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rfc:rfc8453

Internet Engineering Task Force (IETF) D. Ceccarelli, Ed. Request for Comments: 8453 Ericsson Category: Informational Y. Lee, Ed. ISSN: 2070-1721 Huawei

                                                           August 2018
    Framework for Abstraction and Control of TE Networks (ACTN)

Abstract

 Traffic Engineered (TE) networks have a variety of mechanisms to
 facilitate the separation of the data plane and control plane.  They
 also have a range of management and provisioning protocols to
 configure and activate network resources.  These mechanisms represent
 key technologies for enabling flexible and dynamic networking.  The
 term "Traffic Engineered network" refers to a network that uses any
 connection-oriented technology under the control of a distributed or
 centralized control plane to support dynamic provisioning of end-to-
 end connectivity.
 Abstraction of network resources is a technique that can be applied
 to a single network domain or across multiple domains to create a
 single virtualized network that is under the control of a network
 operator or the customer of the operator that actually owns the
 network resources.
 This document provides a framework for Abstraction and Control of TE
 Networks (ACTN) to support virtual network services and connectivity
 services.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are candidates for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8453.

Ceccarelli & Lee Informational [Page 1] RFC 8453 ACTN Framework August 2018

Copyright Notice

 Copyright (c) 2018 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.2.  VNS Model of ACTN . . . . . . . . . . . . . . . . . . . .   7
     2.2.1.  Customers . . . . . . . . . . . . . . . . . . . . . .   9
     2.2.2.  Service Providers . . . . . . . . . . . . . . . . . .   9
     2.2.3.  Network Operators . . . . . . . . . . . . . . . . . .  10
 3.  ACTN Base Architecture  . . . . . . . . . . . . . . . . . . .  10
   3.1.  Customer Network Controller . . . . . . . . . . . . . . .  12
   3.2.  Multi-Domain Service Coordinator  . . . . . . . . . . . .  13
   3.3.  Provisioning Network Controller . . . . . . . . . . . . .  13
   3.4.  ACTN Interfaces . . . . . . . . . . . . . . . . . . . . .  14
 4.  Advanced ACTN Architectures . . . . . . . . . . . . . . . . .  15
   4.1.  MDSC Hierarchy  . . . . . . . . . . . . . . . . . . . . .  15
   4.2.  Functional Split of MDSC Functions in Orchestrators . . .  16
 5.  Topology Abstraction Methods  . . . . . . . . . . . . . . . .  18
   5.1.  Abstraction Factors . . . . . . . . . . . . . . . . . . .  18
   5.2.  Abstraction Types . . . . . . . . . . . . . . . . . . . .  19
     5.2.1.  Native/White Topology . . . . . . . . . . . . . . . .  19
     5.2.2.  Black Topology  . . . . . . . . . . . . . . . . . . .  19
     5.2.3.  Grey Topology . . . . . . . . . . . . . . . . . . . .  20
   5.3.  Methods of Building Grey Topologies . . . . . . . . . . .  21
     5.3.1.  Automatic Generation of Abstract Topology by
             Configuration . . . . . . . . . . . . . . . . . . . .  22
     5.3.2.  On-Demand Generation of Supplementary Topology via
             Path Compute Request/Reply  . . . . . . . . . . . . .  22
   5.4.  Hierarchical Topology Abstraction Example . . . . . . . .  23
   5.5.  VN Recursion with Network Layers  . . . . . . . . . . . .  25
 6.  Access Points and Virtual Network Access Points . . . . . . .  28
   6.1.  Dual-Homing Scenario  . . . . . . . . . . . . . . . . . .  30

Ceccarelli & Lee Informational [Page 2] RFC 8453 ACTN Framework August 2018

7. Advanced ACTN Application: Multi-Destination Service . . . . . 31

   7.1.  Preplanned Endpoint Migration . . . . . . . . . . . . . .  32
   7.2.  On-the-Fly Endpoint Migration . . . . . . . . . . . . . .  33
 8.  Manageability Considerations  . . . . . . . . . . . . . . . .  33
   8.1.  Policy  . . . . . . . . . . . . . . . . . . . . . . . . .  34
   8.2.  Policy Applied to the Customer Network Controller . . . .  34
   8.3.  Policy Applied to the Multi-Domain Service Coordinator  .  35
   8.4.  Policy Applied to the Provisioning Network Controller . .  35
 9.  Security Considerations . . . . . . . . . . . . . . . . . . .  36
   9.1.  CNC-MDSC Interface (CMI)  . . . . . . . . . . . . . . . .  37
   9.2.  MDSC-PNC Interface (MPI)  . . . . . . . . . . . . . . . .  37
 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  37
 11. Informative References  . . . . . . . . . . . . . . . . . . .  38
 Appendix A.  Example of MDSC and PNC Functions Integrated in a
              Service/Network Orchestrator . . . . . . . . . . . .  40
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  41
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

1. Introduction

 The term "Traffic Engineered network" refers to a network that uses
 any connection-oriented technology under the control of a distributed
 or centralized control plane to support dynamic provisioning of end-
 to-end connectivity.  TE networks have a variety of mechanisms to
 facilitate the separation of data planes and control planes including
 distributed signaling for path setup and protection, centralized path
 computation for planning and traffic engineering, and a range of
 management and provisioning protocols to configure and activate
 network resources.  These mechanisms represent key technologies for
 enabling flexible and dynamic networking.  Some examples of networks
 that are in scope of this definition are optical, MPLS Transport
 Profile (MPLS-TP) [RFC5654], and MPLS-TE networks [RFC2702].
 One of the main drivers for Software-Defined Networking (SDN)
 [RFC7149] is a decoupling of the network control plane from the data
 plane.  This separation has been achieved for TE networks with the
 development of MPLS/GMPLS [RFC3945] and the Path Computation Element
 (PCE) [RFC4655].  One of the advantages of SDN is its logically
 centralized control regime that allows a global view of the
 underlying networks.  Centralized control in SDN helps improve
 network resource utilization compared with distributed network
 control.  For TE-based networks, a PCE may serve as a logically
 centralized path computation function.
 This document describes a set of management and control functions
 used to operate one or more TE networks to construct virtual networks
 that can be presented to customers and that are built from
 abstractions of the underlying TE networks.  For example, a link in

Ceccarelli & Lee Informational [Page 3] RFC 8453 ACTN Framework August 2018

 the customer's network is constructed from a path or collection of
 paths in the underlying networks.  We call this set of functions
 "Abstraction and Control of TE Networks" or "ACTN".

2. Overview

 Three key aspects that need to be solved by SDN are:
 o  Separation of service requests from service delivery so that the
    configuration and operation of a network is transparent from the
    point of view of the customer but it remains responsive to the
    customer's services and business needs.
 o  Network abstraction: As described in [RFC7926], abstraction is the
    process of applying policy to a set of information about a TE
    network to produce selective information that represents the
    potential ability to connect across the network.  The process of
    abstraction presents the connectivity graph in a way that is
    independent of the underlying network technologies, capabilities,
    and topology so that the graph can be used to plan and deliver
    network services in a uniform way
 o  Coordination of resources across multiple independent networks and
    multiple technology layers to provide end-to-end services
    regardless of whether or not the networks use SDN.
 As networks evolve, the need to provide support for distinct
 services, separated service orchestration, and resource abstraction
 have emerged as key requirements for operators.  In order to support
 multiple customers each with its own view of and control of the
 server network, a network operator needs to partition (or "slice") or
 manage sharing of the network resources.  Network slices can be
 assigned to each customer for guaranteed usage, which is a step
 further than shared use of common network resources.
 Furthermore, each network represented to a customer can be built from
 virtualization of the underlying networks so that, for example, a
 link in the customer's network is constructed from a path or
 collection of paths in the underlying network.
 ACTN can facilitate virtual network operation via the creation of a
 single virtualized network or a seamless service.  This supports
 operators in viewing and controlling different domains (at any
 dimension: applied technology, administrative zones, or vendor-
 specific technology islands) and presenting virtualized networks to
 their customers.

Ceccarelli & Lee Informational [Page 4] RFC 8453 ACTN Framework August 2018

 The ACTN framework described in this document facilitates:
 o  Abstraction of the underlying network resources to higher-layer
    applications and customers [RFC7926].
 o  Virtualization of particular underlying resources, whose selection
    criterion is the allocation of those resources to a particular
    customer, application, or service [ONF-ARCH].
 o  TE Network slicing of infrastructure to meet specific customers'
    service requirements.
 o  Creation of an abstract environment allowing operators to view and
    control multi-domain networks as a single abstract network.
 o  The presentation to customers of networks as a virtual network via
    open and programmable interfaces.

