[e2e] Latency Variation and Contention.

Joe Touch touch at ISI.EDU
Wed Aug 17 07:37:06 PDT 2005

Detlef Bosau wrote:
> Your comments are both, helpful and enlightning.
> Nevertheless, please, allow me to re-focus the discussion.
> The assertion made by ElRakbawy, Klemm and Lindemann is:
> Ass.1:   Network contention can be measured by measuring the RTT
> variance. A small variance is equivalent to a low degree of contention
> and a high variance is equivalent to a high degree of contention.
> Assertions like these can be met in literature several times and it´s
> simply the question whether this assertion is true or not.
> Personally, I am in great doubt at this.

As am I. Multipath routing can cause it, i.e. All you know when the RTT
is noisy is that the RTT is noisy, and then that anything that depends
on the RTT (e.g., the window size) is necessarily imprecise.

> It´s exactly what David P. Reed pointed out some weeks ago.
> Before building brittle constructs upon questionable assertions, it is
> important to have a solid _basis_.
> Here in Germany, we have a saying: "Das Fundament ist die Grundlage
> jeglicher Basis." I don´t know whether there exists an english
> equivalent, but this makes the very difference whether a space shuttle
> pilot coming home is busy with landing or busy with prayer.
> Detlef

Ours is "correlation != cause & effect". Gets at the same point, at the
end of the day.


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