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A YANG Data Model for Optical Impairment-aware Topology
draft-ietf-ccamp-optical-impairment-topology-yang-15

Document Type Active Internet-Draft (ccamp WG)
Authors Dieter Beller , Esther Le Rouzic , Sergio Belotti , Gabriele Galimberti , Italo Busi
Last updated 2024-03-04
Replaces draft-lee-ccamp-optical-impairment-topology-yang
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draft-ietf-ccamp-optical-impairment-topology-yang-15
CCAMP Working Group                                       D. Beller, Ed.
Internet-Draft                                                     Nokia
Intended status: Standards Track                            E. Le Rouzic
Expires: 5 September 2024                                         Orange
                                                              S. Belotti
                                                                   Nokia
                                                           G. Galimberti
                                                              Individual
                                                                 I. Busi
                                                     Huawei Technologies
                                                            4 March 2024

        A YANG Data Model for Optical Impairment-aware Topology
          draft-ietf-ccamp-optical-impairment-topology-yang-15

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
   Assignment (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 5 September 2024.

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Copyright Notice

   Copyright (c) 2024 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  . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   6
   2.  Reference Architecture  . . . . . . . . . . . . . . . . . . .   6
     2.1.  Control Plane Architecture  . . . . . . . . . . . . . . .   6
     2.2.  Optical Transport Network Data Plane  . . . . . . . . . .   8
     2.3.  OTS and OMS Media Channel Group . . . . . . . . . . . . .   8
       2.3.1.  Optical Tributary Signal (OTSi) . . . . . . . . . . .  10
       2.3.2.  Optical Tributary Signal Group (OTSiG)  . . . . . . .  11
       2.3.3.  Media Channel (MC)  . . . . . . . . . . . . . . . . .  12
       2.3.4.  Media Channel Group (MCG) . . . . . . . . . . . . . .  13
     2.4.  Optical Amplifiers  . . . . . . . . . . . . . . . . . . .  14
     2.5.  Dynamic Gain Equalizers . . . . . . . . . . . . . . . . .  17
     2.6.  Transponders  . . . . . . . . . . . . . . . . . . . . . .  17
       2.6.1.  Standard Modes  . . . . . . . . . . . . . . . . . . .  18
       2.6.2.  Organizational Modes  . . . . . . . . . . . . . . . .  18
       2.6.3.  Explicit Modes  . . . . . . . . . . . . . . . . . . .  20
       2.6.4.  Transponder Capabilities and Current Configuration  .  20
     2.7.  3R Regenerators . . . . . . . . . . . . . . . . . . . . .  22
     2.8.  WSS/Filter  . . . . . . . . . . . . . . . . . . . . . . .  25
     2.9.  Optical Fiber . . . . . . . . . . . . . . . . . . . . . .  25
     2.10. WDM-Node Architectures  . . . . . . . . . . . . . . . . .  26
       2.10.1.  Integrated WDM-node Architecture with Local Optical
               Transponders  . . . . . . . . . . . . . . . . . . . .  27
       2.10.2.  Integrated WDM-node with Integrated Optical
               Transponders and Single Channel Add/Drop Interfaces for
               Remote Optical Transponders . . . . . . . . . . . . .  28
       2.10.3.  Disaggregated WDM-TE-node Subdivided into Degree, Add/
               Drop, and Optical Transponder Subsystems  . . . . . .  29
       2.10.4.  Optical Impairments Imposed by WDM-TE-Nodes  . . . .  30
     2.11. Optical Protection Architectures  . . . . . . . . . . . .  32

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       2.11.1.  Individual OTSi Protection . . . . . . . . . . . . .  32
       2.11.2.  OMS MCG protection . . . . . . . . . . . . . . . . .  44
   3.  YANG Model (Tree Structure) . . . . . . . . . . . . . . . . .  53
   4.  Optical Impairment Topology YANG Model  . . . . . . . . . . .  62
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  98
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 100
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 100
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 100
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . 100
     8.2.  Informative References  . . . . . . . . . . . . . . . . . 101
   Appendix A.  JSON Code Examples for Optical Protection Uses
           Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 104
   Appendix B.  Optical Transponders in a Remote Shelf (Remote
           OTs)  . . . . . . . . . . . . . . . . . . . . . . . . . . 111
     B.1.  JSON Examples for Optical Transponders in a Remote Shelf
           (Remote OTs)  . . . . . . . . . . . . . . . . . . . . . . 114
   Appendix C.  Examples How to Use the organizational-mode
           Attribute . . . . . . . . . . . . . . . . . . . . . . . . 141
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . . 143
   Additional Authors  . . . . . . . . . . . . . . . . . . . . . . . 143
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 144

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].

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   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.

   The optical impairment aware topology for a WSON/SSON network based
   on the YANG data model defined in this document is intended to be
   used for exposing the network topology including optical impairments.
   Therefore, the topology information that is typically provided by a
   Transport PNC is assumed to be read-only (ro) data, i.e., not
   configurable (read-write).  This may change when the same optical
   impairment-aware topology model is used for other use cases than
   exposing the network topology.  E.g, for a path computation engine,
   where topological elements could be added in the context of a what-if
   scenario analysis.  This is outside of the scope of this document.

   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

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   *  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.

   The term "add/drop TE-link" refers to a TE-link representing the
   media channel between a transceiver's media port of a remote optical
   transponder (OT) and an add/drop port of the ROADM in the adjacent
   WDM-node.  The add/drop TE-link typically carries a single OTSi
   signal (modulated optical carrier).

   The term "bundled add/drop TE-link" refers to the TE-link bundling
   concept as defined in [RFC8795].  Multiple component links, add/drop
   TE-links in this case, are bundled into a single bundled add/drop TE-
   Link.

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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                    |
     +==========+=====================+==============================+
     | oit      | ietf-optical-       | [RFCXXXX]                    |
     |          | impairment-topology |                              |
     +----------+---------------------+------------------------------+
     | l0-types | ietf-layer0-types   | [I-D.ietf-ccamp-rfc9093-bis] |
     +----------+---------------------+------------------------------+
     | nw       | ietf-network        | [RFC8345]                    |
     +----------+---------------------+------------------------------+
     | nt       | ietf-network-       | [RFC8345]                    |
     |          | topology            |                              |
     +----------+---------------------+------------------------------+
     | tet      | ietf-te-topology    | [RFC8795]                    |
     +----------+---------------------+------------------------------+

              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 RFC AAAA                        Scope of RFC AAAA

                        Figure 1: Scope of RFC AAAA

   Note: The RFC Editor will replace AAAA above with the number assigned
   to the RFC once draft-ietf-ccamp-dwdm-if-param-yang will become an
   RFC.

   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].

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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.

     +-------------------+                      +-------------------+
     |     WDM-Node 1    |                      |     WDM-Node 2    |
     |                   |                      |                   |
     | 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 (WDM-node 1) is the egress Amplifier and PA (WDM-node 2) is the
   ingress amplifier for the OMS Media Channel Group (MCG) in the
   direction from left to right in Figure 2.

   According to [G.807], a Media Channel Group (MCG) represents "a
   unidirectional point-to-point management/control abstraction that
   represents a set of one or more media channels that are co-routed.  A
   media channel group (MCG) is bounded by a pair of media ports."

2.3.  OTS and OMS Media Channel Group

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

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     (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.

   [G.807] defines an OMS MCG as "The topological relationship between
   the media port on a filter or coupler where a set of media channels
   are aggregated and the media port on a filter or coupler where one or
   more media channel is added to or removed from that aggregate.  All
   of the media channels that are represented by the OMS MCG must be
   carried over the same serial concatenation of OTS MCGs and
   amplifiers."

   An OMS MCG originates at the ROADM in the source WDM-node and
   terminates at the ROADM in the destination WDM-node traversing the
   Booster Amplifier (BA) and the Pre-Amplifier (PA) in the WDM-nodes as
   well as the In-Line Amplifiers (ILAs) between the two WDM-nodes.

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

   An OMS MCG traverses 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 switching
   capabilities.

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   A WDM TE-link is terminated on both ends by a link termination point
   (LTP) as defined in [RFC8795].  Links between WDM nodes in optical
   transport networks are typically bidirectional.  Generally, they have
   different impairments in the two directions and hence they have to be
   modeled as a pair of two unidirectional TE-links following the
   [RFC8795] 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.

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] as "Optical signal that is placed within a network media
   channel for transport across the optical network.  This may consist
   of a single modulated optical carrier or a group of modulated optical
   carriers or subcarriers."  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
   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.

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   The OTSi signals in the YANG model are described by augmenting the
   network and each OTSi signal is uniquely identified by its otsi-
   carrier-id, which is unique within the scope the OTSiG [see
   Section 2.3.2 below] the OTSi belongs to.

2.3.2.  Optical Tributary Signal Group (OTSiG)

   The OTSiG is defined in ITU-T Recommendation G.807 [G.807] as a "set
   of optical tributary signals (OTSi) that supports a single digital
   client".  Hence, 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 [G.807], section 10.2.  The YANG model below
   supports both cases: the single OTSi case where the OTSiG contains a
   single OTSi (see [G.807], Figure 10-2) and the multiple OTSi case
   where the OTSiG consists of more than one OTSi (see [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.

   All OTSiGs are described in the YANG model by augmenting the network
   and each OTSiG is uniquely identified by its otsi-group-id, which is
   unique within the network.  Each OTSiG also contains a list of the
   OTSi signals belonging to the OTSiG.

                                  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

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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.

   In this document, an end-to-end MC is defined as a type of MC, which
   is formed by the serial concatenation of all the MCs from source
   Transceiver media ports to destination transceiver media ports.  This
   end-to-end MC is defined across all the ROADM nodes along the end-to-
   end optical path with the same nominal central frequency n and
   frequency slot of width m, which represents the effective frequency
   slot of the end-to-end MC.  An end-to-end MC can carry a single OTSi,
   or multiple OTSi signals belonging to the same OTSiG.

   [G.807_Amd1] defines a "network media channel (NMC)" as "a type of
   media channel that is formed by the serial concatenation of all media
   channels between the media port of a modulator and the media port of
   a demodulator".  The modulator and demodulator are integral functions
   of a transceiver and their media ports do not necessarily coincide
   with the media port of the transceiver, which is associated with the
   transceiver's physical optical port.  Due to this difference, the
   end-to-end MC is defined above and is used in this document.

   In section Section 2.11, the term "end-to-end MC path" is used to
   describe the topological aspect of the end-to-end MC, i.e., the path
   through the media (see: [G.807_Amd1], section 7.1.2).  This is in
   line with the TE path defined in [RFC8795], section 3.9, where the TE
   path is defined as "an ordered list of TE links and/or TE nodes on
   the TE topology graph" interconnecting a pair of tunnel termination
   points (TTPs).

                                    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: MC Example containing both OTSi signals of an OTSiG

   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 [G.694.1].  In this
   model, the effective frequency slot as defined in [G.807] is equal to
   the frequency slot of this 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)

   ITU-T [G.807] defines the Media Channel Group MCG as "A
   unidirectional point to point management/control abstraction that
   represents a set of one or more media channels that are co-routed."
   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: MCG Example with 2 MCs

   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.  Optical 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.  Three main optical
   amplifier technologies are existing today:

   *  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 (ILAs), 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 may have a variable optical attenuator on the ingress side (in-
   voa attribute) allowing to control the input power of the WDM signal
   (OMS MCG) entering the gain stage of the ILA.  It may also have a
   variable optical attenuator on the egress side, which allows to
   control the optical power of the WDM output signal (OMS MCG) of the
   ILA.  The actual-gain attribute reflects the gain of the ILA gain
   stage and does not include the attenuation of the in-voa and/or out-
   voa.

   To support the modeling of multi-band (e.g., C + L band) and multi-
   stage (cascaded) amplifiers as depicted in Figure 6, the OMS element
   that describes an optical amplifier may contain an unordered list of
   amplifier-elements.  The position of the element is based on the
   following attributes:

   *  lower-frequency and upper-frequency describing the frequency band
      the set of amplifier-elements are operating in.
   *  stage-order describing the sequential order of the cascaded
      amplifier-elements for the frequency band.

   The detailed representation of the amplifier stages is not always
   mandatory.  Abstraction is allowed as long as the optical impairments
   of the multi-stage amplifier are modeled properly.  For example, the
   detailed representation of the cascaded elements is needed in case
   the amplifier supports both amplification of the signal as well as
   the DGE function described in Section 2.5.

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   Multi-band amplifiers like the dual-band amplifier depicted in
   Figure 6 have a band-separating filter at the input and a band-
   combining multiplexer combining all the bands at the output.  This
   filter and multiplexer functions are not modeled explicitly and their
   optical impairments are subsumed in the optical impairments of the
   amplifier components.

                 Dual-band, Multi-stage Amplifier with DGE
             +-----------------------------------------------+
             |                                               |
             |                         C BAND                |
             |                  lower/upper-frequency        |
             |                            |                  |
             |                +-----------+----------+       |
             |                |                      |       |
             |                  OA1      DGE      OA2        |
             |                  |\      +---+     |\         |
             |                  | \     |   |     | \        |
         --->o---+------------->|  +----+   +-----+  +-->+---o--->
             |   |              | /     |   |     | /    |   |
             |   |              |/      +---+     |/     |   |
             |   | stage-order = 1        2        3     |   |
             |   |                                       |   |
             |   |                                       |   |
             |   | stage-order = 1        2        3     |   |
             |   |              |\      +---+     |\     |   |
             |   |              | \     |   |     | \    |   |
             |   +------------->|  +----+   +-----+  +-->+   |
             |                  | /     |   |     | /        |
             |                  |/      +---+     |/         |
             |                  OA1      DGE      OA2        |
             |                |                       |      |
             |                +-----------+-----------+      |
             |                            |                  |
             |                  lower/upper-frequency        |
             |                         L BAND                |
             |                                               |
             +-----------------------------------------------+

      Figure 6: Example of a Dual-band, Multi-stage Amplifier with DGE
                               Functionality

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   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.  Dynamic Gain Equalizers

   A Dynamic Gain Equalizer (DGE) is an optical equipment that is
   capable of adjusting the optical power on a per channel basis in
   order to compensate the channel power variation as a result of
   variable gain or loss the DWDM signals experienced while propagating
   through the network.  The channel power can be configured explicitly
   or in the form of power-spectral-density.

   [Editor's note: This sub-section needs to be completed and is still
   work in progress.]

2.6.  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
   transceivers.  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
   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

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   [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 transceivers.

   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

2.6.1.  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.

2.6.2.  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.

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   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 an operational 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
   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.

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   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.

2.6.3.  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
   common Application Codes or Organizational Modes cannot be met by the
   line system.

2.6.4.  Transponder Capabilities and Current Configuration

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

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   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 describing the transmitter's
      frequency fine tuning steps (the minimum 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.

   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.

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   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

2.7.  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 regeneration 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 2.6 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 7: 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.

      Implemantations may support the change of the carrier frequency
      where the receiver may operate at a different optical frequency as
      the transmitter.  The transceiver mode is a property of the
      transceiver and is applied to the transmitter and the receiver.
      Therefore, the transceiver mode is the same for the two segments
      on the two sides of the 3R regenaretor realised by two
      transceivers operated in the uni-directional mode.

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

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

                         Sig. Proc. = Signal Processing

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                   Figure 8: Cross-3R Regenerator Example

   Due to the fact that 3R regenerators are composed of an optical
   transponder pair, the capability 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
   transponder capabilities regarding the 3R regenerator function are
   described by the following two YANG model attributes:

   *  supported-termination-type

   *  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 attribute describes the
   configuration of the transponder pair forming the 3R regenerator as
   described above.

   More text to be added here!

2.8.  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.

2.9.  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).

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   The loss of a fiber span can be described in two ways: it should be
   described by specifying the loss coefficient (loss-coef) of the fiber
   type in combination with the length of the fiber and it can be
   described by the total-loss attribute.  The total-loss should be
   provided when it can be measured with a power measurement facility at
   the output of the upstream node (input of the fiber span) and a power
   measurement facility at the input of the downstream node (output of
   the fiber span).  This measured loss typically differs from the
   calculated loss based on loss-coef and length as it includes all loss
   contributions including possible accumulated loss due to imperfect
   fiber splices and connector losses.  In case the total-loss cannot be
   measured (no power measurement facilities in place), this optional
   attribute shall be omitted.

