Network Working Group                                Daniele Ceccarelli
Internet Draft                                                 Ericsson

Intended status: Informational                              Luyuan Fang
Expires: July 2014                                            Microsoft

                                                              Young Lee

                                                            Diego Lopez

                                                        January 3, 2014

      Framework for Abstraction and Control of Transport Networks


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   This Internet-Draft will expire on June 3, 2014.

Copyright Notice

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   Copyright (c) 2013 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
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   ( in effect on the date of
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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. Consumers.................................................6
      3.2. Service Providers.........................................6
      3.3. Network Providers.........................................7
   4. Computation Model of ACTN......................................7
      4.1. Request Processing........................................7
      4.2. Types of Network Resources................................8
      4.3. Accuracy of Network Resource Representation...............8
      4.4. Resource Efficiency.......................................8
      4.5. Guarantee of Client Isolation.............................8
      4.6. Computing Time............................................8
      4.7. Admission Control.........................................8
      4.8. Path Constraints..........................................9
   5. Control and Interface Model for ACTN...........................9
      5.1. A High-level ACTN Control Architecture....................9
      5.2. Consumer Controller......................................11
      5.3. Abstracted Topology......................................12
      5.4. Workflows of ACTN Control Modules........................15
      5.5. Programmability of the ACTN Interfaces...................17
   6. Design Principles of ACTN.....................................17
      6.1. Network Security.........................................17
      6.2. Privacy and Isolation....................................17

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      6.3. Scalability..............................................18
      6.4. Manageability and Orchestration..........................18
      6.5. Programmability..........................................18
      6.6. Network Stability........................................18
   7. References....................................................19
      7.1. Informative References...................................19
   8. Contributors..................................................19
   Authors' Addresses...............................................20
   Intellectual Property Statement..................................20
   Disclaimer of Validity...........................................21

1. Terminology

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

   CVI      Consumer-VNC Interface

   PNC      Physical Network Controller

   VL       Virtual Link

   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.

   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

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   networks (e.g., OTN and WSON), 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 network control plane from the data
   plane has been already achieved for 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 wavelength) and a packet
   switched control plane. The physical separation of the control plane
   and the data plane is a major step toward 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
   resource 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 consumers 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 consumers
   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
   consumer control facilitates introduction of new services and
   applications as the consumers are given to create, modify, and
   delete their virtual network services. The level of virtual control
   given to the consumers can vary from a tunnel connecting two end-
   points to virtual network elements that consist of a set of virtual
   nodes and virtual links in a mesh network topology. More flexible,
   dynamic consumer control capabilities are added to the traditional
   VPN along with a consumer specific virtual network view. Consumers
   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

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   services as well as to the particular consumer. As the consumer
   controller is envisioned to support a plethora of distinct
   applications, there would be another level of virtualization from
   the consumer 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 (consumers);

     - Sharing of network resources, to meet specific application and
        users requirements;

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

     - A virtual network controller that adapts consumer 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 consumervia 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
   consumers. This model is simple to operate but has some
   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:

     - Consumers

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     - Network Providers
     - Service Providers

3.1. Consumers

   Consumers are the users of virtual network services. As consumers
   are geographically spread over multiple network provider domains,
   the necessary control and data interfaces to support such consumer
   needs is no longer a single interface between the consumer and one
   single network provider. With this premise, consumers have to
   interface multiple providers to get their end-to-end network
   connectivity servjce and the associated topology information.
   Consumers may have to support multiple virtual network services with
   differing service objectives and QoS requirements. For flexible and
   dynamic applications, consumers may want to control their allocated
   virtual network resources in a dynamic fashion. To allow that,
   consumers should be given an abstracted view of topology on which
   they can perform the necessary control decisions and take the
   corresponding actions.

3.2. Service Providers

   Service providers are the providers of virtual network services to
   their consumers. 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 consumer maintains a single interface with
   a single provider.  When consumer 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
   consumers. In this case, service providers themselves are consumers
   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.

   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 clients, they can lease
   physical network resources from network providers. Internet Service
   Providers (ISP) can be a service provider of internet services to

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   their customers while leasing physical network resources from
   network providers. There may be other types of service providers
   such as mobile virtual network operators (MVNO) that 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
   consumers. The layered model proposed by this draft separates the
   concerns of network providers and consumers, with service providers
   acting as aggregators of consumer requests.

4. Computation Model of ACTN

   This section discusses ACTN from a computational point of view. As
   multiple consumers 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). (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 consumer requests for VN
   creation can be dealt with simultaneously or not. This depends on
   the nature of applications the consumer support. If the consumer
   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.

4.2. Types of Network Resources

   When a consumer makes a VN creation request to the substrate
   network, what kind of network resources is consumed is of concern of
   both the consumer and network providers. 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

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   memory that need to be considered for certain applications. These
   resource types shall be part of the VN request made by the consumer.

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 consumer
   requests into the physical network resource and topology.

4.4. Resource Efficiency

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

4.5. Guarantee of Client Isolation

   While network resource sharing across a set of consumers for
   efficient utilization is an important aspect of network
   virtualization, consumer isolation has to be guaranteed. Admissions
   of new consumer requests or any changes of other existing consumer
   VNs must not affect any particular consumer 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, the
   computation model/algorithm should support this constraint.

