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IETF Network Slice Topology YANG Data Model
draft-liu-teas-transport-network-slice-yang-10

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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 2024-07-07 (Latest revision 2024-03-01)
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draft-liu-teas-transport-network-slice-yang-10
TEAS Working Group                                                X. Liu
Internet-Draft                                                 Alef Edge
Intended status: Standards Track                             J. Tantsura
Expires: 8 January 2025                                        Microsoft
                                                              I. Bryskin
                                                              Individual
                                                          L.M. Contreras
                                                              Telefonica
                                                                   Q. Wu
                                                                  Huawei
                                                              S. Belotti
                                                                   Nokia
                                                                R. Rokui
                                                                   Ciena
                                                                  A. Guo
                                                               Futurewei
                                                                 I. Busi
                                                                  Huawei
                                                             7 July 2024

              IETF Network Slice Topology YANG Data Model
             draft-liu-teas-transport-network-slice-yang-10

Abstract

   An RFC 9543 network slice customer may utilize intent-based
   topologies to express resource reservation intentions within the
   provider's network.  These customer-defined intent topologies allow
   customers to request shared resources for future connections that can
   be flexibly allocated and customized.  Additionally, they provide an
   extensive level of control over underlay service paths within the
   network slice.

   This document describes a YANG data model for expressing customer
   intent topologies which can be used to enhance the RFC 9543 Network
   Slice Services in specific use cases, such as Network wholesale
   scenarios, where both topology and connectivity intents need to be
   expressed.

Status of This Memo

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

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   This Internet-Draft will expire on 8 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Use Case Applicability  . . . . . . . . . . . . . . . . .   5
       1.1.1.  Use Case 1 : Multi-tenancy in Network Wholesaling . .   5
       1.1.2.  Use Case 2 :  . . . . . . . . . . . . . . . . . . . .   5
     1.2.  Terminologies and Notations . . . . . . . . . . . . . . .   6
     1.3.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   7
     1.4.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   7
   2.  Modeling Considerations . . . . . . . . . . . . . . . . . . .   7
     2.1.  Relationship with Traffic Engineering (TE)-based
           Topology  . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Relationship with Service Attachment Point (SAP)
           Topology  . . . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  Relationship with ACTN Virtual Network (VN) . . . . . . .   8
       2.3.1.  Consideration on Reusing ACTN VN for Network
               Slicing . . . . . . . . . . . . . . . . . . . . . . .   9
     2.4.  Data Model Relationship . . . . . . . . . . . . . . . . .  10
   3.  Model Applicability . . . . . . . . . . . . . . . . . . . . .  11
   4.  YANG Model Overview . . . . . . . . . . . . . . . . . . . . .  13
   5.  Model Tree Structure  . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Network Slice Topology Model Tree Structure . . . . . . .  14

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     5.2.  Network Slice Underlay Path Model Tree Structure  . . . .  16
   6.  YANG Modules  . . . . . . . . . . . . . . . . . . . . . . . .  17
     6.1.  YANG Module for Network Slice Topology  . . . . . . . . .  17
     6.2.  YANG Module for Network Slice Underlay Path . . . . . . .  20
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  24
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     10.2.  Informative References . . . . . . . . . . . . . . . . .  27
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  29
   Appendix B.  Data Tree for the Example in Section 3 . . . . . . .  29
     B.1.  Native Topology . . . . . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36

1.  Introduction

   Network service providers utilize topologies to convey controlled
   information about their networks, such as bandwidth availability and
   connectivity, with customers, to facilitates customer service
   requests.  Customers can also define intent-based topologies to
   streamline their internal operations.  When requesting provider
   support for such custom topologies, they are considered as customer
   intent topologies.

   In the context of network slicing, customer intent topologies enables
   customers to express resource reservation preferences.  These
   topologies allow flexible configuration and activation of network
   slices on demand.  By providing full control over resource allocation
   timing and methods, customer intent topologies ensure that resources
   are consistently available.  Moreover, the resources reserved via
   customer intent topologies can be shared across network slices
   created at different times or between different connectivity
   constructs within the same slice.  Compared to network slices with
   dedicated full-mesh connectivity constructs between endpoints,
   network slices utilizing customer intent topologies can reduce
   overall resource requirements, offering significant economic benefits
   to the customer.

