A question of stats..

Daniel Senie dts at openroute.com
Sun Jun 8 15:52:56 UTC 1997


At 09:07 AM 6/8/97 -0400, Brian Horvitz wrote:
>Here is something which has been troubling my mind lately.
>The basic question is, how do I turn an in and an out into
>an aggregate?  Here is a scenario:  I measure usage on a
>customer's T1 at my router port.  Every 5 minutes a sample
>the port and figure the average bps both in and out for the
>last five minutes.  Now, I want to make a number that 
>represents the aggregate usage across that port but, I cannot
>simply add the two ins and outs (as I am doing now) because 
>they were both averages over a period of time.  Doing this
>produces some strange effects which can show nice trends but
>also lies about the real usage.  Perhaps I simply lack the
>math experience to do this correctly but I can't see a good
>way to do it.

If you're doing this for accounting (i.e. money collection) purposes, I see
a cause for customers to be very alarmed. I've seen a lot of attacks lately
that were ping floods or other such traffic, frequently originating from
RFC1918 addresses. I know if my upstream charged by the packet, I'd be all
over them to deduct from my bill EVERY packet I'm not interested in. Could
cause providers a lot of trouble.

Even charging for packets a site transmits is potentially at risk in such
cases, if the systems send back ICMP unreachables or other rejection packets.

Dan

>
>	Brian Horvitz
>	WebSecure, Inc.
>
>
>

Daniel Senie                           mailto:dts at openroute.com
Sr. Staff Engineer                     http://www.openroute.com/
OpenROUTE Networks, Inc.               (a wholly owned subsidiary of
Proteon, Inc.)



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