Re: make-before-break in Gmpls

[Yangguang Xu <xuyg@lucent.com>]

Curtis,

> The ingress would need to know if bandwidth was shareable when doing a
> reroute.  Otherwise, it may pick a path for which the RSVP signaling
> always fails for no apparent reason.  That the RSVP signaling would
> fail would not be apparent from the TE-LSDB before the signaling.
> Reroute by trial and error is not a good option.
> 
> Is there a way for the ingress to know on which "links" bandwidth is
> shareable?  Should it simply be assumed that bandwidth is not
> shareable on any TDM, LSC, and FSC links?
> 

You raised some good points here. For TDM, LSC and FSC, external resources
(link/port) can be in two states. If a internal cross connection is performed,
the associated external resource is committed and thus not sharable anymore.
Otherwise, it is sharable. So we can treat any non-committed resource as
sharable. The rest are not sharable.

Then the complication is when a non-committed resource gets committed, the rest
paths sharing the resource need to be re-arranged in order to guarantee the SLA
in case of double failures. How does FRR handle this?

Thanks,

Yangguang