Network Working Group                                Daniele Ceccarelli
Internet Draft                                                 Ericsson

Intended status: Informational                              Luyuan Fang
Expires: August 2014                                          Microsoft

                                                              Young Lee

                                                            Diego Lopez

                                                      February 14, 2014

      Framework for Abstraction and Control of Transport Networks


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Copyright Notice

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   Copyright (c) 2014 IETF Trust and the persons identified as the
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   warranty as described in the Simplified BSD License.


   This draft provides a framework for abstraction and control of
   transport networks.

Table of Contents

   1. Terminology....................................................3
   2. Introduction...................................................3
   3. Business Model of ACTN.........................................5
      3.1. Customers.................................................6
      3.2. Service Providers.........................................7
      3.3. Network Providers.........................................9
   4. Computation Model of ACTN......................................9
      4.1. Request Processing........................................9
      4.2. Types of Network Resources...............................10
      4.3. Accuracy of Network Resource Representation..............10
      4.4. Resource Efficiency......................................10
      4.5. Guarantee of Client Isolation............................10
      4.6. Computing Time...........................................11
      4.7. Admission Control........................................11
      4.8. Path Constraints.........................................11
   5. Control and Interface Model for ACTN..........................11
      5.1. A High-level ACTN Control Architecture...................11
      5.2. Customer Controller......................................14
      5.3. Abstracted Topology......................................16
      5.4. Workflows of ACTN Control Modules........................21
      5.5. Programmability of the ACTN Interfaces...................23
   6. Design Principles of ACTN.....................................23
      6.1. Network Security.........................................23

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      6.2. Privacy and Isolation....................................23
      6.3. Scalability..............................................24
      6.4. Manageability and Orchestration..........................24
      6.5. Programmability..........................................24
      6.6. Network Stability........................................24
   7. References....................................................25
      7.1. Informative References...................................25
   8. Contributors..................................................25
   Authors' Addresses...............................................26
   Intellectual Property Statement..................................26
   Disclaimer of Validity...........................................27

1. Terminology

   This document uses the terminology defined in [RFC4655], and

   CVI      Customer-VNC Interface

   PCA      Path Computation Agent

   PNC      Physical Network Controller

   VL       Virtual Link

   VN       Virtual Network

   VNM      Virtual Network Mapping

   VNC      Virtual Network Controller

   VNE      Virtual Network Element

   VNS      Virtual Network Service

   VPI      VNC-PNC Interface

2. Introduction

   Transport 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.

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   Transport networks in this draft refer to a set of different type of
   connection-oriented networks, primarily Connection-Oriented Circuit
   Switched (CO-CS) networks and Connection-Oriented Packet Switched
   (CO-PS) networks. This implies that at least the following transport
   networks are in scope of the discussion of this draft: L1 optical
   networks (e.g., OTN and WDM), MPLS-TP, MPLS-TE, as well as other
   emerging connection-oriented networks such as Segment Routing (SR).
   One of the characteristics of these network types is the ability of
   dynamic provisioning and traffic engineering such that resource
   guarantee can be provided to their clients.

   One of the main drivers for Software Defined Networking (SDN) is a
   physical separation 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
   PCE [PCE] for TE-based transport networks. In fact, in transport
   networks such separation of data and control plane was dictated at
   the onset due to the very different natures of the data plane
   (circuit switched TDM or WDM) and a packet switched control plane.
   The physical separation of the control plane and the data plane is a
   major step towards allowing operators to gain the full control for
   optimized network design and operation. Moreover, another advantage
   of SDN is its logically centralized control regime that allows a
   global view of the underlying network under its control. Centralized
   control in SDN helps improve network resources utilization from a
   distributed network control. For TE-based transport network control,
   PCE is essentially equivalent to a logically centralized control for
   path computation function.

   As transport networks evolve, the need to provide network
   abstraction has emerged as a key requirement for operators; this
   implies in effect the virtualization of network resources so that
   the network is "sliced" for different uses, applications, services,
   and customers each being given a different partial view of the total
   topology and each considering that it is operating with or on a
   single, stand-alone and consistent network.

