On Wed, Aug 29, 2007 at 03:35:03PM -0700, David Miller wrote:

From: Rick Jones <redacted>
Date: Wed, 29 Aug 2007 15:29:03 -0700

quoted

David Miller wrote:

quoted

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.

quoted

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 [off-list ref] 46.46.272.1946