計算機網絡專業(yè)論文文獻外文翻譯

1、TheNetworks2BirthoftheNet2HowtheWebWorks2SomeWebHistory3UnderstandingWebAddresses3DomainNames5AboutModem6SpeedItUp7CableModems7DSL8Websites8HomeSweetHomePage8AHome(Page)ofYourOwn9DecodingErrorMessages10WebBrowsers12網絡14網絡的誕生14網絡是如何工作的14一些網絡的歷史15網址15域名16關于調制解調器17加速18凱布爾調制解調器18DSL19網頁(站)19網頁透視19個人主頁20

2、錯誤信息分析21DNS失敗檢索22主機不可用：22主機未知：22不能定位主機22不能定位服務器22TheNetworksBirthoftheNetTheInternethashadarelativelybrief,butexplosivehistorysofar.Itgrewoutofanexperimentbeguninthe1960'sbytheU.S.DepartmentofDefense.TheDoDwantedtocreateacomputernetworkthatwouldcontinuetofunctionintheeventofadisaster,suchasanucl

3、earwai*.Ifpartofthenetworkweredamagedordestroyed,therestofthesystemstillhadtowork.ThatnetworkwasARPANET,whichlinkedU.S.scientificandacademicresearchers.Itwastheforerunneroftoday'sInternet.In1985,theNationalScienceFoundation(NSF)createdNSFNET,aseriesofnetworksforresearchandeducationcommunication.

4、BasedonARPANETprotocols,theNSFNETcreatedanationalbackboneservice,providedfreetoanyU.S.researchandeducationalinstitution.Atthesametime,regionalnetworkswerecreatedtolinkindividualinstitutionswiththenationalbackboneservice.NSFNETgrewrapidlyaspeoplediscovereditspotential,andasnewsoftwareapplicationswere

5、createdtomakeaccesseasier.CorporationssuchasSprinlandMCIbegantobuildtheirownnetworks,whichtheylinkedtoNSFNET.AscommercialfirmsandotherregionalnetworkprovidershavetakenovertheoperationofthemajorInternetarteries,NSFhaswithdrawnfromthebackbonebusiness.NSFalsocoordinatedaservicecalledInterNIC,whichregis

6、teredalladdressesontheIntemefsothatdatacouldberoutedtotherightsystem.ThisservicehasnowbeentakenoverbyNetworkSolutions,Inc.,incooperationwithNSF.HowtheWebWorksTheWorldWideWeb,thegraphicalportionoftheInternet,isthemostpopularpartoftheInternetbyfar.OnceyouspendtimeontheWeb,youwillbegintofeellikethereis

7、nolimittowhatyoucandiscove匚TheWeballowsrichanddiversecommunicationbydisplayingtext,graphics,animation,photos,soundandvideo.Sojustwhatisthismiraculouscreation?TheWebphysicallyconsistsofyourpersonalcomputer,webbrowsersoftware,aconnectiontoanInternetserviceprovider,computerscalledserversthathostdigital

8、dataandroutersandswitchestodirecttheflowofinformation.TheWebisknownasadientservesystem.Yourcomputeristheclient;theremotecomputersthatstoreelectronicfilesaretheservers.Here'showitworks:Let'ssayyouwanttopayavisittothetheLouvremuseumwebsite.FirstyouentertheaddressorURLofthewebsiteinyourwebbrows

9、er(moreaboutthisshortly).ThenyourbrowserrequeststhewebpagefromthewebserverthathoststheLouvre'ssite.TheLouvre'sserversendsthedataovertheInternettoyourcomputer.Yourwebbrowserinterpretsthedata,displayingitonyourcomputerscreen.TheLouvre'swebsitealsohaslinkstothesitesofothermuseums,suchastheV

