Re: [PWE3] [mpls] WG Last Call for draft-ietf-pwe3-endpoint-fast-protection-01 - RFC4447

[Yakov Rekhter <[e-mail]>]

Loa,

> Yakov,
> 
> On 2014-08-08 16:02, Yakov Rekhter wrote:
> > Loa,
> >
> >> Authors, Mingui, Stewart
> >>
> >> On 2014-08-08 04:46, Mingui Zhang wrote:
> >>> Hi Stewart,
> >>>
> >>> I think authors would say the S-PE stitching method involves
> >>> the control plane processing during the repair procedure. They
> >>> emphasized their method uses data plane & local repair, which
> >>> can be faster.
> >>> Here, I want to raise one issue:
> >>
> >> It seems that we take it for granted that the method proposed on this
> >> draft is faster than e.g. the e2e protection a la mpls-tp. Why is that?
> >
> > To answer your question let me quote from "Network Recovery" by JP
> > Vasseur, Mario Pickavet, Piet Demeester (Section 5.8.1, page 336):
> >
> >    With global protection, rerouting is performed by the head-end
> >    LSR, which means that this requires for the head-end LSR to receive
> >    the failure indication to reroute the affected traffic onto their
> >    respective backup paths (whose paths have been precomputed and
> >    signaled). So in terms of recovery time, the delta between global
> >    and local protection is the failure indication signal propagation
> >    time to the head-end LSR.
> >
> > Yakov.
> >
> 
> Well, I won't argue that this is what is said in the book, but it is
> not what I asked about.
> 
> mpls-tp runs e.g. 1:1 or 1:n, i.e. 1 working lsp (or pw) is protected
> by one or more pre-established  lsp's or pw's. detection time can be
> as low as 10ms and the switch over is far shorter.
> 
> While I understand that the draft is much more resource conservative,
> what is the foundation to claim that is faster?

Local protection does not involve propagating failure indication
beyond the point of failure.

Do you think that the detection time at the head-end can be less
than the time it takes to propagate failure indication from the
point of failure to the head-end ?

Furhermore, even if we assume that for some topologies the propagation
time could be 10ms, could it be 10ms irrespective of the distance
and the number of hops spanned by a PW ?

Yakov.