Re: Updated Draft Liaiosn to Q6/15

Greg Bernstein <> Tue, 10 March 2009 16:43 UTC

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Date: Tue, 10 Mar 2009 09:43:15 -0700
From: Greg Bernstein <>
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To: Adrian Farrel <>
Subject: Re: Updated Draft Liaiosn to Q6/15
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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 
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.



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
> 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
> 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.
>   (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"
> "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