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Versions: (draft-ietf-ccamp-transport-nbi-use-cases) 00 01

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

Expires: September 2018                                  March 5, 2018



           Transport Northbound Interface Applicability Statement
              draft-ietf-ccamp-transport-nbi-app-statement-01


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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   This Internet-Draft will expire on September 5, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   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 IETF (TEAS and CCAMP WGs in particular) to support OTN
   single and multi-domain scenarios.

Table of Contents

   1. Introduction..................................................3
      1.1. Scope of this document...................................4
      1.2. Assumptions..............................................5
   2. Terminology...................................................5
   3. Conventions used in this document.............................6
      3.1. Topology and traffic flow processing.....................6
      3.2. JSON code................................................7
   4. Scenarios Description.........................................8
      4.1. Reference Network........................................8
         4.1.1. Single-Domain Scenario.............................10
         4.1.2. Multi-Domain Scenario..............................10
      4.2. Topology Abstractions...................................10
      4.3. Service Configuration...................................12
         4.3.1. ODU Transit........................................13
         4.3.2. EPL over ODU.......................................13
         4.3.3. Other OTN Clients Services.........................14
         4.3.4. EVPL over ODU......................................15
         4.3.5. EVPLAN and EVPTree Services........................16
         4.3.6. Dynamic Service Configuration......................18


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      4.4. Multi-function Access Links.............................18
      4.5. Protection and Restoration Configuration................19
         4.5.1. Linear Protection (end-to-end).....................20
         4.5.2. Segmented Protection...............................21
         4.5.3. End-to-End Dynamic Restoration.....................21
         4.5.4. Segmented Dynamic Restoration......................22
      4.6. Service Modification and Deletion.......................23
      4.7. Notification............................................23
      4.8. Path Computation with Constraint........................23
   5. YANG Model Analysis..........................................24
      5.1. YANG Models for Topology Abstraction....................24
         5.1.1. Domain 1 Topology Abstraction......................25
         5.1.2. Domain 2 Grey (Type A) Topology Abstraction........26
         5.1.3. Domain 3 Grey (Type B) Topology Abstraction........26
         5.1.4. Multi-domain Topology Stitching....................26
         5.1.5. Access Links.......................................27
      5.2. YANG Models for Service Configuration...................28
         5.2.1. ODU Transit Service................................30
         5.2.2. EPL over ODU Service...............................32
         5.2.3. Other OTN Client Services..........................33
         5.2.4. EVPL over ODU Service..............................34
      5.3. YANG Models for Protection Configuration................35
         5.3.1. Linear Protection (end-to-end).....................35
         5.3.2. Segmented Protection...............................35
   6. Detailed JSON Examples.......................................35
      6.1. JSON Examples for Topology Abstractions.................35
         6.1.1. Domain 1 White Topology Abstraction................35
      6.2. JSON Examples for Service Configuration.................35
         6.2.1. ODU Transit Service................................35
      6.3. JSON Example for Protection Configuration...............36
   7. Security Considerations......................................36
   8. IANA Considerations..........................................36
   9. References...................................................36
      9.1. Normative References....................................36
      9.2. Informative References..................................37
   10. Acknowledgments.............................................38
   Appendix A. Detailed JSON Examples..............................39
      A.1. JSON Code: mpi1-otn-topology.json.......................39
      A.2. JSON Code:  mpi1-odu2-service-config.json...............39
   Appendix B. Validating a JSON fragment against a YANG Model.....40
      B.1. DSDL-based approach.....................................40
      B.2. Why not using a XSD-based approach......................40

1. Introduction

   Transport of packet services are critical for a wide-range of
   applications and services, including: data center and LAN


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   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 will be to automate 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 enable also service
   provisioning coordination/automation. This can be achieved by using
   standardized YANG models, used together with an appropriate protocol
   (e.g., RESTCONF).

   This document analyses the applicability of the YANG models being
   defined by IETF (TEAS and CCAMP WGs in particular) to support OTN
   single and multi-domain scenarios.

1.1. 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 [ACTN-Frame].

   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).

   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 [ACTN-Frame].

   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 could be 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].

   The analysis of how to use the attributes in the I2RS Topology YANG
   model, defined in [I2RS-TOPO], is for further study.


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   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 an input for
   defining the reference scenarios analyzed in this document.

1.2. Assumptions

   This document is making the following assumptions, still to be
   validated with TEAS WG:

   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
      TTP (i.e., it would leave the source, destination, src-tp-id and
      dst-tp-id attributes empty) and it would use the explicit-route-
      object list to specify the ingress and egress links 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.

   This document is also making the following assumptions, still to be
   validated with CCAMP WG:

2. Terminology

   Domain: defined as a collection of network elements within a common
   realm of address space or path computation responsibility [RFC5151]

   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]

   Service Model: As described in [RFC8309] it describes a service and
   the parameters of the service in a portable way that can be used


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   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

   MAC Bridging: Virtual LANs (VLANs) on IEEE 802.3 Ethernet network

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 either an adaptation of a client layer into a
   server layer "(client -> server)" or switching at a given layer
   "([switching])". Multi-layer switching is indicated by two layer
   switching with client/server adaptation: "([client] -> [server])".

   For example, the following traffic flow:

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

   Node C-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 C-R3. Node C-R3
   terminates the ODU2 from S6 before switching at the packet (PKT)
   layer.

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

      <node> {, <node>}


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   The order represents the order of traffic flow being forwarded
   through the network in the forward direction. In 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 IETF (TEAS and CCAMP WG in
   particular) can be used.

   The examples are provided using JSON because JSON code is easier for
   humans to read and write.

   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.

   JSON language does not support the insertion of comments that have
   been instead found to be useful when writing the examples. This
   document inserts 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 B, 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
   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",


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   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 validate 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 providing transport services to an IP customer network
   through eight access links:

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

                         Figure 1 Reference network


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

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

                      Figure 2 Controlling Hierarchy

   The ACTN framework facilitates the detachment of the network and
   service control from the underlying technology and help the customer
   express the network as desired by business needs. Therefore, care
   must be taken to keep minimal dependency on the CMI (or no
   dependency at all) with respect to the network domain technologies.