2.1. Terminology

 The following terms are used in this document.  Some of them are
 newly defined, some others reference existing definitions:
 Domain:  A domain as defined by [RFC4655] is "any collection of
    network elements within a common sphere of address management or
    path computation responsibility".  Specifically, within this
    document we mean a part of an operator's network that is under
    common management (i.e., under shared operational management using
    the same instances of a tool and the same policies).  Network
    elements will often be grouped into domains based on technology
    types, vendor profiles, and geographic proximity.
 Abstraction:  This process is defined in [RFC7926].
 TE Network Slicing:  In the context of ACTN, a TE network slice is a
    collection of resources that is used to establish a logically
    dedicated virtual network over one or more TE networks.  TE
    network slicing allows a network operator to provide dedicated
    virtual networks for applications/customers over a common network
    infrastructure.  The logically dedicated resources are a part of
    the larger common network infrastructures that are shared among
    various TE network slice instances, which are the end-to-end
    realization of TE network slicing, consisting of the combination
    of physically or logically dedicated resources.

Ceccarelli & Lee Informational [Page 5] RFC 8453 ACTN Framework August 2018

 Node:  A node is a vertex on the graph representation of a TE
    topology.  In a physical network topology, a node corresponds to a
    physical network element (NE) such as a router.  In an abstract
    network topology, a node (sometimes called an "abstract node") is
    a representation as a single vertex of one or more physical NEs
    and their connecting physical connections.  The concept of a node
    represents the ability to connect from any access to the node (a
    link end) to any other access to that node, although "limited
    cross-connect capabilities" may also be defined to restrict this
    functionality.  Network abstraction may be applied recursively, so
    a node in one topology may be created by applying abstraction to
    the nodes in the underlying topology.
 Link:  A link is an edge on the graph representation of a TE
    topology.  Two nodes connected by a link are said to be "adjacent"
    in the TE topology.  In a physical network topology, a link
    corresponds to a physical connection.  In an abstract network
    topology, a link (sometimes called an "abstract link") is a
    representation of the potential to connect a pair of points with
    certain TE parameters (see [RFC7926] for details).  Network
    abstraction may be applied recursively, so a link in one topology
    may be created by applying abstraction to the links in the
    underlying topology.
 Abstract Topology:  The topology of abstract nodes and abstract links
    presented through the process of abstraction by a lower-layer
    network for use by a higher-layer network.
 Virtual Network (VN):  A VN is a network provided by a service
    provider to a customer for the customer to use in any way it wants
    as though it was a physical network.  There are two views of a VN
    as follows:
    o  The VN can be abstracted as a set of edge-to-edge links (a Type
       1 VN).  Each link is referred as a "VN member" and is formed as
       an end-to-end tunnel across the underlying networks.  Such
       tunnels may be constructed by recursive slicing or abstraction
       of paths in the underlying networks and can encompass edge
       points of the customer's network, access links, intra-domain
       paths, and inter-domain links.
    o  The VN can also be abstracted as a topology of virtual nodes
       and virtual links (a Type 2 VN).  The operator needs to map the
       VN to actual resource assignment, which is known as "virtual
       network embedding".  The nodes in this case include physical
       endpoints, border nodes, and internal nodes as well as

Ceccarelli & Lee Informational [Page 6] RFC 8453 ACTN Framework August 2018

       abstracted nodes.  Similarly, the links include physical access
       links, inter-domain links, and intra-domain links as well as
       abstract links.
    Clearly, a Type 1 VN is a special case of a Type 2 VN.
 Access link:  A link between a customer node and an operator node.
 Inter-domain link:  A link between domains under distinct management
    administration.
 Access Point (AP):  An AP is a logical identifier shared between the
    customer and the operator used to identify an access link.  The AP
    is used by the customer when requesting a Virtual Network Service
    (VNS).  Note that the term "TE Link Termination Point" defined in
    [TE-TOPO] describes the endpoints of links, while an AP is a
    common identifier for the link itself.
 VN Access Point (VNAP):  A VNAP is the binding between an AP and a
    given VN.
 Server Network:  As defined in [RFC7926], a server network is a
    network that provides connectivity for another network (the Client
    Network) in a client-server relationship.

2.2. VNS Model of ACTN

 A Virtual Network Service (VNS) is the service agreement between a
 customer and operator to provide a VN.  When a VN is a simple
 connectivity between two points, the difference between VNS and
 connectivity service becomes blurred.  There are three types of VNSs
 defined in this document.
 o  Type 1 VNS refers to a VNS in which the customer is allowed to
    create and operate a Type 1 VN.
 o  Type 2a and 2b VNS refer to VNSs in which the customer is allowed
    to create and operates a Type 2 VN.  With a Type 2a VNS, the VN is
    statically created at service configuration time, and the customer
    is not allowed to change the topology (e.g., by adding or deleting
    abstract nodes and links).  A Type 2b VNS is the same as a Type 2a
    VNS except that the customer is allowed to make dynamic changes to
    the initial topology created at service configuration time.

Ceccarelli & Lee Informational [Page 7] RFC 8453 ACTN Framework August 2018

 VN Operations are functions that a customer can exercise on a VN
 depending on the agreement between the customer and the operator.
 o  VN Creation allows a customer to request the instantiation of a
    VN.  This could be through offline preconfiguration or through
    dynamic requests specifying attributes to a Service Level
    Agreement (SLA) to satisfy the customer's objectives.
 o  Dynamic Operations allow a customer to modify or delete the VN.
    The customer can further act upon the virtual network to
    create/modify/delete virtual links and nodes.  These changes will
    result in subsequent tunnel management in the operator's networks.
 There are three key entities in the ACTN VNS model:
 o  Customers
 o  Service Providers
 o  Network Operators
 These entities are related in a three tier model as shown in
 Figure 1.
                         +----------------------+
                         |       Customer       |
                         +----------------------+
                                    |
                     VNS       ||   |   /\     VNS
                    Request    ||   |   ||    Reply
                               \/   |   ||
                         +----------------------+
                         |  Service Provider    |
                         +----------------------+
                         /          |           \
                        /           |            \
                       /            |             \
                      /             |              \
  +------------------+   +------------------+   +------------------+
  |Network Operator 1|   |Network Operator 2|   |Network Operator 3|
  +------------------+   +------------------+   +------------------+
                    Figure 1: The Three-Tier Model
 The commercial roles of these entities are described in the following
 sections.

Ceccarelli & Lee Informational [Page 8] RFC 8453 ACTN Framework August 2018

2.2.1. Customers

 Basic customers include fixed residential users, mobile users, and
 small enterprises.  Each requires a small amount of resources and is
 characterized by steady requests (relatively time invariant).  Basic
 customers do not modify their services themselves: if a service
 change is needed, it is performed by the provider as a proxy.
 Advanced customers include enterprises and governments.  Such
 customers ask for both point-to point and multipoint connectivity
 with high resource demands varying significantly in time.  This is
 one of the reasons why a bundled service offering is not enough, and
 it is desirable to provide each advanced customer with a customized
 VNS.  Advanced customers may also have the ability to modify their
 service parameters within the scope of their virtualized
 environments.  The primary focus of ACTN is Advanced Customers.
 As customers are geographically spread over multiple network operator
 domains, they have to interface to multiple operators and may have to
 support multiple virtual network services with different underlying
 objectives set by the network operators.  To enable these customers
 to support flexible and dynamic applications, they need to control
 their allocated virtual network resources in a dynamic fashion; that
 means that they need a view of the topology that spans all of the
 network operators.  Customers of a given service provider can, in
 turn, offer a service to other customers in a recursive way.

2.2.2. Service Providers

 In the scope of ACTN, service providers deliver VNSs to their
 customers.  Service providers may or may not own physical network
 resources (i.e., may or may not be network operators as described in
 Section 2.2.3).  When a service provider is the same as the network
 operator, the case is similar to existing VPN models applied to a
 single operator (although it may be hard to use this approach when
 the customer spans multiple independent network operator domains).
 When network operators supply only infrastructure, while distinct
 service providers interface with the customers, the service providers
 are themselves customers of the network infrastructure operators.
 One service provider may need to keep multiple independent network
 operators because its end users span geographically across multiple
 network operator domains.  In some cases, a service provider is also
 a network operator when it owns network infrastructure on which
 service is provided.

