OReilly linux unwired feb 2004 ISBN 0596005830

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TableofContents
Index
Reviews
ReaderReviews
Errata
Academic

LinuxUnwired
ByEddDumbill,BrianJepson,

RogerWeeks

Publisher :O'Reilly
PubDate :April2004
ISBN :0-596-00583-0
Pages :312
Slots :1.0



LinuxUnwiredisaone-stopwireless
informationsourceforon-the-goLinuxusers.

Whetheryou'reconsideringWi-Fiasa
supplementoralternativetocableandDSL,
usingBluetoothtonetworkdevicesinyour
homeoroffice,orwanttousecellulardata
plansforaccesstodatanearlyeverywhere,
thisbookwillshowyouthefull-spectrum


viewofwirelesscapabilitiesofLinux,and
howtotakeadvantageofthem.



•
•
•
•
•
•


TableofContents
Index
Reviews
ReaderReviews
Errata
Academic

LinuxUnwired
ByEddDumbill,BrianJepson,

RogerWeeks

Publisher :O'Reilly
PubDate :April2004
ISBN :0-596-00583-0
Pages :312
Slots :1.0


Copyright

Foreword

Preface
WhatThisBookCovers

ConventionsUsedinThisBook




CommentsandQuestions
Acknowledgments


Chapter1.IntroductiontoWireless
Section1.1.RadioWaves

Section1.2.ConnectionsWithoutWires

Section1.3.WirelessAlphabetSoup



Section1.5.CellularData

Section1.4.Bluetooth






Section1.6.Infrared


Chapter2.Wi-FionYourLinuxBox
Section2.1.QuickStart

Section2.2.ChipsetCompatibility




Section2.3.FourStepstoWi-Fi
Section2.4.LinuxWi-FiDriversinDepth

Chapter3.GettingOntheNetwork
Section3.1.Hotspots

Section3.2.WirelessNetworkDiscovery


Chapter4.CommunicatingSecurely
Section4.1.ThePitfallsofWEP

Section4.2.TheFutureIs802.11i




Section4.3.WPA:aSubsetof802.11i
Section4.4.WPAonLinux


Chapter5.ConfiguringAccessPointswithLinux
Section5.1.Linux-FriendlyWirelessVendors

Section5.2.CommercialWirelessEquipmentOverview




Section5.3.ConfiguringAccessPoints
Section5.4.FlashingYourAccessPoint

Chapter6.BuildingYourOwnAccessPoint
Section6.1.Hardware

Section6.2.Software



Section6.3.Linux-PoweredOff-the-Shelf


Chapter7.Bluetooth
Section7.1.QuickStart

Section7.2.BluetoothBasics




Section7.3.BluetoothHardware




Section7.5.InstallingtheBlueZUtilities

Section7.7.GraphicalApplications

Section7.4.LinuxBluetoothSupport
Section7.6.BasicConfigurationandOperation
Section7.8.CoolBluetoothTricks


Chapter8.Infrared
Section8.1.IrDAintheKernel

Section8.2.PCLaptopwithBuilt-InIrDA




Section8.3.InfraredDongle




Section8.5.ConnectingtotheInternetwithaCellPhone

Section8.4.SharingaNetworkConnectionoverIrDA
Section8.6.TransferringFileswithOpenOBEX

Section8.7.SynchronizingwithaPalm
Section8.8.PocketPC


Chapter9.CellularNetworking
Section9.1.CellularData

Section9.2.SomeCellularCarriers




Section9.3.PhonesandCards




Section9.5.TextMessaging

Section9.4.SendingaFax
Section9.6.Acceleration



Chapter10.GPS
Section10.1.UsesofGPS

Section10.2.AGPSGlossary

Section10.3.GPSDevices




Section10.5.MappingWi-FiNetworkswithKismet



Section10.7.OtherApplications




Section10.4.ListeningtoaGPS
Section10.6.GpsDrive

Colophon
Index


Copyright©2004O'ReillyMedia,Inc.
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Foreword
Thisisabookabouttworevolutions:freesoftwareandfree
wirelessnetworking.
Thefirstrevolutionwasbornin1991,whenaloneFinnish
hackernamedLinusTorvaldsusedtheGNUProject'sfreeC
compilertobuildLinux,afreeUnix-likeoperatingsystem
kernel.Oneofthehallmarksofthiskernelwasitsreleaseunder
theGNUPublicLicense,whichguaranteedthatanyonewouldbe
abletocustomizeandimprovetheLinuxkerneltosuittheir
computingneeds,andthatthoseimprovementswouldbe
sharedwiththeotherusersoftheLinuxkernel.
Today,LinusTorvaldsisvirtuallyahouseholdname,andhis

