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TEAS Working Group                              Daniele Ceccarelli (Ed)
Internet Draft                                                 Ericsson
Intended status: Informational                           Young Lee (Ed)
Expires: August 2017                                             Huawei


                                                            May 5, 2017


  Framework for Abstraction and Control of Traffic Engineered Networks

                   draft-ietf-teas-actn-framework-05

Abstract

   Traffic Engineered 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.

   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
   Traffic Engineered Networks (ACTN).


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt



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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 5, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   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
      1.1. Terminology...............................................5
   2. Business Model of ACTN.........................................9
      2.1. Customers.................................................9
      2.2. Service Providers........................................10
      2.3. Network Providers........................................12
   3. Virtual Network Service.......................................12
   4. ACTN Base Architecture........................................13
      4.1. Customer Network Controller..............................15
      4.2. Multi Domain Service Coordinator.........................16
      4.3. Physical Network Controller..............................17
      4.4. ACTN Interfaces..........................................17
   5. Advanced ACTN architectures...................................18
      5.1. MDSC Hierarchy for scalability...........................18
      5.2. Functional Split of MDSC Functions in Orchestrators......19
   6. Topology Abstraction Method...................................21
      6.1. No abstraction (native/white topology)...................22
      6.2. One Virtual Node (black topology)........................23
      6.3. Abstraction of TE tunnels for all pairs of border nodes
      (grey topology)...............................................24



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         6.3.1. Grey topology type A: border nodes with a TE links
         between them in a full mesh fashion........................25
         6.3.2. Grey topology Type B................................25
      6.4. Topology Abstraction Granularity Level example...........25
   7. Access Points and Virtual Network Access Points...............27
      7.1. Dual homing scenario.....................................29
   8. Advanced ACTN Application: Multi-Destination Service..........30
      8.1. Pre-Planned End Point Migration..........................31
      8.2. On the Fly End Point Migration...........................32
   9. Advanced Topic................................................32
   10. Manageability Considerations.................................32
      10.1. Policy..................................................33
      10.2. Policy applied to the Customer Network Controller.......34
      10.3. Policy applied to the Multi Domain Service Coordinator..34
      10.4. Policy applied to the Physical Network Controller.......34
   11. Security Considerations......................................35
      11.1. Interface between the Customer Network Controller and Multi
      Domain Service Coordinator (MDSC), CNC-MDSC Interface (CMI)...36
      11.2. Interface between the Multi Domain Service Coordinator and
      Physical Network Controller (PNC), MDSC-PNC Interface (MPI)...36
   12. References...................................................37
      12.1. Informative References..................................37
   13. Contributors.................................................38
   Authors' Addresses...............................................39
   APPENDIX A - Example of MDSC and PNC functions integrated in
   Service/Network Orchestrator.....................................40
   APPENDIX B - Example of IP + Optical network with L3VPN service..40
    APPENDIX C - Example of ODU service connectivity................41

1. Introduction

   Traffic Engineered networks have a variety of mechanisms to
   facilitate separation of data plane and control plane 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.

   The term Traffic Engineered network is used in this document to
   refer 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. Some
   examples of networks that are in scope of this definition are
   optical networks, MPLS Transport Profile (MPLS-TP) networks
   [RFC5654], and MPLS Traffic Engineering (MPLS-TE) networks
   [RFC2702].


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   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 of the control plane from the data plane has
   been already achieved with the development of MPLS/GMPLS [GMPLS] and
   the Path Computation Element (PCE) [RFC4655] for TE-based networks.
   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, PCE is essentially equivalent to a logically centralized
   path computation function.

   Three key aspects that need to be solved by SDN are:

     . Separation of service requests from service delivery so that
        the orchestration of a network is transparent from the point of
        view of the customer but remains responsive to the customer's
        services and business needs.

     . 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 domain.  The process of
        abstraction presents the connectivity graph in a way that is
        independent of the underlying network technologies,
        capabilities, and topology so that it can be used to plan and
        deliver network services in a uniform way

     . Coordination of resources across multiple domains and multiple
        layers to provide end-to-end services regardless of whether the
        domains use SDN or not.

   As networks evolve, the need to provide separated service
   request/orchestration and resource abstraction has emerged as a key
   requirement for operators. In order to support multiple clients each
   with its own view of and control of the server network, a network
   operator needs to partition (or "slice") the network resources.  The
   resulting slices can be assigned to each client for guaranteed usage
   which is a step further than shared use of common network resources.

   Furthermore, each network represented to a client can be built from
   abstractions of the underlying networks so that, for example, a link
   in the client's network is constructed from a path or collection of
   paths in the underlying network.





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   We call the set of management and control functions used to provide
   these features Abstraction and Control of Traffic Engineered
   Networks (ACTN).

   Particular attention needs to be paid to the multi-domain case, 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) as a single virtualized network.

   The ACTN framework described in this document facilitates:

     . Abstraction of the underlying network resources to higher-layer
        applications and customers [RFC7926].

     . Virtualization of particular underlying resources, whose
        selection criterion is the allocation of those resources to a
        particular customer, application or service [ONF-ARCH].

     . Network slicing of infrastructure to meet specific customers'
        service requirements.

     . Creation of a virtualized environment allowing operators to
        view and control multi-domain networks as a single virtualized
        network.

     . The presentation to customers of networks as a virtual network
        via open and programmable interfaces.

1.1. Terminology

   The following terms are used in this document. Some of them are
   newly defined, some others reference existing definition:
     . Network Slicing: Network slicing is a collection of resources
        that are used to establish logically dedicated virtual networks
        over TE networks. It allows a network provider to provide
        dedicated virtual networks for application/customer over a
        common network infrastructure. The logically dedicated
        resources are a part of the larger common network
        infrastructures that are shared among various network slice
        instances which are the end-to-end realization of network
        slicing, consisting of the combination of physically or
        logically dedicated resources.




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     . 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). 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. Just as network slicing and
        network abstraction may be applied recursively, so a node in a
        topology may be created by applying slicing or abstraction on
        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 RFC 7926 for details). Network
        slicing/virtualization and network abstraction may be applied
        recursively, so a link in a topology may be created by applying
        slicing and/or abstraction on the links in the underlying
        topology.

     . CNC: A Customer Network Controller is responsible for
        communicating customer's virtual network service requirements
        to network provider. It has knowledge of the end-point
        associated with virtual network service, service policy, and
        other QoS information related to the service it is responsible
        for instantiating.

     . PNC: A Physical Network Controller is responsible for
        controlling devices or NEs under its direct control. 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 or any
        other means to dynamically control a set of nodes and that is
        implementing an NBI compliant with ACTN specification.

     . PNC domain: 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 can be a link or a node.



