[e2e] Are our models correct? Re: 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
Fri Feb 21 04:17:14 PST 2014

In addition: The Laplace transform is not the problem. The problem is
that the models are inadequate, no matter whether they are stated in
differential equations (where particularly state variables are
unbounded, hence packets may travel with tenfold the speed of the light
or buffers must keep 1000 terabytes of data) or whether the same system
is written in "frequency space".

I know dozens of paper which pursue a control theoretic approach to
Internet congestion control - I did not yet see even a single one which
correctly modelled congestion drop. Most of the work even did not model
the sliding window mechanism but was rate based.

This is always funny as a game with numbers.

But it does not describe the real world!

E.g,, I'm actually sitting here in front of my PC and in a few seconds,
I'm going to have finished this post and will click the "send" button in
my MUA. As we all can imagine, my MUA will establish a TCP connection to
my ISP's Remailer then and submit my mail for delivery.

This TCP connection is most likely (I did not yet verify this in the
Ubuntu kernel code) to be credit driven and not rate driven.
And the relationship between credits/windows on the one hand and rates
on the other is anything but trivial.

I can't help it but I cannot split my brain and think about reality with
the one half and about models with the other one.

I don't want to bother anyone. But I think it is allowed to point out
differences between the real world and models. Particularly as those
differences are not rare in computer networking. 

Detlef Bosau
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