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SUMMARY - 95th percentile calculation
From: Jo Rhett <jrhett () svcolo com>
Date: Mon, 27 Feb 2006 11:44:59 -0800


My thesis that I wanted to prove or disprove was that the market seems to
have standardized how they calculate 95th percentile.  Years ago if you
asked all your uplinks you'd get wildly different answers.  Averages or max
values over days, weeks or months.  Rarely would two answers jive.

But it appeared that most providers are now using 5 minute averages as the 
value input over a billing month for 95th% calculation.  Was this truly 
standard now?

The answer is yes.  All of our paid transit links use 5 minute averages, 
and all but one of the replies to my query here did too.

8 providers use 5 minute averages of 30 second counter checks as the base
value calculated over the billing month.

2 providers use 5 minute averages of 1 minute counter checks as the base
value calculated over the billing month.

8 providers use 5 minute implicit averages (a single counter check) as the 
base value calculated over the billing month.*

1 provider uses the maximum value found in 5 minutes of 1 minute counter 
checks for the 5 minute value, and calculates that over the billing month.

1 provider uses 5 minute implicit averages (a single counter check) but
calculates that over a fixed 30 day month. (I didn't ask what they did with
the extra days)

At first glance my tendancy would be to say that 20 answers is hardly
authoritative, but the 30 second counters (first listed) comprise 6 of the 
top US bit movers, and 2 of the largest bit pushers so I'm satisfied with 
the results for my purposes.

* One very large bit mover that I know uses 32 bit counters claimed to only
be checking every 5 minutes.  We're pushing enough to them to rotate that
counter in that interval, so I actually disbelieve this answer but I'm
reporting it as they said it.

-- 
Jo Rhett
senior geek
SVcolo : Silicon Valley Colocation


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