TEAS Working Group                                               D. King
Internet-Draft                                        Old Dog Consulting
Intended status: Informational                                  J. Drake
Expires: October 2, 2021                                Juniper Networks
                                                                H. Zheng
                                                     Huawei Technologies
                                                               A. Farrel
                                                      Old Dog Consulting
                                                          March 31, 2021

Applicability of Abstraction and Control of Traffic Engineered Networks
                       (ACTN) to Network Slicing


   Network abstraction is a technique that can be applied to a network
   domain.  It utilizes a set of policies to select network resources
   and obtain a view of potential connectivity across the network.

   Network slicing is an approach to network operations that builds on
   the concept of network abstraction to provide programmability,
   flexibility, and modularity.  It may use techniques such as Software
   Defined Networking (SDN) and Network Function Virtualization (NFV) to
   create multiple logical or virtual networks, each tailored for a set
   of services that share the same set of requirements.

   Abstraction and Control of Traffic Engineered Networks (ACTN) is
   described in RFC 8453.  It defines an SDN-based architecture that
   relies on the concept of network and service abstraction to detach
   network and service control from the underlying data plane.

   This document outlines the applicability of ACTN to network slicing
   in a Traffic Engineering (TE) network that utilizes IETF technology.
   It also identifies the features of network slicing not currently
   within the scope of ACTN, and indicates where ACTN might be extended.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   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
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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements for Network Slicing  . . . . . . . . . . . . . .   5
     2.1.  Resource Slicing  . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Network Virtualization  . . . . . . . . . . . . . . . . .   6
     2.3.  Service Isolation . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Control and Orchestration . . . . . . . . . . . . . . . .   7
   3.  Abstraction and Control of Traffic Engineered (TE) Networks
       (ACTN)  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  ACTN Virtual Network as a Network Slice . . . . . . . . .   8
     3.2.  ACTN Virtual Network for Network Slice Aggregation  . . .   9
     3.3.  Management Components for ACTN and Network Slicing  . . .   9
     3.4.  Examples of ACTN Delivering Types of Network Slices . . .  10
       3.4.1.  ACTN Used for Virtual Private Line  . . . . . . . . .  10
       3.4.2.  ACTN Used for VPN Delivery Model  . . . . . . . . . .  12
       3.4.3.  ACTN Used to Deliver a Virtual Consumer Network . . .  13
   4.  YANG Models . . . . . . . . . . . . . . . . . . . . . . . . .  15
     4.1.  Network Slice Service Mapping from TE to ACTN VN Models .  15
     4.2.  Interfaces and Yang Models  . . . . . . . . . . . . . . .  16
     4.3.  ACTN VN Telemetry . . . . . . . . . . . . . . . . . . . .  17
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19

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   9.  Informative References  . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The principles of network resource separation are not new.  For
   years, the concept of separated overlay and logical (virtual)
   networking has existed, allowing multiple services to be deployed
   over a single physical network comprised of single or multiple
   layers.  However, several key differences exist that differentiate
   overlay and virtual networking from network slicing.

   A network slice is a virtual (that is, logical) network with its own
   network topology and a set of network resources that are used to
   provide connectivity that conforms to a specific Service Level
   Agreement (SLA) or set of Service Level Objectives (SLOs).  The
   network resources used to realize a network slice belong to the
   network that is sliced.  The resources may be assigned and dedicated
   to an individual slice, or they may be shared with other slices
   enabling different degrees of service guarantee and providing
   different levels of isolation between the traffic in each slice.

   [I-D.ietf-teas-ietf-network-slice-definition] provides a number of
   useful definitions for network slicing in the context of IETF network
   technologies.  In particular, that document defines the term "IETF
   network slice" to be the generic network slice concept applied to a
   network that uses IETF technologies.  An IETF network slice could
   span multiple technologies (such as IP, MPLS, or optical) and
   multiple administrative domains.  The logical network that is an IETF
   network slice may be kept separate from other concurrent logical
   networks each with independent control and management: each can be
   created or modified on demand.  Since this document is focused
   entirely on IETF technologies, it uses the term "network slice" as a
   more concise expression.  Further dicussion on the topic of IETF
   network slices can be found in

   At one end of the spectrum, a virtual private wire or a virtual
   private network (VPN) may be used to build a network slice.  In these
   cases, the network slices do not require the service provider to
   isolate network resources for the provision of the service - the
   service is "virtual".