Ceccarelli & Lee Informational [Page 9] RFC 8453 ACTN Framework August 2018

2.2.3. Network Operators

 Network operators are the infrastructure operators that provision the
 network resources and provide network resources to their customers.
 The layered model described in this architecture separates the
 concerns of network operators and customers, with service providers
 acting as aggregators of customer requests.

3. ACTN Base Architecture

 This section provides a high-level model of ACTN, showing the
 interfaces and the flow of control between components.
 The ACTN architecture is based on a three-tier reference model and
 allows for hierarchy and recursion.  The main functionalities within
 an ACTN system are:
 o  Multi-domain coordination: This function oversees the specific
    aspects of different domains and builds a single abstracted end-
    to-end network topology in order to coordinate end-to-end path
    computation and path/service provisioning.  Domain sequence path
    calculation/determination is also a part of this function.
 o  Abstraction: This function provides an abstracted view of the
    underlying network resources for use by the customer -- a customer
    may be the client or a higher-level controller entity.  This
    function includes network path computation based on customer-
    service-connectivity request constraints, path computation based
    on the global network-wide abstracted topology, and the creation
    of an abstracted view of network resources allocated to each
    customer.  These operations depend on customer-specific network
    objective functions and customer traffic profiles.
 o  Customer mapping/translation: This function is to map customer
    requests/commands into network provisioning requests that can be
    sent from the Multi-Domain Service Coordinator (MDSC) to the
    Provisioning Network Controller (PNC) according to business
    policies provisioned statically or dynamically at the Operations
    Support System (OSS) / Network Management System (NMS).
    Specifically, it provides mapping and translation of a customer's
    service request into a set of parameters that are specific to a
    network type and technology such that network configuration
    process is made possible.
 o  Virtual service coordination: This function translates information
    that is customer service related into virtual network service
    operations in order to seamlessly operate virtual networks while
    meeting a customer's service requirements.  In the context of

Ceccarelli & Lee Informational [Page 10] RFC 8453 ACTN Framework August 2018

    ACTN, service/virtual service coordination includes a number of
    service orchestration functions such as multi-destination load-
    balancing and guarantees of service quality.  It also includes
    notifications for service fault and performance degradation and so
    forth.
 The base ACTN architecture defines three controller types and the
 corresponding interfaces between these controllers.  The following
 types of controller are shown in Figure 2:
 o  CNC - Customer Network Controller
 o  MDSC - Multi-Domain Service Coordinator
 o  PNC - Provisioning Network Controller
 Figure 2 also shows the following interfaces
 o  CMI - CNC-MDSC Interface
 o  MPI - MDSC-PNC Interface
 o  SBI - Southbound Interface

Ceccarelli & Lee Informational [Page 11] RFC 8453 ACTN Framework August 2018

           +---------+           +---------+             +---------+
           |   CNC   |           |   CNC   |             |   CNC   |
           +---------+           +---------+             +---------+
                 \                    |                       /
                  \                   |                      /
 Boundary  ========\==================|=====================/=======
 between            \                 |                    /
 Customer &          -----------      | CMI  --------------
 Network Operator               \     |     /
                              +---------------+
                              |     MDSC      |
                              +---------------+
                                /     |     \
                    ------------      | MPI  -------------
                   /                  |                   \
              +-------+          +-------+            +-------+
              |  PNC  |          |  PNC  |            |  PNC  |
              +-------+          +-------+            +-------+
                  | SBI            /   |                  /  \
                  |               /    | SBI         SBI /    \
              ---------        -----   |                /      \
             (         )      (     )  |               /        \
             - Control -     ( Phys. ) |              /      -----
            (  Plane    )     ( Net )  |             /      (     )
           (  Physical   )     -----   |            /      ( Phys. )
            (  Network  )            -----        -----     ( Net )
             -         -            (     )      (     )     -----
             (         )           ( Phys. )    ( Phys. )
              ---------             ( Net )      ( Net )
                                     -----        -----
                   Figure 2: ACTN Base Architecture
 Note that this is a functional architecture: an implementation and
 deployment might collocate one or more of the functional components.
 Figure 2 shows a case where the service provider is also a network
 operator.

3.1. Customer Network Controller

 A Customer Network Controller (CNC) is responsible for communicating
 a customer's VNS requirements to the network operator over the CNC-
 MDSC Interface (CMI).  It has knowledge of the endpoints associated
 with the VNS (expressed as APs), the service policy, and other QoS
 information related to the service.

Ceccarelli & Lee Informational [Page 12] RFC 8453 ACTN Framework August 2018

 As the CNC directly interfaces with the applications, it understands
 multiple application requirements and their service needs.  The
 capability of a CNC beyond its CMI role is outside the scope of ACTN
 and may be implemented in different ways.  For example, the CNC may,
 in fact, be a controller or part of a controller in the customer's
 domain, or the CNC functionality could also be implemented as part of
 a service provider's portal.

3.2. Multi-Domain Service Coordinator

 A Multi-Domain Service Coordinator (MDSC) is a functional block that
 implements all of the ACTN functions listed in Section 3 and
 described further in Section 4.2.  Two functions of the MDSC, namely,
 multi-domain coordination and virtualization/abstraction are referred
 to as network-related functions; whereas the other two functions,
 namely, customer mapping/translation and virtual service
 coordination, are referred to as service-related functions.  The MDSC
 sits at the center of the ACTN model between the CNC that issues
 connectivity requests and the Provisioning Network Controllers (PNCs)
 that manage the network resources.  The key point of the MDSC (and of
 the whole ACTN framework) is detaching the network and service
 control from underlying technology to help the customer express the
 network as desired by business needs.  The MDSC envelopes the
 instantiation of the right technology and network control to meet
 business criteria.  In essence, it controls and manages the
 primitives to achieve functionalities as desired by the CNC.
 In order to allow for multi-domain coordination, a 1:N relationship
 must be allowed between MDSCs and PNCs.
 In addition to that, it could also be possible to have an M:1
 relationship between MDSCs and PNCs to allow for network-resource
 partitioning/sharing among different customers that are not
 necessarily connected to the same MDSC (e.g., different service
 providers) but that are all using the resources of a common network
 infrastructure operator.

3.3. Provisioning Network Controller

 The Provisioning Network Controller (PNC) oversees configuring the
 network elements, monitoring the topology (physical or virtual) of
 the network, and collecting information about the topology (either
 raw or abstracted).
 The PNC functions can be implemented as part of an SDN domain
 controller, a Network Management System (NMS), an Element Management
 System (EMS), an active PCE-based controller [RFC8283], or any other
 means to dynamically control a set of nodes that implements a

Ceccarelli & Lee Informational [Page 13] RFC 8453 ACTN Framework August 2018

 northbound interface from the standpoint of the nodes (which is out
 of the scope of this document).  A PNC domain includes all the
 resources under the control of a single PNC.  It can be composed of
 different routing domains and administrative domains, and the
 resources may come from different layers.  The interconnection
 between PNC domains is illustrated in Figure 3.
                   _______                        _______
                 _(       )_                    _(       )_
               _(           )_                _(           )_
              (               )     Border   (               )
             (     PNC     ------   Link   ------     PNC     )
            (   Domain X  |Border|========|Border|  Domain Y   )
            (             | Node |        | Node |             )
             (             ------          ------             )
              (_             _)              (_             _)
                (_         _)                  (_         _)
                  (_______)                      (_______)
                     Figure 3: PNC Domain Borders

3.4. ACTN Interfaces

 Direct customer control of transport network elements and virtualized
 services is not a viable proposition for network operators due to
 security and policy concerns.  Therefore, the network has to provide
 open, programmable interfaces, through which customer applications
 can create, replace, and modify virtual network resources and
 services in an interactive, flexible, and dynamic fashion.
 Three interfaces exist in the ACTN architecture as shown in Figure 2.
 o  CMI: The CNC-MDSC Interface (CMI) is an interface between a CNC
    and an MDSC.  The CMI is a business boundary between customer and
    network operator.  It is used to request a VNS for an application.
    All service-related information is conveyed over this interface
    (such as the VNS type, topology, bandwidth, and service
    constraints).  Most of the information over this interface is
    agnostic of the technology used by network operators, but there
    are some cases (e.g., access link configuration) where it is
    necessary to specify technology-specific details.
 o  MPI: The MDSC-PNC Interface (MPI) is an interface between an MDSC
    and a PNC.  It communicates requests for new connectivity or for
    bandwidth changes in the physical network.  In multi-domain
    environments, the MDSC needs to communicate with multiple PNCs,

Ceccarelli & Lee Informational [Page 14] RFC 8453 ACTN Framework August 2018

    each responsible for control of a domain.  The MPI presents an
    abstracted topology to the MDSC hiding technology-specific aspects
    of the network and hiding topology according to policy.
 o  SBI: The Southbound Interface (SBI) is out of scope of ACTN.  Many
    different SBIs have been defined for different environments,
    technologies, standards organizations, and vendors.  It is shown
    in Figure 3 for reference reason only.

