CCAMP G.M. Martinelli, Ed.
Internet-Draft Cisco
Intended status: Informational X.Z. Zhang, Ed.
Expires: August 05, 2014 Huawei Technologies
G.M.G. Galimberti
A. Z. Zanardi
D. S. Siracusa
february 2014

Information Model for Wavelength Switched Optical Networks (WSONs) with Impairments Validation


This document defines an information model to support Impairment-Aware (IA) Routing and Wavelength Assignment (RWA) function. This operation might be required in Wavelength Switched Optical Networks (WSON) that already support RWA and the information model defined here goes in addition and it is fully compatible with the already defined information model for impairment-free RWA process in WSON.

This information model shall support all control plane architectural options defined for WSON with impairment validation.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on August 05, 2014.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction

In the context of Wavelength Switched Optical Network (WSON), [RFC6163] describes the basic framework for a GMPLS and PCE-based Routing and Wavelength Assignment (RWA) control plane. The associated information model [I-D.ietf-ccamp-rwa-info] defines all information/parameters required by an RWA process.

There are cases of WSON where optical impairments plays a significant role and are considered as important constraints. The framework document [RFC6566] defines problem scope and related control plane architectural options for the Impairment Aware Routing and Wavelength Assignment (IA-RWA) operation. Options include different combinations of Impairment Validation (IV) and RWA functions in term of different combination of control plane functions (i.e., PCE, Routing, Signaling).

This document provides an information model for the impairment aware case to allow the impairment validation function implemented in the control plane or enabled by control plane available information. This model goes in addition to [I-D.ietf-ccamp-rwa-info] and it shall support any control plane architectural option described by the framework document (see sections 4.2 and 4.3 of [RFC6566]) where a set of control plane combinations of control plane functions vs. IV function is provided.

2. Definitions, Applicability and Properties

This section provides some concepts to help understand concepts used along the document and to make a clear sepration about what coming from data plane definitions (ITU-T G recomandations) and are taken as input for this Information Model. The first sub-section provides raw definitions while the Applicability sections reuses the defined concepts to scope this document.

2.1. Definitions

2.2. Applicability

This document targets at Scenario C defined in [RFC6566] section 4.1.1. as approximate impairment estimation. The Approximate concept refer to the fact that this Information Model cover information mainly provided by the [ITU.G680] Computational Model.

Computational models having no approximation, referred as IV-Detailed in the [RFC6566], currently does not exist in term of ITU-T recomandation. They generally refer to non-linear optical impairment and they are usually vendor specific.

The current information model does not speculate about mathematical formula used to fill up information model parameters hence, it does not preclude changing the computational model. At the same time authors does not belive this Information Model is exhaustive and if necessary further documents will cover additional models as long as they become available.

The result of RWA-IV process implementing this Information Model will result in a path (a wavelength in the data plane) that have better chance to be feasible than if it was computed without any IV function. The Existing Service Disruption, as per the definition above, would still be a problem left to network designers: this model does not replace by any means the optical network design phase. The Information Model targets, the GMPLS context with the releated relationship between data plane(s) and control plane.

2.3. Properties

An information model may have several attributes or properties that need to be defined for each optical parameter made available to the control plane. The properties will help to determine how the control plane can deal with a specific impairment parameter, depending on architectural options chosen within the overall impairment framework [RFC6566]. In some case, properties value will help to identify the level of approximation supported by the IV process.

The following table summarize the above considerations where in the first column reports the list of properties to be considered for each optical parameter, while the second column states if this property is taken into account or not by this information model.

Optical Impairment Properties
Property Info Model Awareness
Time Dependency no
Wavelength Dependency yes
Linearity yes
Multi-channel no

3. ITU-T List of Optical Parameters

[EDITOR NOTE: To better integrate material coming from ITU WD06-31 October 2013 and future liasons]

As stated by Section 2.2 this Information Model does not intend to be exaustive and targets an approximate computational model although not precluding future evolutions towards more detailed impairments estimation methods.

On the same line, ITU SG15/Q6 provides a list of optitical parameters with following observations: [ITU.G680] contains many parameters that would be required to estimate linear impairments and [ITU.G697] contains information on which parameters can be monitored in an optical network.

the problem of calculating the non-linear impairments in a multi-vendor environment is not solved. The transfer functions works only for the so called [ITU.G680] "Situation 1".
The generated list of parameters is not definitive or exaustive.

