How to game the system (was Re: What does 95th %tile mean?)

Fri Apr 20 03:46:18 UTC 2001

[ On , April 19, 2001 at 19:12:31 (-0700), Sean Donelan wrote: ]
> Subject: How to game the system (was Re: What does 95th %tile mean?)
>
> By knowing your provider's measurement windows, you could cut your
> usage bill in half while transfering the same amount of data.

Hmmm, but is that any different than rate limiting your own connection?

If you know the provider's sample window is every five minutes and you
only leave your interface up for 2.5 minutes out of every five, then yes
you'll be able to move data at line rate 50% of the time and only be
billed as if you were running at 50% of line rate.  So!?!?!?!?  You gain
what, exactly?

>From the provider's perspective this doesn't really matter a whole lot
and they can reduce the effect of your bursts on their other customers
by simply narrowing their window.  There's no need to do silly sliding
windows, multiple windows, etc. -- the averages are just fine.

> A customer with a relatively random usage (user's surfing the
> web) couldn't do this, but a user transfering batch files on a
> set schedule may see dramatic differences in their bill.

If the user doesn't want to pay for line rate for big batch transfers
then there are a lot better ways to rate-limit their usage in those
cases than to turn their router interfaces on and off at 50% the ISP's
rate sampling window.  One way or another though the user has to move N
bytes in T seconds and whether they move it in short bursts or at a
constant average rate half the speed of the bursts is irrelevant.

Either way the ISP doesn't care -- the user pays for the average peak
*bandwidth* over a given sample time that they're actually using!

BTW, with the price of disks these days it's not too difficult for any
ISP to use even a 5-second sample period.  That's just over 0.5 million
samples per customer per month, and in a well packed data file that's
just 6MB per customer per month even if you keep a timestamp and both
the in and out Counter32 values!  Spread the data out a bit with field
separators and you're still only looking at less than 7MB/customer/month
in the worst of cases.  Tell me again how the customer's going to beat
the system and get more value than I bill him for?  Not only that but
it's now enough of a bother that the customer probably won't bother
trying to collect his own samples and match my calculations!  :-)

-- 
							Greg A. Woods

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