<SNIP>
I think it has been proven a few times that physical fate sharing is only a minor contributor to the total connectivity availability while system complexity mostly controlled by software written and operated by imperfect humans contribute a major share to end-to-end availability.
From this, it can be deduced that reducing unneccessary system complexity and shortening the strings of pearls that make up the system contribute to better availablity and resiliency of the system. Diversity works both ways in this equation. It lessens the probablity of same failure hitting majority of your boxes but at the same time increases the knowledge needed to understand and maintain the whole system.
I would vote for the KISS principle if in doubt.
Hi Pete This train of thought works well for only accidental failures, unfortunately if you have an adversary that is bent on disturbing communications and damaging the critical infrastructure of a country, physical faith sharing makes things less robust than they need to be. By the way, no disagreement from me on any of the points you make. Keeping it simple and robust is definitely a good first step. Having diverse paths in the fiber infrastructure is also necessary. Regards, Bora