   At the other end of the spectrum there may be a detailed description
   of a complex service that will meet the needs of a set of
   applications with connectivity and service function requirements that
   may include compute resource, storage capability, and access to
   content.  Such a service may be requested dynamically (that is,

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   instantiated when an application needs it, and released when the
   application no longer needs it), and modified as the needs of the
   application change.  This type of service is called an enhanced VPN
   and is described in more detail in [I-D.ietf-teas-enhanced-vpn].  It
   is often based on Traffic Engineering (TE) constructs in the underlay

   Abstraction and Control of TE Networks (ACTN) [RFC8453] is a
   framework that facilitates the abstraction of underlying network
   resources to higher-layer applications and that allows nework
   operators to create virtual networks for their customers through the
   abstraction of the operators' network resources.

   As noted in [I-D.ietf-teas-ietf-network-slice-framework], ACTN is a
   toolset capable of delivering network slice functionality.  This
   document outlines the application of ACTN and associated enabling
   technologies to provide network slicing in a network that utilizes
   IETF technologies such as IP, MPLS, or GMPLS.  It describes how the
   ACTN functional components can be used to support model-driven
   partitioning of resources into variable-sized bandwidth units to
   facilitate network sharing and virtualization.  Furthermore, the use
   of model-based interfaces to dynamically request the instantiation of
   virtual networks can be extended to encompass requesting and
   instantiation of specific service functions (which may be both
   physical or virtual), and to partition network resources such as
   compute resource, storage capability, and access to content.
   Finally, this document highlights how the ACTN approach might be
   extended to address the requirements of network slicing where the
   underlying network is TE-capable.

1.1.  Terminology

   As far as is possible, this document re-uses terminology from
   [I-D.ietf-teas-enhanced-vpn] and
   [I-D.ietf-teas-ietf-network-slice-framework].  The terms defined
   below are give context and meaning for use in this document only and
   do not force wider applicability.  As other work matures, it is hoped
   that the terminology will converge.

   Service Provider:  A server network or collection of server networks.
      The persons or organization responsible for operating such

   Consumer:  As defined in
      [I-D.ietf-teas-ietf-network-slice-definition], a consumer is the
      component or entity that requests and uses a network slice.  This
      may be any application, client network, or customer of a service

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      provider.  In the ACTN framework [RFC8453] the consumer of a
      network service is termed a 'customer' because it will often be
      the case that a VPN consumer is a customer of the operator of the
      core network that delivers the service.  In the context of a
      network slice, the consumer may well be a customer, but might also
      be a client network of the service provider (which could also be
      an internal organization of the service provider), or an
      application that engineers traffic in the network.

   Service Functions (SFs):  Components that provide specific functions
      within a network.  SFs are often combined in a specific sequence
      called a service function chain to deliver services [RFC7665].

   Resource:  Any feature including connectivity, bufferage, compute,
      storage, and content delivery that forms part of or can be
      accessed through a network.  Resources may be shared between
      users, applications, and clients, or they may be dedicated for use
      by a unique consumer.

   Infrastructure Resources:  The hardware and software for hosting and
      connecting SFs.  These resources may include computing hardware,
      storage capacity, network resources (e.g., links and switching/
      routing devices enabling network connectivity), and physical
      assets for radio access.

   Service Level Agreement (SLA):  Per [I-D.ietf-teas-ietf-network-slice
      -definition], an SLA is an explicit or implicit contract between
      the consumer of a network slice and the provider of the slice.
      The SLA is expressed in terms of a set of Service Level Objectives
      (SLOs) and may include commercial terms as well as the
      consequences of violating the SLOs.  The SLA describes the quality
      with which features and functions are to be delivered.  It may
      include measures of bandwidth, latency, and jitter; the types of
      service (such as firewalls or billing) to be provided; the
      location, nature, and quantities of services (such as the amount
      and location of compute resources and the accelerators required).

