OReilly 802 dot 11 wireless networks the definitive guide 2nd edition apr 2005 ISBN 0596100523

802.11®WirelessNetworksTheDefinitiveGuide
ByMatthewGast
...............................................
Publisher:O'Reilly
PubDate:April2005
ISBN:0-596-10052-3
Pages:656

TableofContents|Index

Asweallknowbynow,wirelessnetworksoffermanyadvantagesoverfixed(orwired)
networks.Foremostonthatlistismobility,sincegoingwirelessfreesyoufromthetether
ofanEthernetcableatadesk.Butthat'sjustthetipofthecable-freeiceberg.Wireless
networksarealsomoreflexible,fasterandeasierforyoutouse,andmoreaffordableto
deployandmaintain.
Thedefactostandardforwirelessnetworkingisthe802.11protocol,whichincludesWi-Fi
(thewirelessstandardknownas802.11b)anditsfastercousin,802.11g.Witheasy-toinstall802.11networkhardwareavailableeverywhereyouturn,thechoiceseemssimple,
andmanypeoplediveintowirelesscomputingwithlessthoughtandplanningthanthey'd
givetoawirednetwork.Butit'swisetobefamiliarwithboththecapabilitiesandrisks
associatedwiththe802.11protocols.And802.11WirelessNetworks:TheDefinitiveGuide,
2ndEditionistheperfectplacetostart.
Thisupdatededitioncoverseverythingyou'lleverneedtoknowaboutwirelesstechnology.
Designedwiththesystemadministratororserioushomeuserinmind,it'sano-nonsense
guideforsettingup802.11onWindowsandLinux.Amongthewiderangeoftopics
coveredarediscussionson:

deploymentconsiderations
networkmonitoringandperformancetuning
wirelesssecurityissues
howtouseandselectaccesspoints
networkmonitoringessentials

wirelesscardconfiguration
securityissuesuniquetowirelessnetworks


Withwirelesstechnology,theadvantagestoitsusersareindeedplentiful.Companiesno
longerhavetodealwiththehassleandexpenseofwiringbuildings,andhouseholdswith
severalcomputerscanavoidfightsoverwho'sonline.Andnow,with802.11Wireless
Networks:TheDefinitiveGuide,2ndEdition,youcanintegratewirelesstechnologyinto
yourcurrentinfrastructurewiththeutmostconfidence.


802.11®WirelessNetworksTheDefinitiveGuide
ByMatthewGast
...............................................
Publisher:O'Reilly
PubDate:April2005
ISBN:0-596-10052-3
Pages:656

TableofContents|Index

Copyright
Foreword
Preface
PrometheusUntethered:ThePossibilitiesofWirelessLANs
Audience
OvertureforBookinBlackandWhite,Opus2
ConventionsUsedinThisBook
HowtoContactUs
SafariEnabled
Acknowledgments
Chapter1.IntroductiontoWirelessNetworking
WhyWireless?
WhatMakesWirelessNetworksDifferent
ANetworkbyAnyOtherName...
Chapter2.Overviewof802.11Networks
IEEE802NetworkTechnologyFamilyTree
802.11NomenclatureandDesign
802.11NetworkOperations
MobilitySupport
Chapter3.802.11MACFundamentals
ChallengesfortheMAC
MACAccessModesandTiming
Contention-BasedAccessUsingtheDCF

FragmentationandReassembly
FrameFormat

EncapsulationofHigher-LayerProtocolsWithin802.11
Contention-BasedDataService
FrameProcessingandBridging
Chapter4.802.11FraminginDetail
DataFrames
ControlFrames
ManagementFrames
FrameTransmissionandAssociationandAuthenticationStates
Chapter5.WiredEquivalentPrivacy(WEP)
CryptographicBackgroundtoWEP
WEPCryptographicOperations
ProblemswithWEP
DynamicWEP

Chapter6.UserAuthenticationwith802.1X
TheExtensibleAuthenticationProtocol
EAPMethods
802.1X:NetworkPortAuthentication
802.1XonWirelessLANs
Chapter7.802.11i:RobustSecurityNetworks,TKIP,andCCMP
TheTemporalKeyIntegrityProtocol(TKIP)
CounterModewithCBC-MAC(CCMP)
RobustSecurityNetwork(RSN)Operations
Chapter8.ManagementOperations
ManagementArchitecture
Scanning
Authentication
Preauthentication
Association
PowerConservation
TimerSynchronization
SpectrumManagement
Chapter9.Contention-FreeServicewiththePCF
Contention-FreeAccessUsingthePCF
DetailedPCFFraming
PowerManagementandthePCF
Chapter10.PhysicalLayerOverview
Physical-LayerArchitecture
TheRadioLink
RFPropagationwith802.11

