Tải bản đầy đủ

Cisco press wireless networks first step aug 2004 ISBN 1587201119

WirelessNetworksfirst-step
ByJimGeier

Publisher :CiscoPress
PubDate :August03,2004
ISBN :1-58720-111-9
Pages :264


YourFirst-StepintotheWorldofWirelessNetworks
Noexperiencerequired!
Gainanunderstandingofwirelessnetworkingbasicswith
thisreaderfriendlyguide




Tableof

Contents
• Index


Thefirstbookanyoneshouldreadaboutwirelessnetworks
withstep-by-stepinstruction
Learnfromanauthorexperiencedinandknownforwriting
toageneralistwirelessaudiencewithaclear,simple-tounderstandstyle
Asabasicintroductiontowirelessnetworking,>Wireless
NetworksFirst-Step>assumesthatreadershavenoprevious
wirelessexperience.Thebookprovidesanoverviewofwireless
networking,alongwithdetailsofapplicablestandardsand
technologies.Newcomerstowirelesstechnologieswillfind
practicalinformationalongwithanabundanceofexamples.Case
studiesthroughoutthechaptersprovidereal-world
implementationexamples,presentedinanon-technicalfashion.
Implementationdetailsarediscussedonlytotheextentthat
readerscanidentifywhattypeofwirelessnetworkmaybe
appropriatefortheirneeds.
>WirelessNetworksFirst-Step>,writtenbyJimGeier,beginswith
abasicintroductiontowirelessnetworksandanexplanationof
radiowavecommunications.Itthenreviewsdifferenttypesof
wirelessnetworksincludingWPANs(wirelesspersonalarea
networks),WLANs(wirelesslocalareanetworks),wirelessMANs
(metropolitanareanetworks),andWWANs(wirelesswidearea
networks).Thefinalsectioncoverssecuritythreatstowireless
networks,andsolutionstocombatthesethreats.




WirelessNetworksfirst-step
ByJimGeier

Publisher :CiscoPress

PubDate :August03,2004
Tableof
ISBN :1-58720-111-9

Contents
Pages :264

• Index









Copyright
AbouttheAuthor
AbouttheTechnicalReviewers
Acknowledgments
Introduction
GoalsofThisBook




HowThisBookIsOrganized



WhoOughttoReadThisBook
StuffYou'llFindinThisBook


Chapter1.TheWirelessWorld:AnIntroductiontoConcepts
WirelessNetworksDefined

WirelessNetworkApplications



WirelessNetworkBenefits




ChapterSummary
ChapterReviewQuestions


Chapter2.WirelessSystemArchitecture:HowWirelessWorks
WirelessNetworkSystemComponents

NetworkArchitecture




InformationSignals




ChapterSummary

FlowofInformationThroughaWirelessNetwork
ChapterReviewQuestions


Chapter3.RadioFrequencyandLightSignalFundamentals:TheInvisibleMedium
WirelessTransceivers

UnderstandingRFSignals



UnderstandingLightSignals





Modulation:PreparingSignalsforPropagation
ChapterSummary

ChapterReviewQuestions


Chapter4.WirelessPANs:NetworksforSmallPlaces
WirelessPANComponents




WirelessPANSystems




ChapterSummary

WirelessPANTechnologies
ChapterReviewQuestions


Chapter5.WirelessLANs:NetworksforBuildingsandCampuses
WirelessLANComponents

WirelessLANSystems




WirelessLANTechnologies
ChapterSummary

ChapterReviewQuestions


Chapter6.WirelessMANs:NetworksforConnectingBuildingsandRemoteAreas
WirelessMANComponents




