Re: Linux TCP's Robustness to Multipath Packet Reordering

Ilpo Järvinen
2011-06-21T11:25:22Z

On Wed, 27 Apr 2011, Alexander Zimmermann wrote:

> Hi,
>
> Am 27.04.2011 um 18:22 schrieb Dominik Kaspar:
>
> > Hi Carsten,
> >
> > Thanks for your feedback. I made some new tests with the same setup of
> > packet-based forwarding over two emulated paths (600 KB/s, 10 ms) +
> > (400 KB/s, 100 ms). In the first experiments, which showed a step-wise
> > adaptation to reordering, SACK, DSACK, and Timestamps were all
> > enabled. In the experiments, I individually disabled these three
> > mechanisms and saw the following:
> >
> > - Disabling timestamps causes TCP to never adjust to reordering at all.
>
> Reordering detection with DSACK is broken in Linux. We will fix that in
> a couple of weeks...
>
> > - Disabling SACK allows TCP to adapt very rapidly ("perfect" aggregation!).
>
> If you disable SACK, you will use the NewReno detection

Which probably has some reordering over-estimate bugs on its own...
(but I've forgotten details of my suspicion long time ago so please don't
ask for the them).

--
i.