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Link Layer & Network Layer

Chapter 7.B and 7.C. Link Layer & Network Layer. Prof. Dina Katabi. Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden. Previous Lecture. We learned how to share the network infrastructure between many connections/flows

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Link Layer & Network Layer

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  1. Chapter 7.B and 7.C Link Layer & Network Layer Prof. Dina Katabi Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden

  2. Previous Lecture • We learned how to share the network infrastructure between many connections/flows • We also learned about the implications of the sharing scheme (circuit or packet switching) on the service that the traffic receives

  3. This Lecture • An Example: HTTP • Layering • Link Layer

  4. 1 20 2 3 4 19 18 17 14 5 15 6 11 8 16 7 12 9 13 10 Example: HTTP over the Internet Using TCP/IP and Ethernet App App “A” MIT “B”(CNN.Com) OS OS Ethernet Ethernet R5 R1 R2 R3 R4

  5. This Lecture • An Example: HTTP • Layering • Link Layer

  6. Network Architecture Problem • Networks are complex (heterogeneity, distributed, delay, losses, reordering, …) • How do we organize a network implementation? Solution • To deal with complexity  use layering

  7. Layering • Layering is a particular form of abstraction • The 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 below

  8. Layering: Our HTTP Example HTTP Application End-to-End Layer Transport TCP Network IP Link Ethernet The 4-layer Internet model

  9. Where are these layers? • Link and network layers are implemented everywhere • The end-to-end layer (i.e., transport and application) is implemented only at hosts Host Host Peer-layer communication Application Application Router Transport Transport Network Network Network Datalink Datalink Datalink Physical medium

  10. Encapsulation • A layer can use only the service provided by the layer immediate below it • Each layer may change and add a header to data packet data data data data data data data data

  11. Interface • Higher 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 arrival • e.g., Network_Handle()

  12. Multiplexing in the Internet • Many possible applications, transports, and link layers • But they all use IP at the network layer Telnet FTP HTTP Application TCP UDP Transport IP Internet Packet radio Ethernet Link

  13. This Lecture • An Example: HTTP • Layering • Link Layer

  14. This Lecture • To cope with the complexity, the network architecture is organized into layers • The link layer delivers data between two machines that are directly connected using a link

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