Protocol Architecture The “Common Language”Need for ProtocolsNetwork ArchitectureProgramming the CommunicationThe Levels of AbstractionLayered Network ArchitectureService PrimitivesSlide 8Example: Sending a Letter(Un-)Acknowledged ServiceProtocol ArchitecturesOSI Reference ModelOSI LayersOSI Layers and EncapsulationOSI Model in a Switched Communication NetworkA Tour of the OSI LayersSlide 17Slide 18Slide 19Slide 20Slide 21Slide 22TCP/IP Protocol SuiteExample: File TransferEncapsulation in the TCP/IP SuiteSlide 26Comparison of OSI Model and TCP/IP SuiteQuizProtocol ArchitectureThe “Common Language”Copyright by Jorg Liebeherr 98, 99Need for ProtocolsProtocols are a set of rules and conventions. By enforcing that communicating parties adhere to a common protocol, communication is made possible.Copyright by Jorg Liebeherr 98, 99Network ArchitectureA Network Architecture is a structured set of protocols that implement the exchange of information between computersCopyright by Jorg Liebeherr 98, 99Programming the CommunicationAny complex programming task is made simpler by using several levels of abstractionAbstraction hides the programming details of lower levelsCommunication tasks give rise to standard abstractionsCommittees such as the IETF (Internet Engineering Task Force) are in charge for standardizing the abstractions related to internet communicationCopyright by Jorg Liebeherr 98, 99The Levels of AbstractionMultiple levels of communication abstractions have been defined by standardization bodiesEach level is enforced by a corresponding protocolEach level uses the abstract services of the level belowAbstraction achieves separation of concernsA protocol needn’t know how the lower-level abstractions are implemented and what the higher level abstractions are.Copyright by Jorg Liebeherr 98, 99Layered Network ArchitectureIn a Layered Network Architecture, the services are grouped in a hierarchy of layers. A protocol of layer N uses only services of layer N-1.A protocol of layer N provides services only to layer N+1.ACEBD EBlayer 3layer 2layer 1not layered layeredACDCopyright by Jorg Liebeherr 98, 99Service PrimitivesN+1 LayerEntityN+1 LayerEntityN LayerEntityN LayerEntityN+1 Layer ProtocolX. Request X. Indication X. ResponseX. ConfirmAssume that some protocol implements service “X”.Copyright by Jorg Liebeherr 98, 99Service PrimitivesRecall: A layer N+1 protocol entity sees the lower layers only as an abstract service providerN+1 LayerEntityN+1 LayerEntityN+1 Layer ProtocolX. RequestX. IndicationX. Confirm Service ProviderX. ResponseCopyright by Jorg Liebeherr 98, 99Example: Sending a LetterBob’s mailboxBob AliceAlice’smailboxPostmanLogical flow of informationCopyright by Jorg Liebeherr 98, 99(Un-)Acknowledged ServiceUnconfirmed service: Acknowledged service: US MailL.Request L.IndicateL.IndicateL.Confirm US MailL.Request L.IndicateCopyright by Jorg Liebeherr 98, 99Protocol ArchitecturesThere are only few protocol architectures that are relevant today:OSI Reference ModelTCP/IP Protocols SuiteATM Protocol StackCopyright by Jorg Liebeherr 98, 99OSI Reference ModelThe OSI model defines seven layers:Layer 7: Application LayerLayer 6: Presentation LayerLayer 5: Session LayerLayer 4: Transport LayerLayer 3: Network LayerLayer 2: Data Link LayerLayer 1: Physical LayerInterconnection MediaCopyright by Jorg Liebeherr 98, 99OSI LayersPhysicalLayerPhysicalLayerPhysicalLayerPhysicalLayerData LinkLayerData LinkLayerData LinkLayerData LinkLayerNetworkLayerSessionLayerSessionLayerTransportLayerTransportLayerApplicationLayerApplic ationLayerPresentationLayerPresentationLayerNetworkLayerNetworkLayerNetworkLayerApplic ationHOSTNODEHOSTNODEApplicationCopyright by Jorg Liebeherr 98, 99OSI Layers and EncapsulationPhysicalLayerPhysicalLayerData LinkLayerData LinkLayerNetworkLayerSessionLayerSessionLayerTransportLayerTransportLayerApplicationLayerApplicationLayerPresentationLayerPresentationLayerNetworkLayerApplicationApplicationAHPHSHTHNHDHBitsDataAH DataPH AH DataSH PH AH DataTH SH PH AH DataNH TH SH PH AH DataDataApplicationDataHeader ofApplicationLayerCopyright by Jorg Liebeherr 98, 99OSI Model in a Switched Communication NetworkTransportSessionPresentationApplic ationTransportSessionPresentationApplicationPhysic alData LinkNetworkPhysicalData LinkNetworkPhysic alData LinkNetworkPhysicalData LinkNetworkPhysic alData LinkNetworkPhysicalData LinkNetworkStation (Host)Node (Router)Copyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersPhysical Layer (Layer 1):Converts bits into electrical or optical signalsTransmits these signals over the hardware communication mediumExample: RS-232Copyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersData Link Layer (Layer 2):Reliably transfers frames over a linkPerforms synchronization, error control, flow controlExample: PPPCopyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersNetwork Layer (Layer 3):Moves packets inside the networkPerforms routing, addressing, switching, congestion controlExample: IPCopyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersTransport Layer (Layer 4):Controls delivery of data between hostsConnection management, error control, flow control, multiplexing, TCP, UDP.Copyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersSession Layer (Layer 5):Support the dialog between cooperating application programsSession management, synchronizationExample: RPCCopyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersPresentation Layer (Layer 6):Data conversion into application formatEncryption/decryptionSecure socketsCopyright by Jorg Liebeherr 98, 99A Tour of the OSI LayersApplication Layer (Layer 7):Provides network access to application programsEverything is application specificExample: File Transfer, Electronic MailCopyright by Jorg Liebeherr 98, 99TCP/IP Protocol SuiteThe TCP/IP protocol suite was first defined in 1974The TCP/IP protocol suite is the protocol architecture of the InternetThe TCP/IP suite has four layers: Application, Transport, Internet, and Network Interface LayerApplicationLayerTransportLayerInternetNetworkInterfacetelnet, ftp, emailTCP, UDPIP, ICMP, IGMPDevice DriversCopyright by Jorg Liebeherr 98, 99Example: File TransferFTPprogramTCPIPEthernetDriverEthernetDriverEthernetDriverIPFTPprogramTCPIPEthernetDriverFTP protocolTCP protocolIP
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