WirelessMANSystems




ChapterSummary

WirelessMANTechnologies
ChapterReviewQuestions


Chapter7.WirelessWANs:NetworksforWorldwideConnections
WirelessWANComponents

WirelessWANSystems




WirelessWANTechnologies
ChapterSummary

ChapterReviewQuestions


Chapter8.WirelessNetworkSecurity:ProtectingInformationResources
SecurityThreats




Encryption




SecurityPolicies

Authentication
ChapterSummary

ChapterReviewQuestions


AppendixA.AnswerstoChapterReviewQuestions
Chapter1




Chapter2



Chapter4

Chapter3




Chapter5




Chapter6
Chapter7

Chapter8


Glossary

Index


Copyright
Copyright©2005CiscoSystems,Inc.
CiscoPresslogoisatrademarkofCiscoSystems,Inc.
Publishedby:
CiscoPress
800East96thStreet
Indianapolis,IN46240USA
Allrightsreserved.Nopartofthisbookmaybereproducedor
transmittedinanyformorbyanymeans,electronicor
mechanical,includingphotocopying,recording,orbyany
informationstorageandretrievalsystem,withoutwritten
permissionfromthepublisher,exceptfortheinclusionofbrief
quotationsinareview.
PrintedintheUnitedStatesofAmerica1234567890
FirstPrintingAugust2004
LibraryofCongressCataloging-in-PublicationNumber:
2003111981

WarningandDisclaimer
Thisbookisdesignedtoprovideinformationaboutthebasicsof
wirelessnetworking.Everyefforthasbeenmadetomakethis
bookascompleteandasaccurateaspossible,butnowarranty
orfitnessisimplied.
Theinformationisprovidedonan"asis"basis.Theauthors,
CiscoPress,andCiscoSystems,Inc.shallhaveneitherliability
norresponsibilitytoanypersonorentitywithrespecttoany
lossordamagesarisingfromtheinformationcontainedinthis


bookorfromtheuseofthediscsorprogramsthatmay
accompanyit.
Theopinionsexpressedinthisbookbelongtotheauthorand
arenotnecessarilythoseofCiscoSystems,Inc.

Credits
Publisher
JohnWait
Editor-in-Chief
JohnKane
CiscoRepresentative
AnthonyWolfenden
CiscoPressProgramManager
NannetteM.Noble
ExecutiveEditor
BrettBartow
AcquisitionsEditor
MichelleGrandin
ProductionManager
PatrickKanouse


DevelopmentEditor
AndrewCupp
SeniorProjectEditor
SanDeePhillips
CopyEditor
LauraWilliams
TechnicalEditors
JoelBarrett
D.EdLamprecht
JosephRoth
EditorialAssistant
TammiBarnett
BookandCoverDesigner
LouisaAdair
Compositor
MarkShirar
Indexer
BradHerriman
Proofreader


TonyaCupp

FeedbackInformation
AtCiscoPress,ourgoalistocreatein-depthtechnicalbooksof
thehighestqualityandvalue.Eachbookiscraftedwithcare
andprecision,undergoingrigorousdevelopmentthatinvolves
theuniqueexpertiseofmembersfromtheprofessional
technicalcommunity.
Readers'feedbackisanaturalcontinuationofthisprocess.If
youhaveanycommentsregardinghowwecouldimprovethe
qualityofthisbook,orotherwisealterittobettersuityour
needs,youcancontactusthroughemailat
feedback@ciscopress.com.Pleasemakesuretoincludethe
booktitleandISBNinyourmessage.
Wegreatlyappreciateyourassistance.

TrademarkAcknowledgments
Alltermsmentionedinthisbookthatareknowntobe
trademarksorservicemarkshavebeenappropriately
capitalized.CiscoPressorCiscoSystems,Inc.cannotattestto
theaccuracyofthisinformation.Useofaterminthisbook
shouldnotberegardedasaffectingthevalidityofany
trademarkorservicemark.

