Re: [tcpm] Comments on draft-blanton-tcpm-3517bis-01

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Am 14.04.2011 um 11:21 schrieb Markku Kojo:

> On Wed, 13 Apr 2011, Yuchung Cheng wrote:
> 
>> On Wed, Apr 13, 2011 at 5:17 PM, Ethan Blanton <eblanton@cs.ohiou.edu> wrote:
>>> Yuchung Cheng spake unto us the following wisdom:
>>>> Thanks for the clarification. My example assumes SMSS=1460 (sorry for
>>>> not being clear).
>>>> 
>>>> AFAIK, Linux (even with fack disabled) triggers the fast-recovery when
>>>> any 3 packets (of any size) are sacked beyond SND.UNA.
>>> 
>>> And this is correct behavior, and what 3517/3517bis will both do.
>>> 
>> Ah that's right. The subtle difference is that Linux IsLost(sn)
>> returns true if any 3 segments beyond sn are sacked, i.e., the seq# of
>> these segments need not be discontinuous. Therefore the loss marking
>> is more aggressive after F-R starts (even with FACK disabled).
> 
> Right. The difference is that the Linux TCP sender tracks segment 
> boundaries and is therefore able to determine that 3 small segments 
> have made it to the receiver even though these segments are continuous.
> 
> As Ethan noted the draft is written such that it does not require
> a TCP sender to keep track of segment boundaries after a segment
> has been transmitted (Note in Section 3).

AFAIK you and Ilpo pointed out in your draft that in a case of a
segment-based stack the dupthresh counter is not necessary anymore and
we can handle everything with IsLost(). So, I recommend that this should
be included in 3517bis (as a big side note or in an appendix section)

Alex

> 
> /Markku
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//
// Dipl.-Inform. Alexander Zimmermann
// Department of Computer Science, Informatik 4
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