup. In fact, one advantage of Bluetooth is that it
another in a socalled piconet at distances of up todoes not need to be set up—it is
30 feet.always on, running in the background, and looking
Applicationsfor other devices that it can communicate with.
Among the many things users can do withWhen Bluetooth devices come within range of
Bluetooth is swap data and synchronize filesone another, they engage in a service discovery
merely by having the devices come within rangeprocedure, which entails the exchange of
of one another. Images captured with a digitalmessages to become aware of each
camera, for example, can be dropped off at aother’s service and feature capabilities.
personal computer (PC) for editing or a colorHaving located available services within the vicinity,
printer for output on photo-qualitythe user may select from any of them. After
paper—all without having to connectthat, a connection between two or more
cables, load files, open applications, or click buttons.Bluetooth devices can be established.
The technology is a combination of circuitThe radio link itself is very robust, using
switching and packet switching, making it suitablefrequencyhopping spread-spectrum technology to
for voice as well as data. Instead of fumbling withovercome interference and fading. Spread
a cell phone while driving, for example, the userspectrum is a digital coding technique in which the
can wear a lightweight headset to answer a callsignal is taken apart or
and engage in a conversation even if the phone is“spread” so that packets are
tucked away in a briefcase or purse. While usefulsent over time slots of 625 microseconds
in minimizing the need for cables, wireless local(ìs) in length between the master and slave
area networks (LANs) are not intended forunits within a piconet. It sounds more like noise as
interconnecting the range of mobile devices peopleit is sent through the air. With the addition of
carry around everyday between home and office.frequency hopping—having the signals
For this, Bluetooth is needed. And in the office, askip from one frequency to
Bluetooth portable device can be TABLE B-1another—wireless transmissions are
Performance Characteristics of Bluetoothmade even more secure. Bluetooth specifies a
Products Feature/Function Performancerate of 1600 hops per second among 79
Connection type Spread spectrum (frequencyfrequencies. Since only the sender and receiver
hopping) Spectrum 2.4-GHz ISM (industrial,know the hopping sequence for coding and
scientific, and medical) band Transmission power 1decoding the signal, eavesdropping is virtually
milliwatt (mW) Aggregate data rate 1 Mbps usingimpossible. For enhanced security, Bluetooth also
frequency hopping Range Up to 30 feet (9supports device authentication and encryption.
meters) Supported stations Up to eight devicesOther frequency-hopping transmitters in the
per piconet Voice channels Up to threevicinity will be using different hopping patterns and
synchronous channels Data security Formuch slower hop rates than Bluetooth devices.
authentication, a 128-bit key; for encryption, theAlthough the chance of Bluetooth devices
key size is configurable between 8 and 128 bitsinterfering with non-Bluetooth devices that share
Addressing Each device has a 48-bit Media Accessthe same 2.4-GHz band is minimal, should non-
Control (MAC) address that is used to establish aBluetooth transmitters and Bluetooth transmitters
connection with another device in motion whilecoincidentally attempt to use the same frequency
connected to the LAN access point as long as theat the same moment, the data packets
user stays within the 30-foot range. Bluetooth cantransmitted by one or both devices will become
be combined with other technologies to offergarbled in the collision, and a retransmission of the
wholly new capabilities, such as automaticallyaffected data packets will be required. Anew data
lowering the ring volume of cell phones or shuttingpacket will be sent again on the next hopping
them off as users enter quiet zones such ascycle of each transmitter. Voice packets, because
churches, restaurants, theaters, and classrooms.of their sensitivity to delay, are never
On leaving the quiet zone, the cell phones areretransmitted.
returned to their original settings.Points of Convergence
TopologyIn some ways, Bluetooth competes with infrared,
The devices within a piconet play one of twoand in other ways, the two technologies are
roles: that of master or slave. The master is thecomplementary. With both infrared and Bluetooth,
device in a piconet whose clock and hoppingdata exchange is considered to be a fundamental
sequence are used to synchronize all otherfunction. Data exchange can be as simple as
devices (i.e., slaves) in the piconet. The unit thattransferring business card information from a
carries out the paging procedure and establishes amobile phone to a palmtop or as sophisticated as
connection is by default the master of thesynchronizing personal information between a
connection. The slaves are the units within apalmtop and desktop PC. In fact, both
piconet that are synchronized to the master viatechnologies can support many of the same
its clock and hopping sequence.applications, raising the question: Why would users
The Bluetooth topology is best described as aneed both technologies?
multiplepiconet structure. Since Bluetooth supportsThe answer lies in the fact that each technology
both point-topoint and point-to-multipointhas its advantages and disadvantages. The very
connections, several piconets can be establishedscenarios that leave infrared falling short are the
and linked together in a topology called aones where Bluetooth excels, and vice versa.
