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IETF Network Slice Topology YANG Data Model
draft-liu-teas-transport-network-slice-yang-06

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Xufeng Liu , Jeff Tantsura , Igor Bryskin , Luis M. Contreras , Qin Wu , Sergio Belotti , Reza Rokui , Aihua Guo , Italo Busi
Last updated 2023-03-13
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draft-liu-teas-transport-network-slice-yang-06
TEAS Working Group                                                X. Liu
Internet-Draft                                           IBM Corporation
Intended status: Standards Track                             J. Tantsura
Expires: 14 September 2023                                     Microsoft
                                                              I. Bryskin
                                                              Individual
                                                          L.M. Contreras
                                                              Telefonica
                                                                   Q. Wu
                                                                  Huawei
                                                              S. Belotti
                                                                   Nokia
                                                                R. Rokui
                                                                   Ciena
                                                                  A. Guo
                                                               Futurewei
                                                                 I. Busi
                                                                  Huawei
                                                           13 March 2023

              IETF Network Slice Topology YANG Data Model
             draft-liu-teas-transport-network-slice-yang-06

Abstract

   An IETF network slice may use an abstract topology to describe
   intended underlay for connectivities between slice endpoints.
   Abstract topologies help the customer to request network slices with
   shared resources amongst connections, and connections can be
   activated within the slice as needed.

   This document describes a YANG data model for managing and
   controlling abstract topologies for IETF network slices defined in
   RFC YYYY.

   [RFC EDITOR NOTE: Please replace RFC YYYY with the RFC number of
   draft-ietf-teas-ietf-network-slices once it has been published.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 September 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   3
   2.  Modeling Considerations . . . . . . . . . . . . . . . . . . .   4
     2.1.  Relationships to Related Topology Models  . . . . . . . .   4
     2.2.  ACTN for Network Slicing  . . . . . . . . . . . . . . . .   5
   3.  Model Applicability . . . . . . . . . . . . . . . . . . . . .   5
   4.  YANG Model Overview . . . . . . . . . . . . . . . . . . . . .   8
   5.  Model Tree Structure  . . . . . . . . . . . . . . . . . . . .   8
   6.  YANG Modules  . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     10.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Data Tree for the Example in Section 3.1 . . . . . .  20
     B.1.  Native Topology . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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1.  Introduction

   This document defines a YANG [RFC7950] data model for representing,
   managing, and controlling IETF network slices as abstract network
   topologies, where the network slices are defined in
   [I-D.ietf-teas-ietf-network-slices].

   The defined data model is an interface between customers and
   providers for configurations and state retrievals, so as to support
   network slicing as a service.  Through this model, a customer can
   learn the slicing capabilities and the available resources of the
   provider.  A customer can request or negotiate with a network slicing
   provider to create an instance.  The customer can incrementally
   update its requirements on individual topology elements in the slice
   instance, e.g., adding or removing a node or link, updating desired
   bandwidth of a link, and retrieve the operational states of these
   elements.  With the help of other mechanisms and data models defined
   in IETF, the telemetry information can be published to the customer.

   The YANG model defines technology-agnostic constructs common to
   network slicing at network layers of different technologies, e.g.
   IP/MPLS(-TP), OTN and WDM.  Therefore, this model may be used as a
   common base model on which other network slicing models, such as
   [I-D.ietf-ccamp-yang-otn-slicing], may augments with technology-
   specific constructs.

   As described in Section 3 of
   [I-D.contreras-teas-slice-controller-models], the data model defined
   in this document complements the data model defined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].  In addition to the
   provider's view, the data model defined in this document models the
   Type 2 service defined in [RFC8453].

   The YANG data model in this document conforms to the Network
   Management Datastore Architecture (NMDA) [RFC8342].

1.1.  Tree Diagram

   Tree diagrams used in this document follow the notation defined in
   [RFC8340].

