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CS244a: An Introduction to Computer Networks

CS244a: An Introduction to Computer Networks. Handout #2: Introduction. Nick McKeown Professor of Electrical Engineering and Computer Science, Stanford University nickm@stanford.edu http://www.stanford.edu/~nickm. Outline. Introduction What the class is about. Introduction to the TAs.

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CS244a: An Introduction to Computer Networks

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  1. CS244a: An Introduction to Computer Networks Handout #2: Introduction Nick McKeown Professor of Electrical Engineering and Computer Science, Stanford University nickm@stanford.edu http://www.stanford.edu/~nickm CS244a Handout #2

  2. Outline • Introduction • What the class is about. • Introduction to the TAs. • Logistics • Handout #1: Logistics and Text Books. • Some ground rules. CS244a Handout #2

  3. Some Ground Rules • Let’s make this educational and enjoyable. • It’s a big class, and it’s easy for things to get out of hand, so please… • Let me orchestrate the questions. • Listen to other people’s questions. • Be here. • Be here on time. CS244a Handout #2

  4. Let’s begin • Demos • Internet telephony #1 • Internet telephony #2 • An Introduction to the mail system • An Introduction to the Internet • [Three Key Enablers of Networking] CS244a Handout #2

  5. Admin Admin An Introduction to the mail system MIT Stanford Nick Dave CS244a Handout #2

  6. 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? • Need local copies of contents of each envelope. • How long to keep each copy. • What if an acknowledgement is lost? CS244a Handout #2

  7. Admin Admin Network Layer Link Layer An Introduction to the mail system MIT Stanford Application Layer Nick Dave Transport Layer CS244a Handout #2

  8. Application Layer Transport Layer O.S. O.S. Link Layer Network Layer D D D D D D H H H H H H Data Data Header Header An Introduction to the Internet Athena.MIT.edu Leland.Stanford.edu Nick Dave CS244a Handout #2

  9. 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? • Need local copies of contents of each packet. • How long to keep each copy? • What if an acknowledgement is lost? CS244a Handout #2

  10. Characteristics of the Internet (2) • No guarantee of integrity of data. • Packets can be fragmented. • Packets may be duplicated. CS244a Handout #2

  11. Layering in the Internet • Transport Layer • Provides reliable, in-sequence delivery of data from end-to-end on behalf of application. • Network Layer • Provides “best-effort”, but unreliable, delivery of datagrams. • Link Layer • Carries data over (usually) point-to-point links between hosts and routers; or between routers and routers. CS244a Handout #2

  12. Admin Admin Network Layer Link Layer An Introduction to the mail system MIT Stanford Application Layer Nick Dave Transport Layer CS244a Handout #2

  13. Some questions about the mail system • How many sorting offices are needed and where should they be located? • How much sorting capacity is needed? • Should we allocate for Mother’s Day? • How can we guarantee timely delivery? • What prevents delay guarantees? • Or delay variation guarantees? • How do we protect against fraudulent mail deliverers, or fraudulent senders? CS244a Handout #2

  14. Outline • Demos • Internet telephony #1 • Internet telephony #2 • An Introduction to the mail system • An Introduction to the Internet • [Three Key Enablers of Networking] CS244a Handout #2

  15. Three Key Enablers of Networks • Digitization of Signals • Economies of Scale • Network Externalities CS244a Handout #2

  16. Digitization of Signals • Any information bearing signal can be represented by a binary string with arbitrarily high accuracy. • Sample + quantize a Digital stream. • Digital data is cheaper to store, manipulate and, most importantly, reliably communicate. CS244a Handout #2

  17. Economies of Scale • Cost of capacity grows slowly with increased capacity. • A network has fixed costs only: (almost) zero marginal costs. Cost Capacity or # users CS244a Handout #2

  18. Boom! Benefit Network Externalities • Value of the network increases as the number of users increases, which in turn attracts more users. Cost # Users CS244a Handout #2

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