   N.B.: In case of Raman amplifiers, the Raman gain shall not be
   included in the measured loss to properly reflect loss of the fiber
   span only in the total-loss attribute.

   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.

2.10.  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
   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).

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   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.]

2.10.1.  Integrated WDM-node Architecture with Local Optical
         Transponders

   Figure 2 and Figure 9 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.

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

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    Figure 9: Integrated WDM-node Architectiure with Local Transponders

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

   Figure 10 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].

                    . . . . . . . . . . . . . . . . . .
                    .           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 10: Integrated WDM-node Architectiure with Remote Transponders

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2.10.3.  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 11
   below.

   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.

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                   . . . . . . . . . . . . . . . . .  .
                   .            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 11: Disaggregated WDM-TE-node Architecture with Remote
                                Transponders

2.10.4.  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:

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   *  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, add/drop ports deal
   with a single channel signal (single OTSi), but principally this
   could also be a group of OTSi signals (OTSiG).  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.

   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

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   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).

2.11.  Optical Protection Architectures

   The YANG model defined in this document supports the following
   optical protection architectures:

   *  Individual OTSi protection

   *  OMS MCG protection = TE-link protection between adjacent WDM-TE-
      nodes

2.11.1.  Individual OTSi Protection

   Individual OTSi protection is a protection architecture where an
   individual OTSi signal is protected as described in Appendix III of
   ITU-T Recommendation G.873.1 [G.873.1].  This protection architecture
   requires dedicated photonic protection functions in the optical
   domain that are typically provided by dedicated protection hardware.
   These photonic protection functions are a photonic splitter function
   splitting the OTSi signal in transmit direction and a photonic
   selector function selecting the OTSi signal in receive direction from
   one of the two protection legs between the two protection functions
   terminating the individual OTSi protection.  This individual OTSi
   protection scheme can be considered as a photonic 1+1 protection
   scheme (1+1 sub-network connection protection (SNCP) in ITU-T
   terminology).

   In order to achieve short protection switching times, it is necessary
   that the OTSi signals of the two legs are identical in terms of
   wavelength, modulation format, FEC, etc., which means no receiver
   configuration changes when a protection switch at the selector occurs
   selecting the other leg.  This is important when 3R regenerators are
   needed between the two end-points terminating the protected segment,
   which typically is end-to-end.

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   In case of individual OTSi protection without 3R regenerators, two
   end-to-end MC paths are associated with the OTSi signal.  In the YANG
   model, this is modeled as leaf list of the otsi providing the e2e-mc-
   path-id for the two end-to-end MC paths associated with the
   individually 1+1 protected OTSi.  This scenario is depicted in
   Figure 12 (forward direction) and Figure 13 (reverse direction)below.

                           end-to-end MC path1
        |------------------------------------------------------->|

   +-----------+                                          +-----------+
   | WDM Node1 |           +-----+      +-----+           | WDM Node2 |
   |      +----|           | WDM |      | WDM |           |----+      |
   |      |   -o---------->o-----o----->o-----o---------->o-   |      |
   |  OT  |  / |           |Node3|      |Node4|           | \  |  OT  |
   | +--+ | /  |           +-----+      +-----+           |  \ | +--+ |
  -o-o  o-o-   |                                          |   -o-o  o-o-
   | +--+ | \  |     +-----+     +------+     +-----+     |  / | +--+ |
   |      |  \ |     | WDM |     | WDM  |     | WDM |     | /  |      |
   |      |   -o---->o-----o---->o------o---->o-----o---->o-   |      |
   |      +----|     |Node5|     | Node6|     |Node7|     |----+      |
   |   Splitter|     +-----+     +------+     +-----+     |Selector   |
   +-----------+                                          +-----------+

        |------------------------------------------------------->|
                           end-to-end MC path2

      Figure 12: Individual OTSi Protection without 3R regenerators
                           (forward direction)

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                           end-to-end MC path1'
        |<-------------------------------------------------------|

   +-----------+                                          +-----------+
   | WDM Node1 |           +-----+      +-----+           | WDM Node2 |
   |      +----|           | WDM |      | WDM |           |----+      |
   |      |   -o<----------o-----o<-----o-----o<----------o-   |      |
   |  OT  |  / |           |Node3|      |Node4|           | \  |  OT  |
   | +--+ | /  |           +-----+      +-----+           |  \ | +--+ |
  -o-o  o-o-   |                                          |   -o-o  o-o-
   | +--+ | \  |     +-----+     +------+     +-----+     |  / | +--+ |
   |      |  \ |     | WDM |     | WDM  |     | WDM |     | /  |      |
   |      |   -o<----o-----o<----o------o<----o-----o<----o-   |      |
   |      +----|     |Node5|     | Node6|     |Node7|     |----+      |
   |   Selector|     +-----+     +------+     +-----+     |Splitter   |
   +-----------+                                          +-----------+

        |<-------------------------------------------------------|
                           end-to-end MC path2'

      Figure 13: Individual OTSi Protection without 3R regenerators
                           (reverse direction)

   For each OMS MCG (TE-link) along the two end-to-end MC paths in
   forward direction (end-to-end MC path1 and end-to-end MC path2) as
   well as the two end-to-end MC paths in reverse direction (end-to-end
   MC path1' and end-to-end MC path2'), the e2e-mc-path-id is provided
   for the individually protected OTSi signal.  Based on this
   information, it is possible to construct the end-to-end MC paths
   between the optical transponders terminating the individually 1+1
   protected OTSi.

   In the scenario depicted in Figure 12 and Figure 13, the e2e-mc-path-
   id of end-to-end MC path1 and end-to-end MC path1' is provided for
   the TE-links between WDM Node1 and WDM Node3, WDM Node3 and WDM Node4
   as well as WDM Node4 and WDM Node2 while the e2e-mc-path-id of end-
   to-end MC path2 and end-to-end MC path2' is provided for the TE-links
   between WDM Node1 and WDM Node5, WDM Node5 and WDM Node6, WDM Node6
   and WDM Node7 as well as WDM Node7 and WDM Node2.

   If a 3R regenerator is crossed on one of the two legs or even on both
   legs, the end-to-end MCs are terminated on both sides of the 3R
   regenerator.  The configured-termination-type attribute set to "3r-
   regeneration" shall be used to indicate that the transceivers are
   forming a 3R regenerator instead of terminating the layer 0 tunnel
   (layer 0 service).  At WDM-nodes containing a 3R regenerator, the
   end-2-end MCs are stitched together forming the end-to-end path for

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   the layer 0 tunnel (layer 0 service).  This is reflected in the leaf
   list of the OTSi, which now lists all e2e-mc-path-ids of the end-to-
   end MC paths on the two legs of the individually 1+1 protected OTSi
   signal.

   In the scenario depicted in Figure 14 and Figure 15 below where a 3R
   regenerator is crossed in WDM Node6 on the lower leg, the e2e-mc-
   path-id leaf list has 3 entries (assumption: the same e2e-mc-path-id
   can be used for the path in forward and reverse direction):

   1.  The e2e-mc-path-id identifying end-to-end MC path1 from WDM Node1
       via WDM Node3 and WDM Node4 to WDM Node2 as well as end-to-end MC
       path1' in reverse direction (upper leg)

   2.  The e2e-mc-path-id identifying end-to-end MC path2 from WDM Node1
       via WDM Node5 to WDM Node6 containing the 3R regenerator as well
       as end-to-end MC path2' in reverse direction (left hand segment
       of the lower leg)

   3.  The e2e-mc-path-id identifying end-to-end MC path3 from WDM Node6
       containing the 3R regenerator via WDM Node7 to WDM Node2 as well
       as end-to-end MC path3' in reverse direction (right hand segment
       of the lower leg)

   Based on this modeling approach it is possible to identify the end-
   2-end MCs stitched together at 3R regenerators on each of the two
   legs of the individually protected 1+1 OTSi signal.  Like for the
   case without 3R regenerators is also possible to associate two end-
   to-end paths in forward and reverse direction for the two legs
   between the optical transponders terminating the individually 1+1
   protected OTSi in WDM Node1 and WDM Node2, respectively:

   1.  end-to-end MC path1 and end-to-end MC path1' (upper leg)
   2.  end-to-end MC path2 and end-to-end MC path2' stitched together
       with end-to-end MC path3 and end-to-end MC path3' (lower leg)

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                           end-to-end MC path1
        |------------------------------------------------------->|

   +-----------+                                          +-----------+
   | WDM Node1 |           +-----+      +-----+           | WDM Node2 |
   |      +----|           | WDM |      | WDM |           |----+      |
   |      |   -o---------->o-----o----->o-----o---------->o-   |      |
   |  OT  |  / |           |Node3|      |Node4|           | \  |  OT  |
   | +--+ | /  |           +-----+      +-----+           |  \ | +--+ |
  -o-o  o-o-   |                                          |   -o-o  o-o-
   | +--+ | \  |     +-----+     +------+     +-----+     |  / | +--+ |
   |      |  \ |     |     |     | +--+ |     |     |     | /  |      |
   |      |   -o---->o-----o---->o-o  o-o---->o-----o---->o-   |      |
   |      +----|     | WDM |     | +--+ |     | WDM |     |----+      |
   |   Splitter|     |Node5|     |  3R  |     |Node7|     |Selector   |
   +-----------+     +-----+     +------+     +-----+     +-----------+
                                 WDM Node6
                                 with 3R
                                 Regenerator

        |------------------------->|  |------------------------->|
            end-to-end MC path2           end-to-end MC path3

       Figure 14: Individual OTSi Protection with a 3R regenerator
                           (forward direction)

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                           end-to-end MC path1'
        |<-------------------------------------------------------|

   +-----------+                                          +-----------+
   | WDM Node1 |           +-----+      +-----+           | WDM Node2 |
   |      +----|           | WDM |      | WDM |           |----+      |
   |      |   -o<----------o-----o<-----o-----o<----------o-   |      |
   |  OT  |  / |           |Node3|      |Node4|           | \  |  OT  |
   | +--+ | /  |           +-----+      +-----+           |  \ | +--+ |
  -o-o  o-o-   |                                          |   -o-o  o-o-
   | +--+ | \  |     +-----+     +------+     +-----+     |  / | +--+ |
   |      |  \ |     |     |     | +--+ |     |     |     | /  |      |
   |      |   -o<----o-----o<----o-o  o-o<----o-----o<----o-   |      |
   |      +----|     | WDM |     | +--+ |     | WDM |     |----+      |
   |   Selector|     |Node5|     |  3R  |     |Node7|     |Splitter   |
   +-----------+     +-----+     +------+     +-----+     +-----------+
                                 WDM Node6
                                 with 3R
                                 Regenerator

        |<-------------------------|  |<-------------------------|
            end-to-end MC path2'          end-to-end MC path3'

       Figure 15: Individual OTSi Protection with a 3R regenerator
                           (reverse direction)

   Individual OTSi protection use cases:

   (i)    OT and OTSi protection function are an integral part of the
          WDM-TE-node

   (ii)   OT and OTSi protection/ROADM functions are in two adjacent
          WDM-TE-node (remote OT)

   (iii)  OT and OTSi protection function are both in an adjacent WDM-
          TE-node (protected remote OT)

   The different use cases are described in following sub-sections and
   examples are provided how these uses cases can be modeled properly
   using the optical impairment aware TE-topology YANG data model.

2.11.1.1.  OT and OTSi protection function are an integral part of the
           WDM-TE-node

   This use case is based on the architecture illustrated in Figure 9
   and the following entities are all integral parts of the WDM-TE-node:

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   *  Local optical transponder
   *  Splitter/selector protection function
   *  ROADM function

   Figure 16 illustrates such a WDM-TE-node configuration in transmit/
   forward direction where the protection function is an optical
   splitter and Figure 17 illustrates the same WDM-TE-node configuration
   in receive/reverse direction where the protection function is an
   optical selector selecting one of the two incoming OTSi signals and
   switching to the other incoming OTSi signal when the optical power of
   the selected OTSi signal drops below a pre-defined threshold.

   The TE-topology YANG model has been augmented to describe this
   protection architecture.  The already existing optional protection-
   type leaf of the TTP associated with the optical transceiver is used
   to indicate whether the TTP is protected, i.e., whether it is
   connected to a protection function or whether it is unprotected,
   i.e., whether it is directly connected to an add-drop port of the
   ROADM function in the WDM-TE-node.

   For unprotected TTPs associated with an optical transceiver, the
   local-link-connectivity list describes the potential connectivity
   between the TTP and the LTPs of the WDM-TE-node that are the local
   end-points of the TE-links (OMS MCGs) interconnecting the WDM-TE-node
   with its neighbors, also often called degrees of the WDM-TE-node as
   opposed to its add-drop ports.

   For protected TTPs, the local-link-connectivity list has been
   augmented such that is is capable of describing the potential
   connectivity not only between the TTP and a single LTP a (unprotected
   case) but is now capable to describe the potential connectivity to
   additional LTPs including the related optical impairments.  If the
   optical impairments are the same for all local-link-connectivity list
   entries for a particular TTP, which is usually the case, the optical
   impairments shall be omitted for the additional LTPs leading to a
   more compact topology description.  If the optical impairments are
   different, however, they can be described for each additional LTP
   entry separately.

   A local-link-connectivity list example for a protected TTP in JSON
   format is provided in Appendix A.

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                                 WDM-TE-Node
        +---------------------------------------------------------+
        |                                       ROADM             |
        |      Local OT        Splitter    +--------------+       |
        |   +------------+    +--------+   |              | Line  |
        |   |         TTP|    |     ---o-->o------\       | LTP 1 |
        |   |       +----|    |    /   |   |       \------o-------o->
      --o-->|       | Tx o--->o---o    |   |              |       |
        |   |       +----|    |    \   |   |              |       |
      <-o---|       | Rx o    |     ---o-->o---\          | Line  |
        |   |       +----|    +--------+   |    \         | LTP 2 |
        |   |            |                 |     \        o-------o->
        |   +------------+        internal |      \       |       |
        |                         AD ports o       \      |       |
        |                                  |        \     | Line  |
        |                                  |         \    | LTP 3 |
        |                                  |          \---o-------o->
        |                                  o              |       |
        |                                  |              |       |
        |                                  +--------------+       |
        +---------------------------------------------------------+

      Figure 16: OT and OTSi protection function are an integral part
                  of the WDM-TE- node (transmit direction)

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                                 WDM-TE-Node
        +---------------------------------------------------------+
        |      Local OT                                           |
        |   +------------+                      ROADM             |
        |   |            |     Selector    +--------------+       |
        |   |       +----|    +--------+   |              | Line  |
      --o-->|       | Tx o    |     ---o<--o------\       | LPT 1 |
        |   |       +----|    |    /   |   |       \------o-------o<-
      <-o---|       | Rx o<---o---o    |   |              |       |
        |   |       +----|    |    \   |   |              |       |
        |   |         TTP|    |     ---o<--o---\          | Line  |
        |   +------------+    +--------+   |    \         | LTP 2 |
        |                                  |     \        o-------o<-
        |                         internal |      \       |       |
        |                         AD ports o       \      |       |
        |                                  |        \     | Line  |
        |                                  |         \    | LTP 3 |
        |                                  |          \---o-------o<-
        |                                  o              |       |
        |                                  |              |       |
        |                                  +--------------+       |
        +---------------------------------------------------------+

      Figure 17: OT and OTSI protection function are an integral part
                  of the WDM-TE- node (receive direction)

2.11.1.2.  OT and OTSi protection/ROADM functions are in two adjacent
           WDM-TE-node (remote OT)

   This use case is based on the architecture illustrated in Figure 10
   where the optical transponder is not part of the WDM-TE-node
   containing the ROADM function (WDM-TE-Node-2) but is part of a
   separate WDM-TE-node (WDM-TE-Node-1) containing one or more optical
   transponders (remote OTs).  WDM-TE-Node-2 contains:

   *  Splitter/selector protection function
   *  ROADM function

   Figure 18 illustrates such a network configuration in transmit/
   forward direction showing the two WDM-TE-nodes where the protection
   function is the optical splitter in WDM-TE-Node-2 and Figure 19
   illustrates the same network configuration in receive/reverse
   direction where the protection function is the optical selector in
   WDM-TE-Node-2 selecting one of the two incoming OTSi signals and
   switching to the other incoming OTSi signal when the optical power of
   the selected OTSi signal drops below a pre-defined threshold.