1.2.  Prefixes in Data Node Names

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

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             +==========+=======================+===========+
             | Prefix   | YANG Module           | Reference |
             +==========+=======================+===========+
             | yang     | ietf-yang-types       | [RFC6991] |
             +----------+-----------------------+-----------+
             | inet     | ietf-inet-types       | [RFC6991] |
             +----------+-----------------------+-----------+
             | nt       | ietf-network-topology | [RFC8345] |
             +----------+-----------------------+-----------+
             | nw       | ietf-network-topology | [RFC8345] |
             +----------+-----------------------+-----------+
             | tet      | ietf-te-topology      | [RFC8795] |
             +----------+-----------------------+-----------+
             | te-types | ietf-te-types         | [RFC8776] |
             +----------+-----------------------+-----------+
             | ns-topo  | ietf-ns-topo          | RFCXXXX   |
             +----------+-----------------------+-----------+

             Table 1: Prefixes and Corresponding YANG Modules

   RFC Editor Note: Please replace XXXX with the RFC number assigned to
   this document.  Please remove this note.

2.  Modeling Considerations

   An IETF network slice topology is modeled as network topology defined
   in [RFC8345], with augmentations.  A new network type "network-slice"
   is defined in this document.  When a network topology data instance
   contains the network-slice network type, it represents an instance of
   an IETF network slice topology.

2.1.  Relationships to Related Topology Models

   There are several related YANG data models that have been defined in
   IETF.  Some of these are:

   Network Topology Model: Defined in [RFC8345].

   Network Slicing Model: Defined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].

   OTN Slicing: Defined in [I-D.ietf-ccamp-yang-otn-slicing].

   Figure 1 shows the relationships among these models.  The box of
   dotted lines denotes the model defined in this document.

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        +----------+                 +----------+
        | Network  |                 | Network  |
        | Slice    |                 | Topology +
        | NBI YANG >------+          | Model    |
        | Model    |      |          | RFC 8345 |
        +----+-----+      |          +-----+----+
             |            |                |
             |augments    |references      |augments
             |            |                |
        +----^-----+      |          ......^.....
        | OTN      |      +----------: Network  :
        | Slicing  | augments        : Slice    :
        | Model    >-----------------: Topology :
        |          |                 : Model    :
        +----------+                 ''''''''''''

                       Figure 1: Model Relationships

2.2.  ACTN for Network Slicing

   Since ACTN topology data models are based on the network topology
   model defined in [RFC8345], the augmentations defined in this
   document are effective augmentations to the ACTN topology data
   models, resulting in making the ACTN framework [RFC8453] and data
   models [I-D.ietf-teas-actn-yang] capable of slicing networks with the
   required network characteristics.

3.  Model Applicability

   There are many technologies to achieve network slicing.  The data
   model defined in this document can be used to configure resource-
   based network slices, where the resources of a network slice is
   represented in the form of an abstract network topology, which can
   then be mapped to a network resource partition (NRP) according to the
   scenarios defined in [I-D.ietf-teas-ietf-network-slices].

   Network slices may be abstracted differently depending on the
   requirement contained in the configuration provided by the slice
   customer.  A customer may request a network slice to provide just
   connectivity between specified endpoints, in which case the network
   slice can be represented as a set of endpoint-to-endpoint links, with
   each link formed by an end-to-end tunnel across the underlying
   transport networks.  The resources associated with each link of the
   slice is reserved and commissioned in the underlying physical network
   upon the completion of configuring the network slice and all the
   links are active.

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   Alternatively a network slice can also be represented as an abstract
   topology when the customer requests the slice to share resources
   between multiple endpoints and to use the resources on demand.  The
   abstract topology may consist of virtual nodes and virtual links, and
   their associated resources are reserved but not commissioned across
   the underlying transport networks.  The customer can later commission
   resources within the slice dynamically using the NBI provided by the
   service provider.

   According to [I-D.ietf-teas-ietf-network-slices], the IETF Network
   Slice service customer might ask for some level of control of, e.g.,
   to customize the service paths in a network slice.  The abstract
   topology defined in this draft could serve to enable this capability
   and optimize the resource utilization for network slice connections
   activated on top of the abstract topology.

   In the example shown in Figure 2, two network resource partitions are
   created by the provider to support the two network slice topology
   requests from the customers.  In realizing the network resource
   partitions, node virtualization is used to separate and allocate
   resources in physical devices.  Two virtual routers VR1 and VR2 are
   created over physical router R1, and two virtual routers VR3 and VR4
   are created over physical router R2, respectively.  Each of the
   virtual routers,as a partition of the physical router, takes a
   portion of the resources such as ports and memory in the physical
   router.
   Depending on the requirements and the implementations, they may share
   certain resources such as processors, ASICs, and switch fabric.

