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A YANG Data Model for Optical Impairment-aware Topology
draft-ietf-ccamp-optical-impairment-topology-yang-09

Document Type Active Internet-Draft (ccamp WG)
Authors Dieter Beller , Esther Le Rouzic , Sergio Belotti , Gabriele Galimberti , Italo Busi
Last updated 2022-03-07
Replaces draft-lee-ccamp-optical-impairment-topology-yang
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draft-ietf-ccamp-optical-impairment-topology-yang-09
CCAMP Working Group                                       D. Beller, Ed.
Internet-Draft                                                     Nokia
Intended status: Standards Track                            E. Le Rouzic
Expires: 8 September 2022                                         Orange
                                                              S. Belotti
                                                                   Nokia
                                                           G. Galimberti
                                                                   Cisco
                                                                 I. Busi
                                                     Huawei Technologies
                                                            7 March 2022

        A YANG Data Model for Optical Impairment-aware Topology
          draft-ietf-ccamp-optical-impairment-topology-yang-09

Abstract

   In order to provision an optical connection through optical networks,
   a combination of path continuity, resource availability, and
   impairment constraints must be met to determine viable and optimal
   paths through the network.  The determination of appropriate paths is
   known as Impairment-Aware Routing and Wavelength Assignment (IA-RWA)
   for WSON, while it is known as Impairment-Aware Routing and Spectrum
   Assigment (IA-RSA) for SSON.

   This document provides a YANG data model for the impairment-aware TE
   topology in optical networks.

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 https://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 8 September 2022.

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Copyright Notice

   Copyright (c) 2022 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 (https://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 to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   5
   2.  Reference Architecture  . . . . . . . . . . . . . . . . . . .   5
     2.1.  Control Plane Architecture  . . . . . . . . . . . . . . .   5
     2.2.  Optical Transport Network Data Plane  . . . . . . . . . .   6
     2.3.  OTS and OMS Media Channel Group . . . . . . . . . . . . .   7
       2.3.1.  Optical Tributary Signal (OTSi) . . . . . . . . . . .   8
       2.3.2.  Optical Tributary Signal Group (OTSiG)  . . . . . . .   9
       2.3.3.  Media Channel (MC)  . . . . . . . . . . . . . . . . .  10
       2.3.4.  Media Channel Group (MCG) . . . . . . . . . . . . . .  11
     2.4.  Amplifiers  . . . . . . . . . . . . . . . . . . . . . . .  12
     2.5.  Transponders  . . . . . . . . . . . . . . . . . . . . . .  13
       2.5.1.  Standard Modes  . . . . . . . . . . . . . . . . . . .  14
       2.5.2.  Organizational Modes  . . . . . . . . . . . . . . . .  15
       2.5.3.  Explicit Modes  . . . . . . . . . . . . . . . . . . .  16
       2.5.4.  Transponder Capabilities and Current Configuration  .  17
     2.6.  3R Regenerators . . . . . . . . . . . . . . . . . . . . .  18
     2.7.  WSS/Filter  . . . . . . . . . . . . . . . . . . . . . . .  21
     2.8.  Optical Fiber . . . . . . . . . . . . . . . . . . . . . .  21
     2.9.  WDM-Node Architectures  . . . . . . . . . . . . . . . . .  21
       2.9.1.  Integrated WDM-node Architecture with Local Optical
               Transponders  . . . . . . . . . . . . . . . . . . . .  22
       2.9.2.  Integrated WDM-node with Integrated Optical
               Transponders and Single Channel Add/Drop Interfaces for
               Remote Optical Transponders . . . . . . . . . . . . .  23
       2.9.3.  Disaggregated WDM-TE-node Subdivided into Degree, Add/
               Drop, and Optical Transponder Subsystems  . . . . . .  24
       2.9.4.  Optical Impairments Imposed by WDM-TE-Nodes . . . . .  26
   3.  YANG Model (Tree Structure) . . . . . . . . . . . . . . . . .  27
   4.  Optical Impairment Topology YANG Model  . . . . . . . . . . .  34

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   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  62
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  62
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  62
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  62
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  62
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  63
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  66
   Appendix B.  Additional Authors . . . . . . . . . . . . . . . . .  66
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  67

1.  Introduction

   In order to provision an optical connection (an optical path) through
   a wavelength switched optical networks (WSONs) or spectrum switched
   optical networks (SSONs), a combination of path continuity, resource
   availability, and impairment constraints must be met to determine
   viable and optimal paths through the network.  The determination of
   appropriate paths is known as Impairment-Aware Routing and Wavelength
   Assignment (IA-RWA) [RFC6566] for WSON, while it is known as IA-
   Routing and Spectrum Assigment (IA-RSA) for SSON.

   This document provides a YANG data model for the impairment-aware
   Traffic Engineering (TE) topology in WSONs and SSONs.  The YANG model
   described in this document is a WSON/SSON technology-specific Yang
   model based on the information model developed in [RFC7446] and the
   two encoding documents [RFC7581] and [RFC7579] that developed
   protocol independent encodings based on [RFC7446].

   The intent of this document is to provide a YANG data model, which
   can be utilized by a Multi-Domain Service Coordinator (MDSC) to
   collect states of WSON impairment data from the Transport PNCs to
   enable impairment-aware optical path computation according to the
   ACTN Architecture [RFC8453].  The communication between controllers
   is done via a NETCONF [RFC8341] or a RESTCONF [RFC8040].
   Similarly,this model can also be exported by the MDSC to a Customer
   Network Controller (CNC), which can run an offline planning process
   to map latter the services in the network.

   It is worth noting that optical data plane interoperability is a
   complex topic especially in a multi vendor environment and usually
   requires joint engineering, which is independent from control plane
   and management plane capabilities.  The YANG data model defined in
   this draft is providing sufficient information to enable optical
   impairment aware path computation.  Optical data plane
   interoperability is outside the scope of this draft.

   This document augments the generic TE topology YANG model defined in
   [RFC8795] where possible.

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   This document defines one YANG module: ietf-optical-impairment-
   topology (Section 3) according to the new Network Management
   Datastore Architecture [RFC8342].

1.1.  Terminology

   Refer to [RFC6566], [RFC7698], and [G.807] for the key terms used in
   this document.

   The following terms are defined in [RFC7950] and are not redefined
   here:

   *  client

   *  server

   *  augment

   *  data model

   *  data node

   The following terms are defined in [RFC6241] and are not redefined
   here:

   *  configuration data

   *  state data

   The terminology for describing YANG data models is found in
   [RFC7950].

   The term ROADM in this document refers to the term "multi-degree
   reconfigurable optical add/drop multiplexer (MD-ROADM)" as defined in
   [G.672].  It does not include local optical transponders, which can
   be co-located in the same physical device (managed entity).

   The term WDM-node refers to a physical device, which is managed as a
   single network element.

   The term WDM-TE-node refers to those parts of a WDM-node (physical
   device) that are modeled as a TE-node as defined in [RFC8795], which
   may include a ROADM and/or multiple local optical transponders(OTs).
   Hence, a WDM-TE-node may only contain OTs.

   The term "WDM-TE-network" refers to a set of WDM-TE-nodes as defined
   above that are interconnected via TE-links carrying WDM signals.
   These TE-links may include optical amplifiers.

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1.2.  Tree Diagram

   A simplified graphical representation of the data model is used in
   Section 2 of this this document.  The meaning of the symbols in these
   diagrams is defined in [RFC8340].

1.3.  Prefixes in Data Node Names

   In this document, names of data nodes and other data model objects
   are prefixed using the standard prefix associated with the
   corresponding YANG imported modules, as shown in Table 1.

   +==============+===============+===================================+
   | Prefix       | YANG module   | Reference                         |
   +==============+===============+===================================+
   | optical-imp- | ietf-optical- | [RFCXXXX]                         |
   | topo         | impairment-   |                                   |
   |              | topology      |                                   |
   +--------------+---------------+-----------------------------------+
   | layer0-types | ietf-         | [RFC9093]                         |
   |              | layer0-types  |                                   |
   +--------------+---------------+-----------------------------------+
   | l0-types-ext | ietf-layer0-  | [I-D.ietf-ccamp-layer0-types-ext] |
   |              | types-ext     |                                   |
   +--------------+---------------+-----------------------------------+
   | nw           | ietf-network  | [RFC8345]                         |
   +--------------+---------------+-----------------------------------+
   | nt           | ietf-network- | [RFC8345]                         |
   |              | topology      |                                   |
   +--------------+---------------+-----------------------------------+
   | tet          | ietf-te-      | [RFC8795]                         |
   |              | topology      |                                   |
   +--------------+---------------+-----------------------------------+

             Table 1: Prefixes and corresponding YANG modules

   [Editor's note: The RFC Editor will replace XXXX with the number
   assigned to the RFC once this draft becomes an RFC.]

2.  Reference Architecture

2.1.  Control Plane Architecture

   Figure 1 shows the control plane architecture.

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                             +--------+
                             |  MDSC  |
                             +--------+
    Scope of this ID  ------->   ||
                  |              ||
                  |  +------------------------+
                  |  |        OPTICAL         |
     +---------+  |  |         DOMAIN         |     +---------+
     | Device  |  |  |       CONTROLLER       |     | Device  |
     | config. |  |  +------------------------+     | config. |
     +---------+  v  //          ||          \\     +---------+
    ______|______   //           ||           \\   ______|______
   /      OT     \ //            ||            \\ /      OT     \
   | +--------+  |//           __--__           \\|  +--------+ |
   | |Vend. A |--|----+       (      )       +----|--| Vend. A| |
   | +--------+  |    |    ~-(        )-~    |    |  +--------+ |
   | +--------+  |    +---/              \---+    |  +--------+ |
   | |Vend. B |--|--+    /                \    +--|--| Vend. B| |
   | +--------+  |  +---(   OLS Segment    )---+  |  +--------+ |
   | +--------+  |  +---(                  )---+  |  +--------+ |
   | |Vend. C |--|--+    \                /    +--|--| Vend. C| |
   | +--------+  |    +---\              /---+    |  +--------+ |
   | +--------+  |    |    ~-(        )-~    |    |  +--------+ |
   | |Vend. D |--|----+       (__  __)       +----|--| Vend. D| |
   | +--------+  |               --               |  +--------+ |
   \_____________/                                \_____________/
             ^                                        ^
             |                                        |
             |                                        |
            Scope of [I-D.ietf-ccamp-dwdm-if-param-yang]

           Figure 1: Scope of draft-ietf-ccamp-dwdm-if-param-yang

   The topology model developed in this document is an abstracted
   topology YANG model that can be used at the interfaces between the
   MDSC and the Optical Domain Controller (aka MPI) and between the
   Optical Domain Controller and the Optical Device (aka SBI) in
   Figure 1.  It is not intended to support a detailed low-level DWDM
   interface model.  DWDM interface model is supported by the models
   presented in [I-D.ietf-ccamp-dwdm-if-param-yang].

2.2.  Optical Transport Network Data Plane

   This section provides the description of the optical transport
   network reference architecture and its relevant components to support
   optical impairment-aware path computation.

   Figure 2 shows the reference architecture.

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     +-------------------+                      +-------------------+
     |      WDM-Node     |                      |      WDM-Node     |
     |                   |                      |                   |
     | PA  +-------+ BA  |         ILA          | PA  +-------+ BA  |
     | +-+ |       | +-+ |  _____  +--+  _____  | +-+ |       | +-+ |
   --|-| |-| ROADM |-| |-|-()____)-|  |-()____)-|-| |-| ROADM |-| |-|--
     | +-+ |       | +-+ |         +--+         | +-+ |       | +-+ |
     |     +-------+     | optical              |     +-------+     |
     |       | | |       |  fiber               |       | | |       |
     |       o o o       |                      |       o o o       |
     |    local          |                      |    local          |
     |    transponders   |                      |    transponders   |
     +-------------------+                      +-------------------+

                          OTS MCG        OTS MCG
                        <--------->    <--------->
                            OMS MCG = TE-link
                    <-------------------------------->

      BA: Booster Amplifier (or egress amplifier)
      PA: Pre-Amplifier (or ingress amplifier)
      ILA: In-Line Amplifier
      MCG: Media Channel Group

       Figure 2: Reference Architecture for Optical Transport Network

   BA (on the left side WDM-TE-node) is the engress Amplifier and PA (on
   the right side WDM-TE-node is the ingress amplifier for the OMS Media
   Channel Group (MCG) Figure 2.

2.3.  OTS and OMS Media Channel Group

   According to [G.807] and [G.872], an OTS Media Channel Group (MCG)
   represents a topological construct between two adjacent amplifiers,
   such as:

     (i)  between a WDM-TE-node's BA and the adjacent ILA,
    (ii)  between a pair of ILAs,
   (iii)  between an ILA and the adjacent WDM-TE-node's PA.

   According to [G.807] and [G.872], an OMS Media Channel Group (MCG)
   represents a topological construct between two WDM-TE-nodes.