RFEngineeringfor802.11
Chapter11.TheFrequency-Hopping(FH)PHY
Frequency-HoppingTransmission
GaussianFrequencyShiftKeying(GFSK)
FHPHYConvergenceProcedure(PLCP)
Frequency-HoppingPMDSublayer
CharacteristicsoftheFHPHY
Chapter12.TheDirectSequencePHYs:DSSSandHR/DSSS(802.11b)
DirectSequenceTransmission
DifferentialPhaseShiftKeying(DPSK)
The"Original"DirectSequencePHY
ComplementaryCodeKeying
HighRateDirectSequencePHY
Chapter13.802.11aand802.11j:5-GHzOFDMPHY
OrthogonalFrequencyDivisionMultiplexing(OFDM)
OFDMasAppliedby802.11a
OFDMPLCP
OFDMPMD
CharacteristicsoftheOFDMPHY
Chapter14.802.11g:TheExtended-RatePHY(ERP)

802.11gComponents
ERPPhysicalLayerConvergence(PLCP)
ERPPhysicalMediumDependent(PMD)Layer
Chapter15.APeekAheadat802.11n:MIMO-OFDM
CommonFeatures
WWiSE
TGnSync
ComparisonandConclusions
Chapter16.802.11Hardware
GeneralStructureofan802.11Interface
Implementation-SpecificBehavior
ReadingtheSpecificationSheet
Chapter17.Using802.11onWindows
WindowsXP
Windows2000
WindowsComputerAuthentication
Chapter18.802.11ontheMacintosh
TheAirPortExtremeCard
802.1XontheAirPort

Chapter19.Using802.11onLinux

PCMCIASupportonLinux
LinuxWirelessExtensionsandTools
Agere(Lucent)Orinoco
Atheros-BasedcardsandMADwifi
802.1XonLinuxwithxsupplicant
Chapter20.Using802.11AccessPoints
GeneralFunctionsofanAccessPoint
PoweroverEthernet(PoE)
SelectingAccessPoints
Cisco1200AccessPoint
AppleAirPort
Chapter21.LogicalWirelessNetworkArchitecture
EvaluatingaLogicalArchitecture
TopologyExamples
ChoosingYourLogicalArchitecture
Chapter22.SecurityArchitecture
SecurityDefinitionandAnalysis
AuthenticationandAccessControl
EnsuringSecrecyThroughEncryption
SelectingSecurityProtocols
RogueAccessPoints
Chapter23.SitePlanningandProjectManagement
ProjectPlanningandRequirements
NetworkRequirements
PhysicalLayerSelectionandDesign
PlanningAccess-PointPlacement

UsingAntennastoTailorCoverage
Chapter24.802.11NetworkAnalysis
NetworkAnalyzers
Ethereal
802.11NetworkAnalysisChecklist
OtherTools
Chapter25.802.11PerformanceTuning
802.11PerformanceCalculations
ImprovingPerformance
Tunable802.11Parameters
Chapter26.ConclusionsandPredictions
StandardsWork




CurrentTrendsinWirelessNetworking


TheEnd

glossary


AbouttheAuthor

Colophon

Index

802.11®WirelessNetworks:TheDefinitiveGuide,
SecondEdition
byMatthewS.Gast
Copyright©2005MatthewS.Gast.Allrightsreserved.
PrintedintheUnitedStatesofAmerica.
PublishedbyO'ReillyMedia,Inc.,1005GravensteinHighway
North,Sebastopol,CA95472.
O'Reillybooksmaybepurchasedforeducational,business,or
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Editor:

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ProductionEditor:

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PrintingHistory:

April2002:

FirstEdition.

April2005:

SecondEdition.

NutshellHandbook,theNutshellHandbooklogo,andthe
O'ReillylogoareregisteredtrademarksofO'ReillyMedia,Inc.


