Comments on the Performance of Measurement Based Admission Control Algorithms Lee Breslau, S. Jamin, S. Shenker Infocom 2000MBACs surveyedMBACs surveyed (cont)Simulation MethodologyConfiguration ParametersSlide 11Comparing with Ideal CACSlide 19Slide 20Slide 21Ideal vs MS in Long Range DependanceSlide 23Can we predict MBAC loss?Slide 25ConclusionsComments on the Performance of Measurement Based Admission Control AlgorithmsLee Breslau, S. Jamin, S. Shenker Infocom 2000MBACs surveyedMeasured Sum:•Token rate of new flow + aggregate measured rate of existing flows must be less than utilization threshold“Hoeffding” bounds:•Peak rate of new flow + aggregate equiv bdw of existing flows must be less than link bdwTangent of equiv bdw curve:•A given “function” of equiv bdw less than link bdwMeasure CAC:•Peak rate of new flow + “large deviation” equiv bdw estimate less than link bdwAggregate Traffic Envelopes, etcMBACs surveyed (cont)Each one of the surveyed CAC schemes has two components:(a) Load estimate (including new flow)(b) Admission control decisionCan pair up Load estimate and Adm decision across schemes (mix and match)!Simulation MethodologyTwo types of sources:•ON/OFF sources: random ON and OFF intervals•Video tracesSources policed by token bucket•Token bucket parameters used in “parameter based” Call Admission control•For ON/OFF token rate = 64kbps; bucket depth=1Configuration Parameters•Single bottleneck link: 10 Mbps•Bottleneck buffer: 160 pkts•Packet length: 128 bytes•Heavy offered load (to force CAC and rejections)ON/OFF traffic experimentsComparing with Ideal CAC•Ideal CAC algorithm: maintain the “quota” of flows constant = N, where N is determined by target loss rate•Ideal CAC has prior knowledge of current # of flows•Measured Sum alg must “guess” N from load measurements; •Ideal CAC is open loop; it wins as it leads to lower load fluctuations•Measured Sum uses closed loop feedback control; it tend to overreact leading to higher oscillations and possible instabilityIdeal CAC (ie Quota) vs Measured SumTraffic source: ON/OFFIdeal CAC (ie Quota)Measured SumIdeal vs MS in Long Range Dependance•Long Range Dep source: ON/OFF interval Pareto distributed; flow lifetime lognormal•“Quota” does not work very well here: no notion of ideal quota valid all the time•Measured Sum, on the other hand, can track the flow fluctuations => lower loss rate!Quota vs Measured SumLong range dep sourcesCan we predict MBAC loss?•Network operators would like to predict loss to set operating point (eg, target utilization in the Measured Sum scheme)•Question: can we preselect the “control knobs” and expect results consistent with prediction?•Answer: not quite! Better to measure resulting loss rate and adjust knobs accordingly•Results in next slide are based on:–MC scheme: measure CAC – large dev estimate of existing flows + peak of new flow–TE (Traffic Envelope): measured max aggregate envelope of existing + peak of new flowConclusions•All MBAC schemes achieve identical loss-load performance (no matter the effort spent in developing sophisticated measurements)•Flow heterogeneity must be addressed by policy – aggregated measured based control is unfair•MBAC does better than Ideal “Quota” scheme in Long Range Dependency•Predictive “knobs” do not work well; need to monitor loss directly and use
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