Re: UDP Connection tuning questions regarding the -b and -l options

[Jim M. <jim...@ex...>]

Kevin Gibbs wrote:


> Actually you are quoting my post ever so slightly out of context.

Apologies for this, I was just pleased to find something that seemed to 
confirm what I saw.

> It is 
> true that there is no _programatical_ way to before hand compute the 
> amount of headers, i.e. Iperf will never be able to do it. However a 
> user (or more likely network admin) can "easily" compute this 
> information before hand. The caveat being if you are sending data over the 
> Internet in general then you will not be able to calculate it. If you know 
> exactly the path that every packet will take and what those network types 
> are then you can calculate the header size. For instance if I have 2 GigE 
> (or 10 or 100 Mb/s ethernet link) cards connected over a crossover cable 
> then I know that the headers (and footers) are ethernet, IP, UDP. Even if 
> I threw in a ethernet switch I would still get the same headers. However 
> if I connected two machines directly through a ATM link I would get a 
> different set of headers. Since Iperf can not detect these link types or 
> any along a multi-hop path it can not provide the functionality you are 
> looking for. You should be able to provide it yourself given you know your 
> setup.

This is what I thought, but my testing doesn't seem to prove the theory 
that I can calculate -b for a known network configuration. So either my 
logic/understanding is wrong or the server/network set-up cannot deliver 
the calculated throughput. I need to do some more work on this and will 
probably ask further questions if that is OK?

Jim Mozley