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   The MPI instead requires some specialization according to the domain
   technology.

   In this document we address the use case where the CNC controls: the
   customer IP network and requests, at the CMI, transport connectivity
   among IP routers to an MDSC which coordinates, via three MPIs, the
   control of a multi-domain transport network via three PNCs.

   The interfaces within scope of this document are the three MPIs,
   while the interface between the CNC and the IP routers is out of
   scope of this document. It is also assumed that the CMI allows the
   CNC to provide all the information that is required by the MDSC to
   properly configure the transport connectivity requested by the
   customer.

4.1.1. Single-Domain Scenario

   In case the CNC requests transport connectivity between IP routers
   attached to the same transport domain (e.g., between C-R1 and C-R3),
   the MDSC can pass the service request to the PNC (e.g., PNC1) and
   let the PNC takes decisions about how to implement the service.

4.1.2. Multi-Domain Scenario

   In case the CNC requests transport connectivity between IP routers
   attached to different transport domain (e.g., between C-R1 and C-
   R5), the MDSC can split the service request into tunnel segment
   configuration and then pass to multiple PNCs (PNC1 and PNC2 in this
   example) and let the PNC takes decisions about how to deploy the
   service.

4.2. Topology Abstractions

   Abstraction provides a selective method for representing
   connectivity information within a domain. There are multiple methods
   to abstract a network topology. This document assumes the
   abstraction method defined in [RFC7926]:

     "Abstraction is the process of applying 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."



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   [TE-Topo] Describes a YANG base model for TE topology without any
   technology specific parameters. Moreover, it defines how to abstract
   for TE-network topologies.

   [ACTN-Frame] 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 [ACTN-Frame], 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
      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 a 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 a topology abstraction of the
   domain's network topology.

   Each PNC provides topology abstraction of its own domain topology
   independently from each other and therefore it is possible that
   different PNCs provide different types of topology abstractions.

   The MPI operates on the abstract topology regardless on the type of
   abstraction provided by the PNC.

   To analyze how the MPI operates on abstract topologies independently
   from the topology abstraction provided by each PNC and, therefore,
   that that different PNCs can provide different topology
   abstractions, it is assumed that:



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   o PNC1 provides a topology abstraction which exposes at the MPI an
      abstract node and an abstract link for each physical node and
      link within network domain 1

   o PNC2 provides a topology abstraction which exposes at the MPI a
      single abstract node (representing the whole network domain) with
      abstract links representing only the inter-domain physical links

   o PNC3 provides a topology abstraction which exposes at the MPI two
      abstract nodes (AN31 and AN32). They abstract respectively nodes
      S31+S33 and nodes S32+S34. At the MPI, only the abstract nodes
      should be reported: the mapping between the abstract nodes (AN31
      and AN32) and the physical nodes (S31, S32, S33 and S34) should
      be done internally by the PNC.

   The MDSC should be capable to stitch together each abstracted
   topology to build its own view of the multi-domain network topology.
   The process may require suitable oversight, including administrative
   configuration and trust models, but this is out of scope for this
   document.

   A method and process for topology abstraction for the CMI is
   required, and will be discussed in a future revision of this
   document.

4.3. Service Configuration

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

   The type of services could depend of 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, C-Ri (PKT
   -> foo) and C-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 the PNCs. Therefore, these mechanisms are outside the scope of
   this document.

   It is just assumed that the CNC is capable to request the proper
   configuration of the different adaptation functions inside the
   customer's IP routers, by means which are outside the scope of this
   document.




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4.3.1. ODU Transit

   The physical links interconnecting the IP routers and the transport
   network can be OTN links. In this case, the physical/optical
   interconnections below the ODU layer are supposed to be pre-
   configured and not exposed at the MPI to the MDSC.

   To setup a 10Gb IP link between C-R1 and C-R5, an ODU2 end-to-end
   data plane connection needs be created between C-R1 and C-R5,
   crossing transport nodes S3, S1, S2, S31, S33, S34, S15 and S18
   which belong to different PNC domains.

   The traffic flow between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> ODU2), S3 ([ODU2]), S1 ([ODU2]), S2 ([ODU2]),
      S31 ([ODU2]), S33 ([ODU2]), S34 ([ODU2]),
      S15 ([ODU2]), S18 ([ODU2]), C-R5 (ODU2 -> [PKT])

   It is assumed that the CNC requests, via the CMI, the setup of an
   ODU2 transit service, providing all the information that the MDSC
   needs to understand that it shall setup a multi-domain ODU2 segment
   connection between nodes S3 and S18.

   In case the CNC needs the setup of a 10Gb IP link between C-R1 and
   C-R3 (single-domain service request), the traffic flow between C-R1
   and C-R3 can be summarized as:

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

   Since the CNC is unaware of the transport network domains, it
   requests the setup of an ODU2 transit service in the same way as
   before, regardless the fact the fact that this is a single-domain
   service.

   It is assumed that the information provided at the CMI is sufficient
   for the MDSC to understand that this is a single-domain service
   request.

   The MDSC can then just request PNC1 to setup a single-domain ODU2
   data plane segment connection between nodes S3 and S6.

4.3.2. EPL over ODU

   The physical links interconnecting the IP routers and the transport
   network can be Ethernet links.



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   To setup a 10Gb IP link between C-R1 and C-R5, an EPL service needs
   to be created between C-R1 and C-R5, supported by an ODU2 end-to-end
   data plane connection between transport nodes S3 and S18, crossing
   transport nodes S1, S2, S31, S33, S34 and S15 which belong to
   different PNC domains.