   The network slice topology intent requested by the customers is then
   mapped to a corresponding network resource partition.  The provider
   also reports the operational state of the topology, which shows the
   resources that are allocated.  Customers can process the requested
   topology and integrate it with their own topology.

   As an example, Appendix B. shows the JSON encoded data instances of
   the customer topology intent for Network Slice Blue.

       Customer Topology (Merged)          Customer Topology (Merged)
       Network Slice Blue                  Network Slice Red
                            +---+         +---+      +---+
                       -----|R3 |---   ---|R2 |------|R3 |
                      /     +---+         +---+      +---+
      +---+      +---+        ^             ^          ^  \     +---+
   ---|R1 |------|R2 |        |             |          |   -----|R4 |---
      +---+      +---+        |             |          |        +---+
        ^          ^          v             v          v          ^
        |          |        +---+         +---+      +---+        |

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        |          |   -----|VR5|---   ---|VR2|------|VR4|        |
        v          v  /     +---+         +---+      +---+        v
      +---+      +---+                                    \     +---+
   ---|VR1|------|VR3|                                     -----|VR6|---
      +---+      +---+                                          +---+
       Customer Topology (Intended)        Customer Topology (Intended)
       Network Slice Blue                  Network Slice Red

                                 Customers
   ---------------------------------------------------------------------
                                 Provider

        Customized Topology (Network Resouce Partition)
        Provider Network with Virtual Devices

        Network Slice Blue: VR1, VR3, VR5         +---+
                                        ----------|VR5|------
                                       /          +---+
                    +---+         +---+
              ------|VR1|---------|VR3|
                    +---+         +---+
              ------|VR2|---------|VR4|
                    +---+         +---+
                                       \          +---+
                                        ----------|VR6|------
        Network Slice Red: VR2, VR4, VR6          +---+

                                 Virtual Devices
   ---------------------------------------------------------------------
                                 Physical Devices

        Native Topology
        Provider Network with Physical Devices
                                                  +---+
                                        ----------|R3 |------
                                       /          +---+
                    +---+         +---+
              ======|R1 |=========|R2 |
                    +---+         +---+
                                       \          +---+
                                        ----------|R4 |------
                                                  +---+

       Figure 2: Network Slicing Topologies for Virtualization

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4.  YANG Model Overview

   The following constructs and attributes are defined within the YANG
   model:

   *  Network topology, which represent set of shared, reserved
      resources organized as a virtual topology between all of the
      endpoints.  A customer could use such network topology to define
      detailed connectivity path traversing the topology, and allow
      sharing of resources between its multiple endpoint pairs.

   *  Service-level objectives (SLOs) associated with different objects,
      including node, link, termination point of the topology.

5.  Model Tree Structure

   module: ietf-ns-topo

     augment /nw:networks/nw:network/nw:network-types:
       +--rw network-slice!
     augment /nw:networks/nw:network:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         leafref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?              string
                +--rw metric-bounds
                |  +--rw metric-bound* [metric-type]
                |     +--rw metric-type          identityref
                |     +--rw metric-unit          string
                |     +--rw value-description?   string
                |     +--rw percentile-value?    percentile
                |     +--rw bound?               uint64
                +--rw security*                 identityref
                +--rw isolation?                identityref
                +--rw max-occupancy-level?      uint8
                +--rw mtu?                      uint16
                +--rw steering-constraints
                |  +--rw path-constraints
                |  +--rw service-function
                |  +--rw disjointness?
                |          te-types:te-path-disjointness
                +--rw optimization-criterion?   identityref
                +--rw resize-requirement?       identityref
                +--rw service-info?             string
     augment /nw:networks/nw:network/nw:node:
       +--rw (slo-sle-policy)?