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                     _______   Border Link    _______
                    _(       )================(       )_
                  _(           )_          _(           )_
                 (               )  ----  (               )
                (       PNC       )|    |(       PNC       )
                (    Domain X     )|    |(     Domain Y    )
                (                 )|    |(                 )
                 (_             _)  ----  (_             _)
                   (_         _)   Border   (_         _)
                     (_______)      Node      (_______)

                       Figure 1: PNC Domain Borders



     . MDSC: A multi-domain Service Coordinator is a functional block
        that implements all four ACTN main functions, i.e., multi
        domain coordination, virtualization/abstraction, customer
        mapping/translation, and virtual service coordination. The
        first two functions of the MDSC, namely, multi domain
        coordination and virtualization/abstraction are referred to as
        network-related functions while the last two functions, namely,
        customer mapping/translation and virtual service coordination
        are referred to as service-related functions. See details on
        these functions in Section 4.2. In some implementation, PNC and
        MDSC functions can be co-located and implemented in the same
        box.

     . A Virtual Network (VN) is a customer view of the TE
        network.  Depending on the agreement between client and
        provider various VN operations and VN views are possible as
        follows:

          o VN Creation - VN could be pre-configured and created via
             offline negotiation between customer and provider. In
             other cases, the VN could also be created dynamically
             based on a request from the customer with given SLA
             attributes which satisfy the customer's objectives.

          o Dynamic Operations - The VN could be further modified or
             deleted based on a customer request. The customer can
             further act upon the virtual network resources to perform
             end-to-end tunnel management (set-up/release/modify).



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             These changes will result in subsequent LSP management at
             the operator's level.


          o VN Type:

               a. The VN can be seen as set of end-to-end tunnels from a
                 customer point of view, where each tunnel is referred
                 as a VN member. Each VN member can then be formed by
                 recursive slicing or abstraction of paths in
                 underlying networks. Such end-to-end tunnels may
                 comprise of customer end points, access links, intra-
                 domain paths, and inter-domain links. In this view, VN
                 is thus a set of VN members (which is referred to as
                 Type 1 VN)

               b. The VN can also be seen as a topology comprising of
                 physical, sliced, and abstract nodes and links. This
                 VN is referred to as Type 2 VN. The nodes in this case
                 include physical customer end points, border nodes,
                 and internal nodes as well as abstracted nodes.
                 Similarly the links include physical access links,
                 inter-domain links, and intra-domain links as well as
                 abstract links. With VN type 2, it is still possible
                 to view VN member-level.


     . Virtual Network Service (VNS) is requested by the customer and
        negotiated with the provider. There are three types of VNS
        defined in this document. Type 1 VNS refers to VNS in which
        customer is allowed to create and operate a Type 1 VN. Type 2a
        and 2b VNS refers to the VNS in which customer is allowed to
        create and operates a Type 2 VN. With Type 2a VNS, once the VN
        is statically created at service configuration time, the
        customer is not allowed to change the topology (i.e., adding or
        deleting abstract nodes/links). Type 2b VNS is the same as Type
        2a VNS except that the customer is allowed to change topology
        dynamically from the initial topology created at service
        configuration time. See Section 3 for details.

     . Abstraction. This process is defined in [RFC7926].

     . Abstract Link: The term "abstract link" is defined in
        [RFC7926].





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     . 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.

     . Access link: A link between a customer node and a provider
        node.

     . Inter-domain link: A link between domains managed by different
        PNCs. The MDSC is in charge of managing inter-domain links.

     . Access Point (AP): An access point is used to keep
        confidentiality between the customer and the provider. It is a
        logical identifier shared between the customer and the
        provider, used to map the end points of the border node in both
        the customer and the provider NW. The AP can be used by the
        customer when requesting VN service to the provider.

     . VN Access Point (VNAP): A VNAP is defined as the binding
        between an AP and a given VN and is used to identify the
        portion of the access and/or inter-domain link dedicated to a
        given VN.



2. Business Model of ACTN

   The Virtual Private Network (VPN) [RFC4026] and Overlay Network (ON)
   models [RFC4208] are built on the premise that the network provider
   provides all virtual private or overlay networks to its customers.
   These models are simple to operate but have some disadvantages in
   accommodating the increasing need for flexible and dynamic network
   virtualization capabilities.

   There are three key entities in the ACTN model:

     - Customers
     - Service Providers
     - Network Providers

   These are described in the following sections.



    2.1. Customers

   Within the ACTN framework, different types of customers may be taken
   into account depending on the type of their resource needs, and on


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   their number and type of access. For example, it is possible to
   group them into two main categories:

   Basic Customer: Basic customers include fixed residential users,
   mobile users and small enterprises. Usually, the number of basic
   customers for a service provider is high: they require small amounts
   of resources and are characterized by steady requests (relatively
   time invariant). A typical request for a basic customer is for a
   bundle of voice services and internet access. Moreover, basic
   customers do not modify their services themselves: if a service
   change is needed, it is performed by the provider as a proxy and the
   services generally have very few dedicated resources (such as for
   subscriber drop), with everything else shared on the basis of some
   Service Level Agreement (LSA), which is usually best-efforts.

   Advanced Customer: Advanced customers typically include enterprises,
   governments and utilities. Such customers can ask for both point-to
   point and multipoint connectivity with high resource demands varying
   significantly in time and from customer to customer. 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
   virtual network service.

   Advanced customers may own dedicated virtual resources, or share
   resources. They 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
   provider domains, they have to interface to multiple providers and
   may have to support multiple virtual network services with different
   underlying objectives set by the network providers. To enable these
   customers to support flexible and dynamic applications they need to
   control their allocated virtual network resources in a dynamic
   fashion, and that means that they need a view of the topology that
   spans all of the network providers. Customers of a given service
   provider can in turn offer a service to other customers in a
   recursive way.

    2.2. Service Providers

   Service providers are the providers of virtual network services (see
   Section 3 for details) to their customers. Service providers may or
   may not own physical network resources (i.e, may or may not be
   network providers as described in Section 2.3). When a service
   provider is the same as the network provider, this is similar to
   existing VPN models applied to a single provider. This approach


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   works well when the customer maintains a single interface with a
   single provider.  When customer spans multiple independent network
   provider domains, then it becomes hard to facilitate the creation of
   end-to-end virtual network services with this model.

   A more interesting case arises when network providers only provide
   infrastructure, while distinct service providers interface to the
   customers. In this case, service providers are, themselves customers
   of the network infrastructure providers. One service provider may
   need to keep multiple independent network providers as its end-users
   span geographically across multiple network provider domains.

   The ACTN network model is predicated upon this three tier model and
   is summarized in Figure 2:

                       +----------------------+
                       |       customer       |
                       +----------------------+
                                  |
                  VNS       ||    |   /\     VNS
                 Request    ||    |   ||    Reply
                            \/    |   ||
                       +----------------------+
                       |  Service Provider    |
                       +----------------------+
                       /         |            \
                      /          |             \
                     /           |              \
                    /            |               \
   +------------------+   +------------------+   +------------------+
   |Network Provider 1|   |Network Provider 2|   |Network Provider 3|
   +------------------+   +------------------+   +------------------+



                      Figure 2: Three tier model.