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   In the network configuration shown in Figure 18 and Figure 19,
   respectively, the two WDM-TE-nodes are interconnected via a TE-link
   carrying a single OTSi signal.  This TE-link interconnects the remote
   OT with an add-drop port of WDM-TE-Node-2 and in the following the
   qualifier "add-drop" is used to refer to that LTP as opposed to the
   line LTPs representing degrees of WDM-TE-Node-2.  Similar to the
   protected TTP in Section 2.11.1.1, the optional protection-type leaf
   is used to indicate whether the add-drop LTP is connected to a
   protection function and then to two line LTPs via the ROADM function
   inside WDM-TE-Node-2 or whether it is connected to a single line LTP
   via the ROADM function inside WDM-TE-Node-2 (unprotected add-drop
   LTP).  While the protection-type attribute was already defined for
   the TTP, the YANG model has been augmented to also support this
   optional attribute for the LTP.

   For protected LTPs, the connectivity-matrix has been augmented such
   that it is capable of describing the potential connectivity not only
   from an add-drop LTP to a single line LTP (unprotected case) but is
   now capable to describe the potential connectivity to additional line
   LTPs (protected case) including the related optical impairments.  If
   the optical impairments are the same from the protected ad-drop LTP
   to all line LTPs, which is usually the case, the optical impairments
   shall be omitted for the additional LTPs leading to a more compact
   connectivity matrix description.  If the optical impairments are
   different, however, they can be described for each additional LTP
   separately.

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        WDM-TE-Node-1                      WDM-TE-Node-2
     +----------------+      +---------------------------------------+
     |                |      |                     ROADM             |
     |      Remote OT |      |    Splitter    +--------------+       |
     |   +------------+      |   +--------+   |              | Line  |
     |   |         TTP|      |AD |     ---o-->o------\       | LTP 1 |
     |   |       +----|      |LTP|    /   |   |       \------o-------o->
   --o-->|       | Tx o----->o-->o---o    |   |              |       |
     |   |       +----|      |   |    \   |   |              |       |
   <-o---|       | Rx o      |   |     ---o-->o---\          | Line  |
     |   |       +----|      |   +--------+   |    \         | LTP 2 |
     |   |            |      |                |     \        o-------o->
     |   +------------+      |AD LTP          |      \       |       |
     |                |      o----------------o       \      |       |
     |                |      |                |        \     | Line  |
     |                |      |unprot. AD LTPs |         \    | LTP 3 |
     |                |      |                |          \---o-------o->
     |                |      o----------------o              |       |
     |                |      |AD LTP          |              |       |
     |                |      |                +--------------+       |
     +----------------+      +---------------------------------------+

       Figure 18: OT and OTSi protection/ROADM functions are in two
          adjacent WDM-TE- node (remote OT, transmit direction)

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        WDM-TE-Node-1                      WDM-TE-Node-2
     +----------------+      +---------------------------------------+
     |      Remote OT |      |                                       |
     |   +------------+      |                     ROADM             |
     |   |            |      |    Selector    +--------------+       |
     |   |       +----|      |   +--------+   |              | Line  |
   --o-->|       | Tx o      |   |     ---o<--o------\       | LTP 1 |
     |   |       +----|      |   |    /   |   |       \------o-------o<-
   <-o---|       | Rx o<-----o<--o---o    |   |              |       |
     |   |       +----|      |AD |    \   |   |              |       |
     |   |         TTP|      |LTP|     ---o<--o---\          | Line  |
     |   +------------+      |   +--------+   |    \         | LTP 2 |
     |                |      |                |     \        o-------o<-
     |                |      |AD LTP          |      \       |       |
     |                |      o----------------o       \      |       |
     |                |      |                |        \     | Line  |
     |                |      |unprot. AD LTPs |         \    | LTP 3 |
     |                |      |                |          \---o-------o<-
     |                |      o----------------o              |       |
     |                |      |AD LTP          |              |       |
     |                |      |                +--------------+       |
     +----------------+      +---------------------------------------+

       Figure 19: OT and OTSi protection/ROADM functions are in two
           adjacent WDM-TE- node (remote OT, receive direction)

2.11.1.3.  OT and protection function are both in an adjacent WDM-TE-
           node (protected remote OT)

   The use case illustrated in Figure 20 is similar to the use case in
   Section 2.11.1.1.  The difference compared to use case (i) is that
   WDM-TE-Node-1 does not contain the ROADM function but contains:

   *  Optical transponder function including the transceiver
   *  Splitter/selector protection function

   WDM-TE-Node-1 can be a data center device or a router router device
   that supporting 1+1 OTSi protection for its OTs while WDM-TE-Node-2
   is a WDM-TE-node providing add-drop ports for remote OTs as depicted
   in Figure 10.  WDM-TE-Node-1 and WDM-TE-Node-2 are interconnected via
   two separate TE-links, each carrying a single OTSi signal.  The
   protection configuration for the protected TTP in WDM-TE-Node-1 can
   be described in the same way as for use case (i) using the local-
   link-connectivity list.

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            WDM-TE-Node-1                        WDM-TE-Node-2
    +-----------------------------+      +---------------------------+
    |      protected              |      |         ROADM             |
    |      remote OT      Splitter|      |    +--------------+       |
    |   +------------+   +--------+      |AD  |              | Line  |
    |   |         TTP|   |     ---o----->o----o------\       | LTP 1 |
    |   |       +----|   |    /LTP|      |LTP |       \------o-------o->
  --o-->|       | Tx o-->o---o    |      |    |              |       |
    |   |       +----|   |    \   |      |AD  |              |       |
  <-o---|       | Rx o   |     ---o----->o----o---\          | Line  |
    |   |       +----|   |     LTP|      |LTP |    \         | LTP 2 |
    |   |            |   +--------+      |    |     \        o-------o->
    |   +------------+            |      |    |      \       |       |
    |                             |      o----o       \      |       |
    |                             |      |AD  |        \     | Line  |
    |                             |      |LTPs|         \    | LTP 3 |
    |                             |      |    |          \---o-------o->
    |                             |      o----o              |       |
    |                             |      |    |              |       |
    |                             |      |    +--------------+       |
    +-----------------------------+      +---------------------------+

       Figure 20: OT and OTSI protection function are both in an
     adjacent WDM-TE-node (protected remote OT, transmit direction)

2.11.2.  OMS MCG protection

   OMS MCG protection is a 1+1 protection architecture where a TE-link
   representing an OMS MCG between two adjacent WDM-TE-nodes is 1+1
   protected.  This media layer protection type is also described in
   Appendix III of [G.873.1_Amd1].  Figure 21 illustrates this 1+1 OMS
   MCG protection type and shows a 1+1 protected TE-link together with
   an unprotected TE-link between the same two adjacent WDM-TE-Nodes.
   The protected TE-link in Figure 21 is composed of an underlying
   primary and secondary TE-link.  This modeling approach is described
   below.

   1+1 OMS MCG protection is a local protection scheme, which can be
   modeled based on TE-link properties already defined in [RFC8795].
   The 1+1 protected TE-link is associated with the two underlying TE-
   links representing the physical links, which are forming the 1+1
   protection group together with the splitter and selector functions in
   the adjacent WDM-TE-Nodes as depicted in Figure 21.  This modeling
   approach is described in more detail in Section 2.11.2.1.

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   Alternatively, it is possible to model the 1+1 OMS MCG protection as
   single protected TE-link abstracting the two underlying physical
   links as well as the splitter and selector functions in the two
   adjacent WDM-TE-Nodes.  This modeling approach is described in more
   detail in Section 2.11.2.2.

   For both modeling approaches, the splitter and selector functions are
   not represented as separate entities in the model.  Their optical
   impairments can be taken into account in the optical impairments of
   the ROADM paths in the two adjacent WDM-TE-Nodes (connectivity matrix
   and LLCL, respectively) or in the optical impairments of the 1+1
   protected TE-link abstracting the two underlying physical OMS links.

               WDM-TE-Node-1                     WDM-TE-Node-2
         +-----------------------+         +-----------------------+
         |     ROADM     Splitter|         |Selector     ROADM     |
         |   +-------+   +-------+  prot.  +-------+   +-------+   |
         |   |       |   |    -->o-------->o-->    |   |       |   |
         |   |       |   |   /   |  prim.  |   \   |   |       |   |
         |   |       o-->o--o    |         |    o--o-->o       |   |
         |   |       |   |   \   |  second.|   /   |   |       |   |
         |   |       |   |    -->o-------->o-->    |   |       |   |
         |   |       |   +-------+         +-------+   |       |   |
         |   |       |   Selector| Line 1  |Splitter   |       |   |
         |   |       |   +-------+         +-------+   |       |   |
         |   |       |   |    <--o<--------o<--    |   |       |   |
         |   |       |   |   /   |  prim.  |   \   |   |       |   |
         |   |       o<--o--o    |         |    o--o<--o       |   |
         |   |       |   |   \   |  second.|   /   |   |       |   |
         |   |       |   |    <--o<--------o<--    |   |       |   |
         |   |       |   +-------+ TE-link +-------+   |       |   |
         |   |       |           |         |           |       |   |
         |   |       |           | unprot. |           |       |   |
         |   |       o---------->o-------->o---------->o       |   |
         |   |       |           | Line 2  |           |       |   |
         |   |       o<----------o<--------o<----------o       |   |
         |   |       |           | TE-link |           |       |   |
         |   |       |           |         |           |       |   |
         |   +-------+           |         |           +-------+   |
         |                       |         |                       |
         +-----------------------+         +-----------------------+

      Figure 21: Two WDM-TE-Nodes with a protected and an unprotected
                             OMS MCG (TE- link)

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2.11.2.1.  OMS MCG Protection Modeled as Protected TE-link with
           underlying TE-links

   This modeling approach models the 1+1 protected TE-link as an
   additional TE-link entity on top of the primary and secondary TE-link
   between the two adjacent WDM-TE-Nodes terminating the 1+1 OMS MCG
   protection group formed by these two TE-links and the splitter and
   selector functions in the two nodes.  This 1+1 protected TE-link is
   associated with underlying primary and secondary TE-links forming the
   1+1 protection group.  The following "te-link-attributes" already
   defined in [RFC8795] and [I-D.ietf-teas-rfc8776-update] can be used
   for modeling the 1+1 protected TE-link ("te-link-attributes"
   augmentation copied from [RFC8795]:

     augment /nw:networks/nw:network/nt:link:
     +--rw te!
        +--rw te-link-attributes
        |  ....................
        |  +--rw underlay {te-topology-hierarchy}?
        |  |  +--rw enabled?                     boolean
        |  |  +--rw primary-path
        |  |  |  +--rw network-ref?    leafref
        |  |  |     ....................
        |  |  +--rw backup-path* [index]
        |  |  |  +--rw index           uint32
        |  |  |  +--rw network-ref?    leafref
        |  |  |     ....................
        |  ....................
        |  +--rw link-protection-type?           identityref
        |  ....................

   These attributes are used as follows:

   *  "underlay": the presence of this container is indicating that an
      underlying protection scheme exists
   *  "enabled": (boolean) is set to 'true'
   *  "primary-path": is referencing the primary OMS MCG (TE-link)
   *  "backup-path": is referencing the secondary OMS MCG (TE-link)
   *  "link-protection-type" (identityref) set to 'link-protection-1-
      plus-1' as defined in [I-D.ietf-teas-rfc8776-update]

   The optical impairments for the underlying primary and secondary TE-
   link can be described as for unprotected TE-links.  It may also be
   possible to only describe the optical impairments for the 1+1
   protected TE-link.  In this case the optical impairments of the worse
   of the two underlying TE-links shall be used.  This should be
   sufficient as input for path computation (worst case optical
   feasibility consideration).

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM     Splitter|           |Selector     ROADM     |
       |   +-------+   +-------+LTP2   LTP4+-------+   +-------+   |
       |   |       |   |    -->o---------->o-->    |   |       |   |
   LTP1|   |    RP1|   |   /   |  prim.    |   \   |   |RP2    |   |LTP6
   --->o-->o.......o-->o--o    |           |    o--o-->o.......o-->o--->
       |   |       |   |   \   |  second.  |   /   |   |       |   |
       |   |       |   |    -->o---------->o-->    |   |       |   |
       |   +-------+   +-------+LTP3   LTP5+-------+   +-------+   |
       |                       |           |                       |
       +-----------------------+           +-----------------------+

                 --+                                   +--
        ROADM port |                                   | ROADM port
               RP1 o---------------------------------->o RP2
                   |                                   |
                 --+                                   +--
                      1+1 protected OMS MCG (TE-link)
                      between ROADM ports RP1 and RP2

                underlying primary and secondary TE-links:

                             --+           +--
                               |  prim.    |
                          LTP2 o---------->o LTP4
                          LTP3 o---------->o LTP5
                               |  second.  |
                             --+           +--

           connectivity matrix provides optical impairments in
           forward direction between LTPs in the two WDM-TE-Nodes:
           * LTP1 and LTP2,                     * LTP4 and LTP6,
           * LTP1 and LTP3                      * LTP5 and LTP6

     Figure 22: Modeling view of 1+1 protected TE-link with underlying
             primary and secondary TE-link (forward direction)

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM             |           |             ROADM     |
       |   +-------+   +-------+LTP2' LTP4'+-------+   +-------+   |
       |   |       |   |    <--o<----------o<--    |   |       |   |
   LTP1'   |   RP1'|   |   /   |  prim.    |   \   |   |RP2'   |   LTP6'
   <---o<--o.......o<--o--o    |           |    o--o<--o.......o<--o<---
       |   |       |   |   \   |  second.  |   /   |   |       |   |
       |   |       |   |    <--o<----------o<--    |   |       |   |
       |   +-------+   +-------+LTP3' LTP5'+-------+   +-------+   |
       |               Selector|           |Splitter               |
       +-----------------------+           +-----------------------+

                 --+                                   +--
        ROADM port |                                   | ROADM port
               RP1'o<----------------------------------o RP2'
                   |                                   |
                 --+                                   +--
                     1+1 protected OMS MCG (TE-link)
                     between ROADM ports RP1' and RP2'

                underlying primary and secondary TE-links:

                             --+           +--
                               |  prim.    |
                          LTP2'o<----------o LTP4'
                          LTP3'o<----------o LTP5'
                               |  second.  |
                             --+           +--

           connectivity matrix provides optical impairments in
           reverse direction between LTPs in the two WDM-TE-Nodes:
           * LTP2' and LTP1',                   * LTP6' and LTP4',
           * LTP3' and LTP1'                    * LTP6' and LTP5'

     Figure 23: Modeling view of 1+1 protected TE-link with underlying
             primary and secondary TE-link (reverse direction)

   Figure 22 and Figure 23 illustrate this modeling approach including
   the LTPs in WDM-TE-Node-1 and WDM-TE-Node-2, respectively.  In
   addition to the physical view, the following TE-links are shown in
   the two directions:

   *  The 1+1 protected TE-link

   *  The underlying primary TE-link
   *  The underlying secondary TE-link

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   The optical impairments of the splitter (outgoing direction) and the
   selector (incoming direction) are included in the optical impairments
   described by the connectivity matrix and the local link connectivity
   list for the TE node.  For the example shown in Figure 22 in forward
   direction, the connectivity matrix describes the optical impairments
   between LPT1 and LTP2 as well as LTP1 and LTP3 for WDM-TE-Node-1.
   Likewise, the connectivity matrix describes the optical impairments
   between LPT4 and LTP6 as well as LTP5 and LTP6 in WDM-TE-Node-2.  The
   same applies to the corresponding LTPs in reverse direction.

