[e2e] end of interest

John Day day at std.com
Mon May 12 09:37:32 PDT 2008

>Nonetheless, I agree with John Day who pointed out much better than 
>I that perhaps the problem is not to legitimize layer "violations" 
>as good things, but to recognize that maybe the idea of ordered 
>layering was injected way beyond its usefulness into the rhetorical 
>framing of network protocol design, and now threatens clear thinking 
>about a whole range of important issues.

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.

It is peculiar that our response has been to do anything else just 
because there seems to be something wrong with our early idea of 
layer.  (As I said yesterday, the OSI concept of layer for the lower 
4 started out as a reflection of what people thought they were at the 
time.  The detailed definitions associated with it (which I doubt any 
of you are familiar with ;-) and I wish I weren't) are where it 
really goes wrong.  But that is pretty irrelevant to this discussion. 
I would have thought some smart guy would have said, 'let me show you 
dummies how to get it right!' ;-)

>The end-to-end argument paper attempted to discuss a rationale for 
>placement of functions in a modular architecture.
>That serves (imho) as a far better example of discussion of 
>architectural principles than the ISO OSI attempt at a 
>canon/scripture.   The ISO OSI model was introduced without a 
>discussion of tradeoffs (very much the content of the end-to-end 
>argument paper), as a fait accompli.

The problem with the OSI model was 1) very few have ever read it and 
2) the PTTs ensured that the what was written was not really what the 
problem was saying but more the economics they desired.

Constructing such models to develop a better understanding of what is 
going on is generally a good idea.  Letting them be affected by 
politics and business models is generally a bad idea.  The trouble 
was that there was one group who were sure that a different technical 
solution was required for what they saw as technical reasons. IMO, 
they were wrong.  OSI's major mistake was including the phone 
companies, but given the environment at the time it may have been 

>Rather than talk about "breaking with a religion" - perhaps it might 
>be better to talk about the elements of thoughtful design principles 
>The idea of a "connection" or "session" is very useful in some 
>contexts, but highly distorts the conversation on DTNs which leads 
>to odd circumlocutions like "connection *less*" networking.   Well, 
>if we hadn't canonized them, we wouldn't have them.  Books are a 
>form of communications, as are TV broadcasts.   Neither form of 
>communications ever called for connections as a concept.   So to 
>call them connectionless implies that they are somehow "exceptional" 
>or "troublesome".   But they are really only troublesome to people 
>so steeped in the canon that they assume "connections" are 
>first-order axioms of any theory of communications.

This is why I talk about locus of shared state:  distinct entities 
who "understand one another." Regardless of how much, or on what time 
frame.  I don't see a problem with DTNs in this view.  It sounds to 
me that a some people have a narrow view of "connection" just like 
some people in OSI did.  (I once greatly irritated a connection 
advocate when I pointed out that a circuit was just a very long 

>Algebra exists without unique multiplicative inverses.  Geometry 
>exists without the parallel postulate.  Communications exists 
>without layers - especially without "session layers" that presuppose 
>an artificial invention.

Indeed.  I often point out that good design is doing the algebra 
before the arithmetic.  And we seem to get stuck in the arithmetic a 
lot.  And we have known for more than a quarter century that there is 
no session layer.  Why are people still bringing it up?  ;-)

Take care,

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