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   Consider a hub-and-spoke network slice scenario where multiple
   customer spoke sites dynamically connect to a central hub site,
   sharing available bandwidth.  By designing a customer intent topology
   with two virtual nodes - one representing all the spoke sites and the
   other representing the hub site - connected via a shared link, we
   proactively reserve resources for the shared connection.  This
   ensures that bandwidth is readily available whenever the customer
   requires it.  In contrast, achieving equivalent bandwidth assurance
   through individual dedicated connectivity constructs would
   necessitate creating separate links between each spoke and the hub,
   which would lead to substantial bandwidth inefficiency.

   Customer intent topology complements connectivity-based network
   slicing by providing customers a mechanism to specify additional
   underlay service paths to gain extensive control over specific or all
   connectivity constructs within the network slice, as outlined in
   [RFC9543].

   A customer intent topology is defined within the customer's context.
   It can include pure customer information or may also refer to network
   resources identifiable within the provider's context.  There is a
   minimum level of a-prior shared knowledge between the customer and
   the provider, and this is the same information needed to supported
   connectivity-based network slice services as desdribed in [RFC9543].
   The provider's responsibility lies in understanding the customer
   intent topology request and translating that into suitable
   realization within their domain.

   This document introduces a YANG data model, based on [RFC7950], for
   configuring customer intent topologies.  The YANG model extends the
   existing data model from [RFC8345], allowing customers to express
   desired service-level objectives (SLOs) and service-level
   expectations (SLEs) across different elements within the customer
   intent topology.

   The defined data model serves as an interface between customers and
   providers, enabling configurations and state retrievals for network
   slicing as a service.  Customers can use this model to request or
   negotiate the creation of network slice instances.  Additionally,
   they can incrementally adjust requirements for individual topology
   elements within the slice - for instance, adding or removing nodes or
   links, updating link bandwidth - and retrieve operational states.
   Leveraging other IETF mechanisms and data models, telemetry
   information can also be convey to the customer.

   The YANG model encompasses constructs that are independent of
   specific technologies, accommodating network slicing across diverse
   layers (including IP/MPLS, MPLS-TP, OTN, and WDM optical).  As a

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   result, this model serves as a foundational framework upon which
   technology-specific network slicing models - such as
   [I-D.ietf-ccamp-yang-otn-slicing] - can be developed.

   Section 3 of [I-D.contreras-teas-slice-controller-models] outlines
   that the use of customer intent topologies and resource reservation
   control is optional within network slicing.  These features
   complement the data model defined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].

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

1.1.  Use Case Applicability

   In Traffic Engineering (TE)-enabled networks like Layer-0/1 transport
   (OTN, MW, DWDM), customer intent topology is useful for routing RFC
   9543 network slices across varied paths with TE constraints.  Thus,
   most of the use cases for which this model target are transport
   oriented.  Nonetheless, it is also relevant to non-transport networks
   like IP/MPLS, where customers may use intent topologies to influence
   the realization of network slices.  These intents help build the
   logical view of the desired RFC 9543 Network Slice service (and its
   constituent parts), aiding providers in fulfilling slice requests and
   defining the service instantiation.

1.1.1.  Use Case 1 : Multi-tenancy in Network Wholesaling

   A typical use case in which the customer intent topology is essential
   is the wholesale multi-tenant case.  Here, customer C may acquire a
   network slice from provider P and resell sub-slices to other
   customers/tenants.  The creation of these sub-slices within C's slice
   necessitates specifying a topology intent - reflecting the topology
   of C's purchased slice - as a key input parameter.

1.1.2.  Use Case 2 :

   The current expression of slice requests leveraging on
   [I-D.draft-ietf-teas-ietf-network-slice-nbi-yang] allows the customer
   to request distinct connectivity constructs as part of the same
   Network Resource Partition (NRP).  The topology provided by the
   customer could imply different NRPs, instead.

   As an another example, from realization perspective even on the same
   NRP, a slice requests leveraging on
   [I-D.draft-ietf-teas-ietf-network-slice-nbi-yang] without topology
   differentiation could imply the realization of all the connectivity
   constructs on the same manner.  For instance, implementing all of

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   them within the same VRF in a L3VPN.  The usage of the topological
   views can help the provider to infer differentiated realization of
   some of the connectivity constructs, for instance, by implementing
   them on different VRFs.  This can have operational advantages (e.g.,
   adding new nodes / SDPs could affect / imply limit the necessary VRF
   reconfiguration only to the one including affected connectivity
   constructs).

   Finally, by using customer intent topology it can be easier for the
   slice provider to infer different technologies for sets of
   connectivity constructs of every topology segment (e.g., IP/MPLS,
   optical, microwave, etc).