   Specifically, it originates at the ROADM in the source WDM-TE-node
   and terminates at the ROADM in the destination WDM-TE-node including
   the Booster Amplifier (BA) and the Pre-Amplifier (PA) in the WDM-TE-
   nodes as well as the In-Line Amplifiers (ILAs) between the two WDM-
   TE-nodes.

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   An OMS MCG can be decomposed into a sequence of OTS MCGs and
   amplifiers.

   An OMS MCG can be described as a sequence of elements such as BA,
   fiber section, ILA, PA, and concentrated loss wherever there is an
   insertion loss caused for example by a fiber connector.

   In TE-topology terms, the OMS MCG is modeled as a WDM TE-link
   interconnecting two WDM-TE-nodes.  A network controller can retrieve
   the optical impairment data for all the WDM TE-link elements defined
   in the layer-0 topology YANG model.

   The optical impairments related to the link between remote optical
   transponders, located in a different WDM-TE-node (an IP router with
   integrated optical transponders for example), can also be modeled as
   a WDM TE-link using the same optical impairments as those defined for
   a WDM TE-link between WDM-TE-nodes (OMS MCG).  In this scenario, the
   node containing the remote optical transponders can be considered as
   WDM-TE-node with termination capability only and no no switching
   capabilities.

   An OMS MCG is terminated on both ends by a link termination point
   (LTP) as defined in [RFC8345].  Links in optical transport networks
   are typically bidirectional but have to be modeled as a pair of two
   unidirectional links following the [RFC8345] modeling approach.
   Unlike TE-links, which are unidirectional, the LTPs on either end of
   the TE-link pair forming the bidirectional link, are bidirectional as
   described in [I-D.ietf-teas-te-topo-and-tunnel-modeling] and the pair
   of unidirectional links are connected to the same bidirectional LTP
   on either end of the link pair.

   [Editor's note: text below related to [G.807] needs to be revised
   based on the published [G.807] revision!]

2.3.1.  Optical Tributary Signal (OTSi)

   The OTSi is defined in ITU-T Recommendation G.959.1, section 3.2.4
   [G.959.1].  The YANG model defined below assumes that a single OTSi
   consists of a single modulated optical carrier.  This single
   modulated optical carrier conveys digital information.
   Characteristics of the OTSi signal are modulation scheme (e.g.  QPSK,
   8-QAM, 16-QAM, etc.), baud rate (measure of the symbol rate), pulse
   shaping (e.g. raised cosine - complying with the Nyquist inter symbol
   interference criterion), etc.

   Path computation needs to know the existing OTSi signals for each OMS
   link in the topology to determine the optical impairment impact of
   the existing OTSi signals on the optical feasibility of a new OTSi

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   signal and vice versa, i.e., the impact of the new OTSi on the
   existing OTSi signals.  For determining the optical feasibility of
   the new OTSi, it is necessary to know the OTSi properties like
   carrier frequency, baud rate, and signal power for all existing OTSi
   signals on each OMS link.

   Additionally, it is necessary for each WDM-TE-node in the network to
   know the OTSi signals that are added to or dropped from an WDM TE-
   link (OMS MCG)link as well as the optical power of these OTSi signals
   to check whether the WDM-TE-node's optical power constraints are met.

   The optical impairment-aware topology YANG model below defines the
   OTSi properties needed for optical impairment-aware path computation
   including the spectrum occupied by each OTSi signal.  The model also
   defines a pointer (leafref) from the OTSi to the transceiver module
   terminating the OTSi signal.

2.3.2.  Optical Tributary Signal Group (OTSiG)

   The definition of the OTSiG is currently being moved from ITU-T
   Recommendation G.709 [G.709] to the new draft Recommendation G.807
   (still work in progress) [G.807].  The OTSiG is an electrical signal
   that is carried by one or more OTSi's.  The relationship between the
   OTSiG and the the OTSi's is described in ITU-T draft Recommendation
   G.807, section 10.2 [G.807].  The YANG model below supports both
   cases: the single OTSi case where the OTSiG contains a single OTSi
   (see ITU-T draft Recommendation G.807, Figure 10-2) and the multiple
   OTSi case where the OTSiG consists of more than one OTSi (see ITU-T
   draft Recommendation G.807, Figure 10-3).  From a layer 0 topology
   YANG model perspective, the OTSiG is a logical construct that
   associates the OTSi's, which belong to the same OTSiG.  The typical
   application of an OTSiG consisting of more than one OTSi is inverse
   multiplexing.  Constraints exist for the OTSi's belonging to the same
   OTSiG such as: (i) all OTSi's must be co-routed over the same optical
   fibers and nodes and (ii) the differential delay between the
   different OTSi's may not exceed a certain limit.  Example: a 400Gbps
   client signal may be carried by 4 OTSi's where each OTSi carries
   100Gbps of client traffic.

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                                  OTSiG
           _________________________/\__________________________
          /                                                     \
                                    m=7
   - - - +---------------------------X---------------------------+ - - -
   / / / |                                                       | / / /
    / / /|      OTSi         OTSi         OTSi         OTSi      |/ / /
   / / / |        ^            ^            ^            ^       | / / /
    / / /|        |            |            |            |       |/ / /
   / / / |        |            |            |            |       | / / /
    / / /|        |            |            |            |       |/ / /
    -4  -3  -2  -1   0   1   2   3   4   5   6   7   8   9  10  11  12
   --+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
                                   n = 4
                  K1           K2           K3           K4

       Figure 3: MC Example containing all 4 OTSi signals of an OTSiG

2.3.3.  Media Channel (MC)

   [G.807] defines a "media channel" as "A media association that
   represents both the topology (i.e., the path through the media) and
   the resource (i.e., frequency slot or effective frequency slot) that
   it occupies."  In this document, the term "channel" is occasionally
   used to indicate the resource of an MC (i.e., frequency slot or
   effective frequency slot), without representing topology.

   The MC is an end-to-end topological network construct and can be
   considered as an "optical pipe" with a well-defined frequency slot
   between one or more optical transmitters each generating an OTSi and
   the corresponding optical receivers terminating the OTSi's.  If the
   MC carries more than one OTSi, it is assumed that these OTSi's belong
   to the same OTSiG.

                                    m=8
     +-------------------------------X-------------------------------+
     |                               |                               |
     |     +----------X----------+   |   +----------X----------+     |
     |     |        OTSi         |       |        OTSi         |     |
     |     |          ^          |   |   |          ^          |     |
     |     |          |          |       |          |          |     |
    -4  -3  -2  -1   0   1   2   3   4   5   6   7   8   9  10  11  12
   --+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+-
                      |             n=4             |
                      K1                            K2

     <------------------------ Media Channel ----------------------->

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                        Figure 4: Figure Caption TBA

   The frequency slot of the MC is defined by the n value defining the
   central frequency of the MC and the m value that defines the width of
   the MC following the flexible grid definition in ITU-T Recommendation
   G.694.1 [G.694.1].  In this model, the effective frequency slot as
   defined in ITU-T draft Recommendation G.807 is equal to the frequency
   slot of this end-to-end MC.  It is also assumed that ROADM devices
   can switch MCs.  For various reasons (e.g.  differential delay), it
   is preferred to use a single MC for all OTSi's of the same OTSiG.  It
   may however not always be possible to find a single MC for carrying
   all OTSi's of an OTSiG due to spectrum occupation along the OTSiG
   path.

2.3.4.  Media Channel Group (MCG)

   The definition of the MCG is currently work in progress in ITU-T and
   is defined in section 7.1.3 of the new ITU-T draft Recommendation
   G.807 (still work in progress) [G.807].  The YANG model below assumes
   that the MCG is a logical grouping of one or more MCs that are used
   to to carry all OTSi's belonging to the same OTSiG.

   The MCG can be considered as an association of MCs without defining a
   hierarchy where each MC is defined by its (n,m) value pair.  An MCG
   consists of more than one MC when no single MC can be found from
   source to destination that is wide enough to accommodate all OTSi's
   (modulated carriers) that belong to the same OTSiG.  In such a case
   the set of OTSi's belonging to a single OTSiG have to be split across
   2 or more MCs.

                                   MCG1 = {M1.1, M1.2}
          __________________________/\________________________
         /                                                    \
                     M1.1                  M2          M1.2
          ____________/\____________  _____/\_____  ____/\____
         /                          \/            \/          \
   - - - +---------------------------+-------------+-----------+ - - -
   / / / |                           | / / / / / / |           | / / /
    / / /|    OTSi    OTSi    OTSi   |/ / / / / / /|    OTSi   |/ / /
   / / / |     ^       ^       ^     | / / / / / / |     ^     | / / /
    / / /|     |       |       |     |/ / / / / / /|     |     |/ / /
   / / / |     |       |       |     | / / / / / / |     |     | / / /
    / / /|     |       |       |     |/ / / / / / /|     |     |/ / /
        -7    -4    -1 0 1 2 3 4 5 6 7 8    ...    14    17    20
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       n=0                               n=17
               K1      K2      K3                        K4

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                        Figure 5: Figure Caption TBA

   The MCG is relevant for path computation because all end-to-end MCs
   belonging to the same MCG have to be co-routed, i.e., have to follow
   the same path.  Additional constraints may exist (e.g. differential
   delay).

2.4.  Amplifiers

   Optical amplifiers are used in WDM networks for amplifying the
   optical signal in the optical domain without any optical to
   electrical and electrical to optical conversion.  There are three
   main optical amplifier technologies:

   *  Erbium Doped Fiber Amplifiers (EDFAs)

   *  Raman Amplifiers

   *  Semiconductor Optical Amplifiers (SOAs)

   In today's WDM networks EDFAs and Raman amplifiers are widely used.
   Raman amplifiers have become attractive due to their large spectral
   gain bandwidth, which can be quite flat, with similar or even lower
   noise figures compared to EDFAs.  On the other hand, Raman amplifiers
   consume more power and are usually more expensive than EDFAs.

   Raman amplifiers are distributed amplifiers where an optical pump
   signal is injected typically in opposite direction to the optical
   signal that is amplified (backward pump, counter-propagating pump
   light).  Injecting the optical pump signal in the same direction is
   also possible (forward pump, co-propagating pump light).  For optical
   amplifiers, the YANG model defines Raman pump light attributes
   describing the direction (raman-direction) with respect to the signal
   that is amplified and optical frequency and power for the pump light
   source(s) contained in the raman-pump list.  These Raman amplifier-
   specific attributes are optional as they are only applicable to Raman
   amplifiers.  For determining the optical amplifier type, i.e., to
   figure out whether an optical amplifier is a Raman amplifier, the
   type-variety attribute is used.  Due to the distributed nature of the
   Raman amplifier it is difficult to clearly separate the amplifier
   from the fiber span into which the pump signal is injected.  From a
   topology modeling perspective, the Raman amplifier is modeled as two
   OMS line elements:

   1.  a passive fiber element accounting for the fiber loss only and
       not the resulting loss including the Raman gain

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   2.  an amplifier element providing all optical amplifier properties
       (gain, tilt, etc.).  On the OMS-link, the amplifier element is
       placed where the pump is located and the geolocation information
       also indicates the location of the pump.

   Amplifiers can be classified according to their location along the
   TE-link (OMS MCG).  There are three basic amplifier types: In-Line
   Amplifiers, Pre-Amplifiers and Booster Amplifiers.  ILAs are separate
   physical devices while Pre-Amplifiers and Booster Amplifiers are
   integral elements of a WDM-node.  From a data modeling perspective,
   node-internal details should not be modeled and should be abstracted
   as much as possible.  For Pre-Amplifiers and Booster Amplifiers,
   however, a different approach has been taken and they are modeled as
   TE-link elements as they have the same optical impairments as ILAs.

   ILAs are placed at locations where the optical amplification of the
   WDM signal is required on the TE-link (OMS MCG) between two WDM-TE-
   nodes nodes.  Geolocation information is already defined for TE nodes
   in [RFC8795] and is also beneficial for ILAs.  Therefore, the same
   geolocation container has been added to the amplifier element on an
   OMS link containing altitude, latitude, and longitude as optional
   attributes.

   One modeling consideration of the ROADM internal is to model power
   parameter through the ROADM, factoring the output power from the Pre-
   Amplifier minus the ROADM power loss would give the input power to
   the Booster Amplifier.  In other words, Power_in (@ ROADM Booster) =
   Power_out (@ ROADM Pre-Amplifier) - Power_loss (@ ROADM WSS/Filter).

2.5.  Transponders

   [Editor's note: The relationship between the transponder and the OTSi
   in the YANG model described in Section 3 needs further clarification
   and refinement.]

   A Transponder is the element that sends and receives the optical
   signal from a DWDM network.  A transponder can comprise one or more
   transceiver modules.  A transceiver represents a transmitter/receiver
   (Tx/Rx) pair as defined in ITU-T Recommendation G.698.2 [G.698.2].
   In addition to the transceiver, which is terminating an OTSi signal,
   a transponder typically provides additional layer 1 functionality
   like for example aggregation (multiplexing) of client layer signals,
   which is outside the scope of this document addressing layer 0
   aspects of transponders.