10、aticanMuseum.Whenyouclickyourmouseonalink,youaccessthewebserverfortheVaticanMuseum.The"glue"thatholdstheWebtogetheriscalledhypertextandhyperlinks.ThisfeatureallowelectronicfilesontheWebtobelinkedsoyoucaneasilyjumpbetweenthem.OntheWeb,younavigatethroughpagesofinformationbasedonwhatinterests

11、youatthatparticularmoment,commonlyknownasbrowsingorsurfingtheNet.ToaccesstheWebyouneedwebbrowsersoftware,suchasNetscapeNavigatororMicrosoftIrdcmelExplorer.HowdoesyourwebbrowserdistinguishbetweenwebpagesandotherfilesontheInternet?WebpagesarewritteninacomputerlanguagecalledHypertextMarkupLanguageorHTM

12、L.SomeWebHistoryTheWorldWideWeb(WWW)wasoriginallydevelopedin1990atCERN,theEuropeanLaboratoryforParticlePhysics.ItisnowmanagedbyTheWorldWideWebConsortium,alsoknownastheWorldWideWebInitiative.TheWWWConsortiumisfundedbyalargenumberofcorporatemembers,includingAT&T,AdobeSystems,Inc.,MicrosoftCorporat

13、ionandSunMicrosystems,Inc.ItspurposeistopromotethegrowthoftheWebbydevelopingtechnicalspecificationsandreferencesoftwarethatwillbefreelyavailabletoeveryone.TheConsortiumisrunbyMITwithINR1A(TheFrenchNationalInstituteforResearchinComputerScience)actingasEuropeanhost,incollaborationwithCERN.TheNationalC

14、enlerforSupercomputingApplications(NCSA)attheUniversityofIllinoisatUrbana-Chnmpaign,wasinstrumentalinthedevelopmentofearlygraphicalsoftwareutilizingtheWorldWideWebfeaturescreatedbyCERN.NCSAfocusesonimprovingtheproductivityofresearchersbyprovidingsoftwareforscientificmodeling,analysis,andvisualizatio

15、n.TheWorldWideWebwasanobviouswaytofulfillthatmission.NCSAMosaic,oneoftheearliestwebbrowsers,wasdistributedfreetothepublic.ItleddirectlytothephenomenalgrowthoftheWorldWideWeb.UnderstandingWebAddressesYoucanthinkoftheWorldWideWebasanetworkofelectronicfilesstoredoncomputersallaroundtheworld.Hypertextli

16、nkstheseresourcestogether.UniformResourceLocatorsorURLsaretheaddressesusedtolocatethesefiles.TheinformationcontainedinaURLgivesyoutheabilitytojumpfromonewebpagetoanotherwithjustaclickofyourmouse.WhenyoutypeaURLintoyourbrowserorclickonahypertextlink,yourbrowserissendingarequesttoaremotecomputertodown

17、loadafile.WhatdoesatypicalURLlooklike?Herearesomeexamples:Thehomepageforstudyenglish./pub/AdirectoryoffilesatMIT*availablefordownloading.news:rec.gardens.rosesAnewsgrouponrosegardening.ThefirstpartofaURL(beforethetwoslashes*tellsyouthetypeofresourceormethodofaccessatthataddress.For

18、example: http-ahypertextdocumentordirectory gopher-agopherdocumentormenu ftp-afileavailablefordownloadingoradirectoryofsuchfiles news-anewsgroup telnet-acomputersystemthatyoucanlogintoovertheInternet WAIS*-adatabaseordocumentinaWideAreaInformationSearchdatabase fileafilelocatedonalocaldrive(yourhard

19、drive)Thesecondpartistypicallytheaddressofthecomputerwherethedataorserviceislocated.Additionalpartsmayspecifythenamesoffiles,theporttoconnectto,orthetexttosearchforinadatabase.YoucanentertheURLofasitebytypingitintotheLocationbarofyourwebbrowser,justunderthetoolbar.MostbrowsersrecordURLsthatyouwantto

