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Versions: (draft-ietf-ccamp-transport-nbi-use-cases) 00 01 02 03 04 05

CCAMP Working Group                                             I. Busi
Internet Draft                                                   Huawei
Intended status: Informational                                  D. King
                                                     Old Dog Consulting
                                                               H. Zheng
                                                                 Huawei
                                                                  Y. Xu
                                                                  CAICT

Expires: September 2019                                  March 11, 2019





         Transport Northbound Interface Applicability Statement
            draft-ietf-ccamp-transport-nbi-app-statement-05


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
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   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on September 11, 2019.








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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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

Abstract

   Transport network domains, including Optical Transport Network (OTN)
   and Wavelength Division Multiplexing (WDM) networks, are typically
   deployed based on a single vendor or technology platforms. They are
   often managed using proprietary interfaces to dedicated Element
   Management Systems (EMS), Network Management Systems (NMS) and
   increasingly Software Defined Network (SDN) controllers.

   A well-defined open interface to each domain management system or
   controller is required for network operators to facilitate control
   automation and orchestrate end-to-end services across multi-domain
   networks. These functions may be enabled using standardized data
   models (e.g. YANG), and appropriate protocol (e.g., RESTCONF).

   This document analyses the applicability of the YANG models being
   defined by the IETF (Traffic Engineering Architecture and Signaling
   (TEAS) and Common Control and Measurement Plane (CCAMP) WGs in
   particular) to support OTN single and multi-domain scenarios.

Table of Contents

   1. Introduction...................................................4
      1.1. The scope of this document................................4
      1.2. Assumptions...............................................5
   2. Terminology....................................................6
   3. Conventions used in this document..............................7
      3.1. Topology and traffic flow processing......................7
      3.2. JSON code.................................................8


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   4. Scenarios Description..........................................9
      4.1. Reference Network.........................................9
      4.2. Topology Abstractions....................................13
      4.3. Service Configuration....................................15
         4.3.1. ODU Transit.........................................16
         4.3.2. EPL over ODU........................................17
         4.3.3. Other OTN Clients Services..........................18
         4.3.4. EVPL over ODU.......................................19
      4.4. Multi-function Access Links..............................20
      4.5. Protection and Restoration Configuration.................21
         4.5.1. Linear Protection (end-to-end)......................21
         4.5.2. Segmented Protection................................23
      4.6. Notification.............................................23
      4.7. Path Computation with Constraint.........................24
   5. YANG Model Analysis...........................................24
      5.1. YANG Models for Topology Abstraction.....................25
         5.1.1. Domain 1 Black Topology Abstraction.................26
         5.1.2. Domain 2 Black Topology Abstraction.................30
         5.1.3. Domain 3 White Topology Abstraction.................31
         5.1.4. Multi-domain Topology Merging.......................31
      5.2. YANG Models for Service Configuration....................33
         5.2.1. ODU Transit Service.................................36
            5.2.1.1. Single Domain Example..........................38
         5.2.2. EPL over ODU Service................................38
            5.2.2.1. Single Domain Example..........................40
         5.2.3. Other OTN Client Services...........................41
            5.2.3.1. Single Domain Example..........................42
         5.2.4. EVPL over ODU Service...............................42
      5.3. YANG Models for Protection Configuration.................44
         5.3.1. Linear Protection (end-to-end)......................44
      5.4. Notifications............................................44
      5.5. Path Computation with Constraints........................44
   6. Security Considerations.......................................44
   7. IANA Considerations...........................................45
   8. References....................................................45
      8.1. Normative References.....................................45
      8.2. Informative References...................................46
   9. Acknowledgments...............................................47
   Appendix A.    Validating a JSON fragment against a YANG Model...49
      A.1.  Manipulation of JSON fragments..........................49
      A.2.  Comments in JSON fragments..............................50
      A.3.  Validation of JSON fragments: DSDL-based approach.......50
      A.4.  Validation of JSON fragments: why not using a XSD-based
      approach......................................................51



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   Appendix B.    Detailed JSON Examples............................52
      B.1.  JSON Examples for Topology Abstractions.................52
         B.1.1.   JSON Code: mpi1-otn-topology.json.................52
      B.2.  JSON Examples for Service Configuration.................68
         B.2.1.   JSON Code: mpi1-odu2-service-config.json..........68
         B.2.2.   JSON Code: mpi1-odu2-tunnel-config.json...........72
         B.2.3.   JSON Code: mpi1-epl-service-config.json...........72

1. Introduction

   Transport of packet services are critical for a wide-range of
   applications and services, including data center and LAN
   interconnects, Internet service backhauling mobile backhaul and
   enterprise Carrier Ethernet services. These services are typically
   setup using stovepipe NMS and EMS platforms, often requiring
   propriety management platforms and legacy management interfaces. A
   clear goal of operators is to automate the setup of transport
   services across multiple transport technology domains.

   A common open interface (API) to each domain controller and or
   management system is pre-requisite for network operators to control
   multi-vendor and multi-domain networks and also enable service
   provisioning coordination/automation. This can be achieved by using
   standardized YANG models, used together with an appropriate protocol
   (e.g., RESTCONF [RFC8040]).

   This document analyses the applicability of the YANG models being
   defined by IETF (Traffic Engineering Architecture and Signaling
   (TEAS) and Common Control and Measurement Plane (CCAMP) WGs in
   particular) to support Optical Transport Networks (OTN) single and
   multi-domain scenarios.

1.1. The scope of this document

   This document assumes a reference architecture, including
   interfaces, based on the Abstraction and Control of Traffic-
   Engineered Networks (ACTN), defined in [RFC8453].

   The focus of this document is on the MPI (interface between the
   Multi Domain Service Coordinator (MDSC) and a Physical Network
   Controller (PNC), controlling a transport network domain).






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   It is worth noting that the same MPI analyzed in this document could
   be used between hierarchical MDSC controllers, as shown in Figure 4
   of [RFC8453].

   Detailed analysis of the CMI (interface between the Customer Network
   Controller (CNC) and the MDSC) as well as of the interface between
   service and network orchestrators are outside the scope of this
   document. However, some considerations and assumptions about the
   information are described when needed.

   The relationship between the current IETF YANG models and the type
   of ACTN interfaces can be found in [ACTN-YANG]. Therefore, it
   considers the TE Topology YANG model defined in [TE-TOPO], with the
   OTN Topology augmentation defined in [OTN-TOPO] and the TE Tunnel
   YANG model defined in [TE-TUNNEL], with the OTN Tunnel augmentation
   defined in [OTN-TUNNEL]. It also considers the Ethernet Client
   Topology augmentation defined in [CLIENT-TOPO] as well as the Client
   Signal YANG models defined in [CLIENT-SIGNAL] for both Transparent
   and Ethernet clients.

   The ONF Technical Recommendations for Functional Requirements for
   the transport API in [ONF TR-527] and the ONF transport API multi-
   domain examples in [ONF GitHub] have been considered as input for
   defining the reference scenarios analyzed in this document.

1.2. Assumptions

   This document is making the following assumptions:

   1. The MDSC can request, at the MPI, a PNC to setup a Transit Tunnel
      Segment using the TE Tunnel YANG model: in this case, since the
      endpoints of the E2E Tunnel are outside the domain controlled by
      that PNC, the MDSC would not specify any source or destination TE
      Tunnel Termination Point (TTP), i.e., it would leave empty the
      source, destination, src-tp-id and dst-tp-id attributes of the TE
      tunnel instance, and it would use the explicit-route-object (ERO)
      or route-object-include-exclude list to specify the ingress and
      egress links for each path of the Transit Tunnel Segment.

   2. Each PNC provides to the MDSC, at the MPI, the list of available
      timeslots on the inter-domain links using the TE Topology YANG
      model and OTN Topology augmentation. The TE Topology YANG model
      in [TE-TOPO] is being updated to report the label set
      information.



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   See section 1.7 of [TE-TUTORIAL] for more details.

   This document has made the following assumptions:

   1. The topology information for the Ethernet Client access links is
      modelled using the YANG model defined in [CLIENT-TOPO];

   2. The topology information for the OTN and Transparent Client
      access links is modelled using the YANG model defined in [OTN-
      TOPO];

   3. The mapping information for Ethernet and Transparent Client
      signals are modelled using the YANG model defined in [CLIENT-
      SIGNAL].

   Finally, the Network Elements (NEs) described in the scenarios used
   in the document are using ODU switching. It is assumed that the ODU
   links are pre-configured and using mechanisms such as WDM
   wavelength, which are outside the scope of this document.

2. Terminology

   Domain: A domain as defined by [RFC4655] is "any collection of
   network elements within a common sphere of address management or
   path computation responsibility".  Specifically, within this
   document we mean a part of an operator's network that is under
   common management (i.e., under shared operational management using
   the same instances of a tool and the same policies).  Network
   elements will often be grouped into domains based on technology
   types, vendor profiles, and geographic proximity.

   E-LINE: Ethernet Line

   EPL: Ethernet Private Line

   EVPL: Ethernet Virtual Private Line

   OTN: Optical Transport Network

   Service: A service in the context of this document can be considered
   as some form of connectivity between customer sites across the
   network operator's network [RFC8309].





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   Service Model: As described in [RFC8309] it describes a service and
   the parameters of the service in a portable way that can be used
   uniformly and independent of the equipment and operating
   environment.

   UNI: User Network Interface

   MDSC: Multi-Domain Service Coordinator

   CNC: Customer Network Controller

   PNC: Provisioning Network Controller

3. Conventions used in this document

3.1. Topology and traffic flow processing

   The traffic flow between different nodes is specified as an ordered
   list of nodes, separated with commas, indicating within the brackets
   the processing within each node:

      <node> [<processing>]{, <node> [<processing>]}

   The order represents the order of traffic flow being forwarded
   through the network.

   The processing can be just switching at a given layer
   "[(switching)]" or also having an adaptation of a client layer into
   a server layer "[(client) -> server]" or [client -> (server)],
   depending on whether the node is switching in the client or in the
   server layer.

   For example, the following traffic flow:

      R1 [(PKT) -> ODU2], S3 [(ODU2)], S5 [(ODU2)], S6 [(ODU2)],
      R3 [ODU2 -> (PKT)]

   Node R1 is switching at the packet (PKT) layer and mapping packets
   into an ODU2 before transmission to node S3. Nodes S3, S5 and S6 are
   switching at the ODU2 layer: S3 sends the ODU2 traffic to S5 which
   then sends it to S6 which finally sends to R3. Node R3 terminates
   the ODU2 from S6 before switching at the packet (PKT) layer.





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   The paths of working and protection transport entities are specified
   as an ordered list of nodes, separated with commas:

      <node> {, <node>}

   The order represents the order of traffic flow being forwarded
   through the network in the forward direction. In the case of
   bidirectional paths, the forward and backward directions are
   selected arbitrarily, but the convention is consistent between
   working/protection path pairs, as well as across multiple domains.

3.2. JSON code

   This document provides some detailed JSON code examples to describe
   how the YANG models being developed by the IETF (TEAS and CCAMP WG
   in particular) may be used. The scenario examples are provided using
   JSON to facilitate readability.

   Different objects need to have an identifier. The convention used to
   create mnemonic identifiers is to use the object name (e.g., S3 for
   node S3), followed by its type (e.g., NODE), separated by an "-",
   followed by "-ID". For example, the mnemonic identifier for node S3
   would be S3-NODE-ID.

   The JSON language does not support the insertion of comments that
   have been instead found to be useful when writing the examples. This
   document will insert comments into the JSON code as JSON name/value
   pair with the JSON name string starting with the "//" characters.
   For example, when describing the example of a TE Topology instance
   representing the ODU Abstract Topology exposed by the Transport PNC,
   the following comment has been added to the JSON code:

      "// comment": "ODU Abstract Topology @ MPI",

   The JSON code examples provided in this document have been validated
   against the YANG models following the validation process described
   in Appendix A, which would not consider the comments.

   In order to have successful validation of the examples, some
   numbering scheme has been defined to assign identifiers to the
   different entities which would pass the syntax checks. In that case,
   to simplify the reading, another JSON name/value pair formatted as a
   comment and using the mnemonic identifiers is also provided. For
   example, the identifier of node S3 (S3-NODE-ID) has been assumed to



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   be "10.0.0.3" and would be shown in the JSON code example using the
   two JSON name/value pair:

      "// te-node-id": "S3-NODE-ID",

      "te-node-id": "10.0.0.3",

   The first JSON name/value pair will be automatically removed in the
   first step of the validation process while the second JSON
   name/value pair will be validated against the YANG model
   definitions.

