Hi Greg
Whoa....
[Snip]
1) These virtual topologies are for control traffic and they are solid
most of the time.
2) The existing data traffic is not disrupted when the control traffic
has microloops.
3) There may be a delay in signaling of new or rerouted connections when
the control traffic has microloops. This is analogous to Graceful
recovery of the control plane where the data plane is momentarily unable
to adapt to new changes.
4) Many of the optical technologies we have do not need response to
signaling in less than 100s of milliseconds so the delay is not
critical.
5) We need a clear separation of protection which can be locally driven
and fast (50 msec) and routing and rerouting which are slower
restoration mechanisms. As long as protection mechanisms are independent
of the control plane primary protection is safe IMHO.
At the Routing working group, Alex's draft
draft-ietf-rtgwg-microloop-analysis-01.txt provides some
analysis and a method to reduce the impact (duration too) of
the transient loops. More recently the drafts:
(1) draft-bryant-shand-lf-applicability-01.txt
(2) draft-bryant-shand-lf-conv-frmwk-02.txt
(3) draft-francois-ordered-fib-01.txt
Address this problem more generally including in (3) a method
that guarantee loop free convergence.
Loop Free Alternates are a good thing. But with more advanced
mechanisms it is very hard to determine if the cure is worse than the
symptoms.
The problem is that these have generated very little interest
at the RTG WG and may not move forward. This area is not
within PCE or CCAMPs charter but can have an impact on the
adoption of GMPLS in multi-layer/region networking. If you're
interested please take a look and comment to the RTG WG.
Note I wasn't involved with writing these, but came across
them when considering the effects of GMPLS changes on the IP
layer VNT.
There was a lot of interest and a genuine amount of push back.
Personally I would be very concerned about tight coupling of a control
plane convergence to impacts on a GMPLS control data plane.
Regards,
Don
Thanks
Greg B.
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Dr Greg Bernstein, Grotto Networking (510) 573-2237