[e2e] TCP ex Machina

[Fred Baker (fred)]

I'm not sure folks are really concerned about operating boundaries as much as outcomes. In general, and in specific in the words of Nandita Dukkipati and folks like her, I think folks would like to maximize throughput and minimize the wall clock time it takes to deliver an item of data. Most of our algorithms confuse that with maximizing the amount of data in the network at any given time; I'll argue that this maximizes both throughput and the probability of loss, which increases the amount of time it takes to deliver something. Stated in terms of operating boundaries, I think the optimal TCP-or-equivalent probably maximizes throughput while minimizing its effective window - it keeps just enough outstanding to maximize throughput, and as a result minimizes its own loss rate and the loss rates of sessions it interacts with. Literally doing that, as CalTech FAST does, runs the risk of being too gentlemanly, but CAIA CDG, which will detect when it is competing with a sub-optimal transport like CUBIC, will in effect switch to a loss-based algorithm under duress. But I think maximizing throughput while minimizing the probability of loss is probably the holy grail.