1.2.  Terminologies and Notations

   The following terminologies for describing network slices are defined
   in [RFC9543] and are not redefined herein.

   *  Network Slice (NS)

   *  Network Slice Customer

   *  Network Slice Service Provider

   *  Network Slice Controller (NSC)

   *  Network Resource Partition (NRP)

   The following terms are defined and used in this document.

   *  Customer Intent Topology: A topology defined by the customer and
      provided as input to the network slice service provider
      (specifically, the Network Slice Controller or NSC).  It
      represents the customer's desired network topology.

   *  Abstract Topology: A topology exposed to the customer by the
      network slice service provider prior to the creation of network
      slices.  The provider may optionally uses an abstract topology to
      expose useful information, such as available resources to the
      customer, which can facilitate the build-up of customer intent
      topologies by the customer.

   *  NRP Topology: A topology internal to the NSC to facilitate the
      mapping of network slices to underlying network resources.

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1.3.  Tree Diagram

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

1.4.  Prefixes in Data Node Names

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

           +==========+============================+===========+
           | Prefix   | YANG Module                | Reference |
           +==========+============================+===========+
           | 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] |
           +----------+----------------------------+-----------+
           | ns-path  | ietf-ns-underlay-path      | RFC XXXX  |
           +----------+----------------------------+-----------+
           | ns-topo  | ietf-ns-topo               | RFC XXXX  |
           +----------+----------------------------+-----------+
           | ietf-nss | ietf-network-slice-service | RFC YYYY  |
           +----------+----------------------------+-----------+

              Table 1: Prefixes and Corresponding YANG Modules

   RFC Editor Note: Please replace XXXX with the RFC number assigned to
   this document.  Please replace YYYY with the RFC number assigned to
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].  Please remove this
   note.

2.  Modeling Considerations

   A network slice topology is a cusomer intent topology 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 a network slice topology.

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   This data model augments the network topology model by incorporating
   intent-based Service-Level Objectives (SLOs) and Service-Level
   Expectations (SLEs).  These apply to various components within the
   customer intent topology, including nodes, links, and termination
   points (TPs).

2.1.  Relationship with Traffic Engineering (TE)-based Topology

   The model defined in this document can be combined through multi-
   inheritance with other topology data models, such as Traffic
   Engineering (TE) topologies described in [RFC8795] or Optical
   Transport Network (OTN) topologies described in
   [I-D.ietf-ccamp-otn-topo-yang].  This flexibility allows the creation
   of technology-specific customer intent topologies tailored to
   specific network requirements.

2.2.  Relationship with Service Attachment Point (SAP) Topology

   [RFC9408] introduces a YANG data model that represents an abstract
   view of the provider network topology.  This model includes a list of
   Service Attachment Points (SAPs), where customer services can be
   connected.  The SAP topology is made visible to customers by the
   provider before configuring network slice services.  In contrast, the
   customer intent topology described in this document captures a
   customer's intentions, while the provider acts as the recipient of
   these intents.  As a result, these two models serve distinct
   purposes.

   In certain scenarios, customers can leverage the SAP topology to
   construct customer intent topologies to aid in the realization of
   their intended network configurations.  For instance, within a node
   of a customer intent topology, the Link Termination Point (LTP)
   identifiers may explicitly reference their supporting Termination
   Points (TPs), which correspond to the SAPs exposed in the provider's
   SAP model.  However, the specifics of this mechanism fall beyond the
   scope of this document.

2.3.  Relationship with ACTN Virtual Network (VN)

   [RFC8453] and [I-D.ietf-teas-actn-vn-yang] introduce the concept of a
   Virtual Network (VN), which can be presented to customers.  These VNs
   are constructed from abstractions of the underlying networks,
   specifically those that are traffic-engineering (TE) capable.  While
   VNs share similarities with RFC 9543 network slicing, they operate
   under the assumption of TE-capable networks.

   Two distinct types of VNs are defined:

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   *  Type 1 VN: Modeled as a single abstract node with edge-to-edge
      connectivity between customer endpoints.

   *  Type 2 VN: Modeled as a single abstract node with an underlay
      topology, allowing configuration of intended underlay paths for
      connections within the single abstract node.

   The topologies for VNs, including both the single-node abstract
   topology and the underlay topology, can either be mutually agreed
   upon between the Customer Network Controller (CNC) and the Multi-
   Domain Service Coordinator (MDSC) prior to VN creation, or they can
   be created as part of VN instantiation by the customer.

