Link Layer & Network LayerPrevious LectureThis LectureExample: HTTP over the Internet Using TCP/IP and EthernetSlide 15Slide 16Slide 17Layering: Our HTTP ExampleSlide 20Slide 21Slide 22Slide 23Slide 24Slide 291Link Layer & Network Layer Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden Prof. Dina KatabiChapter 7.B and 7.C2Previous LectureWe learned how to share the network infrastructure between many connections/flowsWe also learned about the implications of the sharing scheme (circuit or packet switching) on the service that the traffic receives3This LectureAn Example: HTTPLayeringLink Layer4Example: HTTP over the Internet Using TCP/IP and EthernetAppOSR2R2R3R3R4R4R1R1 R5R5Ethernet“A” MIT“B”(CNN.Com)EthernetAppOS123467201918175910812131115161415This LectureAn Example: HTTPLayeringLink Layer16Network ArchitectureProblemNetworks are complex (heterogeneity, distributed, delay, losses, reordering, …)How do we organize a network implementation?SolutionTo deal with complexity use layering17LayeringLayering is a particular form of abstractionThe system is broken into a vertical hierarchy of logically distinct entities (layers)The service provided by one layer is based solely on the service provided by layer below18Layering: Our HTTP ExampleNetworkLinkTransportThe 4-layer Internet modelApplicationHTTPIPTCPEthernetEnd-to-End Layer20Where are these layers? Link and network layers are implemented everywhereThe end-to-end layer (i.e., transport and application) is implemented only at hostsApplicationTransportNetworkDatalinkApplicationTransportNetworkDatalinkNetworkDatalinkPhysical mediumPeer-layer communicationRouterHostHost21EncapsulationA layer can use only the service provided by the layer immediate below itEach layer may change and add a header to data packetdatadatadatadatadatadatadatadata22InterfaceHigher layer calls lower layer e.g., Link_Send(this_data, this_link)Lower layer uses an up-call function to inform the higher layer of data arrivale.g., Network_Handle()23Multiplexing in the InternetMany possible applications, transports, and link layersBut they all use IP at the network layer InternetLinkTransportApplicationIPEthernetPacketradioTCP UDPTelnet FTP HTTP24This LectureAn Example: HTTPLayeringLink Layer29This LectureTo cope with the complexity, the network architecture is organized into layersThe link layer delivers data between two machines that are directly connected using a
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