Provider(互联网服务供应商)

S3ComputerLiteracyInternetTechnologyConnectingtotheInternet–HardwareRequirementMODEM56KorBroadbandMOdulationandDEModulationTelephoneLineConnectingtotheInternet-ISPISP–InternetServiceProvider(互聯網服務供應商)WhathasISPdoneforyou?Itsendsandreceivesdataforyou.ItprovidesaconnectionbetweenyouandtheotheroftheInternet.Asshownintheanimationbelow,thedataisinfacthandledbyanumberofISP.AnimationforconnectiontotheInternetIsISPrunningtheInternet?NosingleorganizationrunstheInternet.Itisalargenetworkofnetworks.Thesenetworksarelinkedbyhigh-speedcommunicationchannelscalledbackbones.EachInternetcomputer,calledahost,isindependent.ConnectingtotheInternet–TypeofAccessDial-upAccess(撥號上網)ItneedsatelephonelineMODEMUserdialsatelephonenumbergivenbytheISPtoconnecttotheserveroftheISP.ausernameandpasswordtoauthenticatetheuser.UsercanaccesshostsontheInternetDatatransferratemaximumof56Kbps.ConnectingtotheInternet–TypeofAccessBroadbandAccessItsspeedismeasuredinMbps(i.e.Megabitpersecond)Unlikedial-upaccess,itrequiresanetworkcard/LANcardbutnomodemrequired.BroadbandAccess-ADSLADSLatechnologyfortransmittingdigitalinformationatahighbandwidthonexistingphonelinestohomesandbusinesses.ISPadoptingthistechnologyinHK:Netvigator(網上行)GettotheInternetPPPoESomebroadbandInternetserviceproviders(ISPs)identifyyourcomputerontheirnetworksusingPointtoPointProtocoloverEthernet(PPPoE).IfyourISPrequiresyoutosupplyanameandpasswordtoaccesstheInternet,itmostlikelyusesthisprotocol(議定).BroadbandAccess-ADSLADSL(AsymmetricDigitalSubscriberLine)Asymmetric(不對稱)betweendownloadspeedisfaster.DownloadSpeed–1.5Mbpsto8MbpsUploadSpeed–16Kbpsto640KbpsComponents–Networkcard,ADSLMODEM,TelephoneLineBroadbandAccess–CableTVNetworkCableTVNetworkACableMODEMisusedtoenablesusertoconnectthePCtoalocalcableTVlineandreceivedataatabout10Mbps.ISPadoptingthistechnologyinHK:iCable(有線寬頻)BroadbandAccess–CableTVNetworkCableTVNetworkDownloadanduploadspeedarethesame,butthebandwidth(10Mbps)issharedamongusersatthesamelocation(e.g.thesamebuilding)Hardwareused–NetworkCard,CableMODEMBroadbandvsDial-upAccessFasterconnectionspeed–upto1.5Mbpsto10Mbps.Nodialingrequired.Simultaneoususeofdataandvoiceconnectionsie:unlikedial-upaccess,usercantalkonthephonewhilesurfingtheInternet.HowcanweshareInternetaccessinaLANtoaBroadband?Arouter(路由器)isneededtoconnectaLANtotheInternet.ItwillsharethebroadbandaccessfromoneInternetaccountamongallusersintheLAN.CommunicationProtocol–TCP/IPTCP/IPcommunicationprotocoloftheInternetsetofrulesusedinmessagetransmissionontheInternet.computersneedtousethesameprotocoliftheyneedtocommunicateTCPandIPAdvantagesofTCP/IPIfwesendthewholefilewithoutbreakingitintopackets,thewholemessagethenhastobere-sentifthefullmessagefailstoreachitsdestinationifitisbrokendownintopackets,thenonlythepacketthatfailtobesentareresent.PacketAnimationAdvantagesofTCP/IPTransmissionofdataisnotaffectedbythefailureofanypath:therearemorethanonepath.Packetsofdatacanberoutedaroundtheproblem.theloadofthelineisevenlydistributed.AslongastheoperatingsystemsupportsTCP/IP,thecomputerscancommunicatethroughLANandInternet.TCPAnimationIPAddressItidentifieseveryhost(computer)inanynetwork.WhenapacketistransmittedovertheInternet,itmustcarrytheaddressesofthesenderandreceivercomputerssothattherouterscanchoosethebestpath.IPAddress–FormatTheIPaddresssystemcurrentlyusingiscalledtheIPv4addressingsystem.QuestionregardingIPAddressWhatistherangeoftheeachsetofnumbers?AseachcomputerintheInternethasauniqueIPaddress,howmanycomputercanberepresentedintheInternet?WhatcanwedoifthenumberofIPaddressesisnotenough?RealIPandVirtualIPImagineiftherearenotenoughIPaddressesinanetwork,whatcanwedo?ThesolutionistouseVirtualIP.HowVirtualIPworksSomeoftheIPaddressesarereservedforprivatenetwork(ie:LAN).E.g.10.X.X.Xor192.168.X.XTherouterwillnotroutetheseIPstotheInternet,ie:itwillroutethedatasendingtotheseIPsinsidetheLAN.StaticIPandDynamicIPStaticIPIPaddressesthatarefixedeverytimewhentheuserconnecttotheInternet.DynamicIPIPaddressesthatchangeseverytimetheuserconnecttotheInternet.DomainNameSystem(DNS)Atthecommandwindow,typeinthecommand“ping”,whatdidyoufind?Why?Toconnecttoaspecificcomputer,weneedtoknowitsIPaddress.ConnecttotheYahoo!webpage,weneedtoknowitsaddress,ie:typeItisinconvenienttorememberthemeaninglessIPaddress.DNSServerDNSServerresponsiblefortranslatingtheaddressintothecorrespondingIPaddress.Trytogettothenba.comWebServerWebServerisacomputerthatdeliversWebpages.AcomputercanbecomeawebserverbyinstallingWebServerProgramlikeApacheandIIS(InternetInformationServer)WebBrowserAsoftwareapplicationusedtodisplayWebpages.TwomostpopularbrowsersareNetscapeNavigatorandMicrosoftInternetExplorer(IE).Plug-in(外掛程式)Thebrowsercannotplayallformatofaudioorvideofiles,soaplug-inprogramisneededtoaddsupporttothesetypesoffiles.CasestudiesIfthehosts(PCs)cancommunicatewellintheLANbuttheyhavedifficultiestogettotheInternet,whatwouldbetheproblem?Ifyouareateacherandyouh