4.7. Admission Control

   To coordinate the request process of multiple consumers, 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.

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   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 consumer applications can create,
   replace and modify virtual network resources in an interactive,
   flexible and dynamic fashion while having no impact on other network
   consumers. Direct consumer 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 consumer 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 consumer resource requests into virtual network
     paths based on the global network-wide abstracted topology;

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

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

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   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
     assumed by MPLS/GMPLS and PCE, which is termed as the VNC-PNC
     Interface (VPI);

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

   Figure 1 depicts a high-level control and interface architecture for

             |             Application Layer            |
                    /|\       /|\          /|\
                     |         |           \|/   Northbound API
                     |         |          ---------------
                     |        \|/        |     Consumer  |
                     |       ---------------  Controller |
                    \|/     |    Consumer   |------------
                  -------------- Controller |   /|\
                 |   Consumer   |-----------     |
                 |  Controller  |   /|\          |
                  --------------     |           |
                           /|\       |           |  Consumer-VNC
                            |        |           |  Interface (CVI)
                           \|/      \|/         \|/
                   |  Virtual Network Controller (VNC) |
                                      |     VNC-PNC Interface (VPI)
                   | Physical Network Controller (PNC) |
                                      |     Control Interface to NEs

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                        Physical Network Infrastructure

          Figure 1: Control and Interface Architecture for ACTN.

   Figure 1 shows that there are multiple consumer controllers, which
   are independent to one another, and that each consumer supports
   various business applications over its NB API. There are layered
   client-server relationships in this architecture. As various
   applications are clients to the consumer 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.

5.2. Consumer Controller

   A Virtual Network Service is instantiated by the consumer controller
   via the CVI. As the consumer controller directly interfaces the
   application stratum, it understands multiple application
   requirements and their service needs. It is assumed that the
   consumer 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 consumer-
   network physical interfaces that connect consumer premise equipment
   to network provider equipment. Figure 2 shows an example physical
   network topology that supports multiple consumers. In this example,
   consumer A has three end-points A.1, A.2 and A.3. The interfaces
   between consumers 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. Consumer 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. Abstracted Topology

   There are two levels of abstracted topology that needs to be
   maintained and supported for ACTN. Consumer-specific Abstracted
   Topology refers to the abstracted view of network resources
   allocated to the consumer. The granularity of this abstraction

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   varies depending on the nature of consumer applications. Figure 2
   illustrates this.

   Figure 2 shows how three independent consumers A, B and C provide
   its respective traffic demand matrices 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 consumers. 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.

             +------+           +------+          +------+
   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 Consumer A           for Consumer B           for Consumer 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 2: Physical network topology shared with multiple consumers

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   Figure 3 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 consumer 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 3.

       (a)  Abstracted Topology for Consumer 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 Consumer B (3 VNEs and 6 VLs)

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

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

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

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

         Figure 3: Topology Abstraction Examples for Consumers

   As different consumers have different control/application needs,
   abstracted topologies for consumers 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 consumer 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 consumer controller. If the consumer
   controller has applications that require more granular control of
   virtual network resources, then the abstracted topology shown for
   consumer A may be the right abstraction level for such controller.
   For instance, if the consumer is a third-party virtual service

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   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 consumer were only to
   support simple tunnel services to its applications, then the
   abstracted topology shown for consumer C (one VNE and three VLs)
   would suffice.

5.4. Workflows of ACTN Control Modules

   Figure 4 shows workflows across the consumer controller, VNC and PNC
   for the VNS instantiation, topology exchange, and VNS setup.

   The consumer 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 Consumer Controller triggers a path
   computation request by the virtual PCE (vPCE) agent in the VNC after
   VNC's proxy's interlay of this request to the vPCE. vPCE sends a
   concurrent path computation request that is converted according to
   the traffic demand matrix as part of the VNS instantiation request
   from the Consumer Controller. Upon receipt of this path computation
   request, the PCE in the PNC block computes paths and updates network
   topology DB and informs the vPCE agent of the VNC of the paths and
   topology updates.

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   | Consumer   -----------------------------------------------       |
   | 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   -----------------------------------------------     |
   |           -----------------------     -----------------------    |
   |          |      vPCE 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 4. Workflows across Consumer Controller, VNC and PNC

   It is assumed that the PCE in PNC is a stateful PCE [PCE-S]. vPCE
   agent abstracts the network topology into an abstracted topology for
   the consumer based on the agreed-upon granularity level. The
   abstracted topology is then passed to the VNS control of the
   Consumer 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 using control plane
   messages such as GMPLS, etc.

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5.5. Programmability of the ACTN Interfaces

   From Figures 1 and 4, we have identified several interfaces that are
   of interest of the ACTN model. More precisely, ACTN concerns the
   following interfaces:

   - Consumer-VNC Interface (CVI): an interface between a consumer
     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
   consumer so they can create, modify and delete virtual 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 consumers, isolation and privacy for each
   consumer 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 consumers. 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 consumer
   application request.

   Interfaces should also be scalable as a large amount of data needs
   to be transported across consumers 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 consumers 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.

   Part of network instability can be caused when virtual network
   mapping is done on an inaccurate or unreliable resource data. Data

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   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

   Daniel Ceccarelli

   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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