   The traffic flow between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> ETH), S3 (ETH -> [ODU2]), S1 ([ODU2]),
      S2 ([ODU2]), S31 ([ODU2]), S33 ([ODU2]), S34 ([ODU2]),
      S15 ([ODU2]), S18 ([ODU2] -> ETH), C-R5 (ETH -> [PKT])

   It is assumed that the CNC requests, via the CMI, the setup of an
   EPL service, providing all the information that the MDSC needs to
   understand that it shall coordinate the three PNCs to setup a multi-
   domain ODU2 end-to-end connection between nodes S3 and S18 as well
   as the configuration of the adaptation functions inside nodes S3 and
   S18: S3 (ETH -> [ODU2]), S18 ([ODU2] -> ETH), S18 (ETH -> [ODU2])
   and S3 ([ODU2] -> ETH).

   In case the CNC needs the setup of a 10Gb IP link between C-R1 and
   C-R3 (single-domain service request), the traffic flow between C-R1
   and C-R3 can be summarized as:

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

   As described in section 4.3.1, the CNC requests the setup of an EPL
   service in the same way as before and the information provided at
   the CMI is sufficient for the MDSC to understand that this is a
   single-domain service request.

   The MDSC can then just request PNC1 to setup a single-domain EPL
   service between nodes S3 and S6. PNC1 can take care of setting up
   the single-domain ODU2 end-to-end connection between nodes S3 and S6
   as well as of configuring the adaptation functions on these edge
   nodes.

4.3.3. Other OTN Clients Services

   [ITU-T G.709] defines mappings of different 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.).




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   The physical links interconnecting the IP routers and the transport
   network can be any of these types.

   In order to setup a 10Gb IP link between C-R1 and C-R5 using, for
   example SDH physical links between the IP routers and the transport
   network, an STM-64 Private Line service needs to be created between
   C-R1 and C-R5, supported by ODU2 end-to-end data plane connection
   between transport nodes S3 and S18, crossing transport nodes S1, S2,
   S31, S33, S34 and S15 which belong to different PNC domains.

   The traffic flow between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> STM-64), S3 (STM-64 -> [ODU2]), S1 ([ODU2]),
      S2 ([ODU2]), S31 ([ODU2]), S33 ([ODU2]), S34 ([ODU2]),
      S15 ([ODU2]), S18 ([ODU2] -> STM-64), C-R5 (STM-64 -> [PKT])

   As described in section 4.3.2, it is assumed that the CNC is
   capable, via the CMI, to request the setup of an STM-64 Private Line
   service, providing all the information that the MDSC needs to
   coordinate the setup of a multi-domain ODU2 connection as well as
   the adaptation functions on the edge nodes.

   In the single-domain case (10Gb IP link between C-R1 and C-R3), the
   traffic flow between C-R1 and C-R3 can be summarized as:

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

   As described in section 4.3.1, the CNC requests the setup of an STM-
   64 Private Line service in the same way as before and the
   information provided at the CMI is sufficient for the MDSC to
   understand that this is a single-domain service request.

   As described in section 4.3.2, the MDSC could just request PNC1 to
   setup a single-domain STM-64 Private Line service between nodes S3
   and S6.

4.3.4. EVPL over ODU

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

   To setup two 1Gb IP links between C-R1 to C-R3 and between C-R1 and
   C-R5, two EVPL services need to be created, supported by two ODU0
   end-to-end connections respectively between S3 and S6, crossing


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   transport node S5, and between S3 and S18, crossing transport nodes
   S1, S2, S31, S33, S34 and S15 which belong to different PNC domains.

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

   The traffic flow between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> VLAN), S3 (VLAN -> [ODU0]), S1 ([ODU0]),
      S2 ([ODU0]), S31 ([ODU0]), S33 ([ODU0]), S34 ([ODU0]),
      S15 ([ODU0]), S18 ([ODU0] -> VLAN), C-R5 (VLAN -> [PKT])

   The traffic flow between C-R1 and C-R3 can be summarized as:

      C-R1 ([PKT] -> VLAN), S3 (VLAN -> [ODU0]), S5 ([ODU0]),
      S6 ([ODU0] -> VLAN), C-R3 (VLAN -> [PKT])

   As described in section 4.3.2, it is assumed that the CNC is
   capable, via the CMI, to request the setup of these EVPL services,
   providing all the information that the MDSC needs to understand that
   it need to request PNC1 to setup an EVPL service between nodes S3
   and S6 (single-domain service request) and it also needs to
   coordinate the setup of a multi-domain ODU0 connection between nodes
   S3 and S16 as well as the adaptation functions on these edge nodes.

4.3.5. EVPLAN and EVPTree Services

   When the physical links interconnecting the IP routers and the
   transport network are Ethernet links, multipoint Ethernet services
   (e.g, EPLAN and EPTree) can also be supported. It is also possible
   that multiple Ethernet services (e.g, EVPL, EVPLAN and EVPTree)
   share the same physical link using different VLANs.

   Note - it is assumed that EPLAN and EPTree services can be supported
   by configuring EVPLAN and EVPTree with port mapping.

   Since this EVPLAN/EVPTree service can share the same Ethernet
   physical links between IP routers and transport nodes (e.g., with
   the EVPL services described in section 4.3.4), a different VLAN ID
   (e.g., 30) can be associated with this EVPLAN/EVPTree service.

   In order to setup an IP subnet between C-R1, C-R2, C-R3 and C-R5, an
   EVPLAN/EVPTree service needs to be created, supported by two ODUflex
   end-to-end connections respectively between S3 and S6, crossing



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   transport node S5, and between S3 and S18, crossing transport nodes
   S1, S2, S31, S33, S34 and S15 which belong to different PNC domains.

   Some MAC Bridging capabilities are also required on some nodes at
   the edge of the transport network: for example Ethernet Bridging
   capabilities can be configured in nodes S3 and S6:

   o MAC Bridging in node S3 is needed to select, based on the MAC
      Destination Address, whether received Ethernet frames should be
      forwarded to C-R1 or to the ODUflex terminating on node S6 or to
      the other ODUflex terminating on node S18;

   o MAC bridging function in node S6 is needed to select, based on
      the MAC Destination Address, whether received Ethernet frames
      should be sent to C-R2 or to C-R3 or to the ODUflex terminating
      on node S3.