   Network virtualization, in general, refers to allowing the customers
   to utilize a certain amount of network resources as if they own them
   and thus control their allocated resources in a way most optimal
   with higher layer or application processes. This empowerment of
   customer control facilitates introduction of new services and
   applications as the customers are permitted to create, modify, and
   delete their virtual network services. The level of virtual control
   given to the customers can vary from a tunnel connecting two end-
   points to virtual network elements that consist of a set of virtual

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   nodes and virtual links in a mesh network topology. More flexible,
   dynamic customer control capabilities are added to the traditional
   VPN along with a customer specific virtual network view. Customers
   control a view of virtual network resources, specifically allocated
   to each one of them. This view is called an abstracted network
   topology. Such a view may be specific to the set of consumed
   services as well as to a particular customer. As the customer
   controller is envisioned to support a plethora of distinct
   applications, there would be another level of virtualization from
   the customer to individual applications.

   The virtualization framework described in this draft is named
   Abstraction and Control of Transport Network (ACTN) and facilitates:

     - Abstraction of the underlying network resources to higher-layer
        applications and users (customers);

     - Slicing infrastructure to connect multiple customers to meet
        specific application and users requirements;

     - A computation scheme, via an information model, to serve
        various customers that request network connectivity and
        properties associated with it;

     - A virtual network controller that adapts customer requests to
        the virtual resources (allocated to them) to the supporting
        physical network control and performs the necessary mapping,
        translation, isolation and security/policy enforcement, etc.;

     - The coordination of the underlying transport topology,
        presenting it as an abstracted topology to the customers via
        open and programmable interfaces.

   The organization of this draft is as follows. Section 3 provides a
   discussion for a Business Model, Section 4 a Computation Model,
   Section 5 a Control and Interface model and Section 6 Design

3. Business Model of ACTN

   The traditional Virtual Private Network (VPN) and Overlay Network
   (ON) models are built on the premise that one single network
   provider provides all virtual private or overlay networks to its
   customers. This model is simple to operate but has some

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   disadvantages in accommodating the increasing need for flexible and
   dynamic network virtualization capabilities.

   The ACTN model is built upon entities that reflect the current
   landscape of network virtualization environments. There are three
   key entities in the ACTN model [REF probl stat]:

     - Customers
     - Service Providers
     - Network Providers

    3.1. Customers

   Within the ACTN framework, different types of customers may be taken
   into account depending on the type of their resource needs, on their
   number and type of access. As 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 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
   service and internet access.

   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 demand
   significantly varying in time and from customer to customer. This is
   one of reasons why a bundled services offer is not enough but it is
   desirable to provide each of them with customized virtual network
   services. As customers are geographically spread over multiple
   network provider domains, the necessary control and data interfaces
   to support such customer needs is no longer a single interface
   between the customer and one single network provider. With this
   premise, customers have to interface multiple providers to get their
   end-to-end network connectivity service and the associated topology
   information. Customers may have to support multiple virtual network
   services with differing service objectives and QoS requirements. For
   flexible and dynamic applications, customers may want to control
   their allocated virtual network resources in a dynamic fashion. To
   allow that, customers should be given an abstracted view of topology
   on which they can perform the necessary control decisions and take
   the corresponding actions.

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   Customers of a given service provider can in turn offer a service to
   other customers in a recursive way. An example of recursiveness with
   2 service providers is shown below.

     - Customer (of service B)
     - Customer (of service A) & Service Provider (of service B)
     - Service Provider (of service A)
     - Network Provider

   +-----------------------------------------------------------------------+        ---
   |                                                                       |         ^
   |                                                Customer (of service B)|         .
   | +---------------------------------------------------------------+     |         B
   | |                                                               |     |   ---   .
   | |       Customer (of service A) & Service Provider(of service B)|     |    ^    .
   | | +--------------------------------------------------------+    |     |    .    .
   | | |                                                        |    |     |    .    .
   | | |                         Service Provider (of service A)|    |     |    A    .
   | | |+-----------------------------------------------+       |    |     |    .    .
   | | ||                                               |       |    |     |    .    .
   | | ||                               Network provider|       |    |     |    v    v
   | | |+-----------------------------------------------+       |    |     |   ---------
   | | +--------------------------------------------------------+    |     |
   | +---------------------------------------------------------------+     |

    3.2. Service Providers

   Service providers are the providers of virtual network services to
   their customers. Service providers may or may not own physical
   network resources. When a service provider is the same as the
   network provider, this is similar to traditional VPN models. This
   model works well when the customer maintains a single interface with
   a single provider.  When customer location spans across 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 service providers directly interface their
   customers. In this case, service providers themselves are 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.

