Hello!

problem.  The problem is really at the receiver because we only
ACK every other full sized frame.  I had the idea to ACK every 2
frames, regardless of size,

This would solve lots of problems.

		 but that might have other problems.

BSD used to do this, everyone is happy.

It could disclose some new problems in our stack, because we have
quite a lot of code to mitigate problems caused by ACK each 2*MSS.
But they should not be essential. Actually, we could have it adjustable:
normally each 2 frames, but apply efforts to coarsen ACKs up to 2*MSS,
when lots of small frames are ACKed back to back.

There is an assymetry between how we do congestion control on
sending (packet counting) and our ACK policy on receive (packet
sized based).

It is curious fact: BSD has exactly opposite assymetry.
ACK are sent each second packet, but congestion avoidance is made by size. :-)

turn it off by default.

Yes.

Alexey