802.11®WirelessNetworks:TheDefinitiveGuide,Second
Edition,theimageofahorseshoebat,andrelatedtradedress
aretrademarksofO'ReillyMedia,Inc.
802.11®andall802.11-basedtrademarksandlogosare
trademarksorregisteredtrademarksofIEEE,Inc.intheUnited
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ofIEEE.
Manyofthedesignationsusedbymanufacturersandsellersto
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thosedesignationsappearinthisbook,andO'ReillyMedia,Inc.
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Whileeveryprecautionhasbeentakeninthepreparationofthis
book,thepublisherandauthorassumenoresponsibilityfor
errorsoromissions,orfordamagesresultingfromtheuseof

theinformationcontainedherein.
ISBN:0-596-10052-3
[M]


Foreword
MatthewGastwasmymentorlongbeforeImethim.Ibegan
reportingonwirelessdatanetworkinginOctober2000whenI
discoveredthatApple'sclaimsforits802.11b-basedAirPort
BaseStationwereactuallytrue.
I'dbeenburnedwithanotherformofwirelessnetworkingthat
usedinfrared,andhadspentmanyfruitlesshoursusingother
"interesting"networkingtechnologiesthatledtodeadends.I
figured802.11bwasjustanotherone.WasIgladIwaswrong!
Thisdiscoverytookmedownapaththatled,inexorably,tothe
firsteditionof802.11WirelessNetworks.Howdidthisstuff
actuallyworkasadvertised?IknewplentyabouttheISO
model,TCP/IP,andEthernetframes,butIcouldn'treconcilea
mediuminwhichallpartiestalkedinthesamespacewithwhat
IknewaboutEthernet'smethodsofcopingwithshared
contention.
MatthewtaughtmethroughwordsandfiguresthatIdidn't
originallyunderstand,butreturnedtoagainandagainasI
descendedfurtherintotechnicaldetailinmyattemptsto
explainWi-Fitoabroaderandbroaderaudiencethrough
articlesinTheNewYorkTimes,TheSeattleTimes,PCWorld,
andmyownWi-FiNetworkingNews
()siteoverthelastfiveyears.
Istartinglearningacronymsfrom802.11WirelessNetworks
andusedMatthew'sbooktogobeyondexpandingWDSinto

WirelessDistributionSystemintounderstandingpreciselyhow
twoaccesspointscouldexchangedatawitheachotherthrough
abuilt-in802.11mechanismthatallowedfourpartiestoa
packet'stransit.
Nowastimewentbyandthe802.11familygrewandbecame


baroque,thefirsteditionofthistitlestartedfeelingalittleout
ofdatealthoughitremainedsurprisinghowmany"new"
innovationswerefirmlyrootedindevelopmentsoftheearlyto
mid-1990s.Thealphabetsoupofthefirsteditionwasgruel
comparedtothemulligatawnyof2005.
Matthewfilledthegapbetweenthebookandcontemporary
wirelessrealitythroughhisongoingwritingatO'Reilly's
WirelessDevCenter,whichIreadavidly.Andsomewherein
thereIwasintroducedtoMatthewataWi-FiPlanetconference.
Wehititoffimmediately:Istartedpesteringhimfordetails
about802.1X,ifIremembercorrectly,andhewantedtotalk
aboutbooksandbusiness.(Iwoundupwritingtwoeditionsofa
generalmarketWi-Fibook,neitherofwhichdidnearlyaswell
asMatthew'sextraordinarilytechnicalone.)
Sincethen,Ihavebeenintherareandprivilegedpositiontobe
therecipientofMatthew'sgenerositywithhisknowledgeand
humbleinsight.Matthewisn'tonewhoassumes;heresearches.
Hisnaturalcuriositycompelshimtodiguntilhegetsananswer
that'stechnicallyandlogicallyconsistent.
Take,forinstance,theincrediblypoliticalandcomplicated
evolutionofthe802.1Xstandard.(Iknow,fromMatthew,that
it'sproperlycapitalizedsinceit'safreestandingstandardnot
reliantonotherspecifications.EventheIEEEmakesthis

mistake,andit'stheirruleforcapitalizationthatwe'reboth
following.)
802.1XissimpleenoughinitsuseoftheExtensible
AuthenticationProtocol,agenericmethodofpassingmessages
amongpartiestoauthentication.ButthewaysinwhichEAPis
securedare,quitefrankly,insanereflectingMicrosoftandCisco's
parallelbutconflictingattemptstocontrolsupportoflegacy
protocolsinawaythatonlydamageseasyaccesstoitshigher
levelofsecurity.
Mattheweschewedthereligiousdebateandspelledoutthe