   In the context of network slicing, [RFC9543] defines a network slice
   service as a collection of connectivity constructs between pairs of
   Service Demarcation Points (SDPs).  This concept closely resembles
   the Type 1 VN, which is implemented as a single abstract node.

   [I-D.ietf-teas-ietf-network-slice-nbi-yang] further elaborates on
   network slices by incorporating references to a customer intent
   topology based on [RFC8345].  This approach aligns with the ACTN Type
   2 VN, although without specifying the explicit use of such a
   topology.

   Consequently, the data model defined in this document serves as a
   complementary option to the data model outlined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].  It empowers customers
   to define a customized intent topology specifically tailored for
   their network slices.

2.3.1.  Consideration on Reusing ACTN VN for Network Slicing

   The ACTN VN model provides a self-consistent method for expressing
   connectivity intents (Type 1 VN) and optional path constraints (Type
   2 VN) using TE metrics and TE objective functions defined in
   [RFC8795].  Type 2 VN path constraints rely on Type 1 VN for
   expressing connectivity intents.

   On the other hand, RFC9543 network slice services provide
   connectivity intents equivalent to Type 1 VN, using SLO and SLE
   attributes in a technology-agnostic manner not tied to TE
   technologies.  This distinction is detailed in Appendix D of
   [I-D.ietf-teas-ietf-network-slice-nbi-yang].

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   Reusing the Type 2 VN for defining customer intent topologies
   alongside the RFC9543 network slice service model would result in
   duplicated information for connectivity intents (SDPs and
   connectivity-constructs vs. LTPs and connectivity matrices), and
   additionally, would bind the network slice solution to TE
   technologies.

   The proposed models in this draft aim to deliver a solution
   equivalent to Type 2 VN within the context of network slicing.  This
   complements the existing solution outlined in
   [I-D.ietf-teas-ietf-network-slice-nbi-yang], while ensuring
   consistency.

2.4.  Data Model Relationship

   The data model presented in this document builds upon the generic
   network topology model defined in [RFC8345].  Other data models,
   including OTN Slicing (as defined in
   [I-D.ietf-ccamp-yang-otn-slicing]), can leverage this extended model.

   The relationship of the related data models is illustrated in
   Figure 1.  Within this diagram, the box outlined with dotted lines
   specifically represents the data model defined in this document.

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

                        Figure 1: Model Relationship

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3.  Model Applicability

   Network slicing can be achieved through various technologies.  The
   data model defined in this document serves as a means for configuring
   resource reservation-based network slices.  In this approach,
   resources for network slices are reserved and represented using a
   customer intent topology.  This topology can then be mapped to a
   network resource partition (NRP) and realized based on the scenarios
   outlined in [RFC9543].

   Network slices can be abstracted in various ways, depending on the
   specific requirements of the network slice customer.  For instance, a
   customer might request a network slice with direct connectivity
   between pairs of Service Demarcation Points (SDPs).  Within this
   network slice, each connectivity construct could be further supported
   by an end-to-end tunnel that follows a specific path defined in a
   customer intent topology, which the customer provides.  The resources
   associated with each link are immediately commissioned during the
   network slice configuration process.

   Alternatively, a customer can request resources to be reserved for
   potential network slices through a customer intent topology.  These
   reserved resources are not immediately commissioned at the time of
   the request.  Instead, they serve as a pool of allocated resources
   that the customer can utilize to build network slices in the future.
   By adopting this approach, customers gain the flexibility to share
   resources across multiple endpoints and activate them on demand.

   In the example shown in Figure 2, two topology intents named as
   Network Slice Blue and Network Slice Red, are created by separate
   customers and delivered to the network slice service provider.  The
   provider maps the two intents to corresponding network resource
   partitions (NRPs) internally.  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.

   A network slice customer has the capability to configure customer
   intent topologies without needing any prior knowledge of the
   provider's network or resource availability.  However, this approach
   could potentially create challenges for the provider in understanding
   and realizing the intended topology.

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   Alternatively, the provider can choose to describe the available
   resources and capabilities in the form of an abstract topology, which
   is then exposed to the customer before network slice requests.  By
   doing so, the provider empowers the customer to build their
   customized intent topologies based on this pre-exposed information.
   This approach streamlines the process, minimizing unnecessary
   negotiations between the customer and the provider.  The process and
   the data models for the provider to expose abstract topologies are
   outside the scope of this document.

