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Chapter 18. Introduction to Wireless Networking

Chapter 18. Introduction to Wireless Networking

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technology.Useyourcellphonetoreportanautomobile

accident.Putupawirelesscameratomonitorachild.Access

theInternetthroughyourcellphone.Useacameraphoneto

captureon-the-spotphotosorevenvideoofaccidents,crimes,

younameit.Icouldgoonandon...



Note

It'shardtowritethischapterwithoutdiscussingthe

firstwirelessnetwork:radio!(Hey,we'retalking

electronictechnologyhere,notthevillagecrier.)

Broadcastcommercialradioisaone-waytechnique,

buttherearemanyvariantsoftwo-wayradios,from

thoseusedbypoliceandfiredepartmentstotheCB

radiosthatwereahotitemyearsago.However,

todaywe'rediscussingwirelesscommunications

betweencomputers,consumerelectronicdevicesthe

skyisthelimit.



Manymobilephonestodayarealreadyequippedtohandletext

messaging,Internetemail,somelimitedWeb-browsing

capabilities,andlow-resolutiondigitalphotography.This

chapterwillintroduceyoutojustafewofthemanyproblems

thatwirelessnetworkingcansolve,andintroduceyoutosome

ofthetechnologiesbasictomanyofthewirelesstechnologies.

OthernetworkingsolutionsarefoundinChapter23,"Security

andOtherWirelessTechnologies,"andBluetoothiscoveredin

Chapter22,"BluetoothWirelessTechnology."Although

Bluetoothisawirelesstechnology,itsoriginalpurposeisnotas

farreachingastheIEEE802.11b,802.11g,or802.11a

technologies(coveredinChapters19,"IEEE802.11b:Wi-Fi

Pioneer;"20,"FasterService:IEEE802.11a;"and21,"The

IEEE802.11gStandard").Instead,Bluetoothwasinitially



designedtoreplacecablesthatspanonlyaveryshortdistance.

YetnewprofilesdoindeedenableyoutocreateasmallLAN

usingBluetooth.Becauseofdistancelimitations,however,itstill

isnotthewirelessLANtechnologyofchoiceforanythingbuta

smallLANwithminimalbandwidthrequirements.

YoucannowuseBluetoothtoexchangedatabetweenamobile

phoneandaPC.Forexample,properlyconfigured,aBluetoothenabledwirelessphonecanbeusedforamodemconnectionto

aPDAorlaptopsimilarlyequipped.Or,youcanuseaBluetooth

keyboardandmousewithaBluetoothreceiverattachedtoyour

computer.Thisshort-distancecommunicationcapabilitydoes

notaddressthemuchlargerdistancesthatthespecifications

802.11a,802.11b,and801.11gcancover.Butitisimportantto

keepinmindthatalthoughyoucancreateasmallLANusing

Bluetooth,itwasnotdevelopedtocreateaLANorWAN.It

worksbestforshort-distancetransmissionsbetweenperipheral

devicesandconsumerelectronicdevices.Becauseitusesa

radiospectrum,itispossibletocreatemanydevices,suchasa

TVremote,usingBluetooth,becausecurrentdevicesrequirea

line-of-sight.Ifyourcableboxisinthelivingroomandyou're

inthebedroom,youcoulduseaBluetooth-enabledcable

box/remotetochangethechannel,allwhilestayinginbed!

Bluetoothshouldbeseenasacomplimentarywireless

technologyto802.11-basedwirelessnetworksratherthanasa

directcompetitor.

Despitemypredictionsinpreviouseditionsofthisbook,

Bluetoothdeviceshavefinallystartedtomakeittothelow-cost

marketplace,andyoucanexpecttoseemoreofthistechnology

astimemarcheson.Morethanafewusersliketheportability

oftheirkeyboardandmouse,aswellastheconvenienceof

wirelesssynchronizationwithaPDAordownloadingfroma

digitalcamera.







WhyWirelessNetworksHaveProliferated

Ifyoustilldon'talreadyusesometypeofwirelessdevice,it

won'tbelonguntilyoudo.Aswithanytypicalpurchaseof

computer/networkequipment,it'stheapplicationsthatdrive

thepurchases,especiallyinabusinessenvironment.Wireless

technologyisalreadythepreferredmethodfornetworking

homesandsmallbusinesses,andlargeenterprises,particularly

thosewithmulti-buildingcampuses,areusingwireless

networkingtoextendthereachoftheirexisting100Mbpsand

GigabitEthernet-wiredLANstocovereverypartofthecampus,

indoorsoroutdoors.Wirelessnetworkingisnowfastenough

thatitisbeingusedinsteadofwirednetworkinginnew

installationswheretherewasnoexistingwirednetwork.