   Network Slice Service:  An agreement between a consumer and a service
      provider to deliver network resources according to a specific
      service level agreement.

2.  Requirements for Network Slicing

   According to [I-D.ietf-teas-ietf-network-slice-framework] the
   consumer expresses requirements for a particular IETF network slice
   by specifying what is required rather than how the requirement is to
   be fulfilled.  That is, the IETF network slice consumer's view of a
   IETF network slice is an abstract one.

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   The concept of network slicing is a key capability to serve consumers
   with a wide variety of different service needs expressed as SLOs in
   term of latency, reliability, capacity, and service function specific

   This section outlines the key capabilities required to realize
   network slicing in a TE-enabled IETF technology network.

2.1.  Resource Slicing

   Network resources need to be allocated and dedicated for use by a
   specific network slice, or they may be shared among multiple slices.
   This allows a flexible approach that can deliver a range of services
   by partitioning (that is, slicing) the available network resources to
   make them available to meet the consumer's SLA.

2.2.  Network Virtualization

   Network virtualization enables the creation of multiple virtual
   networks that are operationally decoupled from the underlying
   physical network, and are run on top of it.  Slicing enables the
   creation of virtual networks as consumer services.

2.3.  Service Isolation

   A consumer may request, through their SLA, that changes to the other
   services delivered by the service provider do not have any negative
   impact on the delivery of the service.  This quality is refered to as
   "isolation" [I-D.ietf-teas-ietf-network-slice-definition]

   Delivery of such service isolation may be achieved in the underlying
   network by various forms of resource partitioning ranging from
   dedicated allocation of resources for a specific slice, to sharing or
   resources with safeguards.

   Although multiple network slices may utilize resources from a single
   underlying network, isolation should be understood in terms of the
   following three categorisations.

   o  Performance isolation requires that service delivery for one
      network slice does not adversely impact congestion or performance
      levels of other slices.

   o  Security isolation means that attacks or faults occurring in one
      slice do not impact on other slices.  Moreover, the security
      functions supporting each slice must operate independently so that
      an attack or misconfiguration of security in one slice will not

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      prevent proper security function in the other slices.  Further,
      privacy concerns require that traffic from one slice is not
      delivered to an end point in another slice, and that it should not
      be possible to determine the nature or characteristics of a slice
      from any external point.

   o  Management isolation means that each slice must be independently
      viewed, utilized, and managed as a separate network.  Furthermore,
      it should be possible to prevent the operator of one slice from
      being able to control, view, or detect any aspect of any other
      network slice.

2.4.  Control and Orchestration

   Orchestration combines and coordinates multiple control methods to
   provide a single mechanism to operate one or more networks to deliver
   services.  In a network slicing environment, an orchestrator is
   needed to coordinate disparate processes and resources for creating,
   managing, and deploying the network slicing service.  Two aspects of
   orchestration are required:

   o  Multi-domain Orchestration: Managing connectivity to set up a
      network slice across multiple administrative domains.

   o  End-to-end Orchestration: Combining resources for an end-to-end
      service (e.g., underlay connectivity with firewalling, and
      guaranteed bandwidth with minimum delay).

3.  Abstraction and Control of Traffic Engineered (TE) Networks (ACTN)

   ACTN facilitates end-to-end connectivity and provide virtual
   connectivity services (such as virtual links and virtual networks) to
   the user.  The ACTN framework [RFC8453] introduces three functional
   components and two interfaces:

   o  Customer Network Controller (CNC)

   o  Multi-domain Service Coordinator (MDSC)

   o  Provisioning Network Controller (PNC)

   o  CNC-MDSC Interface (CMI)

   o  MDSC-PNC Interface (MPI)

   RFC 8453 also highlights how:

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   o  Abstraction of the underlying network resources is provided to
      higher-layer applications and consumers.

   o  Virtualization is achieved by selecting resources according to
      criteria derived from the details and requirements of the
      consumer, application, or service.

   o  Creation of a virtualized environment is performed to allow
      operators to view and control multi-domain networks as a single
      virtualized network.

   o  A network is presented to a consumer as a single virtual network
      via open and programmable interfaces.