4. Scenarios Description

4.1. Reference Network

   The physical topology of the reference network is shown in Figure 1.
   It represents an OTN network composed of three transport network
   domains which provide transport connectivity services to an IP
   customer network through eight access links:



























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               ........................
   .........   :                      :
           :   :   Network domain 1   :   .............
   Customer:   :                      :   :           :
    domain :   :     S1 -------+      :   :  Network  :
           :   :    /           \     :   :  domain 3 :   ..........
       R1 ------- S3 ----- S4    \    :   :           :   :
           :   :    \        \    S2 --------+        :   :Customer
           :   :     \        \    |  :   :   \       :   : domain
           :   :      S5       \   |  :   :    \      :   :
       R2 ------+    /  \       \  |  :   :    S31 --------- R5
           :   : \  /    \       \ |  :   :   /   \   :   :
       R3 ------- S6 ---- S7 ---- S8 ------ S32   S33 ------ R6
           :   : /        |       |   :   : / \   /   :   :.......
       R4 ------+         |       |   :   :/   S34    :          :
           :   :..........|.......|...:   /    /      :          :
   ........:              |       |      /:.../.......:          :
                          |       |     /    /                   :
               ...........|.......|..../..../...                 :
               :          |       |   /    /   :    ..............
               : Network  |       |  /    /    :    :
               : domain 2 |       | /    /     :    :Customer
               :         S11 ---- S12   /      :    : domain
               :        /          | \ /       :    :
               :     S13     S14   | S15 ------------- R7
               :     |  \   /   \  |    \      :    :
               :     |   S16     \ |     \     :    :
               :     |  /         S17 -- S18 --------- R8
               :     | /             \   /     :    :
               :    S19 ---- S20 ---- S21 ------------ R9
               :                               :    :
               :...............................:    :.............

                        Figure 1 - Reference network

   This document assumes that all the transport network switching nodes
   Si are capable of switching in the electrical domain (ODU switching)
   and that all the Si-Sj OTN links within the transport network
   (intra-domain or inter-domain) are 100G links while the access Ri-Sj
   links are 10G links.

   It is also assumed that, within the transport network, the
   physical/optical interconnections supporting the Si-Sj OTN links (up
   to the OTU4 trail), are pre-configured using mechanisms which are



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   outside the scope of this document and are not exposed at the MPIs
   to the MDSC.

   Different technologies can be used on the access links (e.g.,
   Ethernet, STM-N and OTU). Section 4.3 provides more details about
   the different assumptions on the access links for different services
   types and section 4.4 describes the control of access links which
   can support different technology configuration (e.g., STM-64, 10GE
   or OTU2) depending on the type of service being configured (multi-
   function access links).

   The transport domain control architecture, shown in Figure 2,
   follows the ACTN architecture and framework document [RFC8453], and
   functional components:

































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                           --------------
                          |              |
                          |     CNC      |
                          |              |
                           --------------
                                 |
             ....................|....................... CMI
                                 |
                          ----------------
                         |                |
                         |      MDSC      |
                         |                |
                          ----------------
                            /   |    \
                           /    |     \
            ............../.....|......\................ MPIs
                         /      |       \
                        /   ----------   \
                       /   |   PNC2   |   \
                      /     ----------     \
             ----------         |           \
            |   PNC1   |      -----          \
             ----------     (       )      ----------
                 |         (         )    |   PNC3   |
               -----      (  Network  )    ----------
             (       )    (  Domain 2 )        |
            (         )    (         )       -----
           (  Network  )    (       )      (       )
           (  Domain 1 )      -----       (         )
            (         )                  (  Network  )
             (       )                   (  Domain 3 )
               -----                      (         )
                                           (       )
                                             -----

                    Figure 2 - Controlling Hierarchies

   The ACTN framework facilitates the detachment of the network and
   service control from the underlying technology. It helps the
   customer define the network as desired by business needs. Therefore,
   care must be taken to keep a minimal level of dependency on the CMI
   (or no dependency at all) with respect to the network domain
   technologies. The MPI instead requires some specialization according
   to the domain technology.



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   The control interfaces within the scope of this document are the
   three MPIs shown in Figure 2.

   It is worth noting that the split of functionality at the MPI in the
   ACTN architecture between the MDSC and the PNCs is
   equivalent/analogous to the split of functionality which is assumed
   for the ONF T-API interface when used between a multi-domain
   controller and domain controllers, as described in the ONF T-API
   multi-domain use cases [ONF TR-527], as well as at the MEF PRESTO
   interface between the Service Orchestration Functionality (SOF) and
   the Infrastructure Control and Management (ICM) in the MEF LSO
   Architecture [MEF 55].

   This document does not make any assumption about the control
   architecture of the customer IP network: in line with [RFC8453], the
   CNC is just a functional component within the customer control
   architecture which is capable of requesting, at the CMI, transport
   connectivity between IP routers, when needed.

   The CNC can request transport connectivity services between IP
   routers which can be attached to different transport domains (e.g.,
   between R1 and R8 in Figure 1) or to the same transport domain
   (e.g., between R1 and R3 in Figure 1). Since the CNC is not aware of
   the transport network controlling hierarchy, the mechanisms used by
   the CNC to request, at the CMI, transport connectivity services are
   independent on whether the service request is single-domain or
   multi-domain.

   It is assumed that the CMI allows the CNC to provide all the
   information that is required by the MDSC to understand the
   connectivity service request and to decide the network
   configurations to be requested, at the MPIs, to its underlying PNCs
   to support the requested connectivity service.

   When a single-domain service is requested by the CNC at the CMI
   (e.g., between R1 and R3 in Figure 1), the MDSC can follow the same
   procedures, described above for the multi-domain service, and decide
   the network configuration to request only at the MPI of the PNC
   controlling that domain (e.g., MPI1 of PNC1 in Figure 2).

4.2. Topology Abstractions

   Abstraction provides a selective method for representing
   connectivity information within a domain. There are multiple methods



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   to abstract a network topology. This document assumes the
   abstraction method defined in [RFC7926]:

     "Abstraction is the process of applying the policy to the
     available TE information within a domain, to produce selective
     information that represents the potential ability to connect
     across the domain.  Thus, abstraction does not necessarily offer
     all possible connectivity options, but presents a general view of
     potential connectivity according to the policies that determine
     how the domain's administrator wants to allow the domain resources
     to be used."

   [RFC8453] Provides the context of topology abstraction in the ACTN
   architecture and discusses a few alternatives for the abstraction
   methods for both packet and optical networks. This is an important
   consideration since the choice of the abstraction method impacts
   protocol design and the information it carries.  According to
   [RFC8453], there are three types of topology:

   o  White topology: This is a case where the PNC provides the actual
      network topology to the MDSC without any hiding or filtering. In
      this case, the MDSC has the full knowledge of the underlying
      network topology;

   o  Black topology: The entire domain network is abstracted as a
      single virtual node with the access/egress links without
      disclosing any node internal connectivity information;

   o  Grey topology: This abstraction level is between black topology
      and white topology from a granularity point of view. This is an
      abstraction of TE tunnels for all pairs of border nodes. We may
      further differentiate from a perspective of how to abstract
      internal TE resources between the pairs of border nodes:

       - Grey topology type A: border nodes with TE links between them
          in a full mesh fashion;

       - Grey topology type B: border nodes with some internal
          abstracted nodes and abstracted links.

   Each PNC should provide the MDSC with a network topology
   abstractions hiding the internal details of the physical domain
   network topology controlled by the PNC and this abstraction is
   independent of the abstractions provided by other PNCs. Therefore it



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   is possible that different PNCs provide different types of topology
   abstractions and each MPI operates on the abstract topology
   regardless of, and independently from, the type of abstraction
   provided by the PNC.

   To analyze how the MDSC can operate on abstract topologies
   independently from the topology abstraction provided by each PNC
   and, therefore, that different PNCs can provide different topology
   abstractions, that the following examples are assumed:

   o  PNC1 and PNC2 provide black topology abstractions which expose at
      MPI1, and MPI2 respectively, a single virtual node (representing
      the whole network domain 1, and domain 2 respectively).

   o  PNC3 provides a white topology abstraction which exposes at MPI3
      all the physical nodes and links within network domain 3.

   The MDSC should be capable of stitching together the abstracted
   topologies provided by each PNC to build its own view of the
   multi-domain network topology. The process may require suitable
   oversight, including administrative configuration and trust models,
   a method of how to achieve this is out of scope for this document.

   The MDSC can also provide topology abstraction of its own view of
   the multi-domain network topology at its CMIs depending on the
   customers' needs: it can provide different types of topology
   abstractions at different CMIs. Analyzing the topology abstractions
   provided by the MDSC to its CMIs is outside the scope of this
   document.

4.3. Service Configuration

   In the following scenarios, it is assumed that the CNC is capable of
   requesting service connectivity from the MDSC to support IP routers
   connectivity.

   The type of services could depend on the type of physical links
   (e.g. OTN link, ETH link or SDH link) between the routers and
   transport network.

   The control of different adaptations inside IP routers, Ri (PKT ->
   foo) and Rj (foo -> PKT), are assumed to be performed by means that
   are not under the control of, and not visible to, the MDSC nor to




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   the PNCs. Therefore, these mechanisms are outside the scope of this
   document.

4.3.1. ODU Transit

   The physical links interconnecting the IP routers and the transport
   network can be 10G OTN links.

   In this case, it is assumed that the physical/optical
   interconnections below the ODU layer (up to the OTU2 trail) are
   pre-configured using mechanisms which are outside the scope of this
   document and not exposed at the MPIs between the PNCs and the MDSC.

   For simplicity of the description, it is also assumed that these
   interfaces are not channelized (i.e., they can only support one
   ODU2).

   To setup a 10Gb IP link between R1 and R8, an ODU2 end-to-end
   connection needs to be created, passing through transport nodes S3,
   S1, S2, S31, S33, S34, S15 and S18 which belong to different PNC
   domains (multi-domain service request):

      R1 [(PKT) -> ODU2], S3 [(ODU2]), S1 [(ODU2]), S2 [(ODU2]),
      S31 [(ODU2)], S33 [(ODU2)], S34 [(ODU2)],
      S15 [(ODU2)], S18 [(ODU2)], R8 [ODU2 -> (PKT)]

   The MDSC understands that it needs to establish an ODU2 transit
   service between the access links on S3 and S18, which belong to
   different PNC domains (multi-domain service request). It also
   decides the network configurations to request, at the MPIs, to its
   underlying PNCs, to coordinate the setup of a multi-domain ODU2
   segment connection between the access links on S3 and S18.

   To setup of a 10Gb IP link between R1 and R3, an ODU2 end-to-end
   connection needs to be created, passing through transport nodes S3,
   S5 and S6 which belong to the same PNC domain (single-domain service
   request):

      R1 [(PKT) -> ODU2], S3 [(ODU2)], S5 [(ODU2)], S6 [(ODU2)],
      R3 [ODU2 -> (PKT)]

   As described in section 4.1, the mechanisms used by the CNC at the
   CMI are independent on whether the service request is single-domain
   service or multi-domain.



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   The MDSC can understand that it needs to setup an ODU2 transit
   service between the access links on S3 and S6, which belong to the
   same PNC domain (single-domain service request) and it decides the
   proper network configuration to request PNC1.

4.3.2. EPL over ODU

   The physical links interconnecting the IP routers and the transport
   network can be 10G Ethernet physical links (10GE).

   In this case, it is assumed that the Ethernet physical interfaces
   (up to the MAC layer) are pre-configured using mechanisms which are
   outside the scope of this document and not exposed at the MPIs
   between the PNCs and the MDSC.

   To setup a 10Gb IP link between R1 and R8, an EPL service needs to
   be created, supported by an ODU2 end-to-end connection, between
   transport nodes S3 and S18, passing through transport nodes S1, S2,
   S31, S33, S34 and S15, which belong to different PNC domains (multi-
   domain service request):

      R1 [(PKT) -> ETH], S3 [ETH -> (ODU2)], S1 [(ODU2)],
      S2 [(ODU2)], S31 [(ODU2)), S33 [(ODU2)], S34 [(ODU2)],
      S15 [(ODU2)], S18 [(ODU2) -> ETH], R8 [ETH -> (PKT)]

   The MDSC understands that it needs to setup an EPL service between
   the access links on S3 and S18, which belong to different PNC
   domains (multi-domain service request). It also decides the network
   configurations to request, at the MPIs, to its underlying PNCs, to
   coordinate the setup of an end-to-end ODU2 connection between the
   nodes S3 and S8, including the configuration of the adaptation
   functions inside these edge nodes, such as S3 [ETH -> (ODU2)] and
   S18 [(ODU2) -> ETH].

   To setup a 10Gb IP link between R1 and R2, an EPL service needs to
   be created, supported by an ODU2 end-to-end connection between
   transport nodes S3 and S6, passing through the transport node S5,
   which belong to the same PNC domain (single-domain service request):

      R1 [(PKT) -> ETH], S3 [ETH -> (PKT)] S5 [(ODU2)],
      S6 [(ODU2) -> ETH], R2 [ETH -> (PKT)]






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   As described in section 4.1, the mechanisms used by the CNC at the
   CMI are independent on whether the service request is single-domain
   service or multi-domain.

