Re: What does 95th %tile mean?

[Simon Leinen <simon () limmat switch ch>]

> > > > > "ds" == David Schwartz <davids () webmaster com> writes:
>       Any billing scheme based upon statistical sampling will, with
> some probability, err in the favor of one party or the other
> randomly. But it is important that the customer understands that he
> is being billed based upon statistical sampling and thus there are
> no "exact" measurements.

For methods based on "classic" NetFlow I disagree, see below.

>       I've looked at other ways and can't find any better. Billing
> based upon NetFlow, for example, is still statistical sampling since
> NetFlow loses a percentage of flows. For example, one of my
> VIP2-50's says:

>   368351628 flows exported in 12278484 udp datagrams
>   33838 flows failed due to lack of export packet
>   269989 export packets were dropped enqueuing for the RP
>   108825 export packets were dropped due to IPC rate limiting

Yes, and in addition you may lose flows on the path between the
exporting router and the accounting postprocessor, or due to
resource shortage in the postprocessor.

However the way you handle this is that you don't bill for flows whose
accounting records you have lost, so you always err in favor of your
customer.  This gives you the right incentive to dimension your
accounting infrastructure so that loss is minimized.  As long as the
loss rate is in the ballpark you showed, the lost revenue probably
doesn't justify the effort (VIP upgrades) to fix this.

Of course your sampling problem occurs if the provider uses SAMPLED
NetFlow and multiplies the actually measured traffic rates with the
sampling interval.

Regards,
-- 
Simon.