brainchildhasgoneontostarinmillionsofpersonalcomputers,
webservers,supercomputingclusters,embeddeddevices,
mainframes,andmore.BolsteredbythesuccessofLinuxand
itsBSD-derivedcousins,aglobe-spanningFreeSoftware
movementhastakenhold,spawningthousandsofcommunitysupportedprojects,andfundamentallyalteringhowsoftwareis
madeanddistributedinthe21stcentury.
Althoughthesecondrevolutionhasbeenlurkinginthe
backgroundforyears,itreceivedamajorboostin1999from
thepublicationoftheIEEE802.11bstandard,aspecificationfor
wirelessdatanetworkingthatmadeuseofthe2.4GHz
microwaveband,whichhadlongbeenconsidered"junk"
spectrumintheU.S.Asconsumer802.11bdeviceshitthe
market,moreandmorepeoplewereabletousecomputersand
accessthenetworkfromaneverwideningarrayoflocalesliving
roomcouches,conferencerooms,coffeeshops,andevensunny
parkbenches.
Meanwhile,ordinaryindividualswerediscoveringthat,using


nothingmorethanoff-the-shelfradiohardwareandtheright
antennas,theycouldbuildwide-areaandevenmetropolitanareaIPnetworkinfrastructureforthefirsttimeever,withoutthe
needforcostlyorrestrictivegovernmentlicenses.Theresult
hasbeenaquantumleapinubiquitouscomputing,withmillions
of802.11devicesinuseacrosstheworld.ThenewerIEEE
802.11aand802.11gstandardsarenowimplementedtooffer
evenmorepossibilitiesforfreedatanetworking.
Theoperativewordattheheartofbothoftheserevolutionsis
theword"free,"buttheconceptitreferstoisfreedom.Trivially,
theyoffertheopportunitytodownloadanoperatingsystemfree
ofchargeorperhapstoescapethetyrannyofEthernetcables.

Butonadeeperlevel,theserevolutionspromisebasicfreedoms
ofactionandofspeechthefreedomtoemployyourcomputing
hardwaretocommunicatewithothersasyouseefit,andnot
merelyascommercialinterestsdictate.Unlikemanyofthe
technicalchoicesavailabletoyoutoday,Linuxand802.11serve
toenhanceyourfreedomandexpandyouroptions,ratherthan
toconstrainthem.
Asthetitleimplies,LinuxUnwiredguidesyouthrough
configuringandusingLinuxwiththe802.11protocols,aswell
asBluetooth,IR,cellulardatanetworking,andGPS.Ultimately,
though,thisisabookaboutfreedom.Thisbookshowsyouhow
toharnessthecombinedpowerofthesetechnologiestoexpand
youroptionsandyourtechnicalhorizons.
Welcometotherevolution(s).Mayyoudogoodwork!
SchuylerErle
February,2004


Preface
Takeatriptothecomputerstore,buyaWi-Ficard,andinsertit
intoyourLinuxnotebook.Youwillprobablyheartwobeeps;are
theybothhappybeeps,orisoneofthemanangrybeep?It's
possiblethatyouwillreceiveahappybeep,butwiththevariety
ofhardware,firmware,andsoftwaredriversforWi-Ficards,it's
quitelikelythatyouwillreceivetheangrybeep.Next,go
throughthisexercisewithaBluetoothadapter,cellphone,and
someotherrandomwirelesshardware.
Thisbookisallabouthearingthehappybeeps.
Wirelessnetworksarepoppingupeverywhere;fromWi-Fi
hotspotstocellulardataplans,youcanconnecttotheInternet

virtuallyanywhere.Youcanevencutmorecableswith
technologieslikeBluetoothandInfrared.Linuxisalreadyan
amazingoperatingsystem,andcombinedwithwireless,its
strengthsareamplified.
Butthingsreallyshinewhenyoucombinewirelesstechnologies.
Thisbookalsodiscussesusingwirelesstechnologyin
combination,whetheryouwanttoshareyourWi-Ficonnection
toBluetoothdevicesormapoutWi-FinetworkswithaGlobal
PositioningSystem(GPS)device.


