1、Protocols and the TCP/IP SuiteChapter 4Key Features of a ProtocolnSyntaxnConcerns the format of the data blocksnSemanticsnIncludes control information for coordination and error handlingnTimingnIncludes speed matching and sequencingAgents Involved in CommunicationnApplicationsnExchange data between
2、computers (e.g., electronic mail)nComputersnConnected to networksnNetworksnTransfers data from one computer to anotherTCP/IP Network Access LayernConcerned with the exchange of data between an end system and the network to which its attachednSoftware used depends on type of networknCircuit switching
3、nPacket switching (e.g., X.25)nLANs (e.g., Ethernet)nOthersT:TCP/IP Internet LayernUses internet protocol (IP)nProvides routing functions to allow data to traverse multiple interconnected networksnImplemented in end systems and routersTCP/IP Host-to-Host, or Transport LayernCommonly uses transmissio
4、n control protocol (tcp)nProvides reliability during data exchangenCompletenessnOrderTCP/IP Application LayernLogic supports user applicationsnUses separate modules that are peculiar to each different type of applicationProtocol Data Units (PDUs)Common TCP/IP ApplicationsnSimple mail transfer protoc
5、ol (SMTP)nProvides a basic electronic mail facilitynFile Transfer Protocol (FTP)nAllows files to be sent from one system to anothernTELNETnProvides a remote logon capabilityLayers of the OSI ModelnApplicationnPresentationnSessionnTransportnNetworknData linknPhysicalOSI Application LayernProvides acc
6、ess to the OSI environment for usersnProvides distributed information servicesOSI Presentation LayernProvides independence to the application processes from differences in data representation (syntax)OSI Session LayernProvides the control structure for communication between applicationsnEstablishes,
7、 manages, and terminates connections (sessions) between cooperating applicationsOSI Transport LayernProvides reliable, transparent transfer of data between end pointsnProvides end-to-end error recovery and flow controlOSI Network LayernProvides upper layers with independence from the data transmissi
8、on and switching technologies used to connect systemsnResponsible for establishing, maintaining, and terminating connectionsOSI Data link LayernProvides for the reliable transfer of information across the physical linknSends blocks (frames) with the necessary synchronization, error control, and flow
9、 controlOSI Physical LayernConcerned with transmission of unstructured bit stream over physical mediumnDeals with accessing the physical mediumnMechanical characteristicsnElectrical characteristicsnFunctional characteristicsnProcedural characteristicsComparison of OSI and TCP/IPTCP/IP Architecture D
10、ominancenTCP/IP protocols matured quicker than similar OSI protocolsnWhen the need for interoperability across networks was recognized, only TCP/IP was available and ready to gonOSI model is unnecessarily complexnAccomplishes in seven layers what TCP/IP does with fewer layersElements of Standardizat
11、ion within OSI FrameworknProtocol SpecificationnFormat of protocol data units (PDUs) exchangednSemantics of all fieldsnAllowable sequence of PDUsnService DefinitionnFunctional description that defines what services are provided, but not how the services are to be providednAddressingnEntities are ref
12、erenced by means of a service access point (SAP)Internetworking TermsnCommunication network facility that provides a data transfer service among devices attached to the networknInternet collection of communication networks, interconnected by bridges/routersnIntranet internet used by an organization
13、for internal purposesnProvides key Internet applicationsnCan exist as an isolated, self-contained internetInternetworking TermsnEnd System (ES) device used to support end-user applications or servicesnIntermediate System (IS) device used to connect two networksnBridge an IS used to connect two LANs
14、that use similar LAN protocolsnRouter - an IS used to connect two networks that may or may not be similarFunctions of a RouternProvide a link between networksnProvide for the routing and delivery of data between processes on end systems attached to different networksnProvide these functions in such
15、a way as not to require modifications of the networking architecture of any of the attached subnetworksNetwork Differences Routers Must AccommodatenAddressing schemesnDifferent schemes for assigning addressesnMaximum packet sizesnDifferent maximum packet sizes requires segmentationnInterfacesnDiffering hardware and software interfacesnReliabilitynNetwork may provide unreliable service