4. Advanced ACTN Architectures

 This section describes advanced configurations of the ACTN
 architecture.

4.1. MDSC Hierarchy

 A hierarchy of MDSCs can be foreseen for many reasons, among which
 are scalability, administrative choices, or putting together
 different layers and technologies in the network.  In the case where
 there is a hierarchy of MDSCs, we introduce the terms "higher-level
 MDSC" (MDSC-H) and "lower-level MDSC" (MDSC-L).  The interface
 between them is a recursion of the MPI.  An implementation of an
 MDSC-H makes provisioning requests as normal using the MPI, but an
 MDSC-L must be able to receive requests as normal at the CMI and also
 at the MPI.  The hierarchy of MDSCs can be seen in Figure 4.
 Another implementation choice could foresee the usage of an MDSC-L
 for all the PNCs related to a given technology (e.g., Internet
 Protocol (IP) / Multiprotocol Label Switching (MPLS)) and a different
 MDSC-L for the PNCs related to another technology (e.g., Optical
 Transport Network (OTN) / Wavelength Division Multiplexing (WDM)) and
 an MDSC-H to coordinate them.

Ceccarelli & Lee Informational [Page 15] RFC 8453 ACTN Framework August 2018

                                +--------+
                                |   CNC  |
                                +--------+
                                     |          +-----+
                                     | CMI      | CNC |
                               +----------+     +-----+
                        -------|  MDSC-H  |----    |
                       |       +----------+    |   | CMI
                   MPI |                   MPI |   |
                       |                       |   |
                  +---------+               +---------+
                  |  MDSC-L |               |  MDSC-L |
                  +---------+               +---------+
                MPI |     |                   |     |
                    |     |                   |     |
                 -----   -----             -----   -----
                | PNC | | PNC |           | PNC | | PNC |
                 -----   -----             -----   -----
                       Figure 4: MDSC Hierarchy
 The hierarchy of MDSC can be recursive, where an MDSC-H is, in turn,
 an MDSC-L to a higher-level MDSC-H.

4.2. Functional Split of MDSC Functions in Orchestrators

 An implementation choice could separate the MDSC functions into two
 groups: one group for service-related functions and the other for
 network-related functions.  This enables the implementation of a
 service orchestrator that provides the service-related functions of
 the MDSC and a network orchestrator that provides the network-related
 functions of the MDSC.  This split is consistent with the YANG
 service model architecture described in [RFC8309].  Figure 5 depicts
 this and shows how the ACTN interfaces may map to YANG data models.

Ceccarelli & Lee Informational [Page 16] RFC 8453 ACTN Framework August 2018

                              +--------------------+
                              |           Customer |
                              |   +-----+          |
                              |   | CNC |          |
                              |   +-----+          |
                              +--------------------+
                                       CMI |  Customer Service Model
                                           |
                      +---------------------------------------+
                      |                          Service      |
              ********|***********************   Orchestrator |
              * MDSC  |  +-----------------+ *                |
              *       |  | Service-related | *                |
              *       |  |    Functions    | *                |
              *       |  +-----------------+ *                |
              *       +----------------------*----------------+
              *                              *  |  Service Delivery
              *                              *  |  Model
              *       +----------------------*----------------+
              *       |                      *   Network      |
              *       |  +-----------------+ *   Orchestrator |
              *       |  | Network-related | *                |
              *       |  |    Functions    | *                |
              *       |  +-----------------+ *                |
              ********|***********************                |
                      +---------------------------------------+
                                       MPI |  Network Configuration
                                           |  Model
                             +------------------------+
                             |            Domain      |
                             |  +------+  Controller  |
                             |  | PNC  |              |
                             |  +------+              |
                             +------------------------+
                                       SBI |  Device Configuration
                                           |  Model
                                       +--------+
                                       | Device |
                                       +--------+
 Figure 5: ACTN Architecture in the Context of the YANG Service Models

Ceccarelli & Lee Informational [Page 17] RFC 8453 ACTN Framework August 2018

5. Topology Abstraction Methods

 Topology abstraction is described in [RFC7926].  This section
 discusses topology abstraction factors, types, and their context in
 the ACTN architecture.
 Abstraction in ACTN is performed by the PNC when presenting available
 topology to the MDSC, or by an MDSC-L when presenting topology to an
 MDSC-H.  This function is different from the creation of a VN (and
 particularly a Type 2 VN) that is not abstraction but construction of
 virtual resources.

5.1. Abstraction Factors

 As discussed in [RFC7926], abstraction is tied with the policy of the
 networks.  For instance, per an operational policy, the PNC would not
 provide any technology-specific details (e.g., optical parameters for
 Wavelength Switched Optical Network (WSON) in the abstract topology
 it provides to the MDSC.  Similarly, the policy of the networks may
 determine the abstraction type as described in Section 5.2.
 There are many factors that may impact the choice of abstraction:
 o  Abstraction depends on the nature of the underlying domain
    networks.  For instance, packet networks may be abstracted with
    fine granularity while abstraction of optical networks depends on
    the switching units (such as wavelengths) and the end-to-end
    continuity and cross-connect limitations within the network.
 o  Abstraction also depends on the capability of the PNCs.  As
    abstraction requires hiding details of the underlying network
    resources, the PNC's capability to run algorithms impacts the
    feasibility of abstraction.  Some PNCs may not have the ability to
    abstract native topology while other PNCs may have the ability to
    use sophisticated algorithms.
 o  Abstraction is a tool that can improve scalability.  Where the
    native network resource information is of a large size, there is a
    specific scaling benefit to abstraction.
 o  The proper abstraction level may depend on the frequency of
    topology updates and vice versa.
 o  The nature of the MDSC's support for technology-specific
    parameters impacts the degree/level of abstraction.  If the MDSC
    is not capable of handling such parameters, then a higher level of
    abstraction is needed.

Ceccarelli & Lee Informational [Page 18] RFC 8453 ACTN Framework August 2018

 o  In some cases, the PNC is required to hide key internal
    topological data from the MDSC.  Such confidentiality can be
    achieved through abstraction.

5.2. Abstraction Types

 This section defines the following three types of topology
 abstraction:
 o  Native/White Topology (Section 5.2.1)
 o  Black Topology (Section 5.2.2)
 o  Grey Topology (Section 5.2.3)

5.2.1. Native/White Topology

 This is a case where the PNC provides the actual network topology to
 the MDSC without any hiding or filtering of information, i.e., no
 abstraction is performed.  In this case, the MDSC has the full
 knowledge of the underlying network topology and can operate on it
 directly.

5.2.2. Black Topology

 A black topology replaces a full network with a minimal
 representation of the edge-to-edge topology without disclosing any
 node internal connectivity information.  The entire domain network
 may be abstracted as a single abstract node with the network's
 access/egress links appearing as the ports to the abstract node and
 the implication that any port can be "cross-connected" to any other.
 Figure 6 depicts a native topology with the corresponding black
 topology with one virtual node and inter-domain links.  In this case,
 the MDSC has to make a provisioning request to the PNCs to establish
 the port-to-port connection.  If there is a large number of
 interconnected domains, this abstraction method may impose a heavy
 coordination load at the MDSC level in order to find an optimal end-
 to-end path since the abstraction hides so much information that it
 is not possible to determine whether an end-to-end path is feasible
 without asking each PNC to set up each path fragment.  For this
 reason, the MPI might need to be enhanced to allow the PNCs to be
 queried for the practicality and characteristics of paths across the
 abstract node.