Laptopcomputersprovidedthefirsttruemobilityforcomputer

users.Supportforlinkingthesepowerfulplatformstoa

computernetworkisusuallybuiltintotoday'slaptops,butif

yourlaptopdoesn'thavebuilt-inwirelesssupport,itcanbe

accomplishedeasilybymeansofeitheraPCCard/CardBus

networkadapteroradockingstation.ByusingDHCPtoassign

networkconfigurationinformation,it'seasytomoveaportable

computerfromonelocationtoanotherandstillprovideasimple

connectiontothenetwork.However,untiltheadventofwireless

networkconnectivity,thiskindofmobilitystilldependedona

wiredconnectionofsomesort.Byaddingwirelesscapabilityto

anexistingwirednetwork,themobilityandusefulnessofthe

notebookcomputerareincreaseddramatically.

Foratechnologytogrow,itmustsolvesomekindofproblem.

Thatis,itmustbeusefulinsomeway.Asdescribedpreviously

inthediscussionofthetypesofdevicesthatnowusewireless

networking,themostobviousbenefitthiskindofnetworking

providesismobility.WirelessLANshavebecomeamainstay

networkinginfrastructureformanySOHOnetworksaswellas

homenetworkswheremultiplecomputersmayshareasingle



Internetconnection.Otherbenefitsthatyoumightgetfrom

wirelessnetworkingincludethefollowing:

Fasterinstallationwhencomparedtocablednetworks.Just

configurethenetworkadapter(andAccessPointifyouhave

one)andstartnetworkingwithothers.

Adaptabilityinadynamicenvironment.

ThecapabilityofsharinganInternetorotherWAN

connection.

Thecontinuingdevelopmentofnewelectronicdevices(or

newerversions)thatusewirelesstechnology,suchasPDAs;

network-ready,all-in-onedevices;anddigitalprojectors.

WiththewidespreaddeploymentofwirelessAccessPoints

thatarebeingconstructedinpublicplaces,youcannow

accesstheInternetfrommostanyplacethathasasizable

population.Insomecases,youmightneedtousea

commercialnetworkonaper-hour,per-day,orper-month

accesschargebasisthroughvariouscommercialproviders.

Thesearecommonintruckstops,airports,andsome

restaurants,coffeeshops,andcopyshops.Somelocations

offerfreeservicefortheircustomers,soyoucansurfthe

Webwhileyoudrinkacupofjavaorgrablunch.Also,some

localitiesareconstructingcommunity-widewireless

networks,andmanypublicanduniversitylibrariesoffer

openwirelessLANsthatcanbeusedbyanyoneinthe

vicinity.Thetermshotspotandhotzoneareoftenusedto

indicatelocationsthatofferwirelessInternetaccess.

Reducedcostsinmanysituationsforexample,toavoid

havingtoinstallcablingthroughoutabuilding.



Onecaveattokeepinmindisthatsecurityisabigissuewith

wirelessnetworking.Although802.11bhardwaresupports

WiredEquivalentPrivacy(WEP)security,newerandmuchmore

securestandardshavebeendevelopedandaresupportedby

most802.11a-and802.11g-basednetworkhardware.See

Chapter23formoreinformation.

InatypicalLANsetup,itisnecessarytoinstallandconfigure

thenetworkingsoftwareontheclientcomputerandprovidethe

wiringfromthenetworkswitchtotheuser'sworkarea.Witha

wirelessLAN,youonlyneedtoinstallthewirelessNICand

configurethecomputer'snetworkingsoftware.Youdon'thave

tostringcablesthroughthebuildingforeachuser.Inan

environmentthatchangesrapidly,thiscanbeanadvantage.