WhatThisBookCovers
Thisbookexplainshowtousethefollowingwireless
technologieswithLinux:

WirelessFidelity(Wi-Fi)
Wi-Fiisshort-rangewirelessnetworkingthatsupportsraw
speedsupto54Mbps(about20-25Mbpsactualspeeds).
It'sanaffordablereplacementforwiredEthernet,and
includesthe802.11b,802.11g,and802.11aprotocols.
Chapter1throughChapter6discussWi-Fi.

Bluetooth
Bluetoothisawirelesscable-replacementthatallowsyouto
getridofUSBandserialcables.Youcanuseittoconnecta
PersonalDigitalAssistant(PDA),suchasaPalmorPocket
PC,toLinux;createanad-hocnetwork;ortransferfiles
betweencomputers.BluetoothiscoveredinChapter7.

Infrared

Infraredhasbeenavailableforalongtime,andinsome
cases,it'stheonlywaythattwodeviceswilltalktoeach
other,particularlywitholderPDAs.Infrareduseslight
wavesthatarejustoutsidetherangeofvisiblelight.
InfrarediscoveredinChapter8.


Cellularnetworking
AlthoughWi-Fiisfastandreliable,itdisappearsthe
momentyouleaveitsusefulrange.Cellularnetworkscover
largeareas,reachspeedsbetween40kbpsand100kbps,
andevenworkreliablywhileyouareinamovingvehicle.
Withunlimiteddataplansstartingat$19.99amonthfrom
someproviders,cellulardataplanscanbeauseful
complementtoWi-Fi.Chapter9coverscellulardata.

GlobalPositioningSystem(GPS)
UseaGPStofigureoutyourlocationintwoorthree
dimensions.PluggedintoaLinuxcomputer,aGPSdevice
becomesasourceoflocationdatathatcanbecombined
withfreelyavailablemapstoplotlocationsofwireless
networks,figureoutwhereyouare,ormapoutwhatever
interestsyou.GPSiscoveredinChapter10.


ConventionsUsedinThisBook
Thisbookusesthefollowingabbreviations:

Hz,kHz,MHz,andGHz
Hertz(cyclespersecond),kilohertz(onethousandhertz),

megahertz(onemillionhertz),andgigahertz(onebillion,or
109hertz)

bps,kbps,Mbps
Bitspersecond,kilobits(1,024bits)persecond,and
megabits(1,048,576bits)persecond

KB/s,MB/s
Kilobytes(1,024bytes)persecondandmegabytes
(1,048,576bytes)persecond

MB
Megabytes(1,048,576bytes)ofharddiskorRAMstorage

mW
Milliwatts;onethousandthofawattofpoweroutput


Thisbookusesthefollowingtypographicconventions:

Constantwidth
Usedforlistingtheoutputofcommand-lineutilities

Constantwidthitalic
Usedtoshowitemsthatneedtobereplacedincommands

Italic
Usedforemphasis,forfirstuseofatechnicalterm,andfor
exampleURLs

...
Indicatestextthathasbeenomittedforclarity

Thisiconindicatesatip,suggestion,orgeneralnote.

Thisiconindicatesawarningorcaution.


