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Multimedia-unfriendly TCP Congestion Control and Home Gateway Queue
Management
Lawrence Stewart α, David Hayes α, Grenville Armitageα, Michael Welzlβ, Andreas
Petlundβ
α Centre for Advanced Internet Architectures (CAIA), Swinburne University of Technology
β Department of Informatics, University of Oslo
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Outline 1. Introduction
2. Results
3. Conclusion
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Detailed outline (section 1 of 3) 1. Introduction
2. Results
3. Conclusion
1. Introduction • Motivation • Not All Queues Are Created Equal • TCP CC (Congestion Control) Recap • Methodology
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Motivation Gateway devices often have excessive drop-tail queue buffering1,2
TCP CC algorithms each interact differently with network buffers Real-time multimedia traffic sharing the gateway bottleneck
experiences collateral damage: latency/jitter and loss How does choice of CC algorithm and queue implementation impact
the inflicted collateral damage? 1M. Claypool, R. Kinicki, M. Li, J. Nichols and H. Wu, “Inferring Queue Sizes in Access Networks by Active
Measurement”, PAM Workshop '04 2M. Dischinger, A. Haeberlen, K. P. Gummadi and S. Saroiu, “Characterizing residential broadband networks”,
SIGCOMM IMC '07
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Not All Queues Are Created Equal When is a drop-tail queue full?
Packet/Slot based drop if occupancy ≥ qlen Fixed-byte strict drop if occupancy + pkt ≥ qlen Fixed-byte loose drop if occupancy > qlen
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TCP Congestion Control Recap NewReno is ailing defacto standard (high latency/speed, wireless Many new algorithm proposals: Compound, CUBIC, HTCP, ... BSD still uses NewReno Linux uses CUBIC Windows Vista / 7 have Compound TCP available for testing
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TCP Congestion Control Recap Downstream NewReno Behaviour
Congestion window oscillation coupled with induced queuing delay. ADSL 1 type link: 1500/256 kbps, min 100ms RTT, 20 000 byte queue.
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Methodology Testbed & NS-2 1500/256kbps & 24/1Mbps
(ADSL 1 & 2 speeds) Byte-based [10k, 100k] &
slot-based [7, 67] queues RTTs of 24, 50, 100 and 200ms Dummynet for bandwidth, queue size &
RTT emulation Single bulk TCP flow A->C 186 byte, N(µ=20ms, σ =1ms) CBR UDP
flow B<->D
Testbed
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Detailed outline (section 2 of 3) 1. Introduction
2. Results
3. Conclusion
2. Results • Goodput • Collateral Damage to Voice Stream – Latency • Collateral Damage to Voice Stream - Loss
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Goodput
Downstream goodput vs PS queue length - measured (testbed) and simulated (NS-2), 1500/256 kbps & 24/1 Mbps links, 100ms min RTT.
ADSL 1 (1500/256kbps) ADSL 2 (24/1Mbps)
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CUBIC Induces More OWD Than NewReno
Congestion window oscillation coupled with induced queuing delay. ADSL1 type link: 1500/256kbps, min 100ms RTT, 20 000byte queue.
Downstream NewReno Downstream CUBIC
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Collateral Damage to Voice Stream - Latency
Induced downstream queuing delay - measured (testbed) and simulated (NS-2), 40 000byte FB-loose queue.
ADSL 1 (1500/256kbps) ADSL 2 (24/1Mbps)
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Collateral Damage to Voice Stream - Loss
Proportion of CBR packets lost on the downstream for different packet drop mechanisms - 1500/256kbps link, 100ms minimum RTT.
FB-loose, FB-strict & PS NS-2
FB-loose Testbed & NS-2
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Detailed Simulation: Impact of Queue Size on Loss
[52500, 67500] in 30 byte increments, 1500/256kbps, 100ms min RTT. Dashed line envelope - 5% & 95% confidence intervals.
NewReno CUBIC
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Time Series Analysis of FB-Strict
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Time Series Analysis of PS
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Time Series Analysis of FB-Loose
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Detailed outline (section 3 of 3) 1. Introduction
2. Results
3. Conclusion
3. Conclusion • Summary & Open Questions
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Summary & Open Questions Summary
CUBIC keeps buffers fuller: latency & loss increase FB-Loose disadvantages small, real-time multimedia packets Byte-based queue sizes around integer multiples of TCP packet
size correspond with lowest FB-Loose loss & highest FB-Strict loss Dummynet implements FB-Loose byte-based queues
Open Questions Does using TCP for interactive traffic change things? Can we develop guidelines for home gateway manufacturers?