电子商务导论 2CHAP

ElectronicCommerceChapter2InfrastructureForECSTUDYHOURS：6hoursOBJECTIVES1.Theorigin,growthandcurrentstructureoftheInternet.2.Howpacket-switchednetworksarecombinedtoformtheInternet.3.HowInternetprotocolsandInternetaddressingwork.4.ThehistoryanduseofmarkuplanguagesontheWeb,includingSGML,HTMLandXML.5.HowHTMLtagsandlinksworkontheWorldWideWeb.6.Thedifferencesamonginternets,intranetsandextranets.7.OptionsforconnectingtotheInternet,includingcostandbandwidthfactors8.Internet2andtheSemanticWebImportantPoints1.Theorigin,growthandcurrentstructureoftheInternet2.ThehistoryanduseofmarkuplanguagesontheWeb,includingSGML,HTMLandXML3.Thedifferencesamonginternets,intranetsandextranetsDifficultPoints1.Howpacket-switchednetworksarecombinedtoformtheInternet.2.HowInternetprotocolsandInternetaddressingwork.ContentsPartITheInternetandtheWorldWideWeb()PartIIInternetProtocolsandaddressingPacket-SwitchedNetworksPartIIIIntranetsandExtranetsInternetConnectionOptionsTheInternetandtheWorldWideWeb()TheInternetandtheworldwidewebfuelledthegrowthofe-commerceInthissectionofthecoursewewillinvestigatetheoriginandstructureoftheInternetWhatIstheInternet?TheInternetisalargesystemofinter-connectednetworksthatspantheglobeTheInternetallowscommunicationbye-mail,thereadingofon-linenewspapers,academicjournalsandbooks,thejoiningofdiscussiongroups,participationinsimulationsandgamesaswellasdownloadingsoftwareTheInternetallowsbusinessestomarketandsellproductsandservicesWhatIstheWorldWideWeb()?Theworldwideweb()isasubsetofthecomputersontheInternetthatconnectinacertainway,makingtheircontentaccessibletoeachotherTheIntheearly1960stheUSdepartmentofdefensebeganinvestigatingwaysofcreatingnetworksofcomputersthatcoordinateandcontrolnuclearweaponsThisnetworkwastowithstandattack,sothatevenifpartofitwasdownitwillcontinuetofunctionThisnetworkwastohavenocentralcontrolThesenewnetworksrequiredmultiplechannelstosendinformation(leasedlinesinadequate)OriginsoftheInternet(II)In1969theadvancedresearchagency(ARPA)usedthisnetworkmodeltoconnectfourcomputersThisnetworkwascalledARPANETDuringthe1970sand80stheacademiccommunitycontributedtothisnetworkInthelate1980sthisnetworkbecametheinternetUsesoftheInternetIn1972e-mailwascreatedandusedbythemilitaryandresearchcommunitiesIn1979theuser’snewsnetwork(Usenet)wascreatedallowinguserstopostandreadarticles(newsgroups)In1989thenationalsciencefoundation(whofundedtheinternet)allowedtwocommercemailservices,MCImailandCompuServeIn1990speopleworldwidebeganusingtheInternetformanypurposesincludingcommerceInternetGrowthIn1969ARPANET(theInternet)connected4computersIn1990theInternetconnected300,000In1995theintranetwasprivatisedThestructurewasbasedonfournetworkaccesspoints(NAPs)operatedbydifferenttelecomcompaniesintheUSAstheIntranetgrew,moreNAPswereaddedInternetGrowthTheNAPsbegansellingInternetaccessrightstolargecustomersInternetserviceprovides(ISPs)soldontheservicetosmallbusinessesandindividualsGrowthinInternethostsrosefromunder10millionin1995toover180millionin2004MillionsofpeoplenowusetheInternetBillionsofdollarschangehandsfromthesalesofproductsandservicesEstimatednumberofWebsitesis40millionandbillionsofwebpagesTheWorldWideWeb()Theworldwideweb(orweb)issoftwarethatrunsonmachinesconnectedtotheInternetThenetworktrafficgeneratedbythewebisgreaterthane-mail,filetransfersandotherdatatrafficThewebisbasedontwoconceptsHypertextandgraphicaluserinterfaceHypertextIn1945,VannevarBushwroteanarticleinAtlanticMonthlyaboutasystem,calledMemex,thatwouldstoreallaperson’sbooks,records,lettersandresearchresultsonmicrofilmMicrofilmandindexeswouldthenbeusedtoquicklyaccessthisinformationHypertext(II)Inthe1960s,TedNelsondescribedasimilarsystemHeincorporatedapagelinkingsystemcalledhypertextIn1989,TimBerners-LeedevelopedthecodeforahypertextserverAhypertextserverisacomputerthatstoresfileswritteninhypertextmarkuplanguage(HTML)andallowothercomputerstoreaditHTMLHTMLisalanguagethatincludesasetoftagsattachedtotextThesetagsdescribetherelationshipbetweentextelementsAhypertextlink(orhyperlink)pointstoanotherlocationinthesameoranotherHTMLdocument(thatmightbestoredonthesameoranothercomputer)GraphicalInterfacesforHypertextWebbrowsersAllowuserstoreadHTMLdocumentsandnavigatethroughthemPresentanHTMLdocumentinagraphicaluserinterface(GUI)In1993thewebbrowserMosiacwasdeveloped,laterNetscapeNavigatorandInternetExplorerweredevelopedPacket-switchedNetworksALAN(localareanetwork)isanetworkofcomputersincloseproximityAWAN(wideareanetwork)networkofcomputersareconnectedovergreaterdistancesEarlyWANsusedleasedlinesSinglepathbetweencallerandreceiverThisisknownascircuitswitchingPacket-switchedNetworks(II)Messagesarebrokendownintosmallpiecescalledpacketsandarelabeledelectronicallywiththeirorigin,sequenceanddestinationaddressesEachpacketmaytakeadifferentpathThedestinationcomputerputsthepacketsbacktogetherinthecorrectorderRoutingPacketsComputersthatdec