Subject: [CCAMP] WSON Impairment scenarios -- control plane perspective...

From: Greg Bernstein <[email-masked]>
Date: Wed, 29 Jul 2009 07:30:53 +0200

Hi folks, there seemed to be some questions about where we could get 
started with WSON impairments. On reviewing the Impairment Framework 
draft, it seems like we've got a lot of bases covered but we aren't 
explicit about one could get started dealing with optical impairments.

Below is a short analysis with somewhat "loose" language. Some of this 
could potentially be useful in a liaison to ITU-T Q6.

Comments welcome.

Greg B.

  *Impairment Estimation Categories and the Control Plane*

    Opaque WSON with respect to Impairments

In this case we are given a list of qualified paths between a desired 
source and destination of a connection. These paths may come with 
wavelength restrictions due to impairments (not related to wavelength 
availability in RWA process).

We do not know anything about how these viable paths are computed. We 
don't know and shouldn't care if the impairments are linear or non-linear.

We are assured that if we select one of these paths and assign a 
wavelength to it then the establishment of this connection will not 
impact previously established connections in the network. 

Example usage: a single vendor supplies WDM line systems and ROADMs. We 
wish to use a GMPLS control plane and perhaps PCE based optimization but 
not all paths through the network are viable due to impairments.

ITU-T Q6 implications: My guess it that the Q6 folks would not care 
about this case since this doesn't really call for standardization of 
impairment parameters or procedures.

CCAMP implications: This seems like a very practical case for the 
control plane. We would only want to standardize the way in which we 
obtain the list of qualified paths. */No impairment information model is 
needed here/*. An architecture reflecting this option is already in the 
Impairment Framework draft.

    Partially Opaque WSON

In this case the impairment behavior of certain elements of the WSON can 
be suitably modeled via standardized techniques, e.g., G.680 while other 
parts of the WSON are not. The entity responsible for these other parts 
of the WSON imports the characteristics of these "open" elements and 
uses them as part of a viable path computation process, the details of 
which are opaque to the control plane.

We are assured that if we select one of these paths and assign a 
wavelength to it then the establishment of this connection will not 
impact previously established connections in the network. 

Example usage: The characteristics of the WDM line systems are not 
specified, but well characterized ROADMs are used in the WSON. The WDM 
line system vendor uses these characteristics in its 
internal/proprietary viable path computations.

Q6 and CCAMP implications: here we would be using a standardize 
information model for the "open" WSON network elements. How the other 
"opaque" network elements are characterized and how viable path 
computation is carried out is out of scope of either SDO. Such an 
approach takes advantage of standardized impairment models where it can. 
Implications for CCAMP would be an impairment information model and an 
interface for requesting/receiving qualified paths. An architecture that 
can support this case is already contained in the WSON impairment 
framework draft.

    Linearly Approximated Open WSON Impairment Model

In this case the impairment aspects of the WSON can be well approximated 
by standardized (or to be standardized) "linear" models such as those 
found in G.680. From these models the viability of paths can be evaluated.

We are assured that if we select one of these paths and assign a 
wavelength to it then the establishment of this connection will not 
impact previously established connections in the network. 

Implications for Q6: Current impairment models such as recent version of 
G.680 do not include models for WDM line systems.

Implications for CCAMP: An impairment information model is needed. 
Distributed impairment validation (via signaling) could be possible.

General comments: it would seem to be the responsibility of the WSON 
network designer to insure that the network is operating in a "region" 
where these linear approximations for impairments are valid. This seems 
beyond the purview of a standards organization to specify.

An architecture to accommodate this case is contained in the WSON 
impairment framework draft.

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

---

From: Giovanni Martinelli <[email-masked]>
Date: Sat, 01 Aug 2009 00:08:24 +0200

Hi Greg,

thx for the text, very useful. Few initial comments hoping discussion 
will continue with other contribution as well.

first a terminology consideration about opaque, Don't have a better 
suggestion right now but not sure the term usage.  "Opaque"  is the path 
validation procedure (if any) respect to the control plane? 

plus few others comments inline

Greg Bernstein wrote:
> Example usage: a single vendor supplies WDM line systems and ROADMs. 
> We wish to use a GMPLS control plane and perhaps PCE based 
> optimization but not all paths through the network are viable due to 
> impairments.
>
> obtain the list of qualified paths. */No impairment information model 
> is needed here/*. An architecture reflecting this option is already in 
> the Impairment Framework draft.
>
Agree with all the above. The only point is that probably the fact of 
having a set of qualified path does not preclude the need of having 
impairment considerations as well (sort of mixed solutions).

I  mean, your text above does not preclude it but I want just to make 
the point clear.

>     Partially Opaque WSON
>
> In this case the impairment behavior of certain elements of the WSON 
> can be suitably modeled via standardized techniques, e.g., G.680 while 
> other parts of the WSON are not. The entity responsible for these 
> other parts of the WSON imports the characteristics of these "open" 
> elements and uses them as part of a viable path computation process, 
> the details of which are opaque to the control plane.
>
I would apply here the same as below "this is beyond a purview of a 
standard organization to specify".

> approach takes advantage of standardized impairment models where it can.
just to clarify "standardized impairment model", are you referring to 
G.680 or something else?

> interface for requesting/receiving qualified paths. An architecture 
> that can support this case is already contained in the WSON impairment 
> framework draft.
>
>
> In this case the impairment aspects of the WSON can be well 
> approximated by standardized (or to be standardized) "linear" models 
> such as those found in G.680. From these models the viability of paths 
> can be evaluated.
>
> Implications for Q6: Current impairment models such as recent version 
> of G.680 do not include models for WDM line systems.
>
why this? Isn't a line system a  de-generated case of an ROADM  (1 
ingress, 1  egress)?

thx
G

> where these linear approximations for impairments are valid. This 
> seems beyond the purview of a standards organization to specify.
>
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