   Based on the assumption above, in this case, the MDSC can understand
   that it needs to setup an EPL service between the access links on S3
   and S6, which belong to the same PNC domain (single-domain service
   request) and it decides the proper network configuration to request
   PNC1.

4.3.3. Other OTN Clients Services

   [ITU-T G.709] defines mappings of different Transparent Client
   layers into ODU. Most of them are used to provide Private Line
   services over an OTN transport network supporting a variety of types
   of physical access links (e.g., Ethernet, SDH STM-N, Fibre Channel,
   InfiniBand, etc.) interconnecting the IP routers and the transport
   network.

   In order to setup a 10Gb IP link between R1 and R8 using, with for
   example SDH physical links between the IP routers and the transport
   network, an STM-64 Private Line service needs to be created,
   supported by an ODU2 end-to-end connection, between transport nodes
   S3 and S18, passing through transport nodes S1, S2, S31, S33, S34
   and S15, which belong to different PNC domains (multi-domain service
   request):

      R1 [(PKT) -> STM-64], S3 [STM-64 -> (ODU2)], S1 [(ODU2)],
      S2 [(ODU2)], S31 [(ODU2)], S33 [(ODU2)], S34[(ODU2)],
      S15 [(ODU2)], S18 [(ODU2) -> STM-64], R8 [STM-64 -> (PKT)]

   As already described (section 4.1) CNC provides the essential
   information to permit the MDSC to understand which type of service
   is needed, in this case, an STM-64 Private Line service between the
   access links on S3 and S8, and it also decides the network
   configurations, including the configuration of the adaptation
   functions inside these edge nodes, such as S3 [STM-64 -> (ODU2)] and
   S18 [(ODU2) -> STM-64].

   To setup a 10Gb IP link between R1 and R3), an STM-64 Private Line
   service needs to be created between R1 and R3 (single-domain service
   request):





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      R1 [(PKT) -> STM-64], S3[STM-64 -> (ODU2)], S5 [(ODU2)],
      S6 [(ODU2) -> STM-64], R3[STM-64 -> (PKT)]

   As described in section 4.1, the mechanisms used by the CNC at the
   CMI are independent on whether the service request is single-domain
   service or multi-domain.

   Based on the assumption above, in this case, the MDSC can understand
   that it needs to setup an STM-64 Private Line service between the
   access links on S3 and S6, which belong to the same PNC domain
   (single-domain service request) and it decides the proper network
   configuration to request PNC1.

4.3.4. EVPL over ODU

   When the physical links interconnecting the IP routers and the
   transport network are Ethernet physical links, it is also possible
   that different Ethernet services (e.g., EVPL) can share the same
   physical access link using different VLANs.

   As described in section 4.3.2, it is assumed that the Ethernet
   physical interfaces (up to the MAC layer) are pre-configured.

   To setup two 1Gb IP links between R1 to R2 and between R1 and R8,
   two EVPL services need to be created, supported by two ODU0 end-to-
   end connections:

      R1 [(PKT) -> VLAN], S3 [VLAN -> (ODU0)], S5 [(ODU0)],
      S6 [(ODU0) -> VLAN], R2 [VLAN -> (PKT)]

      R1 [(PKT) -> VLAN], S3[VLAN -> (ODU0)], S1 [(ODU0)],
      S2 [(ODU0)], S31 [(ODU0)], S33 [(ODU0)], S34 [(ODU0)],
      S15 [(ODU0)], S18 [(ODU0) -> VLAN], R8[VLAN -> (PKT)]

   It is worth noting that the fist EVPL service is required between
   access links which belong to the same PNC domain (single-domain
   service request) while the second EVPL service is required between
   access links which belong to different PNC domains (multi-domain
   service request).

   Since the two EVPL services are sharing the same Ethernet physical
   link between R1 and S3, different VLAN IDs are associated with
   different EVPL services: for example, VLAN IDs 10 and 20
   respectively.



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   Based on the assumptions described in section 4.3.2, the CNC
   requests at the CMI the MDSC to setup these EVPL services and the
   MDSC understands the network configurations to request to the
   underlying PNCs, as described in section 4.3.2.

4.4. Multi-function Access Links

   Some physical links interconnecting the IP routers and the transport
   network can be configured in different modes, e.g., as OTU2 trail or
   STM-64 or 10GE physical links.

   This configuration can be done a-priori by means which are outside
   the scope of this document. In this case, these links will appear at
   the MPI as links supporting only one mode (depending on the a-priori
   configuration) and will be controlled at the MPI as discussed in
   section 4.3: for example, a 10G multi-function access link can be
   pre-configured as an OTU2 trail (section 4.3.1), a 10GE physical
   link (section 4.3.2) or an STM-64 physical link (section 4.3.3).

   It is also possible not to configure these links a-priori and let
   the MDSC (or, in case of a single-domain service request, the PNC)
   decide how to configure these links, based on the service
   configuration.

   For example, if the physical link between R1 and S3 is a
   multi-functional access link while the physical links between R4 and
   S6 and between R8 and S18 are STM-64 and 10GE physical links
   respectively, it is possible to configure either an STM-64 Private
   Line service between R1 and R4 or an EPL service between R1 and R8.

   The traffic flow between R1 and R4 can be summarized as:

      R1 [(PKT) -> STM-64], S3 [STM-64 -> (ODU2)], S5 [(ODU2)],
      S6 [(ODU2) -> STM-64], R4 [STM-64 -> (PKT)]

   The traffic flow between R1 and R8 can be summarized as:

      R1 [(PKT) -> ETH], S3 [ETH -> (ODU2)], S1 [(ODU2)],
      S2 [(ODU2)], S31 [(ODU2)), S33 [(ODU2)], S34 [(ODU2)],
      S15 [(ODU2)], S18 [(ODU2) -> ETH], R8 [ETH -> (PKT)]

   The CNC is capable to request at the CMI the setup either an STM-64
   Private Line service, between R1 and R4, or an EPL service, between
   R1 and R8.



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   The MDSC, based on the service being request, decides the network
   configurations to request, at the MPIs, to its underlying PNCs, to
   coordinate the setup of an end-to-end ODU2 connection, either
   between nodes S3 and S6, or between nodes S3 and S18, including the
   configuration of the adaptation functions on these edge nodes, and
   in particular whether the multi-function access link between R1 and
   S3 should operate as an STM-64 or as a 10GE physical link.

4.5. Protection and Restoration Configuration

   Protection switching provides a pre-allocated survivability
   mechanism, typically provided via linear protection methods and
   would be configured to operate as 1+1 unidirectional (the most
   common OTN protection method), 1+1 bidirectional or 1:n
   bidirectional. This ensures fast and simple service survivability.

   Restoration methods would provide the capability to reroute and
   restore connectivity traffic around network faults, without the
   network penalty imposed with dedicated 1+1 protection schemes.

   This section describes only services which are protected with linear
   protection. The description of services using dynamic restoration is
   outside the scope of this document.

   The MDSC needs to be capable of deciding the network configuration
   to request different PNCs to coordinate the protection switching
   configuration to support protected connectivity services described
   in section 4.3.

   Since in these service examples, switching within the transport
   network domain is performed only in the OTN ODU layer. It may also
   be assumed that protection switching within the transport network
   domain is provided at the OTN ODU layer.

4.5.1. Linear Protection (end-to-end)

   In order to protect the connectivity services described in section
   4.3 from failures within the OTN multi-domain transport network, the
   MDSC can decide to request its underlying PNCs to configure ODU2
   linear protection between the access nodes (e.g., nodes S3 and S18
   for the services setup between R1 and R8).






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   It is assumed that the OTN linear protection is configured to with
   1+1 unidirectional protection switching type, as defined in [ITU-T
   G.808.1] and [ITU-T G.873.1], as well as in [RFC4427].

   In these scenarios, a working transport entity and a protection
   transport entity, as defined in [ITU-T G.808.1], (or a working LSP
   and a protection LSP, as defined in [RFC4427]) should be configured
   in the data plane.

   Two cases can be considered:

   o  In one case, the working and protection transport entities pass
      through the same PNC domains:

         Working transport entity:     S3, S1, S2,
                                       S31, S33, S34,
                                       S15, S18

         Protection transport entity:  S3, S4, S8,
                                       S32,
                                       S12, S17, S18

   o  In another case, the working and protection transport entities
      can pass through different PNC domains:

         Working transport entity:     S3, S5, S7,
                                       S11, S12, S17, S18

         Protection transport entity:  S3, S1, S2,
                                       S31, S33, S34,
                                       S15, S18

   The PNCs should be capable to report to the MDSC which is the active
   transport entity, as defined in [ITU-T G.808.1], in the data plane.

   Given the fast dynamic of protection switching operations in the
   data plane (50ms recovery time), this reporting is not expected to
   be in real-time.

   It is also worth noting that with unidirectional protection
   switching, e.g., 1+1 unidirectional protection switching, the active
   transport entity may be different in the two directions.





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4.5.2. Segmented Protection

   To protect the connectivity services defined in section 4.3 from
   failures within the OTN multi-domain transport network, the MDSC can
   decide to request its underlying PNCs to configure ODU2 linear
   protection between the edge nodes of each domain.

   For example, MDSC can request PNC1 to configure linear protection
   between its edge nodes S3 and S2:

      Working transport entity:     S3, S1, S2

      Protection transport entity:  S3, S4, S8, S2

     MDSC can also request PNC2 to configure linear protection between
     its edge nodes S15 and S18:

      Working transport entity:     S15, S18

      Protection transport entity:  S15, S12, S17, S18

   MDSC can also request PNC3 to configure linear protection between
   its edge nodes S31 and S34:

      Working transport entity:     S31, S33, S34

      Protection transport entity:  S31, S32, S34

4.6. Notification

   To realize the topology update, service update and restoration
   function, following notification type should be supported:

   1. Object create

   2. Object delete

   3. Object state change

   4. Alarm

   There are three types of topology abstraction type defined in
   section 4.2, the notification should also be abstracted. The PNC and
   MDSC should coordinate together to determine the notification



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   policy, such as when an intra-domain alarm occurred, the PNC may not
   report the alarm but the service state change notification to the
   MDSC.

4.7. Path Computation with Constraint

   It is possible to define constraints to be taken into account during
   path computation procedures (e.g., IRO/XRO).

   For example, the CNC can request, at the CMI, an ODU transit
   service, as described in section 4.3.1, between R1 and R8 with the
   constraint to pass through the link from S2 to S31 (IRO), such that
   a qualified path could be:

      R1 [(PKT) -> ODU2], S3 [(ODU2]), S1 [(ODU2]), S2 [(ODU2]),
      S31 [(ODU2)], S33 [(ODU2)], S34 [(ODU2)],
      S15 [(ODU2)], S18 [(ODU2)], R8 [ODU2 -> (PKT)]

   If the CNC instead requested to pass through the link from S8 to
   S12, then the above path would not be qualified, while the following
   would be:

      R1 [(PKT) -> ODU2], S3[(ODU2]), S1 [(ODU2]), S2[(ODU2]),
      S8 [(ODU2]), S12[(ODU2]), S15 [(ODU2]), S18[(ODU2]), R8 [ODU2 ->
      (PKT)]

   The mechanisms used by the CNC to provide path constraints at the
   CMI are outside the scope of this document. It is assumed that the
   MDSC can understand these constraints and take them into account in
   its path computation procedures (which would decide at least which
   domains and inter-domain links) and in the path constraints to
   provide to its underlying PNCs, to be taken into account in the path
   computation procedures implemented by the PNCs (with a more detailed
   view of topology).

5. YANG Model Analysis

   This section analyses how the IETF YANG models can be used at the
   MPIs, between the MDSC and the PNCs, to support the scenarios
   described in section 4.

   The YANG models described in [ACTN-YANG] are assumed to be used at
   the MPI.




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   Section 5.1 describes the different topology abstractions provided
   to the MDSC by each PNC via its own MPI.

   Section 5.2 describes how the MDSC can request different PNCs, via
   their own MPIs, the network configuration needed to setup the
   different services described in section 4.3.

   Section 5.3 describes how the protection scenarios can be deployed,
   including end-to-end protection and segment protection, for both
   intra-domain and inter-domain scenario.

5.1. YANG Models for Topology Abstraction

   Each PNC reports its respective OTN abstract topology to the MDSC,
   as described in section 4.2, using the Topology YANG models, defined
   in [RFC8345], with the TE Topology YANG augmentations, provided in
   [TE-TOPO], and the OTN technology-specific YANG augmentations,
   defined in [OTN-TOPO].

   The [OTN-TOPO] model allows reporting within the OTN abstract
   topology also the access links which are capable of supporting the
   transparent client layers, defined in section 4.3.3 and in
   [CLIENT-SIGNAL]. These links can also be multi-function access links
   that can be configured as a transparent client physical links (e.g.,
   STM-64 physical link) as an OTUk trail.