   The termination of an OTSi signal by a transceiver is modeled as a
   function of the tunnel termination point (TTP) as defined in
   [RFC8795].  Due to the fact that optical transport services (TE

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   tunnels) are typically bidirectional, a TTP is also modeled as a
   bidirectional entity like the LTP described above.  Moreover, a TTP
   can terminate one or several OTSiG signals (tunnels) as described in
   [I-D.ietf-teas-te-topo-and-tunnel-modeling] and each OTSiG consists
   of one or multiple OTSi signals as described in Section 2.3.2.
   Therefore, a TTP may be associated with multiple transceiver modules.

   A transponder is typically characterized by its data/symbol rate and
   the maximum distance the signal can travel.  Other transponder
   properties are: carrier frequency for the optical channels, output
   power per channel, measured input power, modulation scheme, FEC, etc.

   From a path computation perspective, the selection of the compatible
   configuration of the source and the destination transceivers is an
   important factor for optical signals to traverse through the DWDM
   network.

   The YANG model defines three different approaches to describe the
   transceiver capabilities (called "modes") that are needed to
   determine optical signal compatibility:

   *  Standard Modes

   *  Organizational Modes

   *  Explicit Modes

2.5.1.  Standard Modes

   A standard mode is related to an optical specification developed by
   an SDO organization.  Currently, the "Standard Modes" can only be
   referred to ITU-T G.698.2 [G.698.2] since G.698.2 is the only
   specification defining "Standard Modes" today.  Nothing is
   precluding, however, to consider other specifications provided by any
   other SDO in the Standard Mode context as soon as such sepcifications
   will be available.  An application code as defined in ITU-T G.698.2
   [G.698.2] is representing a standard ITU-T G.698.2 optical interface
   specification towards the realization of transversely compatible DWDM
   systems.  Two transceivers supporting the same application code and a
   line system matching the constraints, defined in ITU-T G.698.2, for
   that application code will interoperate.  As the characteristics are
   encoded in the application code, the YANG model in this document only
   defines a string, which represents that application code.

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2.5.2.  Organizational Modes

   Organizations like operator groups, industry fora, or equipment
   vendors can define their own optical interface specifications and
   make use of transceiver capabilities going beyond existing standards.

   An organizational mode is identified by the organization-identifier
   attribute defining the scope and an operational-mode that is
   meaningful within the scope of the organization.  Hence, the two
   attributes must always be considered together.  It is the
   responsibility of the organization to assign operational modes and to
   ensure that operational modes are unique and unambiguous within the
   scope of the organization.

   Two transceivers can be interconnected, if they have at least one
   (organization-identifier, operational-mode) pair in common and if the
   supported carrier frequency and power attributes have a matching
   range.  This is a necessary condition for path computation in the
   context of organizational modes.

   An operational mode is a transceiver preset (a configuration with
   well-defined parameter values) subsuming several transceiver
   properties defined by the optical interface specification - these
   properties are not provided for anoperational mode and are therefore
   not defined in the YANG model.  Examples of these properties are:

   *  FEC type

   *  Modulation scheme

   *  Encoding (mapping of bit patterns (code words) to symbols in the
      constellation diagram)

   *  Baud rate (symbol rate)

   *  Carrier bandwidth (typically measured in GHz)

   The major reason for these transceiver presets is the fact that the
   attribute values typically cannot be configured independently and are
   therefore advertised as supported operational mode capabilities.  It
   is the responsibility of the organization to assign operational modes
   and to ensure that operational modes are unique and not ambiguous
   within the scope of the organization.

   In addition to the transceiver properties subsumed by the operational
   mode, optical power and carrier frequency related properties are
   modeled separately, i.e., outside of the operational mode.  This
   modeling approach allows transponders using different transceiver

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   variants (e.g. optical modules) with slightly different power and/or
   frequency range properties to interoperate without defining separate
   operational modes.  Different optical modules (pluggables) from
   different suppliers typically have slightly different input and
   output power ranges or may have slightly different carrier frequency
   tuning ranges.

   The received channel power and the received total power are two
   parameters that can be measured by the receiver and can be provided
   by the transceiver in order to allow a controller to determine the
   expected performance of the end-to-end service taking into account
   the optical impairments along the path.

   An organization may define the operational modes to include the
   optical power and carrier frequency related properties following the
   application code approach as defined in ITU-T Recommendation G.698.2
   [G.698.2].  In such a case, the explicit optical power and carrier
   frequency related optional attributes shall be omitted in order to
   avoid redundant information in the description of the transceiver
   capabilities.  If these attributes are provided in addition to the
   operational modes including these attribute values implicitly, the
   parameter values provided explicitly replace the implicit values and
   take precedence.  This shall, however, only be an done in exceptional
   cases and shall be avoided whenever possible.  In case an implicitly
   given range is extended utilizing the explicit optional attributes, a
   path computation policy rule may be applied to select a value
   preferably from the range defined implicitly and to only select a
   value from the extended range if no path can be found for values in
   the implicitly defined range.  Path computation policy is outside the
   scope of this topology YANG model.

   In summary, the optical power and carrier frequency related
   attributes shall either be described implicitly by the operational
   mode following the definition provided by that organization or shall
   be described explicitly when the optical power and carrier frequency
   related properties are not included in the operational mode
   definition.

2.5.3.  Explicit Modes

   The explicit mode allows to encode, explicitly, any subset of
   parameters e.g., FEC type, Modulation type, etc, to enable a
   controller entity to check for interoperability by means outside of
   this draft.  It shall be noted that using the explicit encoding does
   not guarantee interoperability between two transceivers even in case
   of identical parameter definitions.  The explicit mode shall
   therefore be used with care, but it could be useful when no common
   Application Codes or Organizational Modes exist or the constraints of

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   common Application Codes or Organizational Modes cannot be met by the
   line system.

2.5.4.  Transponder Capabilities and Current Configuration

   The YANG model described in Section 3 defines the optical transceiver
   properties.  They are divided between:

   a.  Optical transceiver capabilities, describing how it can be
       configured

   b.  Current transceiver setting, indicating how it is currently
       configured

   The transceiver capabilities are described by the set of modes the
   transceiver is supporting.  Each mode MUST follow only one of the
   three mode options defined above (choice in the YANG model).  The
   YANG model allows to describe the transceiver capabilities by mixing
   different modes.  A transceiver may support some ITU-T application
   codes and in addition some organizational or explicit modes.

   A transceiver mode description comprises the following properties:

   *  Supported transmitter tuning range with min/max nominal carrier
      frequency [f_tx_min, f_tx_max]

   *  Supported transmitter tunability grid, the distance between two
      adjacent carrier frequencies (in GHz)

   *  Supported transmitter power range [p_tx-min, p_tx_max]

   *  Supported receiver channel power range [p_rx-min, p_rx_max]

   *  Supported maximum total power, rx power for all channels fed into
      the receiver

   These optical transceiver properties are explicitly defined in the
   model for explicit and organizational modes, while they are
   implicitly defined for the application codes (see ITU-T G698.2
   [G.698.2]).

   The set of optical impairment limits, e.g., min OSNR, max PMD, max
   CD, max PDL, Q-factor limit, are explicitly defined for the explicit
   modes while they are defined implicitly for the application codes and
   organizational modes.

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   It is possible that the set of parameter values defined for an
   explicit mode may also be represented in form of an organizational
   mode or one or more application codes.  The "supported-mode"
   container may provide two different lists with pointers to
   application codes and organizational modes, respectively.

   The current transponder configuration describes the properties of the
   OTSi transmitted or received by the transceiver attached to a
   specific transponder port.

   Each OTSi has the following three pointer attributes modeled as
   leafrefs:

   *  Pointer to the transponder instance containing the transceiver
      terminating the OTSi

   *  Pointer to the transceiver instance terminating the OTSi

   *  Pointer to the currently configured transceiver mode

   Additionally, the OTSi is described by the following frequency and
   optical power related attributes:

   *  current carrier-frequency

   *  currently transmitted channel power

   *  currently received channel power

   *  currently received total power

2.6.  3R Regenerators

   Optical transponders are usually used to terminate a layer 0 tunnel
   (layer 0 service) in the WDM layer.  If, however, no optical path can
   be found from the source transponder to the destination transponder
   that is optically feasible due to the optical impairments, one or
   more 3R regenerators are needed for regenerating the optical signal
   in intermediate nodes.  The term "3R" regenerator means:
   reamplification, reshaping, retiming.  As described in [G.807],
   Appendix IV, a 3R regenerator terminates the OTSi and generates a new
   OTSi.  Depending on the 3R regenerator capabilities, it can provide
   functions such as carrier frequency translation (carrier-frequency),
   changes in the modulation scheme (modulation-type) and FEC (FEC-type)
   while passing through the digital signal except the FEC (the FEC is
   processed and errors are corrected).

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   The 3R regeneartion compound function is illustrated in section 10.1
   of [G.798.1], and sections 10.3 and 10.4 provide examples of a ROADM
   architecture and a photonic cross-connect architecture including 3R
   regenerators.  Based on the provided functionality, 3R regenerators
   are considered as topological layer 0 entities because they are
   needed for layer 0 path computation in case the optical impairments
   make it impossible to find an optically feasible end-to-end path from
   the source transponder to the destination transponder without 3R
   regeneration.  When an end-to-end path includes one or more 3R
   regenerators, the corresponding layer 0 tunnel is subdivided into 2
   or more segments between the source transponder and the destination
   transponder terminating the layer 0 tunnel.

   3R regenerators are usually realized by a pair of optical
   transponders, which are described in Section 2.5 above.  If a pair of
   optical transponders is used to perform a 3R regeneratator function,
   two different configurations are possible involving the pair of
   optical transceivers of the two optical transponders:

   *  The two transponders can be operated in a back-to-back
      configuration where the transceiver of each optical transponder
      receives and transmits the optical signal from/to the same segment
      of the end-to-end tunnel.  This means that each transceiver is
      operated in a bi-directional mode.

             Optical Transponder 1        Optical Transponder 2
           +-----------------------+    +-----------------------+
           | Transceiver           |    |           Transceiver |
           |-------------+   +-----|    |-----+   +-------------|
       --->| Receiver    |---|Sig. |--->|Sig. |---| Transmitter |--->
           |-------------+   |     |    |     |   +-------------|
       <---| Transmitter |---|Proc.|<---|Proc.|---|    Receiver |<---
           |-------------+   +-----|    |-----+   +-------------|
           |                       |    |                       |
           +-----------------------+    +-----------------------+

           Sig. Proc. = Signal Processing

               Figure 6: Back-to-back 3R Regenerator Example

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   *  The two transponders can be operated in a configuration where each
      transponder performs the 3R regeneration function in one
      direction, one in forward direction (from source to destination)
      and the other in the reverse direction.  In this configuration,
      the transceiver of each optical transponder receives the signal
      from one segment and transmits the regenerated optical signal into
      the adjacent segment.  This configuration is also called cross-
      regeneration and each transceiver is operated in an uni-
      directional mode.

                       Optical Transponder 1
                  +-----------------------------+
                  | Transceiver                 |
                  |-------------+   +---------+ |
              --->| Receiver    |---|Sig. --+ | |
                  |-------------+   |       | | |
              <---| Transmitter |---|Proc.<-+ | |
                  |-------------+   +---------+ |
                  |                             |
                  +-----------------------------+
                     3R in forward direction

                       Optical Transponder 2
                  +-----------------------------+
                  | Transceiver                 |
                  |-------------+   +---------+ |
              --->| Receiver    |---|Sig. --+ | |
                  |-------------+   |       | | |
              <---| Transmitter |---|Proc.<-+ | |
                  |-------------+   +---------+ |
                  |                             |
                  +-----------------------------+
                     3R in reverse direction

                  Sig. Proc. = Signal Processing

                   Figure 7: Cross-3R Regenerator Example

   Due to the fact that 3R regenerators are composed of an optical
   transponder pair, the capabilitiy whether an optical transponder can
   be used as a 3R regenerator is is added to the transponder
   capabilities.  Hence, no additional entity is required for describing
   3R regenerators in the TE-topology YANG model.  The optical
   transonder capabilities regarding the 3R regenerator function are
   described by the following two YANG model attributes:

   *  supported-termination-type

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   *  supported-3r-mode

   The supported-termination-type attribute describes whether the
   optical transponder can be used as tunnel terminating transponder
   only, as 3R regenerator only, or whether it can support both
   functions.  The supported-3r-mode attrbute describes the
   configuration of the transponder pair forming the 3R regeneartor as
   described above.

   More text to be added here!

2.7.  WSS/Filter

   WSS separates the incoming light input spectrally as well as
   spatially, then chooses the wavelength that is of interest by
   deflecting it from the original optical path and then couple it to
   another optical fibre port.  WSS/Filter is internal to ROADM.  So
   this document does not model the inside of ROADM.

2.8.  Optical Fiber

   There are various optical fiber types defined by ITU-T.  There are
   several fiber-level parameters that need to be factored in, such as,
   fiber-type, length, loss coefficient, pmd, connectors (in/out).