   In order to support an EVPTree service instead of an EVPLAN,
   additional configuration of the Ethernet Bridging capabilities on
   the nodes at the edge of the transport network is required.

   The traffic flows between C-R1 and C-R3, between C-R3 and C-R5 and
   between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> VLAN), S3 (VLAN -> [MAC] -> [ODUflex]),
      S5 ([ODUflex]), S6 ([ODUflex] -> [MAC] -> VLAN),
      C-R3 (VLAN -> [PKT])

      C-R3 ([PKT] -> VLAN), S6 (VLAN -> [MAC] -> [ODUflex]),
      S5 ([ODUflex]), S3 ([ODUflex] -> [MAC] -> [ODUflex]),
      S1 ([ODUflex]), S2 ([ODUflex]), S31 ([ODUflex]),
      S33 ([ODUflex]), S34 ([ODUflex]),
      S15 ([ODUflex]), S18 ([ODUflex] -> VLAN), C-R5 (VLAN -> [PKT])

      C-R1 ([PKT] -> VLAN), S3 (VLAN -> [MAC] -> [ODUflex]),
      S1 ([ODUflex]), S2 ([ODUflex]), S31 ([ODUflex]),
      S33 ([ODUflex]), S34 ([ODUflex]),
      S15 ([ODUflex]), S18 ([ODUflex] -> VLAN), C-R5 (VLAN -> [PKT])

   As described in section 4.3.2, it is assumed that the CNC is
   capable, via the CMI, to request the setup of this EVPLAN/EVPTree
   service, providing all the information that the MDSC needs to
   understand that it need to request PNC1 to setup an ODUflex
   connection between nodes S3 and S6 (single-domain service request)
   and it also needs to coordinate the setup of a multi-domain ODUflex
   connection between nodes S3 and S16 as well as the MAC bridging and
   the adaptation functions on these edge nodes.


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   In case the CNC needs the setup of an EVPLAN/EVPTree service only
   between C-R1, C-R2 and C-R3 (single-domain service request), it
   would request the setup of this service in the same way as before
   and the information provided at the CMI is sufficient for the MDSC
   to understand that this is a single-domain service request.

   The MDSC can then just request PNC1 to setup a single-domain
   EVPLAN/EVPTree service between nodes S3 and S6. PNC1 can take care
   of setting up the single-domain ODUflex end-to-end connection
   between nodes S3 and S6 as well as of configuring the MAC bridging
   and the adaptation functions on these edge nodes.

4.3.6. Dynamic Service Configuration

   Given the service established in the previous sections, there is a
   demand for an update of some service characteristics. A
   straightforward approach would be terminate the current service and
   replace with a new one. Another more advanced approach would be
   dynamic configuration, in which case there will be no interruption
   for the connection.

   An example application would be updating the SLA information for a
   certain connection. For example, an ODU transit connection is set up
   according to section 4.3.1, with the corresponding SLA level of 'no
   protection'. After the establishment of this connection, the user
   would like to enhance this service by providing a restoration after
   potential failure, and a request is generated on the CMI. In this
   case, after receiving the request, the MDSC would need to send an
   update message to the PNC, changing the SLA parameters in TE Tunnel
   model. Then the connection characteristic would be changed by PNC,
   and a notification would be sent to MDSC for acknowledgement.

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 or STM-
   64 or 10GE.

   This configuration can be done a-priori by means outside the scope
   of this document. In this case, these links will appear at the MPI
   either as an ODU Link or as a STM-64 Link or as a 10GE Link
   (depending on the a-priori configuration) and will be controlled at
   the MPI as discussed in section 4.3.

   It is also possible not to configure these links a-priori and give
   the control to the MPI to decide, based on the service
   configuration, how to configure it.


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   For example, if the physical link between C-R1 and S3 is a multi-
   functional access link while the physical links between C-R7 and S31
   and between C-R5 and S18 are STM-64 and 10GE physical links
   respectively, it is possible to configure either an STM-64 Private
   Line service between C-R1 and C-R7 or an EPL service between C-R1
   and C-R5.

   The traffic flow between C-R1 and C-R7 can be summarized as:

      C-R1 ([PKT] -> STM-64), S3 (STM-64 -> [ODU2]), S1 ([ODU2]),
      S2 ([ODU2]), S31 ([ODU2] -> STM-64), C-R3 (STM-64 -> [PKT])

   The traffic flow between C-R1 and C-R5 can be summarized as:

      C-R1 ([PKT] -> ETH), S3 (ETH -> [ODU2]), S1 ([ODU2]),
      S2 ([ODU2]), S31 ([ODU2]), S33 ([ODU2]), S34 ([ODU2]),
      S15 ([ODU2]), S18 ([ODU2] -> ETH), C-R5 (ETH -> [PKT])

   As described in section 4.3.2, it is assumed that the CNC is
   capable, via the CMI, to request the setup either an STM-64 Private
   Line service between C-R1 and C-R7 or an EPL service between C-R1
   and C-R5, providing all the information that the MDSC needs to
   understand that it need to coordinate the setup of a multi-domain
   ODU2 connection, either between nodes S3 and S31, or between nodes
   S3 and S18, as well as the adaptation functions on these edge nodes,
   and in particular whether the multi-function access link on between
   C-R1 and S3 should operate as an STM-64 or as a 10GE 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 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 and with dynamic restoration.

   The MDSC needs to be capable to coordinate different PNCs to
   configure protection switching when requesting the setup of the
   protected connectivity services described in section 4.3.



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

4.5.1. Linear Protection (end-to-end)

   In order to protect any service defined in section 4.3 from failures
   within the OTN multi-domain transport network, the MDSC should be
   capable to coordinate different PNCs to configure and control OTN
   linear protection in the data plane between nodes S3 and node S18.

   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.



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   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.

