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Re: questions on draft-bryant-ipfrr-tunnels-01.txt

Subject: Re: questions on draft-bryant-ipfrr-tunnels-01.txt
From: Curtis Villamizar
Date: Thu, 18 Nov 2004 12:10:10 -0500
In message <[email protected]>
Stewart Bryant writes:
>  
>  
> We also have concerns about the relative frequency of known SRLGs
> members vs unknown SRLG members. Clearly if the proportion of
> unknown SRLG members is significant, then the usefulness of SRLG
> aware repairs is questionable. We decided that we really needed
> some answer to this question before pursuing this additional
> complication to the solution.


If unknown SRLG is a problem and not supporting SRLG makes all SRLG
behave like unknown SRLG, then an approach which does not support SRLG
is more problematic than an approach which does support SRLG.  The
only case where the two are equal (approaches that do and don't
support SRLG) is where SRLG do not exist which we know is not the case
in any real network.

Therefore I think any argument opposing the support of SRLG due to the
possibility (or certainty) that unknown SRLG will exist is quite flawed.

For example, WDM introduces SRLG that have to be considered for a fast
restoration approach to be at all viable.  Logical links that traverse
hundreds of miles on the same fiber are going to have a high
percentage of correlated failure.

Curtis


ps - we not return you to our regularly scheduled arguments about why
SRLG are a hard problem for some approaches.

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