   ITU-T G.652 defines Standard Singlemode Fiber; G.654 Cutoff Shifted
   Fiber; G.655 Non-Zero Dispersion Shifted Fiber; G.656 Non-Zero
   Dispersion for Wideband Optical Transport; G.657 Bend-Insensitive
   Fiber.  There may be other fiber-types that need to be considered.

2.9.  WDM-Node Architectures

   The WDM-node architectures in today's dense wavelength division
   multiplexing (DWDM) networks can be categorized as follows:

   *  Integrated WDM-node architecture with local optical transponders

   *  Integrated WDM-node architecture with local optical transponders
      and single channel add/drop ports for remote optical transponders

   *  Disaggregated WDM-node architecture where the WDM-TE-node is
      composed of degree, add/drop, and optical transponder subsystems
      handled as separate WDM-nodes

   The TE topology YANG model augmentations including optical
   impairments for DWDM networks defined below intend to cover all the 3
   categories of WDM-node architectures listed above.  In the case of a
   disaggregated WDM-node architecture, it is assumed that the optical

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   domain controller already performs some form of abstraction and
   presents the WDM-TE-node representing the disaggregated WDM-node in
   the same way as an integrated WDM-TE-node with local optical
   transponders if the optical transponder subsystems and the add/drop
   subsystems are collocated (short fiber links not imposing any
   significant optical impairments).

   The different WDM-node architectures are briefly described and
   illustrated in the following subsections.

   [Editor's note: The modeling of remote optical transponders located
   for example in the client device with a single channel link between
   the OT and the add/drop port of the WDM-TE-node requires further
   investigations and will be addressed in a future revision of this
   document.]

2.9.1.  Integrated WDM-node Architecture with Local Optical Transponders

   Figure 2 and Figure 8 below show the typical architecture of an
   integrated WDM-node, which contains the optical transponders as an
   integral part of the WDM-node.  Such an integrated WDM-node provides
   DWDM interfaces as external interfaces for interconnecting the device
   with its neighboring WDM-node (see OMS MCG above).  The number of
   these interfaces denote also the degree of the WDM-node.  A degree 3
   WDM-node for example has 3 DWDM links that interconnect the WDM-node
   with 3 neighboring WDM-nodes.  Additionally, the WDM-node provides
   client interfaces for interconnecting the WDM-node with client
   devices such as IP routers or Ethernet switches.  These client
   interfaces are the client interfaces of the integrated optical
   transponders.

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               . . . . . . . . . . . . . . . . . .
               .           WDM-TE-Node           .
         +-----.-------------------------------- .-----+
         |     .             WDM-Node            .     |
         |     .   /|  +-----------------+  |\   .     |
    Line |     .  / |--|                 |--| \  .     | Line
    WEST |  /| . |  |--|                 |--|  | . |\  | EAST
   ------+-/ |-.-|  |--|  photonic       |--|  |-.-| \-+-----
   ------+-\ |-.-|  |--|  cross-connect  |--|  |-.-| /-+-----
         |  \| . |  |--|                 |--|  | . |/  |
         |     .  \ |--|                 |--| /  .     |
         |     .   \|  +-----------------+  |/   .     |
         |     .                                 .     |
         |     .     +---+ +---+ +---+ +---+     .     |
         |     .     | O | | O | | O | | O |     .     |
         |     .     | T | | T | | T | | T |     .     |
         |     .     +---+ +---+ +---+ +---+     .     |
         |     .      | |   | |   | |   | |      .     |
         +-----.------+-+---+-+---+-+---+-+------.-----+
               . . . .|.| . |.| . |.| . |.|. . . .
                      | |   | |   | |   | |
                        Client Interfaces

    Figure 8: Integrated WDM-node Architectiure with Local Transponders

2.9.2.  Integrated WDM-node with Integrated Optical Transponders and
        Single Channel Add/Drop Interfaces for Remote Optical
        Transponders

   Figure 9 below shows the extreme case where all optical transponders
   are not integral parts of the WDM-node but are separate devices that
   are connected to the add/drop ports of the WDM-node.  If the optical
   transponders and the WDM-node are collocated and if short single
   channel fiber links are used to interconnect the optical transponders
   with an add/drop port of the WDM-node, the optical domain controller
   may present these optical transponders in the same way as local
   optical transponders.  If, however, the optical impairments of the
   single channel fiber link between the optical transponder and the
   add/drop port of the WDM-node cannot be neglected, it is necessary to
   represent the fiber link with its optical impairments in the topology
   model This also implies that the optical transponders belong to a
   separate TE-node

   [Editor's note: this requires further study].

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               . . . . . . . . . . . . . . . . . .
               .           WDM-TE-Node           .
         +-----.-------------------------------- .-----+
         |     .            WDM-Node             .     |
         |     .   /|  +-----------------+  |\   .     |
    Line |     .  / |--|                 |--| \  .     | Line
    WEST |  /| . |  |--|                 |--|  | . |\  | EAST
   ------+-/ |-.-|  |--|  photonic       |--|  |-.-| \-+-----
   ------+-\ |-.-|  |--|  cross-connect  |--|  |-.-| /-+-----
         |  \| . |  |--|                 |--|  | . |/  |
         |     .  \ |--|                 |--| /  .     |
         |     .   \|  +-----------------+  |/   .     |
         +-----.---------|----|---|----|---------.-----|
    Colored OT .       +-+   ++   ++   +-+       .
    line I/F   .       |     |     |     |       .
               .     +---+ +---+ +---+ +---+     .
               .     | O | | O | | O | | O |     .
               .     | T | | T | | T | | T |     .
               .     +---+ +---+ +---+ +---+     .
               . . . .|.| . |.| . |.| . |.|. . . .
                      | |   | |   | |   | |
                        Client Interfaces

    Figure 9: Integrated WDM-node Architectiure with Remote Transponders

2.9.3.  Disaggregated WDM-TE-node Subdivided into Degree, Add/Drop, and
        Optical Transponder Subsystems

   Recently, some DWDM network operators started demanding WDM
   subsystems from their vendors.  An example is the OpenROADM project
   where multiple operators and vendors are developing related YANG
   models.  The subsystems of a disaggregated WDM-TE-node are:

   *  Single degree subsystems

   *  Add/drop subsystems

   *  Optical transponder subsystems

   These subsystems are separate network elements and each network
   element provides a separate management and control interface.  The
   subsystems are typically interconnected using short fiber patch
   cables and form together a disaggregated WDM-TE-node.  This
   disaggregated WDM-TE-node architecture is depicted in Figure 10
   below.

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   As this document defines TE topology YANG model augmentations
   [RFC8795] for the TE topology YANG model provided at the north-bound
   interface of the optical domain controller, it is a valid assumption
   that the optical domain controller abstracts the subsystems of a
   disaggregated WDM-TE-node and presents the disaggregated WDM-TE-node
   in the same way as an integrated WDM-node hiding all the
   interconnects that are not relevant from an external TE topology
   view.

              . . . . . . . . . . . . . . . . .  .
              .            WDM-TE-Node           .
        +-----.----------+            +----------.-----+
        | Degree 1       |            |       Degree 2 |
   Line |     .  +-----+ |            + +-----+  .     | Line
    1   |  /| .  |  W  |-|------------|-|  W  |  . |\  |  2
   -----+-/ |-.--|  S  ********  ********  S  |--.-| \-+-----
   -----+-\ |-.--|  S  | |    *  *    | |  S  |--.-| /-+-----
        |  \| .  |     |-|-+  *  *  +-|-|     |  . |/  |
        |     .  +-+-+-+ | |  *  *  | | +-+-+-+  .     |
        +-----.----|-----+ |  *  *  | +-----|----.-----+
              .    |       |  *  *  |       |    .
        +-----.----|-----+ |  *  *  | +-----|----.-----+
        | Degree 4 |     | |  *  *  | |     | Degree 3 |
   Line |     .  +-----+ | |  *  *  | | +-----+  .     | Line
    4   |  /| .  |  W  |-|-|--*--*--+ | |  W  |  . |\  |  3
   -----+-/ |-.--|  S  | | +--*--*----|-|  S  |--.-| \-+-----
   -----+-\ |-.--|  S  |-|----*--*----|-|  S  |--.-| /-+-----
        |  \| .  |     | |    *  *    | |     |  . |/  |
        |     .  +--*--+ |    *  *    | +--*--+  .     |
        +-----.-----*----+    *  *    +----*-----.-----+
              .     *         *  *         *     .
              .  +--*---------*--*---------*--+  .
              .  |          ADD               |  .
              .  |          DROP              |  .
              .  +----------------------------+  .
    Colored OT  .     |     |     |     |     .
     Line I/F   .   +---+ +---+ +---+ +---+   .
                .   | O | | O | | O | | O |   .
                .   | T | | T | | T | | T |   .
                .   +---+ +---+ +---+ +---+   .
                . . .|.| . |.| . |.| . |.|. . .
                     | |   | |   | |   | |
                       Client Interfaces

       Figure 10: Disaggregated WDM-TE-node Architecture with Remote
                                Transponders

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2.9.4.  Optical Impairments Imposed by WDM-TE-Nodes

   [Editor's note: the following text still needs to be updated based on
   the agreed terminology]

   When an optical OTSi signal traverses a ROADM node, optical
   impairments are imposed on the signal by various passive or active
   optical components inside the ROADM node.  Examples of optical
   impairments are:

   *  Chromatic dispersion (CD)

   *  Polarization mode dispersion (PMD)

   *  Polarization dependent loss (PDL)

   *  Optical amplifier noise due to amplified spontaneous emission
      (ASE)

   *  In-band cross-talk

   *  Filtering effects (for further study)

   A ROADM node contains a wavelength selective photonic switching
   function (WSS)that is capable of switching media channels (MCs)
   described in Section 2.3.4.  These MCs can be established between two
   line ports of the ROADM or between a line port and an Add/Drop port
   of the ROADM.  The Add/Drop ports of a ROADM are those ports to which
   optical transponders are connected.  Typically, this is a single
   channel signal (single OTSi), but principally this could also be a
   group of OTSi signals.  The optical impairments associated with these
   MCs are different and the paths of the MCs inside the ROADM node can
   be categorized as follows:

   *  Express path: MC path between two line ports of the ROADM
      (unidirectional)

   *  Add Path: MC path from an Add port to a line port of the ROADM

   *  Drop path: MC path from a line port to a Drop port of the ROADM

   Due to the symmetrical architecture of the ROADM node, the optical
   impairments associated with the express path are typically the same
   between any two line ports of the ROADM whereas the optical
   impairments for the add and drop paths are different and therefore
   have to be modeled separately.

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   The optical impairments associated with each of the three types of
   ROADM-node-internal paths described above are modeled as optical
   impairment parameter sets.  These parameter sets are modeled as an
   augmentation of the te-node-attributes defined in [RFC8795].  The te-
   node-attributes are augmented with a list of roadm-path-impairments
   for the three ROADM path types distinguished by the impairment-type.
   Each roadm-path-impairments list entry contains the set of optical
   impairment parameters for one of the three path types indicated by
   the impairment-type.  For the optical feasibility calculation based
   on the optical impairments, it is necessary to know whether the
   optical power of the OTSi stays within a certain power window.  This
   is reflected by some optical power related parameters such as loss
   parameters or power parameters, which are included in the optical
   impairment parameter sets (see tree view in Section 3).

   [RFC8795] defines a connectivity matrix and a local link connectivity
   list for the TE node.  The connectivity matrix describes the
   connectivity for the express paths between the different lines of the
   ROADM and the local link connectivity list describes the connectivity
   for the Add and Drop paths of the ROADM.  These matrices are
   augmented with a new roadm-path-impairment matrix element, an add-
   path-impairment, and drop-path-impairment matrix element,
   respectively, which are defined as a pointer to the corresponding
   entry in the roadm-path-impairments list (leaf-ref).

