414Lecture10

414Lecture10 - Lecture 10 Transport Layer TCP Throughput...

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Lecture 10 Transport Layer TCP Throughput and Fairness ECSE 414 – Fall 2010
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ECSE 414, Lecture 10 2 Announcements Homework Assignment #2 Due Thursday, October 7 Midterm Exam, next Tuesday, Oct 12 More info at the end of today’s lecture 2010 Michael Rabbat
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ECSE 414, Lecture 10 3 TCP throughput What’s the average throughout of TCP as a function of window size and RTT? Ignore slow start Let W be the window size when loss occurs. When window is W, throughput is W/RTT Just after loss, window drops to W/2, throughput to W/2RTT. Average throughput: .75 W/RTT 2010 Michael Rabbat
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ECSE 414, Lecture 10 4 TCP Throughput • “Macroscopic Description” (fluid model) Ignore slow-start Skip straight to steady state congestion avoidance AIMD W W/2 Congestion Window Size t time (transmission round) 2010 Michael Rabbat
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ECSE 414, Lecture 10 5 Throughput Concrete Example • One user, link with bandwidth R = 1 Mbps • RTT = 100ms • MSS = 1000 bits • Assume packets dropped as soon as throughput exceeds R (no queuing) • Always see triple duplicate ACK (no timeouts) How long does it take to reach steady state? (seconds) What is the average throughput in steady state? (Calculate explicitly. Not using the macroscopic eqn.) 2010 Michael Rabbat
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ECSE 414, Lecture 10 6 TCP Loss Rates: Macroscopic View From the time when the transmission rate goes from
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture10 - Lecture 10 Transport Layer TCP Throughput...

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