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@openroute.com Sr. Staff Engineer http://www.openroute.com/ OpenROUTE Networks, Inc. (a wholly owned subsidiary of Proteon, Inc.)