   [Editor's note: this section is still work in progress]

3.  YANG Model (Tree Structure)

   [Editor's note: tree view below always has to be updated before
   submitting a new revision!]

module: ietf-optical-impairment-topology

  augment /nw:networks/nw:network/nw:network-types/tet:te-topology:
    +--rw optical-impairment-topology!
  augment /nw:networks/nw:network:
    +--ro otsi-group* [otsi-group-id]
       +--ro otsi-group-id    string
       +--ro otsi* [otsi-carrier-id]
          +--ro otsi-carrier-id           uint16
          +--ro otsi-carrier-frequency?   union
          +--ro tx-channel-power?         union
          +--ro rx-channel-power?         union
          +--ro rx-total-power?           union
  augment /nw:networks/nw:network/nw:node:
    +--ro transponder* [transponder-id]
    |  +--ro transponder-id                   uint32

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    |  +--ro termination-type-capabilities?   enumeration
    |  +--ro supported-3r-mode?               enumeration
    |  +--ro transceiver* [transceiver-id]
    |     +--ro transceiver-id                 uint32
    |     +--ro supported-modes
    |     |  +--ro supported-mode* [mode-id]
    |     |     +--ro mode-id                      string
    |     |     +--ro (mode)
    |     |        +--:(G.698.2)
    |     |        |  +--ro standard-mode?         standard-mode
    |     |        +--:(organizational-mode)
    |     |        |  +--ro organizational-mode
    |     |        |     +--ro operational-mode?
    |     |        |     |       operational-mode
    |     |        |     +--ro organization-identifier?
    |     |        |     |       organization-identifier
    |     |        |     +--ro min-central-frequency?
    |     |        |     |       frequency-thz
    |     |        |     +--ro max-central-frequency?
    |     |        |     |       frequency-thz
    |     |        |     +--ro central-frequency-step?
    |     |        |     |       frequency-ghz
    |     |        |     +--ro tx-channel-power-min?      dbm-t
    |     |        |     +--ro tx-channel-power-max?      dbm-t
    |     |        |     +--ro rx-channel-power-min?      dbm-t
    |     |        |     +--ro rx-channel-power-max?      dbm-t
    |     |        |     +--ro rx-total-power-max?        dbm-t
    |     |        +--:(explicit-mode)
    |     |           +--ro explicit-mode
    |     |              +--ro supported-modes
    |     |              |  +--ro supported-application-codes*
    |     |              |  |       -> ../../../mode-id
    |     |              |  +--ro supported-organizational-modes*
    |     |              |          -> ../../../mode-id
    |     |              +--ro line-coding-bitrate?
    |     |              |       identityref
    |     |              +--ro bitrate?
    |     |              |       uint16
    |     |              +--ro max-polarization-mode-dispersion?
    |     |              |       decimal64
    |     |              +--ro max-chromatic-dispersion?
    |     |              |       decimal64
    |     |              +--ro chromatic-and-polarization-dispersion-penalty* []
    |     |              |  +--ro chromatic-dispersion
    |     |              |  |       union
    |     |              |  +--ro polarization-mode-dispersion
    |     |              |  |       union
    |     |              |  +--ro penalty

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    |     |              |          union
    |     |              +--ro max-diff-group-delay?
    |     |              |       int32
    |     |              +--ro max-polarization-dependent-loss-penalty* []
    |     |              |  +--ro max-polarization-dependent-loss
    |     |              |  |       power-in-db-or-null
    |     |              |  +--ro penalty
    |     |              |          union
    |     |              +--ro available-modulation-type?
    |     |              |       identityref
    |     |              +--ro min-OSNR?
    |     |              |       snr
    |     |              +--ro min-Q-factor?
    |     |              |       int32
    |     |              +--ro available-baud-rate?
    |     |              |       uint32
    |     |              +--ro roll-off?
    |     |              |       decimal64
    |     |              +--ro min-carrier-spacing?
    |     |              |       frequency-ghz
    |     |              +--ro available-fec-type?
    |     |              |       identityref
    |     |              +--ro fec-code-rate?
    |     |              |       decimal64
    |     |              +--ro fec-threshold?
    |     |              |       decimal64
    |     |              +--ro min-central-frequency?
    |     |              |       frequency-thz
    |     |              +--ro max-central-frequency?
    |     |              |       frequency-thz
    |     |              +--ro central-frequency-step?
    |     |              |       frequency-ghz
    |     |              +--ro tx-channel-power-min?
    |     |              |       dbm-t
    |     |              +--ro tx-channel-power-max?
    |     |              |       dbm-t
    |     |              +--ro rx-channel-power-min?
    |     |              |       dbm-t
    |     |              +--ro rx-channel-power-max?
    |     |              |       dbm-t
    |     |              +--ro rx-total-power-max?
    |     |                      dbm-t
    |     +--ro configured-mode?
    |     |       -> ../supported-modes/supported-mode/mode-id
    |     +--ro outgoing-otsi
    |     |  +--ro otsi-group-ref?
    |     |  |       -> ../../../../../otsi-group/otsi-group-id
    |     |  +--ro otsi-ref?         leafref

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    |     +--ro incoming-otsi
    |     |  +--ro otsi-group-ref?
    |     |  |       -> ../../../../../otsi-group/otsi-group-id
    |     |  +--ro otsi-ref?         leafref
    |     +--ro configured-termination-type?   enumeration
    +--ro regen-group* [group-id]
       +--ro group-id           uint32
       +--ro regen-metric?      uint32
       +--ro transponder-ref*   -> ../../transponder/transponder-id
  augment /nw:networks/nw:network/nt:link/tet:te
            /tet:te-link-attributes:
    +--ro OMS-attributes
       +--ro generalized-snr?                        l0-types:snr
       +--ro equalization-mode                       identityref
       +--ro (power-param)?
       |  +--:(channel-power)
       |  |  +--ro nominal-carrier-power?
       |  |          l0-types:power-in-dbm-or-null
       |  +--:(power-spectral-density)
       |     +--ro nominal-power-spectral-density?   union
       +--ro media-channel-group* [i]
       |  +--ro i                 int16
       |  +--ro media-channels* [flexi-n]
       |     +--ro flexi-n           l0-types:flexi-n
       |     +--ro flexi-m?          l0-types:flexi-m
       |     +--ro otsi-group-ref?
       |     |       -> /nw:networks/network/otsi-group/otsi-group-id
       |     +--ro otsi-ref*         leafref
       |     +--ro delta-power?      l0-types:power-in-dbm-or-null
       +--ro OMS-elements* [elt-index]
          +--ro elt-index                 uint16
          +--ro oms-element-uid?          union
          +--ro reverse-element-ref
          |  +--ro link-ref?
          |  |       -> ../../../../../../../nt:link/link-id
          |  +--ro oms-element-ref*   leafref
          +--ro (element)
             +--:(amplifier)
             |  +--ro geolocation
             |  |  +--ro altitude?    int64
             |  |  +--ro latitude?    geographic-coordinate-degree
             |  |  +--ro longitude?   geographic-coordinate-degree
             |  +--ro amplifier
             |     +--ro type-variety    string
             |     +--ro operational
             |        +--ro amplifier-element* []
             |           +--ro name?
             |           |       string

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             |           +--ro frequency-range
             |           |  +--ro lower-frequency    frequency-thz
             |           |  +--ro upper-frequency    frequency-thz
             |           +--ro actual-gain
             |           |       l0-types:power-in-db-or-null
             |           +--ro tilt-target
             |           |       l0-types:decimal-2-digits-or-null
             |           +--ro out-voa
             |           |       l0-types:power-in-db-or-null
             |           +--ro in-voa
             |           |       l0-types:power-in-db-or-null
             |           +--ro total-output-power
             |           |       l0-types:power-in-db-or-null
             |           +--ro (power-param)?
             |           |  +--:(channel-power)
             |           |  |  +--ro nominal-carrier-power?
             |           |  |          l0-types:power-in-dbm-or-null
             |           |  +--:(power-spectral-density)
             |           |     +--ro nominal-power-spectral-density?
             |           |             union
             |           +--ro raman-direction?
             |           |       enumeration
             |           +--ro raman-pump* []
             |              +--ro frequency?   l0-types:frequency-thz
             |              +--ro power?
             |                      l0-types:decimal-2-digits-or-null
             +--:(fiber)
             |  +--ro fiber
             |     +--ro type-variety    string
             |     +--ro length
             |     |       l0-types:decimal-2-digits-or-null
             |     +--ro loss-coef
             |     |       l0-types:decimal-2-digits-or-null
             |     +--ro total-loss      l0-types:power-in-db-or-null
             |     +--ro pmd?
             |     |       l0-types:decimal-2-digits-or-null
             |     +--ro conn-in?        l0-types:power-in-db-or-null
             |     +--ro conn-out?       l0-types:power-in-db-or-null
             +--:(concentratedloss)
                +--ro concentratedloss
                   +--ro loss    l0-types:power-in-db-or-null
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:tunnel-termination-point:
    +--ro ttp-transceiver* [transponder-ref transceiver-ref]
       +--ro transponder-ref
       |       -> ../../../../transponder/transponder-id
       +--ro transceiver-ref    leafref
  augment /nw:networks/nw:network/nw:node/tet:te

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            /tet:tunnel-termination-point:
    +--ro sliceable-transponder-list* [carrier-id]
       +--ro carrier-id    uint32
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:te-node-attributes:
    +--ro roadm-path-impairments* [roadm-path-impairments-id]
       +--ro roadm-path-impairments-id    uint32
       +--ro (impairment-type)?
          +--:(roadm-express-path)
          |  +--ro roadm-express-path* []
          |     +--ro frequency-range
          |     |  +--ro lower-frequency    frequency-thz
          |     |  +--ro upper-frequency    frequency-thz
          |     +--ro roadm-pmd?                union
          |     +--ro roadm-cd?                 union
          |     +--ro roadm-pdl?
          |     |       l0-types:power-in-db-or-null
          |     +--ro roadm-inband-crosstalk?
          |     |       l0-types:power-in-db-or-null
          |     +--ro roadm-maxloss?
          |             l0-types:power-in-db-or-null
          +--:(roadm-add-path)
          |  +--ro roadm-add-path* []
          |     +--ro frequency-range
          |     |  +--ro lower-frequency    frequency-thz
          |     |  +--ro upper-frequency    frequency-thz
          |     +--ro roadm-pmd?                union
          |     +--ro roadm-cd?                 union
          |     +--ro roadm-pdl?
          |     |       l0-types:power-in-db-or-null
          |     +--ro roadm-inband-crosstalk?
          |     |       l0-types:power-in-db-or-null
          |     +--ro roadm-maxloss?
          |     |       l0-types:power-in-db-or-null
          |     +--ro roadm-pmax?
          |     |       l0-types:power-in-dbm-or-null
          |     +--ro roadm-osnr?               l0-types:snr-or-null
          |     +--ro roadm-noise-figure?       union
          +--:(roadm-drop-path)
             +--ro roadm-drop-path* []
                +--ro frequency-range
                |  +--ro lower-frequency    frequency-thz
                |  +--ro upper-frequency    frequency-thz
                +--ro roadm-pmd?                union
                +--ro roadm-cd?                 union
                +--ro roadm-pdl?
                |       l0-types:power-in-db-or-null
                +--ro roadm-inband-crosstalk?

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                |       l0-types:power-in-db-or-null
                +--ro roadm-maxloss?
                |       l0-types:power-in-db-or-null
                +--ro roadm-minloss?
                |       l0-types:power-in-db-or-null
                +--ro roadm-typloss?
                |       l0-types:power-in-db-or-null
                +--ro roadm-pmin?
                |       l0-types:power-in-dbm-or-null
                +--ro roadm-pmax?
                |       l0-types:power-in-dbm-or-null
                +--ro roadm-ptyp?
                |       l0-types:power-in-dbm-or-null
                +--ro roadm-osnr?               l0-types:snr-or-null
                +--ro roadm-noise-figure?       union
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:information-source-entry/tet:connectivity-matrices:
    +--ro roadm-path-impairments?   leafref
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:information-source-entry/tet:connectivity-matrices
            /tet:connectivity-matrix:
    +--ro roadm-path-impairments?   leafref
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:te-node-attributes/tet:connectivity-matrices:
    +--ro roadm-path-impairments?
            -> ../../roadm-path-impairments/roadm-path-impairments-id
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:te-node-attributes/tet:connectivity-matrices
            /tet:connectivity-matrix:
    +--ro roadm-path-impairments?   leafref
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:tunnel-termination-point
            /tet:local-link-connectivities:
    +--ro add-path-impairments?    leafref
    +--ro drop-path-impairments?   leafref
  augment /nw:networks/nw:network/nw:node/tet:te
            /tet:tunnel-termination-point
            /tet:local-link-connectivities
            /tet:local-link-connectivity:
    +--ro add-path-impairments?    leafref
    +--ro drop-path-impairments?   leafref
    +--ro llc-transceiver* [ttp-transponder-ref ttp-transceiver-ref]
       +--ro ttp-transponder-ref
       |       -> ../../../../ttp-transceiver/transponder-ref
       +--ro ttp-transceiver-ref
       |       -> ../../../../ttp-transceiver/transceiver-ref
       +--ro is-allowed?              boolean
       +--ro add-path-impairments?    leafref

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       +--ro drop-path-impairments?   leafref

4.  Optical Impairment Topology YANG Model

   [Editor's note: YANG code below always has to be updated before
   submitting a new revision!]

