[e2e] Open the floodgate

[David P. Reed]

At 03:06 AM 4/22/2004, Cannara wrote:
>What control theory does satisfaction with this
>state derive from?

It's odd that "control theory" might be implied to provide satisfaction 
with the state of network control.

Traditional control theory applied to networks requires that they have 
perfect communications reliability - that is, bits get through reliably and 
with bounded latency.

I don't know of any physical situation where that assumption can be made 
true, anymore than that other assumption of communications theory in the 
1970's refereed network theory papers: that network traffic was a random 
process, usually Poisson sometimes synchronous, that *did not respond* to 
network behavior (not "could not respond" but "did not respond").

Your precious theory is helpful, but what your language tells me is that 
you believe that the network design process should be one of developing 
analytic theories, and then *forcing the usage to match the assumptions 
which lead to a tractable theory*.

That's not engineering, even though it pretends to be.    It may give you 
satisfaction, because it lets you "prove systems correct".

A recent set of experiments on automobile control for intelligent 
transportation systems demonstrated that an architecture that delivered 
perfect information to the control loops holding cars in line, by using the 
best known reliable stream protocols, performed far worse on a reliability 
scale than a network that delivered corrupted measurements (random bit 
errors in position measurements) without correcting them.

This was done with the best possible "control theory" at the control level.

I don't mean to disparage theory - theory is enormously helpful in reaching 
an understanding, but it is far from a silver bullet.

In the case of the Internet's control problem, the actual problem - how to 
control a system that is not driven by random packet arrivals and random 
errors - is intractable, and the traditional control theory approach of 
forcing the system to obey simplified assumptions, is practically impossible.