Forexample,point-of-saleterminalsinalargestorecanbe

reconfiguredeasilyforseasonaladjustments,suchastheendof-the-yearChristmasbuyingspree.Hand-helddevicescanbe

usedforinventorycontrolandforcreatingcheckoutticketsthat

canbepresentedtoacashiertospeeduptheprocessofpaying

formerchandise.Inawarehouse,thefloorlayoutmightchange

duringtheyearforsimilarkindsofreasons.Relocating

computersismucheasierwhentherearenocablingissuesto

dealwith.AftertheinitialinvestmentismadeinwirelessLAN

devices,thecapabilitytoreconfigurethephysicalnetwork

topologycanresult,inmanycases,inreducedcostsovertime.

Anadhocnetworkortemporarysetup(seethefollowinglist)is

anotherimportantaspect.Forexample,ifyouareinthe

consultingbusinessandneedtohaveseveralconsultants

exchangeinformation,youcanusewirelessnetworkingtoset

upyourownlocalnetworkandbypassyourcustomer'swired

network.Knowingthisallowsyourclienttoworrylessabout

securitythaniftheclienthastogothroughthetypical

paperworkandothermanagementfunctionstogetyour

consultingteamconnectedtothecompanynetwork.

Inadditiontothesekindsofenvironments,youwillfind

wirelessLANsincreasinglybeingusedinsituationssuchasthe



following:

HospitalsPatientinformationcanbeobtainedeasilyusing

astandardlaptopcomputer,aspecializedterminal,ora

TabletPC.Insteadofhavingtoreturntoacentrallocation,

suchasthenurse'sstationonthehospitalfloor,doctorsand

nursescangetinformationquicklyastheymaketheir

patientrounds.

OlderbuildingsInsomecases,itcanbedifficulttowire

thepremisesforatraditionalnetwork.Someolderbuildings

thatdonothaveplenumareasintheceilingcanbedifficult

toadapt.Usingwirelesscommunicationsmakesnetworking

inthiskindofenvironmentaneasytask.

TemporarysetupsThisfeaturewasmentionedinthe

introductoryparagraphtothislist.Youcanextenditfurther

tosuchsituationsasatradeshow,wherethenetworkis

usuallysetupforonlyafewdays;thecomputerscanbe

configuredaheadoftimesothattheonlythingyour

companyrepresentativehastodoisturnthemon.

WarehouseandfactoryfloorsLaptopcomputersand

handheldbar-codescannersthatusewirelessLAN

technologycanquicklyreturntheinvestmentneededfor

theirimplementation.Inthiskindofsituation,however,itis

importanttotesttheequipmentfirsttoensurethatno

othermachinesordevicesintheareacaninterferewiththe

wirelesstransmissions.



Caution

Inadiscussionoftheapplicationsofwireless

networking,thedialogueshouldnotbelimitedto

computers.Asdatacollectiondevices,suchasbarcodescanners,orhandhelddata-entryterminals,



suchascashregisters,areequippedwithwireless

networkingconnections,manymorepracticaluses

forwirelesscommunicationswilldevelopinthenext

fewyears.

However,youshouldconsiderthatwhenmakinga

transactionatthistypeofservice,youcan'tbesure

ofwhatkindofsecurityisinplace.IfsimpleWEP

securityisused(seeChapter23),withasmallkey

(40bits),thenitisasimplematterforahackerto

usetoolsfreelyavailableontheInternettointercept

thesecommunications.

Beforeyougiveyourcreditcardtoacashier,you

mightwanttofindoutfromthestoremanagerwhat

kindofwirelesstechnologyisbeingusedtoensure

yourprivacy.Youshouldalsocheckyourcredit(or

debit)cardstatementeachmonthtobesureyour

informationhasnotbeencompromised!



AccessPointsandAdHocNetworks

BeforegettingintothespecificsaboutIEEEstandardsandhow

dataistransmittedonradiofrequencies,youfirstshouldlookat

thetopologyawirelessnetworkcantake.InChapter2,

"OverviewofNetworkTopologies,"youlearnedthatawireless

networkdoesn'tuseabustopology.Wirelessnetworksthatuse

aWAPuseaninfrastructurenetwork.TheWAPtransmitsdata

betweenstations.IfasingleWAPisused,thenetworkhasa

startopology;ifmultipleWAPsareused,thenetworkhasatree

topology.ManyWAPsalsoincludearouterforInternetaccess.

Anothertypeofwirelessnetworkisthead-hocnetwork,in

whichallnodesconnectdirectlywitheachother.Thisisamesh

networktopology.



