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

Hi,

Agree with Lou, an update would be good for these documents considering the confusion.

As an author on RFC4427, it's intent was as an informative, generalized document on all types of recovery schemes. The definitions were (quite) shortened and so in this case the 2nd paragraph of G.808.1's definition regarding APS specifics was not included. RFC4427 didn't discuss state machines or any details of any specific scheme. When generalize, it helps with readability but there is always the danger of missed details. So on Eric's items, it falls under a third bullet: "written correctly though lacking in detail causing mis-interpretation":-)

RFC4427 fully intended to align with the ITU-T terminology and in the Recovery Terminology Section (Section 4) referred the reader to the ITU-T Recommendations:
"The reader is invited to read [G.841] and [G.808.1] for references to
   SDH protection and Generic Protection Switching terminology,
   respectively."

Thanks,
Deborah

-----Original Message-----
From: mpls-bounces@ietf.org [mailto:mpls-bounces@ietf.org] On Behalf Of Lou Berger
Sent: Thursday, May 09, 2013 5:25 PM
To: Eric Osborne (eosborne)
Cc: mpls@ietf.org; Morro Roberto; Allasia Andrea; Nervo Giacolino
Subject: Re: [mpls] PSC: draft-rhd-mpls-tp-psc-priority-00

Eric,
	I think you might have missed that rfc6372 section 6.1.2 is consistent
with RFC4427.  So perhaps it would be best to have a standalone
draft/rfc that updates both rfc6372 and rfc4427 on this specific point
alone.  If this is done, no change to rfc5654 is needed.

Lou

On 5/9/2013 11:40 AM, Eric Osborne (eosborne) wrote:
> Hi Alessandro, see inline.
> 
>> -----Original Message-----
>> From: D'Alessandro Alessandro Gerardo
>> [mailto:alessandro.dalessandro@telecomitalia.it]
>> Sent: Tuesday, May 07, 2013 3:27 PM
>> To: Eric Osborne (eosborne); mpls@ietf.org
>> Cc: Cavazzoni Carlo; Allasia Andrea; Nervo Giacolino; Morro Roberto;
>> ryoo@etri.re.kr; lifang@catr.cn; cts@etri.re.kr
>> Subject: R: PSC: draft-rhd-mpls-tp-psc-priority-00
>>
>> Hi Eric,
>> You wrote "is it appropriate to make this priority swap?"
>> My answer is yes, it shall be done for the reasons explained in liaison
>> 1205, bullet 1.
> 
> Let me paraphrase the three points in those bullets, I want to make sure I understand them:
> 
> a. If the protection path fails then the removal of the FS will not be seen because the channel used to provide it is gone.
> b. If there is SF-P and FS is issued by accident then this will cause an outage, which is Bad
> c. (points to Annex 1): similar to (a) above, the loss of the protection channel means there will be an inconsistency in the protection state
> 
> Is that an accurate paraphrase?
> 
>> You wrote "- what do we need to change?  rfc5654?  rfc4427?  "
>> No I don't believe it is required to change any RFC but RFC 6378
> 
> To me this decision is a matter of process rather than of technical behavior.  
> I believe the current set of opinions is this:
> 
> a) some believe that rfc4427 requires the current set of priorities, as per LS1174 point #1 (http://datatracker.ietf.org/liaison/1174/)
> b) some believe it does not, and that rfc6378 misinterpreted rfc4427
> 
> I think we all agree that the chain here is: 6378 must obey 5654, and that 5654 requires 4427.
> 
> So it's going to come down to - is 4427 written wrong but interpreted correctly, or written correctly but misinterpreted?
> If we decide the former, we need to change 4427 and/or 5654 to clarify the requirement.
> If we decide the latter, we do not need to change 4427 and can probably just change 6378.
> 
> Does that sound right?
> 
> 
> 
> eric
> 
>>
>> Best regards,
>> Alessandro
>>
>> ------------------------------------------------------------------
>> Telecom Italia
>> Alessandro Gerardo D'Alessandro
>> Transport Innovation
>> Via Reiss Romoli, 274 - 10148 Torino
>> phone:  +39 011 228 5887
>> mobile: +39 335 766 9607
>> fax: +39 06 418 639 07
>>
>>
>> -----Messaggio originale-----
>> Da: mpls-bounces@ietf.org [mailto:mpls-bounces@ietf.org] Per conto di
>> Eric Osborne (eosborne)
>> Inviato: mercoledì 17 aprile 2013 14:16
>> A: mpls@ietf.org
>> Oggetto: [mpls] PSC: draft-rhd-mpls-tp-psc-priority-00
>>
>> This thread is for discussing draft-rhd-mpls-tp-psc-priority-00.  In
>> brief, the draft proposes swapping the priorities between FS and SF-P
>> (see section 4.3.2 of rfc6378).  This proposed swap has a long history,
>> dating back to when PSC was an ID.  For some history, see
>>
>> http://datatracker.ietf.org/liaison/1229/
>> and
>> http://datatracker.ietf.org/liaison/1234/
>>
>> The questions that I think are relevant here are:
>>
>> - is it appropriate to make this priority swap?
>>   - are there alternative approaches?
>>   - what do we need to change?  rfc5654?  rfc4427?
>> - if we don't make the change, does this expose implementation to
>> problems?
>> - if we do make the change, how do we go about it?
>>
>> but of course any and all discussion is welcome.
>>
>> As with the other threads I'm going to leave my two cents out of this
>> introductory email but I'll chime in when discussion starts.
>>
>>
>>
>>
>>
>> eric
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