[e2e] Just a very quick remark on system theory Re: Why don't we talk about segments/objects instaead of layers? Re: Lost Layer?

Detlef Bosau detlef.bosau at web.de
Wed Feb 19 00:56:27 PST 2014

And this is particularly true for engineers as they often don't see the
"real" system equations but only the Laplace transform.
(And from linear systems we know even the problem of hidden 
oscillations (is the term correct?) which are hidden by the calculus -
not in physical reality. However a VERY TOUGH!!!!    problem for a pure
end to end approach.)

(I don't know, whether this saying is really common in English but it
was common for our former chancellor Schroeder: "When the going gets
tough, the tough get going.)

Am 19.02.2014 09:36, schrieb Detlef Bosau:
> because I'm out and about to see my dentist. (very adequate for a
> networking guy: I will get a bridge.)
> We all remember Ethernet. (This funny network with the yellow garden hose.)
> And - jamming. Why was jamming necessary? Because of the systems step
> response function applied to the first bit of the preamble.
> And "Gibbs phenomenon".
> So a sending Ethernet card ignores excess voltage on the line for the
> first 40 (?) bit in order to ignore a "spurious collision".
> Unfortunately, system theory does not really apply here, otherwise we
> could eventually solve our energy problems because in the mathematical
> abstraction, some voltages and currents in step- or impulse responses
> grow beyond all limits.
> In the formulae.
> Actually, and luckily, some of the voltages and currents are restricted
> by the power supply.
> When you start with control theory on simple systems - and the literally
> station wagon hurtling down the highway (Tanenbaum) runs with ten times
> the speed of the light, you may perhaps discover, may, some people don't
> ever, understand that models are only an approximation to reality and
> perhaps some models are not always helpful.
> And with particular respect to networks: State variables in difference
> or differential equations are never bounded. In theory, they may grow
> beyond all limits. Both for power (infinite storage capacity in bridges,
> hopefully my mouth will be big enough in a few minutes because of the
> dimensions of my new bridge) and "kinetic energy" on links (this damned
> speed of the light, I will send a severe complaint to Albert afterwards).
> That was the long explanation.
> Executive summary for "control theory applied to computer networks":
>                                                               Forget it.

Detlef Bosau
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