Development of a New Efficient and Accurate Available Bandwidth

Estimation Method

Péter Hága

Attila Pásztor

István Csabai

Darryl Veitch

Viktória Hunyadi

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Outline

• Available bandwidth measurements, motivations• Definition of Available Bandwidth • Milestones in the evolution of AB measurement• Measurement Method, and results from simulation• Analytic Approximation• Estimation of AB• Laboratory Experiments • Conclusion and Future Plans

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Importance of available bandwidth measurements,motivations

The knowledge of available bandwidth along a route is important:• for call admission control• congestion control and avoidance• determine the instantaneous free transmission capacity

The motivations behind developing methods to estimate AB:• applications cloud use it to adopt their behaviour• avoid congested paths • determine the optimal transfer rate without losing packets

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Definition of Available Bandwidth

Available bandwidth of hop h, over the time interval T,T(roughly the difference of the link capacity and the average cross traffic)

Available bandwidth of a route is a smallest hop AB on a path:

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Milestones in the evolution of AB measurements problems, advantages

Pathload: binary search algorithm• invasiveness - high rate probing results burst of packet trains• time - iteration requests significant amount of time • non-stationary of cross traffic - binary search can results contradictory results

PathChirp: chirp based measurement• estimation from measured data is heuristic • fine timescale

New class of probing techniques: interaction class (between probes and CT)• not requiring a knowledge of the link bandwidths• not requiring a knowledge which link is a narrow link

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Our goal

improve a method to estimate AB, which:• based on theoretical model• can give us accurate estimations• with high frequency• develop a tool to make our accurate estimations in robust way• make this tool widely accessible for use it in smart applications (eg. transfer protocols)

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Measurement Method

Sending probes with increasing rate

(like pathChirp)

Measuring the one-way delay :as we reach the free capacity of a link the OWD increases sharply

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Measurement Method

Instead of measuring OWD we will measure the ratio of inter arrival time and the inter probe spacing (t*/t)to avoid problem comes from the unsynchronized clocks of the sender and receiver

tt, as LPR (we are below the AB) t*/t linear , as LPR available bandwidth (we above the AB)

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Measurement Method

t*/t is sensitive for the mean of the free capacity along a route, and also for the coefficient of variation () of the CT

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difficulties in real measurements:• fluctuations in the measured data (even in stationary CT)

averaging over some chirps• small number of probes not to cause serious congestion• sparsely spaced probes to cover the whole regions of the possible free capacity • sparsely spaced probes we need a function to fill out the space between two measured points

Measurement Method

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• f x, as probing rate x

• smooth and monotone increasing

• asymptotically linear for large x f xx

The function we are looking for:

The function has at least 3 parameters:

• two to fit the asymptotic slopes

• one to allow for the Cross Traffic dependent speed of transition

Analytic Approximation

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Analytic Approximation

The function is:

We can determine the parameters of best fit using the Levenberg-Marquardt Algorithm.

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Analytic Approximation

The fits were generally good both for Poisson and Weibullian-renweal cross traffic

(with different mean and coefficient of variation ())

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Estimation of Available Bandwidth

thxwhere f xintcloga)

Two algorithms to select the transition scale:

• threshold based: thxf xs (we used s

• intersection based (the intersection of the two asymptotes): int

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Comparing the performance of thandint

th: sensitive to mean,

but worsen as burstiness increases

int: also sensitive to burstiness,

Estimation of Available Bandwidth

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Laboratory Experiments

Validation: compare with the standard pathChirp toolin controlled environment

Network testbed:

Probe stream

Controlled CT

- Receiver tool - DAG monitor

- CT generator

- Sender tool

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Laboratory Experiments

estimations by pathChirp, and by the combinations of the intersection and threshold methods

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Conclusions and Future plans

• we have developed an improved method for available bandwidth estimation, resulting better estimations• first steps to work out the underlying theoretical model for evaluation of the measured data

In the future:• develop a complete measurement package• explore different strategies for sampling the investigated curve• find more robust alternative transition scale selection algorithms

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Thank you for your attention!