On 26/06/2013 14:13, Levente Csikor wrote:
Levente
In each case below the conditions are surely fulfilled if n=e
thus I think that in each case the condition needs to be
changed to :
some node n!={s or e}
In order to not to read our full papers and searching the answers, I
copied here the relevant parts:
*Link-protecting rLFA condition:*
For source /s/, destination /d/, and next-hop /e/, some node /n/ /!=
s,d/ is a link-protecting remote LFA for the /s-d/ pair if and only if
/dist(s, n) < dist(s, e) + dist(e, n)/ (1)
/dist(n, d) < dist(n, s) + dist(s, d)/ (2)
In these equations, one can easily see, that (1) defines the P-space,
while (2) is the condition of Q-space. Furthermore, with these
formalized conditions, one can easily observe, that (2) is actually
the basic loop-free criterion of pure LFA.
*Link-protecting rLFA condition with extended P-space:*
For source /s/, destination /d/, and next-hop /e/, some node /n !=
s,d/ is an extended link-protecting remote LFA for the /s-d/ pair if
and only if
/?v ? neigh(s) : dist(v, n) < dist(v, s) + dist(s, e) + dist(e, n)///
/dist(n, d) < dist(n, s) + dist(s, d) . /
*Node-protecting rLFA condition:*
For source /s/, destination /d/, and next-hop /e/, some /n != s,d/ is
a node-protecting remote LFA for the /s-d/ pair if and only if
/dist(s,n) < dist(s,e) + dist(e,n)/// (3)
/dist(n,d) < dist(n,e) + dist(e,d) / (4)
As it was in the case of link protection, here, (3) defines the
P-space, while (4) characterize the Q-space.
Here, two important observations can be made, which are the followings:
- P-space does not depend on the protection scheme (i.e., link or
node protection)
SB> That falls directly out of the definition of P-space
SB> since in link you cannot traverse the link to e and in
SB> node only get to e if you traverse the link to e
SB> thus the exclusion of the link to e applies in both cases
- (4) again is the basic node-protecting loop-free criterion of pure LFA.
*Node-protecting rLFA condition with extended P-space:*
For source /s/, destination /d/, and next-hop /e/, some node /n !=
s,d/ is an extended node-protecting remote LFA for the /s-d/ pair if
and only if
/?v ? neigh(s) : dist(v, n) < dist(v, e) + dist(e, n)/
/dist(n, d) < dist(n, e) + dist(e, d) ./
Despite the fact that we only considered unit cost networks, the
formal definitions above are *true for any arbitrary weighted network.*
SB> I do not see where the unit costs come into the text above. It looks
SB> like it is already expressed in terms of arbitrary cost.
SB> Additionally in order to limit the number of SPFs to a practical
SB> level, we normally suggest that the repair target in not d, but
SB> instead is e (in the link case) or next hop of e (node case).
SB> Anyway I will work on some text.
- Stewart
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