   In order to support the EPL and EVPL services, described in sections
   4.3.2 and 4.3.4, the access links, which are capable to be
   configured as Ethernet physical links, are reported by each PNC
   within its respective Ethernet abstract topology, using the Topology
   YANG models, defined in [RFC8345], with the TE Topology YANG
   augmentations, defined in [TE-TOPO], and the Ethernet client
   technology-specific YANG augmentations, defined in [CLIENT-TOPO].
   These links can also be multi-function access links that can be
   configured as an Ethernet physical link or as an OTUk trail and/or
   as transparent client physical links (e.g., STM-64 physical link).
   In this case, these physical access links are represented in both
   the OTN and Ethernet abstract topologies.

   It is worth noting that in the network scenarios analyzed in this
   document (where switching is performed only in the ODU layer), the
   Ethernet abstract topologies reported by the PNCs describes only the
   Ethernet client access links: no Ethernet TE switching capabilities
   are reported in these Ethernet abstract topologies.



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5.1.1. Domain 1 Black Topology Abstraction

   PNC1 provides the required black topology abstraction, as described
   in section 4.2. It exposes at MPI1 to the MDSC, two TE Topology
   instances with only one TE node each.

   The first TE Topology instance reports the domain 1 OTN abstract
   topology view (MPI1 OTN Topology), using the OTN technology-specific
   augmentations [OTN-TOPO], with only one abstract TE node (i.e., AN1)
   and only inter-domain and access abstract TE links (which represent
   the inter-domain physical links and the access physical links which
   can support ODU and/or transparent client layers), as shown in
   Figure 3 below.


                   ...................................
                   :                                 :
                   :       +-----------------+       :
                   :       |                 |       :
           (R1)- - --------|                 |-------- - -(S31)
                   : AN1-1 |                 | AN1-7 :
                   :       |                 |       :
           (R3)- - --------|                 |       :
                   : AN1-2 |       AN1       |       :
                   :       |                 |       :
           (R4)- - --------|                 |-------- - -(S32)
                   : AN1-3 |                 | AN1-6 :
                   :       |                 |       :
                   :       +-----------------+       :
                   :          |          |           :
                   :    AN1-4 |          | AN1-5     :
                   :..........|..........|...........:

                              |          |
                            (S11)      (S12)

   Figure 3 - OTN Abstract Topology exposed at MPI1 (MPI1 OTN Topology)

   The second TE Topology instance reports the domain 1 Ethernet
   abstract topology view (MPI1 ETH Topology), using the Ethernet
   technology-specific augmentations [CLIENT-TOPO], with only one
   abstract TE node (i.e., AN1) and only access abstract TE links
   (which represent the access physical links which can support
   Ethernet client layers), as shown in Figure 4 below.



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                   ...................................
                   :                                 :
                   :       +-----------------+       :
                   :       |                 |       :
           (R1)- - --------|                 |       :
                   : AN1-1 |                 |       :
                   :       |                 |       :
           (R2)- - --------|                 |       :
                   : AN1-8 |       AN1       |       :
                   :       |                 |       :
                   :       |                 |       :
                   :       |                 |       :
                   :       |                 |       :
                   :       +-----------------+       :
                   :                                 :
                   :.................................:

   Figure 4 - ETH Abstract Topology exposed at MPI1 (MPI1 ETH Topology)

   As described in section 4.1, it is assumed that the OTU4 trails on
   the inter-domain physical links (e.g., the link between S2 and S31)
   are pre-configured and exposed as external TE Links, within the MPI1
   OTN topology (e.g., the external TE Link terminating on AN1-7 TE
   Link Termination Point (LTP) abstracting the OTU4 trail between S2
   and S31).

   In order to analyze the service scenarios of sections 4.3 and 4.4:

   o  the access link between S3 and R1 is assumed to be a
      multi-function access link, which can be configured as an OTU2
      trail or as an STM-64 or a 10GE physical link;

   o  the access link between S6 and R2 is assumed to be pre-configured
      as a 10GE physical link, up to the MAC layer;

   o  the access link between S6 and R3 is assumed to be a
      multi-function access link which can be configured as an OTU2
      trail or as an STM-64 physical link;

   o  the access link connected to router R4 is assumed to be
      pre-configured as an STM-64 physical link.





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   Therefore PNC1 exports at MPI1 the following external TE Links,
   within the MPI1 OTN topology:

   o  two abstract TE Links, terminating on LTP AN1-1 and AN1-2
      respectively, abstracting the physical access link between S3 and
      R1 and the access link between S6 and R3 respectively, reporting
      that they can support STM-64 client signals as well as ODU2
      connections;

   o  one abstract TE Link, terminating on LTP AN1-3, abstracting the
      physical access link between S6 and R4, reporting that it can
      support STM-64 client signals but no ODU2 connections.

   The information about the 10GE access link between S6 and R2 as well
   as the fact that the access link between S3 and R1 can also be
   configured as a 10GE link cannot be exposed by PNC1 within the MPI1
   OTN topology.

   Therefore, PNC1 exports at MPI1, within the MPI1 ETH topology, two
   abstract TE Links, terminating on LTP AN1-1 and AN1-8 respectively,
   abstracting the physical access link between S3 and R1 and the
   access link between S6 and R2 respectively, reporting that they can
   support Ethernet client signal with port-based and VLAN-based
   classifications. The PNC1 native topology would represent the
   physical network topology of the domain controlled by the PNC, as
   shown in Figure 5.





















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                  ..................................
                  :                                :
                  :     Physical Topology @ PNC1   :
                  :                                :
                  :        +----+        +----+    :
                  :        |    |S1-1    |    |S2-3:
                  :        | S1 |--------| S2 |----- - -(S31)
                  :        +----+    S2-1+----+    :
                  :     S1-2/               |S2-2  :
                  :    S3-4/                |      :
                  :    +----+   +----+      |      :
                  :    |    |3 1|    |      |      :
          (R1)- - -----| S3 |---| S4 |      |      :
                  :S3-1+----+   +----+      |      :
                  :   S3-2 \        \S4-2   |      :
                  :         \S5-1    \      |      :
                  :        +----+     \     |      :
                  :        |    |      \S8-2|      :
                  :        | S5 |       \   |      :
                  :        +----+        \  |S8-1  :
          (R2)- - ------  2/    \3        \ |      :
                  :S6-1 \ /5     \1        \|      :
                  :    +----+   +----+   +----+    :
                  :    |    |   |    |   |    |S8-5:
          (R3)- - -----| S6 |---| S7 |---| S8 |----- - -(S32)
                  :S6-2+----+4 2+----+4 3+----+    :
                  :     /         |        |       :
          (R3)- - ------     S7-3 |        | S8-4  :
                  :S6-3           |        |       :
                  :...............|........|.......:

                                  |        |
                                (S11)    (S12)

              Figure 5 - Physical Topology controlled by PNC1

   The PNC1 native topology is not exposed and therefore it under PNC
   responsibility to abstract the whole domain physical topology as a
   single TE node and to maintain a mapping between the LTPs exposed at
   MPI abstract topologies and the associated physical interfaces
   controlled by the PNC:





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   Physical Interface     OTN Topology LTP     ETH Topology LTP
       (Figure 5)          (Figure 3)            (Figure 4)
           S2-3               AN1-7
           S3-1               AN1-1                 AN1-1
           S6-1                                     AN1-8
           S6-2               AN1-2
           S6-3               AN1-3
           S7-3               AN1-4
           S8-4               AN1-5
           S8-5               AN1-6

   Appendix B.1.1 provides the detailed JSON code example ("mpi1-otn-
   topology.json") describing how the MPI1 ODU Topology is reported by
   the PNC1, using the [RFC8345], [TE-TOPO] and [OTN-TOPO] YANG models,
   at MPI1.

   It is worth noting that this JSON code example does not provide all
   the attributes defined in the relevant YANG models, including:

   o  YANG attributes which are outside the scope of this document are
      not shown;

   o  The attributes describing the set of label values that are
      available at the inter-domain links (label-restriction container)
      are also not shown to simplify the JSON code example;

   o  The comments describing the rationale for not including some
      attributes in this JSON code example even if in the scope of this
      document are identified with the prefix "// __COMMENT" and
      included only in the first object instance (e.g., in the Access
      Link from the AN1-1 description or in the AN1-1 LTP description).

5.1.2. Domain 2 Black Topology Abstraction

   PNC2 provides the required black topology abstraction, as described
   in section 4.2, to expose to the MDSC, at MPI2, two TE Topology
   instances with only one TE node each:

   o  the first instance reports the domain 2 OTN abstract topology
      view (MPI2 OTN Topology), with only one abstract node (i.e., AN2)
      and only inter-domain and access abstract TE links (which
      represent the inter-domain physical links and the access physical
      links which can support ODU and/or transparent client layers);




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   o  the instance reports the domain 2 Ethernet abstract topology view
      (MPI2 ETH Topology), with only one abstract TE node (i.e., AN2)
      and only access abstract TE links (which represent the access
      physical links which can support Ethernet client layers).

5.1.3. Domain 3 White Topology Abstraction

   PNC3 provides the required white topology abstraction, as described
   in section 4.2, to expose to the MDSC, at MPI3, two TE Topology
   instances with multiple TE nodes, one for each physical node:

   o  the first instance reports the domain 3 OTN topology view (MPI3
      OTN Topology), with four TE nodes, which represent the four
      physical nodes (i.e. S31, S32, S33 and S34), and abstract TE
      links, which represent the inter-domain and internal physical
      links;

   o  the second instance reports the domain 3 Ethernet abstract
      topology view (MPI3 ETH Topology), with only two TE nodes, which
      represent the two edge physical nodes (i.e., S31 and S33) and
      only the two access TE links which represent the access physical
      links.

5.1.4. Multi-domain Topology Merging

   As assumed at the beginning of this section, MDSC does not have any
   knowledge of the topologies of each domain until each PNC reports
   its own abstract topologies, so the MDSC needs to merge together
   these abstract topologies, provided by different PNCs, to build its
   own topology view of the multi-domain network (MDSC multi-domain
   native topology), as described in section 4.3 of [TE-TOPO].

   Given the topologies reported from multiple PNCs, the MDSC need to
   merge them into its multi-domain native topology. The topology of
   each domain may be in an abstracted shape (refer to section 5.2 of
   [RFC8453] for a different level of abstraction), while the inter-
   domain link information must be complete and fully configured by the
   MDSC.

   The inter-domain link information is reported to the MDSC by the two
   PNCs, controlling the two ends of the inter-domain link.

   The MDSC needs to understand how to merge together these inter-
   domain links.



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   One possibility is to use the plug-id information, defined in [TE-
   TOPO]: two inter-domain TE links, within two different MPI abstract
   topologies, terminating on two LTPs reporting the same plug-id value
   can be merged as a single intra-domain link, within any MDSC native
   topology.

   The value of the reported plug-id information can be either assigned
   by a central network authority, and configured within the two PNC
   domains. Alternatively, it may be discovered using an automatic
   discovery mechanisms (e.g., LMP-based, as defined in [RFC6898]).

   In case the plug-id values are assigned by a central authority, it
   is under the central authority responsibility to assign unique
   values.

   In case the plug-id values are automatically discovered, the
   information discovered by the automatic discovery mechanisms needs
   to be encoded as a bit string within the plug-id value. This
   encoding is implementation specific, but the encoding rules need to
   be consistent across all the PNCs.

   In case of co-existence within the same network of multiple sources
   for the plug-id (e.g., central authority and automatic discovery or
   even different automatic discovery mechanisms), it is needed that
   the plug-id namespace is partitioned to avoid that different sources
   assign the same plug-id value to different inter-domain links. Also,
   the encoding of the plug-id namespace within the plug-id value is
   implementation specific and will need to be consistent across all
   the PNCs.

   This document assumes that the plug-id is assigned by a central
   authority, with the first octet set to 0x00 to represent the central
   authority namespace. The configuration method used, within each PNC
   domain, are outside the scope of this document.

   Based on the plug-id values, the MDSC can merge together the
   abstract topologies exposed by the underlying PNCs, as described in
   sections 5.1.1, 5.1.2 and 5.1.3 above, into its multi-domain native
   TE topology as shown in Figure 6.








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                ........................
                :                      :
                :   Network domain 1   :   .............
                :   Black Topology     :   :           :
                :     Abstraction      :   :  Network  :
                : AN1-1                :   :  domain 3 :
        (R1)- - ----------+            :   :  (White)  :
                :          \   +--------------+        :
        (R2)- - ---------+ +  /        :   :   \       :
                :         \| /         :   :    \      :
        (R3)- - --------- AN1 --+      :   :    S31 ---- - (R5)
                :         /|\    \     :   :   /   \   :   :
        (R4)- - ---------+ | \    +--------- S32   S33 - - (R6)
                :          |  \        :   :/  \   /   :
                :          |   +---+   :   /    S34    :
                :..........|.......|...:  /:   /       :
                           |       |     / :../........:
                           |       |    /    /
                ...........|.......|.../..../....
                :          |       |  /    /    :
                : Network  |       + /    /     :
                : domain 2 |      / /    /      :
                :          |     / /    /       :
                :          |    + / +--+        :
                :          |    |/ /            :
                : Black    +--- AN2 ------------- - -(R7)
                : Topology      | |     AN2-1   :
                : Abstraction   | +-------------- - -(R8)
                :               |               :
                :               +---------------- - -(R9)
                :                               :
                :...............................:

      Figure 6 - Multi-domain Abstract Topology controlled by an MDSC

5.2. YANG Models for Service Configuration

   The service configuration procedure is assumed to be initiated (step
   1 in Figure 7) at the CMI from CNC to MDSC. Analysis of the CMI
   models is (e.g., L1CSM, L2SM, VN) is outside the scope of this
   document.





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   As described in section 4.3, it is assumed that the CMI YANG models
   provide all the information that allows the MDSC to understand that
   it needs to coordinate the setup of a multi-domain ODU data plane
   connection (which can be either an end-to-end connection or a
   segment connection) and, when needed, also the configuration of the
   adaptation functions in the edge nodes belonging to different
   domains.

                                 |
                                 | {1}
                                 V
                          ----------------
                         |           {2}  |
                         | {3}  MDSC      |
                         |                |
                          ----------------
                           ^     ^      ^
                    {3.1}  |     |      |
                 +---------+     |{3.2} |
                 |               |      +----------+
                 |               V                 |
                 |           ----------            |{3.3}
                 |          |   PNC2   |           |
                 |           ----------            |
                 |               ^                 |
                 V               | {4.2}           |
             ----------          V                 |
            |   PNC1   |       -----               V
             ----------      (Network)        ----------
                 ^          ( Domain 2)      |   PNC3   |
                 | {4.1}   (          _)      ----------
                 V          (        )            ^
               -----       C==========D           | {4.3}
             (Network)    /  (       ) \          V
            ( Domain 1)  /     -----    \       -----
           (           )/                \    (Network)
           A===========B                  \  ( Domain 3)
          / (         )                    \(           )
      AP-1   (       )                      X===========Z
               -----                         (         ) \
                                              (       )   AP-2
                                                -----

                   Figure 7 - Multi-domain Service Setup



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   As an example, the objective in this section is to configure a
   transport service between R1 and R8, such as one of the services
   described in section 4.3. The inter-domain path is assumed to be R1
   <-> S3 <-> S1 <-> S2 <-> S31 <-> S33 <-> S34 <->S15 <-> S18 <-> R8
   (see the physical topology in Figure 1).

   According to the different client signal types, different
   adaptations can be required to be configured at the edge nodes
   (i.e., S3 and S18).

   After receiving such request, MDSC determines the domain sequence,
   i.e., domain 1 <-> domain 3 <-> domain 2, with corresponding PNCs
   and the inter-domain links (step 2 in Figure 7).

   As described in [PATH-COMPUTE], the domain sequence can be
   determined by running the MDSC own path computation on the MDSC
   native topology, defined in section 5.1.4, if and only if the MDSC
   has enough topology information. Otherwise, the MDSC can send path
   computation requests to the different PNCs (steps 2.1, 2.2 and 2.3
   in Figure 7) and use this information to determine the optimal path
   on its internal topology and therefore the domain sequence.

   The MDSC will then decompose the tunnel request into a few tunnel
   segments via tunnel models (both technology agnostic TE tunnel model
   and OTN tunnel model), and request different PNCs to setup each
   intra-domain tunnel segment (steps 3, 3.1, 3.2 and 3.3 in Figure 7).

   The MDSC will take care of the configuration of both the intra-
   domain tunnel segment and inter-domain tunnel via corresponding MPI
   (via TE tunnel model and OTN tunnel model) through all the PNCs
   controlling the domains selected during path computation. More
   specifically, for the inter-domain tunnel hand-off, taking into
   account that the inter-domain links are all OTN links, the list of
   timeslots and the TPN value assigned to that ODUk connection at the
   inter-domain link needs to be configured by the MDSC.

   In any case, the access link configuration is done only on the PNCs
   that control the access links (e.g., PNC-1 and PNC-3) and not on the
   PNCs of transit domain(s) (e.g., PNC-2). An access link will be
   configured by MDSC after the OTN tunnel is set up.

   Access configuration will vary and will be dependent on each type of
   service. Further discussion and examples are provided in the
   following sub-sections.



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5.2.1. ODU Transit Service

   In this scenario, described in section 4.3.1, the physical access
   links are configured as 10G OTN links and, as described in section
   5.1, reported by each PNC as TE Links within the OTN abstract
   topologies they expose to the MDSC.

   To setup this IP link, between R1 and R8, the CNC requests, at the
   CMI, the MDSC to setup an ODU transit service.

   From its native topology, shown in Figure 6, the MDSC understands,
   by means which are outside the scope of this document, that R1 is
   attached to the access link terminating on AN1-1 LTP in the MPI1 OTN
   Abstract Topology (Figure 3), exposed by PNC1, and that R8 is
   attached to the access link terminating on AN2-1 LTP in the MPI2
   Abstract Topology, exposed by PNC2.

   MDSC then performs multi-domain path computation (step 2 in Figure
   7) and requests PNC1, PNC2 and PNC3, at MPI1, MPI2 and MPI3
   respectively, to setup ODU2 (Transit Segment) Tunnels within the OTN
   Abstract Topologies they expose (MPI1 OTN Abstract Topology, MPI2
   OTN Abstract Topology and MPI3 OTN Abstract Topology, respectively).

   MDSC requests, at MPI1, PNC1 to setup an ODU2 (Transit Segment)
   Tunnel with one primary path between AN-1 and AN1-7 LTPs, within the
   MPI1 OTN Abstract Topology (Figure 4), using the TE Tunnel YANG
   model, defined in [TE-TUNNEL], with the OTN technology-specific
   augmentations, defined in [OTN-TUNNEL]:

   o  Source and Destination TTPs are not specified (since it is a
      Transit Tunnel)

   o  Ingress and egress points are indicated in the route-object-
      include-exclude list of the explicit-route-objects of the primary
      path:

       o The first element references the access link terminating on
          AN1-1 LTP

       o The last two element reference respectively the inter-domain
          link terminating on AN1-7 LTP and the data plane resources
          (i.e., the list of timeslots and the TPN) used by the ODU2
          connection over that link.




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   The configuration of the timeslots used by the ODU2 connection on
   the internal links within a PNC domain (i.e., on the internal links
   within domain1) is outside the scope of this document since it is a
   matter of the PNC domain internal implementation.

   However, the configuration of the timeslots used by the ODU2
   connection at the transport network domain boundaries (e.g., on the
   inter-domain links) needs to take into account the timeslots
   available on physical nodes belonging to different PNC domains
   (e.g., on node S2 within PNC1 domain and on node S31 within PNC3
   domain).

   The MDSC, when coordinating the setup of a multi-domain ODU
   connection, also configures the data plane resources (i.e., the list
   of timeslots and the TPN) to be used on the inter-domain links. The
   MDSC can know the timeslots which are available on the physical OTN
   nodes terminating the inter-domain links (e.g., S2 and S31) from the
   OTN Topology information exposed, at the MPIs, by the PNCs
   controlling the OTN physical nodes (e.g., PNC1 and PNC3 controlling
   the physical nodes S2 and S31 respectively).

   Appendix B.2.1 provides the detailed JSON code ("mpi1-odu2-service-
   config.json") describing how the setup of this ODU2 (Transit
   Segment) Tunnel can be requested by the MDSC, using the [TE-TUNNEL]
   and [OTN-TUNNEL] YANG models at MPI1.

   PNC1 knows, as described in the mapping table in Section 5.1.1, that
   AN-1 and AN1-7 LTPs within the MPI1 OTN Abstract Topology it exposes
   at MPI1 correspond to the S3-1 and S2-3 LTPs, respectively, within
   its native topology. Therefore it performs path computation, for an
   ODU2 connection between these LTPs within its native topology, and
   sets up the ODU2 cross-connections within the physical nodes S3, S1
   and S2, as shown in section 4.3.1.

   Since the R1-S3 access link is a multi-function access link, PNC1
   also configures the OTU2 trail before setting up the ODU2
   cross-connection in node S3.

   As part of the OUD2 cross-connection configuration in node S2, PNC1
   configures the data plane resources (i.e., the list of timeslots and
   the TPN), to be used by this ODU2 connection on the S2-S31
   inter-domain link, as requested by the MDSC.





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   Following similar requests from MDSC to setup ODU2 (Transit Segment)
   Tunnels within the OTN Abstract Topologies they expose, PNC2 then
   sets up ODU2 cross-connections on nodes S31 and S33 while PNC3 sets
   up ODU2 cross-connections on nodes S15 and S18, as shown in section
   4.3.1. PNC2 also configures the OTU2 trail on the S18-R8
   multi-function access link.

5.2.1.1. Single Domain Example

   To setup an ODU2 end-to-end connection, supporting an IP link,
   between R1 and R3, the CNC requests, at the CMI, the MDSC to setup
   an ODU transit service.

   Following the procedures described in section 5.2.1, MDSC requests
   only PCN1 to setup the ODU2 (Transit Segment) Tunnel between the
   access links terminating on AN-1 and AN1-2 LTPs within the MPI1
   Abstract Topology and PNC1 sets up ODU2 cross-connections on nodes
   S3, S5 and S6, as shown in section 4.3.1. PNC1 also configures the
   OTU2 trails on the R1-S3 and R3-S6 multi-function access links.

5.2.2. EPL over ODU Service

   In this scenario, described in section 4.3.2, the access links are
   configured as 10GE Links and, as described in section 5.1, reported
   by each PNC as TE Links within the ETH abstract topologies they
   expose to the MDSC.

   To setup this IP link, between R1 and R8, the CNC requests, at the
   CMI, the MDSC to setup an EPL service.

   From its native topology, shown in Figure 6, the MDSC understands,
   by means which are outside the scope of this document, that R1 is
   attached to the access link terminating on AN1-1 LTP in the MPI1 ETH
   Abstract Topology, exposed by PNC1, and that R8 is attached to the
   access link terminating on AN2-1 LTP in the MPI2 ETH Abstract
   Topology, exposed by PNC2.

   The MDSC also understands that it needs to coordinate the setup of a
   multi-domain ODU2 Tunnel between the TTPs, abstracting nodes S3 and
   S18 within the OTN Abstract Topologies exposed by PNC1 and PNC2,
   respectively.

   MDSC then performs multi-domain path computation (step 2 in Figure
   7) and then requests:



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   o  PNC1, at MPI1, to setup an ODU2 (Head Segment) Tunnel within the
      MPI1 OTN Abstract Topology;

   o  PNC1, at MPI1, to steer the Ethernet client traffic from/to AN1-1
      LTP, within the MPI1 ETH Abstract Topology, thought that ODU2
      (Head Segment) Tunnel;

   o  PNC3, at MPI3, to setup an ODU2 (Transit Segment) Tunnel within
      the MPI3 OTN Abstract Topology;

   o  PNC2, at MPI2, to setup ODU2 (Tail Segment) Tunnel within the
      MPI2 OTN Abstract Topology;

   o  PNC2, at MPI2, to steer the Ethernet client traffic to/from AN2-1
      LTP, within the MPI2 ETH Abstract Topology, through that ODU2
      (Tail Segment) Tunnel.

   MDSC requests, at MPI1, PNC1 to setup an ODU2 (Head Segment) Tunnel
   with one primary path between the source TTP and AN1-7 LTP, within
   the MPI1 OTN Abstract Topology (Figure 4), using the TE Tunnel YANG
   model, defined in [TE-TUNNEL], with the OTN technology-specific
   augmentations, defined in [OTN-TUNNEL]:

   o  Only the Source TTP is specified (since it is a Head Segment
      Tunnel): therefore the Destination TTP is not specified

   o  The egress point in indicated in the route-object-include-exclude
      list of the explicit-route-objects of the primary path:

       o The last two element reference respectively the inter-domain
          link terminating on AN1-7 LTP and the data plane resources
          (i.e., the list of timeslots and the TPN) used by the ODU2
          connection over that link.

   Appendix B.2.2 provides the detailed JSON code ("mpi1-odu2-tunnel-
   config.json") describing how the setup of this ODU2 (Head Segment)
   Tunnel can be requested by the MDSC, using the [TE-TUNNEL] and [OTN-
   TUNNEL] YANG models at MPI1.

   MDSC requests, at MPI1, PNC1 to steer the Ethernet client traffic
   from/to AN1-2 LTP, within the MPI1 ETH Abstract Topology (Figure 4),
   thought the MPI1 ODU2 (Head Segment) Tunnel, using the Ethernet
   Client YANG model, defined in [CLIENT-SIGNAL].