20、useagain,byaddingthemtoaspecialmenu.InNetscapeNavigator,it'scalledBookmarks.InMicrosoftExplorer,it'scalledFavorites.OnceyouaddaURLtoyourlist,youcanreturntothatwebpagesimplybyclickingonthenameinyourlist,insteadofretypingtheentireURL.MostoftheURLsyouwillbeusingstartwithhttpwhichstandsforHypert

21、extTransferProtocol*,httpisthemethodbywhichHTMLfilesaretransferredovertheWeb.HerearesomeotherimportantthingstoknowaboutURLs: AURLusuallyhasnospaces. AURLalwaysusesforwardslashes(/).IfyouenteraURLincorrectly,yourbrowserwillnotbeabletolocatethesiteorresourceyouwant.Shouldyougetanerrormessageorthewrong

22、site,makesureyoutypedtheaddresscorrectly.YoucanfindtheURLbehindanylinkbypassingyourmousecursoroverthelink.ThepointerwillturnintoahandandtheURLwillappearinthebrowser'sstatusbar,usuallylocatedatthebottomofyourscreen.DomainNamesWhenyouthinkoftheInternet,youprobablythinkof".com."Justwhatdo

23、thosethreelettersattheendofaWorldWideWebaddressmean?EverycomputerthathostsdataontheInterhasauniquenumericaladdress.Forexample,thenumericaladdressfortheWhiteHouseis19837.24()00.Butsincefewpeoplewantiorememberlongstringsofnumbers,theDomainNameSystem(DNS)*wasdeveloped.DNS,acriticalpartoftheInternet'

24、;stechnicalinfrastructure*,correlates*anumericaladdresstoaword.ToaccesstheWhiteHousewebsite,youcouldtypeitsnumberintotheaddressboxofyourwebbrowser.ButmostpeopleprefertouseH."Inthiscase,.Ingeneral,thethree-letterdomainnamesuffix*isknownasagenerictop

25、-leveldomainanddescribesthetypeoforganization.Inthelastfewyears,thelineshavesomewhatblurred*-business(commercial).-governmentAdomainnamealwayshastwoormorepartsseparatedbydotsandtypicallyconsistsofsomeformofa

26、norganizationsnameandthethree-lettersuffix.Forexample,thedomainnameforIBMis""theUnitedNationsis"."Ifadomainnameisavailable,andprovideditdoesnotinfringe*onanexistingtrademark,anyonecanregisterthenamefor$35ayearthroughNetworkSolutions,Inc.,.domains.Youcanusetheboxbe

27、lowtoseeifanameisaavailable.Don'nameyouwantisalreadytaken,however.Oftheover8milliondomainnames,85%domains.ICANN,theInternetCorporationforAssignedNamesandNumbers,managestheDomainNameSystem.Asofthiswriting,thereareplanstoaddadditionaltop-leveldomains,suchas.weband.store.Whenthatwillactuallyhappeni

28、sanybody'sguess.Tocheckfor,orregisteradomainname,typeitintothesearchbox.Itshouldtakethisform:Inadditiontothegenerictop-leveldomains,244nationaltop-leveldomainswereestablishedforcountriesandterritories*,forexample:.au-Australia.caCanada.fr-France.de-Germany.uk-UnitedKingdomForUS$275pername,youcan

29、alsoregisteraninternationaldomainnamewithNetNames.Beawarethatsomecountrieshaverestrictionsforregisteringnames.Ifyouplantoregisteryourowndomainname,whetherit'ornot,keepthesetipsinmind:Theshorterthename,thebette匚(Bu【itshouldreflectyourfamilyname,interestorbusiness.)Thenameshouldbeeasytoreniember.I

30、tshouldbeeasytotypewithoutmakingmistakes.Remember,theInternetisglobal.Ideally,adomainnamewill"read"inalanguageotherthanEnglish.AboutModemTelephonelinesweredesignedtocarrythehumanvoice,notelectronicdatafromacomputer.Modemswereinventedtoconvertdigitalcomputersignalsintoaformthatallowsthemtot

