Re: Linux TCP's Robustness to Multipath Packet Reordering

Alexander Zimmermann
2011-04-27T18:24:04Z

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Hi,

Am 27.04.2011 um 19:39 schrieb Yuchung Cheng:

> Hi Dominik,
>
> On Wed, Apr 27, 2011 at 9:22 AM, Dominik Kaspar <dokaspar.ietf@gmail.com> wrote:
>>
>> 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.
>> - Disabling SACK allows TCP to adapt very rapidly ("perfect" aggregation!).
>
> Did you enable tcp_fack when sack is enabled? this may make a (big)
> difference. FACK assumes little network reordering and mark packet
> losses more aggressively.

It's not necessary to do it manually. Linux will disable FACK as soon as it
will detected reordering

Alex

//
// Dipl.-Inform. Alexander Zimmermann
// Department of Computer Science, Informatik 4
// RWTH Aachen University
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