Subject: Re: [Pce] Inter-domain-p2mp-procedures

From: Quintin Zhao <[email-masked]>
Date: Fri, 18 Dec 2009 15:41:36 -0500

JP,

Thanks for your comments and suggestions.

I agree with you that for a quickly recovery, FRR is a good choice.  For the
p2mp TE LSP, if the failures are about link failures, FRR can be used for
the recovery. If the failures are about the p2mp nodes which can be the
root/branch/bud/leaf nodes, FRR might not be an easy way to cover these
cases.　This may lead to other possible solutions and the pre-computed
backup sub-tree or the whole backup tree might be needed for the possible
solutions. As you mentioned, using the FRR itself will eventually need the
head end reoptimization using a make before break.

The pre-computed backup p2mp path/sub-path or the new computed path during
reoptimization process using make before breaks are the optimal path subject
to the OF and all other current constrains when the path is computed by the
PCE. I agree with you that we can not draw the conclusion on the potentially
level of sub-optimality of performing local reroute as opposed to global
reoptimization.

Also we can not draw the conclusion if these backup path or optimized path
after the failure is better or worse than the primary path. These
pre-computed backup paths/sub-paths or the optimized paths under the failure
condition are the best path which can be used for the recovery of the
failure while satisfying all the conditions.
 
Regards,
Quintin

-----Original Message-----
From: JP Vasseur [mailto:[email-masked]] 
Sent: Thursday, December 17, 2009 1:26 PM
To: Quintin Zhao
Cc: [email-masked]
Subject: Re: [Pce] Inter-domain-p2mp-procedures

Hi,

Note that this is a fairly well-known issue. The aim of local repair  
has always been to quickly recover from the failure. The degree of  
resources guarantees and optimality depends on the amount of resources  
dedicated to backup, several assumptions with regards to potential  
simultaneous failures, the algorithms used to pre-compute backup  
tunnels, etc ... The approach taken by P2P FRR has been to first  
locally reroute and trigger a head-end reoptimization using a make  
before break. I do not think that you can draw any conclusion on the  
potentially level of sub-optimality of performing local reroute as  
opposed to global reoptimization. It depends on a number of factors.

JP.

On Dec 14, 2009, at 10:15 PM, Quintin Zhao wrote:

>
> Hello PCE'rs,
>
> I would like to follow-up on some discussions from our PCE WG  
> session last
> month. Specifically regarding Dajiang's failure and recomputation
> observations on our draft. We are very interested to hear comments  
> regarding
> the need for computing secondary paths in the event of failure.  
> Currently
> our thinking is to recompute the sub-tree based in the domain where  
> the
> failure has occurred. In this case we would not need to perform a
> recalculation of the entire tree. We could also recompute the entire  
> tree,
> and avoid the failed areas, as long as the TED has the updated  
> topology.
> Realistically one might have a backup core tree pre-computed so you  
> can
> switch over in the event of failure. There are also other  
> considerations.
> Would a partial recomputation provide a "worse" SPT or MCT tree, or  
> would a
> full tree recomputation provide a "better" SPT or MCT? I can think of
> scenarios for both a partial and full recomputation, so perhaps we  
> need to
> implement both but allow the PCC to decide when to issue a partial  
> or full
> recomputation based on some criterion.
>
> Thanks,
>
> Quintin
>
> _______________________________________________
> Pce mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pce

---

From: JP Vasseur <[email-masked]>
Date: Sat, 19 Dec 2009 10:51:27 +0100

Hi,

On Dec 18, 2009, at 9:41 PM, Quintin Zhao wrote:

> cases.　

What makes you think that the use of FRR is less applicable to node  
failures ?
(for which you could either use a set of P2P backup or a single P2MP  
backup)

Thanks

JP.

> This may lead to other possible solutions and the pre-computed