   The provider communicates the operational state of the customer
   intent topology, reflecting the allocated resources that result from
   negotiations between the customer and the provider.  Subsequently,
   customers can process the requested customer intent topology and
   seamlessly integrate it into their own network topology.
   Importantly, this relationship between the customer and provider can
   be recursive.  For instance, a customer who requests network slices
   can also serve as a provider, offering network slice services to its
   own customers further up the hierarchy.

   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          ^
        |          |        +---+         +---+      +---+        |
        |          |   -----|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

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        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

4.  YANG Model Overview

   The YANG data model in this draft consists of two modules for
   flexible use and augmentation: - The first YANG module defines a
   customer intent topology, with SLO and SLE associated with the
   topological constructs.  - The second YANG module extends the YANG
   model defined in [I-D.ietf-teas-ietf-network-slice-nbi-yang] by
   adding underlay paths to the connectivity constructs.

   Within the YANG model, the following constructs and attributes are
   defined: - Network Topology: This represents a set of shared and
   reserved resources, organized as a virtual topology connecting all
   endpoints.  Customers can utilize this network topology to define
   detailed connectivity paths traversing the topology.  Additionally,
   it enables resource sharing between different endpoints.

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   *  Service-Level Objectives (SLOs): These objectives are associated
      with various objects within the topology, including nodes, links,
      and termination points.  SLOs provide guidelines for achieving
      specific performance or quality targets.

5.  Model Tree Structure

5.1.  Network Slice Topology 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?         slice-template-ref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?   string
                +--rw slo-policy
                |  +--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 availability?   identityref
                |  +--rw mtu?            uint32
                +--rw sle-policy
                   +--rw security*              identityref
                   +--rw isolation*             identityref
                   +--rw max-occupancy-level?   uint8
                   +--rw path-constraints
                      +--rw service-functions
                      +--rw diversity
                         +--rw diversity-type?
                                 te-types:te-path-disjointness
     augment /nw:networks/nw:network/nw:node:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         slice-template-ref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?   string
                +--rw slo-policy
                |  +--rw metric-bound* [metric-type]
                |  |  +--rw metric-type          identityref

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                |  |  +--rw metric-unit          string
                |  |  +--rw value-description?   string
                |  |  +--rw percentile-value?    percentile
                |  |  +--rw bound?               uint64
                |  +--rw availability?   identityref
                |  +--rw mtu?            uint32
                +--rw sle-policy
                   +--rw security*              identityref
                   +--rw isolation*             identityref
                   +--rw max-occupancy-level?   uint8
                   +--rw path-constraints
                      +--rw service-functions
                      +--rw diversity
                         +--rw diversity-type?
                                 te-types:te-path-disjointness
     augment /nw:networks/nw:network/nw:node/nt:termination-point:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         slice-template-ref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?   string
                +--rw slo-policy
                |  +--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 availability?   identityref
                |  +--rw mtu?            uint32
                +--rw sle-policy
                   +--rw security*              identityref
                   +--rw isolation*             identityref
                   +--rw max-occupancy-level?   uint8
                   +--rw path-constraints
                      +--rw service-functions
                      +--rw diversity
                         +--rw diversity-type?
                                 te-types:te-path-disjointness
     augment /nw:networks/nw:network/nt:link:
       +--rw (slo-sle-policy)?
          +--:(standard)
          |  +--rw slo-sle-template?         slice-template-ref
          +--:(custom)
             +--rw service-slo-sle-policy
                +--rw description?   string
                +--rw slo-policy

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                |  +--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 availability?   identityref
                |  +--rw mtu?            uint32
                +--rw sle-policy
                   +--rw security*              identityref
                   +--rw isolation*             identityref
                   +--rw max-occupancy-level?   uint8
                   +--rw path-constraints
                      +--rw service-functions
                      +--rw diversity
                         +--rw diversity-type?
                                 te-types:te-path-disjointness

             Figure 3: Tree diagram for network slice topology

5.2.  Network Slice Underlay Path Model Tree Structure

   module: ietf-ns-underlay-path

     augment /ietf-nss:network-slice-services/ietf-nss:slice-service
               /ietf-nss:connection-groups/ietf-nss:connection-group
               /ietf-nss:slo-sle-policy/ietf-nss:custom
               /ietf-nss:service-slo-sle-policy/ietf-nss:sle-policy
               /ietf-nss:path-constraints:
       +--rw underlay-path
          +--rw network-ref?    -> /nw:networks/network/network-id
          +--rw path-element* [index]
             +--rw index            uint32
             +--rw is-strict-hop?   boolean
             +--rw (type)?
                +--:(node-hop)
                |  +--rw node-id?   nw:node-id
                +--:(link-hop)
                |  +--rw link-id?   nt:link-id
                +--:(tp-hop)
                   +--rw tp-id?     nt:tp-id
     augment /ietf-nss:network-slice-services/ietf-nss:slice-service
               /ietf-nss:connection-groups/ietf-nss:connection-group
               /ietf-nss:connectivity-construct/ietf-nss:slo-sle-policy
               /ietf-nss:custom/ietf-nss:service-slo-sle-policy
               /ietf-nss:sle-policy/ietf-nss:path-constraints:
       +--rw underlay-path
          +--rw network-ref?    -> /nw:networks/network/network-id