   There can be multiple service providers to which a customer may
   interface.

   There are multiple types of service providers, for example:



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     . Data Center providers can be viewed as a service provider type
        as they own and operate data center resources for various WAN
        customers, and they can lease physical network resources from
        network providers.
     . Internet Service Providers (ISP) are service providers of
        internet services to their customers while leasing physical
        network resources from network providers.
     . Mobile Virtual Network Operators (MVNO) provide mobile services
        to their end-users without owning the physical network
        infrastructure.

    2.3. Network Providers

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

3. Virtual Network Service

   Virtual Network Service (VNS) is requested by the customer and
   negotiated with the provider. There are three types of VNS defined
   in this document.

   Type 1 VNS refers to VNS in which customer is allowed to create and
   operate a Type 1 VN. Type 1 VN is a VN that comprises a set of end-
   to-end tunnels from a customer point of view, where each tunnel is
   referred as a VN member. With Type 1 VNS, the network operator does
   not need to provide additional abstract VN topology associated with
   the Type 1 VN.

   Type 2a VNS refer to VNS in which customer is allowed to create and
   operates a Type 2 VN, but not allowed to change topology once it is
   configured at service configuration time. Type 2 VN is an abstract
   VN topology that may comprise of virtual/abstract nodes and links.
   The nodes in this case may include physical customer end points,
   border nodes, and internal nodes as well as abstracted nodes.
   Similarly, the links may include physical access links, inter-domain
   links, and intra-domain links as well as abstract links.

   Type 2b VNS refers to VNS in which customer is allowed to create and
   operate a Type 2 VN and the customer is allowed to dynamically
   change abstract VN topology from the initially configured abstract
   VN topology at service configuration time.




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   From an implementation standpoint, Type 2a VNS and Type 2b VNS
   differentiation might be fulfilled via local policy.

   In all types of VNS, customer can specify a set of service related
   parameters such as connectivity type, VN traffic matrix (e.g.,
   bandwidth, latency, diversity, etc.), VN survivability, VN service
   policy and other characteristics.

4. 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 aligned with the ONF SDN architecture [ONF-
   ARCH] and presents a 3-tiers reference model. It allows for
   hierarchy and recursiveness not only of SDN controllers but also of
   traditionally controlled domains that use a control plane. It
   defines three types of controllers depending on the functionalities
   they implement. The main functionalities that are identified are:

     . Multi-domain coordination function: This function oversees the
        specific aspects of the 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.

     . Virtualization/Abstraction function: 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.

     . Customer mapping/translation function: This function is to map
        customer requests/commands into network provisioning requests
        that can be sent to the Physical Network Controller (PNC)
        according to business policies provisioned statically or
        dynamically at the OSS/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.



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     . Virtual service coordination function: This function translates
        customer service-related information into virtual network
        service operations in order to seamlessly operate virtual
        networks while meeting a customer's service requirements. In
        the context of ACTN, service/virtual service coordination
        includes a number of service orchestration functions such as
        multi-destination load balancing, guarantees of service
        quality, bandwidth and throughput. It also includes
        notifications for service fault and performance degradation and
        so forth.

   Figure 3 depicts the base ACTN architecture with three controller
   types and the corresponding interfaces between these controllers.
   The types of controller defined in the ACTN architecture are shown
   in Figure 3 below and are as follows:

     . CNC - Customer Network Controller
     . MDSC - Multi Domain Service Coordinator
     . PNC - Physical Network Controller

   Figure 3 also shows the following interfaces:

     . CMI - CNC-MDSC Interface
     . MPI - MDSC-PNC Interface
     . SBI - South Bound Interface
























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             +--------------+        +---------------+        +--------------+
             |    CNC-A     |        |     CNC-B     |        |     CNC-C    |
             |(DC provider) |        |     (ISP)     |        |     (MVNO)   |
             +--------------+        +---------------+        +--------------+
                  \                          |                           /
   Business        \                         |                          /
   Boundary  =======\========================|=========================/=======
   Between           \                       | CMI                    /
   Customer &         -----------            |          --------------
   Network Provider              \           |         /
                                +-----------------------+
                                |          MDSC         |
                                +-----------------------+
                                 /           |         \
                     ------------            |MPI       ----------------
                    /                        |                          \
               +-------+                 +-------+                   +-------+
               |  PNC  |                 |  PNC  |                   |  PNC  |
               +-------+                 +-------+                   +-------+
                  | GMPLS               /      |                      /   \
                  | trigger            /       |SBI                  /     \
               --------           -----        |                    /       \
              (        )         (     )       |                   /         \
             -         -        ( Phys. )      |                  /       -----
             (  GMPLS   )        ( Net )       |                 /       (     )
            (  Physical  )         ----        |                /       ( Phys. )
             (  Network )                   -----        -----           ( Net )
              -        -                   (     )      (     )           -----
               (       )                  (  Phys. )   (  Phys. )
               --------                    ( Net )      ( Net )
                                            -----        -----



                     Figure 3: ACTN Base Architecture



4.1. Customer Network Controller

   A Virtual Network Service is instantiated by the Customer Network
   Controller via the CNC-MDSC Interface (CMI). As the Customer Network
   Controller directly interfaces to the applications, it understands
   multiple application requirements and their service needs. It is
   assumed that the Customer Network Controller and the MDSC have a
   common knowledge of the end-point interfaces based on their business
   negotiations prior to service instantiation. End-point interfaces


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   refer to customer-network physical interfaces that connect customer
   premise equipment to network provider equipment.



4.2. Multi Domain Service Coordinator

   The Multi Domain Service Coordinator (MDSC) sits between the CNC
   that issues connectivity requests and the Physical Network
   Controllers (PNCs) that manage the physical network resources. The
   MDSC can be collocated with the PNC.

   The internal system architecture and building blocks of the MDSC are
   out of the scope of ACTN. Some examples can be found in the
   Application Based Network Operations (ABNO) architecture [RFC7491]
   and the ONF SDN architecture [ONF-ARCH].

   The MDSC is the only building block of the architecture that can
   implement all four ACTN main functions, i.e., multi domain
   coordination, virtualization/abstraction, customer
   mapping/translation, and virtual service coordination. The first two
   functions of the MDSC, namely, multi domain coordination and
   virtualization/abstraction are referred to as network-related
   functions while the last two functions, namely, customer
   mapping/translation and virtual service coordination are referred to
   as service-related functions.
   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 between MDSCs and PNCs (i.e. 1
   parent MDSC and N child MDSC or 1 MDSC and N PNCs).

   In addition to that, it could also be possible to have an M:1
   relationship between MDSCs and PNC to allow for network resource
   partitioning/sharing among different customers not necessarily
   connected to the same MDSC (e.g., different service providers).






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4.3. Physical Network Controller

   The Physical Network Controller (PNC) oversees configuring the
   network elements, monitoring the topology (physical or virtual) of
   the network, and passing information about the topology (either raw
   or abstracted) to the MDSC.

