[e2e] Question about propagation and queuing delays

Detlef Bosau detlef.bosau at web.de
Mon Aug 22 15:39:28 PDT 2005

Christian Huitema wrote:
> One way to find out is to collect a large set of samples, and then look
> at the minimum value. As long as the route does not change, the
> propagation delay is the sum of the transmission times, which are
> supposed constant, and a set of positive random values. The minimum of a
> large sample is the sum of the transmission times and the minimum of the
> random values, which tends towards zero.

the minimum of the random values, which tends towards zero.....

Is there evidence for this?

I think, this is similar to the rationale given in the "Adaptive
Pacing..." paper, where delay variation indicates congestion:

If the random values represent e.g. queueing delays, why does the sum of
these tends towards zero? Why not to an average value?

If the sum would tend to zero, once again: we had a possibility to
calibrate a "congestion level = f(latency)" function then.

Of course, when you can observe networks in unloaded periods of time,
you may be right as long as you take samples for a long enough period,
sufficiently high sampling rate etc.

However, from my own experience with all this "congestion level =
f(latency)" magic, I became rather relcutant. It´s appealing at the
first glance - however 
it does not look promising at the second.


Detlef Bosau
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70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
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