Re: bandwidth option ( -b ) in udp
Kevin,
We are using Iperf to test Ethernet switch based products in
manufacturing. We are basically sending packets through a switch between 2
PC's. We were experiencing packet loss when sending traffic into a GBE
port and out a FE port on the switch. This was due to using "-b 100M" on
the client (GBE), resulting in a bit rate of faster then 100Mbit including
the overhead of the packets, which got much worse at smaller packet sizes.
If too much data was transmitted switch buffers would overflow and packets
would get lost. Now realizing that the -b option does not include headers,
the -b option can be tuned to get close to the desired line rate.
The idea is a line rate option would cause iperf to try to consider
the size of headers and try to approximate (with a knowledge of the size of
IP headers, UDP headers, checksum, etc) an average line rate rather than a
data rate, for applications that would benefit from this. For our
application we would then not need to worry about overflowing buffers and
getting unexpected packet loss.
This could all be done by in an application that calls iperf, but it
would be nice if iperf could take care of this.
thanks,
Steve
Kevin Gibbs
<kgibbs --at-- ncsa.uiuc To: Steve.Brenne --at-- radisys.com
.edu> cc: iperf-users --at-- dast.nlanr.net
Subject: Re: bandwidth option ( -b ) in udp
01/23/2003 01:14
PM
On Wed, 22 Jan 2003 Steve.Brenne --at-- radisys.com wrote:
> Is the bandwidth option in udp intended to represent the actual bit rate
on
> the line, or is it intended to only measure the rate of data transfer?
> Would there be any value in an option that allows for the bandwidth to
> represent either data rate or line rate. For my application I only care
> about the line rate not about the data transfer rate.
>
I am not exactly sure what you are getting at here. The -b option
specifies at what speed the client sends data to the server. As such I
believe you would call that data rate. There is no way to measure the
exact line rate. The best you can do is determine the highest data rate
which will be close to the line rate. For example we have had TCP tests
get 9.97 Mb/s on a 10Mb/s link so the 9.97 is approximately (and more
importantly it is effectively) the line rate. I am not sure what you think
iperf would do differently with a line rate option vs a data rate option.
If you want to use UDP to determine line rate then send larger amounts of
data than the line rate and look at the results seen by the server.
Kevin