   The internal architecture of the PNC, its building blocks, and the
   way it controls its domain are out of the scope of ACTN. Some
   examples can be found in the Application Based Network Operations
   (ABNO) architecture [RFC7491] and the ONF SDN architecture [ONF-
   ARCH]

   The PNC, in addition to being in charge of controlling the physical
   network, is able to implement two of the four main ACTN main
   functions: multi domain coordination and virtualization/abstraction
   function.
   Note that from an implementation point of view it is possible to
   integrate one or more MDSC functions and one or more PNC functions
   within the same controller.

4.4. ACTN Interfaces

   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 while having no impact on other customers. Direct
   customer control of transport network elements and virtualized
   services is not perceived as a viable proposition for transport
   network providers due to security and policy concerns among other
   reasons. In addition, the network control plane for transport
   networks has been separated from the data plane and as such it is
   not viable for the customer to directly interface with transport
   network elements.

     . CMI Interface: The CNC-MDSC Interface (CMI) is an interface
        between a CNC and an MDSC. As depicted in Figure 3, the CMI is
        a business boundary between customer and network provider. It
        is used to request virtual network services required for the
        applications. Note that all service related information such as
        specific service properties, including virtual network service
        type, topology, bandwidth, and constraint information are
        conveyed over this interface. Most of the information over this
        interface is technology agnostic; however, there are some
        cases, e.g., access link configuration, where it should be


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        possible to explicitly request for a VN to be created at a
        given layer in the network (e.g. ODU VN or MPLS VN).

     . MPI Interface: The MDSC-PNC Interface (MPI) is an interface
        between an MDSC and a PNC. It communicates the creation
        requests for new connectivity or for bandwidth changes in the
        physical network. In multi-domain environments, the MDSC needs
        to establish multiple MPIs, one for each PNC, as there is one
        PNC responsible for control of each domain. The MPI could have
        different degrees of abstraction and present an abstracted
        topology hiding technology specific aspects of the network or
        convey technology specific parameters to allow for path
        computation at the MDSC level. Please refer to CCAMP Transport
        NBI work for the latter case [Transport NBI].

     . SBI Interface: This interface is out of the scope of ACTN. It
        is shown in Figure 3 for reference reason only.

   Please note that for all the three interfaces, when technology
   specific information needs to be included, this info will be add-ons
   on top of the general abstract topology. As far as general topology
   abstraction standpoint, all interfaces are still recursive in
   nature.

5. Advanced ACTN architectures

   This section describes advanced forms of ACTN architectures as
   possible implementation choices.

5.1. MDSC Hierarchy for scalability

   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 higher-level MDSC
   (MDSC-H) the lower-level MDSC (MDSC-L) and the interface between
   them is basically of a recursive nature of the MPI. An
   implementation choice could foresee the usage of an MDSC-L for all
   the PNCs related to a given network layer or technology (e.g.
   IP/MPLS) a different MDSC-L for the PNCs related to another
   layer/technology (e.g. OTN/WDM) and an MDSC-H to coordinate them.

   Figure 4 shows this case.





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                                       +--------+
                                       |   CNC  |
                                       +--------+
                                            |
                                            |
                                      +----------+
                              --------|  MDSC-H  |--------
                              |       +----------+       |
                              |                          |
                         +---------+               +---------+
                         |  MDSC-L |               |  MDSC-L |
                         +---------+               +---------+

                         Figure 4: MDSC Hierarchy

   Note that both the MDSC-H and the MDSC-L in general cases implement
   all four functions of the MDSC discussed in Section 3.2.

5.2. Functional Split of MDSC Functions in Orchestrators

   Another implementation choice could foresee the separation of MDSC
   functions into two groups (i.e., one group for service-related
   functions and another group for network-related functions) which
   will result in a service orchestrator for providing service-related
   functions of MDSC and other non-ACTN functions and a network
   orchestrator for providing network-related functions of MDSC and
   other non-ACTN functions. Figure 5 shows this case and it also
   depicts the mapping between ACTN architecture and the YANG service
   model architecture described in [Service-YANG]. This mapping is
   helpful for the readers who are not familiar with some TEAS specific
   terminology used in this document. A number of key ACTN interfaces
   exist for deployment and operation of ACTN-based networks. These are
   highlighted in Figure 5 (ACTN Interfaces).










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                              +------------------------------+
                              |                     Customer |
                              |   +-----+   +----------+     |
                              |   | CNC |   |Other fns.|     |
                              |   +-----+   +----------+     |
                              +------------------------------+
                                                 |  Customer Service Model
                                                 |
                        +-----------------------------------------------+
                ********|**********************    Service Orchestrator |
                * MDSC  |  +------+  +------+ *  +-----------+          |
                *       |  | MDSC |  | MDSC | *  | Other fns.|          |
                *       |  |  F1  |  |  F2  | *  | (non-ACTN)|          |
                *       |  +------+  +------+ *  +-----------+          |
                *       +---------------------*-------------------------+
                *                             *  |  Service Delivery Model
                *                             *  |
                *       +---------------------*-------------------------+
                *       |                     *  Network Orchestrator   |
                *       |  +------+  +------+ *  +-----------+          |
                *       |  | MDSC |  | MDSC | *  | Other fns.|          |
                *       |  |  F3  |  |  F4  | *  | (non-ACTN)|          |
                *       |  +------+  +------+ *  +-----------+          |
                ********|**********************                         |
                        +-----------------------------------------------+
                                                 |  Network Configuration Model
                                                 |
                          +-------------------------------------------+
                          |                      Domain Controller    |
                          |  +------+  +-----------+                  |
                          |  | PNC  |  | Other fns.|                  |
                          |  +------+  | (non-ACTN)|                  |
                          |            +-----------+                  |
                          +-------------------------------------------+
                                                 |  Device Configuration Model
                                                 |
                                              --------
                                             | Device |
                                              --------

     Figure 5: ACTN Architecture in the context of YANG Service Models




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   In Figure 5, MDSC F1 and F2 correspond to customer
   mapping/translation, and virtual service coordination, respectively,
   which are the MDSC service-related functions as defined in Section
   4. MDSC F3 and F4 correspond to multi domain coordination,
   virtualization/abstraction, respectively, which are the MDSC
   network-related functions as defined in Section 4. In some
   implementation, MDSC F1 and F2 can be implemented as part of a
   Service Orchestrator which may support other non-ACTN functions.
   Likewise, the MDSC F3 and F4 can be implemented as part of a Network
   Orchestrator which may support other non-ACTN MDSC functions.

   Also note that the PNC is not same as domain controller. Domain
   controller in general has a larger set of functions than that of
   PNC. The main functions of PNC are explained in Section 3.3.
   Likewise, Customer has a larger set of functions than that of the
   CNC.

   Customer service model describes a service as offer or delivered to
   a customer by a network operator as defined in [Service-YANG]. The
   CMI is a subset of a customer service model to support VNS. This
   model encompasses other non-TE/non-ACTN models to control non-ACTN
   services (e.g., L3SM).

