Bluetooth n Pan

8/4/2019 Bluetooth n Pan

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BLUETOOTH


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What is Bluetooth?GoalsRequirementsUsage Models

Bluetooth ArchitectureSecurity


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Bluetooth is a new standard developed by agroup of electronics manufacturers that willallow any sort of electronic equipment -- from

computers and cell phones to keyboards andheadphones -- to make its own connections,without wires, cables or any direct action froma user.

A key difference with other existing wirelesstechnologies is that bluetooth enablescombined usability models based on functions provided by different devices .


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The Bluetooth Special Interest Groupcomprises more than 1000 companies.Themajor companies who created the technologyinclude

Intel3 comEriccsonIBMMotorolaNokiaToshiba


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The Name Bluetooth?The name is attributed to Harald Bluetoothwas king of Denmark around the turn of the

last millennium.Choosing this name for the standard indicateshow important companies from the Balticregion (nations including Denmark, Sweden,Norway and Finland) are to thecommunications industry


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Present wireless technology like i n f r a r e d data communication has two problems

1)Line of Sight 2) One to One Using d a t a s y n c h r o n i z in g e.g. hot synon a PDA --- problem of using the rightcradle and cable.BLUETOOTH OVERCOMES THESEPROBLEMS


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It provides agreement at the physical level --Bluetooth is a radio-frequency standard.

Provides agreement at the data link levelwhere products have to agree onwhen bits are senthow many will be sent at a timehow the parties in a conversation can besure that the message received is the sameas the message sent


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The Basic IdeaBluetooth is a standard for a small , cheapradio chip to be plugged into computers,printers, mobile phones, etc

Bluetooth chip is designed to replacecables.Information normally carried bythe cable, is transmitted at a specialfrequency to a receiver Bluetooth chip.

These devices can form a quick ad-hoc securepiconet and start communication.Connections in the piconets can occur evenwhen mobile.


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Piconet A collection of devices connected viaBluetooth technology in an ad hoc fashion.A piconet starts with two connecteddevices, and may grow to eight connecteddevices.All Bluetooth devices are peer units and haveidentical implementations. However, when

establishing a piconet, one unit will act as aMaster and the other(s) as slave (s) for theduration of the piconet connection.


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RequirementsLow cost as cables chip $5Secure as cables must support authentication andencryption

Must support both data and voice.Must connect to a variety of devices.Must be able to function in a noisy environment.Data rates 721kbps , using the 2.45Ghz radio

frequency band I.S.M (Industrial, scientific andmedical)Must support many simultaneous and private

piconets.Must be low power, compact and global.


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Usage Models- Voice/Data Access PointsConnecting a computingdevice to a communicatingdevice.

Allows any device with abluetooth chip to connect tothe internet while locatedwithin the range of theaccess point.

Example- a notebook couldlink to the internet using amobile phone as an accesspoint.Envisions public data accesspoints


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Usage models- Peripheral InterconnectsStandard peripheral deviceslike keyboard, mice, headsetsetc working over a wirelesslink.The same device can be usedin multiple functions e.g aheadset can access phoneswhile in the office and caninterface with a cellular phonewhen mobile.


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Usage model- Personal Area Networking.(PAN) Allows dynamicformation and

breakdown of PICONETS--ad-hocpersonal networks.


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Bluetooth ArchitectureCore Specification -Dealswith the lower layers of the architecture anddescribes how thetechnology works.Profile Specification -Focuses on how to build

interoperating devicesusing the coretechnology.


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RF LayerThe Radio (layer) is the lowest definedlayer of the Bluetooth specification.

It defines the requirements of theBluetooth transceiver device operatingin the 2.4GHz band.


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In order to minimize interference the nominalantenna power is 1 mW which can beextended to 100mW.The low power limits the range to about 10centimeters to 10 meters. With higher powerof 100mW range of 100meters can beachieved.It uses a packet switching protocol based ona technology called s p r e a d - s p e c t r u mf re q u e n c y h o p p i n g to spread the energy

across the ISM band.


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Baseband layer This layer defines thetiming, framing, packets and flow control onthe link.Link Manager Responsible for managingconnection states(authentication & encryption), enforcing fairness among slaves& power mangt.Logical Link Layer Handles multiplexing,segmentation and reassembly of largepackets and device discovery.

Audio The audio data is directly mapped tothe baseband layer.


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Bluetooth FrameEach frame consists of a transmit packet anda receive packet.

Each packet may have either 1, 3 or 5 slots of 625s.Single slot packet max data rate of 172Kbps

Multislot frames support higher rates721Kbps or a max. of 3 voice channels .


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Network Topology All units have a unique global ID(BD_Addr)address( 48 bits)

The unit that initializes the connection isassigned as the master which controls thetraffic of the connection.

A master can simultaneously connect upto

seven slaves.The master/slave roles can be swapped. A device can be a master in only one piconet at a time.


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Network Topology


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Forming a piconetNeeds two parameters --- a) Hopping patternof the radio it wishes to connect. b) Phasewithin the pattern i.e. the clock offset of thehops.The global ID defines the hopping pattern.The master shares its global ID and its clock

offset with the other radios which becomeslaves.The global ID and the clock parameters areexchanged using a FHS (Frequency Hoping

Synchronization) packet.


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Devices not connected to a piconet are in STANDBY mode, using low power.

A connection is made by either a PAGE command if the address is known or by the INQUIRY commandfollowed by a PAGE When a radio sends an INQUIRE command, all thelistening radios respond with their FHS packets, whichtells the inquiring radio of all the radios in the area.

All listening radios perform a page scan and/or aninquiry scan every 1.25 seconds.The master radio sends an FHS to the paged radio.


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Shows a bunch of bluetooth devices

in proximity of each other.Each device hasits own ID and itsclock offset


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Radio A has becomethe master and has

formed a piconetwith B and C as theslaves.Both B and C nowshare As ID and andclock offset.


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HOLD MODEWhen data needs to be transmitted very infrequently,thus conserving power.In this mode only an internal timer is running.No data is transferred when in HOLD mode.The master can put slaves on HOLD mode.

SNIFF MODE A slave device listens to the piconet at a reduced rate.The SNIFF interval is programmable.In both the HOLD and SNIFF states the device retainsits AMA.


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PARK MODEThe device has given up the AMA andhas become passive.The parked device will occasionallylisten to see if the master has sent anybroadcast data asking it to becomeactive.


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Types of Links and PacketsSynchronous Connection Oriented(SCO)

Point to point full duplex link.Typically used for voice data.These packets do not use CRC and arenot retransmitted.Needs an asynchronous connectionless(ACL) type link to be first established.


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Asynchronous Connectionless Link This is a packet switched link between amaster and slave.Supports both isochronous andasynchronous data.

Error Correction SchemesForward error correction(1/3 and 2/3) Automatic Repeat Request scheme.


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Security Authentication andencryption is providedat the Link Managerlayer.

The PIN is translatedinto a 128 bit l ink keywhich is used forauthentication.After authentication theradios will sett le on asuitable lengthencryption key to beused.Bluetooth relies on PINcodes to establish

trusted relationshipsbetween devices.


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ReferencesBluetooth Architecture Overview

James Kardachwww.bluetooth.comwww.palowireless.com
http://www.bluetooth.com/http://www.bluetooth.com/

Documents

Bluetooth n Pan