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

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Authors Giovanni Martinelli  , Moustafa Kattan  , Gabriele Galimberti  , Andrea Zanardi 
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CCAMP                                                 G. Martinelli, Ed.
Internet-Draft                                                 M. Kattan
Intended status: Informational                             G. Galimberti
Expires: August 27, 2013                                           Cisco
                                                         A. Zanardi, Ed.
                                                       February 23, 2013

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


   This document defines the Information Model to support Impairment-
   Aware (IA) Routing an 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 WSON.

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

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal

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   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Properties of an Impairment Information Model  . . . . . . . .  3
   3.  Background from WSON Information Model . . . . . . . . . . . .  5
   4.  Optical Impairment Information Model . . . . . . . . . . . . .  6
     4.1.  Node Information . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Link Information . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Path Information . . . . . . . . . . . . . . . . . . . . .  9
   5.  Encoding Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  Information model versus Control Plane Architectures . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     11.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  G.680 Essential information . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   In the context of Wavelength Switched Optical Network (WSON),
   [RFC6163] defines the basic framework for a GMPLS control plane.  The
   associated info model [I-D.ietf-ccamp-rwa-info] defines all
   parameters required for the related RWA process.  These references
   are the foundation but they do not consider the Optical Impairment

   In case of WSON where optical impairments plays a significant role,
   the framework document [RFC6566] defines related control plane
   architectural options for an Impairment Aware routing and wavelength
   assignment (IA-RWA).  Options include different combinations of
   Impairment Validation (IV) and RWA functions through control plane
   elements and operations (PCE, Routing, Signaling).

   This document provides the 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 is
   independent from any architectural option described by the framework
   [RFC6566]: it shall support all of them.

   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 only the linear impairment
   case.  This perfectly fit with scenario C defined in [RFC6566]
   section 4.1.1 and is considered in scope with WSON activity.  The
   non-linear case is left for further study since currently no ITU
   computational models are available for an accurate optical impairment

   The information model defined here provides a generic enough
   mechanism that could be easily extended to additional impairments

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Properties of an Impairment Information Model

   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

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   plane can deal with it 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.

   o  Time Dependency.
      This will identify how the impairment may vary with time.  There
      could be cases where there is no time dependency, while in other
      cases there may be need of impairment re- evaluation after a
      certain time.  In this category, variations in impairments due to
      environmental factors such as those discussed in [G.sup47] are
      considered.  In some cases a level of approximation will consider
      an impairment that has time dependency as constant.  In this
      Information Model we do neglect this property.

   o  Wavelength Dependency.
      This property will identify if an impairment value can be
      considered as constant over all the wavelength spectrum of
      interest or if it has different values.  Also in this case a
      detailed impairment evaluation might lead to consider the exact
      value while an approximation IV might take a constant value for
      all wavelengths.  In this Information Model we consider both case:
      dependency / not dependency from a specific wavelengths.  This
      property may appear directly in the Information model definitions
      or in the related encoding.

   o  Linearity.
      As impairments are representation of physical effects there are
      some that have a linear behavior while other are non-linear.
      Linear approximation is in scope of scenario C of [RFC6566].
      During the impairment validation process, this property implies
      that the optical effect (or quantity) satisfy the superposition
      principle, thus a final result can be calculated by the sum of
      each component.  The linearity implies the additivity of optical
      quantities considered during an Impairment Validation process.
      The non-linear effects in general does not satisfy this property.
      The information model presented in this document however, easily
      allow introduction of non-linear optical effects with a linear
      approximated contribution to the linear ones.

   o  Multi-Channel.
      There are cases where a channel's impairments take different
      values depending on the aside wavelengths already in place.  In
      this case a dependency among different LSP is introduced and is
      typically a result of linear effects.  This Information Model
      neglect this effects on neighbor LSPs.

