Winter 2008CS244a Handout #21 CS244a: An Introduction to Computer Networks Handout #2: Introduction...
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Winter 2008 CS244a Handout #2 1 CS244a: An Introduction to Computer Networks Handout #2: Introduction Nick McKeown Professor of Electrical Engineering and Computer Science, Stanford University [email protected] http://www.stanford.edu/~nickm
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Transcript of Winter 2008CS244a Handout #21 CS244a: An Introduction to Computer Networks Handout #2: Introduction...
Winter 2008 CS244a Handout #2 1
CS244a: An Introduction to Computer Networks
Handout #2: Introduction
Nick McKeownProfessor of Electrical Engineering and Computer Science, Stanford University
[email protected]://www.stanford.edu/~nickm
Winter 2008 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.
Winter 2008 CS244a Handout #2 3
Let’s begin
An Introduction to the mail system An Introduction to the Internet
Winter 2008 CS244a Handout #2 4
An Introduction to the mail system
Nick Dave
Stanford MIT
Admin Admin
Winter 2008 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?
Winter 2008 CS244a Handout #2 6
An Introduction to the mail system
Nick Dave
Stanford MIT
Admin Admin
Application Layer
Transport Layer
Network Layer
Link Layer
Winter 2008 CS244a Handout #2 7
An Introduction to the Internet
Nick Dave
Leland.Stanford.edu Athena.MIT.edu
Network Layer
Link Layer
Application Layer
Transport Layer
O.S. O.S.HeaderData HeaderData
DatagramDatagram
Winter 2008 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?
Winter 2008 CS244a Handout #2 9
Characteristics of the Internet (2)
No guarantee of integrity of data. Packets can be fragmented. Packets may be duplicated.
Winter 2008 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.
Winter 2008 CS244a Handout #2 11
An Introduction to the mail system
Nick Dave
Stanford MIT
Admin Admin
Application Layer
Transport Layer
Network Layer
Link Layer
Winter 2008 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?
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