No, computation can be distributed on ABRs. This is basically the
scenario 4 of
draft-kompella-mpls-multiarea-te :
"The head-end LSR requests one of the ABRs in the head-end area to
compute a path to the destination. When the ABR in the head-end area
receives the request, the ABR requests one of the ABRs in the tail-
end area to compute paths to the destination from all/some of the
ABRs in the tail-end area. Once the ABR in the head-end area obtains
this information from the ABR in the tail-end area, the ABR in the
head-end area could compute the path through the head-end and the
backbone areas, concatenates the results of this computation with the
appropriate path through the tail-end area, and then return the
result to the head-end LSR."
Well, yes, that could be made to work. Pretty ugly tho (sorry Kireeti ;-).
Again, I'm happy to make the tradeoff of less work for less optimality.
If I'm that concerned about optimality, then I'll do offline computation
and static configuration. Or human intervention. I'm not interested in
spending the rest of my life debugging an incredibly complex solution that
gives me the last 0.0001% of optimality.