There is no clear consensus concerning which of the facilities are "NAPs",
let alone which ones an ISP should participate in to be considered a
credible National/Backbone provider. For instance, while MAE-West was not
one of the original NAPs established by NSF, it clearly qualifies in all
other respects. On the other hand, I don't think it would be considered
necessary to be at LA, Phoenix, Tucson, Dallas, etc right now to be
considered a National/Backbone provider.
Oh, I fully agree.
The criteria I've heard most frequently is "connected to three of the
NAPs, peering with at least 2 national providers at each of those NAPs".
I believe this is what MCI requires in order to establish peering with a
Mumble. Presumably, not every national provider will require peering
with at least two others before agreeing to peer... the possibilities for
deadlock seem a tad high.