CommentsandQuestions
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Toasktechnicalquestionsorcommentonthebook,sendemail
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O'Reillyhasawebsiteforthisbookwhereexamples,errata,
andanyplansforfutureeditionsarelisted.Youcanaccessthis
siteat:
/>Formoreinformationaboutthisbookandothers,seethe
O'Reillywebsite:



Acknowledgments
RogerWeeks

Writingthisbookwouldnothavebeenpossiblewithoutthe
backingandinspirationofmywife,Cynthia.Despiteahouse
sometimestooclutteredwithgeekgear,longtechnical
conversations,andmorethanonelatenight,she'salwaysthere
forme.
ManythanksalsotoSchuylerErle,whonotonlygotthebook
approvedbyO'Reilly,butsomehowmanagedtoconvincethem
thatIshouldbetheauthor.
Allofthe"Cats"shouldbethankedpubliclyfortheiramazing
amountsofknowledge,friendship,andhardwork:Rob
Flickenger,SchuylerErle,AdamFlaherty,NateBoblitt,Jim
Rosenbaum,andRichGibson.Withoutthem,significantpartsof
theWestCoastwouldbeveryboring,andthewireless
communitywouldbemuchpoorer.
Finally,manythankstoBradSilvaforexcellenthardwareadvice
andsolderingskills.

EddDumbill
IwouldliketothankMarcelHoltmannandMaximKrasnyansky
fortheirdevotedworkontheBlueZLinuxBluetoothstackand,
ofcoursemywifeRachaelforherpatientsupport.

BrianJepson


MythanksgoouttoSchuylerErleandRobFlickengerfor
helpingtodeveloptheoriginaloutlineofthisbookandfor
technicalreview.ThanksalsotoAdamFlahertyfortechnical
review.I'mverygratefultoRogerandEddforbeingsuchgreat
coauthors.

I'despeciallyliketothankmywife,Joan,andmystepsons,
SeijiandYeuhi,fortheirsupportandencouragementthrough
mylatenightandweekendwritingsessions,myoccasionaltrips
aroundtowninacarfullofWi-FiandGPSequipment,andthe
variousmilliwattagethatsoakedthroughthewallsofmyhome
officewhileIworkedonthisbook.


Chapter1.IntroductiontoWireless
Wirelessnetworksuseradiowavestomovedatawithoutwires
andtheyhavebeenaroundinoneformoranotherfordecades.
Teletype,ortelex,systemswereestablishedworldwideinthe
early1920s.Thesesystemsusedcopperlinestoconnecttwoor
moreteletypemachines.Governmentinvestmentsinmilitary
radiosleadtoinnovationsinradio;teletypeoverradio(TOR),or
radioteletype,replacedmanyteletypesystems,particularlyin
third-worldcountriesthatlackedcopper-wireinfrastructures.In
manypartsoftheworld,TORisstillusedastheprimary
communicationsmediumforgovernments.TORusesthehigh
frequency(HF)radioband.We'llcoverthetypesofradiobands
laterinthischapter.
In1970,NormAbramson,aprofessorofengineeringatthe
UniversityofHawaii,developedaradio-basedcommunications
systemknownasALOHANET.Thiswastheworld'sfirstwireless
packet-switchednetwork,whichallowsmultipledevicesto
transmitandreceivedatasimultaneously.Theresearchbehind
ALOHANETwasusedbyBobMetcalfetodeveloptheEthernet
standardforwirednetworking.
Presently,therearemanytypesofwirelessnetworksinuse
aroundtheworld.The802.11protocolset,popularlyknownas

Wi-Fi,includeswirelessnetworkstandardsthatallowdata
transmissionuptoatheoretical54Mbps.TheGlobalPositioning
System(GPS)usesawirelessconnectionfromareceivertoa
seriesofsatellitestofixalocationpreciselyontheplanet.
Thereareseveralwirelessnetworkingstandardsinthemobilephoneworld,includingGeneralPacketRadioService(GPRS)
andCodeDivisionMultipleAccess(CDMA)1xRTT(1xRadio
TransmissionTechnology).Subsequentchapterswilldiscussall
oftheseindetail.


1.1RadioWaves
Radiowavesarecreatedwhenelectricallychargedparticles
acceleratewithafrequencythatliesintheradiofrequency(RF)
portionoftheelectromagneticspectrum.Otheremissionsthat
falloutsideoftheRFspectrumincludeX-rays,gammarays,and
infraredandultravioletlight.Whenaradiowavepassesa
copperwireoranotherelectricallysensitivedevice,itproduces
amovingelectriccharge,orvoltage,whichcanbetransformed
intoanaudioordatasignal.
Radiowavescanbedepictedmathematicallyasasinusoidal
curve,asshowninFigure1-1.