variousmethods,difficulties,andinteroperabilityissuesinan
O'ReillyNetworkarticlethat'sthenuggetoftheexpanded
coverageinthisbook.Idefyanyreadertofindascogentand
exhaustiveanexplanationbeforethisbookwaspublished.
There'snothingasclear,comprehensive,andunaffectedby
marketpolitics.
Attimes,Matthewbemoanedthedelaysthatledtothegap
betweeneditionsofthisbook,duepartlytohisjoiningastartup
wirelessLANswitchcompany,butIthinkreadersarebetter
servedthroughhisveryhard-won,late-night,long-hours
knowledge.
Matthew'srelationshipwith802.11mighthavepreviouslybeen
consideredthatofahandymanwhoknewhiswayaroundthe
infrastructureofhishouse.Ifatoiletwasrunning,hecould
replaceavalve.Ifthelivingroomneedednewoutlets,hecould
researchtheprocessandwirethemin.
ButMatthew'snewjobtookhimallegoricallyfromaweekend
householdwarriortoajack-of-all-tradesman.Matthewcantear

outthoseinnerwalls,reframe,plumb,andwirethem,allthe
whilebitchingaboutthelocalbuildingcode.
It'sbeenapleasureknowingMatthew,andit'sevenmorea
pleasuretointroduceyoutohisbook,andletyouallinonwhat
Iandothershavebeenmoreprivaterecipientsofforthelast
fewyears.
GlennFleishman
Seattle,Washington
February2005


Preface
Peoplemove.Networksdon't.
Morethananythingelse,thesetwostatementscanexplainthe
explosionofwirelessLANhardware.Injustafewyears,
wirelessLANshavegrownfromahigh-priced,alpha-geek
curiositytomainstreamtechnology.
Byremovingthenetworkportfromtheequation,wireless
networksseparateuserconnectivityfromadirectphysical
locationattheendofacord.Toabstracttheuserlocationfrom
thenetwork,however,requiresagreatdealofprotocol
engineering.Foruserstohavelocation-independentservices,
thenetworkmustbecomemuchmoreawareoftheirlocation.
Thisbookhasbeenwrittenonmoreairplanes,inmoreairports,
andonmoretrainsthanIcaretocount.Muchoftheresearch
involvedindistillingevolvingnetworktechnologyintoabook
dependsonInternetaccess.Itissafetosaythatwithout
ubiquitousnetworkaccess,thearrivalofthisbookwouldhave
beenmuchdelayed.
Theadvantagesofwirelessnetworkshasmadethemafastgrowingmultibilliondollarequipmentmarket.WirelessLANsare

nowafixtureonthenetworkinglandscape,whichmeansyou
needtolearntodealwiththem.


PrometheusUntethered:ThePossibilitiesof
WirelessLANs
Wirelessnetworksofferseveraladvantagesoverfixed(or
"wired")networks:

Mobility
Usersmove,butdataisusuallystoredcentrally,enabling
userstoaccessdatawhiletheyareinmotioncanleadto
largeproductivitygains.Networksarebuiltbecausethey
offervaluableservicestousers.Inthepast,network
designershavefocusedonworkingwithnetworkports
becausethatiswhattypicallymapstoauser.Withwireless,
therearenoports,andthenetworkcanbedesignedaround
useridentity.

Easeandspeedofdeployment
ManyareasaredifficulttowirefortraditionalwiredLANs.
Olderbuildingsareoftenaproblem;runningcablethrough
thewallsofanolderstonebuildingtowhichtheblueprints
havebeenlostcanbeachallenge.Inmanyplaces,historic
preservationlawsmakeitdifficulttocarryoutnewLAN
installationsinolderbuildings.Eveninmodernfacilities,
contractingforcableinstallationcanbeexpensiveandtimeconsuming.

Flexibility

Nocablesmeansnorecabling.Wirelessnetworksallow
userstoquicklyformamorphous,smallgroupnetworksfor
ameeting,andwirelessnetworkingmakesmovingbetween
cubiclesandofficesasnap.Expansionwithwireless
networksiseasybecausethenetworkmediumisalready
everywhere.Therearenocablestopull,connect,ortrip
over.Flexibilityisthebigsellingpointforthe"hotspot"
market,composedmainlyofhotels,airports,trainstations
(andeventrainsthemselves!),libraries,andcafes.