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          +--rw path-element* [index]
             +--rw index            uint32
             +--rw is-strict-hop?   boolean
             +--rw (type)?
                +--:(node-hop)
                |  +--rw node-id?   nw:node-id
                +--:(link-hop)
                |  +--rw link-id?   nt:link-id
                +--:(tp-hop)
                   +--rw tp-id?     nt:tp-id
     augment /ietf-nss:network-slice-services/ietf-nss:slice-service
               /ietf-nss:connection-groups/ietf-nss:connection-group
               /ietf-nss:connectivity-construct/ietf-nss:type
               /ietf-nss:a2a/ietf-nss:a2a-sdp/ietf-nss:slo-sle-policy
               /ietf-nss:custom/ietf-nss:service-slo-sle-policy
               /ietf-nss:sle-policy/ietf-nss:path-constraints:
       +--rw underlay-path
          +--rw network-ref?    -> /nw:networks/network/network-id
          +--rw path-element* [index]
             +--rw index            uint32
             +--rw is-strict-hop?   boolean
             +--rw (type)?
                +--:(node-hop)
                |  +--rw node-id?   nw:node-id
                +--:(link-hop)
                |  +--rw link-id?   nt:link-id
                +--:(tp-hop)
                   +--rw tp-id?     nt:tp-id

                  Figure 4: Tree diagram for underlay path

6.  YANG Modules

6.1.  YANG Module for Network Slice Topology

   <CODE BEGINS> file "ietf-ns-topo@2024-07-02.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 {

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          prefix "nt";
          reference
           "RFC 8345: A YANG Data Model for Network Topologies";
        }

        import ietf-network-slice-service {
          prefix "ietf-nss";
          reference
            "draft-ietf-teas-ietf-network-slice-nbi-yang-10:
             IETF Network Slice Service YANG Model";
        }

        organization
          "IETF TEAS Working Group";
        contact
          "WG Web: <http://tools.ietf.org/wg/teas/>
           WG List: <mailto:teas@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
           customer intent topologies for RFC9543 network slices.

           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
           BSD License set forth in Section 4.c of the IETF Trust's
           Legal Provisions Relating to IETF Documents

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           (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 2024-07-02 {
          description "Initial revision";
          reference
            "RFC XXXX: IETF Network Slice Topology YANG Data Model";
        }

        /*
         * 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 a Network Slice topology";
            description
              "Its presence identifies the Network Slice type.";
          }
        }

        /* network topology augments */
        augment "/nw:networks/nw:network" {
          when "./nw:network-types/ns-topo:network-slice" {
            description
              "Augmentation parameters apply only for networks
               of type Network Slice topology.";
          }
          description
            "SLO and SLE for topology.";

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

        /* network node augments */
        augment "/nw:networks/nw:network/nw:node" {
          when "../nw:network-types/ns-topo:network-slice" {
            description
              "Augmentation parameters apply only for networks
               of type Network Slice topology.";
          }
          description
            "SLO and SLE for nodes.";

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

        /* 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
              "Augmentation parameters apply only for networks
               of type Network Slice topology.";
          }
          description
            "SLO and SLE for termination points.";

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

        /* network link augments */
        augment "/nw:networks/nw:network/nt:link" {
          when "../nw:network-types/ns-topo:network-slice" {
            description
              "Augmentation parameters apply only for networks
               of type Network Slice topology.";
          }
          description
            "SLO and SLE for links.";

          uses ietf-nss:service-slo-sle-policy;
        }
      }
   <CODE ENDS>

              Figure 5: YANG model for network slice topology

6.2.  YANG Module for Network Slice Underlay Path

   <CODE BEGINS> file "ietf-ns-underlay-path@2024-07-02.yang"
      module ietf-ns-underlay-path {
        yang-version 1.1;
        namespace
          "urn:ietf:params:xml:ns:yang:ietf-ns-underlay-path";
        prefix "ns-path";

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

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

        import ietf-network-slice-service {
          prefix "ietf-nss";
          reference
            "draft-ietf-teas-ietf-network-slice-nbi-yang-05:
             IETF Network Slice Service YANG Model";
        }

        organization
          "IETF TEAS Working Group";
        contact
          "WG Web: <http://tools.ietf.org/wg/teas/>
           WG List: <mailto:teas@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
           the underlay path of connectivity intent over a customer
           intent topology for RFC9543 network slices.