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   Customer            X -----------------------------------X

   Service Provider A  X -----------------------------------X

   Network Provider B                     X-----------------X

   Network Provider A  X------------------X

   The ACTN network model is predicated upon this three tier model and
   is summarized in figure below:

                       |       customer       |
                                 |   /\  Service/Customer specific
                                 |   ||  Abstract Topology
                                 |   ||
                       |         VNC          | E2E abstract
                       |  Service Provider    | topology creation
                       /         |            \
                      /          |             \  Network Topology
                     /           |              \ (raw or abstract)
                    /            |               \
   +------------------+   +------------------+   +------------------+
   |Network Provider 1|   |Network Provider 2|   |Network Provider 3|
   +------------------+   +------------------+   +------------------+

                        Figure 1: Three tier model.

   There can be multiple types of service providers.

     . Data Center providers: can be viewed as a service provider type
        as they own and operate data center resources to various WAN

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        clients, they can lease physical network resources from network
     . Internet Service Providers (ISP): can be a service provider 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

    3.3. Network Providers

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

4. Computation Model of ACTN

   This section discusses ACTN framework from a computational point of
   view. As multiple customers run their virtualized network on a
   shared infrastructure, making efficient use of the underlying
   resources requires effective computational models and algorithms.
   This general problem space is known as Virtual Network Mapping or
   Embedding (VNM or VNE). [Editors's note(Put some reference)].

   As VNM/VNE issues impose some additional compute models and
   algorithms for virtual network path computation, this section
   discusses key issues and constraints for virtual network path

    4.1. Request Processing

   This is concerned about whether a set of customer requests for VN
   creation can be dealt with in real-time or off line, and in the
   latter case, simultaneously or not. This depends on the nature of
   applications the customer support. There are applications and use
   cases, like e.g. management of catastrophic events or real time SLA
   negotiation, that require a real-time VN creation. If the customer
   does not require real-time instantiation of VN creation, the
   computation engine can process a set of VN creation requests
   simultaneously to improve network efficiency.

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    4.2. Types of Network Resources

   When a customer makes a VN creation request to the substrate
   network, what kind of network resources is consumed is of concern of
   both the customer and service/network providers. The customer needs
   to put constraints (e.g. TE parameters, resiliency) for the
   provisioning of the VN, while the service and network providers need
   to choose which resources meet such constraints and possibly have
   fewest impact on the capability of serving other customers. For
   transport network virtualization, the network resource consumed is
   primarily network bandwidth that the required paths would occupy on
   the physical link(s). However, there may be other resource types
   such as CPU and memory that need to be considered for certain
   applications. These resource types shall be part of the VN request
   made by the customer.

    4.3. Accuracy of Network Resource Representation

   As the underlying transport network in itself may consist of a
   layered structure, it is a challenge how to represent these
   underlying physical network resources and topology into a form that
   can be reliably used by the computation engine that assigns customer
   requests into the physical network resource and topology.

    4.4. Resource Sharing and Efficiency

   Related to the accuracy of network resource representation is
   resource efficiency. As a set of independent customer VN is created
   and mapped onto physical network resources, the overall network
   resource utilization is the primary concern of the network provider.

   In order to provide an efficient utilization of the resources of the
   provider network, it should be possible to share given physical
   resources among a number of different VNs. Whether a virtual
   resource is sharable among a set of VNs (and hence of customers) is
   something the service provider needs to agree with each customer.
   Preemption and priority management are tools that could help provide
   an efficient sharing of physical resources among different VNs.

