This paper looks at a mechanism related to Explicit Congestion Notification. It uses a single bit in the IP header to communicate the congestion at each hop in the path. Statistical estimators are used to work out the accuracy of the congestion estimation.
Monia Ghobadi, Soheil Hassas Yeganeh and Yashar Ganjali
The central suggestion is that centrally controlled SDN networks are
in a position to choose which version of TCP will work best. OpenTCP
tunes TCP for traffic and network conditions. Different TCP flavours
perform better at different times or in different conditions e.g.
datacentre TCP (DCTCP).