   The ACTN managed infrastructure consists of traffic engineered
   network resources.  The concept of traffic engineering is broad: it
   describes the planning and operation of networks using a method of
   reserving and partitioning of network resources in order to
   facilitate traffic delivery across a network (see
   [I-D.ietf-teas-rfc3272bis] for more details).  In the context of
   ACTN, traffic engineering network resources may include:

   o  Statistical packet bandwidth.

   o  Physical forwarding plane sources, such as wavelengths and time

   o  Forwarding and cross-connect capabilities.

   The ACTN network is "sliced" with consumers each being given a
   different partial and abstracted topology view of the physical
   underlay network.

3.1.  ACTN Virtual Network as a Network Slice

   To support multiple consumers, each with its own view of and control
   of a virtual network constructed using a server network, a service
   provider needs to partition the server network resources to create
   network slices assigned to each consumer.

   An ACTN Virtual Network (VN) is a consumer view of a slice of the
   ACTN-managed infrastructure.  It is a network slice that is presented
   to the consumer by the ACTN provider as a set of abstracted
   resources.  See [I-D.ietf-teas-actn-vn-yang] for a detailed
   description of ACTN VNs and an overview of how various different
   types of YANG model are applicable to the ACTN framework.

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   Depending on the agreement between consumer and provider, various VN
   operations are possible:

   o  Network Slice Creation: A VN could be pre-configured and created
      through static configuration or through dynamic request and
      negotiation between consumer and service provider.  The VN must
      meet the network slice requirements specified in the SLA to
      satisfy the consumer's objectives.

   o  Network Slice Operations: The VN may be modified and deleted based
      on consumer requests.  The consumer can further act upon the VN to
      manage the consumer's traffic flows across the network slice.

   o  Network Slice View: The VN topology is viewed from the consumer's
      perspective.  This may be the entire VN topology or a collection
      of tunnels that are expressed as consumer end points, access
      links, intra domain paths and inter-domain links.

   [RFC8454] describes a set of functional primitives that support these
   different ACTN VN operations.

3.2.  ACTN Virtual Network for Network Slice Aggregation

   Scaling considerations for IETF network slicing are an important
   consideration.  If the service provider must manage and maintain
   network state for every network slice then this will quickly limit
   the number of customer services that can be supported.

   The importance of network slice aggregation is discussed in
   [I-D.ietf-teas-enhanced-vpn] and further in
   [I-D.dong-teas-enhanced-vpn-vtn-scalability].  That work notes the
   importance of aggregating network slices into groups of similar
   slices before realizing those aggregates in the network.

   The same consideration applies to ACTN VNs.  But fortunately, ACTN
   VNs may be arranged hierarchically by recursing the MDSCs so that one
   VN is realised over another VN.  This allows the VNs presented to the
   customer to be aggregated before they are instantiated in the
   physical network.

3.3.  Management Components for ACTN and Network Slicing

   The ACTN management components (CNC, MDSC, and PNC) and interfaces
   (CMI and MPI) are introduced in Section 3 and described in detail in
   [RFC8453].  The management components for network slicing are
   described in [I-D.ietf-teas-ietf-network-slice-framework] and are
   known as the consumer orchestration system, the IETF network slice
   controller (NSC), and the network controller.  The network slicing

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   management components are separated by the network slice controller
   northbound interface (NSC NBI) and the network slice controller
   southbound interface (NSC SBI).

   [I-D.ietf-teas-ietf-network-slice-framework] describes the mapping
   between network slicing management components and ACTN management
   components.  This is presented visually in Figure 1 and provides a
   useful reference for understanding the material in Section 3.4 and
   Section 4.

          +--------------------------------------+   |    +-----+
          |    Consumer orchestration system     | =====> | CNC |
          +--------------------------------------+   |    +-----+
                            ^                                ^
                            | NSC NBI                |       | CMI
                            v                                v
          +-------------------------------------+    |    +------+
          | IETF Network Slice Controller (NSC) |  =====> | MDSC |
          +-------------------------------------+    |    +------+
                            ^                                ^
                            | NSC SBI                |       | MPI
                            v                                v
          +-------------------------------------+    |    +-----+
          |         Network Controller          |  =====> | PNC |
          +-------------------------------------+    |    +-----+

     Figure 1: Mapping Between IETF Network Slice and ACTN Components

3.4.  Examples of ACTN Delivering Types of Network Slices

   The examples that follow build on the ACTN framework to provide
   control, management, and orchestration for the network slice life-
   cycle.  These network slices utilize common physical infrastructure,
   and meet specific service-level requirements.