           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 2024-07-02 {
          description "Initial revision";
          reference
            "RFC XXXX: IETF Network Slice Topology YANG Data Model";
        }

        /*
         * Groupings
         */
        grouping underlay-path {
          description
            "Underlay explicit path within a customer intent
             topology.";

          container underlay-path {
            description
              "Defines an underlay explicit path within specific
               customer intent topology.";

            uses nw:network-ref;

            list path-element {
             key "index";
             description
               "List of path elements.";
             leaf index {
               type uint32;
               description
                 "Index of the hop within the underlay path.";
             }
             leaf is-strict-hop {
               type boolean;
               description
                 "Indicate whether the hop is strict or loose";
             }
             choice type {
               description
                 "Type of the hop.";
               case node-hop {
                 leaf node-id {

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                   type nw:node-id;
                   description
                     "Node identifier.";
                 }
               }
               case link-hop {
                 leaf link-id {
                   type nt:link-id;
                   description
                     "Link identifier.";
                 }
               }
               case tp-hop {
                 leaf tp-id {
                   type nt:tp-id;
                   description
                     "Termination Point (TP) identifier.";
                 }
               }
             }
            }
          }
        }

        /*
         * Augmented data nodes
         */
        augment "/ietf-nss:network-slice-services" +
                "/ietf-nss:slice-service" +
                "/ietf-nss:connection-groups" +
                "/ietf-nss:connection-group" +
                "/ietf-nss:slo-sle-policy" +
                "/ietf-nss:custom" +
                "/ietf-nss:service-slo-sle-policy" +
                "/ietf-nss:sle-policy" +
                "/ietf-nss:path-constraints" {
          description
            "Underlay path for connection group.";

          uses underlay-path;
        }

        augment "/ietf-nss:network-slice-services" +
                "/ietf-nss:slice-service" +
                "/ietf-nss:connection-groups" +
                "/ietf-nss:connection-group" +
                "/ietf-nss:connectivity-construct" +
                "/ietf-nss:slo-sle-policy" +

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                "/ietf-nss:custom" +
                "/ietf-nss:service-slo-sle-policy" +
                "/ietf-nss:sle-policy" +
                "/ietf-nss:path-constraints" {
          description
            "Underlay path for connectivity construct.";

          uses underlay-path;
        }

        augment "/ietf-nss:network-slice-services" +
                "/ietf-nss:slice-service" +
                "/ietf-nss:connection-groups" +
                "/ietf-nss:connection-group" +
                "/ietf-nss:connectivity-construct" +
                "/ietf-nss:type" +
                "/ietf-nss:a2a" +
                "/ietf-nss:a2a-sdp" +
                "/ietf-nss:slo-sle-policy" +
                "/ietf-nss:custom" +
                "/ietf-nss:service-slo-sle-policy" +
                "/ietf-nss:sle-policy" +
                "/ietf-nss:path-constraints" {
          description
            "Underlay path for a2a connectivity constructs.";

          uses underlay-path;
        }
      }
   <CODE ENDS>

                   Figure 6: YANG model for underlay path

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.

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

   This document registers two YANG modules in the YANG Module Names
   registry [RFC6020].

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

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

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>.

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   [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>.

   [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>.

   [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>.

   [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>.

   [RFC9408]  Boucadair, M., Ed., Gonzalez de Dios, O., Barguil, S., Wu,
              Q., and V. Lopez, "A YANG Network Data Model for Service
              Attachment Points (SAPs)", RFC 9408, DOI 10.17487/RFC9408,
              June 2023, <https://www.rfc-editor.org/info/rfc9408>.

   [RFC9543]  Farrel, A., Ed., Drake, J., Ed., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L., and J. Tantsura, "A
              Framework for Network Slices in Networks Built from IETF
              Technologies", RFC 9543, DOI 10.17487/RFC9543, March 2024,
              <https://www.rfc-editor.org/info/rfc9543>.

10.2.  Informative References

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   [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-05, 13 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-contreras-
              teas-slice-controller-models-05>.

