Re: [tcpm] Some comments on 2581bis

Mark Allman wrote:
>> ** RFC 2581 & SACK
>> Page 3 says:
>>          Alternatively, a TCP that utilizes selective acknowledgments
>>          [RFC2018,RFC2883] can determine an incoming ACK is a "duplicate"
>>          if the ACK contains previously unknown SACK information.
>>
>> And page 7 says:
>> Note that a sender using SACK [RFC2018]
>>          MUST NOT send new data unless the incoming duplicate
>>          acknowledgment contains new SACK information.
>>
>> IMHO, if you keep the "MUST NOT" in page 7, you'd probably
>> s/can/MUST/ in page 3. Also, maybe it would be worth to clarify that
>> the SACK information should be "in window"?
> 
> Well, duplicate ACKs in 2581 are not always to send out new data.
> 
> That said, I am wondering if we should just nuke the sentence you quote
> above.  This document does not deal with SACK-based loss recovery and if
> you have SACK then you should be doing something smarter than this
> document.  And, so maybe we don't need to really define things about
> SACK-based loss recovery in here.  Certainly, I don't think we want to
> get into whether SACK blocks that this document doesn't use at all are
> in window or not.

The notion of the sender "using" SACK is a bit fuzzy anyway, since some 
stacks will send the options but not process them in any meaningful way 
(writing scoreboard code is hard).

   -John

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