Ceccarelli & Lee Informational [Page 19] RFC 8453 ACTN Framework August 2018

                 .....................................
                 : PNC Domain                        :
                 :  +--+     +--+     +--+     +--+  :
              ------+  +-----+  +-----+  +-----+  +------
                 :  ++-+     ++-+     +-++     +-++  :
                 :   |        |         |        |   :
                 :   |        |         |        |   :
                 :   |        |         |        |   :
                 :   |        |         |        |   :
                 :  ++-+     ++-+     +-++     +-++  :
              ------+  +-----+  +-----+  +-----+  +------
                 :  +--+     +--+     +--+     +--+  :
                 :....................................
                              +----------+
                           ---+          +---
                              | Abstract |
                              |   Node   |
                           ---+          +---
                              +----------+
             Figure 6: Native Topology with Corresponding
             Black Topology Expressed as an Abstract Node

5.2.3. Grey Topology

 A grey topology represents a compromise between black and white
 topologies from a granularity point of view.  In this case, the PNC
 exposes an abstract topology containing all PNC domain border nodes
 and an abstraction of the connectivity between those border nodes.
 This abstraction may contain either physical or abstract nodes/links.
 Two types of grey topology are identified:
 o  In a type A grey topology, border nodes are connected by a full
    mesh of TE links (see Figure 7).
 o  In a type B grey topology, border nodes are connected over a more-
    detailed network comprising internal abstract nodes and abstracted
    links.  This mode of abstraction supplies the MDSC with more
    information about the internals of the PNC domain and allows it to
    make more informed choices about how to route connectivity over
    the underlying network.

Ceccarelli & Lee Informational [Page 20] RFC 8453 ACTN Framework August 2018

                .....................................
                : PNC Domain                        :
                :  +--+     +--+     +--+     +--+  :
             ------+  +-----+  +-----+  +-----+  +------
                :  ++-+     ++-+     +-++     +-++  :
                :   |        |         |        |   :
                :   |        |         |        |   :
                :   |        |         |        |   :
                :   |        |         |        |   :
                :  ++-+     ++-+     +-++     +-++  :
             ------+  +-----+  +-----+  +-----+  +------
                :  +--+     +--+     +--+     +--+  :
                :....................................
                         ....................
                         : Abstract Network :
                         :                  :
                         :   +--+    +--+   :
                      -------+  +----+  +-------
                         :   ++-+    +-++   :
                         :    |  \  /  |    :
                         :    |   \/   |    :
                         :    |   /\   |    :
                         :    |  /  \  |    :
                         :   ++-+    +-++   :
                      -------+  +----+  +-------
                         :   +--+    +--+   :
                         :..................:
      Figure 7: Native Topology with Corresponding Grey Topology

5.3. Methods of Building Grey Topologies

 This section discusses two different methods of building a grey
 topology:
 o  Automatic generation of abstract topology by configuration
    (Section 5.3.1)
 o  On-demand generation of supplementary topology via path
    computation request/reply (Section 5.3.2)

Ceccarelli & Lee Informational [Page 21] RFC 8453 ACTN Framework August 2018

5.3.1. Automatic Generation of Abstract Topology by Configuration

 Automatic generation is based on the abstraction/summarization of the
 whole domain by the PNC and its advertisement on the MPI.  The level
 of abstraction can be decided based on PNC configuration parameters
 (e.g., "provide the potential connectivity between any PE and any
 ASBR in an MPLS-TE network").
 Note that the configuration parameters for this abstract topology can
 include available bandwidth, latency, or any combination of defined
 parameters.  How to generate such information is beyond the scope of
 this document.
 This abstract topology may need to be periodically or incrementally
 updated when there is a change in the underlying network or the use
 of the network resources that make connectivity more or less
 available.

5.3.2. On-Demand Generation of Supplementary Topology via Path Compute

      Request/Reply
 While abstract topology is generated and updated automatically by
 configuration as explained in Section 5.3.1, additional supplementary
 topology may be obtained by the MDSC via a path compute request/reply
 mechanism.
 The abstract topology advertisements from PNCs give the MDSC the
 border node/link information for each domain.  Under this scenario,
 when the MDSC needs to create a new VN, the MDSC can issue path
 computation requests to PNCs with constraints matching the VN request
 as described in [ACTN-YANG].  An example is provided in Figure 8,
 where the MDSC is creating a P2P VN between AP1 and AP2.  The MDSC
 could use two different inter-domain links to get from domain X to
 domain Y, but in order to choose the best end-to-end path, it needs
 to know what domain X and Y can offer in terms of connectivity and
 constraints between the PE nodes and the border nodes.
  1. —— ——–

( ) ( )

  1. BrdrX.1——- BrdrY.1 -

(+—+ ) ( +—+)

  1. +—( |PE1| Dom.X ) ( Dom.Y |PE2| )—+-

| (+—+ ) ( +—+) |

             AP1    -      BrdrX.2------- BrdrY.2      -    AP2
                     (       )               (        )
                      -------                 --------
                   Figure 8: A Multi-Domain Example

Ceccarelli & Lee Informational [Page 22] RFC 8453 ACTN Framework August 2018

 The MDSC issues a path computation request to PNC.X asking for
 potential connectivity between PE1 and border node BrdrX.1 and
 between PE1 and BrdrX.2 with related objective functions and TE
 metric constraints.  A similar request for connectivity from the
 border nodes in domain Y to PE2 will be issued to PNC.Y.  The MDSC
 merges the results to compute the optimal end-to-end path including
 the inter-domain links.  The MDSC can use the result of this
 computation to request the PNCs to provision the underlying networks,
 and the MDSC can then use the end-to-end path as a virtual link in
 the VN it delivers to the customer.

5.4. Hierarchical Topology Abstraction Example

 This section illustrates how topology abstraction operates in
 different levels of a hierarchy of MDSCs as shown in Figure 9.

Ceccarelli & Lee Informational [Page 23] RFC 8453 ACTN Framework August 2018

                           +-----+
                           | CNC |  CNC wants to create a VN
                           +-----+  between CE A and CE B
                              |
                              |
                  +-----------------------+
                  |         MDSC-H        |
                  +-----------------------+
                        /           \
                       /             \
               +---------+         +---------+
               | MDSC-L1 |         | MDSC-L2 |
               +---------+         +---------+
                 /    \               /    \
                /      \             /      \
             +----+  +----+       +----+  +----+
   CE A o----|PNC1|  |PNC2|       |PNC3|  |PNC4|----o CE B
             +----+  +----+       +----+  +----+
                 Virtual Network Delivered to CNC
                   CE A o==============o CE B
                 Topology operated on by MDSC-H
                CE A o----o==o==o===o----o CE B
   Topology operated on by MDSC-L1     Topology operated on by MDSC-L2
                _        _                       _        _
               ( )      ( )                     ( )      ( )
              (   )    (   )                   (   )    (   )
     CE A o--(o---o)==(o---o)==Dom.3   Dom.2==(o---o)==(o---o)--o CE B
              (   )    (   )                   (   )    (   )
               (_)      (_)                     (_)      (_)

Ceccarelli & Lee Informational [Page 24] RFC 8453 ACTN Framework August 2018

                            Actual Topology
              ___          ___          ___          ___
             (   )        (   )        (   )        (   )
            (  o  )      (  o  )      ( o--o)      (  o  )
           (  / \  )    (   |\  )    (  |  | )    (  / \  )
 CE A o---(o-o---o-o)==(o-o-o-o-o)==(o--o--o-o)==(o-o-o-o-o)---o CE B
           (  \ /  )    ( | |/  )    (  |  | )    (  \ /  )
            (  o  )      (o-o  )      ( o--o)      (  o  )
             (___)        (___)        (___)        (___)
            Domain 1     Domain 2     Domain 3     Domain 4
 Where
      o   is a node
      --- is a link
      === is a border link
      Figure 9: Illustration of Hierarchical Topology Abstraction
 In the example depicted in Figure 9, there are four domains under
 control of PNCs: PNC1, PNC2, PNC3, and PNC4.  MDSC-L1 controls PNC1
 and PNC2, while MDSC-L2 controls PNC3 and PNC4.  Each of the PNCs
 provides a grey topology abstraction that presents only border nodes
 and links across and outside the domain.  The abstract topology
 MDSC-L1 that operates is a combination of the two topologies from
 PNC1 and PNC2.  Likewise, the abstract topology that MDSC-L2 operates
 is shown in Figure 9.  Both MDSC-L1 and MDSC-L2 provide a black
 topology abstraction to MDSC-H in which each PNC domain is presented
 as a single virtual node.  MDSC-H combines these two topologies to
 create the abstraction topology on which it operates.  MDSC-H sees
 the whole four domain networks as four virtual nodes connected via
 virtual links.