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   Appendix B.2.3 provides the detailed JSON code ("mpi1-epl-service-
   config.json") describing how the setup of this EPL service using the
   ODU2 Tunnel can be requested by the MDSC, using the [CLIENT-SIGNAL]
   YANG model at MPI1.

   PNC1 knows, as described in the table in section 5.1.1, that the
   tunnel source TTP and AN1-7 LTP, within the MPI1 OTN Abstract
   Topology it exposes at MPI1, correspond to node S3 and S2-3 LTP,
   respectively, within its native topology. Therefore it performs path
   computation, for an ODU2 connection between node S3 and S2-3 LTP
   within its native topology, and sets up the ODU2 cross-connections
   within the physical nodes S3, S1 and S2, as shown in section 4.3.2.

   As part of the OUD2 cross-connection configuration in node S2, PNC1
   configures the data plane resources (i.e., the list of timeslots and
   the TPN), to be used by this ODU2 connection on the S2-S31
   inter-domain link, as requested by the MDSC.

   After the configuration of the ODU2 cross-connection in node S3,
   PNC1 also configures the [ETH -> (ODU)] and [(ODU2) -> ETH]
   adaptation functions, within node S3, as shown in section 4.3.2.

   Since the R1-S3 access link is a multi-function access link, PNC1
   also configures the 10GE link before this step.

   Following similar requests from MDSC to setup ODU2 (Segment) Tunnels
   within the OTN Abstract Topologies they expose as well as the
   steering of the Ethernet client traffic, PNC3 then sets up ODU2
   cross-connections on nodes S31 and S33 while PNC2 sets up ODU2
   cross-connections on nodes S15 and S18 as well as the [ETH ->
   (ODU2)] and [(ODU2) -> ETH] adaptation functions in node S18, as
   shown in section 4.3.2. PNC2 also configures the 10GE link on the
   S18-R8 multi-function access link.

5.2.2.1. Single Domain Example

   To setup this IP link, between R1 and R2, the CNC requests, at the
   CMI, the MDSC to setup an EPL service.

   Following the procedures described in section 5.2.2, the MDSC
   requests PCN1 to:






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   o  setup an ODU2 (end-to-end) Tunnel between the TTPs, abstracting
      nodes S3 and S6 within MPI1 OTN Abstract Topology exposed by PNC1
      at MPI1;

   o  steer the Ethernet client traffic between the AN1-1 and AN1-8
      LTPs, exposed by PNC1 within MPI1 ETH Abstract Topology, through
      that ODU2 (end-to-end) Tunnel.

   Then PNC1 sets up ODU2 cross-connections on nodes S3, S5 and S6 as
   well as the [ETH -> (ODU)] and [(ODU2) -> ETH] adaptation functions
   in nodes S3 and S6, as shown in section 4.3.2. PNC1 also configures
   the 10GE link on the R1-S3 multi-function access link (the R2-S6
   access link has been pre-configured as a 10GE link).

5.2.3. Other OTN Client Services

   In this scenario, described in section 4.3.3, the access links are
   configured as STM-64 links and, as described in section 5.1,
   reported by each PNC as TE Links within the OTN Abstract Topologies
   they expose to the MDSC.

   The CNC requests, at the CMI, MDSC to setup an STM-64 Private Line
   service between R1 and R8.

   Following similar procedures as described in section 5.2.2, MDSC
   understands that:

   o  R1 is attached to the access link terminating on AN1-1 LTP in the
      MPI1 OTN Abstract Topology, exposed by PNC1, and that R8 is
      attached to the access link terminating on AN2-1 LTP in the MPI2
      OTN Abstract Topology, exposed by PNC2;

   o  it needs to coordinate the setup of a multi-domain ODU2 Tunnel
      between the TTPs, abstracting nodes S3 and S18 within the OTN
      Abstract Topologies exposed by PNC1 and PNC2, respectively.

   The MDSC then performs multi-domain path computation (step 2 in
   Figure 7) and then requests:

   o  PNC1, at MPI1, to setup an ODU2 (Head Segment) Tunnel within the
      MPI1 OTN Abstract Topology;






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   o  PNC1, at MPI1, to steer the STM-64 transparent client traffic
      from/to AN1-1 LTP, within the MPI1 OTN Abstract Topology, thought
      that ODU2 (Head Segment) Tunnel;

   o  PNC3, at MPI3, to setup an ODU2 (Transit Segment) Tunnel within
      the MPI3 OTN Abstract Topology;

   o  PNC2, at MPI2, to setup ODU2 (Tail Segment) Tunnel within the
      MPI2 OTN Abstract Topology;

   o  PNC2, at MPI2, to steer the STM-64 transparent client traffic
      to/from AN2-1 LTP, within the MPI2 ETH Abstract Topology, through
      that ODU2 (Tail Segment) Tunnel.

   PNC1, PNC2 and PNC3 then sets up the ODU2 cross-connections within
   the physical nodes S3, S1, S2, S31, S33, S15 and S18 as well as the
   [STM-64 -> (ODU)] and [(ODU2) -> STM-64] adaptation functions in
   nodes S3 and S18, as shown in section 4.3.3. PNC1 and PNC2 also
   configure the STM-64 links on the R1-S3 and R8-S18 multi-function
   access links, respectively.

5.2.3.1. Single Domain Example

   To setup this IP link, between R1 and R3, the CNC requests, at the
   CMI, the MDSC to setup an STM-64 Private Line service.

   The MDSC and PNC1 follows similar procedures as described in section
   5.2.2.1 to set up ODU2 cross-connections on nodes S3, S5 and S6 as
   well as the [STM-64 -> (ODU)] and [(ODU2) -> STM-64] adaptation
   functions in nodes S3 and S6, as shown in section 4.3.3. PNC1 also
   configures the STM-64 links on the R1-S3 and R3-S6 multi-function
   access links.

5.2.4. EVPL over ODU Service

   In this scenario, described in section 4.3.4, the access links are
   configured as 10GE links, as described in section 5.2.2 above.

   The CNC requests, at the CMI, the MDSC to setup two EVPL services:
   one between R1 and R2, and another between R1 and R8.

   Following similar procedures as described in section 5.2.2 and
   5.2.2.1, MDSC understands that:




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   o  R1 and R2 are attached to the access links terminating
      respectively on AN1-1 and AN1-8 LTPs in the MPI1 ETH Abstract
      Topology, exposed by PNC1, and that R8 is attached to the access
      link terminating on AN2-1 LTP in the MPI2 ETH Abstract Topology,
      exposed by PNC2;

   o  to setup the first (single-domain) EVPL service, between R1 and
      R2, it needs to coordinate the setup of a single-domain ODU0
      Tunnel between the TTPs, abstracting nodes S3 and S6 within the
      OTN Abstract Topology exposed by PNC1;

   o  to setup the second (multi-domain) EPVL service, between R1 and
      R8, it needs to coordinate the setup of a multi-domain ODU0
      Tunnel between the TTPs, abstracting nodes S3 and S18 within the
      OTN Abstract Topologies exposed by PNC1 and PNC2, respectively.

   To setup the first (single-domain) EVPL service between R1 and R2,
   the MDSC and PNC1 follows similar procedures as described in section
   5.2.2.1 to set up ODU0 cross-connections on nodes S3, S5 and S6 as
   well as the [VLAN -> (ODU0)] and [(ODU0) -> VLAN] adaptation
   functions, in nodes S3 and S6, as shown in section 4.3.4. PNC1 also
   configures the 10GE link on the R1-S3 multi-function access link.

   As part of the [VLAN -> (ODU0)] and [(ODU0) -> VLAN] adaptation
   functions configurations in nodes S2 and S6, PNC1 configures also
   the classification rules required to associated only the Ethernet
   client traffic received with VLAN ID 10 on the R1-S3 and R2-S6
   access links with this EVPL service. The MDSC provides this
   information to PNC1 using the [CLIENT-SIGNAL] model.

   To setup the second (multi-domain) EVPL service between R1 and R8,
   the MDSC, PNC1, PNC2 and PNC3 follows similar procedures as
   described in section 5.2.2 to setup the ODU0 cross-connections
   within the physical nodes S3, S1, S2, S31, S33, S15 and S18 as well
   as the [VLAN -> (ODU0)] and [(ODU0) -> VLAN] adaptation functions in
   nodes S3 and S18, as shown in section 4.3.4. PNC2 also configures
   the 10GE link on the R8-S18 multi-function access link (the R1-S3
   10GE link has been already configured when the first EVPL service
   has been setup).

   As part of the [VLAN -> (ODU0)] and [(ODU0) -> VLAN] adaptation
   functions configurations in nodes S3 and S18, PNC1 and,
   respectively, PNC2 configure also the classification rules required
   to associated only the Ethernet client traffic received with VLAN ID



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   20 on the R1-S3 and R8-S18 access links with this EVPL service. The
   MDSC provides this information to PNC1 and PNC2 using the
   [CLIENT-SIGNAL] model.

5.3. YANG Models for Protection Configuration

5.3.1. Linear Protection (end-to-end)

   To be discussed in future versions of this document.

5.4. Notifications

   Further detailed analysis is outside the scope of this document

5.5. Path Computation with Constraints

   The path computation constraints that can be supported at the MPI
   using the IETF YANG models defined in [TE-TUNNEL] and [PATH-
   COMPUTE].

   When there is a technology specific network (e.g., OTN), the
   corresponding technology (e.g., OTN) model should also be used to
   specify the tunnel information on MPI, with the constraint included
   in TE Tunnel model.

   Further detailed analysis is outside the scope of this document

6. Security Considerations

   This document analyses the applicability of the YANG models being
   defined by the IETF to support OTN single and multi-domain
   scenarios.

   Inherently OTN networks ensure privacy and security via hard
   partitioning of traffic onto dedicated circuits. The separation of
   network traffic makes it difficult to intercept data transferred
   between nodes over OTN-channelized links.

   In OTN the (General Communication Channel) GCC is used for OAM
   functions such as performance monitoring, fault detection, and
   signaling. The GCC control channel should be secured using a
   suitable mechanism.





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   There are no additional or new security considerations introduced by
   this document.

7. IANA Considerations

   This document requires no IANA actions.

8. References

8.1. Normative References

   [RFC4427] Mannie, E., Papadimitriou, D., "Recovery (Protection and
             Restoration) Terminology for Generalized Multi-Protocol
             Label Switching (GMPLS)", RFC 4427, March 2006.

   [RFC4655] Farrel, A. et al., "A Path Computation Element (PCE)-Based
             Architecture", RFC4655, August 2006.

   [RFC7926] Farrel, A. et al., "Problem Statement and Architecture for
             Information Exchange between Interconnected Traffic-
             Engineered Networks", BCP 206, RFC 7926, July 2016.

   [RFC8345] Clemm, A.,Medved, J. et al., "A Yang Data Model for
             Network Topologies", RFC8345, March 2018.

   [RFC8453] Ceccarelli, D., Lee, Y. et al., "Framework for Abstraction
             and Control of TE Networks (ACTN)", RFC8453, August 2018.

   [ITU-T G.709] ITU-T Recommendation G.709 (06/16), "Interfaces for
             the optical transport network", June 2016.

   [ITU-T G.808.1] ITU-T Recommendation G.808.1 (05/14), "Generic
             protection switching - Linear trail and subnetwork
             protection", May 2014.

   [ITU-T G.873.1] ITU-T Recommendation G.873.1 (05/14), "Optical
             transport network (OTN): Linear protection", May 2014.

   [TE-TOPO] Liu, X. et al., "YANG Data Model for TE Topologies",
             draft-ietf-teas-yang-te-topo, work in progress.

   [OTN-TOPO] Zheng, H. et al., "A YANG Data Model for Optical
             Transport Network Topology", draft-ietf-ccamp-otn-topo-
             yang, work in progress.



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   [CLIENT-TOPO]  Zheng, H. et al., "A YANG Data Model for Client-layer
             Topology", draft-zheng-ccamp-client-topo-yang, work in
             progress.

   [TE-TUNNEL] Saad, T. et al., "A YANG Data Model for Traffic
             Engineering Tunnels and Interfaces", draft-ietf-teas-yang-
             te, work in progress.

   [PATH-COMPUTE] Busi, I., Belotti, S. et al, "Yang model for
             requesting Path Computation", draft-ietf-teas-yang-path-
             computation, work in progress.

   [OTN-TUNNEL]   Zheng, H. et al., "OTN Tunnel YANG Model", draft-
             ietf-ccamp-otn-tunnel-model, work in progress.

   [CLIENT-SIGNAL]   Zheng, H. et al., "A YANG Data Model for Optical
             Transport Network Client Signals", draft-zheng-ccamp-otn-
             client-signal-yang, work in progress.