   Three examples are shown.  Each uses ACTN to achieve a different
   network slicing scenario.  All three scenarios can be scaled up in
   capacity or be subject to topology changes as well as changes of
   consumer requirements.

3.4.1.  ACTN Used for Virtual Private Line

   In the example shown in Figure 2, ACTN provides virtual connections
   between multiple consumer locations (sites accessed through Customer
   Edge nodes - CEs).  The service is requested by the consumer (via

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   CNC-A) and delivered as a Virtual Private Line (VPL) service.  The
   benefits of this model include:

   o  Automated: the service set-up and operation is managed by the
      network provider.

   o  Virtual: the private line connectivity is provided from Site A to
      Site C (VPL1) and from Site B to Site C (VPL2) across the ACTN-
      managed physical network.

   o  Agile: on-demand adjustments to the connectivity and bandwidth are
      available according to the consumer's requests.

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                     (Consumer VPL Request)
                            | CNC-A |
      Boundary               -------
      Between  . . . . . . . . .:. . . . . . . . . . .
      Consumer &                :
      Network Provider       ------
                            | MDSC |
                             | PNC |
            Site A          ( ----- )           Site B
            -----          (         )          -----
           | CE1 |========(  Physical )========| CE2 |
            -----\         ( Network )         /-----
                  \         (_______)         /
                   \            ||           /
                    \           ||          /
                VPL1 \          ||         / VPL2
                      \         ||        /
                       \        ||       /
                        \       ||      /
                         |     CE3     |
                              Site C

      Key:   ... ACTN control connectivity
             === Physical connectivity
             --- Logical connectivity

                   Figure 2: Virtual Private Line Model

3.4.2.  ACTN Used for VPN Delivery Model

   In the example shown in Figure 3, ACTN provides VPN connectivity
   between two sites across three physical networks.  The requirements
   for the VPN are expressed by the users of the two sites who are the
   consumers.  Their requests are directed to the CNC, and the CNC
   interacts with the network provider's MDSC.  The benefits of this
   model include:

   o  Provides edge-to-edge VPN multi-access connectivity.

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   o  Most of the function is managed by the network provider, with some
      flexibility delegated to the consumer-managed CNC.

                      --------------     --------------
                     | Site-A Users |   | Site-B Users |
                      --------------     --------------
                                 :         :
                               |     CNC     |
      Boundary                  -------------
      Between   . . . . . . . . . . . : . . . . . . . . . . .
      Consumer &                      :
      Network Provider                :
                     |               MDSC              |
                       :              :              :
                       :              :              :
                    -------        -------        -------
                   |  PNC  |      |  PNC  |      |  PNC  |
                    -------        -------        -------
                       :              :              :
                       :              :              :
        ______     ---------      ---------      ---------     ______
       <      >   (         )    (         )    (         )   <      >
       <Site A>==( Physical  )==( Physical  )==( Physical  )==<Site B>
       <      >   ( Network )    ( Network )    ( Network )   <      >
       <      >    (       )      (       )      (       )    <      >
       <      >     -------        -------        -------     <      >
       <      >-----------------------------------------------<      >
       <______>                                               <______>

      Key:   ... ACTN control connectivity
             === Physical connectivity
             --- Logical connectivity

                            Figure 3: VPN Model

3.4.3.  ACTN Used to Deliver a Virtual Consumer Network

   In the example shown in Figure 4, ACTN provides a virtual network to
   the consumer.  This virtual network is managed by the consumer.  The
   figure shows two virtual networks (Network Slice 1 and Network Slice
   2) each created for a different consumer under the care of a
   different CNC.  There are two physical networks controlled by
   separate PNCs.  Network Slice 2 is built using resources from just

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   one physical network, while Network Slice 1 is constructed from
   resources from both physical networks.

