Congeson causes queues to grow rate mismatch tcp

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Unformatted text preview: router’s queue is building up and congestion will happen—E.g., RTT grows or sending rate flattens. (e.g., sending rate flalens) 70 60 50 40 30 20 10 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time (seconds) 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time (seconds) 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time (seconds) 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 1100 900 700 500 300 100 Queue size in router Sending KBps 0.5 10 5 TCP Vegas •  Compare Actual Rate (A) with Expected Rate (E) 491 –  If E- A > β, decrease cwnd linearly : A isn’t responding –  If E- A < α, increase cwnd linearly : Room for A to grow KB 6.4 Congestion-Avoidance Mechanisms 70 60 50 40 30 20 10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 5.0 5.5 6.0 6.5 7.0 7.5 8.0 KBps Time (seconds) 240 200 160 120 80 40 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time (seconds) Vegas •  Shorter router queues •  Lower jiler •  Problem: –  Doesn’t compete well with Reno. Why? –  Reacts earlier, Reno is more aggressive, ends up with higher bandwidth...
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