Hi,
Note that this is a fairly well-known issue. The aim of local repair
has always been to quickly recover from the failure. The degree of
resources guarantees and optimality depends on the amount of resources
dedicated to backup, several assumptions with regards to potential
simultaneous failures, the algorithms used to pre-compute backup
tunnels, etc ... The approach taken by P2P FRR has been to first
locally reroute and trigger a head-end reoptimization using a make
before break. I do not think that you can draw any conclusion on the
potentially level of sub-optimality of performing local reroute as
opposed to global reoptimization. It depends on a number of factors.
JP.
On Dec 14, 2009, at 10:15 PM, Quintin Zhao wrote:
Hello PCE'rs,
I would like to follow-up on some discussions from our PCE WG
session last
month. Specifically regarding Dajiang's failure and recomputation
observations on our draft. We are very interested to hear comments
regarding
the need for computing secondary paths in the event of failure.
Currently
our thinking is to recompute the sub-tree based in the domain where
the
failure has occurred. In this case we would not need to perform a
recalculation of the entire tree. We could also recompute the entire
tree,
and avoid the failed areas, as long as the TED has the updated
topology.
Realistically one might have a backup core tree pre-computed so you
can
switch over in the event of failure. There are also other
considerations.
Would a partial recomputation provide a "worse" SPT or MCT tree, or
would a
full tree recomputation provide a "better" SPT or MCT? I can think of
scenarios for both a partial and full recomputation, so perhaps we
need to
implement both but allow the PCC to decide when to issue a partial
or full
recomputation based on some criterion.
Thanks,
Quintin
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