2.11.2.2.  OMS MCG Protection Modeled as Single Protected TE-link

   This modeling approach abstracts the two physical OMS links carrying
   the same OMS MCG together with the splitter and selector functions in
   the two WDM-TE-Nodes forming the OMS protection group into a single
   TE-link.  When this modeling approach is used the "te-link-
   attributes" already defined in [RFC8795] and
   [I-D.ietf-teas-rfc8776-update] are used as follows:

    augment /nw:networks/nw:network/nt:link:
     +--rw te!
        +--rw te-link-attributes
        |  ....................
        |  +--rw link-protection-type?           identityref
        |  ....................

   *  "underlay": this container must not be present
   *  "link-protection-type" (identityref) set to 'link-protection-1-
      plus-1' as defined in [I-D.ietf-teas-rfc8776-update]

   The optical impairments exposed for this 1+1 protected TE-link are
   typically based on the optical impairments of the worse of the two
   underlying physical OMS links including the optical impairments
   imposed by the splitter (outgoing direction) and selector (incoming
   direction).

   Figure 24 and Figure 25 illustrate this modeling approach where the
   splitter/selector in the adjacent WDM-TE-Nodes, WDM-TE-Node-1 and
   WDM-TE-Node-2, as well as the two physical OMS MCG links are
   abstracted into a single 1+1 protected TE-link.  This is illustrated
   by the the dotted line surrounding these four physical entities in
   Figure 24 and Figure 25, respectively.  Based on this modeling
   approach, the ROADM port connected to the splitter/selector function
   is modeled as LTP for the 1+1 protected TE-link (LTP2 in WDM-TE-
   Node-1 and LTP3 in WDM-TE-Node-2).  In this example, the connectivity
   matrix describes the optical impairments between LPT1 and LTP2 in
   WDM-TE-Node-1.  Likewise, the connectivity matrix describes the
   optical impairments between LPT3 and LTP4 in WDM-TE-Node-2.

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM     Splitter|           |Selector     ROADM     |
       |   +-------+   +.......+...........+.......+   +-------+   |
       |   |       |   .    -->o---------->o-->    .   |       |   |
   LTP1|   |   LTP2|   .   /   |           |   \   .   |LTP3   |   |LTP4
   --->o-->o.......o-->o--o    |           |    o--o-->o.......o-->o--->
       |   |       |   .   \   |           |   /   .   |       |   |
       |   |       |   .    -->o---------->o-->    .   |       |   |
       |   +-------+   +...................+.......+   +-------+   |
       |                       |           |                       |
       +-----------------------+           +-----------------------+

                 --+                                   +--
        ROADM port |                                   | ROADM port
              LTP2 o---------------------------------->o LTP3
                   |                                   |
                 --+                                   +---
                     Splitter/Selector abstracted into
                     1+1 protected OMS MCG (TE-link)

           connectivity matrix provides optical impairments in
           forward direction between LTPs in the two WDM-TE-Nodes:
           * LTP1 and LTP2                      * LTP3 and LTP4

        Figure 24: Modeling view of abstracted 1+1 protected TE-link
             (forward direction) - ROADM ports modeled as LTPs

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM             |           |             ROADM     |
       |   +-------+   +.......+...........+.......+   +-------+   |
       |   |       |   .    <--o<----------o<--    .   |       |   |
   LTP1'   |  LTP2'|   .   /   |           |   \   .   |LTP3'  |   LTP4'
   <---o<--o.......o<--o--o    |           |    o--o<--o.......o<--o<---
       |   |       |   .   \   |           |   /   .   |       |   |
       |   |       |   .    <--o<----------o<--    .   |       |   |
       |   +-------+   +...................+.......+   +-------+   |
       |               Selector|           |Splitter               |
       +-----------------------+           +-----------------------+

                 --+                                   +--
        ROADM port |                                   | ROADM port
              LTP2 o<----------------------------------o LTP3
                   |                                   |
                 --+                                   +---
                     Splitter/Selector abstracted into
                     1+1 protected OMS MCG (TE-link)

           connectivity matrix provides optical impairments in
           reverse direction between LTPs in the two WDM-TE-Nodes:
           * LTP2' and LTP1'                    * LTP4' and LTP3'

        Figure 25: Modeling view of abstracted 1+1 protected TE-link
             (reverse direction) - ROADM ports modeled as LTPs

   Alternatively, the optical impairments imposed by the splitter and
   selector in each of the two adjacent WDM-TE-Nodes can also be
   included in the optical impairments described by the connectivity
   matrix of the two nodes instead of taking them into account as
   optical impairments of the 1+1 protected TE-link.  This is
   illustrated in Figure 26 in forward direction and Figure 27 in
   reverse direction below.  In this case, the two physical ports on
   both ends of the 1+1 protected TE-link are abstracted into a single
   LTP, LTP2 and LTP3, in forward direction and LTP3' and LTP2' in
   reverse direction.

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM     Splitter|           |Selector     ROADM     |
       |   +-------+   +-------+...........+-------+   +-------+   |
       |   |       |   |    -->o---------->o-->    |   |       |   |
   LTP1|   |       |   |   /   |LTP2   LTP3|   \   |   |       |   |LTP4
   --->o-->o.......o-->o--o    |           |    o--o-->o.......o-->o--->
       |   |       |   |   \   |LTP2   LTP3|   /   |   |       |   |
       |   |       |   |    -->o---------->o-->    |   |       |   |
       |   +-------+   +-------+...........+-------+   +-------+   |
       |                       |           |                       |
       +-----------------------+           +-----------------------+

                             --+           +--
                               |           |
                          LTP2 o---------->o LTP3
                               |           |
                             --+           +--
                               1+1 protected
                               OMS MCG (TE-link)

           connectivity matrix provides optical impairments in
           forward direction between LTPs in the two WDM-TE-Nodes:
           * LTP1 and LTP2                      * LTP3 and LTP4

        Figure 26: Modeling view of abstracted 1+1 protected TE-link
      (forward direction) - physical ports abstracted into single LTP
                             on both link ends

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            WDM-TE-Node-1                         WDM-TE-Node-2
       +-----------------------+           +-----------------------+
       |     ROADM             |           |             ROADM     |
       |   +-------+   +-------+...........+-------+   +-------+   |
       |   |       |   |    <--o<----------o<--    |   |       |   |
   LTP1'   |       |   |   /   |LTP2' LTP3'|   \   |   |       |   LTP4'
   <---o<--o.......o<--o--o    |           |    o--o<--o.......o<--o<---
       |   |       |   |   \   |LTP2' LTP3'|   /   |   |       |   |
       |   |       |   |    <--o<----------o<--    |   |       |   |
       |   +-------+   +-------+...........+-------+   +-------+   |
       |               Selector|           |Splitter               |
       +-----------------------+           +-----------------------+

                             --+           +--
                               |           |
                          LTP2'o<----------o LTP3'
                               |           |
                             --+           +--
                               1+1 protected
                               OMS MCG (TE-link)

           connectivity matrix provides optical impairments in
           reverse direction between LTPs in the two WDM-TE-Nodes:
           * LTP2' and LTP1'                    * LTP4' and LTP3'

        Figure 27: Modeling view of abstracted 1+1 protected TE-link
      (reverse direction) - physical ports abstracted into single LTP
                             on both link ends

3.  YANG Model (Tree Structure)

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

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   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:
       +--rw otsis!
       |  +--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

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       |        +--ro e2e-mc-path-id*           uint16
       +--ro templates
          +--ro roadm-path-impairments
          |  +--ro roadm-path-impairment* [roadm-path-impairments-id]
          |     +--ro roadm-path-impairments-id    string
          |     +--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?
          |        |     |       l0-types:decimal-5-or-null
          |        |     +--ro roadm-pdl?
          |        |     |       l0-types:power-loss-or-null
          |        |     +--ro roadm-inband-crosstalk?
          |        |     |       l0-types:decimal-2-or-null
          |        |     +--ro roadm-maxloss?
          |        |             l0-types:power-loss-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?
          |        |     |       l0-types:decimal-5-or-null
          |        |     +--ro roadm-pdl?
          |        |     |       l0-types:power-loss-or-null
          |        |     +--ro roadm-inband-crosstalk?
          |        |     |       l0-types:decimal-2-or-null
          |        |     +--ro roadm-maxloss?
          |        |     |       l0-types:power-loss-or-null
          |        |     +--ro roadm-pmax?
          |        |     |       l0-types:power-dbm-or-null
          |        |     +--ro roadm-osnr?
          |        |     |       l0-types:snr-or-null
          |        |     +--ro roadm-noise-figure?
          |        |             l0-types:decimal-5-or-null
          |        +--:(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?
          |              |       l0-types:decimal-5-or-null

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          |              +--ro roadm-pdl?
          |              |       l0-types:power-loss-or-null
          |              +--ro roadm-inband-crosstalk?
          |              |       l0-types:decimal-2-or-null
          |              +--ro roadm-maxloss?
          |              |       l0-types:power-loss-or-null
          |              +--ro roadm-minloss?
          |              |       l0-types:power-loss-or-null
          |              +--ro roadm-typloss?
          |              |       l0-types:power-loss-or-null
          |              +--ro roadm-pmin?
          |              |       l0-types:power-dbm-or-null
          |              +--ro roadm-pmax?
          |              |       l0-types:power-dbm-or-null
          |              +--ro roadm-ptyp?
          |              |       l0-types:power-dbm-or-null
          |              +--ro roadm-osnr?
          |              |       l0-types:snr-or-null
          |              +--ro roadm-noise-figure?
          |                      l0-types:decimal-5-or-null
          +--ro explicit-transceiver-modes
             +--ro explicit-transceiver-mode*
                     [explicit-transceiver-mode-id]
                +--ro explicit-transceiver-mode-id        string
                +--ro line-coding-bitrate?                identityref
                +--ro bitrate?                            uint16
                +--ro max-diff-group-delay?               decimal-2
                +--ro max-chromatic-dispersion?           decimal64
                +--ro cd-penalty* []
                |  +--ro cd-value         union
                |  +--ro penalty-value    union
                +--ro max-polarization-mode-dispersion?   decimal64
                +--ro pmd-penalty* []
                |  +--ro pmd-value        union
                |  +--ro penalty-value    union
                +--ro max-polarization-dependant-loss
                |       power-loss-or-null
                +--ro pdl-penalty* []
                |  +--ro pdl-value        power-loss-or-null
                |  +--ro penalty-value    union
                +--ro available-modulation-type?          identityref
                +--ro min-OSNR?                           snr
                +--ro rx-ref-channel-power?               power-dbm
                +--ro rx-channel-power-penalty* []
                |  +--ro rx-channel-power-value    power-dbm-or-null
                |  +--ro penalty-value             union
                +--ro min-Q-factor?                       decimal-2
                +--ro available-baud-rate?                decimal64

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                +--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 in-band-osnr?                       snr
                +--ro out-of-band-osnr?                   snr
                +--ro tx-polarization-power-difference?   power-ratio
                +--ro polarization-skew?                  decimal64
     augment /nw:networks/nw:network/nw:node:
       +--rw transponders!
       |  +--ro transponder* [transponder-id]
       |     +--ro transponder-id                   uint32
       |     +--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
       |        |        |  +--ro line-coding-bitrate*      identityref
       |        |        |  +--ro min-central-frequency?
       |        |        |  |       frequency-thz
       |        |        |  +--ro max-central-frequency?
       |        |        |  |       frequency-thz
       |        |        |  +--ro transceiver-tunability?
       |        |        |  |       frequency-ghz
       |        |        |  +--ro tx-channel-power-min?     power-dbm
       |        |        |  +--ro tx-channel-power-max?     power-dbm
       |        |        |  +--ro rx-channel-power-min?     power-dbm
       |        |        |  +--ro rx-channel-power-max?     power-dbm
       |        |        |  +--ro rx-total-power-max?       power-dbm
       |        |        +--:(organizational-mode)
       |        |        |  +--ro organizational-mode
       |        |        |     +--ro operational-mode?
       |        |        |     |       operational-mode
       |        |        |     +--ro organization-identifier?
       |        |        |     |       organization-identifier
       |        |        |     +--ro line-coding-bitrate*
       |        |        |     |       identityref
       |        |        |     +--ro min-central-frequency?
       |        |        |     |       frequency-thz
       |        |        |     +--ro max-central-frequency?
       |        |        |     |       frequency-thz

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       |        |        |     +--ro transceiver-tunability?
       |        |        |     |       frequency-ghz
       |        |        |     +--ro tx-channel-power-min?
       |        |        |     |       power-dbm
       |        |        |     +--ro tx-channel-power-max?
       |        |        |     |       power-dbm
       |        |        |     +--ro rx-channel-power-min?
       |        |        |     |       power-dbm
       |        |        |     +--ro rx-channel-power-max?
       |        |        |     |       power-dbm
       |        |        |     +--ro rx-total-power-max?
       |        |        |             power-dbm
       |        |        +--:(explicit-mode)
       |        |           +--ro explicit-mode
       |        |              +--ro min-central-frequency?
       |        |              |       frequency-thz
       |        |              +--ro max-central-frequency?
       |        |              |       frequency-thz
       |        |              +--ro transceiver-tunability?
       |        |              |       frequency-ghz
       |        |              +--ro tx-channel-power-min?
       |        |              |       power-dbm
       |        |              +--ro tx-channel-power-max?
       |        |              |       power-dbm
       |        |              +--ro rx-channel-power-min?
       |        |              |       power-dbm
       |        |              +--ro rx-channel-power-max?
       |        |              |       power-dbm
       |        |              +--ro rx-total-power-max?
       |        |              |       power-dbm
       |        |              +--ro compatible-modes
       |        |              |  +--ro supported-application-codes*
       |        |              |  |       leafref
       |        |              |  +--ro supported-organizational-modes*
       |        |              |          leafref
       |        |              +--ro explicit-transceiver-mode-ref?
       |        |                      leafref
       |        +--ro configured-mode?               union
       |        +--ro line-coding-bitrate?           identityref
       |        +--ro tx-channel-power?              power-dbm-or-null
       |        +--ro rx-channel-power?              power-dbm-or-null
       |        +--ro rx-total-power?                power-dbm-or-null
       |        +--ro outgoing-otsi
       |        |  +--ro otsi-group-ref?   leafref
       |        |  +--ro otsi-ref?         leafref
       |        +--ro incoming-otsi
       |        |  +--ro otsi-group-ref?   leafref
       |        |  +--ro otsi-ref?         leafref

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       |        +--ro configured-termination-type?   enumeration
       +--rw regen-groups!
          +--ro regen-group* [group-id]
             +--ro group-id           uint32
             +--ro regen-metric?      uint32
             +--ro transponder-ref*
                     -> ../../../transponders/transponder/transponder-i\
   d
     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
          |  +--ro nominal-carrier-power?   l0-types:power-dbm-or-null
          |  +--ro nominal-psd?             l0-types:psd-or-null
          +--ro media-channel-groups!
          |  +--ro media-channel-group* []
          |     +--ro media-channels* []
          |        +--ro flexi-n?          l0-types:flexi-n
          |        +--ro flexi-m?          l0-types:flexi-m
          |        +--ro otsi-group-ref?   leafref
          |        +--ro otsi-ref* []
          |        |  +--ro otsi-carrier-ref?   leafref
          |        |  +--ro e2e-mc-path-ref*    leafref
          |        +--ro delta-power?      l0-types:power-ratio-or-null
          +--ro OMS-elements!
             +--ro OMS-element* [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-degre\
   e
                   |  |  +--ro longitude?   geographic-coordinate-degre\
   e
                   |  +--ro amplifier
                   |     +--ro type-variety    string
                   |     +--ro operational
                   |        +--ro amplifier-element* []
                   |           +--ro name?
                   |           |       string

