Re: [Planetlab-users] sysctl variables

[Andy B. <ac...@CS...>]

> From: Neil Spring <ns...@cs...>
> Subject: Re: [Planetlab-users] sysctl variables
> Date: Sat, 15 Nov 2003 14:42:02 -0800
> To: pla...@li...
>
>
> On Nov 14, 2003, at 6:12 AM, Larry Peterson wrote:
> > 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, (or anyone well-versed in the raw sockets code)
>
> As Manpreet's last mail suggests he's trying this approach, do you
> think a user-level TCP is sufficient to inflate buffer sizes?  I
> understand that keeping retransmissions in user memory removes the need
> for a send buffer, but I'm worried about the fake receive buffer.  If
> the raw socket kernel->application buffer is limited to the same size
> as the tcp buffer, then advertising a large receive window (now
> possible with the user-level TCP) without being able to provide it
> would lead to packet loss when the machine is busy, exactly what flow
> control is designed to avoid.

That's right, the size of the raw socket receive buffer is currently limited
by rmem_max as well.

Andy