Re: [tcpm] Re: Some feedback on draft-ietf-tcpm-rfc2581bis-01.txt

At 10:51 05/08/2006, Mark Allman wrote:

> > Page 8. The draft says:
> > "    6.  When the next ACK arrives that acknowledges new data, a TCP
> >          MUST set cwnd to ssthresh (the value set in step 1).  This is
> >          termed "deflating" the window.
> >
> >          This ACK should be the acknowledgment elicited by the
> >          retransmission from step 1, one RTT after the retransmission
> >          (though it may arrive sooner in the presence of significant out-
> >          of-order delivery of data segments at the
> >          receiver). "
> >
> > Can the ACK really arrive sooner than one RTT? Unless the RTT for
> > the connection decreases, I cannot see why this would happen.
>
>As noted, out-of-order delivery can make this happen ... i.e., the ACK
>*should* be trigged by the retransmission.  But, if there was just
>reordering and no loss then it might not be.  So, the ACK covering the
>retransmit could be triggered by the original transmission (and, so
>could arrive earlier than one RTT after the rexmt was sent).

This makes perfect sense, of course. However, it wasn't clear to me 
from the draft.

I'd probably change the corresponding paragraph to:

"This ACK should be the acknowledgement elicited by the 
retransmission from step 1, one RTT after the retransmission (though 
it may arrive sooner in case Fast Retransmit has been triggered by 
network packet reordering, rather than by a loss event)"

Kindest regards,

--
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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