藍(lán)牙設(shè)備怎樣工作-通信類(lèi)外文文獻(xiàn)翻譯、中英文翻譯

機(jī)械專(zhuān)業(yè)中英文文獻(xiàn)翻譯第1頁(yè)共14頁(yè)HowBluetoothWorksChatschikBisdikianTherearelotsofdifferentwaysthatelectronicdevicescanconnecttooneanother.Forexample:ManydesktopcomputersystemshaveaCPUunitconnectedtoamouse,akeyboard,aprinterandsoon..Apersonaldigitalassistant(PDA)willnormallyconnecttothecomputerwithacableandadockingcradle.ATVwillnormallyconnecttoaVCRandacablebox,witharemotecontrolforalltherecomponents.Acordlessphoneconnectstoitsbaseunitradiowavesanditmayhaveaheadsetthatconnectstothephonewithawire.Inastereosystem,aCDplayerandotheraudiodevicesconnecttothereceiver,whichconnectstothespeakers.Whenyouusecomputers,entertainmentsystemsortelephones,thevariouspiecesandpartsofthesystemsmakeupacommunityofelectronicdevices.Thesedevicescommunicatewitheachotherusingavarietyofwires,cables,radiosignalsandinfraredlightbeams,andanevengreatervarietyofconnectors,plugsandprotocols.Theartofconnectingthingsisbecomingmoreandmorecomplexeveryday.WesometimesfeelasifweneedaPh.D.inelectricalengineeringjusttosetuptheelectronicsinourhomes!Inthisarticle,wewilllookatacompletelydifferentwaytoformtheconnections,calledBluetooth.Bluetoothiswirelessandautomatic,andhasanumberofinterestingfeaturesthatcansimplifyourdailylives.TheProblemsWhenanytwodevicesneedtotalktoeachother,theyhavetoagreeonanumberofpointsbeforetheconversationcanbegin.Thefirstpointofagreementisphysical:Willtheytalkoverwires,orthroughsomeformofwirelesssignals?Iftheyusewires,howmanyarerequired–one,two,eight,25?Oncethephysicalattributesaredecided,severalmorequestionsarise:Informationcanbesent1bitatatimeinaschemecalledparallelcommunications,oringroupsofbits(usually8or16atatime)inaschemecalledparallelcommunications..Adesktopcomputerusesbothserialandparallelcommunicationstotalktodifferentdevices:Modems,miceandkeyboardstendtotalkthroughseriallinks,whileprinterstendtouseparallellinks.Allofthepartiesinanelectronicdiscussionneedtoknowwhatthebitsmeanandwhetherthemessagetheyreceiveisthesamemessagethatwassent.Inmostcases,thismeansdevelopingalanguageofcommandsandresponsesknowasaprotocol.Sometypesofproductshaveastandardprotocolusedbyvirtuallyallcompaniessothatthecommandsforoneproductwilltendtohavethesameeffectonanother.Modemsfallintothiscategory.Otherproducttypeseachspeaktheirownlanguage,whichmeansthatcommandsintendedforonespecificproductwillseemgibberishifreceivedbyanother.Printersarelikethis,withmultiplestandardslikePCLandPostScript.Companiesthatmanufacturecomputers,entertainmentsystemsandotherelectronicdeviceshaverealizedthattheincrediblearrayofcablesandconnectorsinvolvedintheirproductsmakesitdifficultforevenexperttechnicianstocorrectlysetupacompletesystemonthefirsttry.Settingupcomputerandhomeentertainmentsystembecomesterrificallycomplicatedwhenthepersonbuyingtheequipmenthastolearnandrememberallthedetailstoconnectalltheparts.Inordertomakehomeelectronicmoreuserfriendly,weneedabetterwayforalltheelectronicpartofourmodernlifetotalktoeachother.That’swhereBluetoothcomesin.BluetoothBasicsBluetoothisastandarddevelopedbyagroupofelectronicsmanufacturersthatallowsanysortofelectronicequipment–fromcomputerandcellphonestokeyboardsandheadphones–tomakeitsownconnections,withoutwires,cablesoranydirectactionfromauser.Bluetoothisintendedtobeastandardthatworksattwolevels:Itprovidesagreementatthephysicallevel–Bluetoothisaradio-frequencystandard.Italsoprovidesagreementatthenextlevelup,whereproductshavetoagreeonwhenbitsaresent,howmanywillbesentatatimeandhowthepartiesinconversationcanbesurethatthemessagereceivedissameasthemessagesent.ThecompaniesbelongingtotheBluetoothSpecialInterestGroup,andtherearemorethan1,000ofthem,wanttoletBluetooth’sradiocommunicationstaketheplaceofwiresforconnectingperipherals,telephonesandcomputers.OtherWirelessConnectionsTherearealreadyacoupleofwaystogetaroundusingwires.Oneistocarryinformationbetweencomputersviabeamsoflightintheinfraredspectrum.Infraredreferstolightwavesofalowerfrequencythanhumaneyescanreceiveandinterpret..Infraredisusedinmosttelevisionremotecontrolsystems,andwithastandardcalledIrDA(InfraredDataAssociation)it`susedtoconnectsomecomputerswithperipheraldevices.Formostofthesecomputerandentertainmentpurposes,infraredisusedinadigitalmode–thesignalispulsedonandoffveryquicklytosenddatafromonepointtoanother.Infraredcommunicationsarefairlyreliableanddon`tcostverymuchtobuildintoadevice,butthereareacoupleofdrawbacks.First,infraredisa“l(fā)ineofsight”technology.Forexample,youhavetopointtheremotecontrolatthetelevisionorDVDplayertomakethingshappen.Theseconddrawbackisthatinfraredisalmostalwaysa“onetoone”technology.Youcansenddatabetweenyourdesktopcomputerandyourlaptopcomputer,butnotyourlaptopcomputerandyourPDAatthetime.Thesetwoqualitiesofinfraredareactuallyadvantageousinsomeregards.Becauseinfraredtransmittersandreceivershavetobelinedupwitheachother,interferencebetweendevicesisuncommon.Theone-to-onenatureofinfraredcommunicationsisusefulinthatyoucanmakesureamessagegoesonlytotheintendedrecipient,eveninaroomfullinfraredreceivers.TheBluetoothSolutionBluetoothisintendedtogetaroundtheproblemsthatcomewithbothinfraredandcablesynchronizingsystems.Thehardwarevendors,whichincludeSiemens,Intel,Toshiba,MotorolaandEricsson,havedevelopedaspecificationforaverysmallradiomoduletobebuiltintocomputer,telephoneandentertainmentequipment.Fromtheuser`spointofview,therearethreeimportantfeaturestoBluetooth:It`swireless.Whenyoutravel,youdon`thavetoworryaboutkeepingtrackofabriefcasefullofcablestoattachallofyourcomponents,andyoucandesignyourofficewithoutwonderingwhereallthewireswillgo.It`sinexpensive.Youdon`thavetothinkaboutit.Bluetoothdoesm`trequireyoutodoanythingspecialtomakeitwork.Thedevicesfindoneanotherandstrikeupaconversationwithoutanyuserinputatall.BluetoothFrequencyBluetoothcommunicatesonafrequencyof2.45gigahertz,whichhasbeensetasidebyinternationalagreementfortheuseofindustrial,scientificandmedicaldevices(ISM).Anumberofdevicesthatyoumayalreadyusetakeadvantageofthissameradio-frequencyband.Babymonitors,garage-dooropenersandthenewestgenerationofcordlessphonesallmakeuseoffrequenciesintheISMband.MakingsurethatBluetoothandtheseotherdevicesdon`tinterferewithoneanotherhasbeenacrucialpartofthedesignprocess.AvoidingInterference:LowPowerOneofthewaysBluetoothdevicesavoidinterferingwithothersystemisbysendingoutveryweaksignalsof1milliwatt.Bycomputer,themostpowerfulcellphonescantransmitasignalof3watts.ThelowpowerlimitstherangeofaBluetoothdevicetoabout10meters,cuttingthechancesofinterferencebetweenyourcomputersystemandyourportabletelephoneortelevision.Evenwiththelowpower,thewallsinyourhousewon`tstopaBluetoothsignal,makingthestandardusefulforcontrollingseveraldevicesindifferentrooms.WithmanydifferentBluetoothdevicesinaroom,youmightthinkthey`dinterferewithoneanother,butit`sunlikely.Onthenextpage,we`llseewhy.AvoidingInterference:HoppingItisunlikelythatseveraldeviceswillbeonthesamefrequencyatthesametime,becauseBluetoothusesatechniquecalledspread-spectrumfrequencyhopping.Inthistechnique,adevicewilluse79individual,randomlychosenfrequencieswithinadesignatedrange,changingfromonetoanotheronaregularbasis.InthecasaofBluetooth,thetransmitterschangefrequencies1,600timeseverysecond,meaningthatmoredevicescanmakefulluseofalimitedsliceofradiospectrum.SinceeveryBluetoothtransmitterusesspread-spectrumtransmittingautomatically,itunlikelythattwotransmitterswillbeonthesamefrequencyatthesametime.ThissametechniqueminimizestheriskthatportablephonesorbabymonitorswilldisruptBluetoothdevices,sinceanyinterferenceonaparticularfrequencywilllastonlyatinyfractionofasecond.WhenBluetooth-capabledevicescomewithinrangeofoneanother,anelectronicconversationtakesplacetodeterminewhethertheyhavedatatoshareorwhetheroneneedstocontroltheother.Theuserdoesn`thavetopressabuttonorgiveacommand–theelectronicconversationhappensautomatically.Oncetheconversationhasoccurred,thedevices–whetherthey`repartofacomputersystemorastereo–formanetwork.Bluetoothsystemscreateapersonal-areanetwork(PAN),orpiconet,thatmayfillaroomormayencompassnomoredistancethanthatbetweenthecellphoneonabelt-clipandtheheadsetonyourhead.Onceapiconetisestablished,themembersrandomlyhopfrequenciesinunisonsotheystayintouchwithoneanotherandavoidotherpiconetsthatmatbeoperatinginthesameroom.Example:NetworksLet`stakealookathowtheBluetoothfrequencyhoppingandpersonal-areanetworkkeepsystemfrombecomingconfused.Let`ssayyou`regotatypicalmodernlivingroomwiththetypicalmodernstuffinside.There`sanentertainmentsystemwithastereo,aDVDplayer,asatelliteTVreceiverandatelevision;there`scordlesstelephoneandapersonalcomputer.EachofthesesystemsusesBluetooth,andeachformsitsownpiconettotalkbetweenmainunitandperipheral.ThecordlesstelephonehasoneBluetoothtransmitterinthebaseandanotherinthehandset.Themanufacturerhasprogrammedeachunitwithanaddressthatfallsintoarangeofaddressesithasestablishedforaparticulartypeofdevice.Whenthebaseisfirstturnedon,itsendsradiosignalsaskingforaresponsefromanyunitswithanaddressinaparticularrange.Sincethehandsethasanaddressintherange,itresponds,andatinynetworkisformed.Now,evenifoneofthesedevicesshouldreceiveasignalfromanothersystem,itwillignoreitsinceit`snotfromwithinthenetwork.Thecomputerandentertainmentsystemgothroughsimilarroutines,establishingnetworksamongaddressinrangesestablishedbymanufacturers.Oncethenetworksareestablished,thesystemsbegintalkingamongthemselves.Eachpiconethopsrandomlythroughtheavailablefrequencies,soallofthepiconetsarecompletelyseparatedfromoneanother.Nowthelivingroomhasthreeseparatenetworkestablished,eachonemadeupofdevicesthatknowtheaddressoftransmittersitshouldlistentoandtheaddressofreceiversitshouldtalkto.Sinceeachnetworkischangingthefrequencyofitsoperationthousandoftimesasecond,it’sunlikelythatanytwonetworkwillbeonthesamefrequencyatthesametime.Ifitturnsoutthattheyare,thentheresultingconfusionwillonlycoveratinyfractionofasecond,andsoftwaredesignedtocorrectforsucherrorsweedsouttheconfusinginformationandgetsonwithnetwork’sbusinessExample:Half/FullDuplexMostofthetime,anetworkorcommunicationsmethodeitherworksinonedirectionatatime,calledhalf-duplexcommunication,orinbothdirectionsimultaneously,calledfull-duplexcommunication.Aspeakerphonethatletsyoueitherlistenortalk,butnotboth,isanexampleofhalf-duplexcommunication,whilearegulartelephonehandsetisafull-duplexdevice.BeacauseBluetoothisdesignedtoworkinanumberofdifferentcircumstances,itcanbeeitherhalf-duplexorfull-duplex.Thecordlesstelephoneisanexampleofausethatwillcallforafull-duplex(two-way)link,andBuletoothcansenddataatmorethan64,000bitspersecondinafull-duplexlink—aratehighenoughtosupportseveralhumanvoiceconversation.