Figure1-1.Asinewaverepresentingaradio
wave

Thedistancecoveredbyacompletesinewave(acycle)is
knownasthewavelength.Theheightofthewaveiscalledthe
amplitude.Thenumberofcyclesmadeinasecondisknownas
thefrequency.FrequencyismeasuredinHertz(Hz),alsoknown
ascyclespersecond.So,a1Hzsignalmakesafullcycleonce

persecond.Youshouldbefamiliarwiththisunitof
measurement:ifyournewcomputer'sCPUoperatesat2GHz,
theinternalclockofyourCPUgeneratessignalsroughlyattwo
billioncyclespersecond.


Notethatfrequencyisinverselyproportionaltothewavelength:the
longerthewavelength,thelowerthefrequency;theshorterthe
wavelength,thehigherthefrequency.Thewavelengthofa1Hzsignal
isabout30billioncentimeters,whichisthedistancethatlighttravelsin
onesecond.A1MHzsignalhasawavelengthof300meters.

1.1.1RadioFrequencySpectrum
Toregulatetheuseofthevariousradiofrequencies,theFederal
CommunicationsCommission(FCC)intheUnitedStates
determinestheallocationoffrequenciesforvarioususes.Table
1-1showssomeofthebandsdefinedbytheFCC(see
/>Table1-1.Rangeoffrequenciesdefinedforthevariousbands
Frequency

Band

10kHzto30kHz

VeryLowFrequency(VLF)

30kHzto300kHz

LowFrequency(LF)

300kHzto3MHz

MediumFrequency(MF)

3MHzto30MHz

HighFrequency(HF)

30MHzto328.6MHz

VeryHighFrequency(VHF)

328.6MHzto2.9GHz

UltraHighFrequency(UHF)

2.9GHzto30GHz

SuperHighFrequency(SHF)

30GHzandhigher

ExtremelyHighFrequency(EHF)


Youcangetamoredetailedfrequencyallocationchartfrom
Thefollowing
conversionlistshouldhelpyouunderstandthischart:
1kilohertz(kHz)=1,000Hz
1megahertz(MHz)=1,000kHz

1gigahertz(GHz)=1,000MHz
Wirelessnetworksuseavarietyofradiofrequencies.Table1-2
showssomecommonwirelessnetworkprotocolsandthe
correspondingradiofrequencies.
Table1-2.Frequenciesusedbyvariouswirelessnetworks
Frequencyrange

Wirelessnetwork

2.45GHz

Bluetooth

2.4to2.483GHz

802.11,802.11b,802.11g

5.180GHzto5.805GHz

802.11a

1.2276and1.57542GHz

GPS

1.1.2RadioWaveBehavior
Radiowaves,similartolightwaves,exhibitcertain
characteristicswhencomingintocontactwithobjects.
Reflectionoccurswhenaradiowavehitsanobjectthatislarger
thanthewavelengthoftheradiowave(seeFigure1-2).The

radiowaveisthenreflectedoffthesurface.


Figure1-2.Reflectionofaradiowave

Refractionoccurswhenaradiowavehitsanobjectofahigher
densitythanitscurrentmedium(seeFigure1-3).Theradio
wavenowtravelsatadifferentangleforexample,waves
propagatingthroughclouds.

Figure1-3.Refractionofaradiowave

Scatteringoccurswhenaradiowavehitsanobjectofirregular
shape,usuallyanobjectwitharoughsurfacearea(seeFigure
1-4),andtheradiowavebouncesoffinmultipledirections.

Figure1-4.Scatteringofaradiowave

Absorptionoccurswhenaradiowavehitsanobjectbutisnot
reflected,refracted,orscattered.Rather,theradiowaveis
absorbedbytheobjectandisthenlost(seeFigure1-5).