Cost
Insomecases,costscanbereducedbyusingwireless
technology.Asanexample,802.11®equipmentcanbe
usedtocreateawirelessbridgebetweentwobuildings.
Settingupawirelessbridgerequiressomeinitialcapital
costintermsofoutdoorequipment,accesspoints,and
wirelessinterfaces.Aftertheinitialcapitalexpenditure,
however,an802.11-based,line-of-sightnetworkwillhave
onlyanegligiblerecurringmonthlyoperatingcost.Over
time,point-to-pointwirelesslinksarefarcheaperthan
leasingcapacityfromthetelephonecompany.
Untilthecompletionofthe802.11standardin1997,however,
userswantingtotakeadvantageoftheseattributeswereforced
toadoptsingle-vendorsolutionswithalloftheriskthat
entailed.Once802.11startedtheballrolling,speedsquickly
increasedfrom2Mbpsto11Mbpsto54Mbps.Standardized
wirelessinterfacesandantennashavemadeitmucheasierto
buildwirelessnetworks.Severalserviceprovidershavejumped
attheidea,andenthusiasticbandsofvolunteersinmostmajor

citieshavestartedtobuildpublicwirelessnetworksbasedon
802.11.
802.11hasbecomesomethingofauniversallyassumed
connectivitymethodaswell.Ratherthanwiringpublicaccess


portsupwithEthernet,acollectionofaccesspointscanprovide
connectivitytoguests.Intheyearssince802.11was
standardized,so-called"hotspots"havegonefromanexotic
curiosityinvenuesthatdonotmove,totechnologythatis
providingconnectivityevenwhileintransit.Bycoupling802.11
accesswithasatelliteuplink,itispossibletoprovideInternet
accessevenwhilemovingquickly.Severalcommuterrail
systemsprovidemobilehot-spots,andBoeing'sConnexion
servicecandothesameforanairplane,evenatacruising
speedof550milesperhour.


Audience
Thisbookisintendedforreaderswhoneedtolearnmoreabout
thetechnicalaspectsofwirelessLANs,fromoperationsto
deploymenttomonitoring:
Networkarchitectscontemplatingrollingout802.11
equipmentontonetworksorbuildingnetworksbasedon
802.11
Networkadministratorsresponsibleforbuildingand
maintaining802.11networks
Securityprofessionalsconcernedabouttheexposurefrom
deploymentof802.11equipmentandinterestedin
measurestoreducethesecurityheadaches

Thebookassumesthatyouhaveasolidbackgroundin
computernetworks.Youshouldhaveabasicunderstandingof
IEEE802networks(particularlyEthernet),theOSIreference
model,andtheTCP/IPprotocols,inadditiontoanyother
protocolsonyournetwork.WirelessLANsarenottotallynew
groundformostnetworkadministrators,buttherewillbenew
concepts,particularlyinvolvingradiotransmissions.


OvertureforBookinBlackandWhite,Opus2
Partofthedifficultyinwritingabookonatechnologythatis
evolvingquicklyisthatyouareneverquitesurewhatto
include.Theyearsbetweenthefirstandsecondeditionwere
filledwithmanydevelopmentsinsecurity,andupdatingthe
security-relatedinformationwasoneofthemajorpartsofthis
revision.Thisbookhastwomainpurposes:itismeanttoteach
thereaderaboutthe802.11standarditself,anditoffers
practicaladviceonbuildingwirelessLANswith802.11
equipment.Thesetwopurposesaremeanttobeindependentof
eachothersoyoucaneasilyfindwhatinterestsyou.Tohelp
youdecidewhattoreadfirstandtogiveyouabetterideaof
thelayout,thefollowingarebriefsummariesofallthechapters.
Chapter1,IntroductiontoWirelessNetworking,listswaysin
whichwirelessnetworksaredifferentfromtraditionalwired
networksanddiscussesthechallengesfacedwhenadaptingto
fuzzyboundariesandunreliablemedia.WirelessLANsare
perhapsthemostinterestingillustrationofChristianHuitema's
assertionthattheInternethasnocenter,justaneverexpandingedge.WithwirelessLANtechnologybecoming
commonplace,thatedgeisnowblurring.
Chapter2,Overviewof802.11Networks,describestheoverall

architectureof802.11wirelessLANs.802.11issomewhatlike
Ethernetbutwithanumberofnewnetworkcomponentsanda
lotofnewacronyms.Thischapterintroducesyoutothe
networkcomponentsthatyou'llworkwith.Broadlyspeaking,
thesecomponentsarestations(mobiledeviceswithwireless
cards),accesspoints(glorifiedbridgesbetweenthestations
andthedistributionsystem),andthedistributionsystemitself
(thewiredbackbonenetwork).Stationsaregroupedlogically
intoBasicServiceSets(BSSs).Whennoaccesspointis
present,thenetworkisaloose,ad-hocconfederationcalledan
independentBSS(IBSS).Accesspointsallowmorestructureby