31、raveloverthephonelines.Thosearethescratchysoundsyouhearfromamodem'sspeake匚Amodemontheotherendofthelinecanunderstanditandconvertthesoundsbackintodigitalinformationthatthecomputercanunderstand.Bytheway,thewordmodemstandsforMOdulator/DEModulator.Buyingandusingamodemusedtoberelativelyeasy.Nottoolong

32、ago,almostallmodemstransferreddataatarateof2400Bps(bitspersecond).Today,modemsnotonlyrunfaster,theyarealsoloadedwithfeatureslikeerrorcontrolanddatacompression.So,inadditiontoconvertingandinterpretingsignals,modemsalsoactliketrafficcops,monitoringandregulatingtheflowofinformation.Thatway,onecomputerd

33、oesn'tsendinformationuntilthereceivingcomputerisreadyforit.Eachofthesefeatures,modulation,errorcontrol,anddatacompression,requiresaseparatekindofprotocolandthat'swhatsomeofthosetermsyouseelikeV.32,V.32bis,V.42bisandMNP5referto.Ifyourcomputerdidn*tcomewithaninternalmodem,considerbuyinganexter

34、nalone,becauseitismucheasiertoinstallandoperate.Forexample,whenyourmodemgetsstuck(notanunusualoccurrenee),youneedtoturnitoffandontogetitworkingproperly.Withaninternalmodem,thatmeansrestartingyourcomputer-awasteoftime.Withanexternalmodemit'saseasyasflippingaswitch.Here'satipforyou:inmostareas

35、,ifyouhaveCallWaiting,youcandisableitbyinserting*70infrontofthenumberyoudialtoconnecttotheInternet(oranyonlineservice).Thiswillpreventanincomingcallfromaccidentallykickingyouofftheline.Thistableillustratestherelativedifferenceindatatransmissionspeedsfordifferenttypesoffiles.Amodem'sspeedisnleasu

36、redinbitspersecond(bps).A14.4modemsendsdataat14,400bitspersecond.A28.8modemistwiceasfast,sendingandreceivingdataatarateof28,80()bitspersecond.Untilnearlytheendof1995,theconventionalwisdomwasthat28.8Kbpswasaboutthefastestspeedyoucouldsqueezeoutofaregularcoppertelephoneline.Today,youcanbuy33.6Kbpsmode

37、ms,andmodemsthatarecapableof56Kbps.Thekeyquestionforyou,isknowingwhatspeedmodemsyourInternetserviceprovider(TSP)has.IfyourTSPhasonly28.8Kbpsmodemsonitsendoftheline,youcouldhavethefastestmodemintheworld,andonlybeabletoconnectat28.8Kbps.Beforeyouinvestina33.6Kbpsora56Kbpsmodem,makesureyourISPsupportst

38、hem.SpeedItUpTherearefasterwaystotransmitdatabyusinganISDNorleasedline.InmanypartsoftheU.S.,phonecompaniesareofferinghomeISDNatlessthan$30amonth.ISDNrequiresaso-calledISDNadapterinsteadofamodem,andaphonelinewithaspecialconnectionthatallowsittosendandreceivedigitalsignals.Youhavetoarrangewithyourphon

39、ecompanytohavethisequipmentinstalled.FormoreaboutISDN,visitDanKegel'sISDNPage.AnISDNlinehasadatatransferrateofbetween57,600bitspersecondand12&000bitspersecond,whichisatleastdoubletherateofa28.8Kbpsmodem.Leasedlinescomeintwoconfigurations:T1andT3.AT1lineoffersadatatransferrateof1.54millionbit

40、spersecond.UnlikeISDN,aT-llineisadedicatedconnection,meaningthatitispermanentlyconnectedtotheInternet.ThisisusefulforwebserversorothercomputersthatneedtobeconnectedtotheInternetallthetime.ItispossibletoleaseonlyaportionofaT-llineusingoneoftwosystems:fractionalT-lorFrameRelay.Youcanleasetheminblocksr

