[36760] in North American Network Operators' Group
Re: What does 95th %tile mean?
daemon@ATHENA.MIT.EDU (Geoff Huston)
Thu Apr 19 18:07:34 2001
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Date: Fri, 20 Apr 2001 08:03:02 +1000
To: nanog@merit.edu (North America Network Operators Group Mailing List)
From: Geoff Huston <gih@telstra.net>
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The 95% reading always struck me as a randomly generated number in any case.
Take an extreme example - a customer operates a wire such that both in and
out are at line rate for five minutes, and then both in and out are idle
for five minutes, continually.
Depending on the synchronization between the burst pattern and the sampling
system, and the sampling technique itself, the 95% reading can be zero,
half the line rate, or the line rate, and all answers are equally valid in
some sense.
While real situations do not exhibit such a large range of potential
variability (i.e. 100%), there is still a hefty level of variation in a 95%
reading due to the interactions between the time base of the traffic, the
time base of the meter engine and the sampling technique used by the meter
engine.
It leads to the situation where the provider confidently asserts that the
95% value was xkbps, and the customer confidently asserting ykbps and both
readings are equally valid, with both measurements using the _same_
measurement technique. How is the consequent billing dispute resolved _fairly_?
