The problem isn&#x27;t a lack of research, it&#x27;s lack of deployment. OS vendors aren&#x27;t turning on ECN and they largely aren&#x27;t enabling their new congestion control algorithms by default. Slow-start of some kind is still absolutely required, because with an initial window of 10 packets a single new connection can swamp a 5Mbit or slower link for 24ms or more, and that occurs far too often in the real world to ignore. Interactive usability is more important than shaving a few seconds off bulk downloads.<p>If ECN and fair queuing were generally supported on the internet at large, then senders would get quicker feedback about congestion and the negative side effects of overly-aggressive senders would be greatly reduced. Even without deployment of those throughout the network, delay based congestion control at the endpoints helps, if the sender turns it on.