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
------------------------------------------------------------------------
*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
_______________________________________________
Pce mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/pce