    4.5. Guarantee of Client Isolation

   While network resource sharing across a set of customers for
   efficient utilization is an important aspect of network
   virtualization, customer isolation has to be guaranteed. Admissions
   of new customer requests or any changes of other existing customer

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   VNs must not affect any particular customer in terms of resource
   guarantee, security constraints, and other performance constraints.

    4.6. Computing Time

   Depending on the nature of applications, how quickly a VN is
   instantiated from the time of request is an important factor. For
   dynamic applications that require instantaneous VN creation or VN
   changes from the existing one, the computation model/algorithm
   should support this constraint.

    4.7. Admission Control

   To coordinate the request process of multiple customers, an
   admission control will help maximize an overall efficiency.

    4.8. Path Constraints

   There may be some factors of path constraints that can affect the
   overall efficiency. Path Split can lower VN request blocking if the
   underlying network can support such capability. A packet-based TE
   network can support path split while circuit-based transport may
   have limitations.

   Path migration is a technique that allows changes of nodes or link
   assignments of the established paths in an effort to accommodate new
   requests that would not be accepted without such path migration(s).
   This can improve overall efficiency, yet additional care needs to be
   applied to avoid any adverse impacts associated with changing the
   existing paths.

   Re-optimization is a global process to re-shuffle all existing path
   assignments to minimize network resource fragmentation. Again, an
   extra care needs to be applied for re-optimization.

5. Control and Interface Model for ACTN

   This section provides a high-level control and interface model of

    5.1. A High-level ACTN Control Architecture

   To allow virtualization, the network has to provide open,
   programmable interfaces, in which customer applications can create,
   replace and modify virtual network resources in an interactive,
   flexible and dynamic fashion while having no impact on other

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   customers. Direct customer control of transport network elements
   over existing interfaces (control or management plane) is not
   perceived as a viable proposition for transport network providers
   due to security and policy concerns among other reasons. In
   addition, as discussed in the previous section, the network control
   plane for transport networks has been separated from data plane and
   as such it is not viable for the customer to directly interface with
   transport network elements.

   While the current network control plane is well suited for control
   of physical network resources via dynamic provisioning, path
   computation, etc., a virtual network controller needs to be built on
   top of physical network controller to support network
   virtualization. On a high-level, virtual network control refers to a
   mediation layer that performs several functions:

   - Computation of customer resource requests into virtual network
     paths based on the global network-wide abstracted topology;

   - Mapping and translation of customer virtual network slices into
     physical network resources;

   - Creation of an abstracted view of network slices allocated to each
     customer, according to customer-specific objective functions, and
     to the customer traffic profile.

   In order to facilitate the above-mentioned virtual control
   functions, the virtual network controller (aka., "virtualizer")
   needs to maintain two interfaces:

   - One interface with the physical network controller functions which
     is termed as the VNC-PNC Interface (VPI).

   - Another interface with the customer controller for the virtual
     network, which is termed as Client-VNC Interface (CVI).

   Figure 2 depicts a high-level control and interface architecture for

             |             Application Layer            |
                    /|\       /|\          /|\
                     |         |           \|/   Northbound API
                     |         |          ---------------

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                     |        \|/        |     Customer  |
                     |       ---------------  Controller |
                    \|/     |    Customer   |------------
                  -------------- Controller |   /|\
                 |   Customer   |-----------     |
                 |  Controller  |   /|\          |
                  --------------     |           |
                           /|\       |           |  Customer-VNC
                            |        |           |  Interface (CVI)
                           \|/      \|/         \|/
                   |  Virtual Network Controller (VNC) |
                                      |     VNC-PNC Interface (VPI)
                   | Physical Network Controller (PNC) |
                                      |     Control Interface to NEs

                        Physical Network Infrastructure

          Figure 2: Control and Interface Architecture for ACTN.