5.5. VN Recursion with Network Layers

 In some cases, the VN supplied to a customer may be built using
 resources from different technology layers operated by different
 operators.  For example, one operator may run a packet TE network and
 use optical connectivity provided by another operator.
 As shown in Figure 10, a customer asks for end-to-end connectivity
 between CE A and CE B, a virtual network.  The customer's CNC makes a
 request to Operator 1's MDSC.  The MDSC works out which network
 resources need to be configured and sends instructions to the
 appropriate PNCs.  However, the link between Q and R is a virtual
 link supplied by Operator 2: Operator 1 is a customer of Operator 2.

Ceccarelli & Lee Informational [Page 25] RFC 8453 ACTN Framework August 2018

 To support this, Operator 1 has a CNC that communicates with Operator
 2's MDSC.  Note that Operator 1's CNC in Figure 10 is a functional
 component that does not dictate implementation: it may be embedded in
 a PNC.

Ceccarelli & Lee Informational [Page 26] RFC 8453 ACTN Framework August 2018

    Virtual     CE A o===============================o CE B
    Network
  1. —- CNC wants to create a VN

Customer | CNC | between CE A and CE B

  1. —-

:

  • : Operator 1 ————————— | MDSC | ————————— : : : : : : —– ————- —– | PNC | | PNC | | PNC | —– ————- —– : : : : : Higher v v : v v Layer CE A o—P—–Q===========R—–S—o CE B Network | : | | : | | —– | | | CNC | | | —– | | : | *

| : |

    Operator 2                |  ------   |
                              | | MDSC |  |
                              |  ------   |
                              |     :     |
                              |  -------  |
                              | |  PNC  | |
                              |  -------  |
                               \ :  :  : /
    Lower                       \v  v  v/
    Layer                        X--Y--Z
    Network
    Where
  1. – is a link

=== is a virtual link

              Figure 10: VN Recursion with Network Layers

Ceccarelli & Lee Informational [Page 27] RFC 8453 ACTN Framework August 2018

6. Access Points and Virtual Network Access Points

 In order to map identification of connections between the customer's
 sites and the TE networks and to scope the connectivity requested in
 the VNS, the CNC and the MDSC refer to the connections using the
 Access Point (AP) construct as shown in Figure 11.
  1. ————

( )

  1. -

+—+ X ( ) Z +—+

             |CE1|---+----(                   )---+---|CE2|
             +---+   |     (                 )    |   +---+
                    AP1     -               -    AP2
                             (             )
                              -------------
                    Figure 11: Customer View of APs
 Let's take as an example a scenario shown in Figure 11.  CE1 is
 connected to the network via a 10 Gbps link and CE2 via a 40 Gbps
 link.  Before the creation of any VN between AP1 and AP2, the
 customer view can be summarized as shown in Figure 12.
                          +----------+------------------------+
                          | Endpoint | Access Link Bandwidth  |
                    +-----+----------+----------+-------------+
                    |AP id| CE,port  | MaxResBw | AvailableBw |
                    +-----+----------+----------+-------------+
                    | AP1 |CE1,portX |  10 Gbps |   10 Gbps   |
                    +-----+----------+----------+-------------+
                    | AP2 |CE2,portZ |  40 Gbps |   40 Gbps   |
                    +-----+----------+----------+-------------+
                     Figure 12: AP - Customer View

Ceccarelli & Lee Informational [Page 28] RFC 8453 ACTN Framework August 2018

 On the other hand, what the operator sees is shown in Figure 13
  1. —— ——-

( ) ( )

  1. - - -

W (+—+ ) ( +—+) Y

  1. +—( |PE1| Dom.X )—-( Dom.Y |PE2| )—+-

| (+—+ ) ( +—+) |

               AP1    -         -        -         -     AP2
                       (       )          (       )
                        -------            -------
                  Figure 13: Operator View of the AP
 which results in a summarization as shown in Figure 14.
                          +----------+------------------------+
                          | Endpoint | Access Link Bandwidth  |
                    +-----+----------+----------+-------------+
                    |AP id| PE,port  | MaxResBw | AvailableBw |
                    +-----+----------+----------+-------------+
                    | AP1 |PE1,portW |  10 Gbps |   10 Gbps   |
                    +-----+----------+----------+-------------+
                    | AP2 |PE2,portY |  40 Gbps |   40 Gbps   |
                    +-----+----------+----------+-------------+
                     Figure 14: AP - Operator View
 A Virtual Network Access Point (VNAP) needs to be defined as binding
 between an AP and a VN.  It is used to allow different VNs to start
 from the same AP.  It also allows for traffic engineering on the
 access and/or inter-domain links (e.g., keeping track of bandwidth
 allocation).  A different VNAP is created on an AP for each VN.
 In this simple scenario, we suppose we want to create two virtual
 networks: the first with VN identifier 9 between AP1 and AP2 with
 bandwidth of 1 Gbps and the second with VN identifier 5, again
 between AP1 and AP2 and with bandwidth 2 Gbps.
 The operator view would evolve as shown in Figure 15.

Ceccarelli & Lee Informational [Page 29] RFC 8453 ACTN Framework August 2018

                         +----------+------------------------+
                         | Endpoint |  Access Link/VNAP Bw   |
               +---------+----------+----------+-------------+
               |AP/VNAPid| PE,port  | MaxResBw | AvailableBw |
               +---------+----------+----------+-------------+
               |AP1      |PE1,portW | 10 Gbps  |   7 Gbps    |
               | -VNAP1.9|          |  1 Gbps  |     N.A.    |
               | -VNAP1.5|          |  2 Gbps  |     N.A     |
               +---------+----------+----------+-------------+
               |AP2      |PE2,portY | 4 0Gbps  |   37 Gbps   |
               | -VNAP2.9|          |  1 Gbps  |     N.A.    |
               | -VNAP2.5|          |  2 Gbps  |     N.A     |
               +---------+----------+----------+-------------+
       Figure 15: AP and VNAP - Operator View after VNS Creation

6.1. Dual-Homing Scenario

 Often there is a dual-homing relationship between a CE and a pair of
 PEs.  This case needs to be supported by the definition of VN, APs,
 and VNAPs.  Suppose CE1 connected to two different PEs in the
 operator domain via AP1 and AP2 and that the customer needs 5 Gbps of
 bandwidth between CE1 and CE2.  This is shown in Figure 16.
                                    ____________
                            AP1    (            )    AP3
                           -------(PE1)      (PE3)-------
                        W /      (                )      \ X
                    +---+/      (                  )      \+---+
                    |CE1|      (                    )      |CE2|
                    +---+\      (                  )      /+---+
                        Y \      (                )      / Z
                           -------(PE2)      (PE4)-------
                            AP2    (____________)
                    Figure 16: Dual-Homing Scenario
 In this case, the customer will request a VN between AP1, AP2, and
 AP3 specifying a dual-homing relationship between AP1 and AP2.  As a
 consequence, no traffic will flow between AP1 and AP2.  The dual-
 homing relationship would then be mapped against the VNAPs (since
 other independent VNs might have AP1 and AP2 as endpoints).
 The customer view would be shown in Figure 17.

Ceccarelli & Lee Informational [Page 30] RFC 8453 ACTN Framework August 2018

                    +----------+------------------------+
                    | Endpoint |  Access Link/VNAP Bw   |
          +---------+----------+----------+-------------+-----------+
          |AP/VNAPid| CE,port  | MaxResBw | AvailableBw |Dual Homing|
          +---------+----------+----------+-------------+-----------+
          |AP1      |CE1,portW | 10 Gbps  |   5 Gbps    |           |
          | -VNAP1.9|          |  5 Gbps  |     N.A.    | VNAP2.9   |
          +---------+----------+----------+-------------+-----------+
          |AP2      |CE1,portY | 40 Gbps  |   35 Gbps   |           |
          | -VNAP2.9|          |  5 Gbps  |     N.A.    | VNAP1.9   |
          +---------+----------+----------+-------------+-----------+
          |AP3      |CE2,portX | 50 Gbps  |  45 Gbps    |           |
          | -VNAP3.9|          |  5 Gbps  |     N.A.    |   NONE    |
          +---------+----------+----------+-------------+-----------+
       Figure 17: Dual-Homing -- Customer View after VN Creation

7. Advanced ACTN Application: Multi-Destination Service

 A more-advanced application of ACTN is the case of data center (DC)
 selection, where the customer requires the DC selection to be based
 on the network status; this is referred to as "Multi-Destination
 Service" in [ACTN-REQ].  In terms of ACTN, a CNC could request a VNS
 between a set of source APs and destination APs and leave it up to
 the network (MDSC) to decide which source and destination APs to be
 used to set up the VNS.  The candidate list of source and destination
 APs is decided by a CNC (or an entity outside of ACTN) based on
 certain factors that are outside the scope of ACTN.
 Based on the AP selection as determined and returned by the network
 (MDSC), the CNC (or an entity outside of ACTN) should further take
 care of any subsequent actions such as orchestration or service setup
 requirements.  These further actions are outside the scope of ACTN.
 Consider a case as shown in Figure 18, where three DCs are available,
 but the customer requires the DC selection to be based on the network
 status and the connectivity service setup between the AP1 (CE1) and
 one of the destination APs (AP2 (DC-A), AP3 (DC-B), and AP4 (DC-C)).
 The MDSC (in coordination with PNCs) would select the best
 destination AP based on the constraints, optimization criteria,
 policies, etc., and set up the connectivity service (virtual
 network).