   Service delivery model is used by a network operator to define and
   configure how a service is provided by the network as defined in
   [Service-YANG]. This model is similar to the MPI model as the
   network-related functions of the MDSC, i.e., F3 and F4, provide an
   abstract topology view of the E2E network to the service-related
   functions of the MDSC, i.e., F1 and F2, which translate customer's
   request at the CMI into the network configuration at the MPI.

   Network configuration model is used by a network orchestrator to
   provide network-level configuration model to a controller as defined
   in [Service-YANG]. The MPI is a subset of network configuration
   model to support TE configuration. This model encompasses the MPI
   model plus other non-TE/non-ACTN models to control non-ACTN
   functions of the domain controller (e.g., L3VPN).

   Device configuration model is used by a controller to configure
   physical network elements.


6. Topology Abstraction Method

   This section discusses topology abstraction types and their context
   in ACTN architecture. Topology abstraction is useful in ACTN
   architecture as a way to scale multi-domain network operation. As


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   the MDSC needs to coordinate with the PNCs in multi-domain networks
   for determining a feasible domain sequence and provisioning the end-
   to-end tunnel based on the determined domain sequence, topology
   abstraction provides an efficient network scaling mechanism. Note
   that this is the abstraction performed by the PNC to the MDSC or by
   the MDSC-L to the MDSC-H, and that this is different from the VN
   Type 2 topology (that is created and negotiated between the CNC and
   the MDSC as part of the VNS). The purpose of topology abstraction
   discussed in this section is for an efficient internal network
   operation based on abstraction principle.

   Refer to [ACTN-Abstraction] for detailed discussions on factors that
   affect topology abstraction, how to build topology abstraction,
   various considerations and which method to pick based on abstraction
   types and the nature of underlying transport technology (e.g., MPLS,
   OTN, WSON, etc.).


6.1. No abstraction (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 as shown in
   Figure 6. In this case, the MDSC has the full knowledge of the
   underlying network topology and as such there is no need for the
   MDSC to send a path computation request to the PNC. The computation
   burden will fall on the MDSC to find an optimal end-to-end path and
   optimal per domain paths.


                             +--+     +--+     +--+     +--+
                           +-+  +-----+  +-----+  +-----+  +-+
                             ++-+     ++-+     +-++     +-++
                              |        |         |        |
                              |        |         |        |
                              |        |         |        |
                              |        |         |        |
                             ++-+     ++-+     +-++     +-++
                           +-+  +-----+  +-----+  +-----+  +-+
                             +--+     +--+     +--+     +--+

                   Figure 6a: The native/white topology






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6.2. One Virtual Node (black topology)

   The entire domain network is abstracted as a single virtual node
   (see the definition of virtual node in [RFC7926]) with the
   access/egress links without disclosing any node internal
   connectivity information.
   Figure 6b 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 path computation requests to the PNCs before it
   can determine an end-to-end path. If there are a large number of
   inter-connected domains, this abstraction method may impose a heavy
   coordination load at the MDSC level in order to find an optimal end-
   to-end path.
   The black topology would not give the MDSC any critical network
   resource information other than the border nodes/links information
   and as such it is likely to have a need for complementary
   communications between the MDSC and the PNCs (e.g., Path computation
   Request/Reply).
                      +--+     +--+     +--+     +--+
                    +-+  +-----+  +-----+  +-----+  +-+
                      ++-+     ++-+     +-++     +-++
                       |        |         |        |
                       |        |         |        |
                       |        |         |        |
                       |        |         |        |
                      ++-+     ++-+     +-++     +-++
                    +-+  +-----+  +-----+  +-----+  +-+
                      +--+     +--+     +--+     +--+


                                +--------+
                             +--+        +--+
                                |        |
                                |        |
                                |        |
                                |        |
                                |        |
                                |        |
                             +--+        +--+
                                +--------+

  Figure 6b: The native topology and the corresponding black topology
              with one virtual node and inter-domain links





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6.3. Abstraction of TE tunnels for all pairs of border nodes (grey
   topology)

   This abstraction level, referred to a grey topology is between black
   topology and white topology from a granularity point of view. As
   shown in Figures 7a and 7b, we may further differentiate from a
   perspective of how to abstract internal TE resources between the
   pairs of border nodes:
     . Grey topology type A: border nodes with a TE links between them
        in a full mesh fashion (See Figure 7a)
     . Grey topology type B: border nodes with some internal
        abstracted nodes and abstracted links (See Figure 7b)

                      +--+     +--+     +--+     +--+
                    +-+  +-----+  +-----+  +-----+  +-+
                      ++-+     ++-+     +-++     +-++
                       |        |         |        |
                       |        |         |        |
                       |        |         |        |
                       |        |         |        |
                      ++-+     ++-+     +-++     +-++
                    +-+  +-----+  +-----+  +-----+  +-+
                      +--+     +--+     +--+     +--+


                               +--+    +--+
                             +-+  +----+  +-+
                               ++-+    +-++
                                |  \  /  |
                                |   \/   |
                                |   /\   |
                                |  /  \  |
                               ++-+    +-++
                             +-+  +----+  +-+
                               +--+    +--+

   Figure 7a: The native topology and the corresponding grey topology
                 type A with TE links between border nodes


                          +--+     +--+     +--+
                        +-+  +-----+  +-----+  +-+
                          ++-+     ++-+     +-++
                           |                  |
                           |                  |



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                           |                  |
                           |                  |
                          ++-+     ++-+     +-++
                        +-+  +-----+  +-----+  +-+
                          +--+     +--+     +--+

     Figure 7b: The grey topology type B with abstract nodes/links
                          between border nodes

        6.3.1. Grey topology type A: border nodes with a TE links
           between them in a full mesh fashion

   For each pair of ingress and egress nodes (i.e., border nodes
   to/from the domain), TE link metric is provided with TE attributes
   such as max bandwidth available, link delay, etc. This abstraction
   depends on the underlying TE networks.
   Note that this grey topology can also be represented as a single
   abstract node with the connectivity matrix defined in [TE-Topology],
   abstracting the internal connectivity information. The only thing
   might be different is some additional information about the end
   points of the links of the border nodes (i.e., links outward
   customer-facing) as they cannot be included in the connectivity
   matrix's termination points.

        6.3.2. Grey topology Type B

   The grey abstraction type B would allow the MDSC to have more
   information about the internals of the domain networks by the PNCs
   so that the MDSC can flexibly determine optimal paths. The MDSC may
   configure some of the internal virtual nodes (e.g., cross-connect)
   to redirect its traffic as it sees changes from the domain networks.

6.4. Topology Abstraction Granularity Level example

   This section illustrates how topology abstraction operates in
   different level of granularity over a hierarchy of MDSCs which is
   shown in Figure 8 below.









