A question of stats..

[Brian Horvitz <horvitz () websecure net>]

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.

        Brian Horvitz
        WebSecure, Inc.