Re: cannot fill 100Mbps pipe (over 20ms rtt via netem)?

From: Bill Fink
Date: Thu May 01 2008 - 01:10:13 EST


On Wed, 30 Apr 2008, John Heffner wrote:

> On Wed, Apr 30, 2008 at 5:13 PM, slashdev <slashdev@xxxxxxxxx> wrote:
> >
> > On Wed, Apr 30, 2008 at 4:34 PM, John Heffner <johnwheffner@xxxxxxxxx> wrote:
> >
> > > On Wed, Apr 30, 2008 at 2:45 PM, slashdev <slashdev@xxxxxxxxx> wrote:
> > > > i can provide the tcpdump trace. but that too looks ok. i.e. window
> > > > scale is set to
> > > > healthy "10" and the receiver does endup opening large window. but i
> > > > may be missing
> > > > something.
> > > >
> > > > if you need any other information please do ask.
> > > >
> > > > i am bit puzzled at the moment :-)
> > >
> > > Linux should easily be able to support this "out of the box" these
> > > days. Can you post the binary tcpdump somewhere?
> >
> > http://slashdev.googlepages.com/traces/
> >
> > i've added traces for 20ms rtt and normal lan rtt (aka 0ms rtt :-)
> > let me know if you have trouble accessing them or want any more
> > information.
> >
> > thanks for your help
>
> Both traces show lots of packet loss -- enough to cause an equilibrium
> cwnd of less than 100 KB. With a short RTT, this window is adequate
> to fill a 100 Mbps pipe, but with even a 20 ms RTT, it's hurting you.
> I'm not sure where the packet loss is coming from. Possibly an
> overloaded switch or bad cable?

John,

I was curious what tool/method you used to analyze the packet traces.

-Bill
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