   The following table summarize the above considerations where in the

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   first column reports the list of properties to be considered for each
   optical parameters, while second column state if this property is
   taken into account or not by this Information Model.

             |        Property       | Info Model Awareness |
             |    Time Dependency    |          no          |
             | Wavelength Dependency |          yes         |
             |       Linearity       |          yes         |
             |     Multi-channel     |          no          |

                  Table 1: Optical Impairment Properties

3.  Background from WSON Information Model

   In this section we report terms already defined for the WSON-RWA (not
   impairment aware) 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 follow:

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

   However according to [I-D.ietf-ccamp-general-constraint-encode] this
   definitions 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 node
   connectivity capability due to internal optical node constrain.  It's
   essentially a binary information and tell us if a wavelengths or a
   set of wavelengths can go from an input port to an output port.

   As a additional note, Connectivity Matrix belong to Node Information
   and is purely static.  Dynamic information related to the actual
   usage of the connections are available through specific extension to

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   link information.

4.  Optical Impairment Information Model

   The idea behind this Information Model is to reuse the concept of the
   Connectivity Matrix and defines an Impairment Matrix that summarize
   optical impairments provided by the Node and Links (i.e. fibers).

   The goal of this document is not to rephrase content from [ITU.G680]
   but only provide necessary building blocks that allow the IW-RWA
   process to apply the computational model defined by such
   recommendation.  [ITU.G680] computational models defined in section 9
   provide information to calculate the following optical parameters:

   o  OSNR.  Section 9.1

   o  Chromatic Dispersion (CD).  Section 9.2

   o  Polarization Mode Dispersion (PMD).  Section 9.3

   o  Polarization Dependent Loss (PDL).  Section 9.3

   The recommendation [ITU.G680] call its computational model "transfer
   function" and details formulas for a set of different optical
   equipments.  For the purpose of this information model, only the set
   of parameter is important.

   This Information Model makes the assumption that the each Optical
   Node in the network is able to provide it's own contribution to above
   parameters.  To this extent the Information Model intentionally
   ignore all internal detailed parameters that are used to by the
   formulas (i.e. "transfer function") but simply provide the object to
   carry results of the formulas.  However no assumption is made on how
   the Optical node get the result of parameter contribution (e.g.
   computed, provisioned, known by design, etc.).

   As an additional note, as reported in in [ITU.G680] Section 10, each
   parameter can be reported as an OSNR contribution, in such way the
   Optical Node not necessarily embed optical computational capability
   but can provide an approximated contribution to optical impairments.

   With the above considerations this Information Model provides an
   abstract view for an optical node and link to enable WSON protocol
   extension with optical impairments validation.

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4.1.  Node Information

   This model defines the Impairment Matrix as the following:

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


      MatrixID.  Is a unique identifier for the Matrix.  This ID shall
      be unique in scope among connectivity matrices defined in
      [I-D.ietf-ccamp-rwa-info] and impairment matrices defined here.

      ConnType.  This number identifies the type of matrix and it shall
      be unique in scope with other values defined by WSON documents.

      LinkSet.  Same object definition and usage as

   ImpairmentVector is defined as list of optical parameters associated
   to the internal node connection.

   <ImpairmentVector> ::= [<LinkSet>] <OPTICAL_PARAM> ...

   The optional LinkSet object enable wavelength dependency property as
   per Table 1.

   OPTICAL_PARAM is an object representing an optical parameter.  The
   Impairment vector 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 set of parameters (since
   defined elsewhere, e.g.  ITU-T), however it does not preclude
   extentions by adding new parameters.

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

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                         /        /       /       /       /       /|
                        /        /       /       /       /       / |
                       /________/_______/_______/_______/_______/  |
                      /        /       /       /       /       /| /|
                     /        /       /       /       /       / |  |
                    /________/_______/_______/_______/_______/  | /|
                   /        /       /       /       /       /| /|  |
                  /        /       /       /       /       / |  | /|
                 /________/_______/_______/_______/_______/  | /|  |
                /        /       /       /       /       /| /|  | /|
               /        /       /       /       /       / |  | /|  |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  | /|  | / 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] only defines the two
   dimensional matrix, containining only binary information, through the
   LinkSet pairsa binary information.  In this model a third dimension
   is added by generalizing the bnary information through the
   ImpairmentVector associated with each LinkSet pair.  Optical
   parameter names in the picture are reported just as an example while
   detailed definitions will go into specific encoding drafts

   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 same set of values apply to
   all LinkSet pairs.