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                   |           +--ro type-variety?
                   |           |       string
                   |           +--ro is-dynamic-gain-equalyzer?
                   |           |       boolean
                   |           +--ro frequency-range
                   |           |  +--ro lower-frequency    frequency-th\
   z
                   |           |  +--ro upper-frequency    frequency-th\
   z
                   |           +--ro stage-order?
                   |           |       uint8
                   |           +--ro power-param
                   |           |  +--ro (power-param)
                   |           |     +--:(channel-power)
                   |           |     |  +--ro nominal-carrier-power
                   |           |     |          l0-types:power-dbm-or-n\
   ull
                   |           |     +--:(power-spectral-density)
                   |           |        +--ro nominal-psd
                   |           |                l0-types:psd-or-null
                   |           +--ro pdl?
                   |           |       l0-types:power-loss-or-null
                   |           +--ro (amplifier-element-type)
                   |              +--:(optical-amplifier)
                   |              |  +--ro optical-amplifier
                   |              |     +--ro actual-gain
                   |              |     |       l0-types:power-gain-or-\
   null
                   |              |     +--ro in-voa?
                   |              |     |       l0-types:power-loss-or-\
   null
                   |              |     +--ro out-voa?
                   |              |     |       l0-types:power-loss-or-\
   null
                   |              |     +--ro tilt-target
                   |              |     |       l0-types:decimal-2-or-n\
   ull
                   |              |     +--ro total-output-power
                   |              |     |       l0-types:power-dbm-or-n\
   ull
                   |              |     +--ro raman-direction?
                   |              |     |       enumeration
                   |              |     +--ro raman-pump* []
                   |              |        +--ro frequency?
                   |              |        |       l0-types:frequency-t\
   hz
                   |              |        +--ro power?
                   |              |                l0-types:decimal-2-o\

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   r-null
                   |              +--:(dynamic-gain-equalyzer)
                   |                 +--ro dynamic-gain-equalyzer!
                   |                    +--ro media-channel-groups
                   |                       +--ro media-channel-group* [\
   ]
                   |                          +--ro media-channels* []
                   |                             +--ro flexi-n?
                   |                             |       l0-types:flexi\
   -n
                   |                             +--ro flexi-m?
                   |                             |       l0-types:flexi\
   -m
                   |                             +--ro delta-power?
                   |                                     l0-types:power\
   -ratio-or-null
                   +--:(fiber)
                   |  +--ro fiber
                   |     +--ro type-variety    string
                   |     +--ro length
                   |     |       l0-types:decimal-2-or-null
                   |     +--ro loss-coef
                   |     |       l0-types:decimal-2-or-null
                   |     +--ro total-loss
                   |     |       l0-types:power-loss-or-null
                   |     +--ro pmd?
                   |     |       l0-types:decimal-2-or-null
                   |     +--ro conn-in?
                   |     |       l0-types:power-loss-or-null
                   |     +--ro conn-out?
                   |             l0-types:power-loss-or-null
                   +--:(concentratedloss)
                      +--ro concentratedloss
                         +--ro loss    l0-types:power-loss-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
          |       -> ../../../../transponders/transponder/transponder-i\
   d
          +--ro transceiver-ref    leafref
     augment /nw:networks/nw:network/nw:node/nt:termination-point:
       +--rw protection-type?   identityref
     augment /nw:networks/nw:network/nw:node/nt:termination-point
               /tet:te:
       +--rw inter-layer-sequence-number?   uint32
     augment /nw:networks/nw:network/nw:node/tet:te
               /tet:te-node-attributes:

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     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?   leafref
     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:te-node-attributes/tet:connectivity-matrices
               /tet:connectivity-matrix/tet:from:
       +--ro additional-ltp* [ltp-ref]
          +--ro ltp-ref
          |       -> ../../../../../../../nt:termination-point/tp-id
          +--ro roadm-path-impairments?   leafref
     augment /nw:networks/nw:network/nw:node/tet:te
               /tet:te-node-attributes/tet:connectivity-matrices
               /tet:connectivity-matrix/tet:to:
       +--ro additional-ltp* [ltp-ref]
          +--ro ltp-ref
          |       -> ../../../../../../../nt:termination-point/tp-id
          +--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
       |  +--ro drop-path-impairments?   leafref
       +--ro additional-ltp* [ltp-ref]

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          +--ro ltp-ref
          |       -> ../../../../../../nt:termination-point/tp-id
          +--ro add-path-impairments?    leafref
          +--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> file "ietf-optical-impairment-topology.yang"
   module ietf-optical-impairment-topology {
     yang-version 1.1;
     namespace "urn:ietf:params:xml"
             + ":ns:yang:ietf-optical-impairment-topology";
     prefix "oit";

     import ietf-network {
       prefix "nw";
       reference
         "RFC 8345: A YANG Data Model for Network Topologies";
     }

     import ietf-network-topology {
       prefix "nt";
       reference
         "RFC 8345: A YANG Data Model for Network Topologies";
     }

     import ietf-te-topology {
       prefix "tet";
       reference
         "RFC 8795: YANG Data Model for Traffic Engineering (TE)
         Topologies";
     }

     import ietf-te-types {
       prefix "te-types";
       reference
         "RFC YYYY: Updated Common YANG Data Types for Traffic
         Engineering";
     }

     /* Note: The RFC Editor will replace YYYY with the number assigned
        to the RFC once draft-ietf-teas-rfc8776-update becomes an RFC.*/

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

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       reference
         "RFC ZZZZ: A YANG Data Model for Layer 0 Types";
     }

     /* Note: The RFC Editor will replace ZZZZ with the number assigned
        to the RFC once draft-ietf-ccamp-rfc9093-bis becomes an RFC.*/

     organization
       "IETF CCAMP Working Group";

     contact
       "WG Web: <https://datatracker.ietf.org/wg/ccamp/>
        WG List: <mailto:ccamp@ietf.org>

        Editor:   Young Lee <younglee.tx@gmail.com>
        Editor:   Haomian Zheng <zhenghaomian@huawei.com>
        Editor:   Nicola Sambo <nicosambo@gmail.com>
        Editor:   Victor Lopez <victor.lopez@nokia.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>
        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.

        Copyright (c) 2024 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 Revised BSD
        License set forth in Section 4.c of the IETF Trust's Legal
        Provisions Relating to IETF Documents
        (https://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

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   // replace the revision date with the module publication date
   // the format is (year-month-day)
     revision 2024-02-22 {
       description
         "Initial Version";
       reference
         "RFC XXXX: A Yang Data Model for Impairment-aware
          Optical Networks";
     }

     /*
      * Identities
      */

     identity otsi-protection {
       base te-types:lsp-protection-type;
       description
         "Individual OTSi(G) protection LSP protection type.";
       reference
         "ITU-T G.873.1 v5.2 (02/2022): Optical transport network:
         Linear protection";
     }

     /*
      * 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

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                 "The name of the amplifier element as specified in
                 the vendor's specification associated with the
                 type-variety.";
             }
             leaf type-variety {
               type string;
               description
                 "String identifier of amplifier element type
                 referencing a specification in a separate equipment
                 catalog.

                 This attributes applies only when the type-variety of
                 the amplifier is not sufficient to describe the
                 amplifier element type.";
             }
             leaf is-dynamic-gain-equalyzer {
               type boolean;
               description
                 "Indicates whether the amplifier element is a Dynamic
                 Gain Equalizer (DGE).";
             }
             container frequency-range {
               description
                 "The frequency range amplified by the amplifier
                 element.";
               uses l0-types:frequency-range;
             }
             leaf stage-order {
               type uint8;
               default 1;
               description
                 "It allows defining for each spectrum badwidth the
                 cascade order of each amplifier-element.";
             }
             container power-param {
               description
                 "The optical power after the out-voa of each amplifier
                 element.";
               choice power-param {
                 mandatory true;
                 description
                   "Select the mode: channel power or power spectral
                   density (PSD).";
                 case channel-power {
                   leaf nominal-carrier-power {
                     type l0-types:power-dbm-or-null;
                     mandatory true;
                     description

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                       "Reference channel power.";
                   }
                 }
                 case power-spectral-density {
                   leaf nominal-psd {
                     type l0-types:psd-or-null;
                     mandatory true;
                     description
                       "Reference power spectral density (PSD).";
                   }
                 }
               }
             }   // container power-param
             leaf pdl {
               type l0-types:power-loss-or-null;
               description "Polarization Dependent Loss (PDL)";
             }
             choice amplifier-element-type {
               mandatory true;
               description
                 "Identifies whether the amplifier element is an
                 Optical Amplifier (OA) or a Dynamic Gain Equalyzer
                 (DGE).";
               container optical-amplifier {
                 description
                   "The attributes applicable only to amplifier
                   elements";
                 leaf actual-gain {
                   type l0-types:power-gain-or-null;
                   mandatory true;
                   description
                     "The value of the gain provided by the
                     amplification  stage of the optical amplifier.";
                 }
                 leaf in-voa {
                   type l0-types:power-loss-or-null;
                   description
                     "Loss introduced by the Variable Optical Attenuator
                     (VOA) at the input of the amplification stage of
                     the amplifier, if present";
                 }
                 leaf out-voa {
                   type l0-types:power-loss-or-null;
                   description
                     "Loss introduced by the Variable Optical Attenuator
                     (VOA) at the output of the amplification stage of
                     the amplifier, if present.";
                 }

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                 leaf tilt-target {
                   type l0-types:decimal-2-or-null;
                   units "dB";
                   mandatory true ;
                   description
                     "The tilt target defined between lower and upper
                     frequency of the amplifier frequency range.";
                 }
                 leaf total-output-power {
                   type l0-types:power-dbm-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.";
                 }
                 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
                         "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.";
                   }

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                   leaf power {
                     type l0-types:decimal-2-or-null;
                     units "Watts";
                     description
                       "The total pump power considering a depolarized
                       pump at the raman pump central frequency.";
                   }
                 }
               }   // container optical-amplifier
               container dynamic-gain-equalyzer {
                 presence
                   "When present it indicates that the amplifier element
                   is a Dynamic Gain Equalyzer (DGE)";
                 description
                   "The attributes applicable only to DEG amplifier
                   elements.";
                 container media-channel-groups {
                   description
                     "The top level container for the list of media
                     channel groups.";
                   list media-channel-group {
                     description
                       "The list of media channel groups";
                     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 delta-power {
                         type l0-types:power-ratio-or-null;
                         description
                           " Deviation from the reference carrier power
                           defined for the OMS.";
                       }
                     } // media channels list
                   } // media-channel-groups list
                 }   // container media-channel-groups
               }   // container dynamic-gain-equalyzer
             } // choice amplifier-element-type
           }  // list amplifier-element
         }  // container operational
       }  // container amplifier
     }  // grouping amplifier-params

     grouping fiber-params {

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

     grouping roadm-common-path {
       description
         "The optical impairments of a ROADM which are common to all

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         its paths (express path, add path or drop path).";
       leaf roadm-pmd {
         type union {
           type decimal64 {
             fraction-digits 8;
             range "0..max";
           }
           type empty;
         }
         units "ps";
         description
           "Polarization Mode Dispersion (PMD), when known, or an
           empty value when unknown.";
       }
       leaf roadm-cd {
         type l0-types:decimal-5-or-null;
         units "ps/nm";
         description "Chromatic Dispersion (CD)";
       }
       leaf roadm-pdl {
         type l0-types:power-loss-or-null;
         description "Polarization Dependent Loss (PDL)";
       }
       leaf roadm-inband-crosstalk {
         type l0-types:decimal-2-or-null;
         units "dB";
         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 one blocked";
       }
       leaf roadm-maxloss {
         type l0-types:power-loss-or-null;
         description
           "This is the maximum expected path loss from the
           ROADM ingress to the ROADM egress
           assuming no additional path loss is added";
       }
     } // grouping roadm-common-path

     grouping roadm-express-path {
       description
         "The optical impairments of a ROADM express path.";
       uses roadm-common-path;
     } // grouping roadm-express-path

     grouping roadm-add-path {

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       description
         "The optical impairments of a ROADM add path.";
       uses roadm-common-path {
         refine roadm-inband-crosstalk {
           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 one blocked.

             In the case of add path it is the total
             of the add block + egress WSS crosstalk contributions.";
         }
         refine roadm-maxloss {
           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-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
           "Optical Signal-to-Noise Ratio (OSNR).
           If the add path contains the ability to adjust the
           carrier power levels into an add path amplifier

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           (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 l0-types:decimal-5-or-null;
         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-add-path

     grouping roadm-drop-path {
       description
         "The optical impairments of a ROADM drop path";
       uses roadm-common-path {
         refine roadm-inband-crosstalk {
           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 one blocked.

             In the case of drop path it is the total
             of the ingress
             to drop e.g. WSS and drop block crosstalk
             contributions.";
         }
         refine roadm-maxloss {
           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.

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             It is the maximum output power of the drop
             amplifier.";
         }
       }
       leaf roadm-minloss {
         type l0-types:power-loss-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.";
       }
       leaf roadm-typloss {
         type l0-types:power-loss-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-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

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           detailed in section xxx of the document yyy.";
       }
       leaf roadm-pmax {
         type l0-types:power-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
           is detailed in section xxx of the document yyy";
       }
       leaf roadm-ptyp {
         type l0-types:power-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";
       }

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       leaf roadm-noise-figure {
         type l0-types:decimal-5-or-null;
         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
           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 roadm-drop-path

     grouping concentratedloss-params {
       description "concentrated loss";
       container concentratedloss{
         description "concentrated loss";
         leaf loss {
           type l0-types:power-loss-or-null;
           mandatory true;
           description
             "Loss introduced by the concentrated loss element.";
         }
       }
     }

     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;
         }
         description
           "The equalization mode.

           When not present it indicates that the information about
           the equalization mode is not reported.

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           Reporting this value is needed to support optical
           impairments applications.";
       }
       container power-param {
         description
           "Optical channel power or power spectral densitity (PSD)
           after the ROADM.";
         leaf nominal-carrier-power {
           when "derived-from-or-self(../../equalization-mode, "
              + "'l0-types:carrier-power')";
           type l0-types:power-dbm-or-null;
           description
             "Reference channel power.";
         }
         leaf nominal-psd {
           when "derived-from-or-self(../../equalization-mode, "
              + "'l0-types:power-spectral-density')";
           type l0-types:psd-or-null;
           description
             " Reference power spectral density (PSD).";
         }
       }   // container power-param
     } // grouping oms-general-optical-params

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

       list otsi {
         key "otsi-carrier-id";
         config false;
         description
           "list of OTSi contained in one OTSiG.
           The list could also be of only one element";
         leaf otsi-carrier-id {
           type uint16;
           description "OTSi carrier-id";
         }
         leaf otsi-carrier-frequency {
           type union {
             type l0-types:frequency-thz;
             type empty;
           }
           description
             "OTSi carrier frequency, equivalent to the
             actual configured transmitter frequency, when known, or
             an empty value when unknown.";
         }

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         leaf-list e2e-mc-path-id {
           type uint16;
           description
             "The list of the possible end-to-end Media Channel
             (e2e-MC) paths associated with the OTSi which have
             different optical impairments.

             This list is meaningful in case the OTSi can be associated
             with multiple end-to-end Media Channel (e2e-MC) paths
             (e.g., when OPS protection is configured).