CorporateandGovernmentSales
CiscoPressoffersexcellentdiscountsonthisbookwhen
orderedinquantityforbulkpurchasesorspecialsales.
Formoreinformationpleasecontact:U.S.Corporateand
GovernmentSales1-800-382-3419


corpsales@pearsontechgroup.com
ForsalesoutsidetheU.S.pleasecontact:InternationalSales
international@pearsoned.com

CorporateHeadquarters
CiscoSystems,Inc.
170WestTasmanDrive
SanJose,CA95134-1706
USA
www.cisco.com
Tel:408526-4000
800553-NETS(6387)
Fax:408526-4100
EuropeanHeadquarters
CiscoSystemsInternationalBV
Haarlerbergpark
Haarlerbergweg13-19
1101CHAmsterdam
TheNetherlands
www-europe.cisco.com
Tel:310203571000
Fax:310203571100
AmericasHeadquarters
CiscoSystems,Inc.
170WestTasmanDrive
SanJose,CA95134-1706
USA
www.cisco.com
Tel:408526-7660
Fax:408527-0883
AsiaPacificHeadquarters


CiscoSystems,Inc.
CapitalTower
168RobinsonRoad
#22-01to#29-01
Singapore068912
www.cisco.com
Tel:+6563177777
Fax:+6563177799
CiscoSystemshasmorethan200officesinthefollowing
countriesandregions.Addresses,phonenumbers,andfax
numbersarelistedontheCisco.comWebsiteat
www.cisco.com/go/offices.
Argentina•Australia•Austria•Belgium•Brazil•Bulgaria•
Canada•Chile•ChinaPRC•Colombia•CostaRica•Croatia•
CzechRepublicDenmark•Dubai,UAE•Finland•France•
Germany•Greece•HongKongSAR•Hungary•India•
Indonesia•Ireland•Israel•ItalyJapan•Korea•Luxembourg
•Malaysia•Mexico•TheNetherlands•NewZealand•Norway
•Peru•Philippines•Poland•PortugalPuertoRico•Romania•
Russia•SaudiArabia•Scotland•Singapore•Slovakia•
Slovenia•SouthAfrica•Spain•SwedenSwitzerland•Taiwan
•Thailand•Turkey•Ukraine•UnitedKingdom•UnitedStates
•Venezuela•Vietnam•Zimbabwe
Copyright©2003CiscoSystems,Inc.Allrightsreserved.CCIP,
CCSP,theCiscoArrowlogo,theCiscoPoweredNetworkmark,
theCiscoSystemsVerifiedlogo,CiscoUnity,FollowMe
Browsing,FormShare,iQNetReadinessScorecard,Networking
Academy,andScriptSharearetrademarksofCiscoSystems,
Inc.;ChangingtheWayWeWork,Live,Play,andLearn,The
FastestWaytoIncreaseYourInternetQuotient,andiQuick
StudyareservicemarksofCiscoSystems,Inc.;andAironet,
ASIST,BPX,Catalyst,CCDA,CCDP,CCIE,CCNA,CCNP,Cisco,
theCiscoCertifiedInternetworkExpertlogo,CiscoIOS,the
CiscoIOSlogo,CiscoPress,CiscoSystems,CiscoSystems
Capital,theCiscoSystemslogo,EmpoweringtheInternet


Generation,Enterprise/Solver,EtherChannel,EtherSwitch,Fast
Step,GigaStack,InternetQuotient,IOS,IP/TV,iQExpertise,
theiQlogo,LightStream,MGX,MICA,theNetworkerslogo,
NetworkRegistrar;Packet,PIX,Post-Routing,Pre-Routing,
RateMUX,Registrar,SlideCast,SMARTnet,StrataViewPlus,
Stratm,SwitchProbe,TeleRouter,TransPath,andVCOare
registeredtrademarksofCiscoSystems,Inc.and/orits
affiliatesintheU.S.andcertainothercountries.
AllothertrademarksmentionedinthisdocumentorWebsite
arethepropertyoftheirrespectiveowners.Theuseoftheword
partnerdoesnotimplyapartnershiprelationshipbetweenCisco
andanyothercompany.(0303R)
PrintedintheUSA