   The benefits of this model include:

   o  The MDSC provides the topology to the consumer so that the
      consumer can control their network slice to fit their needs.

   o  Applications can interact with their assigned network slices
      directly.  The consumer may implement their own network control
      methods and traffic prioritization, and manage their own
      addressing schemes.

   o  Consumers may further slice their virtual networks so that this
      becomes a recursive model.

   o  Service isolation can be provided through selection of physical
      networking resources through a combination of efforts of the MSDC
      and PNC.

   o  The network slice may include nodes with specific capabilities.
      These can be delivered as Physical Network Functions (PNFs) or
      Virtual Network Functions (VNFs).

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                 -------------                  (           )
                |    CNC      |---------------->(  Network  )
                 -------------                  (  Slice 2  )
                  ^                             (___________)
                  |                           ___________  ^
                  |   -------------          (           ) :
                  |  |     CNC     |-------->(  Network  ) :
                  |   -------------          (  Slice 1  ) :
                  |       ^                  (___________) :
                  |       |                      ^    ^    :
      Boundary    |       |                      :    :    :
      Between    .|. . . .|. . . . . . . . . . . : . .:. . : . . .
      Consumer &  |       |                      :    :    :
      Network     |       |                      :    :    :
      Provider    v       v                      :    :    :
                -------------                    :    :....:
               |    MDSC     |                   :         :
                -------------                    :         :
                        ^                  ------^--       :
                        |                 (         )      :
                        v                (  Physical )     :
                     -------              ( Network )      :
                    |  PNC  |<------------>(       )    ---^-----
                   -------  |               -------    (         )
                  |  PNC  |-                          (  Physical )
                  |       |<-------------------------->( Network )
                   -------                              (       )

      Key: --- ACTN control connection
           ... Virtualization/abstraction through slicing

                         Figure 4: Network Slicing

4.  YANG Models

4.1.  Network Slice Service Mapping from TE to ACTN VN Models

   The role of the TE-service mapping model
   [I-D.ietf-teas-te-service-mapping-yang] is to create a binding
   relationship across a Layer 3 Service Model (L3SM) [RFC8299], Layer 2
   Service Model (L2SM) [RFC8466], and TE Tunnel model
   [I-D.ietf-teas-yang-te], via the generic ACTN Virtual Network (VN)
   model [I-D.ietf-teas-actn-vn-yang].

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   The ACTN VN model is a generic virtual network service model that
   allows consumers to specify a VN (i.e., network slice) that meets the
   consumer's service objectives with various constraints on how the
   service is delivered.

   The TE-service mapping model [I-D.ietf-teas-te-service-mapping-yang]
   is used to bind the L3SM with TE-specific parameters.  This binding
   facilitates seamless service operation and enables visibility of the
   underlay TE network.  The TE-service model developed in that document
   can also be extended to support other services including L2SM, and
   the Layer 1 Connectivity Service Model (L1CSM)
   [I-D.ietf-ccamp-l1csm-yang] L1CSM network service models.

   Figure 5 shows the relationship between the models discussed above.

        ---------------            -----------
       |    L3SM       |<=========|           |             -----------
        ---------------   augment |           |...........>|  ACTN VN  |
        ---------------           | Augmented | reference   -----------
       |    L2SM       |<=========| Service   |
        ---------------   augment | Model     |             -----------
        ---------------           |           |...........>|  TE-topo  |
       |    L1CSM      |<=========|           | reference   -----------
        ---------------   augment |           |
        ---------------           |           |             -----------
       | TE & Service  |--------->|           |...........>| TE-tunnel |
       | Mapping Types |  import   -----------  reference   -----------

                       Figure 5: TE-Service Mapping

4.2.  Interfaces and Yang Models

   Figure 6 shows the three ACTN components and two ACTN interfaces as
   listed in Section 3.  The figure also shows the Southbound Interface
   (SBI) between the PNC and the devices in the physical network.  That
   interface might be used to install state on every device in the
   network, or might instruct a "head-end" node if a control plane is
   used within the physical network.  In the context of [RFC8309], the
   SBI uses one or more device configuration models.

