Hi Giovanni, thanks for the close read. Looks like you caught some
problems with the text. See below for comments.
Giovanni Martinelli (giomarti) wrote:
Hi Greg,
Sorry
for the delay in replying. I'm working on this topic since a while so
yes, it's interesting. Before going on specific issue I would have some
question/clarification regarding the draft itself.
*
Within Abstract and the following.
You
don't talk about Optical Cross Connects (OXC) is something missing or
understated somewhere?
-->Whoops. We were trying to find a more general term to include
both ROADM (usually a highly asymmetric fabric) and an OXC (a
completely symmetric fabric, e.g., any ingress to any egress), but we
seemed to have gone with using the ROADM terminology to include both
cases. Talked with some equipment makers that planned/make "switches"
that seemed to incorporate both so we made sure the model could deal
with both sparse and dense potential connectivity. Diego had some
terminology ideas but lately his e-mails have been bouncing back to
me. Any suggestions are appreciated, but we are including both ROADM
and OXCs.
*
Section 3.1 where you state:
"A
fixed mapping between the
GMPLS
label space and these ITU-T WDM grids as proposed in [Otani] "
Does it
implies a sort of network level label space? How relate with usual
local label significance?
--> This mapping gives a mapping between labels and
wavelengths/lambda, just like in the SONET/SDH case we mapped the ITU-T
G.707 "S, U, K, L, M " identification of SDH time slots to a label
format in RFC4606 and again this was done in RFC4328 to map G.709
digital wrapper time slot identification into a technology specific
label format. In RFC3471 for lambda switching we just get a 32 bit
integer with no meaning attached. Every network and every node could
potentially map labels to lambdas in a different way. In [Otani] they
are following the RFC4606 and RFC4328 lead and using the ITU-T DWDM and
CWDM lambda grid standards to give a fixed association between labels
and lambdas just like between labels and TDM time slots in the SDH/ODU
case.
This doesn't change the local significance of labels. In the wavelength
switched optical case that is influenced by the presence or absence of
wavelength converters.
*
Section 3.4 Wavelength Converters
"Current
or envisioned contexts for wavelength converters are : ..."
Could
we think to a
description/model for wavelength converter that is technology agnostic? Simply
something like: full conversion capability, partial conversion
capability with some constrains, and may be others.
--> The difference, between the all optical techniques and the OEO
based techniques makes that difficult.
*
Section 3.4. the following:
"4.
Wavelength converters that are O-E-O based will have a restriction
based
on the modulation format and transmission speed"
Not
clear to me the type of restriction here when OEO happens... probably
I'm missing what you mean here.
--> For example a typical O-E-O based wavelength converter would be
build around a 3R regenerator with a tunable laser. A 3R regenerator
cares about the modulation type say NRZ or RZ (and which flavor), and
the symbol rate since its also doing retiming. An all optical
wavelength converter will be fairly independent of these issues (except
when we look at impairment factors). Hence the OEO wavelength is going
to be more signal specific than the all optical.
*
Section 4.1 when you talk about Lightpath temporal characteristics:
"Lightpath
connection duration has typically been thought of as
approximately
three time frames: "
and the
following you define: dynamics, pseudo-static, static.
Why
there’s a need of this classification? When you us Short/long is
compared to what?
--> In most of the research literature and in optimization practice
different techniques are typically used in the dynamic versus static
(or psuedo static cases). In MPLS there is minimum interference
routing optimization techniques for the dynamic case. For the static
case I could apply multi-commodity flow optimization techniques to a
batch of connections. In the RWA literature there is a similar
differentiation. Exactly what information could be sent to help PCE
differentiate I'm not sure. In the case of static, batch optimization
we can just use the existing concurrent optimization hooks in PCE. For
an individual lightpath request it seemed that it would be helpful to
know how long the connection would last so we'd know how much
computational effort we might want to put into optimize it.
minor typo on your mail below: point (c)
rfc4328 (not 4238) right?
--> Yes. The G.709 signaling extensions RFC.
Thanks,
Giovanni
Hi folks, I haven't seen too many comments on our draft "Framework for
GMPLS and PCE Control of Wavelength Switched Optical Networks" ( http://www.ietf.org/internet-drafts/draft-bernstein-ccamp-wavelength-switched-01.txt).
So I figured I'd point out some potentially controversial issues that
the draft brings up.
(a) The draft brings up models for the following WDM network elements:
- WDM links
- Optical transmitters
- Wavelength Converters and OEO regenerators
- ROADMs, FOADMs, optical splitters and combiners.
For items (3) and (4) we are taking the modeling lead rather than
some other SDO. And for ROADMs, in particular, we going beyond the
classic ITU-T "fabric" model (M.3100) which has been the mainstay of
any connection oriented switch (TDM, ATM, MPLS).
(b) The draft brings up three (not one, not two, but three) different
computational models for RWA which can impact GMPLS and PCE protocols:
- A single PCE computing both the path and wavelength
- Two distinct PCEs, where one computes the path, and a
different PCE computes the wavelength assignment
- A PCE computes the path and wavelength assignment is
accomplished in a distributed fashion via signaling (e.g., using label
set objects)
Do we really need all three models?
(c) G.709 includes the Optical Multiplex Section and Optical Channels.
RFC4238 was aimed at GMPLS extensions for G.709 (Optical Transport
Network) control. Weren't we finished with all this optical stuff
years ago?
I'd like to think the draft answers some of these questions. I also
think that network element models and the process models are important
enough to warrant this separate framework document. Your opinions are
solicited.
Regards
Greg B.
--
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Dr Greg Bernstein, Grotto Networking (510) 573-2237
--
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237
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