[e2e] EC++N

David P. Reed dpreed at reed.com
Wed Apr 3 19:08:43 PST 2002

At 11:53 AM 4/3/2002 -0500, J. Noel Chiappa wrote:
>I think a much better architecture is one that "nails up" a 'carrier' for a
>traffic aggregate along the entire path and then normally doesn't move it;
>new 'carriers' can be laid out and installed avoiding loaded elements. Such a
>design would be immune to load-induced oscillation. (There are still some
>second-order problems having to do with overall congestive collapse due to
>non-efficient use of resources when the network is a whole is highly loaded,
>but I'm going to gloss over them.)

I have two reactions to this.

1) What the heck is a "carrier" supposed to be?   Introducing an 
abstraction that has no correspondence to real application behavior or real 
underlying technologies makes little sense.  Unless you are trying to 
transform the problem into a problem that one already knows how to 
solve.   Since none of these is the case, you might as well be introducing 
an abstraction that behaves like a lawn chair, and managing resources as if 
they are patios full of lawn chairs.

2) SInce external loads do oscillate, it isn't oscillations per se that are 
the problem.   Problems like non-linear responses (e.g. the analogy of 
resonance in an excited system) are real problems.   But it's not 
oscillation you want to prevent - it's self-sustaining 
oscillation.   Damping is not to prevent oscillations from travelling 
through the network.   In fact if you prevent oscillatory input from going 
through the network, you are harming the system response (by introducing 
jitter/delay variance that isn't there in the input).

If you look at the flows at some Inter-AS point and they vary in an 
unstable way, you don't have enough information to say that that is a 
problem.   The problems are ones of system behavior, not local behavior.

There is a lot of evidence that flows driven by applications in general 
fluctuate on all time scales.  In fact, except when you saturate network 
capacity, computer-computer applications are designed to do exactly that.

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