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Versions: (draft-martinelli-ccamp-wson-iv-info) 00 01 02 03 04 05

CCAMP                                                 G. Martinelli, Ed.
Internet-Draft                                                     Cisco
Intended status: Informational                             X. Zhang, Ed.
Expires: January 2, 2018                             Huawei Technologies
                                                           G. Galimberti
                                                                   Cisco
                                                              A. Zanardi
                                                             D. Siracusa
                                                           F. Pederzolli
                                                              CREATE-NET
                                                                  Y. Lee
                                                                F. Zhang
                                                     Huawei Technologies
                                                               July 2017


Information Model for Wavelength Switched Optical Networks (WSONs) with
                         Impairments Validation
                    draft-ietf-ccamp-wson-iv-info-05

Abstract

   This document defines an information model to support Impairment-
   Aware (IA) Routing and Wavelength Assignment (RWA) functionality.
   This information model extends the information model for impairment-
   free RWA process in WSON to facilitate computation of paths where
   optical impairment constraints need to considered.

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 http://datatracker.ietf.org/drafts/current/.

   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 January 2, 2018.







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Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) 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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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions, Applicability and Properties . . . . . . . . . .   3
     2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Applicability . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Properties  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  ITU-T List of Optical Parameters  . . . . . . . . . . . . . .   6
   4.  Background from WSON-RWA Information Model  . . . . . . . . .   9
   5.  Optical Impairment Information Model  . . . . . . . . . . . .  10
     5.1.  The Optical Impairment Vector . . . . . . . . . . . . . .  10
     5.2.  Node Information  . . . . . . . . . . . . . . . . . . . .  11
       5.2.1.  Impairment Matrix . . . . . . . . . . . . . . . . . .  11
       5.2.2.  Impairment Resource Block Information . . . . . . . .  12
     5.3.  Link Information  . . . . . . . . . . . . . . . . . . . .  13
     5.4.  Path Information  . . . . . . . . . . . . . . . . . . . .  13
   6.  Encoding Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Control Plane Architectures . . . . . . . . . . . . . . . . .  14
     7.1.  IV-Centralized  . . . . . . . . . . . . . . . . . . . . .  14
     7.2.  IV-Distributed  . . . . . . . . . . . . . . . . . . . . .  15
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     11.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  FAQ  . . . . . . . . . . . . . . . . . . . . . . . .  17
     A.1.  Why the Application Code does not suffice for Optical
           Impairment Validation?  . . . . . . . . . . . . . . . . .  17
     A.2.  Are DWDM network multivendor? . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18





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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 [RFC7446] defines information/parameters
   required by an RWA process without optical impairment considerations.

   There are cases of WSON where optical impairments play a significant
   role and are considered as important constraints.  The framework
   document [RFC6566] defines the problem scope and related control
   plane architectural options for the Impairment Aware RWA (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).

   A Control Plane with RWA-IA will not be able to solve the optical
   impairment problem in a detailed and exhaustive way, however, it may
   take advantage of some data plane knowledge to make better decisions
   during its path computing phase.  The final outcome will be a path,
   instantiated through a wavelength in the data plane, that has a
   "better chance" to work than that path were calculated without IA
   information.  "Better chance" means that path setup may still fail
   and the GMPLS control plane will follow its usual procedures upon
   errors and failures.  A control plane will not replace a the network
   design phase that remains a fundamental step for DWDM Optical
   Networks.  As the non-linear impairments which need to be considered
   in the calculation of an optical path will be vendor-dependent, the
   parameters considered in this document is not an exhaustive list.

   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 [RFC7446] and 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
   combinations of control plane functions vs. IV function is provided.

2.  Definitions, Applicability and Properties

   This section provides some concepts to help understand the model and
   to make a clear separation from data plane definitions (ITU-T
   recommendations).  The first sub-section provides definitions while
   the Applicability sections uses the defined definitions to scope this
   document.