   <CODE BEGINS>
   module ietf-optical-impairment-topology {
     yang-version 1.1;

     namespace "urn:ietf:params:xml"
             + ":ns:yang:ietf-optical-impairment-topology";

     prefix "optical-imp-topo";

     import ietf-network {
       prefix "nw";
     }

     import ietf-network-topology {
       prefix "nt";
     }

     import ietf-te-topology {
       prefix "tet";
     }

     import ietf-layer0-types {
       prefix "l0-types";
     }

     organization
       "IETF CCAMP Working Group";

     contact
       "Editor:   Young Lee <younglee.tx@gmail.com>
        Editor:   Haomian Zheng <zhenghaomian@huawei.com>
        Editor:   Nicola Sambo <nicosambo@gmail.com>
        Editor:   Victor Lopez <victor.lopezalvarez@telefonica.com>
        Editor:   Gabriele Galimberti <ggalimbe@cisco.com>
        Editor:   Giovanni Martinelli <giomarti@cisco.com>
        Editor:   Jean-Luc Auge <jeanluc.auge@orange.com>
        Editor:   Le Rouzic Esther <esther.lerouzic@orange.com>
        Editor:   Julien Meuric <julien.meuric@orange.com>
        Editor:   Italo Busi <Italo.Busi@huawei.com>
        Editor:   Dieter Beller <dieter.beller@nokia.com>

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        Editor:   Sergio Belotti <Sergio.belotti@nokia.com>
        Editor:   Griseri Enrico <enrico.griseri@nokia.com>
        Editor:   Gert Grammel <ggrammel@juniper.net>";

     description
       "This module contains a collection of YANG definitions for
        impairment-aware optical networks.

        Within this module, if the value of a mandatory attribute is
        unknown, it MUST be reported using the empty type.
        If an optional attribute is applicable but its value is unknown,
        it MUST be reported using the empty type.
        If an optional attribute is not applicable to an entity, it MUST
        be omitted (not be present in the datastore).

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
        'MAY', and 'OPTIONAL' in this document are to be interpreted as
        described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.

        Copyright (c) 2022 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD
        License set forth in Section 4.c of the IETF Trust's Legal
        Provisions Relating to IETF Documents
        (http://trustee.ietf.org/license-info).
        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

   // RFC Ed.: replace XXXX with actual RFC number and remove
   // this note

   // replace the revision date with the module publication date
   // the format is (year-month-day)

     revision 2022-03-07 {
       description
         "Initial Version";
       reference
         "RFC XXXX: A Yang Data Model for Impairment-aware
          Optical Networks";
     }

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     // grouping

     grouping sliceable-transponder-attributes {
       description
         "Configuration of a sliceable transponder.";
       list sliceable-transponder-list {
         key "carrier-id";
         config false;
         description "List of carriers";
         leaf carrier-id {
           type uint32;
           config false;
           description "Identifier of the carrier";
         }
       }
     }

     /*
      * Groupings
      */

     grouping amplifier-params {
       description "describes parameters for an amplifier";
       container amplifier {
         description
           "amplifier type, operatonal parameters are described.";
         leaf type-variety {
           type string;
           mandatory true ;
           description
             "String identifier of amplifier type referencing
             a specification in a separate equipment catalog";
         }
         container operational {
           description "amplifier operational parameters";
           list amplifier-element {
             description
               "The list of parallel amplifier elements within an
               amplifier used to amplify different frequency ranges.";
             leaf name {
               type string;
               description
                 "The name of the amplifier element as specified in
                 the vendor's specification associated with the
                 type-variety.";
             }
             container frequency-range {
               description

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                 "The frequency range amplified by the amplifier
                 element.";
               uses l0-types:frequency-range;
             }
             leaf actual-gain {
               type l0-types:power-in-db-or-null;
               mandatory true ;
               description "..";
             }
             leaf tilt-target {
               type l0-types:decimal-2-digits-or-null;
               mandatory true ;
               description "..";
             }
             leaf out-voa {
               type l0-types:power-in-db-or-null;
               units dB;
               mandatory true;
               description "..";
             }
             leaf in-voa {
               type l0-types:power-in-db-or-null;
               mandatory true;
               description "..";
             }
             leaf total-output-power {
               type l0-types:power-in-db-or-null;
               mandatory true;
               description
                 "It represent total output power measured in the range
                 specified by the frequency-range.

                 Optical power is especially needed to re-compute/check
                 consistency of span (fiber+ concentrated loss) loss
                 value, with respect to loss/gain information on
                 elements.";
             }
             uses power-param;
             leaf raman-direction {
               type enumeration {
                 enum co-propagating {
                   description
                     "Co-propagating indicates that optical pump light
                     is injected in the same direction to the optical
                     signal that is amplified (forward pump).";
                 }
                 enum counter-propagating {
                   description

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                     "Counter-propagating indicates that optical pump
                     light is injected in opposite direction to the
                     optical signal that is amplified (backward pump).";
                 }
               }
               description
                 "The direction of injection of the raman pump.";
             }
             list raman-pump {
               description
                 "The list of pumps for the Raman amplifier.";
               leaf frequency {
                 type l0-types:frequency-thz;
                 description
                   "The raman pump central frequency.";
               }
               leaf power {
                 type l0-types:decimal-2-digits-or-null;
                 units "Watts";
                 description
                   "The total pump power considering a depolarized pump
                   at the raman pump central frequency.";
               }
             }
           }  // list amplifier-element
         }  // container operational
       }  // container amplifier
     }  // grouping amplifier-params

     grouping fiber-params {
       description
         "String identifier of fiber type referencing a
          specification in a separate equipment catalog";
       container fiber {
         description "fiber characteristics";
         leaf type-variety {
           type string ;
           mandatory true ;
           description "fiber type";
         }
         leaf length {
           type l0-types:decimal-2-digits-or-null;
           units km;
           mandatory true ;
           description "length of fiber";
         }
         leaf loss-coef {
           type l0-types:decimal-2-digits-or-null;

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           units dB/km;
           mandatory true ;
           description "loss coefficient of the fiber";
         }
         leaf total-loss {
           type l0-types:power-in-db-or-null;
           mandatory true ;
           description
             "includes all losses: fiber loss and conn-in and
              conn-out losses";
         }
         leaf pmd{
           type l0-types:decimal-2-digits-or-null;
           units sqrt(ps);
           description "pmd of the fiber";
         }
         leaf conn-in{
           type l0-types:power-in-db-or-null;
           description "connector-in";
         }
         leaf conn-out{
           type l0-types:power-in-db-or-null;
           description "connector-out";
         }
       }
     }

     grouping roadm-express-path {
       description
         "The optical impairments of a ROADM express path.";
       leaf roadm-pmd {
         type union {
           type decimal64 {
             fraction-digits 8;
             range "0..max";
           }
           type empty;
         }
         units "ps/(km)^0.5";
         description
           "Polarization Mode Dispersion";
       }
       leaf roadm-cd {
         type union {
           type decimal64 {
             fraction-digits 5;
           }
           type empty;

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         }
         units "ps/nm";
         description "Chromatic Dispersion";
       }
       leaf roadm-pdl {
         type l0-types:power-in-db-or-null;
         description "Polarization dependent loss";
       }
       leaf roadm-inband-crosstalk {
         type l0-types:power-in-db-or-null;
         description
           "In-band crosstalk, or coherent crosstalk, can occur in
             components that can have multiple same wavelength inputs
             with the inputs either routed to different output ports,
             or all but 1 blocked";
       }
       leaf roadm-maxloss {
         type l0-types:power-in-db-or-null;
         description
           "This is the maximum expected add path loss from the
             ROADM ingress to the ROADM egress
             assuming no additional add path loss is added";
       }
     }

     grouping roadm-add-path {
       description "The optical impairments of a ROADM add path.";
       leaf roadm-pmd {
         type union {
           type decimal64 {
             fraction-digits 8;
             range "0..max";
           }
           type empty;
         }
         units "ps";
         description
           "Polarization Mode Dispersion";
       }
       leaf roadm-cd {
         type union {
           type decimal64 {
             fraction-digits 5;
           }
           type empty;
         }
         units "ps/nm";
         description "Cromatic Dispersion";

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       }
       leaf roadm-pdl {
         type l0-types:power-in-db-or-null;
         description "Polarization dependent loss";
       }
       leaf roadm-inband-crosstalk {
         type l0-types:power-in-db-or-null;
         description
           "In-band crosstalk, or coherent crosstalk,
             can occur in components that can have multiple same
             wavelength inputs,with the inputs either
             routed to different output ports,
             or all but 1 blocked.
             In the case of add path it is the total
             of the add block
             + egress WSS crosstalk contributions.";
       }
       leaf roadm-maxloss {
         type l0-types:power-in-db-or-null;
         description
           "This is the maximum expected add path loss from
             the add/drop port input to the ROADM egress,
             assuming no additional add path loss is added.
             This is used to establish the minimum required
             transponder output power required
             to hit the ROADM egress target power
             levels and preventing
             to hit the WSS attenuation limits.
             If the add path contains an internal amplifier
             this loss value should be based
             on worst case expected amplifier gain due to
             ripple or gain uncertainty";
       }
       leaf roadm-pmax {
         type l0-types:power-in-dbm-or-null;
         description
           "This is the maximum (per carrier) power level
             permitted at the add block input ports,
             that can be handled by the ROADM node.
             This may reflect either add amplifier power
             contraints or WSS adjustment limits.
             Higher power transponders would need to have
             their launch power reduced
             to this value or lower";
       }
       leaf roadm-osnr {
         type l0-types:snr-or-null;
         description

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           "Optical Signal-to-Noise Ratio (OSNR).
             If the add path contains the ability to adjust the
             carrier power levels into an add path amplifier
             (if present) to a target value,
             this reflects the OSNR contribution of the
             add amplifier assuming this target value is obtained.
             The worst case OSNR based on the input power and
             NF calculation method, and this value, should be used
             (if both are defined).";
       }
       leaf roadm-noise-figure {
         type union {
           type decimal64 {
             fraction-digits 5;
           }
           type empty;
         }
         units "dB";
         description
           "Noise Figure. If the add path contains an amplifier,
             this is the noise figure of that amplifier inferred
             to the add port.
             This permits add path OSNR calculation based
             on the input power levels to the add block
             without knowing the ROADM path losses to
             the add amplifier.";
       }
     }

     grouping roadm-drop-path {
       description "roadm drop block path optical impairments";
       leaf roadm-pmd {
         type union {
           type decimal64 {
             fraction-digits 8;
             range "0..max";
           }
           type empty;
         }
         units "ps/(km)^0.5";
         description
           "Polarization Mode Dispersion";
       }
       leaf roadm-cd {
         type union {
           type decimal64 {
             fraction-digits 5;
           }

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           type empty;
         }
         units "ps/nm";
         description "Chromatic Dispersion";
       }
       leaf roadm-pdl {
         type l0-types:power-in-db-or-null;
         description "Polarization dependent loss";
       }
       leaf roadm-inband-crosstalk {
         type l0-types:power-in-db-or-null;
         description
           "In-band crosstalk, or coherent crosstalk, can occur in
             components that can have multiple same wavelength
             inputs,with the inputs either routed to different
             output ports,or all but 1 blocked.
             In the case of drop path it is the total
             of the ingress
             to drop e.g. WSS and drop block crosstalk
             contributions.";
       }
       leaf roadm-maxloss {
         type l0-types:power-in-db-or-null;
         description
           "The net loss from the ROADM input,to the output
             of the drop block.
             If ROADM ingress to drop path includes an amplifier,
             the amplifier gain reduces the net loss.
             This is before any additional drop path attenuation
             that may be required
             due to drop amplifier power contraints.
             The max value correspond to worst case expected loss,
             including amplifier gain ripple or uncertainty.
             It is the maximum output power of the drop
             amplifier.";
       }
       leaf roadm-minloss {
         type l0-types:power-in-db-or-null;
         description
           "The net loss from the ROADM input, to the
             output of the drop block.
             If this ROADM ingress to drop path includes
             an amplifier,the amplifier gain reduces the net loss.
             This is before any additional drop path attenuation
             that may be required due to drop amplifier power
             contraints.
             The min value correspond to best case expected loss,
             including amplifier gain ripple or uncertainty.";

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       }
       leaf roadm-typloss {
         type l0-types:power-in-db-or-null;
         description
           "The net loss from the ROADM input,
             to the output of the drop block.
             If this ROADM ingress to drop path
             includes an amplifier,
             the amplifier gain reduces the net loss.
             This is before any additional drop path
             attenuation
             that may be required due to drop amplifier
             power contraints.
             The typ value correspond to typical case
             expected loss.";
       }
       leaf roadm-pmin {
         type l0-types:power-in-dbm-or-null;
         description
           "If the drop path has additional loss
             that is added, for example,
             to hit target power levels into a
             drop path amplifier, or simply, to reduce the
             power of a strong carrier
             (due to ripple,for example),
             then the use of the ROADM input power levels and
             the above drop losses is not appropriate.
             This parameter corresponds to the min per
             carrier power levels
             expected at the output of the drop block.
             A detail example of the comparison using
             these parameters is
             detailed in section xxx of the document yyy.";
       }
       leaf roadm-pmax {
         type l0-types:power-in-dbm-or-null;
         description
           "If the drop path has additional loss that is added,
             for example, to hit target power levels into a
             drop path amplifier,or simply,to reduce the power
             of a strong carrier(due to ripple,for example),
             then the use of the ROADM input power levels and the
             above drop losses is not appropriate.
             This parameter corresponds to the best case per
             carrier power levels expected at the output of the
             drop block.
             A detail example of the comparison using
             these parameters