In particular,

[ITU.G671] contains some additional parameters defintions required by here above recomandation.

The list of optical parameters starts from [ITU.G680] Section 9 which provides the optical computational models for the following:

OSNR. Section 9.1
Optical Power. As per Section 9.1, required by Optical Computation Model for OSNR calculation.
Chromatic Dispersion (CD). Section 9.2
Polarization Mode Dispersion (PMD). Section 9.3
Polarization Dependent Loss (PDL). Section 9.3

In addition to the above, the following list of parameters has been mentioned by ITU SG15/Q6.

Channel Frequency Range [ITU.G671].
Channel Signal-Spontaneous noise figure. This is considered within OSNR computational model above.
Differential Group Delay [ITU.G671]. Required for PMD above.
Channel extintion.
Non-Linear Coefficient (for a fibre segment). Needed for non-linear impairment

4. Background from WSON-RWA Information Model

In this section we report terms already defined for the WSON-RWA (impairment free) as in [I-D.ietf-ccamp-rwa-info] and [I-D.ietf-ccamp-general-constraint-encode]. The purpose is to provide essential information that will be reused or extended for the impairment case.

In particular [I-D.ietf-ccamp-rwa-info] defines the connectivity matrix as the following:

ConnectivityMatrix ::= <MatrixID> <ConnType> <Matrix>

According to [I-D.ietf-ccamp-general-constraint-encode], this definition is further detailed as:

ConnectivityMatrix ::= 
      <MatrixID> <ConnType> ((<LinkSet> <LinkSet>) ...)

This second formula highlights how the connectivity matrix is built by pairs of LinkSet objects identifying the internal connectivity capability due to internal optical node constraint(s). It's essentially binary information and tell if a wavelength or a set of wavelengths can go from an input port to an output port.

As an additional note, connectivity matrix belongs to node information and is purely static. Dynamic information related to the actual usage of the connections is available through specific extension to link information.

Furthermore [I-D.ietf-ccamp-rwa-info] define the resource block as follow:

 ResourceBlockInfo ::= <ResourceBlockSet> [<InputConstraints>]
   [<ProcessingCapabilities>] [<OutputConstraints>]

Which is an efficient way to model constrains of a WSON node.

5. Optical Impairment Information Model

The idea behind this information model is to categorize the impairment parameters into three types and extend the information model already defined for impairment-free WSONs. The three categories are:

All the above three categories will make use of a generic container, the Impairment Vector, to transport optical impairment information.

This information model however will allow however to add additional parameters beyond the one defined by [ITU.G680] in order to support additional computational models. This mechanism could eventually applicable to both linear and non-linear parameters.

This information model makes the assumption that the each optical node in the network is able to provide the control plane protocols with its own parameter values however, no assumption is made on how the optical node gets those value information (e.g. internally computed, provisioned by a network management system, etc.). To this extent, the information model intentionally ignores all internal detailed parameters that are used by the formulas of the Optical Computational Model (i.e., "transfer function") and simply provides the object containers to carry results of the formulas.

5.1. The Optical Impairment Vector

Optical Impairment Vector (OIV) is defined as a list of optical parameters to be associated to a WSON node or a WSON link. It is defined as:

<OIV> ::= ([<LabelSet>] <OPTICAL_PARAM>) ...

The optional LabelSet object enables wavelength dependency property as per Table 1. LabelSet has its definition in [I-D.ietf-ccamp-general-constraint-encode].

OPTICAL_PARAM. This object represents an optical parameter. The Impairment vector can contain a set of parameters as identified by [ITU.G697] since those parameters match the terms of the linear impairments computational models provided by [ITU.G680]. This information model does not speculate about the set of parameters (since defined elsewhere, e.g. ITU-T), however it does not preclude extentions by adding new parameters.

5.2. Node Information

5.2.1. Impairment Matrix

Impairment matrix describes a list of the optical parameters that applies to a network element as a whole or ingress/egress port pairs of a network element. Wavelength dependency property of optical paramters is also considered.

ImpairmentMatrix ::=  <MatrixID> <ConnType> 
      ((<LinkSet> <LinkSet> <OIV>) ...)


