Re: [Roll] [roll] #132: draft-ietf-roll-trickle-mcast-04 - Clarify scope value of 3 - subnet-local

[Richard Kelsey <[e-mail]>]

> Date: Tue, 15 Oct 2013 13:17:35 -0400
> From: Kerry Lynn <[e-mail]>
> 
> Link-local scope is essentially defined by a combination of link layer
> connectivity and routing behavior.  I believe we need something similar
> in order to automatically define scope 0x03.  To the extent that we need
> scope 0x03 at all, I think it's to emulate classic link-local behavior in a
> mesh.  There are only so many ways that meshes can be distinguished:
> either by location, frequency, or code diversity (assuming any two of
> three overlap).  In Ralph's example, he assumes location and frequency
> overlap.  In Michael's example, I suspect he assumes location and PAN
> ID overlap.
> 
> Finally, we may need to constrain Ralph's definition a bit further and
> define an 802.15.4  scope 0x03 zone as a set of interfaces that share
> a common PAN coordinator and PAN ID.
> 
> -K-

I think you have to fall back on routing behavior.  Consider a
mixed-PHY mesh, such as a a combination of 802.15.4 and PLC
links.  If the routing layer considers it all one mesh, then it
is, regardless of whether or not there are any 802.15.4 nodes in
direct communication using the same PAN ID.  On the other hand,
the routing layer could take the same physical setup and treat it
as distinct 802.15.4 meshes with PLC interconnects, in which case
you would get multiple 0x03 scopes.

  I shall not today attempt further to define 0x03 scope; and
  perhaps I could never succeed in intelligibly doing so. But I
  know it when I see it.
                         (paraphrasing Justice Potter Stewart)

-Richard
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