Figure1-5.Absorptionofaradiowave



RadioInterferenceandAbsorption
Radiowavesaresubjecttointerferencecausedbyobjectsandobstaclesinthe
air.Suchobstaclescanbeconcretewalls,metalcabinets,orevenraindrops.
Generally,transmissionsmadeathigherfrequenciesaremoresubjecttoradio

absorption(bytheobstacles)andlargersignalloss.Largerfrequencieshave
smallerwavelengths;hence,signalswithsmallerwavelengthstendtobe
absorbedbytheobstaclesthattheycollidewith.Thiscauseshigh-frequency
devicestohaveashorteroperatingrange.
Fordevicesthattransmitdataathighfrequencies,muchmorepowerisneeded
inorderforthemtocoverthesamerangeascomparedtolower-frequency
transmittingdevices.

Diffractionoccurswhenobjectsblockaradiowave'spath.In
thiscase,theradiowavebreaksupandbendsaroundthe
cornersoftheobject(seeFigure1-6).Thispropertyallows
radiowavestooperatewithoutavisuallineofsight.

Figure1-6.Diffractionofradiowaves


1.2ConnectionsWithoutWires
Therearemanytypesofwirelessnetworks,suchasCellular
(wide-areawirelessnetworking),Wi-Fi(localandwidearea
wirelessnetworking),andBluetooth(cable-replacementand
short-rangewirelessnetworking).Allofthesenetworksrunwith
Linux.HereisalistoftasksyoucancompletewithLinuxand
wirelessnetworks:
Buildyourownwirelessaccesspoint.Athome,usea
Linuxboxasyourwirelessaccesspointandsecurefirewall
forabroadbandconnection,anduseaLinuxnotebookasa
wirelessclient.Tocontrolwhousesyouraccesspoint,build
acaptiveportal.It'salsopossiblethatyourbroadband
connectioniswirelessandusesapoint-to-pointdirectional
wirelessnetwork.

Synchronizeyourcontacts.Attheoffice,keepyour
contactslistfromyourLinuxdesktopsynchronizedwith
yourcellphoneusingBluetoothoraninfraredport.
UseacellularnetworkandGPSfortheultimateroad
warriorexperience.Ontheroad,useyourLinux-powered
PDAtocheckemailfromawirelesshotspot.Connectyour
cellphoneandlaptop,anduseahigh-speeddatanetwork
wherethereisadigitalcellsignal.HookaGPSreceiverto
yourlaptopandfindthatout-of-the-wayhotel.


1.3WirelessAlphabetSoup
Whileitisnotthesolefocusofthisbook,thereareseveral
chaptersthatdealentirelywith"Wi-Fi,"orWirelessFidelity.
ThisphraseistrademarkedbytheWi-FiAlliance,agroupthat
consistsofnearlyall802.11manufacturers.TheWi-FiAlliance
doesproducttestingandcertificationforinteroperability.
802.11wasdefinedasaprotocolbytheInstituteofElectrical
andElectronicsEngineers(IEEE)in1997.Thisprotocol
specificationallowedfor1and2Mbpstransferratesusingthe
2.4GHzISM(Industrial,Scientific,andMedical)band,whichis
opentounlicensedpublicuse.Priortotheadoptionofthis
standard,therewerevariouswirelessnetworkvendors
manufacturingproprietaryequipmentusingboththe2.4GHz
andthe900MHzbands.Theearlyadoptersoftheproprietary
technologiesand802.11wereprimarilythemanufacturingand
healthcareindustries,whichrapidlybenefitedfromtheir
employees'mobileaccesstodata.The802.11standarduses
spreadspectrummodulationtoachievehighdatarates.Two
typesofmodulationwerespecified:FrequencyHoppingand

DirectSequence.802.11alsousestheCarrierSenseMultiple
Access(CSMA),whichwasdevelopedforEthernetin1975with
theadditionofCollisionAvoidance(CA)referredtoasCSMA-CA.
In1999,theIEEEadoptedtwosupplementstothe802.11
standard:802.11aand802.11b.The802.11bstandardisalso
referredtoasHighRateDSandisanextensionoftheDirect
SequenceSpreadSpectrumtypeofmodulationspecifiedin
802.11.802.11buses14overlapping,staggeredchannels,each
channeloccupying22MHzofthespectrum.Thisstandard's
primarybenefitisthatitoffersdataratesof5.5and11Mbpsin
additiontothe12megabitsprovidedby802.11.802.11bhas
beenwidelyadoptedaroundtheworld,anditsproductshave
beenreadilyavailablesince1999.