Re: [tcpm] early retransmit done?

["Ilpo Järvinen" <ilpo.jarvinen at helsinki.fi>]

On Fri, 13 Nov 2009, Mark Allman wrote:

> 
> > > I would be surprised if stacks retain an understanding of whether they
> > > transmitted a FIN with a data packet or without.  There isn't harm, per
> > > se, except for complexity (and perhaps a small bit of extra state).  
> > 
> > I don't perhaps fully follow what is the problem here. If it wasn't
> > sent separately, there won't be that dup ACK then either because both
> > FIN and final data are either lost or delivered in unison. But then it
> > would have been counted as one outstanding segment anyway (if it was
> > counted as two for some reason, I'd say the implementation is just
> > broken).
> > 
> > Secondly, if one counts window in segments, I cannot see how it can be
> > done robustly without knowing segment boundaries (after all, negative
> > in-flight isn't that nice thing) and there is very little need to
> > create exception for FIN but treat its boundary the same way. ...Plus
> > I suppose the implentation still wants to know that FIN was acked
> > :-). Once segment boundaries are known, it is insignificant in context
> > of early rexmit whether the last segment is pure-FIN or not..
> 
> I don't really follow this at all.
> 
> If you are tracking segments and include the implicit sequence number
> consumed by the FIN then this all just works, I guess.  Is that what
> you're saying?

Yes. ...And there's more, I also tried to say that one has to track that 
FIN sequence number anyway in order to be able to discern that the FIN was 
acked.

-- 
 i.