计算机概论Cha 31页

Chapter4:NetworkingandtheInternet4.1NetworkFundamentals4.2TheInternet4.3TheWorldWideWeb4.4InternetProtocols4.5Security1\nNetworkClassificationsScopeLocalAreaNetwork(LAN,局域网)MetropolitanAreaNetwork(MAN,城域网)WideAreaNetwork(WAN,广域网)OwnershipClosedvs.Open(封闭式网络vs.开放式网络)Topology(thepatterninwhichthemachinesareconnected)Bus(总线型)EthernetStar(星型)WirelessnetworkswithcentralAccessPoint2\nFigure4.1Networktopologies3\nFigure4.1Networktopologies(continued)4\nProtocolsCSMA/CD（CarrierSense,MultipleAccesswithCollisionDetection,带冲突检测的载波侦听多路访问）UsedinEthernetSilentbusprovidesrighttointroducenewmessageCSMA/CA（CarrierSense,MultipleAccesswithCollisionAvoidance,带冲突避免的载波侦听多路访问）UsedinWiFiHiddenterminalproblem5\nFigure4.2Communicationoverabusnetwork6\nFigure4.3Thehiddenterminalproblem7\nConnectingNetworksRepeater（中继器）:ExtendsanetworkBridge（网桥）:ConnectstwocompatiblenetworksSwitch（交换机）:ConnectseveralcompatiblenetworksRouter（路由器）:Connectstwoincompatiblenetworksresultinginanetworkofnetworkscalledaninternet8\nFigure4.4Buildingalargebusnetworkfromsmallerones9\nFigure4.5RoutersconnectingtwoWiFinetworksandanEthernetnetworktoformaninternet10\nInter-processCommunicationClient-server（客户机/服务器模型）Oneserver,manyclientsServermustexecutecontinuouslyClientinitiatescommunicationPeer-to-peer(P2P，对等模型)TwoprocessescommunicatingasequalsPeerprocessescanbeshort-lived11\nFigure4.6Theclient/servermodelcomparedtothepeer-to-peermodel12\nDistributedSystems（分布式系统）SystemswithpartsthatrunondifferentcomputersInfrastructurecanbeprovidedbystandardizedtoolkitsExample:EnterpriseJavaBeans（企业级JavaBeans）fromSunMicrosystemsExample:.NETframework（.NET框架）fromMicrosoft13\nTheInternetTheInternet:AninternetthatspanstheworldOriginalgoalwastodevelopameansofconnectingnetworksthatwouldnotbedisruptedbylocaldisasters.Todayithasshiftedfromanacademicresearchprojecttoacommercialundertaking.14\nInternetArchitectureInternetServiceProvider(ISP,应特网服务提供商）Tier-1Tier-2AccessISP(因特网接入服务提供商):ProvidesconnectivitytotheInternetTraditionaltelephone(dialupconnection)CableconnectionsDSL（DigitalSubscriberLine，数字用户线路）Wireless15\nFigure4.7InternetComposition16\nInternetAddressingIPaddress（IP地址）:patternof32or128bitsoftenrepresentedindotteddecimalnotationMnemonicaddress:DomainnamesTop-LevelDomains（顶级域名）Domainnamesystem(DNS，域名系统)NameserversDNSlookupExample：www.gnnu.cn218.64.216.10617\nInternetCorporationforAssignedNames&Numbers(ICANN)：因特网名称与数字地址分配机构AllocatesIPaddressestoISPswhothenassignthoseaddresseswithintheirregions.Overseestheregistrationofdomainsanddomainnames.18\nTraditionalInternetApplicationsElectronicMail(E-mail，电子邮件)Domainmailserver（邮件服务器）collectsincomingmailandtransmitsoutingmailMailserverdeliverscollectedincomingmailtoclientsviaPOP3orIMAPFileTransferProtocol(FTP,文件传输协议)Telnet（远程登录）andSSH（安全壳）19\nMoreRecentApplicationsVoiceOverIP(VoIP)InternetRadio（因特网广播）N-unicast（多点广播）Multicast（多路广播）20\nWorldWideWebHypertext（超文本）andHTTP（HypertextTransferProtocol，超文本传输协议）Browser（浏览器）getsdocumentsfromWebserver（Web服务器）DocumentsidentifiedbyURLs（UniformResourceLocator，统一资源定位器）21\nFigure4.8AtypicalURL22\nHypertextDocumentFormatEncodedastextfileHTML（HypertextMarkupLanguage，超文本标记语言）XML（eXtensibleMarkupLanguage，可扩展标记语言）23\nFigure4.12Package-shippingexampleInternetProtocols24\nInternetSoftwareLayersApplicationlayer（应用层）:ConstructsmessagewithaddressTransportLayer（传输层）:ChopsmessageintopacketsNetworkLayer（网络层）:HandlesroutingthroughtheInternetLink（链路层）:Handlesactualtransmissionofpackets25\nFigure4.13TheInternetsoftwarelayers26\nFigure4.14FollowingamessagethroughtheInternet27\nTCP/IPProtocolSuiteTransportLayerTCP（TransmissionControlprotocol，传输控制协议）UDP（UserDatagramProtocol，用户数据报协议）NetworkLayerIP(IPv4andIPv6)：InternetProtocol，网际协议28\nFigure4.15ChoosingbetweenTCPandUDP29\nSecurityAttacksMalware（恶意软件）viruses病毒,worms懦虫Trojanhorses特洛尹木马,spyware(sniffing)间谍软件（嗅探软件）phishingsoftware电子诱饵软件)DenialofService（DoS，拒绝服务攻击）Spam（垃圾邮件）30\nSecurityProtectionFirewalls（防火墙）Spamfilters（垃圾邮件过滤器）ProxyServers（代理服务器）Antivirussoftware（防病毒软件）Encryption（加密）Legalapproaches（法律途径）31