Re: [mpls] PSC: draft-rhd-mpls-tp-psc-sd-00

Dear Sasha, Eric, et al.,
I too share Sasha's concern in regard to SD in packet transport networks. I think that before we as WG discuss SD handling by PSC, the SD in Packet Transport Network must be clearly defined. Otherwise it looks as we've been asked to discuss Something Happens and You Must React.

	Regards,
		Greg

-----Original Message-----
From: mpls-bounces@ietf.org [mailto:mpls-bounces@ietf.org] On Behalf Of Alexander Vainshtein
Sent: Sunday, April 21, 2013 8:45 AM
To: Eric Osborne (eosborne)
Cc: mpls@ietf.org; Shell Nakash; Gideon Agmon
Subject: Re: [mpls] PSC: draft-rhd-mpls-tp-psc-sd-00

Eric, and all,
The issue has been discussed actively in the past.

I can only re-state my position during these discussions, namely that there is no way to define a reasonable analog of Signal Degrade (SD) in MPLS and, by implication, in the MPLS-TP data plane. By "reasonable" here I mean a method that does not depend on the actual traffic going thru the LSP.

The fact that we could not reach any consensus for such a definition in the past is not, of course, a mathematical proof of non-existence of SD.
But it is a good indication of a fundamental problem IMO.

As a consequence, IMHO and FWIW, there is no need in defining SD-related state transitions, behavior etc.

My 2c,
     Sasha

> -----Original Message-----
> From: mpls-bounces@ietf.org [mailto:mpls-bounces@ietf.org] On Behalf 
> Of Eric Osborne (eosborne)
> Sent: Wednesday, April 17, 2013 3:26 PM
> To: mpls@ietf.org
> Subject: [mpls] PSC: draft-rhd-mpls-tp-psc-sd-00
> 
> This thread is for discussing draft-rhd-mpls-tp-psc-sd-00.  The draft 
> provided extensions to the PSC state machine to handle Signal Degrade 
> (SD).  It does not define SD or provide scope around where or how SD 
> may be used.  There are some expired drafts that touch on the definition and use of SD, including:
> 
> draft-zhl-mpls-tp-sd-03
> draft-rkhd-mpls-tp-sd-03
> 
> (this is not an exhaustive list.  It's the top two google hits.)
> 
> 
> The questions I think are relevant are:
> 
> - do we need an SD mechanism in MPLS-TP?
> - if so, is it reasonable to define state transitions for it before we 
> have defined SD itself?
> - if yes to both of the above, does this draft provide the right 
> behavior?  Are there alternative approaches?
> 
> but of course any and all discussion is welcome.
> 
> 
> 
> eric
> 
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