Re: [mpls] MPLS-RT review of draft-atlas-mpls-te-express-path

[Alia Atlas <[e-mail]>]

Please see in-line

On Thu, Apr 11, 2013 at 2:49 AM, Xuxiaohu <[e-mail]> wrote:
<cut>

>
> >    Comment: According to an above statement of " an end-to-end latency
> > bound merely requires that the path computed be no more than that bound
> > without being the minimum ", it seems that latency is not used as a
> metric for
> > SPF algorithm but only used as a constraint. If so, how do you decide
> which
> > specific link(s) of the first-round calculated SPF path should be pruned
> prior to
> > executing the second-round SPF calculation?  The same question exists
> when
> > considering end-to-end packet loss ratio and latency variation bounds.
> The
> > example illustrated in the draft seems not clear to me. Would any
> co-author
> > please clarify the above doubt?
>
> Here I meant when the first-round calculated SPF path with existing
> constraints (e.g., bandwidth, resource color etc) being met can't meet the
> end-to-end latency bound constraint, how do you decide which specific
> link(s) of that first-round calculated SPF path should be pruned prior to
> executing the second-round SPF calculation? In other words, it would be
> very hard to use a cumulated value of a given type of link metric (e.g.,
> end to end path latency, end to end latency variation) as a constraint for
> the CSPF algorithm, IMHO.


So your concern is what constraint to relax if a path can't be found?  I
don't think that is something that needs to be standardized...  It depends
on what you want to trade-off for the various constraints.  I can easily
see storing the lowest latency over the latency bound that was seen - or
other techniques.

Alia