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             is detailed in section xxx of the document yyy";
       }
       leaf roadm-ptyp {
         type l0-types:power-in-dbm-or-null;
         description
           "If the drop path has additional loss that is added,
             for example, to hit target power levels into a
             drop path amplifier,or simply,to reduce the
             power of a strong carrier(due to ripple,for example),
             then the use of the ROADM input power levels and
             the above drop losses is not appropriate.
             This parameter corresponds to the typical case
             per carrier power levels expected
             at the output of the drop block.";
       }
       leaf roadm-osnr {
         type l0-types:snr-or-null;
         description
           "Optical Signal-to-Noise Ratio (OSNR).
             Expected OSNR contribution of the drop path
             amplifier(if present)
             for the case of additional drop path loss
             (before this amplifier)
             in order to hit a target power level (per carrier).
             If both, the OSNR based on the ROADM
             input power level
             (Pcarrier =
             Pref+10Log(carrier-baudrate/ref-baud) + delta-power)
             and the input inferred NF(NF.drop),
             and this OSNR value, are defined,
             the minimum value between these two should be used";
       }
       leaf roadm-noise-figure {
         type union {
           type decimal64 {
             fraction-digits 5;
           }
           type empty;
         }
         units "dB";
         description
           "Drop path Noise Figure.
             If the drop path contains an amplifier,
             this is the noise figure
             of that amplifier, inferred to the
             ROADM ingress port.
             This permits to determine
             amplifier OSNR contribution

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             without having to specify the
             ROADM node’s losses to that amplifier.
             This applies for the case of no
             additional drop path loss,
             before the amplifier, in order to reduce the power
             of the carriers to a target value";
       }
     }

     grouping concentratedloss-params{
       description "concentrated loss";
       container concentratedloss{
         description "concentrated loss";
         leaf loss {
           type l0-types:power-in-db-or-null;
           mandatory true;
           description "..";
         }
       }
     }

     grouping power-param{
       description
         "optical power or PSD after the ROADM or after the out-voa";
       choice power-param {
         description
           "select the mode: channel power or power spectral density";
         case channel-power {
           when "/nw:networks/nw:network/nt:link/tet:te
               /tet:te-link-attributes/OMS-attributes
               /equalization-mode='carrier-power'";
           leaf nominal-carrier-power{
             type l0-types:power-in-dbm-or-null;
             description
               " Reference channel power. Same grouping is used for the
               OMS power after the ROADM (input of the OMS) or after the
               out-voa of each amplifier. ";
           }
         }
         case power-spectral-density{
           when "/nw:networks/nw:network/nt:link/tet:te
               /tet:te-link-attributes/OMS-attributes
               /equalization-mode='power-spectral-density'";
           leaf nominal-power-spectral-density{
             type union {
               type decimal64 {
                   fraction-digits 16;
               }

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               type empty;
             }
             units W/Hz ;
             description
               " Reference power spectral density after
                 the ROADM or after the out-voa.
                 Typical value : 3.9 E-14, resolution 0.1nW/MHz";
           }
         }
       }
     }

     grouping oms-general-optical-params {
       description "OMS link optical parameters";
       leaf generalized-snr {
         type l0-types:snr;
         description "generalized snr";
       }
       leaf equalization-mode{
         type identityref {
           base l0-types:type-power-mode;
         }
         mandatory true;
         description "equalization mode";
       }
       uses power-param;
     }

     grouping otsi-group {
       description "OTSiG definition , representing client
        digital information stream supported by 1 or more OTSi";

       list otsi {
         key "otsi-carrier-id";
         config false;
         description
           "list of OTSi contained in 1 OTSiG.
           The list could also be of only 1 element";
         leaf otsi-carrier-id {
           type uint16;
           description "OTSi carrier-id";
         }
         uses l0-types:common-transceiver-configured-param;
       } // OTSi list
     } // OTSiG grouping

     grouping media-channel-groups {
       description "media channel groups";

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       list media-channel-group {
       key "i";
         description
           "list of media channel groups";
         leaf i {
           type int16;
             description "index of media channel group member";
         }

         list media-channels {
           key "flexi-n";
           description
             "list of media channels represented as (n,m)";

    // this grouping add both n.m values
           uses l0-types:flexi-grid-frequency-slot;

           leaf otsi-group-ref {
             type leafref {
               path "/nw:networks/nw:network/otsi-group/otsi-group-id";
             }
             description
               "Reference to the otsi-group list to get otsi-group
               identifier of the
               OTSiG carried by this media channel
               that reports the transient stat";
           }
           leaf-list otsi-ref {
             type leafref {
               path "/nw:networks/nw:network/"
                  + "otsi-group[otsi-group-id=current()"
                  + "/../otsi-group-ref]/"
                  + "otsi/otsi-carrier-id" ;
             }
             description
                "Reference to the otsi list supporting
                the related OTSiG to get otsi identifier";
           }
           leaf delta-power{
             type l0-types:power-in-dbm-or-null;
             description
               " Deviation from the reference carrier power defined for
               the OMS.";
           }
         } // media channels list
       } // media-channel-groups list
     } // media media-channel-groups grouping

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     grouping oms-element {
       description "OMS description";
       list OMS-elements {
         key "elt-index";
         description
           "defines the spans and the amplifier blocks of
           the amplified lines";
         leaf elt-index {
           type uint16;
           description
             "ordered list of Index of OMS element
             (whether it's a Fiber, an EDFA or a
             Concentratedloss)";
         }
         leaf oms-element-uid {
           type union {
             type string;
             type empty;
           }
           description
             "unique id of the element if it exists";
         }
         container reverse-element-ref {
           description
             "It contains references to the elements which are
             associated with this element in the reverse
             direction.";
           leaf link-ref {
             type leafref {
               path "../../../../../../../nt:link/nt:link-id";
             }
             description
               "The reference to the OMS link which the OMS elements
               belongs to.";
           }
           leaf-list oms-element-ref {
             type leafref {
               path "../../../../../../../nt:link[nt:link-id="
                   + "current()/../link-ref]/tet:te/"
                   + "tet:te-link-attributes/OMS-attributes/"
                   + "OMS-elements/elt-index";
             }
             description
               "The references to the OMS elements.";
           }
         }
         choice element {
           mandatory true;

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           description "OMS element type";
           case amplifier {
             uses tet:geolocation-container;
             uses amplifier-params;
           }
           case fiber {
             uses fiber-params;
           }
           case concentratedloss {
             uses concentratedloss-params ;
           }
         }
       }
     }

     grouping otsi-ref {
       description
         "References to an OTSi.
         This grouping is intended to be reused within the
         transceiver's list only.";
       leaf otsi-group-ref {
         type leafref {
           path "../../../../../otsi-group/otsi-group-id";
         }
         description
           "The OTSi generated by the transceiver's transmitter.";
       }
       leaf otsi-ref {
         type leafref {
           path "../../../../../otsi-group[otsi-group-id=" +
                "current()/../otsi-group-ref]/otsi/otsi-carrier-id";
         }
         description
           "The OTSi generated by the transceiver's transmitter.";
       }
     }
   /* Data nodes */

     augment "/nw:networks/nw:network/nw:network-types"
           + "/tet:te-topology" {
      description "optical-impairment topology augmented";
      container optical-impairment-topology {
        presence "indicates an impairment-aware topology of
        optical networks";
        description
        "Container to identify impairment-aware topology type";
      }
     }

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     augment "/nw:networks/nw:network" {
       when "nw:network-types/tet:te-topology" +
            "/optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment.";
       }
       description
         "Network augmentation for optical impairments data.";
       list otsi-group {
         key "otsi-group-id";
         config false;
         description
           "the list of possible OTSiG representing client digital
           stream";
         leaf otsi-group-id {
           type string;
           description
             "A network-wide unique identifier of otsi-group element.
             It could be structured e.g., as an URI or as an UUID.";
         }
         uses otsi-group;
       } // list of OTSiG
     }

     augment "/nw:networks/nw:network/nw:node" {
       when "../nw:network-types/tet:te-topology" +
            "/optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment.";
       }
       description
         "Node augmentation for optical impairments data.";
       list transponder {
         key "transponder-id";
         config false;
         description "list of transponder";
         leaf transponder-id {
           type uint32;
           description "transponder identifier";
         }
         leaf termination-type-capabilities {
           type enumeration {
             enum tunnel-only {
               description
                 "The transponder can only be used in an Optical
                 Tunnel termination configuration.";
             }
             enum 3r-only {

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               description
                 "The transponder can only be used in a 3R
                 configuration.";
             }
             enum 3r-or-tunnel {
               description
                 "The transponder can be configure to be used either
                 in an Optical Tunnel termination configuration or in
                 a 3R configuration.";
             }
           }
           description
             "Describes whether the transponder can be used in an
             Optical Tunnel termination configuration or in a 3R
             configuration (or both).";
         }
         leaf supported-3r-mode {
           when '(../termination-type-capabilities = "3r-only") or
                 (../termination-type-capabilities = "3r-or-tunnel")'
                 {
             description
               "Applies only when the transponder supports 3R
               configuration.";
           }
           type enumeration {
             enum unidir {
               description
                 "Unidirectional 3R configuration.";
             }
             enum bidir {
               description
                 "Bidirectional 3R configuration.";
             }
           }
           description
             "Describes the supported 3R configuration type.";
         }
         list transceiver {
           key "transceiver-id";
           config false;
           description "list of transceiver related to a transponder";
           leaf transceiver-id {
             type uint32;
             description "transceiver identifier";
           }
           uses l0-types:transceiver-capabilities;
           leaf configured-mode {
             type leafref {

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               path "../supported-modes/supported-mode/mode-id";
             }
             description
               "Reference to the configured mode for transceiver
               compatibility approach.";
           }
           container outgoing-otsi {
             description
               "The OTSi generated by the transceiver's transmitter.";
             uses otsi-ref;
           }
           container incoming-otsi {
             description
               "The OTSi received by the transceiver's received.";
             uses otsi-ref;
           }
           leaf configured-termination-type {
             type enumeration {
               enum tunnel-termination {
                 description
                   "The transceiver is currently used in an Optical
                   Tunnel termination configuration.";
               }
               enum 3r-regeneration {
                 description
                   "The transceiver is currently used in a 3R
                   configuration.";
               }
             }
             description
               "Describes whether the current configuration of the
               transceiver is used in an Optical Tunnel termination
               configuration or in a 3R configuration.

               If empty, it means that the transcevier is not used.";
           }
         } // end of list of transceiver
       } // end list of transponder
       list regen-group {
         key "group-id";
         config false;
         description
           "List of 3R groups.
           Any 3R group represent a group of transponder in which an a
           an electrical connectivity is either in place or could be
           dynamically provided, to associated transponders used for 3R
           regeneration.";
         leaf group-id {

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           type uint32;
           description
             "Group identifier used an index to access elements in the
             list of 3R groups.";
         }
         leaf regen-metric {
           type uint32;
           description
             "The cost permits choice among different group of
             transponders during path computation";
         }
         leaf-list transponder-ref {
           type leafref {
             path "../../transponder/transponder-id";
           }
           description
             "The list of transponder belonging to this 3R group.";
         }
       } // end 3R-group
     }

     augment "/nw:networks/nw:network/nt:link/tet:te"
           + "/tet:te-link-attributes"   {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment.";
       }
       description "Optical Link augmentation for impairment data.";
       container OMS-attributes {
         config false;
         description "OMS attributes";
         uses oms-general-optical-params;
         uses media-channel-groups;
         uses oms-element;
       }
     }

     augment "/nw:networks/nw:network/nw:node/tet:te"
           + "/tet:tunnel-termination-point" {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Impairment with
            non-sliceable transponder model";
       }

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       description
         "Tunnel termination point augmentation for non-sliceable
          transponder model.";

       list ttp-transceiver {
         key "transponder-ref transceiver-ref";
         config false;
         description
           "The list of the transceivers used by the TTP.";
         leaf transponder-ref {
           type leafref {
             path "../../../../transponder/transponder-id";
           }
           description
             "The reference to the transponder hosting the transceiver
             of the TTP.";
         }
         leaf transceiver-ref {
           type leafref {
             path "../../../../transponder[transponder-id=current()" +
                  "/../transponder-ref]/transceiver/transceiver-id";
           }
           description
             "The reference to the transceiver of the TTP.";
         }
       } // list of transceivers
     } // end of augment

     augment "/nw:networks/nw:network/nw:node/tet:te"
      + "/tet:tunnel-termination-point" {
      when "/nw:networks/nw:network/nw:network-types"
       +"/tet:te-topology/"
       + "optical-imp-topo:optical-impairment-topology" {
       description
         "This augment is only valid for optical impairment
          with sliceable transponder model";
      }
      description
        "Tunnel termination point augmentation for sliceable
         transponder model.";
      uses sliceable-transponder-attributes;
     }

     augment "/nw:networks/nw:network/nw:node/tet:te"
           + "/tet:te-node-attributes" {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology"
          + "/optical-imp-topo:optical-impairment-topology" {

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         description
           "This augment is only valid for Optical Impairment
           topology";
       }
       description
         "node attributes augmentantion for optical-impairment ROADM
          node";

       list roadm-path-impairments {
         key "roadm-path-impairments-id";
         config false;
         description
           "The set of optical impairments related to a ROADM path.";

         leaf roadm-path-impairments-id {
           type uint32;
           description "index of the ROADM path-impairment list";
         }
         choice impairment-type {
           description "type path impairment";
           case roadm-express-path {
             list roadm-express-path {
               description
                 "The list of optical impairments on a ROADM express
                 path for different frequency ranges.

