[e2e] end of interest

Craig Partridge craig at aland.bbn.com
Tue Jun 10 14:21:02 PDT 2008

Finally getting to read a rich collection of postings at a time I
can think and had a quick comment:

In message <a06240829c44e1ba23724@[]>, John Day writes:

> ...
>I tend to think of this in terms of "loci" of shared state and their 
>scopes. (I use locus to indicate that the amount of shared state 
>could be small or large)  The problem with our early thinking on 
>layering whether OSI or not was confusing the layer as a  model of 
>distributed components with the implementation of such a thing.  (I 
>tend to be proponent of letting the problem tell me what is going on 
>rather me imposing what I think is going on. ;-)  It is less 
>Also, it seems that if networking is composed of "loci of shared 
>state with different scopes that we want to treat as black boxes" 
>then there seems to be something vaguely like a layer going on from 
>one perspective.  Given the problems we have had with layers this 
>would seem to imply that there is something about them that we aren't 
>getting right.  Something we aren't seeing.

Let me suggest that there is no "loci of shared state" -- or perhaps,
better said, the "shared state" is incomplete.

So, like many folks, I'm on a team playing with dynamic spectrum
access: briefly the idea is N nodes want to talk to each other, they figure
out what part of the spectrum is underutilized/available and meets their
needs and use that.   One challenge is that, to well and fully
understand what parts of the spectrum might feasible, each of the N
nodes could need to see a snapshot of the current spectrum from the
N-1 neighbors (for instance, frequency F may look clear of noise at
node 7 but see a tremendous level of noise [power] at node 19).
The snapshots can easily get quite large (read megabytes).
So you rapidly conclude that you can't send around complete information --
instead you send snippets -- and everyone's information about the
collective state is incomplete...

(I'll note in passing, there are ways to evade this problem but they
often end up with lots of exchanges of information -- so the radios
are chattering incessantly about what they will do rather than doing it.
In some ways, it is a question of RIP vs. SPF through a carnival looking

Anyway, so we find ourselves thinking hard about how well we can communicate
with incomplete information and what fallback schemes to use when
communication fails, not due to physics but confusion.



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