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                                +-----+
                                | CNC |  CNC wants to create a VN
                                +-----+  between CE A and CE B
                                   |
                                   |
                         +-----------------------+
                         |          MDSC-H       |
                         +-----------------------+
                              /            \
                             /              \
                     +--------+              +--------+
                     | MDSC-L1|              | MDSC-L2|
                     +--------+              +--------+
                       /    \                  /    \
                      /      \                /      \
                   +-----+  +-----+        +-----+  +-----+
         CE A o----|PNC 1|  |PNC 2|        |PNC 3|  |PNC 4|----o CE B
                   +-----+  +-----+        +-----+  +-----+


                        Topology operated by MDSC-H

                               --o=o=o=o--



        Topology operated by MDSC-L1          Topology operated by MDSC-L2
                     _        _                       _        _
                    ( )      ( )                     ( )      ( )
                   (   )    (   )                   (   )    (   )
                --(o---o)==(o---o)==             ==(o---o)==(o---o)--
                   (   )    (   )                   (   )    (   )
                    (_)      (_)                     (_)      (_)


                             Actual Topology
                  ___          ___          ___          ___
                 (   )        (   )        (   )        (   )
                (  o  )      (  o  )      ( o--o)      (  o  )
                (  / \  )    (   |\  )    (  |  | )    (  / \  )
           ----(o-o---o-o)==(o-o-o-o-o)==(o--o--o-o)==(o-o-o-o-o)----
                (  \ /  )    ( | |/  )    (  |  | )    (  \ /  )
                (  o  )      (o-o  )      ( o--o)      (  o  )
                 (___)        (___)        (___)        (___)

                Domain 1     Domain 2     Domain 3     Domain 4

              Where o is a node and -- is a link and === a border link

   Figure 8: Illustration of topology abstraction granularity levels


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   In the example depicted in Figure 8, there are four domains under
   control of the respective PNCs, namely, PNC 1, PNC 2, PNC3 and PNC4.
   Assume that MDSC L-1 is controlling PNC 1 and PNC 2 while MDSC L-2
   is controlling PNC 3 and PNC 4. Let us assume that each of the PNCs
   provides a grey topology abstraction in which to present only border
   nodes and links within and outside the domain. The abstract topology
   MDSC-L1 would operate is basically a combination of the two
   topologies the PNCs (PNC 1 and PNC 2) provide. Likewise, the
   abstract topology MDSC-L2 would operate is shown in Figure 8. Both
   MDSC-L1 and MDSC-L2 provide a black topology abstraction in which
   each PNC domain is presented as one virtual node to its top level
   MDSC-H. Then the MDSC-H combines these two topologies updated by
   MDSC-L1 and MDSC-L2 to create the abstraction topology to which it
   operates. MDSC-H sees the whole four domain networks as four virtual
   nodes connected via virtual links. This illustrates the point
   discussed in Section 5.1: The top level MDSC may operate on a higher
   level of abstraction (i.e., less granular level) than the lower
   level MSDCs.

7. Access Points and Virtual Network Access Points

   In order not to share unwanted topological information between the
   customer domain and provider domain, a new entity is defined which
   is referred to as the Access Point (AP). See the definition of AP in
   Section 1.1.

   A customer node will use APs as the end points for the request of
   VNS as shown in Figure 9.

                         -------------
                        (             )
                       -               -
        +---+ X       (                 )      Z +---+
        |CE1|---+----(                   )---+---|CE2|
        +---+   |     (                 )    |   +---+
               AP1     -               -    AP2
                        (             )
                         -------------


                  Figure 9: APs definition customer view

   Let's take as an example a scenario shown in Figure 7. CE1 is
   connected to the network via a 10Gb link and CE2 via a 40Gb link.
   Before the creation of any VN between AP1 and AP2 the customer view
   can be summarized as shown in Table 1:


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                      +----------+------------------------+
                      |End Point | Access Link Bandwidth  |
                +-----+----------+----------+-------------+
                |AP id| CE,port  | MaxResBw | AvailableBw |
                +-----+----------+----------+-------------+
                | AP1 |CE1,portX |   10Gb   |    10Gb     |
                +-----+----------+----------+-------------+
                | AP2 |CE2,portZ |   40Gb   |    40Gb     |
                +-----+----------+----------+-------------+



                      Table 1: AP - customer view

   On the other hand, what the provider sees is shown in Figure 10.

                        -------            -------
                       (       )          (       )
                      -         -        -         -
                 W  (+---+       )      (       +---+)  Y
              -+---( |PE1| Dom.X  )----(  Dom.Y |PE2| )---+-
               |    (+---+       )      (       +---+)    |
               AP1    -         -        -         -     AP2
                       (       )          (       )
                        -------            -------


                    Figure 10: Provider view of the AP

   Which results in a summarization as shown in Table 2.

                      +----------+------------------------+
                      |End Point | Access Link Bandwidth  |
                +-----+----------+----------+-------------+
                |AP id| PE,port  | MaxResBw | AvailableBw |
                +-----+----------+----------+-------------+
                | AP1 |PE1,portW |   10Gb   |    10Gb     |
                +-----+----------+----------+-------------+
                | AP2 |PE2,portY |   40Gb   |    40Gb     |
                +-----+----------+----------+-------------+


                        Table 2: AP - provider view

   A Virtual Network Access Point (VNAP) needs to be defined as binding
   between the AP that is linked to a VN and that is used to allow for
   different VNs to start from the same AP. It also allows for traffic


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   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 the simple scenario depicted above we suppose we want to create
   two virtual networks. The first with VN identifier 9 between AP1 and
   AP2 with bandwidth of 1Gbps, while the second with VN id 5, again
   between AP1 and AP2 and with bandwidth 2Gbps.

   The provider view would evolve as shown in Table 3.

                        +----------+------------------------+
                        |End Point |  Access Link/VNAP Bw   |
              +---------+----------+----------+-------------+
              |AP/VNAPid| PE,port  | MaxResBw | AvailableBw |
              +---------+----------+----------+-------------+
              |AP1      |PE1,portW |  10Gbps  |    7Gbps    |
              | -VNAP1.9|          |   1Gbps  |     N.A.    |
              | -VNAP1.5|          |   2Gbps  |     N.A     |
              +---------+----------+----------+-------------+
              |AP2      |PE2,portY |  40Gbps  |    37Gbps   |
              | -VNAP2.9|          |   1Gbps  |     N.A.    |
              | -VNAP2.5|          |   2Gbps  |     N.A     |
              +---------+----------+----------+-------------+


        Table 3: AP and VNAP - provider view after VNS creation

7.1. 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 5Gbps of
   bandwidth between CE1 and CE2. This is shown in Figure 11.

                               ____________
                       AP1    (            )    AP3
                      -------(PE1)       (PE3)-------
                   W /      (                 )      \X
               +---+/      (                   )      \+---+
               |CE1|      (                     )      |CE2|
               +---+\      (                   )      /+---+
                   Y \      (                 )      /Z
                      -------(PE2)       (PE4)-------
                       AP2    (____________)



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                      Figure 11: Dual homing scenario

   In this case, the customer will request for 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 end points).

   The customer view would be shown in Table 4.

