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Re: On Labels for Wavelength Switched Optical Networks...
Hi Greg and Diego,
Thank you for your initiation and clarification.
As Diego clearly pointed out, we actually rely on the data plane which
is especially
defined by ITU-T. All transmitters, MUX/DEMUXs, ROADMs and WSS's follow
the ITU-T frequency (wavelength) grid now. In that sense, it is
advantageous for us to
compliant with that specification in terms of the control plane.
Furthermore, taking advantage of this e-mail message, I would like to
clarify, again, the
label format definition. During the meeting, there seems to be an
misunderstanding about
the label definition. It has some bits to indicate a wavelength spacing,
but this info. is utilized
only to calculate the wavelength value for switching, not to control the
channel spacing of
the node itself.
Regards,
Tomo
Diego Caviglia さんは書きました:
HI Greg,
Thanks for this very useful summary.
I’m one of the author of this ID so my comment is not fully neutral J
btw in IETF we always state that the data plane is not part of our
work and in-fact we rely as much as possible on other standard bodies
(IEEE, ITU-T, …) for data plane definition.
For G.709 and G.707 (SDH) we used as label what was defined in the
ITU-T. As example the RFC4606 defines the SONET/SDH label as extension
of the numbering scheme defined in G.707.
My view is that we already have a standard body (ITU-T) that defined
how to identify a wavelength and that definition fits well in our 32
bits format so IMHO it is straightforward to use that definition.
My two cents
Diego
------------------------------------------------------------------------
*From:* owner-ccamp@ops.ietf.org [mailto:owner-ccamp@ops.ietf.org] *On
Behalf Of *Greg Bernstein
*Sent:* venerdì 14 dicembre 2007 17.17
*To:* ccamp
*Subject:* On Labels for Wavelength Switched Optical Networks...
Hi folks, at the Vancouver meeting the lambda label format of Otani,
et. al. draft-otani-ccamp-gmpls-lambda-labels-01.txt
<http://tools.ietf.org/html/draft-otani-ccamp-gmpls-lambda-labels-01.txt>
[Otani] was presented for a second time and a few new issues seemed to
arise. I'm writing this note to see if we can resolve these on the
list so this work can move forward, since the label format is
valuable, in general, to the control of wavelength switched optical
networks (WSON).
First, a general 32 bit lambda label has been defined in RFC3471. This
previous label does not directly relate to either the wavelength or
frequency of the light used in a lambda LSP in a standardized way
(folks can use the 32 bits as they see fit).
To come up with a completely general "lambda label" one could/should
define both a (i) wavelength label specified in meters and (ii) a
frequency label specified in Hertz (Hz). These could be specified
either with a 32 bit IEEE floating point number or via a suitable 32
bit integer by suitably adjusting the base units. We could represent
the frequency via a 32 bit integer in MHz, then a 193.1THz light
source could be characterized by the integer 193,100,000. Similarly we
could represent the wavelength label via a 32 bit integer in pico
meters (10-12 meters), then a 1550nm wavelength could be characterized
by the integer 1,550,000.
Now any of the previous formats could be used with the 32 bit lambda
label already defined. The problem here is to pick a format for
interoperability and compatibility with potentially common wavelength
switched control operations.
Issues with the previously mentioned formats:
(a) While floating point numbers provide great flexibility, as a label
they have issues when it comes to comparison operations.
(b) An integer format with a suitably scaled exponent is relatively
simple and just leaves the choice of “exponent” to be decided.
(c) Neither format contains any “context” information about the WDM
system in general.
The format proposed in [Otani]. avoids the above three issues and
enhances common control plane operations as follows:
(a) The format is integer based, hence avoids issues with floating
point comparisons.
(b) The format is based on the widely recognized ITU-T standard grids
(ITU-T G.694.1 and .2) and fosters interoperability more than
potentially any other choice.
(c) The ITU-T grids come in various widths and hence have an inherent
growth path.
(d) The ITU-T grids come in both frequency (G.694.1) and wavelength
(G.694.2) flavored versions an both are incorporated in the [Otani]
label format.
(e) The format includes information on the grid spacing which is
important WDM context information useful in many label selection
processes. For example a tunable laser associated with a 50GHz spacing
WDM system could specify acceptable label range via the inclusive
range label set mechanism. Note that only those frequencies (labels)
that fall on the grid are supported and not intermediate frequencies.
At the CCAMP WG meeting in Vancouver it was pointed out (by Lou
Berger) that since a lambda label already exists and that existing
implementations may make use of it that the proposed label of [Otani]
would be better off referred to as a “G.694 label”. With such a change
I think that this label format (and accompanying draft) should move
forward as a working group document.
Comments, suggestions, issues?
Regards
Greg B.
--
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237