That's showing the average utilization. Really average utilization is the only way to look at it. It just depends on how much time you average over. Max instantaneous utilization will always end up being 100%. Why? Because communications can only happen at wire speed. When packets get to a router, they can be staggered out over several layer 2 frames/cells, so that the utilization averages out to whatever is configured or bandwidth is shared among many conversations. But when a packet IS sent out, the only thing that can be done is to fill entire frames/cells. So during the time that it takes to play out a frame or cell the communication is taking 100% of the bandwidth. It might wait several frames or cells before sending another chunk of data, and average out at less than 100%. But during any particular INSTANT (0 time elapsed - e.g. 1 bit) the utilization will be either 100% or 0% - a bit either contains valid data or it does not. Does that make sense?
I would suggest that MRTG (www.mrtg.org) might be a better tool for measuring utilization - it's pretty much designed to graph this type of info and is lighter weight if you're not worried about what's actually being sent in the packets. Chris -----Original Message----- Date: Tue, 13 Jul 2004 09:45:56 -0700 From: "John Atkinson" <[EMAIL PROTECTED]> Subject: [Ntop] Measuring Peak Bandwidth Use To: <[EMAIL PROTECTED]> Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset="us-ascii" Hi, there. My goal is to measure the peak bandwidth utilization of our T1 line, to learn whether are needs are low enough to be serviced by a fractional T1. I'm new to ntop. I purchased and registered the pre-built Windows installation package ( from http://www.snark.it/ntop/cart.php) and installed it on a Windows 2000 Pro system. I placed a simple 10/100 hub between my firewall and my T1 router, and connected the Win2K computer to that hub, alongside the firewall. I believe this lash-up will expose all the Internet traffic we send and receive to ntop. Right? I played around with the start-up parameters, to try to make ntop's job easy, given that it's running on an old Pentium 2 system with only 128MB of RAM. I used these start-up parameters: ntop /c -z -b -n I've been running ntop for a few days, and watching it from another computer. I focus mainly on the Network Load Statistics graph under Summary > Network Load. I notice the graph plots a data point every 120 seconds. My question is this: Does the plotted data point represent the largest instantaneous bandwidth utilization seen during the 120 seconds, or does it represent the average bandwidth over the 120 seconds, as in TwoMinuteTotalTrafficBitCount/120 ? If it's the former, great! It's what I need. If it's the latter, can you suggest how I might obtain a measurement of the highest instantaneous bandwidth utilization we experience? Am I even using the proper tool for this job? fyi, my router is a Cisco 1700, and is owned and managed by our T1 provider, XO. Thanks! John Atkinson _______________________________________________ Ntop mailing list [EMAIL PROTECTED] http://listgateway.unipi.it/mailman/listinfo/ntop