4.5.2. Segmented Protection

   To protect any service defined in section 4.3 from failures within
   the OTN multi-domain transport network, the MDSC should be capable
   to request each PNC to configure OTN intra-domain protection when
   requesting the setup of the ODU2 data plane connection segment.

   If PNC1 provides linear protection, the working and protection
   transport entities could be:

      Working transport entity:   S3, S1, S2

      Protection transport entity: S3, S4, S8, S2

   If PNC2 provides linear protection, the working and protection
   transport entities could be:

      Working transport entity:   S15, S18

      Protection transport entity: S15, S12, S17, S18

   If PNC3 provides linear protection, the working and protection
   transport entities could be:

      Working transport entity:   S31, S33, S34

      Protection transport entity: S31, S32, S34

4.5.3. End-to-End Dynamic restoration

   To restore any service defined in section 4.3 from failures within
   the OTN multi-domain transport network, the MDSC should be capable
   to coordinate different PNCs to configure and control OTN end-to-end
   dynamic Restoration in the data plane between nodes S3 and node S18.
   For example, the MDSC can request the PNC1, PNC2 and PNC3 to create
   a service with no-protection, MDSC set the end-to-end service with
   the dynamic restoration.




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

   When a link failure between S1 and s2 occurred in network domain 1,
   PNC1 does not restore the tunnel and send the alarm notification to
   the MDSC, MDSC will perform the end-to-end restoration.

         Restored transport entity:   S3, S4, S8,
                             S12, S15, S18

4.5.4. Segmented Dynamic Restoration

   To restore any service defined in section 4.3 from failures within
   the OTN multi-domain transport network, the MDSC should be capable
   to coordinate different PNCs to configure and control OTN segmented
   dynamic Restoration in the data plane between nodes S3 and node S18.

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

   When a link failure between S1 and s2 occurred in network domain 1,
   PNC1 will restore the tunnel and send the alarm or tunnel update
   notification to the MDSC, MDSC will update the restored tunnel.

         Restored transport entity:   S3, S4, S8, S2
                             S31, S33, S34,
                             S15, S18

   When a link failure between network domain 1 and network domain 2
   occurred, PNC1 and PNC2 will send the alarm notification to the
   MDSC, MDSC will update the restored tunnel.

         Restored transport entity:   S3, S4, S8,
                             S12, S15, S18

   In order to improve the efficiency of recovery, the controller can
   establish a recovery path in a concurrent way. When the recovery
   fails in one domain or one network element, the rollback operation
   should be supported.

   The creation of the recovery path by the controller can use the
   method of "make-before-break", in order to reduce the impact of the
   recovery operation on the services.




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4.6. Service Modification and Deletion

   To be discussed in future versions of this document.

4.7. 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

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

4.8. Path Computation with Constraint

   It is possible to have constraint during path computation procedure,
   typical cases include IRO/XRO and so on. This information is carried
   in the TE Tunnel model and used when there is a request with
   constraint. Consider the example in section 4.3.1, the request can
   be a Tunnel from C-R1 to C-R5 with an IRO from S2 to S31, then a
   qualified feedback would become:

   C-R1 ([PKT] -> ODU2), S3 ([ODU2]), S1 ([ODU2]), S2 ([ODU2]),
   S31 ([ODU2]), S33 ([ODU2]), S34 ([ODU2]),
   S15 ([ODU2]), S18 ([ODU2]), C-R5 (ODU2 -> [PKT])

   If the request covers the IRO from S8 to S12, then the above path
   would not be qualified, while a possible computation result may be:

   C-R1 ([PKT] -> ODU2), S3 ([ODU2]), S1 ([ODU2]), S2 ([ODU2]),
   S8 ([ODU2]), S12 ([ODU2]), S15 ([ODU2]), S18 ([ODU2]), C-R5 (ODU2 ->
   [PKT])

   Similarly, the XRO can be represented by TE tunnel model as well.




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

5. YANG Model Analysis

   This section provides a high-level overview of how IETF YANG models
   can be used at the MPIs, between the MDSC and the PNCs, to support
   the scenarios described in section 4.

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

   Section 0 describes how the MDSC can coordinate different requests
   to different PNCs, via their own MPIs, to setup different services,
   as defined 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 abstract topology to the MDSC, as
   described in section 4.1.2.






















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5.1.1. Domain 1 Topology Abstraction

   PNC1 provides the required topology abstraction to expose at its MPI
   toward the MDSC (called "MPI1") one TE Topology instance for the ODU
   layer (called "MPI1 ODU Topology"), containing one TE Node (called
   "ODU Node") for each physical node, as shown in Figure 3. below.

                  ..................................
                  :                                :
                  :   ODU Abstract Topology @ MPI  :
                  :        Gotham City Area        :
                  :     Metro Transport Network    :
                  :                                :
                  :        +----+        +----+    :
                  :        |    |S1-1    |    |S2-1:
                  :        | S1 |--------| S2 |- - - - -(C-R4)
                  :        +----+    S2-2+----+    :
                  :     S1-2/               |S2-3  :
                  :    S3-2/ Robinson Park  |      :
                  :    +----+   +----+      |      :
                  :    |    |3 1|    |      |      :
        (C-R1)- - - - -| S3 |---| S4 |      |      :
                  :S3-1+----+   +----+      |      :
                  :   S3-4 \        \S4-2   |      :
                  :         \S5-1    \      |      :
                  :        +----+     \     |      :
                  :        |    |      \S8-3|      :
                  :        | S5 |       \   |      :
                  :        +----+ Metro  \  |S8-2  :
        (C-R2)- - - - -   2/ E  \3 Main   \ |      :
                  :S6-1 \ /3 a E \1 Ring   \|      :
                  :    +----+s-n+----+   +----+    :
                  :    |    |t d|    |   |    |S8-1:
                  :    | S6 |---| S7 |---| S8 |- - - - -(C-R5)
                  :    +----+4 2+----+3 4+----+    :
                  :     /                          :
        (C-R3)- - - - -                            :
                  :S6-2                            :
                  :................................:

       Figure 3 Abstract Topology exposed at MPI1 (MPI1 ODU Topology)

   The ODU Nodes in Figure 3 are using the same names as the physical
   nodes to simplify the description of the mapping between the ODU
   Nodes exposed by the Transport PNCs at the MPI and the physical
   nodes in the data plane. This does not


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   correspond to the reality of the usage of the topology model, as
   described in section 4.3 of [TE-TOPO], in which renaming by the
   client it is necessary.