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          +--:(standard)
          |  +--rw slo-sle-template?         leafref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?              string
                +--rw metric-bounds
                |  +--rw metric-bound* [metric-type]
                |     +--rw metric-type          identityref
                |     +--rw metric-unit          string
                |     +--rw value-description?   string
                |     +--rw percentile-value?    percentile
                |     +--rw bound?               uint64
                +--rw security*                 identityref
                +--rw isolation?                identityref
                +--rw max-occupancy-level?      uint8
                +--rw mtu?                      uint16
                +--rw steering-constraints
                |  +--rw path-constraints
                |  +--rw service-function
                |  +--rw disjointness?
                |          te-types:te-path-disjointness
                +--rw optimization-criterion?   identityref
                +--rw resize-requirement?       identityref
                +--rw service-info?             string
     augment /nw:networks/nw:network/nw:node/nt:termination-point:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         leafref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?              string
                +--rw metric-bounds
                |  +--rw metric-bound* [metric-type]
                |     +--rw metric-type          identityref
                |     +--rw metric-unit          string
                |     +--rw value-description?   string
                |     +--rw percentile-value?    percentile
                |     +--rw bound?               uint64
                +--rw security*                 identityref
                +--rw isolation?                identityref
                +--rw max-occupancy-level?      uint8
                +--rw mtu?                      uint16
                +--rw steering-constraints
                |  +--rw path-constraints
                |  +--rw service-function
                +--rw optimization-criterion?   identityref
                +--rw resize-requirement?       identityref
                +--rw service-info?             string

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     augment /nw:networks/nw:network/nt:link:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         leafref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?              string
                +--rw metric-bounds
                |  +--rw metric-bound* [metric-type]
                |     +--rw metric-type          identityref
                |     +--rw metric-unit          string
                |     +--rw value-description?   string
                |     +--rw percentile-value?    percentile
                |     +--rw bound?               uint64
                +--rw security*                 identityref
                +--rw isolation?                identityref
                +--rw max-occupancy-level?      uint8
                +--rw mtu?                      uint16
                +--rw steering-constraints
                |  +--rw path-constraints
                |  +--rw service-function
                |  +--rw disjointness?
                |          te-types:te-path-disjointness
                +--rw optimization-criterion?   identityref
                +--rw resize-requirement?       identityref
                +--rw service-info?             string

             Figure 3: Tree diagram for network slice topology

6.  YANG Modules

   <CODE BEGINS> file "ietf-ns-topo@2023-03-11.yang"
      module ietf-ns-topo {
        yang-version 1.1;
        namespace
          "urn:ietf:params:xml:ns:yang:ietf-ns-topo";
        prefix "ns-topo";

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

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        import ietf-te-types {
          prefix "te-types";
          reference
            "RFC 8776: Traffic Engineering Common YANG Types";
        }

        import ietf-network-slice-service {
          prefix "ietf-nss";
          reference
            "draft-ietf-teas-ietf-network-slice-nbi-yang-00:
             IETF Network Slice Service YANG Model";
        }

        organization
          "IETF CCAMP Working Group";
        contact
          "WG Web: <http://tools.ietf.org/wg/ccamp/>
           WG List: <mailto:ccamp@ietf.org>

           Editor: Xufeng Liu
                   <mailto:xufeng.liu.ietf@gmail.com>

           Editor: Italo Busi
                   <mailto:italo.busi@huawei.com>

           Editor: Aihua Guo
                   <mailto:aihuaguo.ietf@gmail.com>

           Editor: Sergio Belotti
                   <mailto:sergio.belotti@nokia.com>

           Editor: Luis M. Contreras
                   <mailto:luismiguel.contrerasmurillo@telefonica.com>";

        description
          "This module defines a base YANG data model for configuring
           generic network slices in optical transport networks, e.g.,
           Optical Transport Network (OTN).

           The model fully conforms to the Network Management Datastore
           Architecture (NMDA).

           Copyright (c) 2023 IETF Trust and the persons
           identified as authors of the code.  All rights reserved.

           Redistribution and use in source and binary forms, with
           or without modification, is permitted pursuant to, and
           subject to the license terms contained in, the Revised

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           BSD License set forth in Section 4.c of the IETF Trust's
           Legal Provisions Relating to IETF Documents
           (https://trustee.ietf.org/license-info).