Dedications
ToMadison,Sierra,andEric


AbouttheAuthor
JimGeieristhefounderandprincipalconsultantofWirelessNets,Ltd.(www.wireless-nets.com),anindependentconsulting
firm,whichassistscompanieswiththedevelopmentand
deploymentofwirelessLANproductsandsystems.His20years
ofexperienceincludetheanalysis,design,software
development,installation,andsupportofnumerous
client/serverandwirelessnetwork-basedsystemsfor
enterprises,airports,homes,retailstores,manufacturing
facilities,warehouses,andhospitalsthroughouttheworld.
JimisavotingmemberwithintheWi-FiAlliance,responsiblefor
certifyinginteroperabilityof802.11(Wi-Fi)wirelessLANs.He
servedaschairmanoftheIEEEComputerSociety,Dayton
Section,andchairmanoftheIEEEInternationalConferenceon
WirelessLANImplementation.Hehasbeenanactivemember
oftheIEEE802.11WorkingGroup,responsiblefordeveloping
internationalstandardsforwirelessLANs.Jimisanadvisory
boardmemberofseveralleadingwirelessLANcompanies.
JimistheauthorofseveralbooksincludingWirelessLANs
(SAMS,ISBN:0672320584),WirelessNetworkingHandbook
(MTP,ISBN:156205631X),andNetworkReengineering
(McGraw-Hill,ISBN:007023034X),aswellasnumerous
articles.Heisalsoeditor-in-chiefofMobilizedSoftware.com,an
onlinepublicationassistingdeveloperswithimplementing
mobileapplications.
Jim'seducationincludesabachelor'sandmaster'sdegreein
electricalengineeringandamaster'sdegreeinbusiness
administration.
ContactJimGeieratjimgeier@wireless-nets.com.


AbouttheTechnicalReviewers
JoelBarrettisawirelessspecialistwithCiscoSystems.Hehas
attainedtheCiscoCCNP,CCDP,andwirelessspecialization,as
wellasCWNA,MCSE,andMasterCNE.WithinCisco,Joelisthe
teamleaderfortheChannelsTechnologyAdvisoryTeamfor
Mobility,anadvisorfortheEnterpriseMobilityVirtualTeam,and
amemberofCisco'sEnterpriseMobilityTechnologyLeadership
Program.HeisanadvisorfortheWirelessTechnologyForum,
andacoauthorandprincipletechnicaleditorforwirelessLAN
technologybooksincludingCWSPOfficialStudyGuideand
ManagingandSecuringaCiscoStructuredWireless-Aware
Network.
Joelandhiswife,BarbaraKurth,livenearAtlanta,Georgiawith
theirtwodaughtersandson.Hispersonalwebsiteis
http://www.brainslap.com/joel.
D.EdLamprechtisthemanageroftheProfessionalServices
GroupatMonarchMarkingSystems,whichfocusesoncustom
softwareandnetworksolutions.Hehasover17yearsof
programmingexperienceinapplications,operatingsystems,
andnetworkprogramming.In1988,EdjoinedMonarchMarking
Systems,acompanyspecializinginbarcodeprintersand
labels.Since1996,Edhasbeeninvolvedindata-collection
systemsprovidingwirelessnetworkconnectivitysolutionsof
handheldprintersanddatacollectionterminalsforretail,
industrial,manufacturing,andhealth-caremarkets.
AtMonarch,Edhasdevelopedclient/serverapplications,visited
customersitesforanalysisandproblemsolving,andprovided
internationaltrainingonproductsandwirelessconnectivity.Ed
holdssevenpatentsinbarcodesoftwareandhandheld
printer/datacollectors.
Edliveswithhiswife,Michelle,andhisson,Colin,inDayton,