8.2. Informative References

   [RFC5151] Farrel, A. et al., "Inter-Domain MPLS and GMPLS Traffic
             Engineering --Resource Reservation Protocol-Traffic
             Engineering (RSVP-TE) Extensions", RFC 5151, February
             2008.

   [RFC6898] Li, D. et al., "Link Management Protocol Behavior
             Negotiation and Configuration Modifications", RFC 6898,
             March 2013.

   [RFC8040] Bierman, A. et al., "RESTCONF Protocol", RFC 8040, January
             2017.

   [RFC8309] Wu, Q. et al., "Service Models Explained", RFC 8309,
             January 2018.

   [ACTN-YANG] Zhang, X. et al., "Applicability of YANG models for
             Abstraction and Control of Traffic Engineered Networks",
             draft-zhang-teas-actn-yang, work in progress.

   [RFC-FOLD]  Watsen, K. et al., "Handling Long Lines in Artwork in
             Internet-Drafts and RFCs", draft-ietf-netmod-artwork-
             folding, work in progress




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   [TE-TUTORIAL]  Bryskin, I. et al., "TE Topology and Tunnel Modeling
             for Transport Networks", draft-ietf-teas-te-topo-and-
             tunnel-modeling, work in progress

   [ONF TR-527] ONF Technical Recommendation TR-527, "Functional
             Requirements for Transport API", June 2016.

   [ONF GitHub] ONF Open Transport (SNOWMASS),
             <https://github.com/OpenNetworkingFoundation/Snowmass-
             ONFOpenTransport>

   [MEF 55] Metro Ethernet Forum, "Lifecycle Service Orchestration
             (LSO): Reference Architecture and Framework", Technical
             Specification MEF 55, March 2016,
             <https://www.mef.net/Assets/Technical_Specifications/PDF/M
             EF_55.pdf>

9. Acknowledgments

   The authors would like to thank all members of the Transport NBI
   Design Team involved in the definition of use cases, gap analysis
   and guidelines for using the IETF YANG models at the Northbound
   Interface (NBI) of a Transport SDN Controller.

   The authors would like to thank Xian Zhang, Anurag Sharma, Sergio
   Belotti, Tara Cummings, Michael Scharf, Karthik Sethuraman, Oscar
   Gonzalez de Dios, Hans Bjursrom and Italo Busi for having initiated
   the work on gap analysis for transport NBI and having provided
   foundations work for the development of this document.

   The authors would like to thank the authors of the TE Topology and
   Tunnel YANG models [TE-TOPO] and [TE-TUNNEL], in particular, Igor
   Bryskin, Vishnu Pavan Beeram, Tarek Saad and Xufeng Liu, for their
   support in addressing any gap identified during the analysis work.

   The authors would like to thank Henry Yu and Aihua Guo for their
   input and review of the URIs structures used within the JSON code
   examples.

   This work was supported in part by the European Commission funded
   H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727).

   This document was prepared using 2-Word-v2.0.template.dot.




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Appendix A. Validating a JSON fragment against a YANG Model

   The objective is to have a tool that allows validating whether a
   piece of JSON code embedded in an Internet-Draft is compliant with a
   YANG model without using a client/server.

A.1.  Manipulation of JSON fragments

   This section describes the various ways JSON fragments are used in
   the I-D processing and how to manage them.

   Let's call "folded-JSON" the JSON embedded in the I-D: it fits the
   72 chars width and it is acceptable for it to be invalid JSON.

   We then define "unfolded-JSON" a valid JSON fragment having the same
   contents of the "folded-JSON " without folding, i.e. limits on the
   text width. The folding/unfolding operation may be done according to
   [RFC-FOLD]. The "unfolded-JSON" can be edited by the authors using
   JSON editors with the advantages of syntax validation and pretty-
   printing.

   Both the "folded" and the "unfolded" JSON fragments can include
   comments having descriptive fields and directives we'll describe
   later to facilitate the reader and enable some automatic processing.

   The presence of comments in the "unfolded-JSON" fragment makes it an
   invalid JSON encoding of YANG data. Therefore we call "naked JSON"
   the JSON where the comments have been stripped out: not only it is
   valid JSON but it is a valid JSON encoding of YANG data.

   The following schema resumes these definitions:

                       unfold_it -->             stripper -->

             Folded-JSON           Unfolded-JSON             Naked JSON

                       <-- fold_it              <-- author edits

   <=72-chars?    MUST              MAY                      MAY

   valid JSON?     MAY             MUST                     MUST

   JSON-encoding   MAY              MAY                     MUST




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   of YANG data

   Our validation toolchain has been designed to take a JSON in any of
   the three formats and validate it automatically against a set of
   relevant YANG modules using available open-source tools. It can be
   found at: https://github.com/GianmarcoBruno/json-yang/

A.2.  Comments in JSON fragments

   We found useful to introduce two kinds of comments, both defined as
   key-value pairs where the key starts with "//":

   - free-form descriptive comments, e.g."// COMMENT" : "refine this"
   to describe properties of JSON fragments.

   - machine-usable directives e.g. "// __REFERENCES__DRAFTS__" : {
   "ietf-routing-types@2017-12-04": "rfc8294",} which can be used to
   automatically download from the network the relevant I-Ds or RFCs
   and extract from them the YANG models of interest. This is
   particularly useful to keep consistency when the drafting work is
   rapidly evolving.

A.3.  Validation of JSON fragments: DSDL-based approach

   The idea is to generate a JSON driver file (JTOX) from YANG, then
   use it to translate JSON to XML and validate it against the DSDL
   schemas, as shown in Figure 8.

   Useful link: https://github.com/mbj4668/pyang/wiki/XmlJson

                           (2)
               YANG-module ---> DSDL-schemas (RNG,SCH,DSRL)
                      |                  |
                      | (1)              |
                      |                  |
      Config/state  JTOX-file            | (4)
             \        |                  |
              \       |                  |
               \      V                  V
      JSON-file------------> XML-file ----------------> Output
                 (3)

           Figure 8 - DSDL-based approach for JSON code validation




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   In order to allow the use of comments following the convention
   defined in section 3, without impacting the validation process,
   these comments will be automatically removed from the JSON-file that
   will be validate.

A.4.  Validation of JSON fragments: why not using a XSD-based approach

   This approach has been analyzed and discarded because no longer
   supported by pyang.

   The idea is to convert YANG to XSD, JSON to XML and validate it
   against the XSD, as shown in Figure 9:

                     (1)
         YANG-module ---> XSD-schema - \       (3)
                                        +--> Validation
         JSON-file------> XML-file ----/
                     (2)

           Figure 9 - XSD-based approach for JSON code validation

   The pyang support for the XSD output format was deprecated in 1.5
   and removed in 1.7.1. However pyang 1.7.1 is necessary to work with
   YANG 1.1 so the process shown in Figure 9 will stop just at step
   (1).






















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Appendix B. Detailed JSON Examples

   The JSON code examples provided in this appendix have been validated
   using the tools in Appendix A and folded using the tool in [RFC-
   FOLD].

B.1.  JSON Examples for Topology Abstractions

B.1.1.   JSON Code: mpi1-otn-topology.json

   This is the JSON code reporting the OTN Topology @ MPI:




































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   ========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) ===========

   {
     "// __TITLE__": "ODU Black Topology @ MPI1",
     "// __LAST_UPDATE__": "October 18, 2018",
     "// __MISSING_ATTRIBUTES__": true,
     "// __REFERENCE_DRAFTS__": {
       "ietf-routing-types@2017-12-04": "rfc8294",
       "ietf-otn-types@2017-10-30": "draft-ietf-ccamp-otn-tunnel-model-\
   \01",
       "ietf-network@2018-02-26": "rfc8345",
       "ietf-network-topology@2018-02-26": "rfc8345",
       "ietf-te-types@2018-06-12": "draft-ietf-teas-yang-te-15",
       "ietf-te-topology@2018-06-15": "draft-ietf-teas-yang-te-topo-18",
       "ietf-otn-topology@2017-10-30": "draft-ietf-ccamp-otn-topo-yang-\
   \02"
     },
     "// __RESTCONF_OPERATION__": {
       "operation": "GET",
       "url": "http://{{PNC1-ADDR}}/restconf/data/ietf-network:networks"
     },
     "ietf-network:networks": {
       "network": [
         {
           "network-id": "providerId/201/clientId/300/topologyId/otn-bl\
   \ack-topology",
           "network-types": {
             "ietf-te-topology:te-topology": {
               "ietf-otn-topology:otn-topology": {}
             }
           },
           "ietf-te-topology:provider-id": 201,
           "ietf-te-topology:client-id": 300,
           "ietf-te-topology:te-topology-id": "otn-black-topology",
           "// ietf-te-topology:te": "presence container requires: prov\
   \ider, client and te-topology-id",
           "ietf-te-topology:te": {
             "name": "OTN Black Topology @ MPI1"
           },
           "// ietf-network:node": "Access LTPs to be reviewed in a fut\
   \ure update",
           "ietf-network:node": [
             {
               "// __NODE__:__DESCRIPTION__": {



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                 "name": "AN1",
                 "identifier": "10.0.0.1",
                 "type": "Abstract Node",
                 "physical node(s)": "whole network domain 1"
               },
               "node-id": "10.0.0.1",
               "ietf-te-topology:te-node-id": "10.0.0.1",
               "ietf-te-topology:te": {
                 "te-node-attributes": {
                   "name": "AN11",
                   "admin-status": "up",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay-topology": "To be discussed\
   \ with TE Topology authors"
                 },
                 "oper-status": "up",
                 "// __DISCUSS__ tunnel-termination-point": []
               },
               "ietf-network-topology:termination-point": [
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-1 LTP",
                     "link type(s)": "OTU-2",
                     "physical node": "S3",
                     "unnumberd/ifIndex": 1,
                     "port type": "tributary port",
                     "connected to": "R1"
                   },
                   "tp-id": "1",
                   "ietf-te-topology:te-tp-id": 1,
                   "ietf-te-topology:te": {
                     "name": "AN1-1 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/1)",
                     "// __DISCUSS__ inter-domain-plug-id": "Access Lin\
   \k",
                     "// __COMMENT__ inter-layer-lock-id": "Empty: OTN \
   \Links are pre-configured",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "List of ODU clients?",
                     "// __DISCUSS__ ietf-otn-topology:client-facing": \



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   \true
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-2 LTP",
                     "link type(s)": "OTU-4",
                     "physical node": "S2",
                     "unnumberd/ifIndex": 1,
                     "port type": "inter-domain port",
                     "connected to": "S31"
                   },
                   "tp-id": "2",
                   "ietf-te-topology:te-tp-id": 2,
                   "ietf-te-topology:te": {
                     "name": "AN1-2 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/2)",
                     "// __DISCUSS__ inter-domain-plug-id": "Inter-doma\
   \in Link",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "Empty? (inter-domain OTN link)",
                     "// __DEFAULT__ ietf-otn-topology:client-facing": \
   \false
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-3 LTP",
                     "link type(s)": "OTU-2",
                     "physical node": "S6",
                     "unnumberd/ifIndex": 1,
                     "port type": "tributary port",
                     "connected to": "R2"
                   },
                   "tp-id": "3",
                   "ietf-te-topology:te-tp-id": 3,
                   "ietf-te-topology:te": {
                     "name": "AN1-3 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/3)",



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                     "// __DISCUSS__ inter-domain-plug-id": "Access Lin\
   \k",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "List of ODU clients?",
                     "// __DISCUSS__ ietf-otn-topology:client-facing": \
   \true
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-4 LTP",
                     "link type(s)": "OTU-4",
                     "physical node": "S8",
                     "unnumberd/ifIndex": 1,
                     "port type": "inter-domain port",
                     "connected to": "S32"
                   },
                   "tp-id": "4",
                   "ietf-te-topology:te-tp-id": 4,
                   "ietf-te-topology:te": {
                     "name": "AN1-4 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/4)",
                     "// __DISCUSS__ inter-domain-plug-id": "Inter-doma\
   \in Link",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "Empty? (inter-domain OTN link)",
                     "// __DEFAULT__ ietf-otn-topology:client-facing": \
   \false
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-5 LTP",
                     "link type(s)": "OTU-4",
                     "physical node": "S8",
                     "unnumberd/ifIndex": 5,
                     "port type": "inter-domain port",
                     "connected to": "S12"
                   },
                   "tp-id": "5",



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                   "ietf-te-topology:te-tp-id": 5,
                   "ietf-te-topology:te": {
                     "name": "AN1-5 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/5)",
                     "// __DISCUSS__ inter-domain-plug-id": "Inter-doma\
   \in Link",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "Empty? (inter-domain OTN link)",
                     "// __DEFAULT__ ietf-otn-topology:client-facing": \
   \false
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-6 LTP",
                     "link type(s)": "OTU-4",
                     "physical node": "S7",
                     "unnumberd/ifIndex": 4,
                     "port type": "inter-domain port",
                     "connected to": "S11"
                   },
                   "tp-id": "6",
                   "ietf-te-topology:te-tp-id": 6,
                   "ietf-te-topology:te": {
                     "name": "AN1-6 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/6)",
                     "// __DISCUSS__ inter-domain-plug-id": "Inter-doma\
   \in Link",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "Empty? (inter-domain OTN link)",
                     "// __DEFAULT__ ietf-otn-topology:client-facing": \
   \false
                   }
                 },
                 {
                   "// __DESCRIPTION__:__LTP__": {
                     "name": "AN1-7 LTP",
                     "link type(s)": "OTU-2",