connectingdisparatephysicalBSSsintoafurtherlogical
groupingcalledanExtendedServiceSet(ESS).
Chapter3,802.11MACFundamentals,describestheMedia
AccessControl(MAC)layerofthe802.11standardindetail.
802.11,likeallIEEE802networks,splitstheMAC-layer
functionalityfromthephysicalmediumaccess.Severalphysical
layersexistfor802.11,buttheMACisthesameacrossallof
them.Themainmodeforaccessingthenetworkmediumisa
traditionalcontention-basedaccessmethod,thoughitemploys
collisionavoidance(CSMA/CA)ratherthancollisiondetection
(CSMA/CD).Thechapteralsodiscussesdataencapsulationin
802.11framesandhelpsnetworkadministratorsunderstand
theframesequencesusedtotransferdata.
Chapter4,802.11FraminginDetail,buildsontheendof
Chapter3bydescribingthevariousframetypesandwherethey
areused.Thischapterisintendedmoreasareferencethan
actualreadingmaterial.Itdescribesthethreemajorframe

classes.Dataframesaretheworkhorseof802.11.Control
framesservesupervisorypurposes.Managementframesassist
inperformingtheextendedoperationsofthe802.11MAC.
Beaconsannouncetheexistenceofan802.11network,assistin
theassociationprocess,andareusedforauthenticating
stations.
Chapter5,WiredEquivalentPrivacy(WEP),describestheWired
EquivalentPrivacyprotocol.Inspiteofitsflaws,WEPisthe
basisformuchofthefollowingworkinwirelessLANsecurity.
ThischapterdiscusseswhatWEPis,howitworks,andwhyyou
can'trelyonitforanymeaningfulprivacyorsecurity.
Chapter6,UserAuthenticationwith802.1X,describesthe
802.1Xauthenticationframework.Inconjunctionwiththe
ExtensibleAuthenticationProtocol,802.1Xprovidesstrong
authenticationsolutionsandimprovedencryptiononWireless
LANs.


Chapter7,802.11i:RobustSecurityNetworks,TKIP,andCCMP,
describesthe802.11istandardforwirelessLANsecurity.In
recognitionofthefundamentalflawsofWEP,twonewlink-layer
encryptionprotocolsweredesigned,completewithnew
mechanismstoderiveanddistributekeys.
Chapter8,ManagementOperations,describesthemanagement
operationson802.11networks.Tofindnetworkstojoin,
stationsscanforactivenetworksannouncedbyaccesspointsor
theIBSScreator.Beforesendingdata,stationsmustassociate
withanaccesspoint.ThischapteralsodiscussesthepowermanagementfeaturesincorporatedintotheMACthatallow
battery-poweredstationstosleepandpickupbufferedtrafficat
periodicintervals.

Chapter9,Contention-FreeServicewiththePCF,describesthe
pointcoordinationfunction.ThePCFisnotwidelyimplemented,
sothischaptercanbeskippedformostpurposes.ThePCFis
thebasisforcontention-freeaccesstothewirelessmedium.
Contention-freeaccessislikeacentrallycontrolled,tokenbasedmedium,whereaccesspointsprovidethe"token"
function.
Chapter10,PhysicalLayerOverview,describesthegeneral
architectureofthephysicallayer(PHY)inthe802.11model.
ThePHYitselfisbrokendownintotwo"sublayers."ThePhysical
LayerConvergenceProcedure(PLCP)addsapreambletoform
thecompleteframeanditsownheader,whilethePhysical
MediumDependent(PMD)sublayerincludesmodulationdetails.
ThemostcommonPHYsuseradiofrequency(RF)asthe
wirelessmedium,sothechaptercloseswithashortdiscussion
onRFsystemsandtechnologythatcanbeappliedtoanyPHY
discussedinthebook.
Chapter11,TheFrequency-Hopping(FH)PHY,describesthe
oldestphysicallayerwith802.11.ProductsbasedontheFHPHY
arenolongerwidelysold,butagreatdealofearly802.11
equipmentwasbasedonthem.Organizationswithalong


