**GIT-CERCS-05-15**

Manish Jain, Constantinos Dovrolis,

**End-to-end Estimation of the Available Bandwidth Variation Range**

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The available bandwidth (avail-bw) of a network path
is an important performance metric and its end-to-end estimation
has recently received significant attention. Previous work
focused on the estimation of the average avail-bw,
ignoring the significant variability of this metric in different time scales.
In this paper, we show how to estimate a given percentile
of the avail-bw distribution at a user-specified time scale.
If two estimated percentiles cover the bulk of
the distribution (say 10% to 90%), the user can obtain
a practical estimate for the avail-bw variation range.
We present two estimation techniques.
The first is iterative and non-parametric, meaning that
it is more appropriate for very short time scales (typically less than 100ms),
or in bottlenecks with limited flow multiplexing (where
the avail-bw distribution may be non-Gaussian).
The second technique is parametric, because it assumes that the
avail-bw follows the Gaussian distribution, and it can
produce an estimate faster because it is not iterative.
The two techniques have been implemented in a measurement
tool called Pathvar. Pathvar can track the avail-bw
variation range within 10-20%, even under non-stationary conditions.
We identify four factors that play a crucial role
in the variation range of the avail-bw:
traffic load, number of competing flows, rate of competing
flows, and of course the measurement time scale.
Finally, we present a new way to detect whether a probing rate is larger
than the
avail-bw, without relying on the fluid traffic assumption or on static
thresholds.
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