   As described in section 4.1.2, it is assumed that the physical links
   between the physical nodes are pre-configured up to the OTU4 trail
   using mechanisms which are outside the scope of this document. PNC1
   exports at MPI1 one TE Link (called "ODU Link") for each of these
   OTU4 trails.

5.1.2. Domain 2 Grey (Type A) Topology Abstraction

   PNC2 provides the required topology abstraction to expose at its MPI
   towards the MDSC (called "MPI2") only one abstract node (i.e., AN2),
   with only inter-domain and access links, is reported at the MPI2.

5.1.3. Domain 3 Grey (Type B) Topology Abstraction

   PNC3 provides the required topology abstraction to expose at its MPI
   towards the MDSC (called "MPI3") only two abstract nodes (i.e., AN31
   and AN32), with internal links, inter-domain links and access links.

5.1.4. Multi-domain Topology Stitching

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

   Given the topologies reported from multiple PNCs, the MDSC need to
   stitch the multi-domain topology and obtain the full map of
   topology. The topology of each domain main be in an abstracted shape
   (refer to section 5.2 of [ACTN-Frame] for 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 "stitch" together these inter-
   domain links.

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


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   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, or it can be discovered using 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 recommended
   that the plug-id namespace is partitioned to avoid that different
   sources assign the same plug-id value to different inter-domain
   link. The encoding of the plug-id namespace within the plug-id value
   is implementation specific but needs to be consistent across all the
   PNCs.

   Another possibility is to pre-configure, either in the adjacent PNCs
   or in the MDSC, the association between the inter-domain link
   identifiers (topology-id, node-id and tp-id) assigned by the two
   adjacent PNCs to the same inter-domain link.

   This last scenario requires further investigation and will be
   discussed in a future version of this document.

5.1.5. Access Links

   Access links in Figure 3. are shown as ODU Links: the modeling of
   the access links for other access technologies is currently an open
   issue.

   The modeling of the access link in case of non-ODU access technology
   has also an impact on the need to model ODU TTPs and layer
   transition capabilities on the edge nodes (e.g., nodes S2, S3, S6
   and S8 in Figure 3.).

   If, for example, the physical NE S6 is implemented in a "pizza box",
   the data plane would have only set of ODU termination resources
   (where up to 2xODU4, 4xODU3, 20xODU2, 80xODU1, 160xODU0 and



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   160xODUflex can be terminated). The traffic coming from each of the
   10GE access links can be mapped into any of these ODU terminations.

   Instead if, for example, the physical NE S6 can be implemented as a
   multi-board system where access links reside on different/dedicated
   access cards with separated set of ODU termination resources (where
   up to 1xODU4, 2xODU3, 10xODU2, 40xODU1, 80xODU0 and 80xODUflex for
   each resource can be terminated). The traffic coming from one 10GE
   access links can be mapped only into the ODU terminations which
   reside on the same access card.

   The more generic implementation option for a physical NE (e.g., S6)
   would be case is of a multi-board system with multiple access cards
   with separated sets of access links and ODU termination resources
   (where up to 1xODU4, 2xODU3, 10xODU2, 40xODU1, 80xODU0 and
   80xODUflex for each resource can be terminated). The traffic coming
   from each of the 10GE access links on one access card can be mapped
   only into any of the ODU terminations which reside on the same
   access card.

   In the last two cases, only the ODUs terminated on the same access
   card where the access links resides can carry the traffic coming
   from that 10GE access link. Terminated ODUs can instead be sent to
   any of the OTU4 interfaces

   In all these cases, terminated ODUs can be sent to any of the OTU4
   interfaces assuming the implementation is based on a non-blocking
   ODU cross-connect.

   If the access links are reported via MPI in some, still to be
   defined, client topology, it is possible to report each set of ODU
   termination resources as an ODU TTP within the ODU Topology of
   Figure 1. and to use either the inter-layer lock-id or the
   transitional link, as described in sections 3.4 and 3.10 of
   [TE-TOPO], to correlate the access links, in the client
   topology, with the ODU TTPs, in the ODU topology, to which access
   link are connected to.

5.2. YANG Models for Service Configuration

   The service configuration procedure is assumed to be initiated (step
   1 in Figure 4) at the CMI from CNC to MDSC. Analysis of the CMI
   models is (e.g., L1SM, L2SM, Transport-Service, VN, et al.) is
   outside the scope of this document.

   As described in section 4.3, it is assumed that the CMI YANG models
   provides all the information that allows the MDSC to understand that


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   it needs to coordinate the setup of a multi-domain ODU connection
   (or connection segment) 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 4 Multi-domain Service Setup

   As an example, the objective in this section is to configure a
   transport service between C-R1 and C-R5. The cross-domain routing is
   assumed to be C-R1 <-> S3 <-> S2 <-> S31 <-> S33 <-> S34 <->S15 <->
   S18 <-> C-R5.



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   According to the different client signal type, there is different
   adaptation required.

   After receiving such request, MDSC determines the domain sequence,
   i.e., domain 1 <-> domain 2 <-> domain 3, with corresponding PNCs
   and inter-domain links (step 2 in Figure 4).

   As described in [PATH-COMPUTE], the domain sequence can be
   determined by running the MDSC own path computation on the MDSC
   internal 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 4) 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 model (including both 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 4).

