[Sis-csi] Green book thoughts

[Scott Burleigh]

Ed Criscuolo wrote:

> (I inadvertently replied this to Scott instead of
> posting it to the list this morning, so I'm resending
> it)
>
> I think we're mostly in violent agreement. The language
> semantics are just getting in the way.
>
> The network folks are counting from the bottom up: Whatever is
> three layers up from the physical is THE Transport layer.
> Anything above that, like CFDP, is application.
>
> The application folks are counting from the top down: Whatever
> is one layer down from the application is THE transport layer.
> In this view, CFDP is transport.
>
> Note that nothing has changed, were really just argueing over
> what to call it.

And here's my reply, which only went back to Ed:

Yeah, this is a problem we run up against again and again.  The idea 
that protocol layers have fixed names and numbers has been helpful for a 
long time, but I would say it doesn't accurately describe contemporary 
networking reality.  When you set up a Mobile IP tunnel, which layer of 
IP is at the "network layer"?  And what layer is the other one at?

Eventually I think we're going to have to come to terms with the idea 
that each protocol layer name serves two useful and orthogonal purposes: 
(a) it serves as a shorthand for the expected functional capabilities of 
protocols that claim to operate "at" that layer and (b) it connotes the 
functional relationships between protocols at that layer and those at 
the layers immediately above and below it.  Neither of those purposes 
requires that the name be pinned to a particular elevation from the 
bottom of the stack, nor that it occur only once in the stack.  
Protocols' "layer" designations are actually relative rather than 
absolute, exactly as you point out.

Which I think is an interesting topic, but not necessarily central to 
the main question we're trying to resolve here.

Scott