Tony, All the control systems I know of that allow rapid change of rate use mass (a known fixed quatity) as a major damping component. Same goes for knowing the amount of reactant at any time in chemical processes. I see no comparable function on packet switched networks, thus the hardness in creating fast stable control systems. Tell me what the knowns are for an ISP network and compare it to the knowns of an airplane (mass, moment, thrust, control surfaces, characteristics of air, ...) No wonder you can make a F18 turn faster than an ISP routing table. On the other hand, being wrong on an ISP routing table has lower cost than an out of control F18. How many of us are old enough to have taken an analog circuits class in college? They say build a circuit that has the following resonse, and it sounds so easy in class. Three or four hours of lab work later, the fact that even simple stuff is hard gets drilled in deeply. jerry