           This version of this YANG module is part of RFC XXXX; see
           the RFC itself for full legal notices.";

        revision 2023-03-11 {
          description "Initial revision";
          reference
            "RFC XXXX: IETF Network Slice Topology YANG Data Model";
        }

        /*
         * Identities
         */
        identity resize-option {
          description
            "Base identity for link or connectivity resizing options";
        }

        identity resize-none {
          base resize-option;
          description
            "Not resizable";
        }

        identity resize-with-hit {
          base resize-option;
          description
            "Resizable with traffic hits";
        }

        identity resize-hitless {
          base resize-option;
          description
            "Hitless resizable";
        }

        /*
         * Groupings
         */

        grouping ns-topo-slo-sle-policy {
          description
            "Policy grouping for Transport Network Slices.";

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          leaf optimization-criterion {
              type identityref {
                base te-types:objective-function-type;
              }
              description
                "Optimization criterion applied to this topology.";
          }
          leaf resize-requirement {
            type identityref {
              base resize-option;
            }
            description
              "Indicates resizing requirments";
          }
          leaf service-info {
            type string;
            description
              "Describe type of services running on the slice. It may be
               useful information to help the slice controller to
               optimize resource allocation";
          }
        }

        grouping ns-topo-steering-constraints {
          description
            "Policy grouping for specifying steering constraints for
             Transport Network Slices.";

          leaf disjointness {
            type te-types:te-path-disjointness;
            description
              "Indicate the level of disjointness for slice
               resources.";
          }
        }

        /*
         * Augmented data nodes
         */
        /* network type augments */
        augment "/nw:networks/nw:network/nw:network-types" {
          description
            "Defines the Network Slice topology type.";
          container network-slice {
            presence "Indicates Network Slice topology";
            description
              "Its presence identifies the Network Slice type.";
          }

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        }

        /* network topology augments */
        augment "/nw:networks/nw:network" {
          when "./nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment topology configuration and state.";
          uses ietf-nss:service-slo-sle-policy;
        }

        augment "/nw:networks/nw:network" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" {
          when "../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment topology configuration and state.";
          uses ns-topo-slo-sle-policy;
        }

        augment "/nw:networks/nw:network" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" +
          "/ns-topo:steering-constraints" {
          when "../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment topology configuration and state.";
          uses ns-topo-steering-constraints;
        }

        /* network node augments */
        augment "/nw:networks/nw:network/nw:node" {
          when "../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment node configuration and state.";
          uses ietf-nss:service-slo-sle-policy;
        }

        augment "/nw:networks/nw:network/nw:node" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" {
          when "../../nw:network-types/ns-topo:network-slice" {

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            description "Augment only for Network Slice topology.";
          }
          description "Augment node configuration and state.";
          uses ns-topo-slo-sle-policy;
        }

        augment "/nw:networks/nw:network/nw:node" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" +
          "/ns-topo:steering-constraints" {
          when "../../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description
          "Augment IETF network slice services to include steering
             constraints for nodes.";
          uses ns-topo-steering-constraints;
        }

        /* network node's termination point augments */
        augment "/nw:networks/nw:network/nw:node" +
                "/nt:termination-point" {
          when "../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment node configuration and state.";

        uses ietf-nss:service-slo-sle-policy;
        }

        augment "/nw:networks/nw:network/nw:node" +
                "/nt:termination-point" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" {
          when "../../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment node configuration and state.";

          uses ns-topo-slo-sle-policy;
        }

        /* network link augments */
        augment "/nw:networks/nw:network/nt:link" {
          when "../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";

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          }
          description "Augment link configuration and state.";
          uses ietf-nss:service-slo-sle-policy;
        }

        augment "/nw:networks/nw:network/nt:link" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" {
          when "../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description "Augment link configuration and state.";
          uses ns-topo-slo-sle-policy;
        }

        augment "/nw:networks/nw:network/nt:link" +
                "/ns-topo:slo-sle-policy" +
                "/ns-topo:custom" +
                "/ns-topo:service-slo-sle-policy" +
                "/ns-topo:steering-constraints" {
          when "../../../nw:network-types/ns-topo:network-slice" {
            description "Augment only for Network Slice topology.";
          }
          description
          "Augment IETF network slice services to include steering
             constraints for links within a resource-based transport
             network slice.";
          uses ns-topo-steering-constraints;
        }
      }
   <CODE ENDS>

              Figure 4: YANG model for network slice topology

7.  Manageability Considerations

   To ensure the security and controllability of physical resource
   isolation, slice-based independent operation and management are
   required to achieve management isolation.  Each network slice
   typically requires dedicated accounts, permissions, and resources for
   independent access and O&M.  This mechanism is to guarantee the
   information isolation among slice tenants and to avoid resource
   conflicts.  The access to slice management functions will only be
   permitted after successful security checks.