Ohio.WhennottinkeringwithPCsandnetworksathome,he
enjoysmodelrailroading,railroadmemorabiliacollecting,
golfing,traveling,andspendingtimewithhisfamily.
JosephRothisaLieutenantCommanderintheU.S.Navy
currentlyservingasamilitaryprofessorandNetworkSecurity
GroupdepartmentheadattheNavalPostgraduateSchool
(NPS).Heholdsfourmaster'sdegrees:computerscience
(NPS),informationsystemtechnology(NPS),public
administration(UniversityofMaryland),andnationalsecurity
andstrategicstudies(NavalWarCollege).Josephalsoholdsa
bachelor'sdegreeincomputerengineeringfromGeorge
WashingtonUniversityandtwocertificatesofhighereducation
fromtheUniversityofCambridge.Hehasobtainednumerous
industrycertificationsincludingCCNA,CWNA,Security+,
Network+,andMCP.Hisarticleshavebeenpublishedin
InfoWorldandFederalComputerWeek.Josephservedin
EuropeforfiveyearsandhasbeendeployedtotheBalkansand
theMiddleEast.


Acknowledgments
I'dliketoofferthankstomyson,EricGeier,forassistingme
withtheresearchforthisbook.Ericisamemberofthe
technicalstaffofmyconsultingcompany,Wireless-Nets,Ltd.,
whereheresearchesandanalyzeswirelessnetwork
technologies,performswirelessLANanalysis,anddevelops
computer-basedtrainingcourses.
EricisaCertifiedWirelessNetworkProfessional(CWNP)and
founderofwww.wirelessnetworks4homes.com,awebsite
focusingonthedeploymentofwirelessLANsforhomesand
smalloffices.


Introduction
Forseveraldecades,peoplehavebeenusingcomputer
networkstointerconnectpersonalcomputersandserversin
companies,colleges,andcities.Anevolutionhasbeentaking
place,however,towardusingnetworkswirelessly.Infact,today
wirelessinterfacesareavailabletoutilizenetworkservicesthat
allowustousee-mailandaccessapplications,andbrowsethe
Internetfromjustaboutanywhere.
Thesewirelessapplicationsareenablingpeopletoextendtheir
workplaceinawaythatresultsinsignificantbenefits.Business
travelers,forexample,areabletorespondtoe-mailswhile
waitingforaflightatanairport.Ahomeownercaneasilyshare
acommonInternetconnectionamongmultiplePCsandlaptops
withoutrunningcabling.Thisbookexplainstheunderlying
technologiesthatmakethesetypesofapplicationspossible.


GoalsofThisBook
Theintentofthisbookistoofferabasicintroductiontowireless
networkapplications,components,andtechnologies.These
conceptsprovideasolidbasisforunderstandingvarious
wirelessnetworktopicsinmoredetail.Afterreadingthisbook,
you'llbeabletoeffectivelycontinueastudyofspecificwireless
networks.


WhoOughttoReadThisBook
Thisbookwaswrittenforanyonebeginningastudyofwireless
networks.Thereisnoneedforreaderstohaveatechnical
background.CEOs,managers,andbusinessownerswillbenefit
fromreadingthisbook,aswillengineersandtechnicians.Even
userswantingtounderstandtheinnerworkingsofwireless
networkswillfindthisbookinteresting.


