Subject: Re: issue with cost-based formulation of extended P-space in draft-ietf-rtgwg-remote-lfa-02

From: Levente Csikor <[email-masked]>
Date: Thu, 01 Aug 2013 09:51:38 +0200

Dear Chris,

you have right that the draft's conditionof ext-P-space in cost terms is 
incorrect and not well-specified.

I foundthat (2)is exactly the same that we found and described in our 
related papers (check previous mails in the rlfa-rtgwg thread). However, 
(1)is actually the condition of the simple P-space in costterms.

If you are interested, how these conditions regarding to costterms 
change if node-protection is also taken into account, just read our last 
paper (http://csikor.tmit.bme.hu/remoteLFA/remote_lfa_telsys.pdf).

Regards,
Levente

On 07/30/2013 02:08 PM, Chris Bowers wrote:
> It appears that the cost-based formulation for determining the 
> extended P-space in draft-ietf-rtgwg-remote-lfa-02 is incorrect.  In 
> particular, section 4.2.2 says:
> “In cost terms a router is in extended P-space if the shortest path 
> cost S-N->P is strictly less than the shortest path cost S-E->P.”
> Instead, the requirement should be that the shortest path cost N->P is 
> strictly less than cost N-S-E->P.
> I propose the following text for section 4.2.2.
> “In terms of cost, a router Y is in the extended P-space of S with 
> respect to the failure of link S-E, if either of the two following 
> conditions is true:
> (1) D_opt(S,Y) < D_opt(S,E) + D_opt(E,Y)
> OR
> (2) S has a neighbor N satisfying the inequality:
> D_opt(N,Y) < D_opt(N,S) + D_opt(S,E) + D_opt(E,Y)”
> This text corrects the error noted above, and it puts both of the 
> criteria for determining extended P-space in terms of cost in one 
> place in the text.
> Chris
>
>
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