             The list can be empty when the OTSi has only one
             e2e-MC path.";
         }
       } // OTSi list
     } // OTSiG grouping

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

         This grouping is not intended to be reused outside of this
         module.";

       container media-channel-groups {
         presence
           "When present, it indicates that the list media channel
           groups is reported.";
         description
           "The top level container for the list of media channel
           groups.";
         list media-channel-group {
           description
             "The list of media channel groups";
           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 "../../../../../../../../otsis/" +
                     "otsi-group/otsi-group-id";
               }
               description

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                 "Reference to the OTSiG to which the OTSis carried by
                 this media channel belong to.";
             }
             list otsi-ref {
               description
                 "The list of references to the OTSis and their
                 end-to-end Media Channel (e2e-MC) paths within the
                 OTSiG carried by this media channel.";
               leaf otsi-carrier-ref {
                 type leafref {
                   path  "../../../../../../../../../otsis/" +
                         "otsi-group[otsi-group-id=current()" +
                         "/../../otsi-group-ref]/" +
                         "otsi/otsi-carrier-id" ;
                 }
                 description
                   "Reference to the OTSi within the OTSiG carried
                   by this media channel.";
               }
               leaf-list e2e-mc-path-ref {
                 type leafref {
                   path  "../../../../../../../../../otsis/" +
                         "otsi-group[otsi-group-id=current()" +
                         "/../../otsi-group-ref]/" +
                         "otsi[otsi-carrier-id=current()" +
                         "/../otsi-carrier-ref]/e2e-mc-path-id";
                 }
                 description
                   "References to the end-to-end Media Channel (e2e-MC)
                   paths of this OTSi which are routed through this
                   media channel.";
               }
             }
             leaf delta-power {
               type l0-types:power-ratio-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

     grouping oms-element {
       description "OMS description";
       container OMS-elements {
         presence

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           "When present, it indicates that the list of OMS elements
           is reported.";
         description
           "The top level container for the list of OMS elements.";
         list OMS-element {
           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 and it is known.

               When unknown, an empty value is reported.

               When it does not exist, the attribute is not present.";
           }
           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/OMS-element/elt-index";
               }

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               description
                 "The references to the OMS elements.";
             }
           }
           choice element {
             mandatory true;
             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  "../../../../../../otsis/otsi-group/" +
                 "otsi-group-id";
         }
         description
           "The OTSi generated by the transceiver's transmitter.";
       }
       leaf otsi-ref {
         type leafref {
           path  "../../../../../../otsis/otsi-group" +
                 "[otsi-group-id=current()/../otsi-group-ref]/otsi/" +
                 "otsi-carrier-id";
         }
         description
           "The OTSi generated by the transceiver's transmitter.";
       }
     }

   /*

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    * 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";
         reference
           "RFC8345: A YANG Data Model for Network Topologies.";
      }
     }

     augment "/nw:networks/nw:network" {
       when "./nw:network-types/tet:te-topology" +
            "/oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology.";
       }
       description
         "Network augmentation for optical impairments data.";
       container otsis {
         presence
           "When present, it indicates that OTSi information is
           reported.";
         description
           "The information about the OTSis configured on the WDM-TE
           link.";
         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
       }

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       container templates {
         config false;
         description
           "Templates for set of parameters which can be common to
           multiple elements.";
         container roadm-path-impairments {
           description
             "The top level container for the list of the set of
             optical impairments related to ROADM paths.";
           list roadm-path-impairment {
             key "roadm-path-impairments-id";
             description
               "The list of the set of optical impairments related to
               ROADM paths.";

             leaf roadm-path-impairments-id {
               type string;
               description
                 "The identifier of the set of optical impairments
                 related to a ROADM path.";
             }
             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.";

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                   container frequency-range {
                     description
                       "The frequency range for which these optical
                       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 roadm-path-impairments
         } // container roadm-path-impairments
         container explicit-transceiver-modes {
           description
             "The top level container for the list of the
             transceivers' explicit modes.";
           list explicit-transceiver-mode {
             key explicit-transceiver-mode-id;
             description
               "The list of the transceivers' explicit modes.";
             leaf explicit-transceiver-mode-id {
               type string;
               description
                 "The identifier of the transceivers' explicit mode.";
             }
             uses l0-types:explicit-mode;
           }   // list explicit-transceiver-mode
         }   // container explicit-transceiver-modes
       }   // container templates
     } // augment network

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     augment "/nw:networks/nw:network/nw:node" {
       when "../nw:network-types/tet:te-topology" +
            "/oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment.";
       }
       description
         "Node augmentation for optical impairments data.";
       container transponders {
         presence
           "If present, it indicates that the list of transponders is
           reported.";
         description
           "The top level container for the list of transponders.";
         list transponder {
           key "transponder-id";
           config false;
           description "The list of transponders.";
           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 {
                 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

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                   (../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;
             min-elements 1;
             description "list of transceiver related to a transponder";
             leaf transceiver-id {
               type uint32;
               description "transceiver identifier";
             }
             uses l0-types:transceiver-capabilities {
               augment "supported-modes/supported-mode/mode/"
                     + "explicit-mode/explicit-mode" {
                 description
                   "Augment the explicit-mode container with the
                   proper leafref.";
                 leaf explicit-transceiver-mode-ref {
                   type leafref {
                     path "../../../../../../../../oit:templates"
                         + "/oit:explicit-transceiver-modes"
                         + "/oit:explicit-transceiver-mode"
                         + "/oit:explicit-transceiver-mode-id";
                   }
                   description
                     "The refernce to the explicit transceiver
                     mode template.";
                 }
               }
             }
             leaf configured-mode {

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               type union {
                 type empty;
                 type leafref {
                   path "../supported-modes/supported-mode/mode-id";
                 }
               }
               description
                 "Reference to the configured mode for transceiver
                 compatibility approach.

                 The empty value is used to report that no mode has
                 been configured and there is no default mode.

                 When not present, the configured-mode is not reported
                 by the server.";
             }
             uses l0-types:common-transceiver-param;
             container outgoing-otsi {
               when "../../../../../otsis" {
                 description
                   "It applies only when the OTSi information is
                   reported.";
               }
               description
                 "The OTSi generated by the transceiver's transmitter.";
               uses otsi-ref;
             }
             container incoming-otsi {
               when "../../../../../otsis" {
                 description
                   "It applies only when the OTSi information is
                   reported.";
               }
               description
                 "The OTSi received by the transceiver's received.";
               uses otsi-ref;
             }
             leaf configured-termination-type {
               type enumeration {
                 enum unused-transceiver {
                   description
                     "The transcevier is not used.";
                 }
                 enum tunnel-termination {
                   description
                     "The transceiver is currently used in an Optical
                     Tunnel termination configuration.";
                 }

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                 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 information about the
                 configured-termination-type is not reported.";
             }
           } // end of list of transceiver
         } // end list of transponder
       }
       container regen-groups {
         presence
           "When present, it indicates that the list of 3R groups
           is reported.";
         description
           "The top level container for the list of 3R groups.";
         list regen-group {
           key "group-id";
           config false;
           description
             "The 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 {
             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 "../../../transponders/transponder/transponder-id";

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             }
             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:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology.";
       }
       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:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology.";
       }
       description
         "Tunnel termination point augmentation for impairment data.";

       list ttp-transceiver {
         when "../../../transponders" {
           description
             "It applies only when the list of transponders is
             reported.";
         }
         key "transponder-ref transceiver-ref";
         config false;
         min-elements 1;
         description
           "The list of the transceivers used by the TTP.";

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

     // Should this leaf be moved to te-topology?
     augment "/nw:networks/nw:network/nw:node/nt:termination-point" {
       when "../../nw:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology";
       }
       description
         "Augment LTP";
       leaf protection-type {
         type identityref {
           base te-types:lsp-protection-type;
         }
         description
           "The protection type that this LTP is capable of.

           When not present it indicates that the information about
           the protection type is not reported.";
       }
     }

     augment "/nw:networks/nw:network/nw:node/nt:termination-point"
           + "/tet:te" {
       when "../../../nw:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment

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           topology";
       }
       description
         "Augment TE attributes of an LTP";

       leaf inter-layer-sequence-number {
         type uint32;
         description
           "The inter-layer-sequence-number (ILSN) is used to report
           additional connectivity constraints between a client layer
           Link Termination Point (LTP), such as a muxponder port, and
           the server layer Tunnel Termination Point (TTP).

           A client service cannot be setup between two client layer
           LTPs which report different values of the ILSN.

           This attribute is not reported when there are no additional
           connectivity constraints.

           Therefore, a client service can be setup when at least one
           of the two client layer LTPs does not report any ILSN or
           both client layer LTPs report the same ILSN value and the
           corresponding server layer TTPs have at least one common
           server-layer switching capability and at least one common
           client-layer switching capability.";
       }
     }

     augment "/nw:networks/nw:network/nw:node/tet:te"
           + "/tet:te-node-attributes" {
       when "../../../nw:network-types/tet:te-topology"
          + "/oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment
           topology";
       }
       description
         "node attributes augmentantion for optical-impairment ROADM
          node";

     } // augmentation for optical-impairment ROADM

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

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

       leaf roadm-path-impairments {
         type leafref {
           path "../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id";
         }
         config false;
         description
           "Pointer to the list set of ROADM optical impairments";
       }
     } // 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:network-types/tet:te-topology/"
          + "oit: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 "../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id";
         }
         config false;
         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:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for Optical Impairment

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           topology ";
       }
       description
         "Augment default TE node connectivity matrix.";
       leaf roadm-path-impairments {
         type leafref {
           path "../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit: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*/
         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:network-types/tet:te-topology/"
          + "oit: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 "../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit: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:te-node-attributes/tet:connectivity-matrices/"
           + "tet:connectivity-matrix/tet:from" {
       when "../../../../../../nw:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for

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           Optical Impairment topology ";
       }
       description
         "Augment the attributes for the 'from' LTP for the TE node
         connectivity matrix entry.";
       list additional-ltp {
         when "derived-from-or-self(../../../../../../"
            + "nt:termination-point"
            + "[nt:tp-id=current()/../../tet:to/tet:tp-ref]/"
            + "oit:protection-type,"
            + "'oit:otsi-protection')" {
           description
             "This list applies only when the 'to' LTP for this
             connectivity matrix entry supports individual OTSi(G)
             protection.";
         }
         key "ltp-ref";
         config false;
         description
           "The restricted list of the potential secondary LTPs that
           can be selected when the 'from' LTP of this connectivity
           matrix entry is selected as a working LTP.

           If this list is empty, all the other LTPs that can reach
           the 'to' LTP of this connectivity matrix entry can be
           selected as secondary LTPs.";
         leaf ltp-ref {
           type leafref {
             path "../../../../../../../nt:termination-point/nt:tp-id";
           }
           description
             "The reference to the potential secondary LTP that can be
             selected when the 'from' LTP of this connectivity matrix
             entry is selected as a working LTP";
         }
         leaf roadm-path-impairments {
           type leafref {
             path "../../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id";
           }
           description
             "Pointer to ROADM optical impairments of the ROADM path
             between this secondary 'from' LTP and the 'to' LTP of
             this connectivity matrix entry.";
         }
       }
     } // augmentation connectivity-matrix from

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     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:te-node-attributes/tet:connectivity-matrices/"
           + "tet:connectivity-matrix/tet:to" {
       when "../../../../../../nw:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for
           Optical Impairment topology ";
       }
       description
         "Augment the attributes for the 'to' LTP for the TE node
         connectivity matrix entry.";
       list additional-ltp {
         when "derived-from-or-self(../../../../../../"
            + "nt:termination-point"
            + "[nt:tp-id=current()/../../tet:from/tet:tp-ref]/"
            + "oit:protection-type,"
            + "'oit:otsi-protection')" {
           description
             "This list applies only when the 'from' LTP for this
             connectivity matrix entry supports individual OTSi(G)
             protection.";
         }
         key "ltp-ref";
         config false;
         description
           "The restricted list of the potential secondary LTPs that
           can be selected when the 'to' LTP of this connectivity
           matrix entry is selected as a working LTP.

           If this list is empty, all the other LTPs that can be
           reached from the 'from' LTP of this connectivity matrix
           entry can be selected as secondary LTPs.";
         leaf ltp-ref {
           type leafref {
             path "../../../../../../../nt:termination-point/nt:tp-id";
           }
           description
             "The reference to the potential secondary LTP that can be
             selected when the 'to' LTP of this connectivity matrix
             entry is selected as a working LTP";
         }
         leaf roadm-path-impairments {
           type leafref {
             path "../../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id";
           }

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           description
             "Pointer to ROADM optical impairments of the ROADM path
             between the 'from' LTP of this connectivity matrix entry
             and this secondary LTP.";
         }
       }
     } // augmentation connectivity-matrix to

     augment "/nw:networks/nw:network/nw:node/tet:te/"
           + "tet:tunnel-termination-point/"
           + "tet:local-link-connectivities" {
       when "../../../../nw:network-types/tet:te-topology/"
          + "oit: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 "../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM optical
          impairments";
       }
       leaf drop-path-impairments {
         type leafref {
           path "../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit: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:network-types/tet:te-topology/"
          + "oit:optical-impairment-topology" {
         description
           "This augment is only valid for

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            Optical Impairment topology ";
       }
       description
         "Augment TTP LLC entry.";
       leaf add-path-impairments {
         type leafref {
           path "../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM optical
          impairments";
       }
       leaf drop-path-impairments {
         type leafref {
           path "../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
         }
         config false;
         description "pointer to the list set of ROADM optical
         impairments";
       }
       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

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             "'true' - connectivity from this transceiver is allowed;
             'false' - connectivity from this transceiver is
             disallowed.";
         }
         leaf add-path-impairments {
           type leafref {
             path "../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
           }
           description "pointer to the list set of ROADM optical
           impairments";
         }
         leaf drop-path-impairments {
           type leafref {
             path "../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
           }
           description "pointer to the list set of ROADM
           optical impairments";
         }
       }
       list additional-ltp {
         when "derived-from-or-self(../../../tet:protection-type,"
            + "'oit:otsi-protection')" {
           description
             "This list applies only to TTPs that support individual
             OTSi(G) protection.";
         }
         key "ltp-ref";
         config false;
         description
           "The restricted list of the potential secondary LTPs that
           can be selected when the LTP associated with this LLCP
           entry is selected as a working LTP.

           If this list is empty, all the other LTPs that can be
           reached by this TTP can be selected as secondary LTPs.";
         leaf ltp-ref {
           type leafref {
             path "../../../../../../nt:termination-point/nt:tp-id";
           }
           description
             "The reference to potential secondary LTP that can be
             selected when the LTP associated with this LLCP entry is
             selected as a working LTP";
         }

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         leaf add-path-impairments {
           type leafref {
             path "../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
           }
           description "pointer to the list set of ROADM optical
           impairments";
         }
         leaf drop-path-impairments {
           type leafref {
             path "../../../../../../../oit:templates"
              + "/oit:roadm-path-impairments/oit:roadm-path-impairment"
              + "/oit:roadm-path-impairments-id" ;
           }
           description "pointer to the list set of ROADM
           optical impairments";
         }
       }
     } // augmentation local-link-connectivity
   }
   <CODE ENDS>

5.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   The YANG module specified in this document imports the ietf-network
   and ietf-network-topology models defined in [RFC8345].  This YANG
   module augments te-topology defined in [RFC8795] and consequently
   inherits te-topology subtrees and data nodes and their potential
   sensitivities and vulnerabilities.  Therefore, the security
   considerations from [RFC8345] also apply to the YANG module defined
   in this document.

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   The data nodes in this YANG module are not writable nor creatable nor
   deletable (i.e., config true) the data nodes are readable only (i.e.,
   config false, which is the default).  Although the data nodes are not
   susceptible to write operations or attacks (e.g., edit-config),
   network information may be exposed using read access (e.g., get, get-
   config, or notification) operations.  Thus, controlling read access
   to specific data nodes containing sensitive or vulnerable information
   is important.  Below are the specific subtrees, data nodes and
   subsequent sensitivity/vulnerability:

   /nw:networks/nw:network/nw:network-types/tet:te-topology
      Unauthorized access to this subtree can disclose the TE topology
      type.

   /nw:networks/tet:te
      Unauthorized access to this subtree can disclose the TE node
      templates and TE link templates.

   /nw:networks/nw:network
      Unauthorized access to this subtree can disclose the topology-wide
      configurations, including the TE topology ID, the topology-wide
      policies, and the topology geolocation.

   /nw:networks/nw:network/nw:node
      Unauthorized access to this subtree can disclose the operational
      state information of TE nodes.

   /nw:networks/nw:network/nt:link/tet:te
      Unauthorized access to this subtree can disclose the operational
      state information of TE links.

   /nw:networks/nw:network/nw:node/nt:termination-point
      Unauthorized access to this subtree can disclose the operational
      state information of TE link termination points.