The model can be represented as a multidimensional matrix shown in the following picture

                      /        /       /       /       /       /|
                     /        /       /       /       /       / |
                    /________/_______/_______/_______/_______/  |
                   /        /       /       /       /       /| /|
                  /        /       /       /       /       / |  |    
                 /________/_______/_______/_______/_______/  | /|
                /        /       /       /       /       /| /|  |
               /        /       /       /       /       / |  | /|   
              /________/_______/_______/_______/_______/  | /|  |
             /        /       /       /       /       /| /|  | /|
            /        /       /       /       /       / |  | /|  |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  | /|  | / PDL
<LinkSet#1> |   -   |       |       |       |       | /|  | /|/
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  | /|  /
<linkSet#2> |       |   -   |       |       |       | /|  | / PND
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  | /|/
<linkSet#3> |       |       |   -   |       |       | /|  /
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  | / Chr.Disp.
<linkSet#4> |       |       |       |   -   |       | /|/
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  /
<linkSet#5> |       |       |       |       |   -   | / OSNR
             <LS#1>  <LS#2>  <LS#3>  <LS#4>  <LS#5>

The connectivity matrix from [I-D.ietf-ccamp-general-constraint-encode] is only a two dimensional matrix, containing only binary information, through the LinkSet pairs. In this model, a third dimension is added by generalizing the binary information through the Optical Impairment Vector associated with each LinkSet pair. Optical parameters in the picture are reported just as examples while details go into specific encoding draft [I-D.martinelli-ccamp-wson-iv-encode].

This representation shows the most general case however, the total amount of information transported by control plane protocols can be greatly reduced by proper encoding when the same set of values apply to all LinkSet pairs.

[EDITOR NODE: first run of the information model does looks for generality not for optimizing the quantity of information. We'll deal with optimization in a further step.]

5.2.2. Impariment Resource Block Information

This information model reuse the definition of Resource Block Information adding the associated impairment vector.

 ResourceBlockInfo ::= <ResourceBlockSet> [<InputConstraints>]
   [<ProcessingCapabilities>] [<OutputConstraints>] [<OIV>]

The object ResourceBlockInfo is than used as specified within [I-D.ietf-ccamp-rwa-info].

5.3. Link Information

For the list of optical parameters associated to the link, the same approach used for the node-specific impairment information can be applied. The link-specific impairment information is extended from [I-D.ietf-ccamp-rwa-info] as the following:

<DynamicLinkInfo> ::=  <LinkID> <AvailableLabels>
        [<SharedBackupLabels>] [<OIV>]

DynamicLinkInfo is already defined in [I-D.ietf-ccamp-rwa-info] while OIV is the Optical Impairment Vector is defined in the previous section.

5.4. Path Information

There are cases where the optical impariments can only be described as a contrains on the overall end to end path. In such case, the optical impariment and/or parameter, cannot be derived (using a simple function) from the set of node / link contributions.

An equivalent case is the option reported by [RFC6566] on IV-Candidate paths where, the control plane knows a list of optically feasible paths so a new path setup can be selected among that list. Independent from the protocols and functions combination (i.e. RWA vs. Routing vs. PCE), the IV-Candidates imply a path property stating that a path is optically feasible.

<PathInfo> ::=  <OIV>

[EDITOR NOTE: section to be completed, especially to evaluate protocol implications. Likely resemble to RSVP ADSPEC].

6. Encoding Considerations

Details about encoding will be defined in a separate document [I-D.martinelli-ccamp-wson-iv-encode] however worth remembering that, within [ITU.G697] Appending V, ITU already provides a guideline for encoding some optical parameters.

In particular [ITU.G697] indicates that each parameter shall be represented by a 32 bit floating point number.

Values for optical parameters are provided by optical node and it could provide by direct measurement or from some internal computation starting from indirect measurement. In such cases could be useful to un understand the variance associated with the value of the optical parmater hence, the encoding shall provide the possibility to include a variance as well.

This kind of information will enable IA-RWA process to make some additional considerations on wavelength feasibility. [RFC6566] Section 4.1.3 reports some considerations regarding this degree of confidence during the impairment validation process.

7. Control Plane Architectures

This section briefly describes how the defintions contained in this information model will match the architectural options described by [RFC6566].

The first assumption is that the WSON GMPLS extentions are available and operational. To such extent, the WSON-RWA will provide the following information through its path computation (and RWA process):

7.1. IV-Centralized

Centralized IV process is performed by a single entity (e.g., a PCE). Given sufficient impairment information, it can either be used to provide a list of paths between two nodes, which are valid in terms of optical impairments. Alternatively, it can help validate whether a particular selected path and wavelength is feasiable or not. This requires distribution of impairment information to the entity performing the IV process.

