[e2e] fast restoration/protection

[Craig Partridge]

In message <449178BE.2020403 at info.ucl.ac.be>, Olivier Bonaventure writes:

>Yes, but this approach of precomputing FIBs has a few drawbacks :
>- you may need to compute a lot of different FIB to cover all possible
>failures in the network
>- updating a FIB is not necessary fast on current routers. For example,
>on a Cisco 12k, updating a FIB requries about 110 microsecond per prefix
>http://citeseer.ist.psu.edu/francois05achieving.html

Sounds like two good research problems.

In fact, one solution to the second problem is known -- have two FIB
memories -- one active, one backup -- and make it possible to switch.
We showed how to do that about ten years ago in the MultiGigabit Router
project (the major nuisance was invalidating the NP caches).

As for the first -- do we know or have we thought of ways to determine
which FIBs it would be useful to have?  I.e., don't solve all possible
failures -- pick the best subset of FIBS given a limit on the number of
FIBS (say 5) and current statistics on link outages.  There's also a clear
metric for goodness -- namely, take the list of outages, weighted by
their likelihood, and see what fraction of [weighted] outages are covered
by the set of alternate FIBS.  Obviously a metric of 1.0 is desired, but
I'll bet any metric over, say, 0.6 has an impact.

Craig