   /nw:networks/nw:network/nt:link/tet:te/tet:te-link-attributes
      Unauthorized access to this subtree can disclose the operational
      state information of TE link attributes.

   /nw:networks/nw:network/nw:node/tet:te/tet:tunnel-termination-
   point
      Unauthorized access to this subtree can disclose the operational
      state information of TE link tunnel termination points.

   /nw:networks/nw:network/nw:node/tet:te/tet:te-node-attributes
      Unauthorized access to this subtree can disclose the operational
      state information of TE node attributes.

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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:    oit
   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

   [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>.

   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [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>.

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   [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>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [I-D.ietf-teas-rfc8776-update]
              Busi, I., Guo, A., Liu, X., Saad, T., and I. Bryskin,
              "Common YANG Data Types for Traffic Engineering", Work in
              Progress, Internet-Draft, draft-ietf-teas-rfc8776-update-
              10, 22 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              rfc8776-update-10>.

   [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

   [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>.

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   [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>.

   [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>.

   [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>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/info/rfc8792>.

   [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-rfc9093-bis]
              Belotti, S., Busi, I., Beller, D., Rouzic, E. L., and A.
              Guo, "A YANG Data Model for Layer 0 Types", Work in
              Progress, Internet-Draft, draft-ietf-ccamp-rfc9093-bis-09,
              4 March 2024,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ietf-ccamp-rfc9093-bis/>.

   [I-D.ietf-ccamp-dwdm-if-param-yang]
              Galimberti, G., Hiremagalur, D., Grammel, G., Manzotti,
              R., and D. Breuer, "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-10, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ccamp-
              dwdm-if-param-yang-10>.

   [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://datatracker.ietf.org/doc/html/draft-ietf-teas-te-
              topo-and-tunnel-modeling-06>.

   [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.807_Amd1]
              "Generic functional architecture of the optical media
              network Amendment 1", ITU-T Recommendation G.807 Amendment
              1, January 2021.

   [G.873.1_Amd1]
              "Optical transport network: Linear protection Amendment
              1", ITU-T Recommendation G.873.1 Amendment 1, February
              2022.

   [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.

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   [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.

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

   [G.873.1]  "Optical transport network: Linear protection",
              ITU-T Recommendation G.873.1, October 2017.

Appendix A.  JSON Code Examples for Optical Protection Uses Cases

   [Editor's note: JSON examples for optical protection use cases TBA!

   (1)  JSON example for use case in Section 2.11.1.1:

   [Editor's note: The JSON example below needs to be updated and
   aligned with Figure 16 and Figure 17.]

   {
     "roadm-path-impairments": [
       {
         "roadm-path-impairments-id": 1,
         "roadm-add-path":
         "Add path impairments from TTP 1 or TTP 2 to any LTPs."
       },
       {
         "roadm-path-impairments-id": 2,
         "roadm-add-path": "Add path impairments from TTP 3 or TTP 4
          to LTP 1 or LTP 3, through AD1."
       },
       {
         "roadm-path-impairments-id": 3,
         "roadm-add-path": "Add path impairments from TTP 3 or TTP 4
          to LTP 1 or LTP 2, through AD2."
       }
     ],
     "tunnel-termination-point": [
       {
         "tunnel-tp-id": 1,
         "protection-type": "ops-protection",
         "local-link-connectivities": {

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           "is-allowed": true,
           "add-path-impairments": 1
         }
       },
       {
         "tunnel-tp-id": 2,
         "local-link-connectivities": {
           "is-allowed": true,
           "add-path-impairments": 1,
           "local-link-connectivity": [
             {
               "link-tp-ref": "LTP-1",
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-2",
                   "link-tp-ref": "LTP-3"
                 }
               ]
             },
             {
               "link-tp-ref": "LTP-2",
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "link-tp-ref": "LTP-3"
                 }
               ]
             },
             {
               "link-tp-ref": "LTP-3",
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "link-tp-ref": "LTP-2"
                 }
               ]
             }
           ]
         }
       },
       {
         "tunnel-tp-id": 3,
         "protection-type": "ops-protection",
         "local-link-connectivities": {
           "is-allowed": false,
           "local-link-connectivity": [
             {
               "link-tp-ref": "LTP-1",

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               "is-allowed": true,
               "add-path-impairments": 2,
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "add-path-impairments": 3
                 },
                 {
                   "link-tp-ref": "LTP-2",
                   "add-path-impairments": 3
                 }
               ]
             },
             {
               "link-tp-ref": "LTP-3",
               "is-allowed": true,
               "add-path-impairments": 2,
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "add-path-impairments": 3
                 },
                 {
                   "link-tp-ref": "LTP-2",
                   "add-path-impairments": 3
                 }
               ]
             }
           ]
         }
       },
       {
         "tunnel-tp-id": 4,
         "protection-type": "ops-protection",
         "local-link-connectivities": {
           "is-allowed": false,
           "local-link-connectivity": [
             {
               "link-tp-ref": "LTP-1",
               "is-allowed": true,
               "add-path-impairments": 2,
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "add-path-impairments": 3
                 },
                 {
                   "link-tp-ref": "LTP-2",

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                   "add-path-impairments": 3
                 }
               ]
             },
             {
               "link-tp-ref": "LTP-2",
               "is-allowed": true,
               "add-path-impairments": 3,
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "add-path-impairments": 2
                 },
                 {
                   "link-tp-ref": "LTP-3",
                   "add-path-impairments": 2
                 }
               ]
             },
             {
               "link-tp-ref": "LTP-3",
               "is-allowed": true,
               "add-path-impairments": 2,
               "additional-ltp": [
                 {
                   "link-tp-ref": "LTP-1",
                   "add-path-impairments": 3
                 },
                 {
                   "link-tp-ref": "LTP-2",
                   "add-path-impairments": 3
                 }
               ]
             }
           ]
         }
       }
     ]
   }

   (2)  JSON example for use case in Section 2.11.1.2 with connectivity
        constraints:

   [Editor's note: UC (ii) JSON example below needs to be updated and
   aligned with Figure 18 and Figure 19.]

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   {
     "roadm-path-impairments": [
       {
         "roadm-path-impairments-id": 1,
         "roadm-add-path":
         "Add path impairments from LTP 10 to LTP 1 or LTP 2 or LTP 3."
       },
       {
         "roadm-path-impairments-id": 2,
         "roadm-add-path":
         "Add path impairments from LTP 20 or LTP 30 to LTP 1 or LTP 3,
          through AD1."
       },
       {
         "roadm-path-impairments-id": 3,
         "roadm-add-path":
         "Add path impairments from LTP 20 or LTP 30 to LTP 1 or LTP 2,
         through AD2."
       }
     ],

     "connectivity-matrix"[
       {
         "id": 1,
         "from": {
           "tp-ref" : 20
         },
         "to" :  {
           "tp-ref" : 1,
           "additional-ltp": [
              {
                 "link-tp-ref": 1,
                 "roadm-path-impairments": 3
              },
              {
                 "link-tp-ref": 2,
                 "roadm-path-impairments": 3
              }
           ]
         },
         "is-allowed": true,
         "roadm-path-impairments": 2
       },
       {
         "id": 2,
         "from": {
           "tp-ref" : 20
         },

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         "to" :  {
           "tp-ref" : 3,
           "additional-ltp": [
              {
                 "link-tp-ref": 1,
                 "roadm-path-impairments": 3
              },
              {
                 "link-tp-ref": 2,
                 "roadm-path-impairments": 3
              }
           ]
         },
         "is-allowed": true,
         "roadm-path-impairments": 2
       },
       {
         "id": 3,
         "from": {
           "tp-ref" : 30
         },
         "to" :  {
           "tp-ref" : 1,
           "additional-ltp": [
              {
                 "link-tp-ref": 1,
                 "roadm-path-impairments": 2
              },
              {
                 "link-tp-ref": 2,
                 "roadm-path-impairments": 2

              }
           ]
         },
         "is-allowed": true,
         "roadm-path-impairments": 2
       },
       {
         "id": 4,
         "from": {
           "tp-ref" : 30
         },
         "to" :  {
           "tp-ref" : 2,
           "additional-ltp": [
              {
               "link-tp-ref": 1,

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               "roadm-path-impairments": 2
              },
              {
               "link-tp-ref": 3,
               "roadm-path-impairments": 2

              }
           ]
         },
         "is-allowed": true,
         "roadm-path-impairments": 3
       },
       {
         "id": 5,
         "from": {
           "tp-ref" : 30
         },
         "to" :  {
           "tp-ref" : 3,
           "additional-ltp": [
              {
               "link-tp-ref": 1,
               "roadm-path-impairments": 3
              },
              {
               "link-tp-ref": 2,
               "roadm-path-impairments": 3

              }
           ]
         },
         "is-allowed": true,
         "roadm-path-impairments": 2
       },
       {
         "id": 6,
         "from": {
           "tp-ref" : 40
         },
         "to" :  {
           "tp-ref" : 1
         },
         "is-allowed": true,
         "roadm-path-impairments": 3
       },
       {
         "id": 7,
         "from": {

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           "tp-ref" : 40
         },
         "to" :  {
           "tp-ref" : 2,
         },
         "is-allowed": true,
         "roadm-path-impairments": 3
       }

     ]
   }

   (3)  JSON example for use case in Section 2.11.1.3

   [Editor's note: UC (iii) JSON example TBA!]

Appendix B.  Optical Transponders in a Remote Shelf (Remote OTs)

   Figure 28 illustrates a configuration where the optical transponders
   and the ROADM are located in a different WDM-TE-nodes.

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           WDM-TE-Node-1                    WDM-TE-Node-2
        +----------------+           +--------------------------+
        |     Remote OTs |           |         ROADM            |
        |   +------------+           |     +------------+       |
        |   |            |           | AD  |            |       |
        |   |       +----|           | LTP |            | Line  |
      --o-->|       | Tx o---------->o---->o            | LTP 1 |
        |   | OT 1  +----|           |     |            o-------o<--->
      <-o---|       | Rx o<----------o<----o            |       |
        |   |       +----|           | AD  |            |       |
        |   |            |           | LTP |            |       |
        |   +------------+           |     |            |       |
        |                |           |     |            | Line  |
        |   +------------+           |     |            | LTP 2 |
        |   |            |           | AD  |            o-------o<--->
        |   |       +----|           | LTPs|            |       |
      --o-->|       | Tx o---------->o---->o            |       |
        |   |       +----|           |     |            |       |
      <-o---|       | Rx o<----------o<----o            |       |
        |   | OT 2  +----|           |     |            | Line  |
      --o-->|       | Tx o---------->o---->o            | LTP 3 |
        |   |       +----|           |     |            o-------o<--->
      <-o---|       | Rx o<----------o<----o            |       |
        |   |       +----|           |     |            |       |
        |   |            |           |     |            |       |
        |   +------------+           |     +------------+       |
        |                |           |                          |
        +----------------+           +--------------------------+

       Figure 28: Optical Transponders in a Remote Shelf (Remote OTs)

   As described in Section 2.3, the external shelf can be modeled as
   WDM-TE-Node with termination capability only (not switching) and the
   add/drop link between a remote optical transceiver and a ROADM add/
   drop port can be modeled as a WDM TE-link with the same optical
   impairments as those defined for a WDM TE-link between WDM-TE-nodes
   (OMS MCG).

   If the two WDM-TE-Nodes are reported in different network topology
   instances, the plug-id attribute, defined in [RFC8795], can be used
   to discover the adjacency for add/drop TE-links.

   It is worth noting that there are no standard protocols for automatic
   discovery of the adjacency between an external transceiver and a
   ROADM add/drop port and therefore the information reported in the
   plug-id can be either statically configured or provided through
   vendor-specific discovery mechanisms.

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   Each add/drop TE-link carries a single OTSi between the transceiver
   and ROADM add/drop port and one or more OTSis in the reverse
   direction (between the ROADM add/drop and the transceiver).

   Depending on control architecture (e.g., when the two WDM-TE-Nodes
   are reported in different network topology instances by different
   controllers), the controller reporting the WDM-TE-Node, abstracting
   the external OT shelf, may be not able to provide the information
   about the end-to-end MC configuration (i.e.,flexi-n and flexi-m) nor
   of all the received OTSis, within the end-to-end MC, besides the
   configured incoming OTSi, since the end-to-end MC configuration
   depends on how the ROADM network is configured and the remote OT
   shelf is not aware of that.

   In this case only the incoming-otsi and outgoing-otsi can be reported
   within anend-to-end MC with an unspecified frequency-slot (i.e.,
   without reporting flexi-n and flexi-m configuration of the end-to-end
   MC).

   When an OTSiG has more than one OTSi, its OTSis are carried by
   different parallel add/drop TE-links.  In order to represent the fact
   that these OTSis are co-routed, the add/drop TE-links are bundled
   together in a bundled add/drop TE-link.  The finest granularity for
   the bundled add/drop TE-link is the set of all the add/drop TE-links
   terminating on the same OT.

   For example, in Figure 28, it is possible to define two bundled add/
   drop TE-links, one for OT1 and one for OT2 or just one add/drop TE-
   link both OTs.

   The model for a bundled add/drop TE-link and the relationship with
   its component TE-links is already defined in the bundled-links
   container of [RFC8795].

   In the general case, the optical impairments and connectivity
   constraints are reported for each add/drop TE-link and therefore no
   optical impairments are reported in the bundled add/drop TE-link that
   is used just to model the co-routing aspects of the OTSis belonging
   to the same OTSiG.

   The per-transceiver Local Link Connectivity (LLC) is used in the WDM-
   TE-Node which abstracts the remote OT shelf (e.g., WDM-TE-Node-1 in
   Figure 28), to represent the association between each transceiver and
   each LTP terminating the add/drop TE-link which models the
   transceiver port.

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   The connectivity matrix in the WDM-TE-Node which abstract the edge
   ROADM (e.g., WDM-TE-Node-2 in Figure 28) references the LTPs
   terminating the add/drop TE-links which models the ROADM add/drop
   ports.

B.1.  JSON Examples for Optical Transponders in a Remote Shelf (Remote
      OTs)

   [Editor's note: Introductory text TBA here.]

   The JSON example below describes ... (TBA)

   Line-folding as defined in [RFC8792] has been used for the JSON code
   example below.