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8.  Security Considerations

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

   The NETCONF access control model [RFC8341] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  Considerations in Section 8 of
   [RFC8795] are also applicable to their subtrees in the module defined
   in this document.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  Considerations in Section 8 of
   [RFC8795] are also applicable to their subtrees in the module defined
   in this document.

9.  IANA Considerations

   It is proposed to IANA to assign new URIs from the "IETF XML
   Registry" [RFC3688] as follows:

      URI: urn:ietf:params:xml:ns:yang:ietf-ns-topo
      Registrant Contact: The IESG
      XML: N/A; the requested URI is an XML namespace.

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

      name: ietf-ns-topo
      namespace: urn:ietf:params:xml:ns:yang:ietf-ns-topo
      prefix: ns-topo
      reference: RFC XXXX

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10.  References

10.1.  Normative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

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

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

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

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

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

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

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

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

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

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

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

   [RFC8776]  Saad, T., Gandhi, R., Liu, X., Beeram, V., and I. Bryskin,
              "Common YANG Data Types for Traffic Engineering",
              RFC 8776, DOI 10.17487/RFC8776, June 2020,
              <https://www.rfc-editor.org/info/rfc8776>.

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

10.2.  Informative References

   [I-D.contreras-teas-slice-controller-models]
              Contreras, L. M., Rokui, R., Tantsura, J., Wu, B., Liu,
              X., Dhody, D., and S. Belotti, "IETF Network Slice
              Controller and its associated data models", Work in
              Progress, Internet-Draft, draft-contreras-teas-slice-
              controller-models-04, 24 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-contreras-
              teas-slice-controller-models-04>.

   [I-D.ietf-ccamp-yang-otn-slicing]
              Guo, A., Contreras, L. M., Belotti, S., Rokui, R., Xu, Y.,
              Zhao, Y., and X. Liu, "Framework and Data Model for OTN
              Network Slicing", Work in Progress, Internet-Draft, draft-
              ietf-ccamp-yang-otn-slicing-03, 24 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ccamp-
              yang-otn-slicing-03>.

   [I-D.ietf-teas-actn-yang]
              Lee, Y., Zheng, H., Ceccarelli, D., Yoon, B. Y., and S.
              Belotti, "Applicability of YANG models for Abstraction and
              Control of Traffic Engineered Networks", Work in Progress,

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              Internet-Draft, draft-ietf-teas-actn-yang-11, 7 March
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              teas-actn-yang-11>.

   [I-D.ietf-teas-ietf-network-slice-nbi-yang]
              Wu, B., Dhody, D., Rokui, R., Saad, T., Han, L., and J.
              Mullooly, "A YANG Data Model for the IETF Network Slice
              Service", Work in Progress, Internet-Draft, draft-ietf-
              teas-ietf-network-slice-nbi-yang-04, 13 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slice-nbi-yang-04>.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
              K., Contreras, L. M., and J. Tantsura, "A Framework for
              IETF Network Slices", Work in Progress, Internet-Draft,
              draft-ietf-teas-ietf-network-slices-19, 21 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slices-19>.

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

Appendix A.  Acknowledgments

   The TEAS Network Slicing Design Team (NSDT) members included Aijun
   Wang, Dong Jie, Eric Gray, Jari Arkko, Jeff Tantsura, John E Drake,
   Luis M.  Contreras, Rakesh Gandhi, Ran Chen, Reza Rokui, Ricard
   Vilalta, Ron Bonica, Sergio Belotti, Tomonobu Niwa, Xuesong Geng, and
   Xufeng Liu.

Appendix B.  Data Tree for the Example in Section 3.1

B.1.  Native Topology

   This section contains an example of an instance data tree in the JSON
   encoding [RFC7951].  The example instantiates "ietf-network" for the
   topology of Network Slice Blue depicted in Figure 2.