Ceccarelli & Lee Informational [Page 31] RFC 8453 ACTN Framework August 2018

  1. —— ——-

( ) ( )

  1. - - -

+—+ ( ) ( ) +—-+

        |CE1|---+---(  Domain X   )----(  Domain Y   )---+---|DC-A|
        +---+   |    (           )      (           )    |   +----+
                 AP1  -         -        -         -    AP2
                       (       )          (       )
                        ---+---            ---+---
                           |                  |
                       AP3-+              AP4-+
                           |                  |
                        +----+              +----+
                        |DC-B|              |DC-C|
                        +----+              +----+
         Figure 18: Endpoint Selection Based on Network Status

7.1. Preplanned Endpoint Migration

 Furthermore, in the case of DC selection, a customer could request a
 backup DC to be selected, such that in case of failure, another DC
 site could provide hot stand-by protection.  As shown in Figure 19,
 DC-C is selected as a backup for DC-A.  Thus, the VN should be set up
 by the MDSC to include primary connectivity between AP1 (CE1) and AP2
 (DC-A) as well as protection connectivity between AP1 (CE1) and AP4
 (DC-C).
  1. —— ——-

( ) ( )

  1. - __ - -

+—+ ( ) ( ) +—-+

 |CE1|---+----(  Domain X   )----(  Domain Y   )---+---|DC-A|
 +---+   |     (           )      (           )    |   +----+
         AP1    -         -        -         -    AP2    |
                 (       )          (       )            |
                  ---+---            ---+---             |
                     |                  |                |
                 AP3-|              AP4-|         HOT STANDBY
                     |                  |                |
                  +----+             +----+              |
                  |DC-D|             |DC-C|<-------------
                  +----+             +----+
               Figure 19: Preplanned Endpoint Migration

Ceccarelli & Lee Informational [Page 32] RFC 8453 ACTN Framework August 2018

7.2. On-the-Fly Endpoint Migration

 Compared to preplanned endpoint migration, on-the-fly endpoint
 selection is dynamic in that the migration is not preplanned but
 decided based on network condition.  Under this scenario, the MDSC
 would monitor the network (based on the VN SLA) and notify the CNC in
 the case where some other destination AP would be a better choice
 based on the network parameters.  The CNC should instruct the MDSC
 when it is suitable to update the VN with the new AP if it is
 required.

8. Manageability Considerations

 The objective of ACTN is to manage traffic engineered resources and
 provide a set of mechanisms to allow customers to request virtual
 connectivity across server-network resources.  ACTN supports multiple
 customers, each with its own view of and control of a virtual network
 built on the server network; the network operator will need to
 partition (or "slice") their network resources, and manage the
 resources accordingly.
 The ACTN platform will, itself, need to support the request,
 response, and reservations of client- and network-layer connectivity.
 It will also need to provide performance monitoring and control of TE
 resources.  The management requirements may be categorized as
 follows:
 o  Management of external ACTN protocols
 o  Management of internal ACTN interfaces/protocols
 o  Management and monitoring of ACTN components
 o  Configuration of policy to be applied across the ACTN system
 The ACTN framework and interfaces are defined to enable traffic
 engineering for virtual network services and connectivity services.
 Network operators may have other Operations, Administration, and
 Maintenance (OAM) tasks for service fulfillment, optimization, and
 assurance beyond traffic engineering.  The realization of OAM beyond
 abstraction and control of TE networks is not discussed in this
 document.

Ceccarelli & Lee Informational [Page 33] RFC 8453 ACTN Framework August 2018

8.1. Policy

 Policy is an important aspect of ACTN control and management.
 Policies are used via the components and interfaces, during
 deployment of the service, to ensure that the service is compliant
 with agreed-upon policy factors and variations (often described in
 SLAs); these include, but are not limited to connectivity, bandwidth,
 geographical transit, technology selection, security, resilience, and
 economic cost.
 Depending on the deployment of the ACTN architecture, some policies
 may have local or global significance.  That is, certain policies may
 be ACTN component specific in scope, while others may have broader
 scope and interact with multiple ACTN components.  Two examples are
 provided below:
 o  A local policy might limit the number, type, size, and scheduling
    of virtual network services a customer may request via its CNC.
    This type of policy would be implemented locally on the MDSC.
 o  A global policy might constrain certain customer types (or
    specific customer applications) only to use certain MDSCs and be
    restricted to physical network types managed by the PNCs.  A
    global policy agent would govern these types of policies.
 The objective of this section is to discuss the applicability of ACTN
 policy: requirements, components, interfaces, and examples.  This
 section provides an analysis and does not mandate a specific method
 for enforcing policy, or the type of policy agent that would be
 responsible for propagating policies across the ACTN components.  It
 does highlight examples of how policy may be applied in the context
 of ACTN, but it is expected further discussion in an applicability or
 solution-specific document, will be required.

8.2. Policy Applied to the Customer Network Controller

 A virtual network service for a customer application will be
 requested by the CNC.  The request will reflect the application
 requirements and specific service needs, including bandwidth, traffic
 type and survivability.  Furthermore, application access and type of
 virtual network service requested by the CNC, will be need adhere to
 specific access control policies.

Ceccarelli & Lee Informational [Page 34] RFC 8453 ACTN Framework August 2018

8.3. Policy Applied to the Multi-Domain Service Coordinator

 A key objective of the MDSC is to support the customer's expression
 of the application connectivity request via its CNC as a set of
 desired business needs; therefore, policy will play an important
 role.
 Once authorized, the virtual network service will be instantiated via
 the CNC-MDSC Interface (CMI); it will reflect the customer
 application and connectivity requirements and specific service-
 transport needs.  The CNC and the MDSC components will have agreed-
 upon connectivity endpoints; use of these endpoints should be defined
 as a policy expression when setting up or augmenting virtual network
 services.  Ensuring that permissible endpoints are defined for CNCs
 and applications will require the MDSC to maintain a registry of
 permissible connection points for CNCs and application types.
 Conflicts may occur when virtual network service optimization
 criteria are in competition.  For example, to meet objectives for
 service reachability, a request may require an interconnection point
 between multiple physical networks; however, this might break a
 confidentially policy requirement of a specific type of end-to-end
 service.  Thus, an MDSC may have to balance a number of the
 constraints on a service request and between different requested
 services.  It may also have to balance requested services with
 operational norms for the underlying physical networks.  This
 balancing may be resolved using configured policy and using hard and
 soft policy constraints.

8.4. Policy Applied to the Provisioning Network Controller

 The PNC is responsible for configuring the network elements,
 monitoring physical network resources, and exposing connectivity
 (direct or abstracted) to the MDSC.  Therefore, it is expected that
 policy will dictate what connectivity information will be exchanged
 on the MPI.
 Policy interactions may arise when a PNC determines that it cannot
 compute a requested path from the MDSC, or notices that (per a
 locally configured policy) the network is low on resources (for
 example, the capacity on key links became exhausted).  In either
 case, the PNC will be required to notify the MDSC, which may (again
 per policy) act to construct a virtual network service across another
 physical network topology.

Ceccarelli & Lee Informational [Page 35] RFC 8453 ACTN Framework August 2018

 Furthermore, additional forms of policy-based resource management
 will be required to provide VNS performance, security, and resilience
 guarantees.  This will likely be implemented via a local policy agent
 and additional protocol methods.

