Subject: [Gen-art] Gen-ART review of draft-ietf-ccamp-flexi-grid-fwk-05

From: "Black, David" <[email-masked]>
Date: Mon, 3 Aug 2015 01:09:57 +0000

I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at

<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-ccamp-flexi-grid-fwk-05
Reviewer: David Black
Review Date: August 2, 2015
IESG Telechat date: August 6, 2015

Summary: This draft is on the right track, but has open issues
 		described in the review.

This draft requires significant GMPLS expertise to fully understand,
but is generally well written and clear.  It describes the use of a
GMPLS control plane with flexible optical networks that can vary
optical frequency assignment on a per-link basis along an optical
path.

All of the issues that I found are minor, and some of them may
be mostly reflections of my lack of GMPLS expertise.

Major issues: None

Minor issues:

[1] 3.2.5 - the last bullet item is not completely clear to me.  What
does it mean for two slot compositions to be the same?  Is this saying
that the same set of effective frequency slots need to be present
end-to-end for the media channel?  I suspect not, but I don't understand
what is intended.

[2] p.21 last sentence in 1st para:

   Regardless of the actual encoding,
   the LSP setup message specifies a minimum frequency slot width that
   needs to be fulfilled in order to successful establish the requsted
   LSP.

Should "minimum frequency slot width" be "minimum effective frequency slot
width"?  I think it's  possible for the effective frequency slot width to
be smaller than all of the individual slot widths involved in the absence
of frequency shifters/converters.

[3] p.21 - RSA acronym is unfortunate, due to collision w/widespread usage
of that acronym for a security algorithm.  I strongly suggest changing to
another acronym (e.g., R+SA).

[4] 4.8.4 - The information model is informal or abstract (can't generate
anything from it), even though RBNF was used - this should be noted.

[5] 5.5 - I'm surprised that the first requirement (neighbor discovery
support) is a MAY.  I wonder about its operational consequences, and at the
very least suggest expanding Section 8 to discuss them.  The text in 5.5
should be expanded to add some explanation of how things work when there's
no neighbor discovery support.

Nits/editorial comments:

Section: 3.2.1 - Editorial suggestion: Changing "+" -> "+/-" in the
formula for nominal central frequency and re-defining n as a
non-negative integer would be slightly clearer.

p.6 - please state that slot width is +/- wrt nominal central frequency.

p.8 - Fig 4 could use a bit more explanation - the two frequency
slots occur at different points along the path.

Nit: First nominal central frequency 'X' in Fig 5 needs to move 2
chars left.

Section 4 - TE link term shows up w/o acronym expansion or definition.
Please define it before use.

Sections 4.2 and 4.3 - this may be my unfamiliarity, but it would have
helped to have some sort of heads-up at the start of the figures that
the top (non-GMPLS) portion of the figures prior to Figure 12 are
entirely in the optical domain.  Perhaps explaining what the two
planes are (and how they're realized/implemented) in Figure 8 would help.

Last paragraph on p.16: "trnaponders" -> "transponders".  Also, I saw
"transceivers" earlier - if that's the same concept, only one term
should be used.

p.19 - Even after expanding acronyms, I don't understand this sentence:

   If two OTSis must be
   switched to different ports, it is better to carry them by different
   FSC channels, and the media layer switch is enough in this scenario.

A sentence or two explaining what an "FSC channel" is earlier in that
paragraph would help.

p.21, 1st para:

   messages, and a specific frequency slot can be requeste on any

s/requeste/requested

p.21:

   In GMPLS the requested effective frequency slot is represented to the
   TSpec present in the Path message, and the effective frequency slot
   is mapped to the FlowSpec carried in the Resv message.

I believe those are RSVP-TE messages - that should be stated.

p. 22:

   d.  n can change, but m needs to remain the same along the path.
       This ensures that the effective frequency slot remains valid, but
       allows the frequency slot to be moved within the spectrum from
       hop to hop.

In full generality, that may require the ability to shift or convert a
frequency slot, which is a concept that doesn't appear to occur in the
draft prior to this point.

Figures 15 and 16 need their variables (e.g., m_a, FSb) somehow
labelled or explained

After Figure 16, the switch to the EFS acronym is a surprise, given
the extensive prior usage of the spelled-out term.  This paragraph
contains all uses of the EFS acronym - I suggest removing that acronym
and spelling out the term.

Section 4.6: I don't understand why this sentence is in the middle of
the paragraph - it doesn't seem to describe an example of different
slot width granularities:

   Consider a node with an application where the nominal
   central frequency granularity is 12.5 GHz and where slot widths are
   multiples of 25 GHz. 

I'd suggest removing it.

5.1.1. What is L-band?  This is the first time it's mentioned.

idnits 2.13.02 didn't find anything that needs attention.