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

   {
     "ietf-network:networks": {
       "network": [
         {
           "network-id": "example-customized-blue-topology",

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           "network-types": {
             "ietf-ns-topo:network-slice": {
             }
           },
           "node": [
             {
               "node-id": "VR1",
               "ietf-ns-topo:service-slo-sle-policy": {
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated",
                 "resize-requirement": "resize-hitless"
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1-0-1"
                 },
                 {
                   "tp-id": "1-3-1"
                 }
               ]
             },
             {
               "node-id": "VR3",
               "ietf-ns-topo:service-slo-sle-policy": {
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-shared",
                 "resize-requirement": "resize-hitless"
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "3-1-1"
                 },
                 {
                   "tp-id": "3-5-1"
                 }
               ]
             },
             {
               "node-id": "VR5",
               "ietf-ns-topo:service-slo-sle-policy": {
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-shared",
                 "resize-requirement": "resize-hitless"
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "5-3-1"
                 },

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                 {
                   "tp-id": "5-0-1"
                 }
               ]
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "VR1,1-0-1,,",
               "source": {
                 "source-node": "VR1",
                 "source-tp": "1-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 60
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-shared"
               }
             },
             {
               "link-id": ",,VR1,1-0-1",
               "destination": {
                 "dest-node": "VR1",
                 "dest-tp": "1-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 60
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }

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             },
             {
               "link-id": "VR1,1-3-1,VR3,3-1-1",
               "source": {
                 "source-node": "VR1",
                 "source-tp": "1-3-1"
               },
               "destination": {
                 "dest-node": "VR3",
                 "dest-tp": "3-1-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 30
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }
             },
             {
               "link-id": "VR3,3-1-1,VR1,1-3-1",
               "source": {
                 "source-node": "VR3",
                 "source-tp": "3-1-1"
               },
               "destination": {
                 "dest-node": "R1",
                 "dest-tp": "1-3-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 30
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\

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   tion-dedicated"
               }
             },
             {
               "link-id": "VR3,3-5-1,VR5,5-3-1",
               "source": {
                 "source-node": "VR3",
                 "source-tp": "3-5-1"
               },
               "destination": {
                 "dest-node": "VR5",
                 "dest-tp": "5-3-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 35
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }
             },
             {
               "link-id": "VR5,5-3-1,VR3,3-5-1",
               "source": {
                 "source-node": "VR5",
                 "source-tp": "5-3-1"
               },
               "destination": {
                 "dest-node": "VR3",
                 "dest-tp": "3-5-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 35
                     }
                   ]

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                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }
             },
             {
               "link-id": "VR5,5-0-1,,",
               "source": {
                 "source-node": "VR5",
                 "source-tp": "5-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 25
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }
             },
             {
               "link-id": ",,VR5,5-0-1",
               "destination": {
                 "dest-node": "VR5",
                 "dest-tp": "5-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "metric-bounds": {
                   "metric-bound": [
                     {
                       "metric-type": "ietf-network-slice-service:servi\
   ce-slo-two-way-delay",
                       "metric-unit": "ms",
                       "bound": 25
                     }
                   ]
                 },
                 "isolation": "ietf-network-slice-service:service-isola\
   tion-dedicated"
               }
             }
           ],

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           "ietf-ns-topo:service-slo-sle-policy": {
             "isolation": "ietf-network-slice-service:service-isolation\
   -dedicated",
             "optimization-criterion": "ietf-te-types:of-minimize-cost-\
   path"
           }
         }
       ]
     }
   }

Authors' Addresses

   Xufeng Liu
   IBM Corporation
   Email: xufeng.liu.ietf@gmail.com

   Jeff Tantsura
   Microsoft
   Email: jefftant.ietf@gmail.com

   Igor Bryskin
   Individual
   Email: i_bryskin@yahoo.com

   Luis M. Contreras
   Telefonica
   Email: luismiguel.contrerasmurillo@telefonica.com

   Qin Wu
   Huawei
   Email: bill.wu@huawei.com

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

   Reza Rokui
   Ciena
   Email: rrokui@ciena.com

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   Aihua Guo
   Futurewei
   Email: aihuaguo.ietf@gmail.com

   Italo Busi
   Huawei
   Email: italo.busi@huawei.com

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