TCP Ex Machina: Computer-Generated Congestion Control (2013)
web.mit.edu
web.mit.edu
The many iterations of TCP congestion control algorithms (Tahoe/Reno/NewReno/Vegas/BIC/CUBIC) all rely on pretty hard-and-fast rules for detecting congestion and anticipating certain failure conditions, but these are limited by our ability to parse patterns from complex emergent behavior and reduce those to rules that, at least on some level, "make sense".
This project, Remy, keeps track of three variables: - exponential-weighted moving average of interarrival time of acknowledgements - exponential-weighted moving average of time between sender timestamps - ratio between most recent round-trip-time (RTT) and the minimum RTT seen
From these three variables it generates an "action", which is really three parameters that are plugged into a simple rule to determine whether to send more packets. The three parameters are: - A multiple m of the current congestion window - An increment b (possibly negative) to the congestion window - A lower bound r > 0 on the time between sending segments
If the window isn't full, then the algorithm will send more packets, but not more frequently than r units of time. And Remy will occasionally update its action based on new data.
The key then is that Remy generates different actions for different input state variables, providing different behavior based on the observed state of the network in a way that's orders of magnitude more fine-grained than any human written algorithm. (I think these lookup tables are generated offline; not sure if they can be adjusted while running.)