41、angingfrom128Kbpsto1.5Mbps.Thedifferencesarenotworthgoingintoindetail,butfractionalT-lwillbemoreexpensiveatthesloweravailablespeedsandFrameRelaywillbeslightlymoreexpensiveasyouapproachthefullT-lspeedof1.5Mbps.AT-3lineissignificantlyfaster,at45millionbitspersecond.ThebackboneoftheInternetconsistsofT-

42、3lines.LeasedlinesareveryexpensiveandaregenerallyonlyusedbycompanieswhosebusinessisbuiltaroundtheInternetorneedtotransfermassiveamountsofdata.ISDN,ontheotherhand,isavailableinsomecitiesforaveryreasonableprice.NotallphonecompaniesofferresidentialISDNservice.Checkwithyourlocalphonecompanyforavailabili

43、tyinyourarea.CableModemsArelativelynewdevelopmentisadevicethatprovideshigh-speedInternetaccessviaacableTVnetwork.Withspeedsofupto36Mbps,cablemodemscandownloaddatainsecondsthatmighttakefiftytimeslongerwithadial-upconnection.BecauseitworkswithyourTVcable,itdoesn'ttieupatelephoneline.Bestofall,it&#

44、39;salwayson,sothereisnoneedtoconnecnomorebusysignals!ThisserviceisnowavailableinsomecitiesintheUnitedStatesandEurope.Thedownloadtimesinthetableabovearerelativeandaremeanttogiveyouageneralideaofhowlongitwouldtaketodownloaddifferentsizedfilesatdifferentconnectionspeeds,underthebestofcircumstances.Man

45、ythingscaninterferewiththespeedofyourfiletransfer.Thesecanrangefromexcessivelinenoiseonyourtelephonelineandthespeedofthewebserverfromwhichyouaredownloadingfiles,tothenumberofotherpeoplewhoaresimultaneouslytryingtoaccessthesamefileorotherfilesinthesamedirectory.DSLDSL(DigitalSubscriberLine)isanotherh

46、igh-speedtechnologythatisbecomingincreasinglypopular.DSLlinesarealwaysconnectedtotheInternet,soyoudon'tneedtodial-up.Typically,datacanbetransferredatratesupto1.544Mbpsdownstreamandabout128Kbpsupstreamoverordinarytelephonelines.SinceaDSLlinecarriesbothvoiceanddata,youdon'thavetoinstallanother

47、phoneline.YoucanuseyourexistinglinetoestablishDSLservice,providedserviceisavailableinyourareaandyouarewithinthespecifieddistancefromthetelephonecompany'scentralswitchingoffice.DSLservicerequiresaspecialmodem.Pricesforequipment,DSLinstallationandmonthlyservicecanvaryconsiderably,socheckwithyourlo

48、calphonecompanyandInternefserviceprovider.Thegoodnewsisthatpricesarecomingdownascompetitionheatsup.WebsitesAnatomyofaWebPageAwebpageisanelectronicdocumentwritteninacomputerlanguagecalledHTML,shortforHypertextMarkupLanguage.Eachwebpagehasauniqueaddress,calledaURL*orUniformResourceLocator,whichidentif

49、iesitslocationonthenetwork.Awebsitehasoneormorerelatedwebpages,dependingonhowitdesigned.Webpagesonasitearelinkedtogetherthroughasystemofhyperlinks*,enablingyoutojumpbetweenthembyclickingonalink.OntheWeb,younavigatethroughpagesofinformationaccordingtoyourinterests.HomeSweetHomePageWhenyoubrowsetheWor