   [I-D.draft-ietf-teas-ietf-network-slice-nbi-yang]
              Wu, B., Dhody, D., Rokui, R., Saad, T., and J. Mullooly,
              "A YANG Data Model for the RFC 9543 Network Slice
              Service", Work in Progress, Internet-Draft, draft-ietf-
              teas-ietf-network-slice-nbi-yang-13, 9 May 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slice-nbi-yang-13>.

   [I-D.ietf-ccamp-otn-topo-yang]
              Zheng, H., Busi, I., Liu, X., Belotti, S., and O. G. de
              Dios, "A YANG Data Model for Optical Transport Network
              Topology", Work in Progress, Internet-Draft, draft-ietf-
              ccamp-otn-topo-yang-19, 25 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ccamp-
              otn-topo-yang-19>.

   [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-06, 24 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ccamp-
              yang-otn-slicing-06>.

   [I-D.ietf-teas-actn-vn-yang]
              Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B. Y.
              Yoon, "A YANG Data Model for Virtual Network (VN)
              Operations", Work in Progress, Internet-Draft, draft-ietf-
              teas-actn-vn-yang-29, 22 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              actn-vn-yang-29>.

   [I-D.ietf-teas-ietf-network-slice-nbi-yang]
              Wu, B., Dhody, D., Rokui, R., Saad, T., and J. Mullooly,
              "A YANG Data Model for the RFC 9543 Network Slice
              Service", Work in Progress, Internet-Draft, draft-ietf-
              teas-ietf-network-slice-nbi-yang-13, 9 May 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-teas-
              ietf-network-slice-nbi-yang-13>.

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Appendix A.  Acknowledgments

   The authors would like to thank Danielle Ceccarelli, Bo Wu, Mohamed
   Boucadair, and Vishnu Beeram for providing valuable insights.

Appendix B.  Data Tree for the Example in Section 3

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",
           "network-types": {
             "ietf-ns-topo:network-slice": {
             }
           },
           "node": [
             {
               "node-id": "VR1",
               "ietf-ns-topo:service-slo-sle-policy": {
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "1-0-1"
                 },
                 {
                   "tp-id": "1-3-1"
                 }
               ]
             },
             {
               "node-id": "VR3",

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               "ietf-ns-topo:service-slo-sle-policy": {
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               },
               "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": {
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               },
               "ietf-network-topology:termination-point": [
                 {
                   "tp-id": "5-3-1"
                 },
                 {
                   "tp-id": "5-0-1"
                 }
               ]
             }
           ],
           "ietf-network-topology:link": [
             {
               "link-id": "VR1,1-0-1,,",
               "source": {
                 "source-node": "VR1",
                 "source-tp": "1-0-1"
               },

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               "ietf-ns-topo:service-slo-sle-policy": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 60
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               }
             },
             {
               "link-id": ",,VR1,1-0-1",
               "destination": {
                 "dest-node": "VR1",
                 "dest-tp": "1-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 30
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }

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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": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 30
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               }
             },
             {
               "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": {

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                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 30
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               }
             },
             {
               "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": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 35
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {

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                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               }
             },
             {
               "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": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 35
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
               }
             },
             {
               "link-id": "VR5,5-0-1,,",
               "source": {
                 "source-node": "VR5",
                 "source-tp": "5-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "slo-policy": {

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                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 25
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }
                           }
             },
             {
               "link-id": ",,VR5,5-0-1",
               "destination": {
                 "dest-node": "VR5",
                 "dest-tp": "5-0-1"
               },
               "ietf-ns-topo:service-slo-sle-policy": {
                 "slo-policy": {
                   "metric-bounds": {
                     "metric-bound": [
                       {
                         "metric-type": "ietf-network-slice-service:se\
   rvice-slo-two-way-delay",
                         "metric-unit": "ms",
                         "bound": 25
                       }
                     ]
                   }
                 },
                 "sle-policy": {
                   "isolation": [
                     {
                       "ietf-network-slice-service:service-traffic-iso\
   lation"
                     }
                   ]
                 }

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               }
             }
           ],
           "ietf-ns-topo:service-slo-sle-policy": {
             "sle-policy": {
               "isolation": [
                 {
                   "ietf-network-slice-service:service-traffic-isolati\
   on"
                 }
               ]
             }
           }
         }
       ]
     }
   }

Authors' Addresses

   Xufeng Liu
   Alef Edge
   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

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   Reza Rokui
   Ciena
   Email: rrokui@ciena.com

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

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

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