Re: comments on draft-shiba-ccamp-gmpls-lambda-labels-00.txt

["Adrian Farrel" <adrian@olddog.co.uk>]

Dimitri,

Thanks for your work reviewing these recent I-Ds. It is really valuable
and I'd welcome other people doing similar reviews.

> there is a specific point to be clarified in this document:
>
> semanticless vs semanticful label (even here there is a distinction
> between spectral vs indexes i.e. using the wavelength index)
>
> domain-wide vs link local significant label

Without being too picky, I think all labels are semanticful otherwise, we
would not know what resource they refered to.

So the point reduces to whether the scope of the semantics are link-local
or wider.

> so, the comparison from this perspective with TDM labels is difficult to
> parse, the latter is semanticful but link local
>
> now, i don't specifically see what has changed the late 90's, early
> y2k's, to have a change in the wavelength label definition;

This is the question I would like to get to the bottom of. In other words:
do we need this function?

It seems to me that the question being asked is this:

   If I want to compute a path that has some form of wavelength
   constraints, what information do I need access to?

Another question might be:

   If I want to signal a path with wavelength constraints what
   information do I need to include in the signaling message?


I'd suggest that when we started on GMPLS, we were enthusiastic about
transparent optical networks, but we were not properly focusing wavelength
constraints because lambda-switching PXCs didn't take off. Therefore we
didn't examine the requirements for wavelength constraints in routing and
signaling. The authors of this I-D are claiming new hardware requirements
for the same function.

> there are
> several solution possible
>
> - absolute values: the freq. of the wavelength: difficult to adopt
> because referenced values are nominal and knowing all interactions
> between wavelengths this knowledge is at the end of little practical
> usage; (introduces implicit ordering)
>
> - indexed values: the # of the wavelength: it does not provide for a
> future proof label space for inst. in case new frequencies are inserted
> in the grid (introduces explicit ordering)
>
> - diff. values e.g. freq spacing starting from a reference value: pauses
> the question of the reference value and does suffer from the former
> issue (introduces implicit ordering)
>
> - the solution available today - cumbersome in some control plane
> operations (e.g. label set translation) and not easy to troubleshoot but
> independent of any physical consideration (spectral), scale to any
> number of wavelength per fiber, does not introduce any ordering, the
> most flexible (since allowing each system to maintain its specific
> control operations) and the less constraining since maintaining the
> control plane operations independent of any data plane specifics
>
>
<http://www.ietf.org/internet-drafts/draft-shiba-ccamp-gmpls-lambda-labels
-00.txt>