historyofinvolvementwith802.11technologymayneedtobe
familiarwiththisPHY.
Chapter12,TheDirectSequencePHYs:DSSSandHR/DSSS
(802.11b),describestwophysicallayersbasedondirect
sequencespreadspectrumtechnology.Theinitial802.11
standardincludedalayerwhichofferedspeedsof1Mbpsand2
Mbps.Whileinteresting,itwasnotuntil802.11badded5.5
Mbpsand11Mbpsdataratesthatthetechnologyreallytook

off.Thischapterdescribesthetwoclosely-relatedPHYsasa
singlepackage.
Chapter13,802.11aand802.11j:5-GHzOFDMPHY,describes
the5-GHzPHYstandardizedwith802.11a,whichoperatesat54
Mbps.Thisphysicallayerusesanothermodulationtechnique
knownasorthogonalfrequencydivisionmultiplexing(OFDM).
SlightmodificationswererequiredtousethisPHYinJapan,
whichweremadebythe802.11jstandard.
Chapter14,802.11g:TheExtended-RatePHY(ERP),describes
aPHYwhichusesOFDMtechnology,butinthe2.4GHz
frequencybandsharedby802.11b.Ithaslargelysupplanted
802.11b,andisacommonoptionforbuilt-inconnectivitywith
newnotebookcomputers.ThePHYitselfisalmostidenticalto
the802.11aPHY.Thedifferencesareinallowingforbackwards
compatibilitywitholderequipmentsharingthesamefrequency
band.
Chapter15,APeekAheadat802.11n:MIMO-OFDM,describes
thePHYcurrentlyindevelopment.802.11nusesaPHYbased
onmultiple-input/multiple-output(MIMO)technologyformuch
higherspeed.Atthetimethisbookwenttopress,twoproposed
standardswereduelinginthecommittee.Thischapter
describesboth.
Chapter16,802.11Hardware,beginsthetransitionfrom
theoreticalmattersbasedonthestandardstohowthe
standardsareimplemented.802.11isarelativelyloose


standard,andallowsalargenumberofimplementationchoices.
Cardsmaydifferintheirspecifiedperformance,orinthe
mannerinwhichcertainprotocolsareimplemented.Manyof

thesevariationsarebasedonhowtheyarebuilt.
Chapter17,Using802.11onWindows,describesthebasic
driverinstallationprocedureinWindows,andhowtoconfigure
securitysettings.
Chapter18,802.11ontheMacintosh,describeshowtousethe
AirPortcardonMacOSXtoconnectto802.11networks.It
focusesonMacOSX10.3,whichwasthefirstsoftwareversion
toinclude802.1Xsupport.
Chapter19,Using802.11onLinux,discusseshowtoinstall
802.11supportonaLinuxsystem.Afterdiscussinghowtoadd
PCCardsupporttotheoperatingsystem,itshowshowtouse
thewirelessextensionsAPI.Itdiscussestwocommondrivers,
onefortheolderOrinoco802.11bcard,andtheMADwifidriver
fornewercardsbasedonchipsetsfromAtheros
Communications.Finally,itshowshowtoconfigure802.1X
securityusingxsupplicant.
Chapter20,Using802.11AccessPoints,describesthe
equipmentusedontheinfrastructureendof802.11networks.
Commercialaccesspointproductshavevaryingfeatures.This
chapterdescribesthecommonfeaturesofaccesspoints,offers
buyingadvice,andpresentstwopracticalconfiguration
examples.
Chapter21,LogicalWirelessNetworkArchitecture,marksthe
thirdtransitioninthebook,fromtheimplementationof802.11
onthescaleofanindividualdevice,tohowtobuild802.11
networksonalargerscale.Thereareseveralmajorstylesthat
canbeusedtobuildthenetwork,eachwithitsadvantagesand
disadvantages.Thischaptersortsthroughthecommontypesof
networktopologiesandoffersadviceonselectingone.