“scatternet” whenever theTake the electronic exchange of business card
need arises.information between two devices. This application
Piconets are uncoordinated, with frequencyusually will take place in a conference room or
hopping occurring independently. Several piconetsexhibit floor where a number of other devices
can be established and linked together ad hoc,may be attempting to do the same thing. This is
where each piconet is identified by a differentthe situation where infrared excels. The
frequency-hopping sequence. All users participatingshortrange and narrow angle of
on the same piconet are synchronized to thisinfrared—30 degrees or
hopping sequence. Although synchronization ofless— allow each user to aim his or her
different piconets is not permitted in thedevice at the intended recipient with
unlicensed ISM band, Bluetooth units maypoint-and-shoot ease. Close proximity to another
participate in different piconets through Timeperson is natural in a business card exchange
Division Multiplexing (TDM). This enables a unit tosituation, as is pointing one device at another. The
sequentially participate in different piconets bylimited range and angle of infrared allow other
being active in only one piconet at a time.users to perform a similar activity with ample
With its service discovery protocol, Bluetoothsecurity and no interference. In the same
enables a much broader vision of networking,situation, a Bluetooth device would not perform as
including the creation of personal area networks,well as an infrared device. With its omnidirectional
where all the devices in a person’s lifecapability, the Bluetooth device must first discover
can communicate and work together. Technicalthe intended recipient. The user cannot simply
safeguards ensure that a cluster of Bluetoothpoint at the intended recipient—a
devices in public places, such as an airport loungeBluetooth device must perform a discovery
or train terminal, would not suddenly start talkingoperation that probably will reveal several other
to one another.Bluetooth devices within range, so close proximity
Technologyoffers no advantage here. The user will be forced
Two types of links have been defined forto select from a list of discovered devices and
Bluetooth in support of voice and data applications:apply a security mechanism to prevent
an asynchronous connectionless (ACL) link and aunauthorized access. All this makes the use of
synchronous connection-oriented (SCO) link. ACLBluetooth for business card exchange an
links support data traffic on a best-effort basis.awkward and needlessly time-consuming process.
The information carried can be user data orHowever, in other data-exchange situations,
control data. SCO links support real-time voice andBluetooth might be the preferred choice.
multimedia traffic using reserved bandwidth. BothBluetooth’s ability to penetrate solid
data and voice are carried in the form of packets,objects and its ability to communicate with other
and Bluetooth devices can support active ACLdevices in a piconet allow for data-exchange
and SCO links at the same time. ACL linksopportunities that are very difficult or impossible
support symmetric or asymmetricwith infrared. For example, Bluetooth allows a user
packetswitched point-to-multipoint connectionsto synchronize a mobile phone with a notebook
used for data. For symmetric connections, thecomputer without taking the phone out of a
maximum data rate is 433.9 kbps in bothjacket pocket or purse. This would allow the user
directions, send and receive. For asymmetricto type a new address at the computer and
connections, the maximum data rate is 723.2move it to the mobile phone’s
kbps in one direction and 57.6 kbps in the reversedirectory without unpacking the phone and setting
direction. If errors are detected at the receivingup a cable connection between the two devices.
device, a notification is sent in the header of theThe omnidirectional capability of Bluetooth allows
return packet so that only lost or corrupt packetssynchronization to occur instantly, assuming that
need to be retransmitted.the phone and computer are within 30 feet of
SCO links provide symmetric circuit-switchedeach other.
point-topoint connections, which are typically usedUsing Bluetooth for synchronization does not
for voice. Three synchronous channels of 64 kbpsrequire that the phone remain in a fixed location.
each are available for voice. The channels areIf a phone is carried about in a briefcase, the
derived through the use of either Pulse Codesynchronization can occur while the user moves
Modulation (PCM) or Continuous Variable Slopearound. This is not possible with infrared because
Delta (CVSD) Modulation. PCM is the standard forthe signal is not able to penetrate solid objects,
encoding speech in analog form into the digitaland the devices must be within a few feet of
format of ones and zeros. CVSD is anothereach other. Furthermore, the use of infrared
standard for analog-to-digital encoding but offersrequires that both devices remain stationary while
more immunity to interference and therefore isthe synchronization occurs.
better suited than PCM for voice communicationWhen it comes to data transfers, infrared does
over a wireless link. Bluetooth supports both PCMoffer a big speed advantage over Bluetooth. While
and CVSD; the appropriate voice-coding schemeBluetooth moves data between devices at an
is selected after negotiations between the linkaggregate rate of 1 Mbps, infrared offers 4 Mbps
managers of each Bluetooth device before theof data throughput. Ahigher -speed version of
call takes place.infrared is now available that can transmit data
Voice and data are sent as packets.between devices at up to 16 Mbps—a
Communication is handled with Time Divisionfour times improvement over the previous
Duplexing (TDD), which divides the channel intoversion. The higher speed is achieved with the
time slots, each 625 microseconds (ìs) inVery Fast Infrared (VFIR) Protocol, which is
length. The time slots are numbered according todesigned to address the new demands of
the clock of the piconet master. In the time slots,transferring large image files between digital
master and slave can transmit packets. In thecameras, scanners, and PCs. Even when Bluetooth
TDD scheme, master and slave alternativelyis enhanced for higher data rates in the future,
transmit. The master starts its transmission ininfrared is likely to maintain its speed advantage
even-numbered time slots only, and the slavefor many years to come. Bluetooth complements
starts its transmission in odd-numbered time slotsinfrared’s point-and-shoot ease of use
only. The start of the packet is aligned with thewith omnidirectional signaling, longer-distance
slot start. Packets transmitted by the master orcommunications, and capacity to penetrate walls.
the slave may extend over as many as five timeFor some users, having both Bluetooth and
slots.infrared will provide the optimal short-range
With TDD, bandwidth can be allocated on anwireless solution. For others, the choice of adding
as-needed basis, changing the makeup of theBluetooth or infrared will be based on the
traffic flow as demand warrants. For example, ifapplications and intended usage.
the user wants to download a large data file, as