Re: Max. MBit/sec ?

[János Löbb <janos.lobb () yale edu>]

Hi Martin,

I am collecting 540000 packets before I stop the capture.  That is about 3 minutes, or so.  The .ksh file on Aix 5.3 is 
this:

#!/bin/ksh
. $HOME/.profile
export DHSM=`date +%Y_%m_%d_%H`
tcpdump -c540000 -ien8 -w/tmp/tcpdump$DHSM.pcap host sequoia and not bml0028

the bml0028 machine is my Mac from where I ssh to the sequoia box.

The IO Graph has to do some calculation similar to (bits(t+dt)-bits(t))/dt  where t is a given time and dt is a chosen 
time interval to provide a meaningful result.  Of course I can awk the result and collect how many bits were 
transferred back and forth via the pipe in a given time interval - let say 1 second - and calculate the "velocity" of 
the bits at that particilar time of the capture, but IO Graph is already doing it, so I do not want to reinvent the 
wheel.

So the question is if I can tap into and get the Maximum bit rate for the duration of the capture.

Thanks a lot,

János


On Jun 3, 2010, at 9:40 AM, Martin Visser wrote:

> Maximum throughput is dependent on the sample time - if you change from 1 second to 0.1s to 0.01s you will notice 
> higher and higher peaks. 
>
> A 1Gbps ethernet pipe is clocked at 1000000000 bits per second so that is the maximum rate bits will go. But because 
> of the overhead from headers and encapsulation, enforced gaps between packets, the actual thorughput (and data 
> goodput) will be different.
>
>  The IO graph is based (I think) simply on the sum of frame lengths in the sample period you have chosen.
>  
> Regards, Martin
>
> MartinVisser99 () gmail com
>
>
> On Thu, Jun 3, 2010 at 11:29 PM, János Löbb <janos.lobb () yale edu> wrote:
> Hi,
>
> Under the Statistics menu there is the Summary menu item displaying the Avg. MBit/sec at the bottom.  Is there a way 
> to find the Maximum MBit/sec value somehow, or find a way to calculate it ?
>
> On a 1 Gbit/sec pipe I am getting 130M/bit/sec spikes when I look the I/O diagram of the capture.  I am trying to 
> find out if that pipe is capable for more or not taking into account the network subsystem configuration of the 
> machine.  How I/O Diagram is calculating it ?
>
> Thanks ahead,
>
> János
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