On Wed, Aug 29, 2007 at 03:35:03PM -0700, David Miller wrote:
> From: Rick Jones <[EMAIL PROTECTED]>
> Date: Wed, 29 Aug 2007 15:29:03 -0700
>
> > David Miller wrote:
> > > None of the research folks want to commit to saying a lower value is
> > > OK, even though it's quite clear that on a local 10 gigabit link a
> > > minimum value of even 200 is absolutely and positively absurd.
> > >
> > > So what do these cellphone network people want to do, increate the
> > > minimum RTO or increase it? Exactly how does it help them?
> >
> > They want to increase it. The folks who triggered this want to make it
> > 3 seconds to avoid spurrious RTOs. Their experience the "other
> > platform" they widh to replace suggests that 3 seconds is a good value
> > for their network.
> >
> > > If the issue is wireless loss, algorithms like FRTO might help them,
> > > because FRTO tries to make a distinction between capacity losses
> > > (which should adjust cwnd) and radio losses (which are not capacity
> > > based and therefore should not affect cwnd).
> >
> > I was looking at that. FRTO seems only to affect the cwnd calculations,
> > and not the RTO calculation, so it seems to "deal with" spurrious RTOs
> > rather than preclude them. There is a strong desire here to not have
> > spurrious RTO's in the first place. Each spurrious retransmission will
> > increase a user's charges.
>
> All of this seems to suggest that the RTO calculation is wrong.
>
> It seems that packets in this network can be delayed several orders of
> magnitude longer than the usual round trip as measured by TCP.
>
> What exactly causes such a huge delay? What is the TCP measured RTO
> in these circumstances where spurious RTOs happen and a 3 second
> minimum RTO makes things better?
I don't know what they are doing, but it reminds me of what happens when
you run TCP over a reliable medium. You don't see loss, instead the
RTT starts to jitter alot.
IIRC FRTO does help avoid unnecessary retransmits (although the RTO still
hits).
Best regards
--
Programmer
Edgar E. Iglesias <[EMAIL PROTECTED]> 46.46.272.1946
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