                  +----------+------------------------+
                  |End Point |  Access Link/VNAP Bw   |
        +---------+----------+----------+-------------+-----------+
        |AP/VNAPid| CE,port  | MaxResBw | AvailableBw |Dual Homing|
        +---------+----------+----------+-------------+-----------+
        |AP1      |CE1,portW |  10Gbps  |    5Gbps    |           |
        | -VNAP1.9|          |   5Gbps  |     N.A.    | VNAP2.9   |
        +---------+----------+----------+-------------+-----------+
        |AP2      |CE1,portY |  40Gbps  |    35Gbps   |           |
        | -VNAP2.9|          |   5Gbps  |     N.A.    | VNAP1.9   |
        +---------+----------+----------+-------------+-----------+
        |AP3      |CE2,portX |  40Gbps  |   35Gbps    |           |
        | -VNAP3.9|          |   5Gbps  |     N.A.    |   NONE    |
        +---------+----------+----------+-------------+-----------+

          Table 4: Dual homing - customer view after VN creation



8. Advanced ACTN Application: Multi-Destination Service

   A further advanced application of ACTN is in the case of Data Center
   selection, where the customer requires the Data Center selection to
   be based on the network status; this is referred to as Multi-
   Destination in [ACTN-REQ]. In terms of ACTN, a CNC could request a
   connectivity service (virtual network) between a set of source Aps
   and destination APs and leave it up to the network (MDSC) to decide
   which source and destination access points to be used to set up the
   connectivity service (virtual network). The candidate list of source
   and destination APs is decided by a CNC (or an entity outside of
   ACTN) based on certain factors which 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


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   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 12, where three data centers are
   available, but the customer requires the data center 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 setup the connectivity
   service (virtual network).

                    -------            -------
                   (       )          (       )
                  -         -        -         -
   +---+         (           )      (           )        +----+
   |CE1|---+----(  Domain X   )----(  Domain Y   )---+---|DC-A|
   +---+   |     (           )      (           )    |   +----+
           AP1    -         -        -         -    AP2
                   (       )          (       )
                    ---+---            ---+---
                   AP3 |              AP4 |
                    +----+              +----+
                    |DC-B|              |DC-C|
                    +----+              +----+

          Figure 12: End point selection based on network status



8.1. Pre-Planned End Point Migration

   Further in case of Data Center selection, customer could request for
   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 13
   DC-C is selected as a backup for DC-A. Thus, the VN should be setup
   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).









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                    -------            -------
                   (       )          (       )
                  -         -    __  -         -
   +---+         (           )      (           )        +----+
   |CE1|---+----(  Domain X   )----(  Domain Y   )---+---|DC-A|
   +---+   |     (           )      (           )    |   +----+
           AP1    -         -        -         -    AP2    |
                   (       )          (       )            |
                    ---+---            ---+---             |
                   AP3 |              AP4 |         HOT STANDBY
                    +----+             +----+              |
                    |DC-D|             |DC-C|<-------------
                    +----+             +----+

                Figure 13: Pre-planned end point migration



8.2. On the Fly End Point Migration

   Compared to pre-planned end point migration, on the fly end point
   selection is dynamic in that the migration is not pre-planned 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 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.

9. Advanced Topic

   This section describes how ACTN architecture supports some
   deployment scenarios. See Appendix A for details on MDSC and PNC
   functions integrated in Service/Network Orchestrator and Appendix B
   for IP + Optical with L3VPN service.

10. Manageability Considerations

   The objective of ACTN is to manage traffic engineered resources, and
   provide a set of mechanism to allow clients to request virtual
   connectivity across server network resources. ACTN will support
   multiple clients each with its own view of and control of the server
   network, the network operator will need to partition (or "slice")
   their network resources, and manage them resources accordingly.




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   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
   traffic engineered resources. The management requirements may be
   categorized as follows:

     . Management of external ACTN protocols
     . Management of internal ACTN protocols
     . Management and monitoring of ACTN components
     . Configuration of policy to be applied across the ACTN system

10.1. Policy

   It is expected that a policy will be an important aspect of ACTN
   control and management. Typically, policies are used via the
   components and interfaces, during deployment of the service, to
   ensure that the service is compliant with agreed policy factors
   (often described in Service Level Agreements - SLAs), these include,
   but are not limited to: connectivity, bandwidth, geographical
   transit, technology selection, security, resilience, and economic
   cost.

   Depending on the deployment the ACTN deployment 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:

     . 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.

     . A global policy might constrain certain customer types (or
       specific customer applications) to only use certain MDSCs, and
       be restricted to physical network types managed by the PNCs. A
       global policy agent would govern these types of policies.

   This 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



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   context of ACTN, but it is expected further discussion in an
   applicability or solution specific document, will be required.

10.2. Policy applied to the Customer Network Controller

   A virtual network service for a customer application will be
   requested from the CNC. It will reflect the application requirements
   and specific service policy 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.

10.3. Policy applied to the Multi Domain Service Coordinator

   A key objective of the MDSC is to help the customer express the
   application connectivity request via its CNC as set of desired
   business needs, therefore policy will play an important role.

   Once authorised, 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
   connectivity end-points, use of these end-points should be defined
   as a policy expression when setting up or augmenting virtual network
   services. Ensuring that permissible end-points are defined for CNCs
   and applications will require the MDSC to maintain a registry of
   permissible connection points for CNCs and application types.

   It may also be necessary for the MDSC to resolve policy conflicts,
   or at least flag any issues to administrator of the MDSC itself.
   Conflicts may occur when virtual network service optimization
   criterion 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 specific type of end-to-end
   service. This type of situation may be resolved using hard and soft
   policy constraints.

10.4. Policy applied to the Physical Network Controller

   The PNC is responsible for configuring the network elements,
   monitoring physical network resources, and exposing connectivity
   (direct or abstracted) to the MDSC. It is therefore expected that
   policy will dictate what connectivity information will be exported
   between the PNC, via the MDSC-PNC Interface (MPI), and MDSC.




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   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 become 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.

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

11. Security Considerations

   The ACTN framework described in this document defines key components
   and interfaces for managed traffic engineered networks. Securing the
   request and control of resources, confidentially 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 as
   a rule implementations should consider encrypting data that flow
   between components, especially when they are implemented at remote
   nodes, regardless if these are external or internal network
   interfaces.

   The ACTN security discussion is further split into two specific
   categories described in the following sub-sections:


     . Interface between the Customer Network Controller and Multi
       Domain Service Coordinator (MDSC), CNC-MDSC Interface (CMI)

     . Interface between the Multi Domain Service Coordinator and
       Physical 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


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   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.



11.1. Interface between the Customer Network Controller and Multi
   Domain Service Coordinator (MDSC), CNC-MDSC Interface (CMI)

   The role of the MDSC is to detach the network and service control
   from underlying technology to help the customer express the network
   as desired by business needs. It should be noted that data stored by
   the MDSC will reveal details of the virtual network services, and
   which CNC and application is consuming the resource. The data stored
   must therefore be considered as a candidate for encryption.

