Hi Adrian and all. I tried fixing the text to meet Malcolm's issues and
added some more specific questions. On the measurement side of things,
I think it is premature to either include or exclude. If we are
starting with impairment aware routing and wavelength assignment (a
form of constrained path estimation) then we can assume that the
impairment parameters are given to us for the purpose of estimation of
impairment impacts.
I've seen some recent drafts that present some concrete and reasonable
uses of the control plane in optical measurements, however these have
not been discussed and hence doesn't seem appropriate to include in the
Q6 discussions this time around.
Cheers
Greg
P.S. View in HTML mode since I tried using the "strike through" feature
to indicate deletions.
Adrian Farrel wrote:
Hi,
Had some comments off-list.
New version with minor changes...
===
Dear Peter,
CCAMP experts are looking forward to our joint meeting with Q6/5 on
March 20th to discuss optical impairments and the control plane
operation of wavelength switched optical networks (WSONs).
This liaison is to summarise the activity within CCAMP on this subject
so far and to set out our objectives for this work.
As you will be aware, the GMPLS control plane is designed to provide a
dynamic control plane for a variety of switching technologies. Amongst
these is the "lambda switch capable" data plane where devices are OEOs,
ROADMs, and photonic cross-connects (PXCs). In
---------------------------------------------------------------------------GMPLS-----------------------------------
fact, lambda switching was the technology that led to the
development of MPLS from the packet switching MPLS
control plane.
The IETF's CCAMP working group is the design authority for all
extensions to the GMPLS family of protocols.
The original work on lambda switching networks within CCAMP recognised
that there is a subset of optical networks in which it is possible to
disregard optical impairments and where the number of regeneration
points is high. In these environments, path computation can be
performed on a reachability graph, and lambda conversion can be
performed as necessary within the network.
As PXCs were introduced into WSONs, it remained the case that optical
impairments could be disregarded by the control plane. Where necessary,
optimal impairment-aware paths could be computed off-line and supplied
to the control plane, leaving the control plane to handle establishment
of connections and recovery after failure. Failure recovery scenarios
might lead to contention for wavelengths or suboptimal optical paths,
but these could be handled by crankback within the signaling protocol.
More recent work on WSONs indicates that the proportion of pure optical
devices (ROADMs and PXCs) is increasing. This means that it is
necessary to compute paths that offer end-to-end lambda continuity.
This problem (called the routing and wavelength assignment (RWA)
problem) must be solved, and may be compounded by devices with limited
cross-connect capabilities (for example, with glass-through, a limited
OEO matrix, or restricted port-to-port capabilities). In approaching
this problem it is convenient if there is a common identification
scheme for wavelengths across the whole network (previously, wavelength
identification was a local matter between the nodes at the ends of each
link). To aid with this, the CCAMP working group has developed
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-g-694-lambda-labels-03.txt
that provides a protocol-independent encoding for wavelengths in a way
that is compliant with G.694. Further work on this problem space can be
seen in the following CCAMP documents:
"Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON)"
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-rwa-wson-framework-01.txt
"Routing and Wavelength Assignment Information Model for Wavelength
Switched Optical Networks"
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-rwa-info-01.txt
"Routing and Wavelength Assignment Information Encoding for Wavelength
Switched Optical Networks"
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-rwa-wson-encode-00.txt
CCAMP participants have further identified cases where they believe it
would be helpful to consider optical impairments during the control
plane operation of a WSON. This gives rise to four distinct deployment
scenarios:
1. No concern for impairments or lambda continuity.
(Original GMPLS)
2. No concern for impairments, but lambda continuity is
important. (The RWA problem)
3. Concern for "basic" impairments
--> Or Networks in which approximate impairment estimation is
sufficient
4. Concern for "advanced" impairments
--> Or Networks in which detail impairment validation is necessary
In focusing on the third of these categories, CCAMP intends to base its
work on G.680 and related recommendations with the following
understanding:
- G.680 (et al.) provides a complete list of simple constraints
Better - G.680 (et al) provides us with the definitions of optical
impairments, optical parameters, and insights into their use
- Where G.680 refers to "single vendor" domains, it does
not
mean single manufacturer, but rather "single system integrator".
That is, the equipment is not "plug and play", but has been
tested to interoperate and the network has been planned.
- There is no requirement to measure impairments.
- The initial focus of our work is on the constraints imposed by
optical impairments on path selection. The parameters characterizing
these impairments are assumed to be given. We do not currently address
how these parameters are originally measured or estimated. It is for
further study whether the control plane has a role in the measurement
of optical parameters.
- Many networks are engineered such that
configured
impairment values are enough information
- Measuring can often produce ambiguous values
- Equipment to perform measurement may be expensive
However, if an implementer chooses to measure impairments
on their device, this should not be prohibited, and should be
accommodated.
With this in mind, CCAMP is looking to Q6/15 to work as a partner in
establishing:
- the complete list of impairments suitable for this type of network
- whether these parameters are "NE wide", or exhibit
dependencies on a per port or a "port-to-port" basis.
- frequency/wavelength dependency of parameters, if any, and
recommended interpolation functions.
- and the complete list of Recommendations to use as
references
- depending upon the computational model the rules by which such
impairments are accumulated along a path
- the rules by which such impairments are
accumulated along a path
- generic encodings and ranges of values for the impairments
For reference, some early work on impairment-aware GMPLS is listed
below. This work is not yet adopted as CCAMP work, but is likely to
form the basis of such work once we have discussed the way forward with
Q6/15.
"A Framework for the Control of Wavelength Switched Optical Networks
(WSON) with Impairments"
http://www.ietf.org/internet-drafts/draft-bernstein-ccamp-wson-impairments-02.txt
"Information Model for Impaired Optical Path Validation"
http://www.ietf.org/internet-drafts/draft-bernstein-wson-impairment-info-00.txt
Looking forward to a profitable meeting,
Deborah Brungard and Adrian Farrel
CCAMP Working Group Co-Chairs
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Dr Greg Bernstein, Grotto Networking (510) 573-2237
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