4.2.  Link Information

   The same approach used for the Node information can be used at Link
   Level.  The Link information for WSON is extended in
   [I-D.ietf-ccamp-rwa-info].  This information model provide the
   following additional extension:

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

   DynamicLinkInfo is exactly the only already defined in
   [I-D.ietf-ccamp-rwa-info] while ImpairmentVector is defined in the
   previous section.  Is considered as optional since apply as an
   extention to existing Link information.

   In this case the list of contained optical parameters are associated
   to the link.

4.3.  Path Information

   In case of a control plane with impairment validation awareness
   there's might be cases where informations apply to the whole path and
   cannot be composed by individual contributions of links and nodes.
   The cases where this kind of information might be required are
   reported within [RFC6566] (Section 4.2.2 IV-Canditates or Sharing

   <PathInfo> ::=  <ImpairmentVector>

   [EDITOR NOTE: section to be completed].

5.  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 parameters shall be
   represented by a 32 bit floating point number.

   As an additional consideration, actual values for parameters defined
   in the information models are provided by the Optical Node and it
   could provide by direct measurement or from some internal computation
   starting from indirect measurement.  In any case the encoding shall
   provide an the possibility to associate a variance with the
   parameter.  This information will enable the function implementing
   IV-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

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6.  Information model versus Control Plane Architectures

   This section will briefly describe how the wholes set of informations
   defined by this info model will match the architectural options
   defined in [RFC6566]

   The first assumption is that the RWA-WSON extentions are available
   and operationals.  To such extent, the RWA-WSON will provide the
   following information through it's path computation (and RWA

   o  The wavelenght connectivity (considering also the connectivity
      constrains by limited reconfigurable optics).

   o  The interface compatibility at the physical level.

   o  The Optical-Elettro-Optical (OEO) availability within the network
      (and releater physical interface compatibility as here above).

   [EDITOR NOTE: to be completed]

7.  Acknowledgements


8.  Contributors

   Tim Gibbon
   Department of Physics
   Nelson Mandela Metropolitan University


9.  IANA Considerations

   This document does not contain any IANA requirement

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10.  Security Considerations

   All drafts are required to have a security considerations section.
   See RFC 3552 [RFC3552] for a guide.

11.  References

11.1.  Normative References

              International Telecommunications Union, "Physical transfer
              functions of optical network elements", ITU-
              T Recommendation G.680, July 2007.

              International Telecommunications Union, "Optical
              monitoring for dense wavelength division multiplexing
              systems", ITU-T Recommendation G.697, February 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

11.2.  Informative References

              Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "General
              Network Element Constraint Encoding for GMPLS Controlled
              Networks", draft-ietf-ccamp-general-constraint-encode-08
              (work in progress), July 2012.

              Lee, Y., Bernstein, G., Li, D., and W. Imajuku, "Routing
              and Wavelength Assignment Information Model for Wavelength
              Switched Optical Networks", draft-ietf-ccamp-rwa-info-14
              (work in progress), March 2012.

              Martinelli, G., Kattan, M., Galimberti, G., and A.
              Zanardi, "Encoding for WSON Information Model with
              Impairments Validation.",
              draft-martinelli-ccamp-wson-iv-encode-00 (work in
              progress), July 2012.

              Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs",
              draft-narten-iana-considerations-rfc2434bis-09 (work in

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              progress), March 2008.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [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.

Appendix A.  G.680 Essential information

   TBD if we need some info instead of reading [ITU.G680]

Authors' Addresses

   Giovanni Martinelli (editor)
   via Philips 12
   Monza,   20900

   Phone: +39 039 2092044

   Moustafa Kattan
   DUBAI,   500321


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   Gabriele M. Galimberti
   Via Philips,12
   Monza  20900

   Phone: +39 039 2091462

   Andrea Zanardi (editor)
   via alla Cascata 56 C, Povo
   Trento  38100


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