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node disjoint and SRLG (was: questions on draft-bryant-ipfrr-tunnels-01.

Subject: node disjoint and SRLG was: questions on draft-bryant-ipfrr-tunnels-01.txt
From: Curtis Villamizar
Date: Mon, 22 Nov 2004 15:09:14 -0500
In message <[email protected]>
mike shand writes:
> At 12:39 22/11/2004 -0500, Alia Atlas wrote:
> >What can you get with a single primary repair?
> Some examples of the percentage of node repairs which require secondaries 
> below. This is calculated by taking the number of repairs for node repair 
> which require a secondary repair divided by the total number of repairs. 
> Where a repair is a repair to a single neighbor's neighbor.
> e.g.
>            V
>            |
> S---------E----U
>            |
>            T
> The repairs for node E failing would be
> etc.
> 0.79%
> 13.77%
> 3.98%
> 1.47%
> 0.50%
> 4.64%
> 0.00%
> (Note that the 13% one is a hub and spoke like network which gives only 
> about 70% coverage for U-turns (link repair; I haven't simulated U-turns 
> for node repair).  It is quite a nasty topology for any IPFRR mechanism)
>          Mike

So what you are saying seems to be that covering the node disjoint
problem is mostly not needed.  I think some providers would dispute
that (if providers ever did speak up in IETF and if one does please
disregard my speculation on what providers might say).

Also this does not address SRLG at all which was another part of this
thread.  Thats why I changed the subject line.  You could further
split that into node disjoint and SRLG since they are different
problems (though the node disjoint problem can be considered a proper
subset of SRLG).


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