Re: [Planetlab-users] sysctl variables

[Larry P. <ll...@CS...>]

Neil is right that you currently have no way of adjusting the
TCP window sizes. The question is should you be able to.

I'd be interested in hearing what kind of bandwidth you're
getting now and what level you'd hope to get with a larger
window. At some point, you're going to hit a per-slice limit
simply because you're sharing the outgoing link with a bunch
of other users trying to do similar things. It seems unlikely
that we're going to be able to support applications that are
trying to achieve heroic TCP numbers in general.

In fact, as a generalization of this issue, some people would
like to run alternative versions of TCP that are tuned for
high-speed networks (e.g., FAST). One way of doing this, which
you do as well, is run a user-level version of TCP. Then you
can tweak it as much as you want. Of course, there's still going
to be a limit on how much shared bandwidth is available, but if
you selectively use nodes connected by fat pipes (e.g., the
Abilene nodes) you might be able to do what you want.

Larry


On Thursday, November 13, 2003, at 11:38 PM, Manpreet Singh wrote:

>
> Hello,
>
>    Sorry to bother everyone, but I am also new on planetlab. Am I 
> allowed
> to change some sysctl variables? I tried 'su' on some nodes, but that
> also does not permit me to do this.
>
>     In particular, I want to change the default send/receive window 
> sizes.
> I know that I can use setsockopt, but that is ultimately limited by the
> sysctl variables.
>
> Thanks and Regards,
> Manpreet Singh.
>
>
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