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U of I CS 241 - Protocol Architecture

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1Protocol ArchitectureThe “Common Language”Copyright by Jorg Liebeherr 98, 99Need for Protocols Protocols are a set of rules and conventions. By enforcing that communicating parties adhere to a common protocol, communication is made possible.2Copyright by Jorg Liebeherr 98, 99Network Architecture A Network Architecture is a structured set of protocols that implement the exchange of information between computersCopyright by Jorg Liebeherr 98, 99Programming the Communication Any complex programming task is made simpler by using several levels of abstraction Abstraction hides the programming details of lower levels Communication tasks give rise to standard abstractions Committees such as the IETF (Internet Engineering Task Force) are in charge for standardizing the abstractions related to internet communication3Copyright by Jorg Liebeherr 98, 99The Levels of Abstraction Multiple levels of communication abstractions have been defined by standardization bodies Each level is enforced by a corresponding protocol Each level uses the abstract services of the level below Abstraction achieves separation of concerns A 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 Architecture In 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 layeredlayeredACD4Copyright by Jorg Liebeherr 98, 99Service PrimitivesN+1 LayerN+1 LayerN+1 LayerN+1 LayerEntityEntityEntityEntityN+1 LayerN+1 LayerN+1 LayerN+1 LayerEntityEntityEntityEntityN LayerN LayerN LayerN LayerEntityEntityEntityEntityN LayerN LayerN LayerN LayerEntityEntityEntityEntityN+1 Layer ProtocolN+1 Layer ProtocolN+1 Layer ProtocolN+1 Layer ProtocolX. RequestX. RequestX. RequestX. Request X. IndicationX. IndicationX. IndicationX. Indication X. ResponseX. ResponseX. ResponseX. ResponseX. ConfirmX. ConfirmX. ConfirmX. Confirm Assume 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 LayerN+1 LayerN+1 LayerN+1 LayerEntityEntityEntityEntityN+1 LayerN+1 LayerN+1 LayerN+1 LayerEntityEntityEntityEntityN+1 Layer ProtocolN+1 Layer ProtocolN+1 Layer ProtocolN+1 Layer ProtocolX. RequestX. RequestX. RequestX. RequestX. IndicationX. IndicationX. IndicationX. IndicationX. ConfirmX. ConfirmX. ConfirmX. ConfirmService ProviderService ProviderService ProviderService ProviderX. ResponseX. ResponseX. ResponseX. Response5Copyright by Jorg Liebeherr 98, 99Example: Sending a LetterBobBobBobBob’’’’s s s s mailboxmailboxmailboxmailboxBobBobBobBob AliceAliceAliceAliceAliceAliceAliceAlice’’’’ssssmailboxmailboxmailboxmailboxPostmanPostmanPostmanPostmanLogical flow of informationLogical flow of informationLogical flow of informationLogical flow of informationCopyright by Jorg Liebeherr 98, 99(Un-)Acknowledged Service Unconfirmed service:  Acknowledged service: US MailUS MailUS MailUS MailL.RequestL.RequestL.RequestL.Request L.IndicateL.IndicateL.IndicateL.IndicateL.IndicateL.IndicateL.IndicateL.IndicateL.ConfirmL.ConfirmL.ConfirmL.ConfirmUS MailUS MailUS MailUS MailL.RequestL.RequestL.RequestL.Request L.IndicateL.IndicateL.IndicateL.Indicate6Copyright by Jorg Liebeherr 98, 99Protocol Architectures There are only few protocol architectures that are relevant today: OSI Reference Model TCP/IP Protocols Suite ATM Protocol StackCopyright by Jorg Liebeherr 98, 99OSI Reference Model The 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 Media7Copyright by Jorg Liebeherr 98, 99OSI LayersPhysicalLayerPhysicalLayerPhysicalLayerPhysicalLayerData LinkLayerData LinkLayerData LinkLayerData LinkLayerNetworkLayerSessionLayerSessionLayerTransportLayerTransportLayerApplicationLayerApplicationLayerPresentationLayerPresentationLayerNetworkLayerNetworkLayerNetworkLayerApplicationHOSTNODEHOSTNODEApplicationCopyright 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 ofApplicationLayer8Copyright by Jorg Liebeherr 98, 99OSI Model in a Switched Communication NetworkTransportSessionPresentationApplicationTransportSessionPresentationApplicationPhysicalData LinkNetworkPhysicalData LinkNetworkPhysicalData LinkNetworkPhysicalData LinkNetworkPhysicalData LinkNetworkPhysicalData LinkNetworkStation (Host)Node (Router)Copyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Physical Layer (Layer 1): Converts bits into electrical or optical signals Transmits these signals over the hardware communication medium Example: RS-2329Copyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Data Link Layer (Layer 2): Reliably transfers frames over a link Performs synchronization, error control, flow control Example: PPPCopyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Network Layer (Layer 3): Moves packets inside the network Performs routing, addressing, switching, congestion control Example: IP10Copyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Transport Layer (Layer 4): Controls delivery of data between hosts Connection management, error control, flow control, multiplexing, TCP, UDP.Copyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Session Layer (Layer 5): Support the dialog between cooperating application programs Session management, synchronization Example: RPC11Copyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Presentation Layer (Layer 6): Data conversion into application format Encryption/decryption Secure socketsCopyright by Jorg Liebeherr 98, 99A Tour of the OSI Layers Application Layer (Layer 7): Provides network access to application programs Everything is application


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U of I CS 241 - Protocol Architecture

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