Re: Re-Updated Draft Liaison to Q6/15

Greg Bernstein <> Tue, 10 March 2009 17:45 UTC

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Date: Tue, 10 Mar 2009 10:45:56 -0700
From: Greg Bernstein <>
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To: Adrian Farrel <>
Subject: Re: Re-Updated Draft Liaison to Q6/15
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Looks good to me!


Adrian Farrel wrote:
> 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 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
> 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)"
> "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 
> establishing:
> - 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

Dr Greg Bernstein, Grotto Networking (510) 573-2237