[EDITOR NOTE: to be completed]

7.2. IV-Distributed

For the distributed IV process, common computational models are needed together with the information model defined in this document. Computational models for the optical impairments are defined by ITU standard body. The currently available computation models are reported in [ITU.G680] and only cover the linear impairment case. This does not require the distribution of impairment information since they can be collected hop-by-hop using a control plane signaling protocol.

[EDITOR NOTE: to be completed]

8. Acknowledgements

Authors would like to thank ITU SG15/Q6 and in particular Pete Anslow for providing text and information to CCAMP through join meetings and liasons.

9. Contributing Authors

This document was the collective work of several authors. The text and content of this document was contributed by the editors and the co-authors listed below (the contact information for the editors appears in appropriate section and is not repeated below):


Moustafa Kattan
DUBAI,   500321


Young Lee 
1700 Alma Drive, Suite 100 
Plano, TX  75075 

Phone: +1 972 509 5599 x2240 
Fax:   +1 469 229 5397 

Greg M. Bernstein
Grotto Networking
Fremont, CA

Phone: +1 510 573 2237
Fatai Zhang 
F3-5-B R&D Center, Huawei Base 
Bantian, Longgang District 
P.R. China 
Phone: +86-755-28972912 

Federico Pederzolli
via alla Cascata 56/D, Povo
Trento  38123



10. IANA Considerations

This document does not contain any IANA requirement.

11. Security Considerations

This document defines an information model for impairments in optical networks. If such a model is put into use within a network it will by its nature contain details of the physical characteristics of an optical network. Such information would need to be protected from intentional or unintentional disclosure.

12. References

12.1. Normative References

[ITU.G671] International Telecommunications Union, "Transmission characteristics of optical components and subsystems ", ITU-T Recommendation G.671, February 2012.
[ITU.G680] International Telecommunications Union, "Physical transfer functions of optical network elements ", ITU-T Recommendation G.680, July 2007.
[ITU.G697] International Telecommunications Union, "Optical monitoring for dense wavelength division multiplexing systems ", ITU-T Recommendation G.697, February 2012.

12.2. Informative References

[RFC6163] Lee, Y., Bernstein, G. and W. Imajuku, "Framework for GMPLS and Path Computation Element (PCE) Control of Wavelength Switched Optical Networks (WSONs)", RFC 6163, April 2011.
[RFC6566] Lee, Y., Bernstein, G., Li, D. and G. Martinelli, "A Framework for the Control of Wavelength Switched Optical Networks (WSONs) with Impairments", RFC 6566, March 2012.
[I-D.ietf-ccamp-rwa-info] Lee, Y., Bernstein, G., Li, D. and W. Imajuku, "Routing and Wavelength Assignment Information Model for Wavelength Switched Optical Networks", Internet-Draft draft-ietf-ccamp-rwa-info-19, November 2013.
[I-D.ietf-ccamp-general-constraint-encode] Bernstein, G., Lee, Y., Li, D. and W. Imajuku, "General Network Element Constraint Encoding for GMPLS Controlled Networks", Internet-Draft draft-ietf-ccamp-general-constraint-encode-13, November 2013.
[I-D.martinelli-ccamp-wson-iv-encode] Martinelli, G., Zanardi, A., Zhang, X., Galimberti, G. and D. Siracusa, "Information Encoding for WSON with Impairments Validation", Internet-Draft draft-martinelli-ccamp-wson-iv-encode-02, July 2013.

Appendix A. ITU-T Liason Tracking

[EDITOR NOTE: appendix reserved to track liason to/from ITU related to this draft]

Authors' Addresses

Giovanni Martinelli (editor) Cisco via Philips 12 Monza, 20900 Italy Phone: +39 039 2092044 EMail:
Xian Zhang (editor) Huawei Technologies F3-5-B R&D Center, Huawei Base Bantian, Longgang District Shenzen, 518129 P.R. China Phone: +86 755 28972465 EMail:
Gabriele M. Galimberti Cisco Via Philips,12 Monza, 20900 Italy Phone: +39 039 2091462 EMail:
Andrea Zanardi CREATE-NET via alla Cascata 56/D, Povo Trento, 38123 Italy EMail:
Domenico Siracusa CREATE-NET via alla Cascata 56/D, Povo Trento, 38123 Italy EMail: