[ 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 <gwoods@acm.org> <woods@robohack.ca> Planix, Inc. <woods@planix.com>; Secrets of the Weird <woods@weird.com>