                 Two elements in the list must not have the same range
                 or overlapping ranges.";
               container frequency-range {
                 description
                   "The frequency range for which these optical
                   impairments apply.";
                 uses l0-types:frequency-range;
               }
               uses roadm-express-path;
             }
           }
           case roadm-add-path {
             list roadm-add-path {
               description
                 "The list of optical impairments on a ROADM add
                 path for different frequency ranges.

                 Two elements in the list must not have the same range
                 or overlapping ranges.";
               container frequency-range {
                 description
                   "The frequency range for which these optical

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                   impairments apply.";
                 uses l0-types:frequency-range;
               }
               uses roadm-add-path;
             }
           }
           case roadm-drop-path {
             list roadm-drop-path {
               description
                 "The list of optical impairments on a ROADM add
                 path for different frequency ranges.

                 Two elements in the list must not have the same range
                 or overlapping ranges.";
               container frequency-range {
                 description
                   "The frequency range for which these optical
                   impairments apply.";
                 uses l0-types:frequency-range;
               }
               uses roadm-drop-path;
             }
           }
         }
       } // list path impairments
     } // augmentation for optical-impairment ROADM

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:information-source-entry/tet:connectivity-matrices"{
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology ";
       }

       description
         "Augment default TE node connectivity matrix information
         source.";

       leaf roadm-path-impairments {
         type leafref {
           path "../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id";
         }
         description "pointer to the list set of ROADM optical
         impairments";

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       }
     } // augmentation connectivity-matrices information-source

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:information-source-entry/tet:connectivity-matrices/"
           + "tet:connectivity-matrix" {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
            topology ";
       }

       description
         "Augment TE node connectivity matrix entry information
         source.";

       leaf roadm-path-impairments {
         type leafref {
           path "../../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id";
         }
         description "pointer to the list set of ROADM optical
         impairments";
       }
     } // augmentation connectivity-matrix information-source

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:te-node-attributes/tet:connectivity-matrices" {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology ";
       }

       description
         "Augment default TE node connectivity matrix.";
       leaf roadm-path-impairments {
         type leafref {
           path "../../roadm-path-impairments/"
           + "roadm-path-impairments-id";
         }
         config false; /*the identifier in the list */
          /*"roadm-path-impairments" of ROADM optical impairment*/
                       /*is read-only as the rest of attributes*/

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         description "pointer to the list set of ROADM optical
         impairments";
       }
     } // augmentation connectivity-matrices

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:te-node-attributes/"
           + "tet:connectivity-matrices/tet:connectivity-matrix" {
       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for
           Optical Impairment topology ";
       }

       description
         "Augment TE node connectivity matrix entry.";

       leaf roadm-path-impairments {
         type leafref {
           path "../../../roadm-path-impairments/"
           + "roadm-path-impairments-id";
         }
         config false;
         description "pointer to the list set of ROADM optical
          impairments";
       }
     } // augmentation connectivity-matrix

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:tunnel-termination-point/"
           + "tet:local-link-connectivities" {

       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
         "This augment is only valid for Optical Impairment topology ";
       }

       description
         "Augment default TTP LLC.";
       leaf add-path-impairments {
         type leafref {
           path "../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id" ;
         }

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         config false;
         description "pointer to the list set of ROADM optical
          impairments";
       }
       leaf drop-path-impairments {
         type leafref {
           path "../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM
         optical impairments";
       }
     } // augmentation local-link-connectivities

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:tunnel-termination-point/"
           + "tet:local-link-connectivities/"
           + "tet:local-link-connectivity" {

       when "/nw:networks/nw:network/nw:network-types"
          + "/tet:te-topology/"
          + "optical-imp-topo:optical-impairment-topology" {
         description
           "This augment is only valid for
            Optical Impairment topology ";
       }

       description
         "Augment TTP LLC entry.";
       leaf add-path-impairments {
         type leafref {
           path "../../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM optical
          impairments";
       }
       leaf drop-path-impairments {
         type leafref {
           path "../../../../tet:te-node-attributes/"
           + "roadm-path-impairments/roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM optical
         impairments";
       }

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       list llc-transceiver {
         key "ttp-transponder-ref ttp-transceiver-ref";
         config false;
         description
           "The list of transceivers having a LLC different from the
           default LLC.";
         leaf ttp-transponder-ref {
           type leafref {
             path "../../../../ttp-transceiver/transponder-ref";
           }
           description
             "The reference to the transponder hosting the transceiver
             of this LLCL entry.";
         }
         leaf ttp-transceiver-ref {
           type leafref {
             path "../../../../ttp-transceiver/transceiver-ref";
           }
           description
             "The reference to the the transceiver of this LLCL entry.";
         }
         leaf is-allowed {
           type boolean;
           description
             "'true' - connectivity from this transceiver is allowed;
             'false' - connectivity from this transceiver is
             disallowed.";
         }
         leaf add-path-impairments {
           type leafref {
             path "../../../../../tet:te-node-attributes/"
             + "roadm-path-impairments/roadm-path-impairments-id" ;
           }
           config false;
           description "pointer to the list set of ROADM optical
           impairments";
         }
         leaf drop-path-impairments {
           type leafref {
             path "../../../../../tet:te-node-attributes/"
             + "roadm-path-impairments/roadm-path-impairments-id" ;
           }
           config false;
           description "pointer to the list set of ROADM
           optical impairments";
         }
       }
     } // augmentation local-link-connectivity

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   }
   <CODE ENDS>

5.  Security Considerations

   The configuration, state, and action data defined in this document
   are designed to be accessed via a management protocol with a secure
   transport layer, such as NETCONF [RFC6241].  The NETCONF access
   control model [RFC8341] provides the means to restrict access for
   particular NETCONF users to a preconfigured subset of all available
   NETCONF protocol operations and content.

   A number of configuration data nodes defined in this document are
   read-only; however, these data nodes may be considered sensitive or
   vulnerable in some network environments (TBD).

6.  IANA Considerations

   This document registers the following namespace URIs in the IETF XML
   registry [RFC3688]:

   --------------------------------------------------------------------
   URI: urn:ietf:params:xml:ns:yang:ietf-optical-impairment-topology
   Registrant Contact: The IESG.
   XML: N/A, the requested URI is an XML namespace.
   --------------------------------------------------------------------

   This document registers the following YANG modules in the YANG Module
   Names registry [RFC7950]:

   --------------------------------------------------------------------
   name:      ietf-optical-impairment-topology
   namespace: urn:ietf:params:xml:ns:yang:ietf-optical-impairment-
   topology
   prefix:    optical-imp-topo
   reference: RFC XXXX (TDB)
   --------------------------------------------------------------------

7.  Acknowledgments

   We thank Daniele Ceccarelli and Oscar G.  De Dios for useful
   discussions and motivation for this work.

8.  References

8.1.  Normative References

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8795]  Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Gonzalez de Dios, "YANG Data Model for Traffic
              Engineering (TE) Topologies", RFC 8795,
              DOI 10.17487/RFC8795, August 2020,
              <https://www.rfc-editor.org/info/rfc8795>.

8.2.  Informative References

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [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,
              <https://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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7579>.

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   [RFC7581]  Bernstein, G., Ed., Lee, Y., Ed., Li, D., Imajuku, W., and
              J. Han, "Routing and Wavelength Assignment Information
              Encoding for Wavelength Switched Optical Networks",
              RFC 7581, DOI 10.17487/RFC7581, June 2015,
              <https://www.rfc-editor.org/info/rfc7581>.

   [RFC7698]  Gonzalez de Dios, O., Ed., Casellas, R., Ed., Zhang, F.,
              Fu, X., Ceccarelli, D., and I. Hussain, "Framework and
              Requirements for GMPLS-Based Control of Flexi-Grid Dense
              Wavelength Division Multiplexing (DWDM) Networks",
              RFC 7698, DOI 10.17487/RFC7698, November 2015,
              <https://www.rfc-editor.org/info/rfc7698>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8345]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
              2018, <https://www.rfc-editor.org/info/rfc8345>.

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,
              <https://www.rfc-editor.org/info/rfc8453>.

   [RFC9093]  Zheng, H., Lee, Y., Guo, A., Lopez, V., and D. King, "A
              YANG Data Model for Layer 0 Types", RFC 9093,
              DOI 10.17487/RFC9093, August 2021,
              <https://www.rfc-editor.org/info/rfc9093>.

   [RFC9094]  Zheng, H., Lee, Y., Guo, A., Lopez, V., and D. King, "A
              YANG Data Model for Wavelength Switched Optical Networks
              (WSONs)", RFC 9094, DOI 10.17487/RFC9094, August 2021,
              <https://www.rfc-editor.org/info/rfc9094>.

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   [I-D.ietf-ccamp-layer0-types-ext]
              Beller, D., Belotti, S., Zheng, H., Busi, I., and E. L.
              Rouzic, "A YANG Data Model for Layer 0 Types - Revision
              2", Work in Progress, Internet-Draft, draft-ietf-ccamp-
              layer0-types-ext-00, 10 August 2021,
              <https://www.ietf.org/archive/id/draft-ietf-ccamp-layer0-
              types-ext-00.txt>.

   [I-D.ietf-ccamp-dwdm-if-param-yang]
              Galimberti, G., Kunze, R., Burk, A., Hiremagalur, D., and
              G. Grammel, "A YANG model to manage the optical interface
              parameters for an external transponder in a WDM network",
              Work in Progress, Internet-Draft, draft-ietf-ccamp-dwdm-
              if-param-yang-06, 12 July 2021,
              <https://www.ietf.org/archive/id/draft-ietf-ccamp-dwdm-if-
              param-yang-06.txt>.

   [I-D.ietf-teas-te-topo-and-tunnel-modeling]
              Bryskin, I., Beeram, V. P., Saad, T., and X. Liu, "TE
              Topology and Tunnel Modeling for Transport Networks", Work
              in Progress, Internet-Draft, draft-ietf-teas-te-topo-and-
              tunnel-modeling-06, 12 July 2020,
              <https://www.ietf.org/archive/id/draft-ietf-teas-te-topo-
              and-tunnel-modeling-06.txt>.

   [G.672]    "Characteristics of multi-degree reconfigurable optical
              add/drop multiplexers", ITU-T Recommendation G.672,
              October 2020.

   [G.807]    "Generic functional architecture of the optical media
              network", ITU-T Recommendation G.807, February 2020.

   [G.709]    "Interfaces for the Optical Transport Network (OTN)",
              ITU-T Recommendation G.709, June 2016.

   [G.694.1]  "Spectral grids for WDM applications: DWDM frequency
              grid", ITU-T Recommendation G.694.1, February 2012.

   [G.959.1]  "Optical transport network physical layer interfaces",
              ITU-T Recommendation G.959.1, February 2012.

   [G.872]    "Architecture of optical transport networks",
              ITU-T Recommendation G.872, December 2019.

   [G.698.2]  "Amplified multichannel dense wavelength division
              multiplexing applications with single channel optical
              interfaces", ITU-T Recommendation G.698.2, November 2018.

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   [G.798.1]  "Types and characteristics of optical transport network
              equipment", ITU-T Recommendation G.798.1, January 2013.

Appendix A.  Contributors

   Aihua GuoHuawei Technologies

   Email: aguo@futurewei.com

   Jonas MartenssonRISE

   Email: jonas.martensson@ri.se

Appendix B.  Additional Authors

   Young LeeSamsung Electronics

   Email: younglee.tx@gmail.com

   Haomian ZhengHuawei Technologies

   Email: zhenghaomian@huawei.com

   Nicola SamboScuola Superiore Sant'Anna

   Email: nicosambo@gmail.com

   Giovanni MartinelliCisco

   Email: giomarti@cisco.com

   Jean-Luc AugeOrange

   Email: jeanluc.auge@orange.com

   Julien MeuricOrange

   Email: julien.meuric@orange.com

   Victor LopezNokia

   Email: Victor.Lopez@nokia.com

   Griseri EnricoNokia

   Email: Enrico.Griseri@nokia.com

   Gert GrammelJuniper

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   Email: ggrammel@juniper.net

Authors' Addresses

   Dieter Beller (editor)
   Nokia
   Email: Dieter.Beller@nokia.com

   Esther Le Rouzic
   Orange
   Email: esther.lerouzic@orange.com

   Sergio Belotti
   Nokia
   Email: Sergio.Belotti@nokia.com

   G. Galimberti
   Cisco
   Email: ggalimbe@cisco.com

   Italo Busi
   Huawei Technologies
   Email: Italo.Busi@huawei.com

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