   Assume that each intra-domain tunnel segment can be set up
   successfully, and each PNC response to the MDSC respectively. Based
   on each segment, 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). More
   specifically, for the inter-domain configuration, the ts-bitmap and
   tpn attributes need to be configured using the OTN Tunnel model
   [xxx]. Then the end-to-end OTN tunnel will be ready.

   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 in our example)
   and not on the PNCs of transit domain (e.g., PNC-2 in our example).
   Access link will be configured by MDSC after the OTN tunnel is set
   up. Access configuration is different and dependent on the different
   type of service. More details can be found in the following
   sections.

5.2.1. ODU Transit Service

   In this scenario, the access links are configured as ODU Links.

   As described in section 4.3.1, the CNC needs to setup an ODU2 end-
   to-end connection, supporting an IP link, between C-R1 and C-R5 and
   requests via the CMI to the MDSC the setup of an ODU transit
   service.




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   From the topology information described in section 5.1 above, the
   MDSC understands that C-R1 is attached to the access link
   terminating on S3-1 LTP in the ODU Topology exposed by PNC1 and that
   C-R5 is attached to the access link terminating on AN2-1 LTP in the
   ODU Topology exposed by PNC2.

   Based on the assumption 0) in section 1.2, MDSC would then request
   the PNC1 to setup an ODU2 (Transit Segment) Tunnel between S3-1 and
   S6-2 LTPs:

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

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

        o The first element of the explicit-route-objects references
          the access link terminating on S3-1 LTP

        o Last element of the explicit-route-objects references the
          access link terminating on S6-2 LTP

   The configuration of the timeslots used by the ODU2 connection
   within the transport network domain (i.e., on the internal links) is
   a matter of the Transport PNC and its interactions with the physical
   network elements and therefore is outside the scope of this
   document.

   However, the configuration of the timeslots used by the ODU2
   connection at the edge of the transport network domain (i.e., on the
   access links) needs to take into account not only the timeslots
   available on the physical nodes at the edge of the transport network
   domain (e.g., S3 and S6) but also on the devices, outside of the
   transport network domain, connected through these access links
   (e.g., C-R1 and C-R3).

   Based on the assumption 2) in section 1.2, the MDSC, when requesting
   the Transport PNC to setup the (Transit Segment) ODU2 Tunnel, it
   would also configure the timeslots to be used on the access links.
   The MDSC can know the timeslots which are available on the edge OTN
   Node (e.g., S3 and S6) from the OTN Topology information exposed by
   the Transport PNC at the MPI as well as the timeslots which are
   available on the devices outside of the transport network domain
   (e.g., C-R1 and C-R3), by means which are outside the scope of this
   document.




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   The Transport PNC performs path computation and sets up the ODU2
   cross-connections within the physical nodes S3, S5 and S6, as shown
   in section 4.3.1.

   The Transport PNC reports the status of the created ODU2 (Transit
   Segment) Tunnel and its path within the ODU Topology as shown in
   Figure 5 below:

                   ..................................
                   :                                :
                   :   ODU Abstract Topology @ MPI  :
                   :                                :
                   :        +----+        +----+    :
                   :        |    |        |    |    :
                   :        | S1 |--------| S2 |- - - - -(C-R4)
                   :        +----+        +----+    :
                   :         /               |      :
                   :        /                |      :
                   :    +----+   +----+      |      :
                   :    |    |   |    |      |      :
         (C-R1)- - - - -  S3 |---| S4 |      |      :
                   :S3-1 <<== +   +----+     |      :
                   :       =        \        |      :
                   :       = \       \       |      :
                   :       == ---+    \      |      :
                   :        =    |     \     |      :
                   :        = S5 |      \    |      :
                   :        == --+       \   |      :
         (C-R2)- - - - -     =  \         \  |      :
                   :S6-1 \ / =   \         \ |      :
                   :    +--- =   +----+   +----+    :
                   :    |    =   |    |   |    |    :
                   :    | S6 = --| S7 |---| S8 |- - - - -(C-R5)
                   :    +--- =   +----+   +----+    :
                   :     /   =                      :
         (C-R3)- - - - -  <<==                      :
                   :S6-2                            :
                   :................................:

                        Figure 5 ODU2 Transit Tunnel

5.2.2. EPL over ODU Service

   In this scenario, the access links are configured as Ethernet Links.





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   As described in section 4.3.2, the CNC needs to setup an EPL
   service, supporting an IP link, between C-R1 and C-R3 and requests
   this service at the CMI to the MDSC.

   MDSC needs to setup an EPL service between C-R1 and C-R3 supported
   by an ODU2 end-to-end connection between S3 and S6.

   As described in section 5.1.5 above, it is not clear in this case
   how the Ethernet access links between the transport network and the
   IP router, are reported by the PNC to the MDSC.

   If the 10GE physical links are not reported as ODU links within the
   ODU topology information, described in section 5.1.1 above, than the
   MDSC will not have sufficient information to know that C-R1 and C-R3
   are attached to nodes S3 and S6.

   Assuming that the MDSC knows how C-R1 and C-R3 are attached to the
   transport network, the MDSC would request the Transport PNC to setup
   an ODU2 end-to-end Tunnel between S3 and S6.

   This ODU Tunnel is setup between two TTPs of nodes S3 and S6. In
   case nodes S3 and S6 support more than one TTP, the MDSC should
   decide which TTP to use.

   As discussed in 5.1.5, depending on the different hardware
   implementations of the physical nodes S3 and S6, not all the access
   links can be connected to all the TTPs. The MDSC should therefore
   not only select the optimal TTP but also a TTP that would allow the
   Tunnel to be used by the service.

   It is assumed that in case node S3 or node S6 supports only one TTP,
   this TTP can be accessed by all the access links.

   Once the ODU2 Tunnel setup has been requested, unless there is a
   one-to-one relationship between the S3 and S6 TTPs and the Ethernet
   access links toward C-R1 and C-R3 (as in the case, described in
   section 5.1.5, where the Ethernet access links reside on
   different/dedicated access card such that the ODU2 tunnel can only
   carry the Ethernet traffic from the only Ethernet access link on the
   same access card where the ODU2 tunnel is terminated), the MDSC also
   needs to request the setup of an EPL service from the access links
   on S3 and S6, attached to C-R1 and C-R3, and this ODU2 Tunnel.

