I agree that being able to specify minimum path "quality" (where the specific quality measure still needs to be specified) is something that needs to be provided by the PCC to the PCE.
That said I'm not certain that PRE-FEC BER is necessarily a good measure for optical path quality as it still is a discussion of the quality seen by the client of the modulation scheme in use. The BER can be radically different for different modulations in the face of the different types of impairments. This feels like an area where the experts in Q6/15 can provide beneficial council. Jonathan Sadler -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Young Lee Sent: Friday, April 03, 2009 12:01 PM To: 'Jonas Mårtensson'; [email protected] Cc: [email protected] Subject: Re: [Pce] Comment on WSON Requirements Hi Jonas and Julien, I was thinking PRE-FEC BER when I mentioned the BER threshold. I also agree with Julien that we may need to specify other optical parameters such as OSNR margin. Regarding the BER threshold, please refer to G.698.1 and G.698.2 in which to discuss black link definition and optical parameters required. In particular, please read section 7.1.3 that discusses two cases where Pre-FEC BER requirement. Let's continue on the discussion. Thanks. Regards, Young -----Original Message----- From: Jonas Mårtensson [mailto:[email protected]] Sent: Friday, April 03, 2009 11:30 AM To: [email protected]; [email protected] Cc: [email protected] Subject: RE: Comment on WSON Requirements Hi Young and Julien, I missed this discussion in San Francisco but I tend to agree with (most of) Julien's comments. But if the PCE is expected to compute paths taking optical impairments into account it makes sense for a PCC to be able to set a "threshold" constraint, or minimum acceptable signal quality, although I find it a bit difficult to see under what circumstances anyone would be satisfied with anything else than "virtually zero" BER (or "error-free") for an optical path. In addition, some OSNR margin is usually required in order to allow for aging and other effects. In this case I think it might be better to specify the pre-FEC BER (or equivalent Q-factor if that sounds more related to the optical layer) and maybe in addition the desired OSNR margin. Regards, Jonas > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of [email protected] > Sent: den 3 april 2009 17:18 > To: [email protected] > Cc: [email protected] > Subject: Re: [Pce] Comment on WSON Requirements > > Hi Young. > > If I understand correctly, your actual requirement is to find > a "threshold criteria" to request a route that is "healthy > enough" for the PCC. So why have you chosen the BER which > more relative to a digital client layer? Why not considering > a more optical criteria, like OSNR for instance? > > Have a good week-end, > > Julien > > > -----Original Message----- > From: Young Lee [mailto:[email protected]] > > Hi Julien, > > The reason why we put the BER threshold in the PCEP request > is to "approximate" if the optical path in consideration > would be "healthy" > enough > from the BER perspective. Please note that we have defined > two different computation types of IA-PCE functions in the > IA-WSON framework draft: > (i) > approximate approach; (ii) candidate approach. Approximate > approach is a quick way of estimating the affects of > impairment while the candidate approach is to give a list of > acceptable paths with more thorough data/model. > > The BER can be estimated in various ways given the > availability of other impairment parameters. In any IA-RWA > (approximate) type computation where we are given impairment > parameters to estimate the affects of impairments, we must > use some threshold criteria to accept/reject paths. The BER > parameter was our first attempt at providing some control > over this criterion. > > Best Regards, > Young > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] > > Hi Young. > > This is a try to resume our discussion started during the SF meeting. > Indeed, I still don't get the rationale behind adding the BER > as a requirement for PCEP request. > > First, I wonder what your intend is when requesting a BER > threshold at computation time while you can't really know it > before LSP provisioning. > Obviously, what we look for is a low BER, but the way I see > using BER in routing would be to request a 2nd route *after* > a poor BER measurement on a firstly established LSP. > Then, considering what you called a "BER estimation", I don't > clearly see how you intend to estimate (or model?) it. The > BER associated to an LSP is highly dependent on so many > parameters: link DGD at measurement time, performance of the > FEC used for the to-be-provisioned LSP , possible cross-talk > and thus impact of potential adjacent channels... > Furthermore, I > don't really understand why focusing on the measurable BER > range while a typical PMD (in)accuracy may just move us > between an acceptable route and an unacceptable one, the > latter being the very 1st problem we should try to solve. > Finally, I don't get the use of such feature. Even if we > could, why would I request a 10^(-6) maximum BER? I don't see > any room for anything else than "the best one", so do we > really need something else? I tend to see BER as a varying > quality feed*back*, not as an indicator that we can > accurately target at routing time. > > I completely agree that PCEP must support optical > requirements, but my concern is to understand actual needs > before loading the protocol. > Therefore, I look forward to reading some clarification on > those issues. > > Best regards, > > Julien > > _______________________________________________ > Pce mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/pce > > _______________________________________________ Pce mailing list [email protected] https://www.ietf.org/mailman/listinfo/pce ============================================================ The information contained in this message may be privileged and confidential and protected from disclosure. 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