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2.1.  Definitions

   o  Computational Model / Optical Computational Model.
      Defined by ITU standard documents.  In this context we look for
      models able to compute optical impairments for a given lightpath.

   o  Information Model.
      Defined by IETF (this document) and provides the set of
      information required by control plane to apply the Computational
      Model.

   o  Level of Approximation.
      This concept refers to the Computational Model as it may compute
      optical impairment with a certain level of uncertainty.  This
      level is generally not measured but [RFC6566] Section 4.1.1
      provides a rough classification about it.

   o  Feasible Path.
      It is the output of the C-SPF with RWA-IV capability.  It's an
      optical path that satisfies optical impairment constraints.  The
      path, instantiated through wavelength(s), may actually work or not
      work depending of the level of approximation.

   o  Existing Service Disruption.
      An effect known to optical network designers is the cross-
      interaction among spectrally adjacent wavelengths: an existing
      wavelength may experience increased BER due to the setup of an
      adjacent wavelength.  Solving this problem is a typical optical
      network design activity.  Just as an example, a simple solution is
      adding optical margins (e.g., additional OSNR), although complex
      and detailed methods exist.

   o  DWDM Line Segments.
      [ITU.G680] provides definition and picture for the "Situation 1"
      DWDM Line segments: " Situation 1 - The optical path between two
      consecutive 3R regenerators is composed of DWDM line segments from
      a single vendor and OADMs and PXCs from another vendor".  Document
      [RFC6566] Figure 1 shows an LSP composed by two DWDM line segments
      according to [ITU.G680] definition.

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 covers
   information mainly provided by [ITU.G680] Computational Model.





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

   The Information Model defined in this document does not speculate
   about the mathematical formulas used to fill up information model
   parameters, hence it does not preclude changing the computational
   model.  At the same time, the authors do not believe this Information
   Model is exhaustive and if necessary further documents will cover
   additional models after they become available.

   The result of RWA-IV process implementing this Information Model is a
   path (and a wavelength in the data plane) that has 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 a network design phase.

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.

   o  Time Dependency
      This identifies how an impairment parameter may vary with time.
      There could be cases where there is no time dependency, while in
      other cases there may be need of re-evaluation after a certain
      time.  In this category, variations in impairments due to
      environmental factors such as those discussed in [ITU.GSUP47] are
      considered.  In some cases, an impairment parameter that has time
      dependency may be considered as a constant for approximation.  In
      this information model, we do neglect this property.

   o  Wavelength Dependency
      This property identifies if an impairment parameter can be
      considered as constant over all the wavelength spectrum of
      interest or not.  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 / no
      dependency on a specific wavelength.  This property appears
      directly in the information model definitions and related
      encoding.



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   o  Linearity
      As impairments are representation of physical effects, there are
      some that have a linear behaviour 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) satisfies 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 do 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, this
      is mostly due to non-linear impairments.  The result would be a
      dependency among different LSPs sharing the same path.  This
      information model do not consider this kind of property.

   The following table summarise 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.

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

                  Table 1: Optical Impairment Properties

3.  ITU-T List of Optical Parameters

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

   On the same line, ITU SG15/Q6 provides (through [LS78]) a list of
   optical parameters with following observations:





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   (a)  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".

   (b)  The generated list of parameters is not exhaustive however
        provide a guideline for control plane optical impairment
        awareness.

   In particular, [ITU.G680] contains many parameters that would be
   required to estimate linear impairments.  Some of the Computational
   Models defined within [ITU.G680]  requires parameters defined in
   other documents like [ITU.G671].  The purpose of the list here below
   makes this match between the two documents.

   [ITU.G697] defines parameters can be monitored in an optical network.
   This Information Model and associated encoding document will reuse
   [ITU.G697]  parameters identifiers and encoding for the purpose of
   path computation.

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

   G-1  OSNR.  Section 9.1

   G-2  Chromatic Dispersion (CD).  Section 9.2

   G-3  Polarization Mode Dispersion (PMD).  Section 9.3

   G-4  Polarization Dependent Loss (PDL).  Section 9.3

   In addition to the above, the following list of parameters has been
   mentioned by [LS78]:

   L-1   "Channel frequency range", [ITU.G671].  This parameter is part
         of the application code and encoded through Optical Interface
         Class as defined in [RFC7446].