Ifaparticularusecallsforahalf-duplexlink—connectingtoacomputerprinter,forexample—Bluetoothcantransmitupto721kilobitspersecond(Kbps)inonedirection,with57.6Kpsintheother.Iftheusecallsforthesamespeedinbothdirections,alinkwith432.6-Kbpscapacityineachdirectioncanbemade.BluetoothSpaceHerearesomespecificationdetailsfromtheBluetoothWebsiteThedevicesinapiconetshareacommoncommunicationdatachannel.Thechannelhasatotalcapacityof1megabitpersecond(Mbps).Headersandhandshakinginformationconsumeabout20percentofthiscapacity.IntheUnitedStatesandEurope,thefrequencyrangeis2,400to2,483.5MHz,with791-MHzradiofrequency(RF)channels.Inpractice,therangeis2,402MHzto2,480MHz.InJapan,thefrequencyrangeis2,497MHzwith231-MHzrfchannels.Adatachannelhopsrandomly1,600timespersecondbetweenthe79(or23)RFchannels.Eachchannelisdividedintotimeslots625microsecondslong.Apiconethasamasteranduptosevenslzves.Packetscanbeuptofivetimeslotswide.Datainapacketcanbeupto2,745bitsinlength.Therearecurrentlytwotypesofdatatransferbetweendevices:SCO(synchronousconnectionoriented)andACL(asynchronousconnectionless).Inapiconet,therecanbeuptothreeSCOlinksof64,000bitspersecondeach.Toavoidtimingandcollisionproblems,theSCOlinksusereservedslotssetupbythemaster.MasterscansupportuptothreeSCOlinkswithone,twoorthreeslaves.OnemasterandslavecanhaveasingleACLlink.ACLiseitherpoint-to-point(mastertooneslave)orbroadcasttoalltheslaves.ACLslavescanonlytransmitwhenrequestedbythemaster.TheheartoftheBluetoothspecificationistheBluetoothprotocolstack.Byprovidingwell-definedlayersoffunctionality,theBluetoothspecificationensuresinteroperabilityofBluetoothdevicesandencouragesadoptionofBluetoothtechnology.Asyoucanseeinfigure1-1,theselayersrangefromthelow-levelradiolinktotheprofiles.Figure1-1：TheBluetoothprotocolstackLowerLayersAtthebaseoftheBluetoothprotocolstackistheradiolayer.TheradiomoduleinaBluetoothdeviceisresponsibleforthemodulationanddemodulationofdataintoRFsignalsfortransmissionintheair.TheradiolayerdescribesthephysicalcharacteristicsaBluetoothdevice`sreceiver-transmittercomponentmusthave.Theseincludemodulationcharacteristics,radiofrequencytolerance,andsensitivitylevel.Abovetheradiolayeristhebasebandandlinkcontrollerlayer.TheBluetoothspecificationdoesn`testablishacleardistinctionbetweentheresponsibilitiesofthebasebandandthoseofthelinkcontroller.Thebestwaytothinkaboutitisthatthebasebandportionofthelayerisresponsibleforproperlyformattingdatafortransmissiontoandfromtheradiolayer.Inaddition,ithandlesthesynchronizationoflinks.Thelinkcontrollerportionofthislayerisresponsibleforcarryingoutthelinkmanager`scommandsandestablishingandmaintainingthelinkstipulatedbylinkmanager.Thelinkmanageritselftranslatesthehostcontrollerinterface(HCI)commandsitreceivesintobaseband-leveloperations.Itisresponsibleforestablishingandconfiguringlinksandmanagingpower-changerequests,amongothertasks.You`venoticedlinksmentionednumeroustimeintheprecedingparagraphs.TheBluetoothspecificationdefinestwotypesoflinksbetweenBluetoothdevices:Synchronous,Connection-Oriented(SCO),forisochronousandvoicecommunicationusing,forexample,headsetsAsynchronous,Connectionless(ACL),fordatacommunication,suchastheexchangeofvCards.Eachlinktypeisassociatedwithaspecificpacket.ASCOlinkprovidesreservedchannelbandwidthforcommunicationbetweenamasterandaslave,andsupportsregular,periodicexchangeofdatawithnoretransmissionofSCOpackets.AnACLlinkexistsbetweenamasterandaslavethemomentaconnectionisestablished.ThedatapacketsBluetoothusesforACLlinksallhave142bitsofencodinginformationinadditiontoapayloadthatcanbeaslargeas2712bits.Theextraamountofdataencodingheightenstransmissionsecurity.Italsohelpstomaintainarobustcommunicationlinkinanenvironmentfillwithotherdevicesandcommonnoise.TheHCI(hostcontrollerinterface)layeractsasaboundarybetweenthelowerlayersoftheBluetoothprotocolstackandupperlayersTheBluetoothspecificationdefinesastandardHCItosupportBluetoothsystemsthatareimplementedacrosstwoseparateprocessors,Forexample,aBluetoothsystemoncomputermightuseaBluetoothmodule`sprocessortoimplementthelowerlayersofthestack(radio,baseband,linkcontroller,andlinkmanager).Itmightthenuseitsownprocessortoimplementtheupperlayers(L2CAP,RFCOMM,OBEX,andselectedprofiles).Inthisscheme,thelowerportionisknownastheBluetoothmoduleandtheupperportionastheBluetoothhost.Ofcourse,it`snotrequiredtopartitiontheBluetoothstackinthisway.Bluetoothheadsets,forexample,combinethemoduleandthehostportionsofstackononeprocessorbecausetheyneedtobesmallandself-contained.Insuchdevices,theHCImaynotbeimplementedatallunlessatallunlessdevicetestingisrequired.BecausetheBluetoothHCIiswelldefined,youcanwritedriversthathandledifferentBluetoothmodulesfromdifferentmanufacturers.AppleprovidesanHCIcontrollerobjectthatsupportsaUSBimplementationoftheHCIlayer..ReferencesBN.Sklavosetal.,"RandomNumberGeneratorArchitectureandVLSIImplementation,"Proc.IEEEInt'1Symp.Circuits&Systems(ISCAS02),IEEECircuitsandSystemsSoBluetoothsecuritywhitepaper;BluetoothSIGsecurityexpertgroup.c.Press,Piscataway,M.Abramovici,M.A.Breuer,andA.D.Friedman,DigitalSystemsTestingandTestableDesign,IEEEPress,Piscataway,N.J.,1990.P.Chandrakasan,S.Sheng,andR.W.Brodersen,"LowPowerCMOSDigitalDesign,"IEEEJ.Solid-StateCircuits,vo1.27,no.4,Apr.1992,pp.473-X84.J.L.Massey,G.H.Khachatrian,andM.K.Kuregian,"NominationofSAFER+asCandidateAlgorithmfortheAdvanceEncryptionStandard,"Proc.1stAdvancedEncryptionStandardCandidateConf.,1998;/}rblee/safer+.BluetoothSIG,SpecificationoftheBluetoothsystem,Core,PartB;'Basebandspecification';Version1.1,22February2001,at血S.Sengodan,T.Luo,R.Bansal,H.Herlin;"End-to-endSecurityIssuesWireless-IPNetworks,”IASTEDAppliedInformatics,Austria,Februaryin15-17,2000M.Bellare,R.Canetti,H.Krawczykz,"KeyingHashFunctionsforMessageAuthentication,"AdvancesinCrypto96Proceedings,LectureNotesinComputerSciencesVo1.1109,N.Koblitzed.,Springer-Verlag,1996藍(lán)牙設(shè)備怎樣工作在電氣設(shè)備中存在很多種連接方式。例如：許多臺(tái)式計(jì)算機(jī)系統(tǒng)有一個(gè)CPU單位連接到鼠標(biāo)、鍵盤(pán)、打印機(jī)等等。個(gè)人數(shù)字助理(PDA)通常將一根電纜和一個(gè)連接設(shè)備接在計(jì)算機(jī)上。電視通常連接著錄像機(jī)和一個(gè)線盒，對(duì)三種成分實(shí)現(xiàn)細(xì)微的控制。無(wú)繩電話利用無(wú)線電波和其基座單元連接在一起，它有一個(gè)頭戴式耳機(jī)用一根導(dǎo)線連接到電話上。在立體聲系統(tǒng)中，CD唱機(jī)和其他的聲音設(shè)備連接到接收器上，接收器連接到揚(yáng)聲器。當(dāng)使用電腦、娛樂(lè)設(shè)備或者電話的時(shí)候，各種小的系統(tǒng)組成了整個(gè)電子器件。這些裝置通過(guò)金屬絲、電纜、無(wú)線電信號(hào)和紅外線以及多種連接器、插頭和協(xié)議相互通信。設(shè)備之間的連接現(xiàn)在正變得越來(lái)越復(fù)雜。有時(shí)候我們感覺(jué)為了在家里建立電氣化我們似乎需要一個(gè)電機(jī)工程中的PhD.。在這篇文章中，我們將看到一種完全不同的連接方式——藍(lán)牙。藍(lán)牙是一種無(wú)線的自動(dòng)化裝置，它有很多能使我們?nèi)粘Ｉ詈?jiǎn)化的有趣的特點(diǎn)。問(wèn)題在于當(dāng)兩個(gè)設(shè)備之間要進(jìn)行通信的時(shí)候，在通信開(kāi)始之前，它們不得不相互統(tǒng)一很多的因素。第一點(diǎn)是物理的協(xié)議：它們是用線纜還是無(wú)線信號(hào)？如果他們用電纜，需要多長(zhǎng)呢？1m，2m，8m還是25m？一旦物理特征被決定了，又會(huì)出現(xiàn)一些新的問(wèn)題：信號(hào)在串行通信口中一次能傳輸1bit，在并行通信口中能傳輸多位（通常是8或者16bit一次）臺(tái)式計(jì)算機(jī)采用串行和并行兩重方式與其他外圍設(shè)備通信，如：調(diào)制解調(diào)器、鼠標(biāo)和鍵盤(pán)安裝串行的方式通信，而打印機(jī)用并行數(shù)據(jù)傳輸。所有的電子方面的討論均圍繞的是bit是什么意思，接受的消息是否和發(fā)出的數(shù)據(jù)是一樣的。這需要命令語(yǔ)言和一個(gè)已作為協(xié)議的回應(yīng)。現(xiàn)在多數(shù)產(chǎn)品已經(jīng)有了一個(gè)標(biāo)準(zhǔn)的協(xié)議，事實(shí)上現(xiàn)在大多數(shù)公司都這么做以使一種產(chǎn)品能和其他的產(chǎn)品相互通信。調(diào)制解調(diào)器就屬于這個(gè)范疇。其他設(shè)備用他們自己的方式通信，這就意味著一種產(chǎn)品收到的其他的產(chǎn)品的消息可能會(huì)出現(xiàn)亂碼。打印機(jī)就是這樣，它有特別的標(biāo)準(zhǔn)，像打印機(jī)控制語(yǔ)言和PostScript。電腦制造商、娛樂(lè)設(shè)備系統(tǒng)和其他的電子設(shè)備生產(chǎn)商就意識(shí)到錯(cuò)綜復(fù)雜的電纜和連接器會(huì)使得即使是專(zhuān)業(yè)的技術(shù)員在第一次試的時(shí)候也很難建立正確的系統(tǒng)連接。當(dāng)人們買(mǎi)了各種部件準(zhǔn)備學(xué)著和回憶著要在家里把電腦和娛樂(lè)設(shè)備裝起來(lái)的時(shí)候是極其可怕的。為了使家庭電器使用起來(lái)跟人性化，我們需要更好的方式把這些電子設(shè)備方便的連接在一起。這就是為什么出現(xiàn)了藍(lán)牙設(shè)備的原因。藍(lán)牙基礎(chǔ)藍(lán)牙是有一群同意任何電器裝備如：電腦、移動(dòng)電話、鍵盤(pán)、耳機(jī)等的電子設(shè)備生產(chǎn)商產(chǎn)生的一個(gè)標(biāo)準(zhǔn)協(xié)議，它有自己的連接方式，沒(méi)有金屬絲，沒(méi)有電纜，用戶也沒(méi)有任何直接的行為來(lái)控制。藍(lán)牙是一個(gè)確定的工作在兩個(gè)層面的標(biāo)準(zhǔn)：它提供一個(gè)物理層的標(biāo)準(zhǔn)——藍(lán)牙是一種無(wú)線射頻標(biāo)準(zhǔn)。它也在物理層之上的層面提供協(xié)議，在這里數(shù)據(jù)要被發(fā)送的時(shí)候，產(chǎn)品必須確定一次應(yīng)該發(fā)送多少數(shù)據(jù)，在一次連接中怎么能確定從屬設(shè)備收到的消息就是發(fā)送設(shè)備發(fā)出的消息。