Re: [mpls] Working group last call on draft-ietf-mpls-tp-ring-protection

[cheng weiqiang <[e-mail]>]

Dear Greg, et al.,
I would like to clarify the meaning of the 'multiple failures'. The
Annex 1 of liaison-2012-10-03-itu-t-sg-15-mpls-requirements-and-analysis-of-ring-protection-for-mpls-tp-networks
is from the “T09-SG15-C-2097 PTN requirements on Ring protection”, and
I am the author of the contribution and the figure was drawn by me.
In that context, I intend to illustrate the ring protection have more
capability on ‘multiple failures’. By default, the ‘multiple failures’
include the adjacent links or nodes failure in single ring. Because
both linear protections and all previous ring protection solutions can
provide it already, I did not describe it at that time.
As well known, the meaning of multiple failures is “a single event may
impact multiple failures including scenarios of both “in single ring”
and “in multiple rings”. Multiple failures in one ring should be the
basic function.
--“fiber shared by multiple rings cut” in the ITU-T contribution gives
the example of multiple failures in multiple rings
-- "Micro-wave system impacted by whether and the nodes shared same
power supply system " in the mail I wrote to Adrian as following link
http://www.ietf.org/mail-archive/web/mpls/current/msg08804.html give
the good examples of multiple failures in single ring.


In one words, it is really essential function for MPLS-TP ring
protection to support the multiple failures in single ring.


B.R.
Cheng Weiqiang


2012/10/5 Daniele Ceccarelli <[e-mail]>:
> Hi Josh,
>
> in addition to what already said by Greg, the protection of interconnected
> rings is not in the scope of the ring protection applicability draft but in
> the scope of this one:
> http://tools.ietf.org/id/draft-liu-mpls-tp-interconnected-ring-protection-02.txt
>
> BR
> Daniele
>
> ________________________________
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Rogers, Josh
> Sent: giovedì 4 ottobre 2012 19.13
> To: Gregory Mirsky; cheng weiqiang; [e-mail]
>
> Cc: [e-mail]
> Subject: Re: [mpls] Working group last call on
> draft-ietf-mpls-tp-ring-protection
>
> Greg, when I read ITU document, I suspected the concern about 'multiple
> failures' was surrounding situations where a single event (fiber cut for
> instance) may impact multiple rings (imagine two rings entering a facility
> at the same entry, possibly same sheath).  The diagram showing failure
> points 1, 2, 3, and 4 seemed to me to be relatively close, where a single
> event could cause multiple impacts (break more than one ring).
>
> Of course, I'm guessing because it didn't appear all that clear that was the
> intent.
>
> From: Gregory Mirsky <[e-mail]>
> Date: Thursday, October 4, 2012 11:46 AM
> To: cheng weiqiang <[e-mail]>, "[e-mail]"
> <[e-mail]>
> Cc: "[e-mail]" <[e-mail]>
> Subject: Re: [mpls] Working group last call on
> draft-ietf-mpls-tp-ring-protection
>
> Dear Cheng, et al.,
> I would note that "multiple failure" scenario, illustrated in Annex 1  of
> liaison-2012-10-03-itu-t-sg-15-mpls-requirements-and-analysis-of-ring-protection-for-mpls-tp-networks,
> is, in my understanding, series of single failures in interconnected rings.
> I believe that protection architectures described in the document under
> discussion (wrapping, steering without and wit SPME) can be easily applied
> to interconnected ring topology as presented in the Annex 1. I've noticed
> that, referring to the Annex 1, that scenarios with dual failure on the same
> ring are not considered, i.e. failure at point 1 and 2 or 3 and 4. Should it
> be interpreted as "multiple failure" scenario implies failures in multiple
> interconnected rings over which a protected path spans but with only single
> failure in any given ring of the chain?
>
>         Regards,
>                 Greg
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> cheng weiqiang
> Sent: Thursday, October 04, 2012 4:02 AM
> To: [e-mail]
> Cc: [e-mail]
> Subject: Re: [mpls] Working group last call on
> draft-ietf-mpls-tp-ring-protection
>
> Hi,
>
> R106 of RFC 5654 mentioned "SHOULD protect against multiple failures".
> And well known, the multi-failures recovery is a basic function for ring
> protection. And the double failures scenario I mentioned is the most basic
> multiple failures condition.
>
> By the way, the wrapping solution of the draft cannot handle the adjacent
> nodes failures also.
>
> I don't think they are corner cases. I give you some examples for your
> reference.
>
> For the Micro-wave system, the adjacent hops often are impacted by whether
> or other facts at the same time.
>
> For the adjacent nodes, they often share the same power supply system.
> When issues happen on power system, they may shut down simultaneous.
>
> So for the carrier grade system, the multi-failures scenarios I mentioned
> should be the basic functionality.
>
> B.R.
>
> Cheng Weiqiang
>