   Figure 2 shows that there are multiple customer controllers, which
   are independent to one another, and that each customer supports
   various business applications over its NB API. There are layered
   client-server relationships in this architecture. As various
   applications are clients to the customer controller, it also becomes
   itself a client to the virtual network controller. Likewise, the
   virtual network controller is also a client to the physical network
   controller. This layered relationship is important in the protocol
   definition work on the NB API, the CVI and VPI interfaces as this
   allows third-party software developers to program client controllers
   and virtual network controllers independently.

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   There are several ways in which the Physical Network Controller
   manages the network elements, e.g. via management protocols,
   PCEP+GMPLS, or any other type of protocol. In other words the ACTN
   architecture both applies to physical networks controlled by control
   plane protocols (e.g. PCEP+GMPLS) or management plane protocols
   (e.g. SNMP).

    5.2. Customer Controller

   A Virtual Network Service is instantiated by the customer controller
   via the CVI. As the customer controller directly interfaces the
   application stratum, it understands multiple application
   requirements and their service needs. It is assumed that the
   customer controller and the VNC have a common knowledge on the end-
   point interfaces based on their business negotiation prior to
   service instantiation. End-point interfaces refer to customer-
   network physical interfaces that connect customer premise equipment
   to network provider equipment. Figure 5 shows an example physical
   network topology that supports multiple customers. In this example,
   customer A has three end-points A.1, A.2 and A.3. The interfaces
   between customers and transport networks are assumed to be 40G OTU
   links. For simplicity's sake, all network interfaces are assumed to
   be 40G OTU links and all network ports support ODU switching and
   grooming on the level of ODU1 and ODU2. Customer controller for A
   provides its traffic demand matrix that describes bandwidth
   requirements and other optional QoS parameters (e.g., latency,
   diversity requirement, etc.) for each pair of end-point connections.

    5.3. Virtual Network Controller

   The virtual network controller sits between the consumer controller
   (the one issuing connectivity requests) and the physical network
   controller (the one managing the resources). The Virtual Network
   controller can be collocated with the physical network controller,
   especially in those cases where the service provider and the network
   provider are the same entity.

   The virtual network controller is composed by the following
   functional components:

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   |                                                                  |
   | Virtual     +-------------+        +------------------------+    |
   | Network     | VNS Proxy   |        | Abstract Topology DB   |    |
   | Controller  +-------------+        +------------------------+    |
   |                                                                  |
   | +-------------------+  +-------------------+   +---------------+ |
   | | Resource Manager  |  | vConnection Agent |   |VNC OAM handler| |
   | +-------------------+  +-------------------+   +---------------+ |

     . VNS proxy: The VNS proxy is the functional module in charge of
        performing policy management and AAA (Authentication,
        authorization, and accounting) functions. It is the one that
        receives that VN instantiation and resource allocation requests
        from the Customer controllers.
     . Abstract Topology DB: This is the database where the abstract
        topology, generated by the VNC or received from the PNC, is
        stored. A different VN instance is kept for every different
     . Resource Manager: The resource manager is in charge of
        receiving VNS instantiation requests from the customer
        controller and, as a consequence, triggering a concurrent path
        computation request to the PCE in the PNC based on the traffic
        matrix. The Resource manager is also in charge of generating
        the abstract topology for the customer.
     . vConnection Agent: This module is in charge of mapping VN setup
        commands into network provisioning requests to the PNC.
     . VNC OAM handler: The VNC OAM handler is the module that is in
        charge of understanding how the network is operating, detecting
        faults and reacting to problems related to the abstract

    5.4. Physical Network Controller

   The physical network controller is the one in charge of configuring
   the network elements, monitoring the physical topology of the
   network and passing it, either raw or abstracted, to the VNC.