Chapter22,SecurityArchitecture,shouldbereadintandem
withthepreviouschapter.Maintainingnetworksecuritywhile
offeringnetworkaccessonanopenmediumisamajor
challenge.Securitychoicesandarchitecturechoicesare
mutuallyinfluential.Thischapteraddressesthemajorchoices
tobemadeindesigninganetwork:whattypeofauthentication
willbeusedandhowitintegrateswithexistinguserdatabases,
howtoencrypttraffictokeepitsafe,andhowtodealwith
unauthorizedaccesspointdeployment.
Chapter23,SitePlanningandProjectManagement,isthefinal
componentofthebookfornetworkadministrators.Designinga
large-scalewirelessnetworkisdifficultbecausethereisgreat
userdemandforaccess.Ensuringthatthenetworkhas
sufficientcapacitytosatisfyuserdemandsinallthelocations
whereitwillbeusedrequiressomeplanning.Choosing
locationsforaccesspointsdependsagreatdealontheradio
environment,andhastraditionallybeenoneofthemosttimeconsumingtasksinbuildinganetwork.
Chapter24,802.11NetworkAnalysis,teachesadministrators
howtorecognizewhat'sgoingonwiththeirwirelessLANs.
Networkanalyzershaveproventheirworthtimeandtimeagain
onwirednetworks.Wirelessnetworkanalyzersarejustas
valuableatoolfor802.11networks.Thischapterdiscusseshow
tousewirelessnetworkanalyzersandwhatcertainsymptoms
mayindicate.Italsodescribeshowtobuildananalyzerusing
Ethereal,andwhattolookfortotroubleshootcommon
problems.
Chapter25,802.11PerformanceTuning,describeshow
networkadministratorscanincreasethroughput.Itbeginsby
describinghowtocalculateoverallthroughputforpayloaddata,

andcommonwaysofincreasingperformance.Inrarecases,it
maymakesensetochangecommonlyexposed802.11
parameters.
Chapter26,ConclusionsandPredictions,summarizescurrent


standardsworkinthe802.11workinggroup.Aftersummarizing
theworkinprogress,IgettoprognosticateandhopethatI
don'thavetorevisethistooextensivelyinfutureeditions.

MajorChangesfromtheFirstEdition
Thethreeyearsbetween2002and2005sawagreatdealof
changeinwirelessLANs.Thestandardsthemselvescontinued
toevolvetoprovidegreatersecurityandinteroperability.
Followingthetypicaltechnologypathof"faster,better,and
cheaper,"thedatarateofmost802.11interfaceshasshotfrom
2or11Mbpswith802.11bto54Mbpswith802.11aand
802.11g.Increasedspeedwithbackwardscompatibilityhas
provedtobeacommerciallysuccessfulformulafor802.11g,
evenifithaslimitationswhenusedforlarge-scalenetworks.
Thecomingstandardizationof802.11nissettoboostspeeds
evenfarther.NewdevelopmentsinPHYtechnologyare
anxiouslyawaitedbyusers,asshownbythepopularreleasesof
pre-standardtechnology.Twoentirelynewchaptersaredevoted
to802.11gand802.11n.Europeanadoptionof802.11awas
contingentonthedevelopmentofspectrummanagementin
802.11h,whichresultedinextensiverevisionstothe
managementchapter.
Whenthefirsteditionwasreleasedin2002,theperceptionof
insecuritydominateddiscussionsofthetechnology.WEPwas

clearlyinsufficient,buttherewasnogoodalternative.Most
networkadministratorsweremakingdowithremoteaccess
systemsturnedinward,ratherthantheirnaturaloutward
orientation.Thedevelopmentof802.11iwasdoneagreatdeal
tosimplifynetworksecurity.Securityisnowbuiltintothe
specification,ratherthansomethingwhichmustbeaddedon
aftergettingthenetworkright.Securityimprovements
permeatethebook,fromnewchaptersshowinghowthenew
protocolswork,toshowinghowtheycanbeusedontheclient
side,tohowtosortthroughdifferentoptionswhenbuildinga


network.Sortingthroughsecurityoptionsismuchmore
complexnowthanitwasthreeyearsago,andmadeit
necessarytoexpandasectionofthedeploymentdiscussionin
thefirsteditionintoitsownchapter.
Threeyearsago,mostaccesspointswereexpensivedevices
thatdidnotworkwellinlargenumbers.Networkdeployment
wasoftenanexerciseinworkingaroundthelimitationsofthe
devicesofthetime.Threeyearslater,vastlymorecapable
devicesallowmuchmoreflexibledeploymentmodels.Rather
thanjusta"onesizefitsall"deploymentmodel,therearenow
multipleoptionstosortthrough.Securityprotocolshave
improvedenoughthatdiscussionsofdeployingtechnologyare
basedonwhatitcandofortheorganization,notonfearand
howtokeepitcontrolled.Asaresult,theoriginalchapteron
networkdeploymenthasgrownintothree,eachtacklinga
majorpartofthedeploymentprocess.