U Innsbruck Informatik - U Innsbruck Informatik - 1 Scalable Performance Scalable Performance Signalling Signalling and Congestion Avoidance and Congestion Avoidance Michael Welzl Michael Welzl [email protected]University of Linz -> University of Innsbruck University of Linz -> University of Innsbruck PhD presentation PhD presentation Supervisor: Max Mühlhäuser 2nd supervisor: Jon Crowcroft Supervisor: Max Mühlhäuser 2nd supervisor: Jon Crowcroft Abteilung Telekooperation, TU Darmstadt, Nov. 18th 2002 Abteilung Telekooperation, TU Darmstadt, Nov. 18th 2002
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Scalable Performance Signalling and Congestion Avoidance
Scalable Performance Signalling and Congestion Avoidance. PhD presentation Supervisor: Max Mühlhäuser 2nd supervisor: Jon Crowcroft Abteilung Telekooperation, TU Darmstadt, Nov. 18th 2002. Michael Welzl [email protected] University of Linz -> University of Innsbruck. Outline. - PowerPoint PPT Presentation
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U Innsbruck Informatik - U Innsbruck Informatik - 11
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Throughput Loss
Avg. Queue Length Fairness
CADPC vs. TCP-friendly CC. CADPC vs. TCP-friendly CC. mechanismsmechanisms
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CADPC vs. 3 TCP(+ECN) flavorsCADPC vs. 3 TCP(+ECN) flavors
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Further simulations (in the thesis)Further simulations (in the thesis)
• Dynamic:– Dependence on smoothness parameter a and packet size– Robustness against fast routing changes– Effect of mixing converged flows– Performance across highly asymmetric connections + noisy links
• Long-term (throughput, loss, average queue length, fairness):– Check valid parameter space: bandwidth, no. of flows, packet
size– Varying bottleneck bandwidth– Varying feedback delay– RED, REM and AVQ Active Queue Management– Behaviour with varying amount of web background traffic– Max-min fairness (scenario with 2 bottlenecks)
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OutlineOutline
• Problem identification / motivation
• Proposed solution
• Simulation results
• Conclusion
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CADPC Advantages /2CADPC Advantages /2
• Useful for asymmetric links
• Useful for noisy (wireless) links + “long fat pipes”
• Useful for QoS and load-based charging
DisadvantagesDisadvantages
• Requires router support
• Requires traffic isolation because…– not tcp-friendly– slowly responsive: bad results with web traffic
but: sticks to KISS principle
but: see future work...
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IMHO:IMHO: considerable step towards considerable step towardsbetter congestion controlbetter congestion control
...b...based on drastic departure from ased on drastic departure from existing approachesexisting approaches
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Future workFuture work
• So far, ...– only max-min-fairness supported– only greedy sources simulated
• Gradual deployment ideas:
– CADPC / PTP within a DiffServ class (QoS “in the small“):“we offer QoS + provide router support,you use CADPC and obtain a good result[and we can calculate your rate, too]“
– If CADPC works with non-greedy senders:edge2edge PTP signalling
• PTP supported traffic engineering (TCP over CADPC)• CADPC <=> TCP translation at edge routers?
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The End ...The End ...
• Related publications
• PTP ns code
• PTP Linux code (router kernel patch + end system implementation)
• Future updates: thesis, CADPC code, ..
http://fullspeed.to/ptp
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Additional informationAdditional information
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The end2end argumentThe end2end argument
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This thesis and the end2end This thesis and the end2end argumentargument
• „Lower-level layers, which support many independent applications, should provide only resources of broad utility across applications, while providing to applications usable means for effective sharing of resources and resolution of resource conflicts. (network transparency)“
[Active Networking and End-To-End Arguments, Comment by David P. Reed, Jerome H. Saltzer, and David D. Clark]
• Goals of this thesis:
– provide such means– use it!
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AIMD BackgroundAIMD Background
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U ser 1 A lloca tion x1
F a irnessL ine
E ffic iencyL ine
Use
r 2
Allo
catio
n x
2
StartingPoint
A IM D
D esirab le
StartingPoint
A IA D
M IM D
U nderload
O verload
AIMD in Theory (equal RTTs)AIMD in Theory (equal RTTs)
U ser 1 A lloca tion x1
F a irnessL ine
E ffic iencyL ine
Use
r 2
Allo
catio
n x
2
StartingPoint
A IM D
D esirab le
StartingPoint
A IA D
M IM D
U nderload
O verload
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CADPC synchronous case fluid CADPC synchronous case fluid analysisanalysis
• Final formula per user:
x(t+1) = x(t)a(1-x(t)-traffic)+x(t)
x(t) ... normalised rate at time ta... smoothness factor(should be 0 < a <= 1)traffic (normalised) ... from PTP
• Converges to: n/(n+1)
• Continuous-time version of synchronous case (traffic=nx):logistic growth x‘(t) = x(t)a(1-x(t)/c) [c = 1/(1+n)]asymptotically stable equilibrium point: c