Re: [mpls-tp] [mpls] [PWE3] [AHMPLS-TP] Re: pollondraft-he-mpls-tp-csf-03.txt

[Benjamin Niven-Jenkins <[e-mail]>]

Yuanlong,

On 3 Dec 2010, at 14:46, Jiang Yuanlong wrote:
> From: "Ben Niven-Jenkins" <[e-mail]>
> 
> The CSF draft covers two cases:
> - PWs
> - LSPs (and by implication the three clients supported by LSPs, namely IP, PWs and other LSPs)
> 
> PWs have a mechanism already and the CSF draft acknowledges that.
> 
> LSPs have BFD and other tools to detect failures.
> 
> IP has a bunch of mechanisms e.g. IGP hellos if you're building an IP network or various keepalive mechanisms if you're layering IP tunnels on something else.
> 
> The premise of the draft is "This document defines such a MPLS-TP OAM tool as Client Signal Fail indication (CSF) to propagate client failures and their clearance across a MPLS-TP domain" based on the fact that "the client layer OAM functionality does not provide an alarm notification/propagation functionality"
> 
> For the three possible clients of MPLS-TP, the second sentence I quote above does not hold true and therefore the draft is not needed.
> 
> [JYL] IGP hello is not so fast, maybe BFD is also needed for such a use case.
> In fact, there is also VCCV BFD available in PW, so do we need any more PW OAM mapping in draft-ietf-pwe3-static-pw-status (except bits defined for the PW redundancy )?
> 

The draft states that CSF is required for client technologies that can not detect faults themselves. You are now stating the purpose to be to compensate for client technologies where fault detection is not fast enough. That is a different use case.

In the case that IGP hello is not fast enough (and the timers can always be tuned) detecting the fault is only part of the time it takes for the network to reconverge. 

It is still not clear to me why MPLS-TP requires CSF for IP clients when other server technologies that IP runs over do not provide it and IP networks have operated fine

> However, if I am wrong and the draft really is needed it should be straightforward for someone to post a description of a practical deployment use case where the existing IP mechanisms are insufficient and the CSF functionality is required in MPLS-TP to proxy for the lack of client level functionality.

Ben