藍(lán)牙特別小組的超過(guò)1000個(gè)的成員公司想在電話，電腦和外圍設(shè)備之間讓藍(lán)牙無(wú)線通信代替各式各樣的電纜。其他的無(wú)線連接方式：現(xiàn)在有多種無(wú)線連接方式。一種是用紅外線譜來(lái)攜帶消息，紅外線要求一種肉眼看不見(jiàn)也說(shuō)不明白的低頻光波。紅外線大多用在電視系統(tǒng)的遙控系統(tǒng)中，存在一個(gè)紅外線數(shù)據(jù)協(xié)會(huì)（IrDA），過(guò)去大多數(shù)用在電腦和外圍設(shè)備的連接中。在這些電腦和娛樂(lè)設(shè)備使用紅外線的目的和方式中，多數(shù)是使用一種數(shù)字模式——信號(hào)的發(fā)射和關(guān)閉以及數(shù)從一點(diǎn)傳送到另一點(diǎn)是非常快速的。紅外線通信是非常值得信賴的，而且在一個(gè)設(shè)備中裝上紅外設(shè)備價(jià)格不高，但紅外線也有其不足的地方：一、紅外線是一種“視線”技術(shù)，如：你不得不把遙控器對(duì)準(zhǔn)電視機(jī)或者DVD來(lái)使它正常工作。二、紅外線是一種“點(diǎn)對(duì)點(diǎn)”的技術(shù)，你可以在臺(tái)式機(jī)和筆記本電腦上傳輸數(shù)據(jù)，但不能同時(shí)在筆記本和掌上設(shè)備上利用紅外線傳輸數(shù)據(jù)。紅外線的這兩個(gè)特性有時(shí)候也是它的優(yōu)點(diǎn)所在，因?yàn)榧t外線的發(fā)射和接收裝置要被連接在一條線上，所以在他們之間很少出現(xiàn)干擾信號(hào)。點(diǎn)對(duì)點(diǎn)的特性也使得消息只能發(fā)送到特定的接收者，即使是在滿是紅外線探測(cè)器的房間也可以做到這一點(diǎn)。藍(lán)牙解決方案藍(lán)牙技術(shù)有意解決紅外線和電纜同步系統(tǒng)的問(wèn)題。硬件生產(chǎn)商，包括西門(mén)子、英特爾、東芝、摩托羅拉和愛(ài)立信發(fā)明了一種非常小的射頻模塊來(lái)裝在電腦、電話機(jī)和娛樂(lè)電子設(shè)備中，從用戶的角度來(lái)說(shuō)，藍(lán)牙設(shè)備有三個(gè)重要的特點(diǎn)：它是無(wú)線的，當(dāng)走動(dòng)的時(shí)候，你不需要擔(dān)心公文包里會(huì)出現(xiàn)好多電纜連接你的各種設(shè)備，你可以隨心設(shè)計(jì)你的辦公室而不必為各種線應(yīng)該從那里穿過(guò)而煩心。它的廉價(jià)性，這個(gè)問(wèn)題你根本不必考慮。藍(lán)牙不需要你做什么特別的事情來(lái)使它工作。設(shè)備會(huì)找到其他設(shè)備并建立其連接，而用戶不需要輸入任何東西。藍(lán)牙的工作頻率，藍(lán)牙通信的工作頻率在2.45GHz，這個(gè)頻段被國(guó)際社會(huì)專(zhuān)門(mén)留出來(lái)供工業(yè)、科學(xué)和醫(yī)療器械使用（ISM）。你所使用的大多數(shù)設(shè)備可能已經(jīng)利用上這個(gè)射頻帶了，嬰兒監(jiān)聽(tīng)器、車(chē)庫(kù)門(mén)的開(kāi)啟器以及新一代的無(wú)繩電話都在利用這個(gè)ISM頻帶?？梢钥隙ǖ氖撬{(lán)牙及這些設(shè)備在設(shè)計(jì)的工程中不會(huì)出現(xiàn)與現(xiàn)有的設(shè)備形成很大的相互干擾的情況。避免干擾：低能量藍(lán)牙設(shè)備為了避免干擾情況的一種方式就是發(fā)出功率只有1毫瓦的信號(hào)。經(jīng)比較，最消耗能量的蜂窩電話能發(fā)射3瓦的信號(hào)。低能量限制了藍(lán)牙的傳輸范圍大概只有10m，這樣就切斷了個(gè)人電腦與便攜電話或者電視機(jī)之間的相互干擾。即使這樣低的能耗。你的房間的墻壁也不能阻止藍(lán)牙信號(hào)，這樣的標(biāo)準(zhǔn)有利于控制在不同房間的多個(gè)設(shè)備。這么多的藍(lán)牙設(shè)備存在于你的房間，你可能會(huì)想它們之間會(huì)存在相互干擾，但這是不可能的。在下面的文字中，我們來(lái)看看這是為什么？避免干擾：跳頻幾種設(shè)備在同一時(shí)間使用同一頻率是不可能出現(xiàn)的，因?yàn)樗{(lán)牙使用一種技術(shù)一一跳頻。在這一技術(shù)中，一個(gè)設(shè)備將在指定的范圍內(nèi)用到79個(gè)獨(dú)立的、為經(jīng)安排選擇出來(lái)的頻道，在有規(guī)律的基礎(chǔ)上從一個(gè)頻率變到另一個(gè)頻率。在藍(lán)牙技術(shù)中，信號(hào)發(fā)生者每秒改變頻率1600次，這意味著更多的設(shè)備能充分地利用一個(gè)有限的無(wú)線射頻光譜段。正因?yàn)榘l(fā)生器能自動(dòng)的使用跳頻技術(shù)，所以在同一時(shí)間兩個(gè)發(fā)生器會(huì)使用相同的頻率的情況不可能出現(xiàn)。這種技術(shù)把藍(lán)牙設(shè)備中的便攜電話或者嬰兒監(jiān)聽(tīng)器等會(huì)使設(shè)備中斷的風(fēng)險(xiǎn)降到了最低，因?yàn)槿魏卧谝惶囟ǖ念l率上的相互干擾只會(huì)在一秒內(nèi)的很微小的一部分時(shí)間內(nèi)發(fā)生。當(dāng)一個(gè)藍(lán)牙設(shè)備和另一個(gè)在一起的時(shí)候，一段信息交換將會(huì)發(fā)生以決定是否他們之間有數(shù)據(jù)需要共享或者一個(gè)設(shè)備需要控制另一個(gè)設(shè)備。用戶不需要按一下按紐或發(fā)出命令，這段信息交換的過(guò)程是自動(dòng)發(fā)生的