   CNC Access rights to an MDSC must be managed. MDSC resources must be
   properly allocated, and methods to prevent policy conflicts,
   resource wastage and denial of service attacks on the MDSC by rogue
   CNCs, should also be considered.

   A CNC-MDSC protocol interface will likely be an external protocol
   interface. Again, 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.

11.2. Interface between the Multi Domain Service Coordinator and
   Physical Network Controller (PNC), MDSC-PNC Interface (MPI)

   The function of the Physical Network Controller (PNC) is to
   configure network elements, provide performance and monitoring
   functions of the physical elements, and export physical topology
   (full, partial, or abstracted) to the MDSC.

   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.

   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.


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12. References

12.1. Informative References

   [RFC2702] Awduche, D., et. al., "Requirements for Traffic
             Engineering Over MPLS", RFC 2702, September 1999.

   [RFC4026] L. Andersson, T. Madsen, "Provider Provisioned Virtual
             Private Network (VPN) Terminology", RFC 4026, March 2005.

   [RFC4208] G. Swallow, J. Drake, H.Ishimatsu, Y. Rekhter,
             "Generalized Multiprotocol Label Switching (GMPLS) User-
             Network Interface (UNI): Resource ReserVation Protocol-
             Traffic Engineering (RSVP-TE) Support for the Overlay
             Model", RFC 4208, October 2005.

   [RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
             Computation Element (PCE)-Based Architecture", IETF RFC
             4655, August 2006.

   [RFC5654] Niven-Jenkins, B. (Ed.), D. Brungard (Ed.), and M. Betts
             (Ed.), "Requirements of an MPLS Transport Profile", RFC
             5654, September 2009.

   [RFC7149] Boucadair, M. and Jacquenet, C., "Software-Defined
             Networking: A Perspective from within a Service Provider
             Environment", RFC 7149, March 2014.

   [RFC7926] A. Farrel (Ed.), "Problem Statement and Architecture for
             Information Exchange between Interconnected Traffic-
             Engineered Networks", RFC 7926, July 2016.

   [GMPLS]   Manning, E., et al., "Generalized Multi-Protocol Label
             Switching (GMPLS) Architecture", RFC 3945, October 2004.

   [ONF-ARCH] Open Networking Foundation, "SDN architecture", Issue
             1.1, ONF TR-521, June 2016.

   [RFC7491] King, D., and Farrel, A., "A PCE-based Architecture for
             Application-based Network Operations", RFC 7491, March
             2015.

   [Transport NBI] Busi, I., et al., "Transport North Bound Interface
             Use Cases", draft-tnbidt-ccamp-transport-nbi-use-cases,
             work in progress.



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   [ACTN-Abstraction] Y. Lee, et al., "Abstraction and Control of TE
             Networks (ACTN) Abstraction Methods", draft-lee-teas-actn-
             abstraction, work in progress.



13. Contributors

   Adrian Farrel
   Old Dog Consulting
   Email: adrian@olddog.co.uk

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

   Khuzema Pithewan
   Infinera
   Email: kpithewan@infinera.com

   Michael Scharf
   Nokia
   Email: michael.scharf@nokia.com


























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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, USA
   Phone: (469)277-5838
   Email: leeyoung@huawei.com

   Luyuan Fang
   Microsoft
   Email: luyuanf@gmail.com

   Diego Lopez
   Telefonica I+D
   Don Ramon de la Cruz, 82
   28006 Madrid, Spain
   Email: diego@tid.es

   Sergio Belotti
   Alcatel Lucent
   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

   Gert Grammel
   Juniper Networks
   Email: ggrammel@juniper.net





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APPENDIX A - Example of MDSC and PNC functions integrated in
Service/Network Orchestrator

   This section provides an example of a possible deployment scenario,
   in which Service/Network Orchestrator can include a number of
   functionalities, among which, in the example below, PNC
   functionalities for domain 2 and MDSC functionalities to coordinate
   the PNC1 functionalities (hosted in a separate domain controller)
   and PNC2 functionalities (co-hosted in the network orchestrator).

   Customer
               +-------------------------------+
               |    +-----+                    |
               |    | CNC |                    |
               |    +-----+                    |
               +-------|-----------------------+
                       |-CMI
   Service/Network     |
   Orchestrator        |
               +-------|------------------------+
               |    +------+   MPI   +------+   |
               |    | MDSC |----|--> | PNC2 |   |
               |    +------+         +------+   |
               +-------|------------------|-----+
                       |-MPI              |
   Domain Controller   |                  |
               +-------|-----+            |
               |   +-----+   |            |
               |   |PNC1 |   |            |
               |   +-----+   |            |
               +-------|-----+            |
                       v                  v
                    -------            -------
                   (       )          (       )
                  -         -        -         -
                 (           )      (           )
                (  Domain 1   )----(  Domain 2   )
                 (           )      (           )
                  -         -        -         -
                   (       )          (       )
                    -------            -------

APPENDIX B - Example of IP + Optical network with L3VPN service

   This section provides a more complex deployment scenario in which
   ACTN hierarchy is deployed to control a multi-layer network via an
   IP/MPLS PNC and an Optical PNC. The scenario is further enhanced by
   the introduction of an upper layer service configuration (e.g.



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   L3VPN). The provisioning of the L3VPN service is outside ACTN scope
   but it is worth showing how the two parts are integrated for the end
   to end service fulfilment. An example of service configuration
   function in the Service/Network Orchestrator is discussed in [I-
   D.dhjain-bess-bgp-l3vpn-yang].

   Customer
               +-------------------------------+
               |    +-----+                    |
               |    | CNC |                    |
               |    +-----+                    |
               +-------|--------+--------------+
                       |-CMI    | Customer Service Model
                       |        | (non-ACTN interface)
   Service/Network     |        |
   Orchestrator        |        |
               +-------|--------|--------------------------+
               |       |      +-------------------------+  |
               |       |      |Service Mapping Function |  |
               |       |      +-------------------------+  |
               |       |       |         |                 |
               |    +------+   |   +---------------+       |
               |    | MDSC |---    |Service Config.|       |
               |    +------+       +---------------+       |
               +------|------------------|-----------------+
                  MPI-|     +------------+ (non-ACTN Interf.)
                      |    /
              +-----------/------------+
   IP/MPLS    |          /             |
   Domain     |         /              |         Optical Domain
   Controller |        /               |         Controller
     +--------|-------/----+       +---|--------------+
     |   +-----+  +-----+  |       | +-----+          |
     |   |PNC1 |  |Serv.|  |       | |PNC2 |          |
     |   +-----+  +-----+  |       | +-----+          |
     +---------------------+       +------------------+
              |                               |
              v                               |
       +---------------------------------+    |
      /         IP/MPLS Network           \   |
     +-------------------------------------+  |
                                              V
        +--------------------------------------+
       /           Optical Network              \
      +------------------------------------------+






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