   {
     "ietf-network:networks": {
       "network": [
         {
           "network-id": "WDM-Network-1",
           "network-types": {
             "ietf-te-topology:te-topology": {
               "ietf-optical-impairment-topology:optical-impairment-top\
   ology": {}
             }
           },
           "ietf-te-topology:te-topology-identifier": {
             "topology-id": "WDM-Network-1"
           },
           "ietf-te-topology:te": {},
           "ietf-optical-impairment-topology:otsi-information": {
             "otsi-group": [
               {
                 "otsi-group-id": "Red OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }
                 ]
               },
               {
                 "otsi-group-id": "Red OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }
                 ]
               },

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               {
                 "otsi-group-id": "Green OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               },
               {
                 "otsi-group-id": "Green OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               }
             ]
           },
           "node": [
             {
               "node-id": "WDM-TE-Node-1",
               "ietf-te-topology:te-node-id": "192.0.2.1",
               "ietf-te-topology:te": {
                 "ietf-te-topology:tunnel-termination-point": [
                   {
                     "tunnel-tp-id": "AQ==",
                     "ietf-optical-impairment-topology:ttp-transceiver"\
   : [
                       {
                         "transponder-ref": 1,
                         "transceiver-ref": 1
                       }
                     ],
                     "local-link-connectivities": {
                       "is-allowed": false,
                       "local-link-connectivity": [
                         {
                           "link-tp-ref": "1",
                           "ietf-optical-impairment-topology:llc-transc\
   eiver": [
                             {
                               "ttp-transponder-ref": 1,

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                               "ttp-transceiver-ref": 1,
                               "is-allowed": true
                             }
                           ]
                         }
                       ]
                     }
                   },
                   {
                     "tunnel-tp-id": "Ag==",
                     "ietf-optical-impairment-topology:ttp-transceiver"\
   : [
                       {
                         "transponder-ref": 2,
                         "transceiver-ref": 1
                       },
                       {
                         "transponder-ref": 2,
                         "transceiver-ref": 2
                       }
                     ],
                     "local-link-connectivities": {
                       "is-allowed": false,
                       "local-link-connectivity": [
                         {
                           "link-tp-ref": "2",
                           "ietf-optical-impairment-topology:llc-transc\
   eiver": [
                             {
                               "ttp-transponder-ref": 2,
                               "ttp-transceiver-ref": 1,
                               "is-allowed": true
                             }
                           ]
                         },
                         {
                           "link-tp-ref": "3",
                           "ietf-optical-impairment-topology:llc-transc\
   eiver": [
                             {
                               "ttp-transponder-ref": 2,
                               "ttp-transceiver-ref": 2,
                               "is-allowed": true
                             }
                           ]
                         }
                       ]
                     }

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                   }
                 ]
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1",
                   "ietf-te-topology:te-tp-id": 1,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "AQ=="
                   }
                 },
                 {
                   "tp-id": "2",
                   "ietf-te-topology:te-tp-id": 2,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "Ag=="
                   }
                 },
                 {
                   "tp-id": "3",
                   "ietf-te-topology:te-tp-id": 3,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "Awo="
                   }
                 },
                 {
                   "tp-id": "23",
                   "ietf-te-topology:te-tp-id": 23
                 }
               ],
               "ietf-optical-impairment-topology:transponders": {
                 "transponder": [
                   {
                     "transponder-id": 1,
                     "transceiver": [
                       {
                         "transceiver-id": 1,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Red OTSiG (Forward)",
                           "otsi-ref": 1
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Red OTSiG (Reverse)",
                           "otsi-ref": 1
                         }
                       }
                     ]
                   },

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                   {
                     "transponder-id": 2,
                     "transceiver": [
                       {
                         "transceiver-id": 1,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Green OTSiG (Forward)",
                           "otsi-ref": 1
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Green OTSiG (Reverse)",
                           "otsi-ref": 1
                         }
                       },
                       {
                         "transceiver-id": 2,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Green OTSiG (Forward)",
                           "otsi-ref": 2
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Green OTSiG (Reverse)",
                           "otsi-ref": 2
                         }
                       }
                     ]
                   }
                 ]
               }
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "Add-Drop-Link-1-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",
                 "source-tp": "1"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "otsi-group-ref": "Red OTSiG (Forward)",

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                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-1-Reverse",
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "1"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",

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                 "source-tp": "2"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Reverse",
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "2"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                       "media-channel-groups": {
                         "media-channel-group": [
                           {
                             "i": 1,
                             "media-channels": [
                               {
                                 "otsi-group-ref": "Green OTSiG (Revers\
   e)",
                                 "otsi-ref": [
                                   {
                                     "otsi-carrier-ref": 1
                                   }

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                                 ]
                               }
                             ]
                           }
                         ]
                       }
                     }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",
                 "source-tp": "3"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Reverse",
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "3"
               },
               "ietf-te-topology:te": {

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                 "ietf-te-topology:te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Bundled-Link-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",
                 "source-tp": "23"
               },
               "ietf-te-topology:te": {
                 "bundled-links": {
                   "bundled-link": [
                     {
                       "sequence": 1,
                       "src-tp-ref": "2"
                     },
                     {
                       "sequence": 2,
                       "src-tp-ref": "3"
                     }
                   ]
                 }
               }
             },
             {
               "link-id": "Add-Drop-Bundled-Link-Reverse",
               "destination": {

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                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "23"
               },
               "ietf-te-topology:te": {
                 "bundled-links": {
                   "bundled-link": [
                     {
                       "sequence": 1,
                       "des-tp-ref": "2"
                     },
                     {
                       "sequence": 2,
                       "des-tp-ref": "3"
                     }
                   ]
                 }
               }
             }
           ]
         },
         {
           "network-id": "WDM-Network-2",
           "network-types": {
             "ietf-te-topology:te-topology": {
               "ietf-optical-impairment-topology:optical-impairment-top\
   ology": {}
             }
           },
           "ietf-te-topology:te-topology-identifier": {
             "topology-id": "WDM-Network-2"
           },
           "ietf-te-topology:te": {},
           "ietf-optical-impairment-topology:otsi-information": {
             "otsi-group": [
               {
                 "otsi-group-id": "Red OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }
                 ]
               },
               {
                 "otsi-group-id": "Red OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }

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                 ]
               },
               {
                 "otsi-group-id": "Green OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               },
               {
                 "otsi-group-id": "Green OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               }
             ]
           },
           "node": [
             {
               "node-id": "WDM-TE-Node-2",
               "ietf-te-topology:te-node-id": "192.0.2.2",
               "ietf-te-topology:te": {},
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1",
                   "ietf-te-topology:te-tp-id": 1,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "2",
                   "ietf-te-topology:te-tp-id": 2,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "3",
                   "ietf-te-topology:te-tp-id": 3,
                   "ietf-te-topology:te": {}
                 },
                 {

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                   "tp-id": "4",
                   "ietf-te-topology:te-tp-id": 4,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "AQ=="
                   }
                 },
                 {
                   "tp-id": "5",
                   "ietf-te-topology:te-tp-id": 5,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "Ag=="
                   }
                 },
                 {
                   "tp-id": "6",
                   "ietf-te-topology:te-tp-id": 6,
                   "ietf-te-topology:te": {
                     "inter-domain-plug-id": "Awo="
                   }
                 }
               ]
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "Add-Drop-Link-1-Forward",
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "4"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": -10,
                               "otsi-group-ref": "Red OTSiG (Forward)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]

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                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-1-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "4"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         },
                         {
                           "i": 2,
                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }

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                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Forward",
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "5"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": -20,
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "5"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {

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                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         },
                         {
                           "i": 2,
                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Forward",
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "6"
               },
               "ietf-te-topology:te": {

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                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": -20,
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "6"
               },
               "ietf-te-topology:te": {
                 "ietf-te-topology:te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }

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                           ]
                         },
                         {
                           "i": 2,
                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             }
           ]
         },
         {
           "network-id": "WDM-Network-Complete",
           "network-types": {
             "ietf-te-topology:te-topology": {
               "ietf-optical-impairment-topology:optical-impairment-top\
   ology": {}
             }
           },
           "ietf-te-topology:te-topology-identifier": {
             "topology-id": "WDM-Network-Complete"
           },
           "ietf-te-topology:te": {},
           "ietf-optical-impairment-topology:otsi-information": {
             "otsi-group": [
               {
                 "otsi-group-id": "Red OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }

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                 ]
               },
               {
                 "otsi-group-id": "Red OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   }
                 ]
               },
               {
                 "otsi-group-id": "Green OTSiG (Forward)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               },
               {
                 "otsi-group-id": "Green OTSiG (Reverse)",
                 "otsi": [
                   {
                     "otsi-carrier-id": 1
                   },
                   {
                     "otsi-carrier-id": 2
                   }
                 ]
               }
             ]
           },
           "node": [
             {
               "node-id": "WDM-TE-Node-1",
               "ietf-te-topology:te-node-id": "192.0.2.1",
               "ietf-te-topology:te": {
                 "ietf-te-topology:tunnel-termination-point": [
                   {
                     "tunnel-tp-id": "AQ==",
                     "ietf-optical-impairment-topology:ttp-transceiver"\
   : [
                       {
                         "transponder-ref": 1,
                         "transceiver-ref": 1
                       }

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                     ],
                     "local-link-connectivities": {
                       "is-allowed": false,
                       "local-link-connectivity": [
                         {
                           "link-tp-ref": "1",
                           "ietf-optical-impairment-topology:llc-transc\
   eiver": [
                             {
                               "ttp-transponder-ref": 1,
                               "ttp-transceiver-ref": 1,
                               "is-allowed": true
                             }
                           ]
                         }
                       ]
                     }
                   },
                   {
                     "tunnel-tp-id": "Ag==",
                     "ietf-optical-impairment-topology:ttp-transceiver"\
   : [
                       {
                         "transponder-ref": 2,
                         "transceiver-ref": 1
                       },
                       {
                         "transponder-ref": 2,
                         "transceiver-ref": 2
                       }
                     ],
                     "local-link-connectivities": {
                       "is-allowed": false,
                       "local-link-connectivity": [
                         {
                           "link-tp-ref": "2",
                           "ietf-optical-impairment-topology:llc-transc\
   eiver": [
                             {
                               "ttp-transponder-ref": 2,
                               "ttp-transceiver-ref": 1,
                               "is-allowed": true
                             }
                           ]
                         },
                         {
                           "link-tp-ref": "3",
                           "ietf-optical-impairment-topology:llc-transc\

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   eiver": [
                             {
                               "ttp-transponder-ref": 2,
                               "ttp-transceiver-ref": 2,
                               "is-allowed": true
                             }
                           ]
                         }
                       ]
                     }
                   }
                 ]
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1",
                   "ietf-te-topology:te-tp-id": 1,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "2",
                   "ietf-te-topology:te-tp-id": 2,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "3",
                   "ietf-te-topology:te-tp-id": 3,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "23",
                   "ietf-te-topology:te-tp-id": 23
                 }
               ],
               "ietf-optical-impairment-topology:transponders": {
                 "transponder": [
                   {
                     "transponder-id": 1,
                     "transceiver": [
                       {
                         "transceiver-id": 1,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Red OTSiG (Forward)",
                           "otsi-ref": 1
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Red OTSiG (Reverse)",
                           "otsi-ref": 1

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                         }
                       }
                     ]
                   },
                   {
                     "transponder-id": 2,
                     "transceiver": [
                       {
                         "transceiver-id": 1,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Green OTSiG (Forward)",
                           "otsi-ref": 1
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Green OTSiG (Reverse)",
                           "otsi-ref": 1
                         }
                       },
                       {
                         "transceiver-id": 2,
                         "outgoing-otsi": {
                           "otsi-group-ref": "Green OTSiG (Forward)",
                           "otsi-ref": 2
                         },
                         "incoming-otsi": {
                           "otsi-group-ref": "Green OTSiG (Reverse)",
                           "otsi-ref": 2
                         }
                       }
                     ]
                   }
                 ]
               }
             },
             {
               "node-id": "WDM-TE-Node-2",
               "ietf-te-topology:te-node-id": "192.0.2.2",
               "ietf-te-topology:te": {},
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1",
                   "ietf-te-topology:te-tp-id": 1,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "2",
                   "ietf-te-topology:te-tp-id": 2,
                   "ietf-te-topology:te": {}

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                 },
                 {
                   "tp-id": "3",
                   "ietf-te-topology:te-tp-id": 3,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "4",
                   "ietf-te-topology:te-tp-id": 4,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "5",
                   "ietf-te-topology:te-tp-id": 5,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "6",
                   "ietf-te-topology:te-tp-id": 6,
                   "ietf-te-topology:te": {}
                 },
                 {
                   "tp-id": "56",
                   "ietf-te-topology:te-tp-id": 56,
                   "ietf-te-topology:te": {}
                 }
               ]
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "Add-Drop-Link-1-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",
                 "source-tp": "1"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "4"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [

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                             {
                               "flexi-n": -10,
                               "otsi-group-ref": "Red OTSiG (Forward)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-1-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "4"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "1"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         },
                         {
                           "i": 2,

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                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-1",
                 "source-tp": "2"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "5"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": -20,
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }

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                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-2-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "5"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "2"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         },
                         {
                           "i": 2,
                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {

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                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Forward",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "4"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-2",
                 "dest-tp": "6"
               },
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": -20,
                               "otsi-group-ref": "Green OTSiG (Forward)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         }
                       ]
                     }
                   }

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                 }
               }
             },
             {
               "link-id": "Add-Drop-Link-3-Reverse",
               "source": {
                 "source-node": "WDM-TE-Node-2",
                 "source-tp": "6"
               },
               "destination": {
                 "dest-node": "WDM-TE-Node-1",
                 "dest-tp": "3"
               },
               "ietf-te-topology:te": {
                 "ietf-te-topology:te-link-attributes": {
                   "ietf-optical-impairment-topology:OMS-attributes": {
                     "media-channel-groups": {
                       "media-channel-group": [
                         {
                           "i": 1,
                           "media-channels": [
                             {
                               "flexi-n": 10,
                               "otsi-group-ref": "Red OTSiG (Reverse)",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 }
                               ]
                             }
                           ]
                         },
                         {
                           "i": 2,
                           "media-channels": [
                             {
                               "flexi-n": 20,
                               "otsi-group-ref": "Green OTSiG (Reverse)\
   ",
                               "otsi-ref": [
                                 {
                                   "otsi-carrier-ref": 1
                                 },
                                 {
                                   "otsi-carrier-ref": 2
                                 }
                               ]
                             }

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                           ]
                         }
                       ]
                     }
                   }
                 }
               }
             }
           ]
         }
       ]
     }
   }

Appendix C.  Examples How to Use the organizational-mode Attribute

   One option to describe the transceiver capabilities of an optical
   transponder (supported-mode list in the supported-modes container as
   defied in [I-D.ietf-ccamp-rfc9093-bis]) is to describe the
   organizational-modes a transceiver supports as described in section
   Section 2.6.2.

   [I-D.ietf-ccamp-rfc9093-bis]) defines the operational-mode of type
   identityref, which means that the identity the operational-mode
   attribute is referring to needs to be defined in a separate
   organization-specific or vendor-specific YANG module.  An example of
   such an organization-specific YANG module as well as a vendor-
   specific YANG module is provided below.

   YANG module example containing the identity definition for a 400G
   operational-mode specified by the organization Forum A:

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   module forum-a-operational-modes {
     yang-version 1.1;

     import "ietf-layer0-types"{
       prefix "id-base"};

     namespace "urn:forum-a:example:forum-a-op-modes";
     prefix "op-modes";

   ...

     identity 400G-operational-mode {
       base "id-base:operational-mode"
         description "Forum A 400G specific mode.";
     }

   ...

   }

   YANG module example containing the identity definition for a 400G
   operational-mode specified by the organization Vendor B with the same
   identity name "400G-operational-mode" as an operational mode that
   specified by Forum A.

   module vendor-b-operational-modes {
     yang-version 1.1;

     import "ietf-layer0-types"{
       prefix "id-base"};

     namespace "urn:vendor-b:example:vendor-b-op-modes";
     prefix "op-modes";

   ...

     identity 400G-operational-mode {
       base "id-base:operational-mode"
         description "Vendor B 400G mode.";
     }

   ...

   }

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   If there are transceivers in a network that are supporting any of the
   two 400G operational modes, the one specified by Forum A or the one
   specified by Vendor B or even both, the different name spaces allow
   to unambiguously identify the two modes that are defined in the YANG
   modules above with exactly the same identity name.

   The NETCONF server providing the optical impairment-aware topology
   will have to support both YANG modules above and will have to
   advertise both as capability in the NETCONF hello message indicating
   that these operational mode identities are used in the description of
   the optical impairment-aware topology model defined in this document.

Contributors

   Thanks to all of the contributors.

   Aihua Guo
   Huawei Technologies
   Email: aguo@futurewei.com

   Jonas Martensson
   Smartoptics
   Email: jonas.martensson@smartoptics.com

Additional Authors

   Young Lee
   Samsung Electronics
   Email: younglee.tx@gmail.com

   Haomian Zheng
   Huawei Technologies
   Email: zhenghaomian@huawei.com

   Nicola Sambo
   Scuola Superiore Sant'Anna
   Email: nicosambo@gmail.com

   Giovanni Martinelli
   Cisco
   Email: giomarti@cisco.com

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   Jean-Luc Auge
   Orange
   Email: jeanluc.auge@orange.com

   Julien Meuric
   Orange
   Email: julien.meuric@orange.com

   Victor Lopez
   Nokia
   Email: Victor.Lopez@nokia.com

   Enrico Griseri
   Nokia
   Email: Enrico.Griseri@nokia.com

   Gert Grammel
   Juniper
   Email: ggrammel@juniper.net

   Roberto Manzotti
   Cisco
   Email: rmanzott@cisco.com

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

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   G. Galimberti
   Individual
   Email: ggalimbe56@gmail.com

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

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