Re: [6lo] draft-chairs-6lo-dispatch-iana-registry-00.txt

[james woodyatt <[e-mail]>]

On Jul 29, 2015, at 01:34, Robert Cragie <[e-mail]> wrote:
> 
> In an abstract sense, there is what I call a "hierarchy of constraints". By this I mean at lower ranks, more things are optional and superior ranks reclassify options into mandatory or excluded. At the top of the hierarchy, an interoperable implementation can be built where devices can autonomously figure out based on a configuration how they operate. In this case, the superior rank to the RFC rank simply states which dispatch codes are being used and which aren't.

I generally agree that a hierarchy of constraints is a good idea, but where I grow concerned is with protecting the integrity of the least constrained, most general specification. This is where the idea of a switch mechanism makes me uneasy. With a switch, which would permit the alteration of the syntax of 6LO encodings beneath it, we pretty much destroy the idea of a “most general” or “least constrained” syntax. Given any particular 6LO encoded packet it could mean anything depending on the context in which it is inserted, because any particular context might have a switch applied that alters the syntax of the encodings within it. Indeed, in the least constrained language, there is no limit on what switches defined in the future might do to alter the syntax.

I hope we can agree that it’s a bad idea to do that.

—james	[As an individual contributor]