   It is composed by the following functional components:

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   |                                                                  |
   | Physical    +-----------+ +-----+   +------------------------+   |
   | Network     | VNC Proxy | | PCE |   | Abstract Topology Gen. |   |
   | Controller  +-----------+ +-----+   +------------------------+   |
   |                                                                  |
   | +---------------+ +--------------------+ +--------------------+  |
   | |PNC OAM Handler| |Provisioning Manager| |Physical Topology DB|  |
   | +---------------+ +--------------------+ +--------------------+  |

     . VNC proxy: The VNC proxy is the functional module in charge of
        performing policy management and AAA (Authentication,
        authorization, and accounting) functions on requests coming
        from the VNC.
     . PCE: This is the stateful PCE performing the path computation
        over the physical topology and that provides the vConnection
        agent with the network topology.
     . Abstract topology generator: the network topology can be passed
        to the VNC as raw or abstract. In case the topology is passed
        as abstract topology, this module is in charge of generating it
        from the physical topology DB. The module is optional.
     . ONC OAM handler: it verifies that connections exists,
        implements monitoring functions to see if failures occurs. It
        is the proxy to an OSS/NMS system but does not duplicate any of
        OSS/NMS functionalities.
     . Physical topology database: The physical topology database is
        mainly composed by two databases: the Traffic Engineering
        Database (TED) and the LSP Database (LSP-DB).
     . Provisioning manager: The Provisioning Manager is responsible
        for making or channeling requests for the establishment of
        LSPs.  This may be instructions to the control plane running in
        the networks, or may involve the programming of individual
        network devices.  In the latter case, the Provisioning Manager
        may act as an OpenFlow Controller [ONF].

    5.5. Abstracted Topology

   There are two levels of abstracted topology that needs to be
   maintained and supported for ACTN. Customer-specific Abstracted
   Topology refers to the abstracted view of network resources
   allocated (shared or dedicated) to the customer. The granularity of
   this abstraction varies depending on the nature of customer
   applications. Figure 3 illustrates this.

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   Figure 2 shows how three independent customers A, B and C provide
   its respective traffic demand matrix to the VNC. The physical
   network topology shown in Figure 2 is the provider's network
   topology generated by the PNC topology creation engine such as the
   link state database (LSDB) and Traffic Engineering DB (TEDB) based
   on control plane discovery function. This topology is internal to
   PNC and not available to customers. What is available to them is an
   abstracted network topology (a virtual network topology) based on
   the negotiated level of abstraction. This is a part of VNS
   instantiation between a client control and VNC.

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             +------+           +------+          +------+
   A.1 ------o      o-----------o      o----------o      o------- A.2
   B.1 ------o   1  |           |   2  |          |   3  |
   C.1 ------o      o-----------o      o----------o      o------- B.2
             +-o--o-+           +-o--o-+          +-o--o-+
               |  |               |  |              |  |
               |  |               |  |              |  |
               |  |               |  |              |  |
               |  |             +-o--o-+          +-o--o-+
               |  `-------------o      o----------o      o------- B.3
               |                |   4  |          |   5  |
               `----------------o      o----------o      o------- C.3
                                +-o--o-+          +------+
                                  |  |
                                  |  |
                                C.2  A.3

       Traffic Matrix           Traffic Matrix           Traffic Matrix
       for Customer A           for Customer B           for Customer C

         A.1  A.2  A.3            B.1  B.2  B.3           C.1  C.2  C.3
    -------------------      ------------------       -----------------
    A.1  -    20G  20G       B.1  -    40G  40G       C.1 -    20G  20G
    A.2  20G   -   10G       B.2  40G   -   20G       C.2 20G   -   10G
    A.3  20G  10G   -        B.3  40G  20G   -        C.3 20G  10G   -

   Figure 3: Physical network topology shared with multiple customers

   Figure 4 depicts illustrative examples of different level of
   topology abstractions that can be provided by the VNC topology
   abstraction engine based on the physical topology base maintained by
   the PNC.  The level of topology abstraction is expressed in terms of
   the number of virtual network elements (VNEs) and virtual links
   (VLs). For example, the abstracted topology for customer A shows
   there are 5 VNEs and 10 VLs. This is by far the most detailed
   topology abstraction with a minimal link hiding compared to other
   abstracted topologies in Figure 4.