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                     "physical node": "S6",
                     "unnumberd/ifIndex": 2,
                     "port type": "tributary port",
                     "connected to": "R3"
                   },
                   "tp-id": "7",
                   "ietf-te-topology:te-tp-id": 7,
                   "ietf-te-topology:te": {
                     "name": "AN1-7 LTP",
                     "admin-status": "up",
                     "// __DISCUSS__ interface-switching-capability": "\
   \See Link attributes (teNodeId/10.0.0.1/teLinkId/7)",
                     "// __DISCUSS__ inter-domain-plug-id": "Access Lin\
   \k",
                     "oper-status": "up",
                     "// __DISCUSS__ ietf-otn-topology:supported-payloa\
   \d-types": "List of ODU clients?",
                     "// __DISCUSS__ ietf-otn-topology:client-facing": \
   \true
                   }
                 }
               ]
             }
           ],
           "// ietf-network-topology:link": "Access links to be reviewe\
   \d in a future update",
           "ietf-network-topology:link": [
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Access Link from AN1-1",
                 "type": "access link",
                 "physical link": "Link from S3-1 to R1"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/1",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Access Link from AN1-1",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __COMMENT__ external-domain": "Empty: the plug-i\
   \d is used instead of this container",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",



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                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU2"
                         }
                       ]
                     }
                   ],
                   "// __COMMENT__ label-restrictions": "Not described \
   \in this JSON example",
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   },
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU2"
                     }
                   ]
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 1
               },



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               "// __EMPTY__ destination": "access link"
             },
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Inter-domain Link from AN1-2",
                 "type": "inter-domain link",
                 "physical link": "Link from S2-1 to S31"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/2",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Inter-domain Link from AN1-2",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU4"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },



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                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                     }
                   ]
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 2
               },
               "// __EMPTY__ destination": "inter-domain link"
             },
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Access Link from AN1-3",
                 "type": "access link",
                 "physical link": "Link from S6-1 to R2"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/3",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Access Link from AN1-3",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {



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                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU2"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU2"
                     }
                   ],
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   }
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 3
               },
               "// __EMPTY__ destination": "access link"
             },
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Inter-domain Link from AN1-4",
                 "type": "inter-domain link",
                 "physical link": "Link from S8-1 to S32"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/4",
               "ietf-te-topology:te": {



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                 "te-link-attributes": {
                   "name": "Inter-domain Link from AN1-4",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU4"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                     }
                   ],
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   }
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",



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                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 4
               },
               "// __EMPTY__ destination": "inter-domain link"
             },
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Inter-domain Link from AN1-5",
                 "type": "inter-domain link",
                 "physical link": "Link from S8-5 to S12"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/5",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Inter-domain Link from AN1-5",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU4"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",



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                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                     }
                   ]
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 5
               },
               "// __EMPTY__ destination": "inter-domain link"
             },
             {
               "// __DESCRIPTION__:__LINK__": {
                 "name": "Inter-domain Link from AN1-6",
                 "type": "inter-domain link",
                 "physical link": "Link from S7-4 to S11"
               },
               "link-id": "teNodeId/10.0.0.1/teLinkId/6",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Inter-domain Link from AN1-6",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",



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                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU4"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,
                       "// __DISCUSS__ te-bandwidth": "1xODU4, ..."
                     }
                   ]
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 6
               },
               "// __EMPTY__ destination": "inter-domain link"
             },
             {



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               "// __DESCRIPTION__:__LINK__": {
                 "name": "Access Link from AN1-7",
                 "type": "access link",
                 "physical link": "Link from S6-2 to R3"
               },
               "link-id": "teNodeId/10.0.0.1teLinkId/7",
               "ietf-te-topology:te": {
                 "te-link-attributes": {
                   "name": "Access Link from AN1-7",
                   "// __DISCUSS__ access-type": "Can we assume point-t\
   \o-point as the default value?",
                   "access-type": "point-to-point",
                   "// __DISCUSS__ is-abstract": "To be discussed with \
   \TE Topology authors",
                   "// __DISCUSS__ underlay": "To be discussed with TE \
   \Topology authors",
                   "admin-status": "up",
                   "interface-switching-capability": [
                     {
                       "switching-capability": "ietf-te-types:switching\
   \-otn",
                       "encoding": "ietf-te-types:lsp-encoding-oduk",
                       "max-lsp-bandwidth": [
                         {
                           "priority": 0,
                           "// __DISCUSS__ te-bandwidth": "ODU2"
                         }
                       ],
                       "// __DISCUSS__ label-restrictions": "To be adde\
   \d?"
                     }
                   ],
                   "// __DISCUSS__ link-protection-type": "Can we assum\
   \e unprotected as the default value?",
                   "link-protection-type": "unprotected",
                   "max-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   },
                   "max-resv-link-bandwidth": {
                     "// __DISCUSS__ te-bandwidth": "1xODU2"
                   },
                   "unreserved-bandwidth": [
                     {
                       "priority": 0,



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                       "// __DISCUSS__ te-bandwidth": "1xODU2"
                     }
                   ]
                 },
                 "oper-status": "up",
                 "// __EMPTY__ is-transitional": "It is not a transitio\
   \nal link",
                 "// __DISCUSS__ underlay ": "To be discussed with TE T\
   \opology authors"
               },
               "source": {
                 "source-node": "10.0.0.1",
                 "source-tp": 7
               },
               "// __EMPTY__ destination": "access link"
             }
           ]
         }
       ]
     }
   }

B.2.  JSON Examples for Service Configuration

B.2.1.   JSON Code: mpi1-odu2-service-config.json

   This is the JSON code reporting the ODU2 transit service
   configuration @ MPI:



















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   ========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) ===========

   {
     "// __TITLE__": "ODU2 Service Configuration @ MPI1",
     "// __LAST_UPDATE__": "October 22, 2018",
     "// __MISSING_ATTRIBUTES__": true,
     "// __REFERENCE_DRAFTS__": {
       "ietf-routing-types@2017-12-04": "rfc8294",
       "ietf-otn-types@2018-06-07": "draft-ietf-ccamp-otn-tunnel-model-\
   \02",
       "ietf-te-types@2018-07-01": "draft-ietf-teas-yang-te-16",
       "ietf-te@2018-07-01": "draft-ietf-teas-yang-te-16",
       "ietf-otn-tunnel@2018-06-07": "draft-ietf-ccamp-otn-tunnel-model\
   \-02"
     },
     "// __RESTCONF_OPERATION__": {
       "operation": "PUT",
       "url": "http://{{PNC1-ADDR}}/restconf/data/ietf-te:te"
     },
     "ietf-te:te": {
       "tunnels": {
         "tunnel": [
           {
             "name": "mpi1-odu2-service",
             "// identifier": "ODU2-SERVICE-TUNNEL-ID @ MPI1",
             "identifier": 1,
             "description": "ODU2 Service implemented by ODU2 OTN Tunne\
   \l Segment @ MPI1",
             "// encoding and switching-type": "ODU",
             "encoding": "ietf-te-types:lsp-encoding-oduk ",
             "switching-type": "ietf-te-types:switching-otn",
             "// source": "None: transit tunnel segment",
             "// destination": "None: transit tunnel segment",
             "// src-tp-id": "None: transit tunnel segment",
             "// dst-tp-id": "None: transit tunnel segment",
             "// ietf-otn-tunnel:src-client-signal": "None: ODU transit\
   \ tunnel segment",
             "// ietf-otn-tunnel:dst-client-signal": "None: ODU transit\
   \ tunnel segment",
             "bidirectional": true,
             "// protection": "No protection",
             "// __ DEFAULT __ protection": {
               "// __ DEFAULT __ enable": false
             },



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             "// restoration": "No restoration",
             "// __ DEFAULT __ restoration": {
               "// __ DEFAULT __ enable": false
             },
             "// te-topology-identifier": "ODU Black Topology @ MPI1",
             "te-topology-identifier": {
               "provider-id": 201,
               "client-id": 300,
               "topology-id": "otn-black-topology"
             },
             "te-bandwidth": {
               "ietf-otn-tunnel:odu-type": "ietf-otn-types:prot-ODU2"
             },
             "// hierarchical-link": "None: transit tunnel segment",
             "p2p-primary-paths": {
               "p2p-primary-path": [
                 {
                   "name": "mpi1-odu2-service-primary-path",
                   "path-scope": "ietf-te-types:path-scope-segment",
                   "// te-bandwidth": "None: only the tunnel bandwidth \
   \needs to be specified in transport applications",
                   "explicit-route-objects": {
                     "route-object-include-exclude": [
                       {
                         "// comment": "Tunnel hand-off OTU2 ingress in\
   \terface (S3-1)",
                         "index": 1,
                         "explicit-route-usage": "ietf-te-types:route-i\
   \nclude-ero",
                         "num-unnum-hop": {
                           "// node-id": "AN1 Node",
                           "node-id": "10.0.0.1",
                           "// link-tp-id": "AN1-1 LTP",
                           "link-tp-id": 1,
                           "hop-type": "STRICT",
                           "direction": "INCOMING"
                         }
                       },
                       {
                         "// comment": "Tunnel hand-off ODU2 ingress la\
   \bel (ODU2 over OTU2) at S3-1",
                         "index": 2,
                         "explicit-route-usage": "ietf-te-types:route-i\
   \nclude-ero",



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                         "label-hop": {
                           "te-label": {
                             "// __ DISCUSS __ odu-label": "How are HO-\
   \ODU (ODUk over OTUk) label represented?",
                             "// __ DISCUSS __ direction": "Check with \
   \TE Tunnel authors",
                             "direction": "FORWARD "
                           }
                         }
                       },
                       {
                         "// comment": "Tunnel hand-off OTU4 egress int\
   \erface (S2-1)",
                         "index": 3,
                         "explicit-route-usage": "ietf-te-types:route-i\
   \nclude-ero",
                         "num-unnum-hop": {
                           "// node-id": "AN1 Node",
                           "node-id": "10.0.0.1",
                           "// link-tp-id": "AN1-2 LTP",
                           "link-tp-id": 1,
                           "hop-type": "STRICT",
                           "direction": "OUTGOING"
                         }
                       },
                       {
                         "// comment": "Tunnel hand-off ODU2 egress lab\
   \el (ODU2 over OTU4) at S2-1",
                         "index": 4,
                         "explicit-route-usage": "ietf-te-types:route-i\
   \nclude-ero",
                         "label-hop": {
                           "te-label": {
                             "ietf-otn-tunnel:tpn": 1,
                             "ietf-otn-tunnel:tsg": "ietf-otn-types:tsg\
   \-1.25G",
                             "ietf-otn-tunnel:ts-list": "1-8",
                             "// __ DISCUSS __ direction": "Check with \
   \TE Tunnel authors",
                             "direction": "FORWARD "
                           }
                         }
                       }
                     ]



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                   }
                 }
               ]
             }
           }
         ]
       }
     }
   }

B.2.2.   JSON Code: mpi1-odu2-tunnel-config.json

   The JSON code for this use case will be added in a future version of
   this document

   An incomplete version is located on GitHub at:

   https://github.com/danielkinguk/transport-nbi

B.2.3.   JSON Code: mpi1-epl-service-config.json

   The JSON code for this use case will be added in a future version of
   this document

   An incomplete version is located on GitHub at:

   https://github.com/danielkinguk/transport-nbi




















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   Authors' Addresses

   Italo Busi (Editor)
   Huawei

   Email: italo.busi@huawei.com


   Daniel King (Editor)
   Old Dog Consulting

   Email: daniel@olddog.co.uk


   Haomian Zheng (Editor)
   Huawei

   Email: zhenghaomian@huawei.com


   Yunbin Xu (Editor)
   CAICT

   Email: xuyunbin@ritt.cn


   Yang Zhao
   China Mobile

   Email: zhaoyangyjy@chinamobile.com


   Sergio Belotti
   Nokia

   Email: sergio.belotti@nokia.com


   Gianmarco Bruno
   Ericsson

   Email: gianmarco.bruno@ericsson.com





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   Young Lee
   Huawei

   Email: leeyoung@huawei.com


   Victor Lopez
   Telefonica

   Email: victor.lopezalvarez@telefonica.com


   Carlo Perocchio
   Ericsson

   Email: carlo.perocchio@ericsson.com


   Ricard Vilalta
   CTTC

   Email: ricard.vilalta@cttc.es

























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