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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