   L-2   "Modulation format and rate".  This parameter is part of the
         application code and encoded through Optical Interface Class as
         defined in [RFC7446].

   L-3   "Channel power".  Required by G-1.

   L-4   "Ripple".  According to [ITU.G680], this parameter can be taken
         into account as additional OSNR penalty.

   L-5   "Channel signal-spontaneous noise figure", [ITU.G680].
         Required by OSNR calculation (see G-1) above.



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   L-6   "Channel chromatic dispersion (for fibre segment or network
         element)".  Already in G-2 above.

   L-7   "Channel local chromatic dispersion (for a fibre segment)".
         Already in G-2 above (since consider both local and fiber
         dispersions).

   L-8   "Differential group delay (for a network element)", [ITU.G671].
         Required by G-3.

   L-9   "Polarisation mode dispersion (for a fibre segment)",
         [ITU.G650.2], [ITU.G680].  Defined above as G-3.

   L-10  "Polarization dependent loss (for a network element)",
         [ITU.G671] and [ITU.G680].  Defined above as G-4.

   L-11  "Reflectance".  From [ITU.G671] Section 3.2.2.37 is the ratio
         of reflected power Pr to incident power Pi at a given port of a
         passive component, for given conditions of spectral
         composition, polarization and geometrical distribution.
         Generally expressed in dB.  Might be monitored in some critical
         cases.  We neglect this effect as first approximation.

   L-12  "Channel Isolation".  From [ITU.G671] Section 3.2.2.2 (Adjacent
         Channel Isolation) and Section 3.2.2.29 (Non Adjacent Channel
         Isolation).  Document [ITU.GSUP39] provide the formula for
         calculation as channel cross-talk and measure it in dB.  This
         parameterer shall be considered for path computation.

   L-13  "Channel extinction".  From [ITU.G671] Section 3.2.2.9 needed
         for Interferometric Crosstalk.  Document [ITU.GSUP39] has the
         formula for penalty computation.  Unit of measurement is dB.

   L-14  "Attenuation coefficient (for a fibre segment)".  Document
         [ITU.G650.1] Section 3.6.2.  The unit of measure is dB.  This
         is a typical link parameter (as associated to a fiber).

   L-15  "Non-linear coefficient (for a fibre segment)", [ITU.G650.2].
         Required for Non-Linear Optical Impairment Computational
         Models.  Neglected by this document.

   The final list of parameters is G-1, G-2, G-3, G-4, L-3, L-4, L-5,
   L-8, L-12, L-13, L-14.








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4.  Background from WSON-RWA Information Model

   In this section we report terms already defined for the WSON-RWA
   (impairment free) as in [RFC7446] and [RFC7579].  The purpose is to
   provide essential information that will be reused or extended for the
   impairment case.

   In particular [RFC7446] Section 4.1 defines the ConnectivityMatrix
   and states that such matrix does not represent any particular
   internal blocking behaviour but indicates which input ports and
   wavelengths could possibly be connected to a particular output port.


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


   According to [RFC7579], this definition is further detailed as:


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


   This second formula highlights how the ConnectivityMatrix 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, ConnectivityMatrix belongs to node
   information, is uniquely identified by advertising node and is a
   static information.  Dynamic information related to the actual state
   of connections is available through specific extension to link
   information.

   The [RFC7446] introduces the concept of ResourceBlockInfo and
   ResourcePool for the WSON nodes.  The resource block is a collection
   of resources behaving in the same way and having similar
   characteristics.  The ResourceBlockInfo is defined as follow:


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


   The usage of resource block and resource pool is an efficient way to
   model constrains within a WSON node.