   The figure also shows the Network Slice Service Interface.  This
   interface allows a consumer of a service to make requests for
   delivery of the service, and it facilitates the consumer modifying
   and monitoring the service.  In the context of [RFC8309], this

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   "northbound interface (NBI)" is a customer service interface and uses
   a service model.

   When an ACTN system is used to manage the delivery of network slices,
   a network slice resource model is needed.  This model will be used
   for instantiation, operation, and monitoring of network and function
   resource slices.  The YANG model defined in
   [I-D.wd-teas-transport-slice-yang] provides a suitable basis for
   requesting, controlling, and deleting, network slices.

                         | Consumer |
                        .......:....... Network Slice Service Interface
                        |     CNC     |
                        .......:....... CMI
                       |      MDSC     |
                        .......:....... MPI
                           |  PNC  |
                        .......:....... SBI
                          (          )
                         (  Physical  )
                          ( Network  )

                 Figure 6: The Yang Interfaces in Context

4.3.  ACTN VN Telemetry

   The ACTN VN KPI telemetry model
   [I-D.ietf-teas-actn-pm-telemetry-autonomics] provides a way for a
   consumer to define performance monitoring relevant for its VN/network
   slice via the NETCONF subscription mechanisms [RFC8639], [RFC8640],
   or using the equivalent mechanisms in RESTCONF [RFC8641], [RFC8650].

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   Key characteristics of [I-D.ietf-teas-actn-pm-telemetry-autonomics]

   o  An ability to provide scalable VN-level telemetry aggregation
      based on consumer subscription model for key performance
      parameters defined by the consumer.

   o  An ability to facilitate proactive re-optimization and
      reconfiguration of VNs/network slices based on network autonomic
      traffic engineering scaling configuration mechanism.

5.  IANA Considerations

   This document makes no requests for action by IANA.

6.  Security Considerations

   Network slicing involves the control of network resources in order to
   meet the service requirements of consumers.  In some deployment
   models, the consumer is able to directly request modification in the
   behaviour of resources owned and operated by a service provider.
   Such changes could significantly affect the service provider's
   ability to provide services to other consumers.  Furthermore, the
   resources allocated for or consumed by a consumer will normally be
   billable by the service provider.

   Therefore, it is crucial that the mechanisms used in any network
   slicing system allow for authentication of requests, security of
   those requests, and tracking of resource allocations.

   It should also be noted that while the partitioning or slicing of
   resources is virtual, as mentioned in Section 2.3 the consumers
   expect and require that there is no risk of leakage of data from one
   slice to another, no transfer of knowledge of the structure or even
   existence of other slices, and that changes to one slice (under the
   control of one consumer) should not have detrimental effects on the
   operation of other slices (whether under control of different or the
   same consumers) beyond the limits allowed within the SLA.  Thus,
   slices are assumed to be private and to provide the appearance of
   genuine physical connectivity.

   Some service providers may offer secure network slices as a service.
   Such services may claim to include edge-to-edge encryption for the
   consumer's traffic.  However, a consumer should take full
   responsibility for the privacy and integrity of their traffic and
   should carefully consider using their own edge-to-edge encryption.

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   ACTN operates using the NETCONF [RFC6241] or RESTCONF [RFC8040]
   protocols and assumes the security characteristics of those
   protocols.  Deployment models for ACTN should fully explore the
   authentication and other security aspects before networks start to
   carry live traffic.

7.  Acknowledgements

   Thanks to Qin Wu, Andy Jones, Ramon Casellas, Gert Grammel, and Kiran
   Makhijani for their insight and useful discussions about network

8.  Contributors

   The following people contributed text to this document.

         Young Lee
         Email: younglee.tx@gmail.com

         Mohamed Boucadair
         Email: mohamed.boucadair@orange.com

         Sergio Belotti
         Email: sergio.belotti@nokia.com

         Daniele Ceccarelli
         Email: daniele.ceccarelli@ericsson.com

9.  Informative References

              Dong, J., Li, Z., Qin, F., and G. Yang, "Scalability
              Considerations for Enhanced VPN (VPN+)", draft-dong-teas-
              enhanced-vpn-vtn-scalability-01 (work in progress),
              November 2020.

