[Ecn-sane] rfc3168 sec 6.1.2

[Jonathan Morton]

> On 29 Aug, 2019, at 5:08 am, Dave Taht <dave.taht at gmail.com> wrote:
> 
> 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.

Nowadays the same effect can be obtained from the pacing timer.  Just set the CA scale factor to 50% to get an effective minimum cwnd of 1, or lower still if needed.

In most of our SCE testing, we're now setting the SS scale factor to 100% (the default is 200%, which means the cwnd is sent over half an RTT and the other half is idle) and the CA scale factor to 40% (default is 120%, so the effective minimum cwnd is actually 2.4 from a packet-pair standpoint).  See the last substantive slide in the IETF-105 SCE deck.

 - Jonathan Morton