文件传输技术发展与产品趋势

ThefirstFTPstandardwasRFC114,publishedinApril1971,beforeTCPandIPevenexisted.HTTP/0.9TheoriginalversionofHTTPwasintendedonlyforthetransferofhypertextdocuments,andwasdesignedtobeverysimpletomakeimplementationofthefledglingWebeasier.ThisearlyHTTPspecifiesthatanHTTPclientestablishesaconnectiontoanHTTPserverusingTCP.Theclientthenissuesasingle“GET”requestspecifyingaresourcetoberetrieved.Theserverrespondsbysendingthefileasastreamoftextbytes,andtheconnectionisterminated.TheentiredocumentdefiningthisversionofHTTPisonlyacoupleofpageslong!HTTP/1.0TheskeletonoffunctionalitythatHTTP/0.9formedthebasisforarapidevolutionofHTTPintheearly1990s.AstheWorldWideWebgrewinsizeandacceptance,manynewideasandfeatureswereincorporatedintoHTTP.TheresultofagreatdealofdevelopmenteffortwastheformalizationofthefirstHTTPstandard:version1.0.ThismuchenhancedHTTPwaspublishedinMay1996asRFC1945,HypertextTransferProtocol—HTTP/1.0.Ithadbeeninuseforseveralyearspriortothatformalpublicationdate,however.HTTP/1.1Whileimpatientpunditscoinedsarcastictermssuchasthe“WorldWideWait”,theIETFcontinuedtoworktoimproveHTTP.InJanuary1997,thefirstdraftversionofHTTP/1.1appeared:inRFC2068.ThisdocumentwaslaterrevisedandpublishedasRFC2616,HypertextTransferProtocol—HTTP/1.1,inJune1999.HTTP/1.1retainsbackwardscompatibilitywithbothHTTP/1.0andHTTP/0.9.ItisaccompaniedbyRFC2617,HTTPAuthentication:BasicandDigestAccessAuthentication,whichdealswithsecurityandauthenticationissues.Someofthemoreimportantimprovementsinversion1.1are:MultipleHostNameSupport:InHTTP/1.0,therewasnowaytospecifythehostnameoftheservertowhichtheclientneededtoconnect.Asaresult,theWebserverataparticularIPaddresscouldonlysupportonedomainname.Thiswasnotonlyinefficient,itwasexacerbatingthedepletionofIPaddressesinthe1990s,becauseeachnewWebservertocomeonlinerequiredanewIPaddress.HTTP/1.1allowsoneWebservertohandlerequestsfordozensorevenhundredsofdifferentvirtualhosts.PersistentConnections:HTTP/1.1allowsaclienttosendmultiplerequestsforrelateddocumentstoaserverinasingleTCPsession.ThisgreatlyimprovesperformanceoverHTTP/1.0,whereeachrequestrequiredanewconnectiontotheserver.PartialResourceSelection:InHTTP/1.1,aclientcanaskforonlypartofaresourceratherthantheentiredocument,whichreducestheloadontheserverandsavestransferbandwidth.BetterCachingandProxyingSupport:HTTP/1.1includesmanyprovisionstomakecachingandproxyingmoreefficientandeffectivethantheywereinHTTP/1.0.Thesetechniquescanimproveperformancebyprovidingclientswithfasterrepliestotheirrequestswhilereducingtheloadonservers,aswellasenhancingsecurityandimplementingotherfunctionality.ContentNegotiation:Anegotiationfeaturewasaddedthatallowstheclientandservertoexchangeinformationtohelpselectthebestresourceorversionofaresourcewhenmultiplevariantsareavailable.BetterSecurity:HTTP/1.1definesauthenticationmethodsandisgenerallymore“securityaware”thanHTTP/1.0was.%ftpcs.colorado.eduConnectedtocs.colorado.edu.220brunoFTPserver(SunOS4.1)ready.Name(cs.colorado.edu:yourlogin):anonymous331Guestloginok,sendidentaspassword.Password:230-ThisserveriscourtesyofSunMicrosystems,Inc.230-230Guestloginok,accessrestrictionsapply.ftpcd/pub/HPSC250CWDcommandsuccessful.ftpls200PORTcommandsuccessful.150ASCIIdataconnectionfor/bin/ls(128.138.242.10,3133)(0bytes).ElementsofAVS.ps.Z226ASCIITransfercomplete.418bytesreceivedin0.043seconds(9.5Kbytes/s)ftpgetElementsofAVS.ps.Z200PORTcommandsuccessful.150ASCIIdataconnectionforElementsofAVS.ps.Z(128.138.242.10,3134)(2881bytes).226ASCIITransfercomplete.local:READMEremote:ElementsofAVS.ps.Z2939bytesreceivedin0.066seconds(43Kbytes/s)ftpbye221Goodbye.2000314AOLNullsoftP2PGnutellaNapsterGnutellaGnutellaFastTrackGnutella22007••Web••FTP•••