AdHocNetworks

Asimplepeer-to-peernetwork,composedofcomputersthat

havecompatiblewirelessnetworkadaptercards,canbeusedto

quicklysetupasmallnetworkon-the-fly.Thiskindof

workgroupLANcanbeusefulwhenonlyafewstationsneedto

communicateinasmallgeographicalarea(seeFigure18.1).

Youcansetupyourownindividualnetworkatatradeshow,in

aconferenceroom,orevenforanentiresmall-business

enterprise.Wirelessbridges,whichyou'lllearnaboutinChapter

24,canextendthedistancebetweenwirelessAccessPointsso

thatinabusinessyoucancreateanetworkwithouthavingto

pullcablesatall.Forahomeoffice,whereyouprobablydon't

wanttodrillholesinyourwallsandpullcables,wireless

productscanbethebestsolutionpossible.



Figure18.1.Allyouneedtocreateanetworkonthe-flyareafewcomputers,eachwithawireless



networkadapter.



Thisnetworkisreferredtoasanadhocnetworkbecauseit

involvessimplepeer-to-peerconnectionsinawireless

environment.Nocentralhuborswitchcoordinatesthe

communicationsthatoccur.Instead,anycomputerequipped

withacompatiblewirelessadaptercanjointhead-hocnetwork,

providedthattheappropriatesecuritymechanismshavebeen

implemented.Forexample,ifyouareusingaWindows

operatingsystemandasimpleworkgroupsetupfornetwork

communications,anycomputerthatusesthatsameworkgroup

namecanjoinyoursmalladhocnetwork.Ifanyfileorprint

sharesareofferedbymembersofthisadhocnetwork,youcan

protectthembyusingapassword.Thisisnotagreatwayto

protectfiles,becauseanyonewhoneedstomaptoaresource

sharewillusethesamepassword.



Tip

Inaverysmallnetwork,usingsimplefilesharesisa

goodcompromiseconsideringtheadministrative

overheadinvolvedinmanagingamoresophisticated



securitysystem,suchasthatofferedbytheNTFS

filesystemusedbyWindowsNT/2000/XPand

WindowsServer.Ifyouneedtosegregateuserswho

needaccesstosome,butnotall,ofthesamefiles,

thendividethosefilesintoadirectory(andshareit

onthenetwork),andthencreateseparatefile

sharesforotherfilesneededbydifferentgroupsof

users.Folderscanbeconfiguredforread-onlyorfull

accessasneeded.



Ifyouusemoresecuremethods,suchasaUnixorLinux

systemwitheachworkstationrequiringausername/password,

youcancreateamoresecurewirelessadhocnetwork.The

samegoesforusingaWindowsdomain.Theonlydifferenceis

thatthenetworkiswirelesstherearenocablesandthesame

securitymechanismsyou'duseforawirednetworkshouldbe

usedforthissimplepeer-to-peernetwork.



Tip

Althoughthetermadhocnetworkisusuallyusedfor

aquicksetupofwirelessstations,anotherterm

you'llhearwhenreadingtheliteratureisBasic

ServiceSet(BSS).ABSSisnothingmorethantwo

ormorewirelesscomputersthathaveestablished

communicationsamongthemselves.Thesimplest

BSS,consistingofjustwirelesscomputersdescribed

inthissection,isalsocalledanIndependentBasic

ServiceSet(IBSS)becauseitdoesn'thaveanAPto

coordinatethecommunicationsbetweenthewireless

computers.



UsinganAccessPointtoMediateWireless

Communications

YoualsocanuseawirelessAccessPoint(AP)tocreateasmall

wirelessnetwork.Thisdevicecanalsobeattachedtoawired

network,whichisdiscussednext,orasastandalonedevicethat

caneffectivelydoublethedistanceofthewirelessnetwork.As

youcanseeinFigure18.2,iftheAccessPointdeviceisplaced

inthecenterofthenetwork,eachcomputerequippedwitha

wirelessnetworkadaptercanbeplacedfartherawayfromother

computers.Thisisbecauseeachcomputeronlyneedstobe

abletocommunicatewiththeAP,whichinturnrelaysthe

signalstoothercomputersthatparticipateinthewirelessLAN.

Essentially,anAPperformsthesamefunctionasaswitchina

traditionalwiredEthernetnetwork.



Figure18.2.Asyoucansee,anAPcandoublethe

rangeofawirelessnetwork.



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