              Lee, Y., Lee, K., Zheng, H., Dios, O., and D. Ceccarelli,
              "A YANG Data Model for L1 Connectivity Service Model
              (L1CSM)", draft-ietf-ccamp-l1csm-yang-13 (work in
              progress), November 2020.

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              Lee, Y., Dhody, D., Karunanithi, S., Vilata, R., King, D.,
              and D. Ceccarelli, "YANG models for VN/TE Performance
              Monitoring Telemetry and Scaling Intent Autonomics",
              draft-ietf-teas-actn-pm-telemetry-autonomics-04 (work in
              progress), November 2020.

              Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., and B.
              Yoon, "A YANG Data Model for VN Operation", draft-ietf-
              teas-actn-vn-yang-10 (work in progress), November 2020.

              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-ietf-teas-enhanced-vpn-06 (work in
              progress), July 2020.

              Rokui, R., Homma, S., Makhijani, K., Contreras, L., and J.
              Tantsura, "Definition of IETF Network Slices", draft-ietf-
              teas-ietf-network-slice-definition-00 (work in progress),
              January 2021.

              Gray, E. and J. Drake, "Framework for IETF Network
              Slices", draft-ietf-teas-ietf-network-slice-framework-00
              (work in progress), March 2021.

              Farrel, A., "Overview and Principles of Internet Traffic
              Engineering", draft-ietf-teas-rfc3272bis-10 (work in
              progress), December 2020.

              Lee, Y., Dhody, D., Fioccola, G., WU, Q., Ceccarelli, D.,
              and J. Tantsura, "Traffic Engineering (TE) and Service
              Mapping Yang Model", draft-ietf-teas-te-service-mapping-
              yang-05 (work in progress), November 2020.

              Saad, T., Gandhi, R., Liu, X., Beeram, V., and I. Bryskin,
              "A YANG Data Model for Traffic Engineering Tunnels, Label
              Switched Paths and Interfaces", draft-ietf-teas-yang-te-25
              (work in progress), July 2020.

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              Bo, W., Dhody, D., Han, L., and R. Rokui, "A Yang Data
              Model for Transport Slice NBI", draft-wd-teas-transport-
              slice-yang-02 (work in progress), July 2020.

   [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,

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [RFC8299]  Wu, Q., Ed., Litkowski, S., Tomotaki, L., and K. Ogaki,
              "YANG Data Model for L3VPN Service Delivery", RFC 8299,
              DOI 10.17487/RFC8299, January 2018,

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,

   [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,

   [RFC8454]  Lee, Y., Belotti, S., Dhody, D., Ceccarelli, D., and B.
              Yoon, "Information Model for Abstraction and Control of TE
              Networks (ACTN)", RFC 8454, DOI 10.17487/RFC8454,
              September 2018, <https://www.rfc-editor.org/info/rfc8454>.

   [RFC8466]  Wen, B., Fioccola, G., Ed., Xie, C., and L. Jalil, "A YANG
              Data Model for Layer 2 Virtual Private Network (L2VPN)
              Service Delivery", RFC 8466, DOI 10.17487/RFC8466, October
              2018, <https://www.rfc-editor.org/info/rfc8466>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,

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   [RFC8640]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Dynamic Subscription to YANG Events
              and Datastores over NETCONF", RFC 8640,
              DOI 10.17487/RFC8640, September 2019,

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC8650]  Voit, E., Rahman, R., Nilsen-Nygaard, E., Clemm, A., and
              A. Bierman, "Dynamic Subscription to YANG Events and
              Datastores over RESTCONF", RFC 8650, DOI 10.17487/RFC8650,
              November 2019, <https://www.rfc-editor.org/info/rfc8650>.

Authors' Addresses

   Daniel King
   Old Dog Consulting

   Email: daniel@olddog.co.uk

   John Drake
   Juniper Networks

   Email: jdrake@juniper.net

   Haomian Zheng
   Huawei Technologies

   Email: zhenghaomian@huawei.com

   Adrian Farrel
   Old Dog Consulting

   Email: adrian@olddog.co.uk

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