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RE: What does 95th %tile mean?

  • From: Greg A. Woods
  • Date: Thu Apr 19 22:26:17 2001

[ On Friday, April 20, 2001 at 10:30:19 (+1000), Geoff Huston wrote: ]
> Subject: RE: What does 95th %tile mean?
>
> In general (minus 'paid bandwidth' and taking the view that all bytes 
> passed between the customer and the provider have the same billable value) 
> byte transferred systems are more reliable if you take as your yardstick of 
> 'reliability' that the same algorithm applied to the same raw data should 
> yield the same result. As long as both parties can agree (precisely) when 
> the measurement interval starts and stops, of course.

For almost any value of N < 100, there is absolutely no synchronisation
of sampling periods required when calculating an Nth percentile
bandwidth usage, at least not with "normal" Internet usage.

For many users even if N==100 you can still get a reasonably fair
measure of peak usage by ignoring any rate which matches the maximum
line rate (obviously this fails if the user does actually have a 90th
percentile, or so, usage equal to the line rate).  Nth percentile
metering is simply a statistically fair way to find an agreeable peak
rate usage that is not the maximum line rate.

My guess is that the shorter the counter sample period the closer the
customer will want the value of N to approach 90 (or even less! :-).

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <[email protected]>     <[email protected]>
Planix, Inc. <[email protected]>;   Secrets of the Weird <[email protected]>