Thanks,
--David
----------------------------------------------------
David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
----------------------------------------------------

---

From: "Adrian Farrel" <[email-masked]>
Date: Mon, 3 Aug 2015 18:37:58 +0100

Hello David,

Responding as a contributing author who wants to see this work move forward
promptly...

Many thanks for taking the time to review.

> end-to-end for the media channel?  I suspect not, but I don't understand

I think you mean the penultimate bullet: the last one on page 9.

It does not mean that the same set has to be available end-to-end. As the text
says "...the specific slots and their spacing may vary hop by hop." But it does
mean that the composition of the media channel will be the same on each hop. So
what is "the composition" of a media channel?  Well, as the first bullet says:
"A composite media channel carries a group of OTSi" and you can go back one
section to find what that means, but, in summary...

You can make an end-to-end connection from a set of parallel channels. You can
place those channels at different spots in the spectrum from one hop to the
next, but you cannot vary the number of channels from one hop to the next (e.g.
two channels on one hop mapped to one thick channel on the next hop mapped to
four thin channels on the next hop).

> of frequency shifters/converters.

Pedantically (and what's wrong with pedantry?), yes.
Indeed, a user that requested a minimum frequency slot might be very
disappointed.
Thus it is taken for granted that a user requests usable bandwidth :-)

But adding "effective" would not be harmful.

> another acronym (e.g., R+SA).

Please see RFC 5513.

R+SA would be unfortunate because in this field the "+" is used to indicate a
separation in processing whereas the concatenation shows processing as one
piece.

Since the text expands and explains "RSA" I don't think a change is necessary.

> anything from it), even though RBNF was used - this should be noted.

I am not clear why you make this assertion. It is true that I would not attempt
to "generate" anything from the information model if, by that, we mean
automatically using a script or compiler. But there is nothing that precludes
someone from doing this.

> no neighbor discovery support.

Although some work has been done on plug and play in transport networks, there
is also a lot of "legacy" thought with respect to plugging 100G fibers in at
random and seeing what is connected to what today. In general, when one
provisions a fiber and a pair of expensive line cards, one has a good idea what
one is connecting and the processes that are run are validation rather than
discovery.

Thus the second paragraph aims for link property correlation such as is provided
in LMP, but the first paragraph only considers the element of discovery to be
something that someone could look at if they are really enthusiastic.

Since this is pretty much established behavior across GMPLS optical networks,
I'm not sur more needs to be said.
 
> non-negative integer would be slightly clearer.

This is something you'd need to take up with the ITU-T, I think.
We don't want to change the formulae in common use where the data plane is
defined.

> p.6 - please state that slot width is +/- wrt nominal central frequency.

Ah, took me a moment to see what you mean. 
Yes, this could be clarified with

OLD
   o  Slot Width: The slot width determines the "amount" of optical
      spectrum regardless of its actual "position" in the frequency
      axis.  A slot width is constrained to be m x SWG (that is, m x
      12.5 GHz), where m is an integer greater than or equal to 1.
NEW
   o  Slot Width: The slot width determines the "amount" of optical
      spectrum regardless of its actual "position" in the frequency
      axis.  A slot width is constrained to be m x SWG (that is, m x
      12.5 GHz), where m is an integer greater than or equal to 1.
      The slot width defines the amount of spectrum in use on
      each side of the central frequency, thus the amount of
      frequency in use is actually twice the value of the slot width.

> slots occur at different points along the path.

Maybe...

OLD
   o  Effective Frequency Slot [G.870]: The effective frequency slot of
      a media channel is that part of the frequency slots of the filters
      along the media channel that is common to all of the filters'
      frequency slots.  Note that both the Frequency Slot and Effective
      Frequency Slot are local terms.
NEW
   o  Effective Frequency Slot [G.870]: The effective frequency slot of
      a media channel is that part of the frequency slots of the filters
      along the media channel that is common to all of the filters'
      frequency slots.  Note that both the Frequency Slot and Effective
      Frequency Slot are local terms.

      Figure 4 shows the effect of combining two filters along a channel.
      The combination of frequency slot 1 and frequency slot 2 applied to
       the media channel is effective frequency slot shown.
END

> Nit: First nominal central frequency 'X' in Fig 5 needs to move 2

I think it is one char :-)

> Please define it before use.

Yes. Last line of section 4.

> planes are (and how they're realized/implemented) in Figure 8 would help.

Hmmm. I think the reader should be coming at this with the concepts of TE link
and LSR in their heads so that the mapping is clear.

> "transceivers" earlier - if that's the same concept, only one term

While "transponder" is technically correct, using "transceiver" would be more
consistent.

> draft prior to this point.

Penultimate paragraph of page 21.

> idnits 2.13.02 didn't find anything that needs attention.

Many thanks,
Adrian