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       (a)  Abstracted Topology for Customer A (5 VNEs and 10 VLs)

             +------+           +------+          +------+
   A.1 ------o      o-----------o      o----------o      o------- A.2
             |   1  |           |   2  |          |   3  |
             |      |           |      |          |      |
             +-o----+           +-o----+          +-o----+
               |                  |                 |
               |                  |                 |
               |                  |                 |
               |                +-o----+          +-o--o-+
               |                |      |          |      |
               |                |   4  |          |   5  |
               `----------------o      o----------o      |
                                +----o-+          +------+

        (b)  Abstracted Topology for Customer B (3 VNEs and 6 VLs)

             +------+                             +------+
   B.1 ------o      o-----------------------------o      o------ B.2
             |   1  |                             |   3  |
             |      |                             |      |
             +-o----+                             +-o----+
                \                                    |
                 \                                   |
                  \                                  |
                   `-------------------              |
                                       `          +-o----+
                                        \         |      o------ B.3
                                         \        |   5  |
                                          `-------o      |

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        (c)  Abstracted Topology for Customer C (1 VNE and 3 VLs)

             |                                           |
             |                                           |
   C.1 ------o                                           |
             |                                           |
             |                                           |
             |                                           |
             |                                           o--------C.3
             |                                           |

         Figure 4: Topology Abstraction Examples for Customers

   As different customers have different control/application needs,
   abstracted topologies for customers B and C, respectively show a
   much higher degree of abstraction. The level of abstraction is
   determined by the policy (e.g., the granularity level) placed for
   the customer and/or the path computation results by the PCE operated
   by the PNC. The more granular the abstraction topology is, the more
   control is given to the customer controller. If the customer
   controller has applications that require more granular control of
   virtual network resources, then the abstracted topology shown for
   customer A may be the right abstraction level for such controller.
   For instance, if the customer is a third-party virtual service
   broker/provider, then it would desire much more sophisticated
   control of virtual network resources to support different
   application needs. On the other hand, if the customer were only to
   support simple tunnel services to its applications, then the
   abstracted topology shown for customer C (one VNE and three VLs)
   would suffice.

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    5.6. Workflows of ACTN Control Modules

   Figure 5 shows workflows across the customer controller, VNC and PNC
   for the VNS instantiation, topology exchange, and VNS setup.

   The customer controller "owns" a VNS and initiates it by providing
   the instantiation identifier with a traffic demand matrix that
   includes path selection constraints for that instance. This VNS
   instantiation request from the Customer Controller triggers a path
   computation request by the Resource Manager in the VNC after VNC's
   proxy's interlay of this request to the Resource Manager. PCA sends
   a concurrent path computation request that is converted according to
   the traffic demand matrix as part of the VNS instantiation request
   from the Customer Controller. Upon receipt of this path computation
   request, the PCE in the PNC block computes paths and updates network
   topology DB and informs the Resource Manager of the VNC of the paths
   and topology updates.

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   | Customer   -----------------------------------------------       |
   | Controller |               VNS Control                    |      |
   |            -----------------------------------------------       |
   1.VNS           |    /|\  4. Abstracted          |    /|\
   Instantiation   |     |   Topology               |     |
   (instance id,   |     |                          |     |
    Traffic Matr.) |     |                          |     | 8. VNS
                   |     |                  5. VNS  |     | Set-up
                  \|/    |                  Set-up \|/    | Confirm
   | Virtual     -----------------------------------------------      |
   | Network     |               VNS Proxy                      |     |
   | Controller   -----------------------------------------------     |
   |           -----------------------     -----------------------    |
   |          |Path Computation Agent |   |  vConnection Agent    |   |
   |           -----------------------     -----------------------    |
   2. Path         |    /|\  3. PC Reply            |    /|\
   Computation     |     |   with updated           |     |
   Request         |     |   topology               |     |
                   |     |             6. Network   |     |8.Network
                   |     |             Provisioning |     |Provisioning
                  \|/    |             Request     \|/    |Confirm
   | Physical      -------------           -------------------------- |
   | Network      |     PCE     |         |  Network Provisioning    ||
   | Controller    -------------           -------------------------- |

           Figure 5. Workflows across Customer Controller, VNC and PNC

   It is assumed that the PCE in PNC is a stateful PCE [PCE-S]. PCA
   abstracts the physical network topology into an abstracted topology
   for the customer based on the agreed-upon granularity level. The
   abstracted topology is then passed to the VNS control of the
   Customer Controller. This controller computes and assigns virtual
   network resources for its applications based on the abstracted
   topology and creates VNS setup command to the VNC. The VNC
   vConnection module turns this VN setup command into network
   provisioning requests over the network elements.

