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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. Some Ground Rules. Let’s make this educational and enjoyable.

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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. 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

  3. Let’s begin • An Introduction to the mail system • An Introduction to the Internet CS244a Handout #2

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

  5. 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

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

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

  8. 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

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

  10. 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

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

  12. 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

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