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5.  Optical Impairment Information Model

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

   o  Node Information.  The concept of connectivity matrix is reused
      and extended to introduce an impairment matrix, which represents
      the impairments suffered on the internal path between two ports.
      In addition, the concept of Resource Block is also reused and
      extended to provide an efficient modelization of per-port
      impairment.

   o  Link Information representing impairment information related to a
      specific link or hop.

   o  Path Information representing the impairment information related
      to the whole path.

   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 nodes get 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>) ...






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   The optional LabelSet object enables wavelength dependency property
   as per Table 1.  LabelSet has its definition in [RFC7579].

   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
   parameters is also considered.


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


   Where:

      MatrixID.  This ID is a unique identifier for the matrix.  It
      shall be unique in scope among connectivity matrices defined in
      [RFC7446] 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 impairment-free
      WSON documents.

      LinkSet.  Same object definition and usage as [RFC7579].  The
      pairs of LinkSet identify one or more internal node constrain.

      OIV.  The Optical Impairment Vector defined above.

   The model can be represented as a 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 [RFC7579] 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 an example: proper list and encoding shall be
   defined by other documents.

   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.

5.2.2.  Impairment Resource Block Information

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


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




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   The object ResourceBlockInfo is than used as specified within
   [RFC7446].

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
   [RFC7446] as the following:


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


   DynamicLinkInfo is already defined in [RFC7446] while OIV is the
   Optical Impairment Vector is defined in the previous section.

5.4.  Path Information

   There are cases where the optical impairments can only be described
   as a constrains on the overall end to end path.  In such case, the
   optical impairment 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.



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   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, it could be
   useful to understand the variance associated with the value of the
   optical parameter 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 definitions contained in this
   information model will match the architectural options described by
   [RFC6566].

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

   o  The wavelengths connectivity, considering also the connectivity
      constraints limited by reconfigurable optics, and wavelengths
      availability.

   o  The interface compatibility at the physical level.

   o  The Optical-Elettro-Optical (OEO) availability within the network
      (and related physical interface compatibility).  As already stated
      by the framework this information it's very important for
      impairment validation:

      A.  If the IV functions fail (path optically infeasible), the path
          computation function may use an available OEO point to find a
          feasible path.  In normally operated networks OEO are mainly
          uses to support optically unfeasible path than mere wavelength
          conversion.

      B.  The OEO points reset the optical impairment information since
          a new light is generated.

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



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   a particular selected path and wavelength is feasible or not.  This
   requires distribution of impairment information to the entity
   performing the IV process.

   This Information Model doesn't make any hypothesis on distribution
   method for optical parameters but only defines the essential build
   blocks.  A centralized entity may get knowledge of required
   information through routing protocols or other mechanism such as BGP-
   LS.

7.2.  IV-Distributed

   Assuming the information model is implemented through a routing
   protocol, every node in the WSON network shall be able to perform an
   RWA-IV function.

   The signalling phase may provide additional checking as others
   traffic engineering parameters.

8.  Acknowledgements

   Authors would like to acknoledge Greg Bernstein and Moustafa Kattan
   as authors of a previous similar draft whose content partially
   converged here.

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

9.  IANA Considerations

   This document does not contain any IANA requirement.

10.  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.

11.  References

11.1.  Normative References







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   [ITU.G650.1]
              International Telecommunications Union, "Transmission
              media and optical systems characteristics - Optical fibre
              cable", ITU-T Recommendation G.650.1, July 2010.

   [ITU.G650.2]
              International Telecommunications Union, "Definitions and
              test methods for statistical and non-linear related
              attributes of single-mode fibre and cable",
              ITU-T Recommendation G.650.2, August 2015.

   [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.

   [ITU.GSUP39]
              International Telecommunications Union, "Optical System
              Design and Engineering Considerations",
              ITU-T Recommendation G. Supplement 39, September 2012.

   [ITU.GSUP47]
              International Telecommunications Union, "General aspects
              of optical fibres and cables", ITU-T Recommendation G.
              Supplement 47, September 2012.