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    5.7. Programmability of the ACTN Interfaces

   From Figures 2 and 5, we have identified several interfaces that are
   of interest of the ACTN model. More precisely, ACTN concerns the
   following interfaces:

   - Customer-VNC Interface (CVI): an interface between a customer
     controller and a virtual network controller.

   - VNC-PNC Interface (VPI): an interface between a virtual network
     controller and a physical network controller.

   The NBI interfaces and direct control interfaces to NEs are outside
   of the scope of ACTN.

   The CVI interface should allow programmability, first of all, to the
   customer so they can create, modify and delete virtual network
   service instances. This interface should also support open standard
   information and data models that can transport abstracted topology.

   The VPI interface should allow programmability to service
   provider(s) (through VNCs) in such ways that control functions such
   as path computation, provisioning, and restoration can be
   facilitated. Seamless mapping and translation between physical
   resources and virtual resources should also be facilitated via this

6. Design Principles of ACTN

    6.1. Network Security

   Network security concerns are always one of the primary principles
   of any network design. ACTN is no exception. Due to the nature of
   heterogeneous VNs that are to be created, maintained and deleted
   flexibly and dynamically and the anticipated interaction with
   physical network control components, secure programming models and
   interfaces have to be available beyond secured tunnels, encryption
   and other network security tools.

    6.2. Privacy and Isolation

   As physical network resources are shared with and controlled by
   multiple independent customers, isolation and privacy for each
   customer has to be guaranteed.

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   Policy should be applied per client.

6.3. Scalability

   As multiple VNs need to be supported seamlessly, there are
   potentially several scaling issues associated with ACTN. The VN
   Controller system should be scalable in supporting multiple parallel
   computation requests from multiple customers. New VN request should
   not affect the control and maintenance of the existing VNs. Any VN
   request should also be satisfied within a time-bound of the customer
   application request.

   Interfaces should also be scalable as a large amount of data needs
   to be transported across customers to virtual network controllers
   and across virtual network controllers and physical network

    6.4. Manageability and Orchestration

   As there are multiple entities participating in network
   virtualization, seamless manageability has to be provided across
   every layer of network virtualization. Orchestration is an important
   aspect of manageability as the ACTN design should allow
   orchestration capability.

   ACTN orchestration should encompass network provider multi-domains,
   relationships between service provider(s) and network provider(s),
   and relationships between customers and service/network providers.

   Ease of deploying end-to-end virtual network services across
   heterogeneous network environments is a challenge.

    6.5. Programmability

   As discussed earlier in Section 5.5, the ACTN interfaces should
   support open standard interfaces to allow flexible and dynamic
   virtual service creation environments.

    6.6. Network Stability

   As multiple VNs are envisioned to share the same physical network
   resources, combining many resources into one should not cause any
   network instability. Provider network oscillation can affect readily
   both on virtual networks and the end-users.

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   Part of network instability can be caused when virtual network
   mapping is done on an inaccurate or unreliable resource data. Data
   base synchronization is one of the key issues that need to be
   ensured in ACTN design.

7. References

                               7.1. Informative References

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

   [PCE-S]   Crabbe, E, et. al., "PCEP extension for stateful
             PCE",draft-ietf-pce-stateful-pce, work in progress.

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

   [NFV-AF]  "Network Functions Virtualization (NFV); Architectural
             Framework", ETSI GS NFV 002 v1.1.1, October 2013.

8. Contributors

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Authors' Addresses

   Daniele Ceccarelli
   Via Melen, 77
   Genova, Italy

   Luyuan Fang

   Young Lee
   Huawei Technologies
   5340 Legacy Drive
   Plano, TX 75023, USA
   Phone: (469)277-5838

   Diego Lopez
   Telefonica I+D
   Don Ramon de la Cruz, 82
   28006 Madrid, Spain

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