Hi Greg,
________________________________
From: Greg Bernstein [mailto:[EMAIL PROTECTED]
Sent: venerdì 28 settembre 2007 21.47
To: Giovanni Martinelli (giomarti)
Cc: ccamp; [EMAIL PROTECTED]
Subject: Re: [Pce] Some key issues with Wavelength Switched Optical
Networks...
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.
My doubt was coming from the ROADM definition in section 2 and picture used
later on the draft. At least in my understanding the OXC is a general case for
ROADM (sort of multi-degree ROADM) but ok, it's a matter of terminology.
* 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.
Ok. Local significance but global semantic (as pointed out by Adrian in a
previous mail).
* 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.
ok more clear now, although it would be nice having a general model as you
marked with TBD.
* 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.
ok, clear. I still have doubt about quantifiers but fine for the moment.
Thanks,
Giovanni
minor typo on your mail below: point (c) rfc4328 (not 4238)
right?
--> Yes. The G.709 signaling extensions RFC.
Thanks,
Giovanni
________________________________
From: Greg Bernstein [mailto:[EMAIL PROTECTED]
Sent: giovedì 27 settembre 2007 1.42
To: ccamp; [EMAIL PROTECTED]
Subject: [Pce] Some key issues with Wavelength Switched
Optical Networks...
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:
1. WDM links
2. Optical transmitters
3. Wavelength Converters and OEO regenerators
4. 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:
1. A single PCE computing both the path and
wavelength
2. Two distinct PCEs, where one computes the path,
and a different PCE computes the wavelength assignment
3. 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.
--
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237
--
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237
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