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An Introduction to Computer Networks

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Chapter 7. An Introduction to Computer Networks. Prof. Dina Katabi. Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden . Chapter Outline. Introduction (slides and 7.A) Layered Architecture (slides and 7.B & 7.D)

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An Introduction to Computer Networks

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  1. Chapter 7 An Introduction to Computer Networks Prof. Dina Katabi Some slides are from lectures by Nick Mckeown, Ion Stoica, Frans Kaashoek, Hari Balakrishnan, and Sam Madden

  2. Chapter Outline • Introduction (slides and 7.A) • Layered Architecture (slides and 7.B & 7.D) • Routing (slides and 7.D) • Reliable Transmission & Flow Control (slides and read 7.E) • Congestion Control (slides and read 7.F)

  3. This Lecture • What is a network? • Sharing the infrastructure • Circuit switching • Packet switching • Best Effort Service • Analogy: the mail system • Internet’s Best Effort Service

  4. This Lecture • What is a network? • Sharing the infrastructure • Circuit switching • Packet switching • Best Effort Service • Analogy: the mail system • Internet’s Best Effort Service

  5. Two ways to share • Circuit switching (isochronous) • Packet switching (asynchronous)

  6. Internet Traffic Is Bursty Daily traffic at an MIT-CSAIL router Max In:12.2Mb/s Avg. In: 2.5Mb/s Max Out: 12.8Mb/s Avg. Out: 3.4 Mb/s

  7. Packet switching also show reordering Packets in a flow may not follow the same path (depends on routing as we will see later)  packets may be reordered Host C Host D Host A Node 1 Node 2 Node 3 Node 5 Host B Host E Node 7 Node 6 Node 4

  8. This Lecture • What is a network? • Sharing the Infrastructure • Circuit switching • Packet switching • Best Effort Service • Analogy: the mail system • Internet’s Best Effort Service

  9. Admin Admin The mail system Stanford MIT Dina Nick

  10. Characteristics of the mail system • Each envelope is individually routed • No time guarantee for delivery • No guarantee of delivery in sequence • No guarantee of delivery at all! • Things get lost • How can we acknowledge delivery? • Retransmission • How to determine when to retransmit? Timeout? • If message is re-sent too soon  duplicates

  11. Admin Admin The mail system Stanford MIT Dina Nick

  12. O.S. O.S. Data Data Header Header The Internet Leland.Stanford.edu Nms.csail.mit.edu Dina Nick Packet

  13. Characteristics of the Internet • Each packet is individually routed • No time guarantee for delivery • No guarantee of delivery in sequence • No guarantee of delivery at all! • Things get lost • Acknowledgements • Retransmission • How to determine when to retransmit? Timeout? • If packet is re-transmitted too soon  duplicate

  14. Best Effort No Guarantees: • Variable Delay (jitter) • Variable rate • Packet loss • Duplicates • Reordering • (notes also state maximum packet length)

  15. Differences Between Circuit & Packet Switching

  16. This 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

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