One special case to consider - your provider gets taken over, and the new owner regrooms the combined fiber networks, such that formerly physically diverse paths no longer are...
These are lessons many learned 7 years ago... No circuit is "set and forget", including so-called "protected" services. The way long distance and international capacity is swapped/bartered/remarketed reminds me of the complaints about the current credit-default swap market (with all of the opacity!) If you care about your reliability/survivability, you have to watch all of the motions that an acquisition/transition will have on your infrastructure [not just your future needs, but your current ones]. In BK's, we've seen plenty of fiber providers hand over entrance facilities that they had previously constructed to new entities and contract back for the capacity they need. So it *looks* like the provider X build out to your facility is completely diverse from provider Y, but they are no longer diverse [with little -> no internal to the facility change]. Be careful out there... Deepak Jain AiNET