Re-Updated Draft Liaison to Q6/15

"Adrian Farrel" <> Tue, 10 March 2009 17:33 UTC

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From: "Adrian Farrel" <>
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Subject: Re-Updated Draft Liaison to Q6/15
Date: Tue, 10 Mar 2009 17:33:52 -0000
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Continuing to try to reach some sort of grudging consensus...


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 fact, lambda switching was the 
technology that led to the development of GMPLS 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 

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
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 

"Routing and Wavelength Assignment Information Model for Wavelength Switched 
Optical Networks"

"Routing and Wavelength Assignment Information Encoding for Wavelength 
Switched Optical Networks"

 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
   because there is sufficent margin in all impairments.
   (Original GMPLS)
2. No concern for impairments (again because there is
    sufficient margin), but lambda continuity is important.
   (The RWA problem)
3. Networks in which it is necessary to consider impairments,
   but there is sufficient margin such that approximate
   impairment estimation (using "simple" computation of the
   accumulation) could be used and still have a high
   probability that the optical path would be viable and would
   not perturb any existing paths.
4. Networks in which detailed impairment validation is
   necessary to perform a full computation of the accumulation
   of impairments including the impact on existing paths.

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 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.
   - 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, and this can be achieved within the mechanisms
   and definitions defined by the ITU-T, then this should not be
   prohibited by the CCAMP protocol mechanisms, and the
   communication of the information collected should be
   accommodated within GMPLS.

With this in mind, CCAMP is looking to Q6/15 to work as a partner in 
- The complete list of impairments suitable for this type of network,
   and the complete list of Recommendations to use as references
- The rules by which such impairments are accumulated along a path.
   That is, that CCAMP is looking for the rules by which the end-to-
   end impairments of a path may be determined from a knowldedge
   of paramters of the path and impairments on the path segments.
 - 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"

"Information Model for Impaired Optical Path Validation"

Looking forward to a profitable meeting,
Deborah Brungard and Adrian Farrel
CCAMP Working Group Co-Chairs