Re: [tcpm] Review: draft-ietf-tcpm-early-rexmt-01

[Joe Touch <touch at ISI.EDU>]

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Works for me.

Joe

Alexander Zimmermann wrote:
> Hi Joe, hi Mark,
> 
> may be we can reuse a paragraph from RFC 3517:
> 
> "We define a variable "DupThresh" that holds the number of duplicate
> acknowledgments required to trigger a retransmission. Per [RFC2581] this
> threshold is defined to be 3 duplicate acknowledgments. However,
> implementers should consult any updates to [RFC2581] to determine the
> current value for DupThresh (or method for determining its value)."
> 
> First, it's easier to see where the magic *4* comes from, second it's 
> future-proof when "5681bis" alters the number of duplicate Acks required
> for fast retransmit. :-)
> 
> Alex
> 
> Am 23.09.2009 um 16:28 schrieb Joe Touch:
> 
>> ...
>>>> In 2.1, do you want to define this in terms a fixed value of 4*SMSS,
>>>> or define it as a pointer (i.e., to the initial CWND, so if init CWND
>>>> increases, so does this?) same for the part about packet-based (again,
>>>> would that be segment-based?) not referring to 4, but the number of
>>>> segments in the initial CWND (e.g., as "currently 4" -- PS, should
>>>> that be 4, or shouldn't it be "initial_CWND/SMSS", i.e., a max of 4,
>>>> but in most current cases it seems like this would still be 3).
>>>
>>> No, I don't.  This doesn't have anything to do with the initial
>>> congestion window size.  The "4"---which I thought was well motivated,
>>> perhaps not---comes from fast retransmit's magic constant of "3".  I.e.,
>>> if there are at least 4 segments outstanding and we lose one then we'll
>>> have a shot at getting 3 dupacks.  If there are fewer segments
>>> outstanding then we will have no chance at getting 3 dupacks.  So, this
>>> has nothing to do with the initial window.
>>
>> I didn't get that as clearly. It might be useful to reiterate it when
>> the number is introduced (maybe a few times for people like me who
>> miss it).
> 
> //
> // Dipl.-Inform. Alexander Zimmermann
> // Department of Computer Science, Informatik 4
> // RWTH Aachen University
> // Ahornstr. 55, 52056 Aachen, Germany
> // phone: (49-241) 80-21422, fax: (49-241) 80-22220
> // email: zimmermann at cs.rwth-aachen.de
> // web: http://www.umic-mesh.net
> //
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