50、ldWideWebyou'llseethetermhomepageoften.Thinkofahomepageasthestartingpointofawebsite.Likethetableofcontentsofabookormagazine,thehomepageusuallyprovidesanoverviewofwhatyou'llfindatthewebsite.Asitecanhaveonepage,manypagesorafewlongones,dependingonhowit'sdesigned.Ifthereisn'talotofinform

51、ation,thehomepagemaybetheonlypage.Butusuallyyouwillfindatleastafewotherpages.Webpagesvarywildlyindesignandcontent,butmostuseatraditionalmagazineformat.Atthetopofthepageisamasthead*orbannergraphic*,thenalistofitems,suchasarticles,oftenwithabriefdescription.Theitemsinthelistusuallylinktootherpagesonth

52、ewebsite,ortoothersites.Sometimestheselinksarehighlighted*wordsinthebodyofthetext,orarearrangedinalist,likeanindex.Theycanalsobeacombination*ofboth.Awebpagecanalsohaveimagesthatlinktoothercontent.Howcanyoutellwhichtextarelinks?Textlinksappearinadifferentcolorfromtherestofthetexttypicallyinblueandund

53、erlined.Whenyoumoveyourcursoroveratextlinkoroveragraphiclink,itwillchangefromanarrowtoahand.Thehypertextwordsoftenhint*atwhatyouwilllinkto.Whenyoureturntoapagewithalinkyou'vealreadyvisited,thehypertextwordswilloftenbeinadifferentcolor,soyouknowyou'vealreadybeenthere.Butyoucancertainlygothere

54、again.Don'tbesurprisedthough,ifthenexttimeyouvisitasite,thepagelooksdifferentandtheinformationhaschanged.TheWebisadynamic*medium.Toencouragevisitorstoreturntoasite,somewebpublisherschangepagesoften.That'swhatrruikesbrowsingtheWebsoexcitingAHome(Page)ofYourOwnInthe60s,peopleaskedaboutyourastr

55、ological*sign.Inthe90s,theywanttoknowyourURL.Thesedays,havingawebaddressisalmostasimportantasastreetaddress.Yourwebsiteisanelectronicmeetingplaceforyourfamily,friendsandpotentially*,millionsofpeoplearoundtheworld.Buildingyourdigitaldomaincanbeeasierthanyoumaythink.Bestofall,youmaynothavetospendacent

56、.TheWebbrimswithallkindsoffreeservices,fromtoolstohelpyoubuildyoursite,tofreegraphics,aniniationandsitehosting.Allittakesissometimeandcreativity.Thinkofyourhomepageasthestartingpointofyourwebsite.Likethetableofcontentsofabookormagazine,thehomepageisthefrontdoor.Yoursitecanhaveoneormorepages,dependin

57、gonhowyoudesignit.Ifthereisn'talotofinformationjustyet,yoursitewillmostlikelyhaveonlyahomepage.Butthesiteissuretogrowovertime.Whilewebpagesvarydramatically*intheirdesignandcontent,mostuseatraditionalmagazinelayout.Atthetopofthepageisabannergraphic.Nextcomesagreetingandashortdescriptionofthesite.

58、Pictures,text,andlinkstootherwebsitesfollow.Ifthesitehasmorethanonepage,there'stypicallyalistofitems-similartoanindex-oftenwithabriefdescription.Theitemsinthelistlinktootherpagesonthewebsite.Sometimestheselinksarehighlightedwordsinthebodyofthetext.Itcanalsobeacombinationofboth.Additionally,awebp

59、agemayhaveimagesthatlinktoothercontent.Beforeyoustartbuildingyoursite,dosomeplanning.Thinkaboutwhomthesiteisforandwhatyouwanttosay.Next,gatherupthematerialthatyouwanttoputonthesite:writethecopy,scanthephotos,designorfindthegraphics.Drawaroughlayoutonasheetofpaper.Whiletherearenorulesyouhavetofollow,thereareafewthingstokeepinmind: Startsimply.Ifyouaretooambitiousatthebeginning,youmaynevergetthesiteoffthe