9. Security Considerations

 The ACTN framework described in this document defines key components
 and interfaces for managed TE networks.  Securing the request and
 control of resources, confidentiality of the information, and
 availability of function should all be critical security
 considerations when deploying and operating ACTN platforms.
 Several distributed ACTN functional components are required, and
 implementations should consider encrypting data that flows between
 components, especially when they are implemented at remote nodes,
 regardless of whether these data flows are on external or internal
 network interfaces.
 The ACTN security discussion is further split into two specific
 categories described in the following subsections:
 o  Interface between the Customer Network Controller and Multi-Domain
    Service Coordinator (MDSC), CNC-MDSC Interface (CMI)
 o  Interface between the Multi-Domain Service Coordinator and
    Provisioning Network Controller (PNC), MDSC-PNC Interface (MPI)
 From a security and reliability perspective, ACTN may encounter many
 risks such as malicious attack and rogue elements attempting to
 connect to various ACTN components.  Furthermore, some ACTN
 components represent a single point of failure and threat vector and
 must also manage policy conflicts and eavesdropping of communication
 between different ACTN components.
 The conclusion is that all protocols used to realize the ACTN
 framework should have rich security features, and customer,
 application and network data should be stored in encrypted data
 stores.  Additional security risks may still exist.  Therefore,
 discussion and applicability of specific security functions and
 protocols will be better described in documents that are use case and
 environment specific.

Ceccarelli & Lee Informational [Page 36] RFC 8453 ACTN Framework August 2018

9.1. CNC-MDSC Interface (CMI)

 Data stored by the MDSC will reveal details of the virtual network
 services and which CNC and customer/application is consuming the
 resource.  Therefore, the data stored must be considered a candidate
 for encryption.
 CNC Access rights to an MDSC must be managed.  The MDSC must allocate
 resources properly, and methods to prevent policy conflicts, resource
 waste, and denial-of-service attacks on the MDSC by rogue CNCs should
 also be considered.
 The CMI will likely be an external protocol interface.  Suitable
 authentication and authorization of each CNC connecting to the MDSC
 will be required; especially, as these are likely to be implemented
 by different organizations and on separate functional nodes.  Use of
 the AAA-based mechanisms would also provide role-based authorization
 methods so that only authorized CNC's may access the different
 functions of the MDSC.

9.2. MDSC-PNC Interface (MPI)

 Where the MDSC must interact with multiple (distributed) PNCs, a PKI-
 based mechanism is suggested, such as building a TLS or HTTPS
 connection between the MDSC and PNCs, to ensure trust between the
 physical network layer control components and the MDSC.  Trust
 anchors for the PKI can be configured to use a smaller (and
 potentially non-intersecting) set of trusted Certificate Authorities
 (CAs) than in the Web PKI.
 Which MDSC the PNC exports topology information to, and the level of
 detail (full or abstracted), should also be authenticated, and
 specific access restrictions and topology views should be
 configurable and/or policy based.

10. IANA Considerations

 This document has no IANA actions.

Ceccarelli & Lee Informational [Page 37] RFC 8453 ACTN Framework August 2018

11. Informative References

 [ACTN-REQ]
            Lee, Y., Ceccarelli, D., Miyasaka, T., Shin, J., and K.
            Lee, "Requirements for Abstraction and Control of TE
            Networks", Work in Progress,
            draft-ietf-teas-actn-requirements-09, March 2018.
 [ACTN-YANG]
            Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., Yoon, B.,
            Wu, Q., and P. Park, "A Yang Data Model for ACTN VN
            Operation", Work in Progress,
            draft-ietf-teas-actn-vn-yang-01, June 2018.
 [ONF-ARCH]
            Open Networking Foundation, "SDN Architecture", Issue
            1.1, ONF TR-521, June 2016.
 [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
            McManus, "Requirements for Traffic Engineering Over MPLS",
            RFC 2702, DOI 10.17487/RFC2702, September 1999,
            <https://www.rfc-editor.org/info/rfc2702>.
 [RFC3945]  Mannie, E., Ed., "Generalized Multi-Protocol Label
            Switching (GMPLS) Architecture", RFC 3945,
            DOI 10.17487/RFC3945, October 2004,
            <https://www.rfc-editor.org/info/rfc3945>.
 [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
            Element (PCE)-Based Architecture", RFC 4655,
            DOI 10.17487/RFC4655, August 2006,
            <https://www.rfc-editor.org/info/rfc4655>.
 [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
            Sprecher, N., and S. Ueno, "Requirements of an MPLS
            Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
            September 2009, <https://www.rfc-editor.org/info/rfc5654>.
 [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
            Networking: A Perspective from within a Service Provider
            Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
            <https://www.rfc-editor.org/info/rfc7149>.

Ceccarelli & Lee Informational [Page 38] RFC 8453 ACTN Framework August 2018

 [RFC7926]  Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
            Ceccarelli, D., and X. Zhang, "Problem Statement and
            Architecture for Information Exchange between
            Interconnected Traffic-Engineered Networks", BCP 206,
            RFC 7926, DOI 10.17487/RFC7926, July 2016,
            <https://www.rfc-editor.org/info/rfc7926>.
 [RFC8283]  Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
            Architecture for Use of PCE and the PCE Communication
            Protocol (PCEP) in a Network with Central Control",
            RFC 8283, DOI 10.17487/RFC8283, December 2017,
            <https://www.rfc-editor.org/info/rfc8283>.
 [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
            Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
            <https://www.rfc-editor.org/info/rfc8309>.
 [TE-TOPO]  Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
            O. Dios, "YANG Data Model for Traffic Engineering (TE)
            Topologies", Work in Progress,
            draft-ietf-teas-yang-te-topo-18, June 2018.

Ceccarelli & Lee Informational [Page 39] RFC 8453 ACTN Framework August 2018

Appendix A. Example of MDSC and PNC Functions Integrated in a Service/

           Network Orchestrator
 This section provides an example of a possible deployment scenario,
 in which Service/Network Orchestrator can include the PNC
 functionalities for domain 2 and the MDSC functionalities.
            Customer
                        +-------------------------------+
                        |    +-----+                    |
                        |    | CNC |                    |
                        |    +-----+                    |
                        +-------|-----------------------+
                                |
            Service/Network     | CMI
            Orchestrator        |
                        +-------|------------------------+
                        |    +------+   MPI   +------+   |
                        |    | MDSC |---------| PNC2 |   |
                        |    +------+         +------+   |
                        +-------|------------------|-----+
                                | MPI              |
            Domain Controller   |                  |
                        +-------|-----+            |
                        |   +-----+   |            | SBI
                        |   |PNC1 |   |            |
                        |   +-----+   |            |
                        +-------|-----+            |
                                v SBI              v
                             -------            -------
                            (       )          (       )
                           -         -        -         -
                          (           )      (           )
                         (  Domain 1   )----(  Domain 2   )
                          (           )      (           )
                           -         -        -         -
                            (       )          (       )
                             -------            -------

Ceccarelli & Lee Informational [Page 40] RFC 8453 ACTN Framework August 2018

Contributors

 Adrian Farrel
 Old Dog Consulting
 Email: adrian@olddog.co.uk
 Italo Busi
 Huawei
 Email: Italo.Busi@huawei.com
 Khuzema Pithewan
 Peloton Technology
 Email: khuzemap@gmail.com
 Michael Scharf
 Nokia
 Email: michael.scharf@nokia.com
 Luyuan Fang
 eBay
 Email: luyuanf@gmail.com
 Diego Lopez
 Telefonica I+D
 Don Ramon de la Cruz, 82
 28006 Madrid
 Spain
 Email: diego@tid.es
 Sergio Belotti
 Nokia
 Via Trento, 30
 Vimercate
 Italy
 Email: sergio.belotti@nokia.com
 Daniel King
 Lancaster University
 Email: d.king@lancaster.ac.uk
 Dhruv Dhody
 Huawei Technologies
 Divyashree Techno Park, Whitefield
 Bangalore, Karnataka  560066
 India
 Email: dhruv.ietf@gmail.com

Ceccarelli & Lee Informational [Page 41] RFC 8453 ACTN Framework August 2018

 Gert Grammel
 Juniper Networks
 Email: ggrammel@juniper.net

Authors' Addresses

 Daniele Ceccarelli (editor)
 Ericsson
 Torshamnsgatan, 48
 Stockholm
 Sweden
 Email: daniele.ceccarelli@ericsson.com
 Young Lee (editor)
 Huawei Technologies
 5340 Legacy Drive
 Plano, TX 75023
 United States of America
 Email: leeyoung@huawei.com

Ceccarelli & Lee Informational [Page 42]

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