I am asking for a categorization of the control mechanism that TCP uses for flow and congestion control. Obviously, it is closed-loop but would that be discrete? Event-based? Continuous?
I would say it is event based. You send out some packets and then nothing happens until you either receive an ACK, a NACK, or a certain amount of time passes without receiving anything. Once one of those events occurs, then you take some actions (e.g. send out more packets or re-send dropped packets, possibly more or less packets than you sent out the first time).