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CS536-2009-03-05

CS536-2009-03-05 - Congestion Control for High...

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Congestion Control for High Bandwidth-Delay Product Environments Dina Katabi Mark Handley Charlie Rohrs
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TCP congestion control performs poorly as bandwidth or delay increases Round Trip Delay (sec) A v g . T C P U t i l i z a t i o n Bottleneck Bandwidth (Mb/s) A v g . T C P U t i l i z a t i o n Shown analytically in [Low01] and via simulations Because TCP lacks fast response Spare bandwidth is available TCP increases by 1 pkt/RTT even if spare bandwidth is huge When a TCP starts, it increases exponentially Too many drops Flows ramp up by 1 pkt/RTT, taking forever to grab the large bandwidth 50 flows in both directions Buffer = BW x Delay RTT = 80 ms 50 flows in both directions Buffer = BW x Delay BW = 155 Mb/s
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Proposed Solution: Decouple Congestion Control from Fairness High Utilization; Small Queues; Few Drops Bandwidth Allocation Policy
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Proposed Solution: Decouple Congestion Control from Fairness Example: In TCP, Additive-Increase Multiplicative-Decrease (AIMD) controls both Coupled because a singlemechanism controls both How does decoupling solvetheproblem? 1. To control congestion: use MIMD which shows fast response 2. To control fairness: use AIMD which converges to fairness
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