On Fri, 20 Aug 2004, Patrick W Gilmore wrote: : On Aug 20, 2004, at 5:06 PM, Drew Weaver wrote: : : > ����������� Does anyone know of a solution that offers precise methods : > of tracking bandwidth utilizations at the per Megabyte or Gigabyte : > level and not at the rate of transfer level? : : I don't know of any equipment that does NOT measure per-byte : transferred. The Mbps is done by taking the bytes transferred : (multiply by 8) and divide by the time involved, usually 5 minute : periods. I just want to point out that this is not a strict average over 5 minutes in the case of cisco's output for the "show interface" bits per second. It's an exponentially weighted average: http://cisco.com/en/US/products/sw/iosswrel/ps1818/products_tech_note09186a0... Bits per second include all packet/frame overhead. It does not include stuffed zeros. The size of each frame is added to the total bytes of output. The rate is calculated by taking the difference every 5 seconds. The algorithm for the five-minute moving average is: new average = ((average - interval) * exp (-t/C)) + interval where: - t is five seconds and C is 5 minutes. exp(-5/(60*5)) == .983 - newaverage = the value we are trying to compute - average = the "newaverage" value calculated from the previous sample - interval = the value of the current sample - (.983) is the weighting factor What you are basically doing is taking the average from the last sample less what we gathered in this sample and weighting that down by a decay factor. This quantity can be referred to as an "historical average". To the weighted (decayed) historical average, we add our current sample and come up with a new weighted (decayed) average. scott