[Ecn-sane] rfc3168 sec 6.1.2

[Dave Taht <dave.taht@gmail.com>]

It would explain a lot if this was not actually implemented in Linux.
I'm afraid to look. cwnd reduction is capped to 2. 1 should put you
in quickack mode AND to go lower seemingly it's supposed to
then rely on the retransmit timer.

...

If the congestion window consists of only one MSS (maximum
   segment size), and the sending TCP receives an ECN-Echo ACK packet,
   then the sending TCP should in principle still reduce its congestion
   window in half. However, the value of the congestion window is
   bounded below by a value of one MSS.  If the sending TCP were to
   continue to send, using a congestion window of 1 MSS, this results in
   the transmission of one packet per round-trip time.  It is necessary
   to still reduce the sending rate of the TCP sender even further, on
   receipt of an ECN-Echo packet when the congestion window is one.

^^^^^^^^^^^^^^^^^^^^^^^^
We
   use the retransmit timer as a means of reducing the rate further in
   this circumstance.  Therefore, the sending TCP MUST reset the

^^^^^^^^^^^^^^^^^^^^^^^^
   retransmit timer on receiving the ECN-Echo packet when the congestion
   window is one.  The sending TCP will then be able to send a new
   packet only when the retransmit timer expires.


-- 

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-205-9740