11.2.  Informative References

   [I-D.martinelli-ccamp-wson-iv-encode]
              Martinelli, G., Zhang, X., Galimberti, G., Siracusa, D.,
              Zanardi, A., Pederzolli, F., Lee, Y., and F. Zhang,
              "Information Encoding for WSON with Impairments
              Validation", draft-martinelli-ccamp-wson-iv-encode-07
              (work in progress), October 2016.







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   [LS78]     International Telecommunications Union SG15/Q6, "LS/s on
              CCAMP Liaison to ITU-T SG15 Q6 and Q12 on WSON",
              LS https://datatracker.ietf.org/liaison/1288/, October
              2013.

   [RFC6163]  Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
              "Framework for GMPLS and Path Computation Element (PCE)
              Control of Wavelength Switched Optical Networks (WSONs)",
              RFC 6163, DOI 10.17487/RFC6163, April 2011,
              <http://www.rfc-editor.org/info/rfc6163>.

   [RFC6566]  Lee, Y., Ed., Bernstein, G., Ed., Li, D., and G.
              Martinelli, "A Framework for the Control of Wavelength
              Switched Optical Networks (WSONs) with Impairments",
              RFC 6566, DOI 10.17487/RFC6566, March 2012,
              <http://www.rfc-editor.org/info/rfc6566>.

   [RFC7446]  Lee, Y., Ed., Bernstein, G., Ed., Li, D., and W. Imajuku,
              "Routing and Wavelength Assignment Information Model for
              Wavelength Switched Optical Networks", RFC 7446,
              DOI 10.17487/RFC7446, February 2015,
              <http://www.rfc-editor.org/info/rfc7446>.

   [RFC7579]  Bernstein, G., Ed., Lee, Y., Ed., Li, D., Imajuku, W., and
              J. Han, "General Network Element Constraint Encoding for
              GMPLS-Controlled Networks", RFC 7579,
              DOI 10.17487/RFC7579, June 2015,
              <http://www.rfc-editor.org/info/rfc7579>.

Appendix A.  FAQ

A.1.  Why the Application Code does not suffice for Optical Impairment
      Validation?

   Application Codes are encoded within GMPLS WSON protocol through the
   Optical Interface Class as defined in [RFC7446].

   The purpose of the Application Code in RWA is simply to assess the
   interface compatibility: same Application Code means that two
   interfaces can have an LSP connecting the two.

   Application Codes contain other information useful for IV process
   (e.g., see the list of parameters) so they are required however
   Computational Models requires more parameteres to assess the path
   feasibility.






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A.2.  Are DWDM network multivendor?

   According to [ITU.G680] "Situation 1" the DWDM line segments are
   single are single vendor but an LSP can make use of different data
   planes entities from different vendors.  For example: DWDM interfaces
   (represented in the control plane through the Optical Interface
   Class) from a vendor and network elements described by Stutation 1
   from another vendor.

Authors' Addresses

   Giovanni Martinelli (editor)
   Cisco
   via Santa Maria Molgora, 48/C
   Vimercate, MB  20871
   Italy

   Phone: +39 039 2092044
   Email: giomarti@cisco.com


   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: zhang.xian@huawei.com


   Gabriele M. Galimberti
   Cisco
   Via Santa Maria Molgora, 48/C
   Vimercate, MB  20871
   Italy

   Phone: +39 039 2091462
   Email: ggalimbe@cisco.com











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   Andrea Zanardi
   CREATE-NET
   via alla Cascata 56/D, Povo
   Trento  38123
   Italy

   Email: andrea.zanardi@create-net.org


   Domenico Siracusa
   CREATE-NET
   via alla Cascata 56/D, Povo
   Trento  38123
   Italy

   Email: domenico.siracusa@create-net.org


   Federico Pederzolli
   CREATE-NET
   via alla Cascata 56/D, Povo
   Trento  38123
   Italy

   Email: federico.perderzolli@create-net.org


   Young Lee
   Huawei Technologies
   1700 Alma Drive, Suite 100
   Plano, TX  75075
   U.S.A

   Email: ylee@huawei.com


   Fatai Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzen  518129
   P.R. China

   Email: zhang.fatai@huawei.com







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