[38291] in North American Network Operators' Group
Re: 95th Percentile again (was RE: C&W Peering Problem?)
daemon@ATHENA.MIT.EDU (Joe Abley)
Sat Jun 2 23:31:38 2001
Date: Sat, 2 Jun 2001 23:30:24 -0400
From: Joe Abley <jabley@automagic.org>
To: "Richard A. Steenbergen" <ras@e-gerbil.net>
Cc: Timothy Brown <tcb@ga.prestige.net>, nanog@merit.edu
Message-ID: <20010602233024.M21377@buddha.home.automagic.org>
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In-Reply-To: <Pine.BSF.4.21.0106022240580.29677-100000@overlord.e-gerbil.net>; from ras@e-gerbil.net on Sat, Jun 02, 2001 at 11:17:48PM -0400
Errors-To: owner-nanog-outgoing@merit.edu
On Sat, Jun 02, 2001 at 11:17:48PM -0400, Richard A. Steenbergen wrote:
> There are only two ways you can poll the rate, either you poll a "rate"
> value maintained on the device, or you poll a difference in bytes divide
> by the length of time between samples to calculate a rate. Either way, if
> the device does not support polling of the "interface" in question you are
> pretty screwed.
Not necessarily; you just have to find other ways of measuring, as we did,
to good effect.
> No matter how you stack it, if you miss a rate sample there is no way to
> go back and get the data again. You either discard it and lose the ability
> to bill the customer for it (which demands high availability polling
> systems), or you make up a number and hope the customer doesn't notice.
No -- there is no need to do that. You don't need a sample for every single
five-minute interval during the month to produce a meaningful 95%ile
measurement for the month; you just need a representative sample population.
You increase the chances of your sample population being representative
if you consider lots of samples, but dropping one or two does not mean
you lose revenue.
> Volume polling does not suffer from this problem.
It does, if you don't have per-customer interface counters. You need to
count every packet using some other method, and if you can't count packets,
you can't bill for them.
Joe
