Subject: Re: [mpls-tp] [mpls] I-D Action:draft-ietf-mpls-tp-survive-fwk-04.txt

From: "Adrian Farrel" <[email-masked]>
Date: Tue, 13 Apr 2010 13:52:36 +0100

Hi Liu,

Many thanks for your comments.
Nurit and I are just updating the document.

> 1 section 4.4.1
>  " As with recovery in layered networks, a protecion mechanism at
>    the lower layer needs to be coordinated with protection actions
>    at the upper layer in order to avoid race conditions"
> i don't know how to coordinate state of protection switching between
> the lower layer and the upper layer. do we need a new type of state
> packet to coordinate protection switching between the lower and
> upper layer?

There are several ways to coordinate between layers for protection. The
first way is, of course, the Hold-off Timer as described in Section 4.7.

As you point out, getting the right hold-off timer configuration can be very 
important to ensure correct recovery times. This problem is not new, but 
exists in all multi-layer transport networks and is familiar to many 
engineers working in the ITU-T or deploying networks. In practice, the 
problem reduces to the need for exceptionally careful network planning.

There will also be times when direct coordination between layers is
required. In the normal case, the layer boundary will be within a node; this
means that it is an implementation-specific issue and does not need
standardisation.

In the case where the layer boundary is external, we discover that the
interactions between MEPs and MIPs are nevertheless internal to nodes and so
also implementation-specific.

We have added a note to Section 4.7 to cover this.

> 2 I review all context of this draft. I don't notice the 1:n
> protection framework for P2MP.
> is it necessary to consider the 1:n protection solution for
> P2MP in the following Draft version: my answer is yes.
> do you think so?

We think that 1:n protection of P2MP is a very unlikely deployment scenario.
However, it is fundamentally the same as 1:1 P2MP protection with the
additional coordination that is used to tell the n-1 paths that they are no
longer protected (just as in P2P).

By the way, a better way to ensure efficient protection resource sharing in 
networks that carry P2MP services may be to use 1:1 mesh protection. Mesh 
protection for P2MP services is very complicated to plan, but the mechanisms 
for operation are no different to those used for P2P.

We don't believe that any additional text is required in the draft. But we
would be happy to hear any specific suggestions.

Thanks,
Adrian and Nurit