5.2.3. Other OTN Client Services

   In this scenario, the access links are configured as one of the OTN
   clients (e.g., STM-64) links.


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   As described in section 4.3.3, the CNC needs to setup an STM-64
   Private Link service, supporting an IP link, between C-R1 and C-R3
   and requests this service at the CMI to the MDSC.

   MDSC needs to setup an STM-64 Private Link service between C-R1 and
   C-R3 supported by an ODU2 end-to-end connection between S3 and S6.

   As described in section 5.1.5 above, it is not clear in this case
   how the access links (e.g., the STM-N access links) between the
   transport network and the IP router, are reported by the PNC to the
   MDSC.

   The same issues, as described in section 5.2.2, apply here:

   o the MDSC needs to understand that C-R1 and C-R3 are connected,
      thought STM-64 access links, with S3 and S6

   o the MDSC needs to understand which TTPs in S3 and S6 can be
      accessed by these access links

   o the MDSC needs to configure the private line service from these
      access links through the ODU2 tunnel

5.2.4. EVPL over ODU Service

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

   As described in section 4.3.4, the CNC needs to setup EVPL services,
   supporting IP links, between C-R1 and C-R3, as well as between C-R1
   and C-R4 and requests these services at the CMI to the MDSC.

   MDSC needs to setup two EVPL services, between C-R1 and C-R3, as
   well as between C-R1 and C-R4, supported by ODU0 end-to-end
   connections between S3 and S6 and between S3 and S2 respectively.

   As described in section 5.1.5 above, it is not clear in this case
   how the Ethernet access links between the transport network and the
   IP router, are reported by the PNC to the MDSC.

   The same issues, as described in section 5.1.5 above, apply here:

   o the MDSC needs to understand that C-R1, C-R3 and C-R4 are
      connected, thought the Ethernet access links, with S3, S6 and S2

   o the MDSC needs to understand which TTPs in S3, S6 and S2 can be
      accessed by these access links


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   o the MDSC needs to configure the EVPL services from these access
      links through the ODU0 tunnels

   In addition, the MDSC needs to get the information that the access
   links on S3, S6 and S2 are capable to support EVPL (rather than just
   EPL) as well as to coordinate the VLAN configuration, for each EVPL
   service, on these access links (this is a similar issue as the
   timeslot configuration on access links discussed in section 4.3.1
   above).

5.3. YANG Models for Protection Configuration

5.3.1. Linear Protection (end-to-end)

   To be discussed in future versions of this document.

5.3.2. Segmented Protection

   To be discussed in future versions of this document.

6. Detailed JSON Examples

6.1. JSON Examples for Topology Abstractions

6.1.1. Domain 1 White Topology Abstraction

   Section 5.1.1 describes how PNC1 can provide a white topology
   abstraction to the MDSC via the MPI. Figure 3. is an example of
   such ODU Topology.

   This section provides the detailed JSON code describing how this ODU
   Topology is reported by the PNC, using the [TE-TOPO] and [OTN-TOPO]
   YANG models at the MPI.

   JSON code "mpi1-otn-topology.json" has been provided at in the
   appendix of this document.

6.2. JSON Examples for Service Configuration

6.2.1. ODU Transit Service

   Section 5.2.1 describes how the MDSC can request PNC1, via the MPI,
   to setup an ODU2 transit service over an ODU Topology described in
   section 5.1.1.





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   This section provides the detailed JSON code describing how the
   setup of this ODU2 transit service can be requested by the MDSC,
   using the [TE-TUNNEL] and [OTN-TUNNEL] YANG models at the MPI.

   JSON code "mpi1-odu2-service-config.json" has been provided at in
   the appendix of this document.

6.3. JSON Example for Protection Configuration

   To be added

7. Security Considerations

   This section is for further study

8. IANA Considerations

   This document requires no IANA actions.

9. References

9.1. Normative References

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

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

   [ACTN-Frame] Ceccarelli, D., Lee, Y. et al., "Framework for
             Abstraction and Control of Transport Networks", draft-
             ietf-teas-actn-framework, work in progress.

   [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.


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

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

9.2. 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.

   [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.

   [I2RS-TOPO] Clemm, A. et al., "A Data Model for Network Topologies",
             draft-ietf-i2rs-yang-network-topo, work in progress.

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



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

10. 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.

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

























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Appendix A.                 Detailed JSON Examples

A.1. JSON Code: mpi1-otn-topology.json

   The JSON code for this use case is currently located on GitHub at:

   https://github.com/danielkinguk/transport-nbi/blob/master/Internet-
   Drafts/Applicability-Statement/01/mpi1-otn-topology.json

A.2. JSON Code:  mpi1-odu2-service-config.json

   The JSON code for this use case is currently located on GitHub at:

   https://github.com/danielkinguk/transport-nbi/blob/master/Internet-
   Drafts/Applicability-Statement/01/mpi1-odu2-service-config.json

































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Appendix B. Validating a JSON fragment against a YANG Model

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

B.1. 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 6.

   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 6 - DSDL-based approach for JSON code validation

   In order to allow the use of comments following the convention
   defined in section Section 2. without impacting the validation
   process, these comments will be automatically removed from the
   JSON-file that will be validate.

B.2. 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 7:








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

            Figure 7 - 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 7 will stop just at step
   (1).




































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   Authors' Addresses

   Italo Busi (Editor)
   Huawei

   Email: italo.busi@huawei.com


   Daniel King (Editor)
   Lancaster University

   Email: d.king@lancaster.ac.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







Busi, King, et al.    Expires September 5, 2018              [Page 42]


Internet-Draft  Transport NBI Applicability-Statement       March 2018


   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


























Busi, King, et al.    Expires September 5, 2018              [Page 43]


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