HowThisBookIsOrganized
Thisbookcoversallaspectsofwirelessnetworks,with
emphasisontheuniqueattributesofwirelesssystems.Thefirst
threechaptersprovidethebasicbuildingblocksforabetter
understandingofthedifferenttypesofwirelessnetworksthat
thesubsequentchaptersdescribe.Thefinalchapteroffers
detailsonsecuringwirelessnetworks.
Chapter1,"TheWirelessWorld:AnIntroductionto
Concepts"Thischapterfullydefinesawirelessnetwork
andbrieflydefinesthevarioustypes.Manyexamplesof
wirelessnetworkapplicationsaregivenwithdiscussionof
resultingbenefits.
Chapter2,"WirelessSystemArchitecture:How
WirelessWorks"Thischapteroffersabroadexplanation
ofthevariouscomponentsofawirelessnetwork.By
illustratinghowinformationflowsthroughthenetwork,this
chapterprovidesanexcellentbasisforunderstandinghow
differenttypesofwirelessnetworksoperate.
Chapter3,"RadioFrequencyandLightSignal
Fundamentals:TheInvisibleMedium"Thischapter
detailshowradiofrequencyandlightsignalscarry
informationthroughtheairmedium.Thesearetheprimary
elementsthatdefineawirelessnetwork.
Chapter4,"WirelessPANs:NetworksforSmallPlaces"
Thischapterexplainsthecomponents,technologies,and
configurationsofawirelesspersonal-areanetwork(PAN).
Chapter5,"WirelessLANs:NetworksforBuildings
andCampuses"Thischapterexplainsthecomponents,


technologies,andconfigurationsofawirelesslocal-area
network(LAN).
Chapter6,"WirelessMANs:NetworksforConnecting
BuildingsandRemoteAreas"Thischapterexplainsthe
components,technologies,andconfigurationsofawireless
metropolitan-areanetwork(MAN).
Chapter7,"WirelessWANs:NetworksforWorldwide
ConnectionsResources"Thischapterexplainsthe
components,technologies,andconfigurationsofawireless
wide-areanetwork(WAN).
Chapter8,"WirelessNetworkSecurity:Protecting
InformationResources"Thischapterdescribespotential
securitythreatstoandcountermeasuresforwireless
networks.Wheninstallingawirelessnetwork,securityis
importantbecauseofthenatureofwirelesssignals.
AppendixA,"AnswerstoChapterReviewQuestions"
Thisappendixcontainsanswersandexplanationstothe
chapterreviewquestionsthatappearattheendofeach
chapter.
GlossaryTheglossaryisatoolthatyoucaneasily
referenceasyoucomeacrosskeytermsthroughoutthe
book.


StuffYou'llFindinThisBook
Thisbookincludesseveralfeaturesthatshouldhelpyoumaster
wirelesstopics.Here'sasummaryoftheelementsthatyou'll
find:
WhatYouWillLearnEverychapterbeginswithalistof
objectivesthatareaddressedinthechapter.Theobjectives
summarizewhatyouwilllearninthechapter.
KeytermsandGlossaryThroughoutthisbook,youwill
seekeytermsformattedwithboldanditalics.Theseterms
areparticularlysignificantinwirelessnetworking.So,ifyou
findyouaren'tfamiliarwiththetermoratanypointneeda
refresher,justlookupthetermintheGlossarytowardthe
endofthebooktofindafulldefinition.
ChaptersummariesEverychapterconcludeswitha
comprehensivechaptersummarythatreviewschapter
objectives,ensuringcompletecoverageanddiscussingthe
chapter'srelationshiptofuturecontent.
ChapterreviewquestionsEverychapterconcludeswith
reviewquestions.Thesequestionstestthebasicideasand
conceptscoveredineachchapter.Youcanfindtheanswers
andexplanationstothequestionsinAppendixA.
NontechieheadingsandexplanationsTheheadingsand
textusedthroughoutthisbookavoidtheuseoftechnical
termswhenpossible,focusinginsteadonwordsthat
connotesomethingabouttheunderlyingconcepts.
Theillustrationsinthisbookusethefollowingiconsfor
networkingdevicesandconnections:



Chapter1.TheWirelessWorld:An
IntroductiontoConcepts
WhatYouWillLearn
Afterreadingthischapter,youshouldbeableto
CompareandcontrastwirelessPANs,LANs,MANs,and
WANs
Recognizegeneralexamplesofwirelessnetwork
applications
Understandthebenefitsofwirelessnetworks
Wirelessnetworksplayacrucialroleinthelivesofpeopleat
work,home,andpublicplaces.Eventhoughawirelessnetwork
hasasimplepurpose,whichistoprovideconnectionsbetween
usersandinformationsourceswithouttheuseofwires,critical
conceptsofwirelessnetworksmustbemasteredbefore
understandinghowtheyoperate.Thischapterpresentsa
thoroughdefinitionofwirelessnetworksandhowtheybenefit
usersindifferentapplications.


WirelessNetworksDefined
Awirelessnetworkenablespeopletocommunicateandaccess
applicationsandinformationwithoutwires.Thisprovides
freedomofmovementandtheabilitytoextendapplicationsto
differentpartsofabuilding,city,ornearlyanywhereinthe
world.Forexample,peopleathomeresearchingontheInternet
candosoinaquietareaawayfromnoisychildrenorinfrontof
thetelevisionwiththeentirefamilynearby.Wirelessnetworks
allowpeopletointeractwithe-mailorbrowsetheInternetfrom
alocationthattheyprefer.
Wirelessnetworkshavebeenaroundformanyyears.Infact,
earlyformsofwirelesscommunicationsincludeNative
Americanswavingbuffaloskinsoverafiretosendsmoke
signalstoothersovergreatdistances.Also,theuseofpulsing
lightscarryinginformationthroughMorsecodebetweenships
hasbeenandstillisanimportantformofcommunications.Of
course,cellphonesarealsoatypeofwirelesscommunication
andarepopulartodayforpeopletalkingtoeachother
worldwide.
Manytypesofwirelesscommunicationsystemsexist,buta
distinguishingattributeofawirelessnetworkisthat
communicationtakesplacebetweencomputerdevices.These
devicesincludepersonaldigitalassistants(PDAs),laptops,
personalcomputers(PCs),servers,andprinters.Computer
deviceshaveprocessors,memory,andameansofinterfacing
withaparticulartypeofnetwork.Traditionalcellphonesdon't
fallwithinthedefinitionofacomputerdevice;however,newer
phonesandevenaudioheadsetsarebeginningtoincorporate
computingpowerandnetworkadapters.Eventually,most
electronicswillofferwirelessnetworkconnections.
Aswithnetworksbasedonwire,oropticalfiber,wireless
networksconveyinformationbetweencomputerdevices.The


informationcantaketheformofe-mailmessages,webpages,
databaserecords,streamingvideoorvoice.Inmostcases,
wirelessnetworkstransferdata,suchase-mailmessagesand
files,butadvancementsintheperformanceofwireless
networksisenablingsupportforvideoandvoice
communicationsaswell.
AsdiscussedinChapter3,"RadioFrequencyandLightSignal
Fundamentals:TheInvisibleMedium,"wirelessnetworksuse
eitherradiowavesorinfraredlightasamediumfor
communicationbetweenusers,servers,anddatabases.This
typeofcommunicationisinvisibletothehumaneye.In
addition,theactualmedium(air)istransparenttotheuser.
Mostmanufacturersarenowintegratingthewirelessnetwork
interfacecard(NIC;alsoreferredtoasanadapter)andantenna
intocomputingdevicesandoutofviewfromtheuser.This
makeswirelesscomputingdevicesmobileandeasytouse.
Wirelessnetworksfallintoseveralcategories,dependingonthe
sizeofthephysicalareathattheyarecapableofcovering.The
followingtypesofwirelessnetworkssatisfydiverseuser
requirements:
WirelessPersonal-AreaNetwork(PAN)
WirelessLocal-AreaNetwork(LAN)
WirelessMetropolitan-AreaNetwork(MAN)
WirelessWide-AreaNetwork(WAN)
Thesetermsaremerelyanextensionofthemorebasicformsof
wirednetworks(suchasLANorWAN)thathavebeeninusefor
yearsbeforewirelessnetworkscameabout.
Table1-1showsabriefcomparisonoftheseformsofwireless


Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Tải bản đầy đủ ngay

×

×