Internet Engineering Task Force                                  D. King
Internet-Draft                                        Old Dog Consulting
Intended status: Informational                                 A. Farrel
Expires: 15 February 2015                               Juniper Networks
                                                          15 August 2014

   A PCE-based Architecture for Application-based Network Operations



   Services such as content distribution, distributed databases, or
   inter-data center connectivity place a set of new requirements on the
   operation of networks.  They need on-demand and application-specific
   reservation of network connectivity, reliability, and resources (such
   as bandwidth) in a variety of network applications (such as point-to-
   point connectivity, network virtualization, or mobile back-haul) and
   in a range of network technologies from packet (IP/MPLS) down to
   optical.  Additionally, existing services or capabilities like
   pseudowire connectivity or global concurrent optimization can benefit
   from a operational scheme that considers the application needs and
   the network status.  An environment that operates to meet these types
   of requirement is said to have Application-Based Network Operations

   ABNO brings together many existing technologies for gathering
   information about the resources available in a network, for
   consideration of topologies and how those topologies map to
   underlying network resources, for requesting path computation, and
   for provisioning or reserving network resources.  Thus, ABNO may be
   seen as the use of a toolbox of existing components enhanced with a
   few new elements.  The key component within an ABNO is the Path
   Computation Element (PCE), which can be used for computing paths and
   is further extended to provide policy enforcement capabilities for

   This document describes an architecture and framework for ABNO
   showing how these components fit together.  It provides a cookbook of
   existing technologies to satisfy the architecture and meet the needs
   of the applications.

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Status of this Memo

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   provisions of BCP 78 and BCP 79.

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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
   publication of this document.  Please review these documents
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   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.

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Table of Contents

   1.  Introduction ................................................ 4
    1.1  Scope ..................................................... 5
   2. Application-based Network Operations (ABNO) .................. 5
    2.1  Assumptions and Requirements .............................. 5
    2.2  Implementation of the Architecture ........................ 6
    2.3  Generic Architecture ...................................... 8
      2.3.1 ABNO Components ........................................ 9
      2.3.2 ABNO Functional Interfaces ............................ 15
   3. ABNO Use Cases .............................................. 23
    3.1 Inter-AS Connectivity ..................................... 23
    3.2 Multi-Layer Networking .................................... 29
      3.2.1 Data Center Interconnection across Multi-Layer Networks 33
    3.3 Make-Before-Break ......................................... 36
      3.3.1 Make-Before-Break for Re-optimization ................. 36
      3.3.2 Make-Before-Break for Restoration ..................... 37
      3.3.3 Make-Before-Break for Path Test and Selection ......... 38
    3.4 Global Concurrent Optimization ............................ 40
      3.4.1 Use Case: GCO with MPLS LSPs .......................... 41
    3.5 Adaptive Network Management (ANM) ......................... 43
        3.5.1. ANM Trigger ........................................ 44
        3.5.2. Processing request and GCO computation ............. 44
        3.5.3. Automated Provisioning Process ..................... 45
    3.6 Pseudowire Operations and Management ...................... 46
        3.6.1 Multi-Segment Pseudowires ........................... 46
        3.6.2 Path-Diverse Pseudowires ............................ 48
        3.6.3 Path-Diverse Multi-Segment Pseudowires .............. 49
        3.6.4 Pseudowire Segment Protection ....................... 49
        3.6.5 Applicability of ABNO to Pseudowires ................ 50
    3.7 Cross-Stratum Optimization ................................ 51
        3.7.1.  Data Center Network Operation ..................... 51
        3.7.2.  Application of the ABNO Architecture .............. 53
    3.8 Other Potential Use Cases ................................. 55
        3.8.1 Grooming and Regrooming ............................. 55
        3.8.2 Bandwidth Scheduling ................................ 55
        3.8.3 ALTO Server ......................................... 56
   4. Survivability and Redundancy within the ABNO Architecture ... 58
   5. Security Consideration ...................................... 59
   6. Manageability Considerations ................................ 60
   7. IANA Considerations ......................................... 60
   8. Acknowledgements ............................................ 60
   9. References .................................................. 60
     9.1 Informative References ................................... 60
   10. Contributors' Addresses .................................... 64
   11. Authors' Addresses ......................................... 65
   A. Undefined Interfaces ........................................ 66

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1.  Introduction

   Networks today integrate multiple technologies allowing network
   infrastructure to deliver a variety of services to support the
   different characteristics and demands of applications.  There is an
   increasing demand to make the network responsive to service requests
   issued directly from the application layer.  This differs from the
   established model where services in the network are delivered in
   response to management commands driven by a human user.

   These application-driven requests and the services they establish
   place a set of new requirements on the operation of networks.  They
   need on-demand and application-specific reservation of network
   connectivity, reliability, and resources (such as bandwidth) in a
   variety of network applications (such as point-to-point connectivity,
   network virtualization, or mobile back-haul) and in a range of
   network technologies from packet (IP/MPLS) down to optical.  An
   environment that operates to meet this type of application-aware
   requirement is said to have Application-Based Network Operation

   The Path Computation Element (PCE) [RFC4655] was developed to provide
   path computation services for GMPLS and MPLS networks.  The
   applicability of PCE can be extended to provide path computation and
   policy enforcement capabilities for ABNO platforms and services.

   ABNO can provide the following types of service to applications by
   coordinating the components that operate and manage the network:

   - Optimization of traffic flows between applications to create an
     overlay network for communication in use cases such as file
     sharing, data caching or mirroring, media streaming, or real-time
     communications described as Application Layer Traffic Optimization
     (ALTO) [RFC5693].

   - Remote control of network components allowing coordinated
     programming of network resources through such techniques as
     Forwarding and Control Element Separation (ForCES) [RFC3746],
     OpenFlow [ONF], and the Interface to the Routing System (I2RS)

   - Interconnection of Content Delivery Networks (CDNi) [RFC6707]
     through the establishment and resizing of connections between
     content distribution networks.  Similarly, ABNO can coordinate
     inter-data center connections.

   - Network resource coordination to automate provisioning, facilitate
     grooming and regrooming, bandwidth scheduling, and global

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     concurrent optimization [RFC5557].

   - Virtual Private Network (VPN) planning in support of deployment of
     new VPN customers and to facilitate inter-data center connectivity.

   This document outlines the architecture and use cases for ABNO, and
   shows how the ABNO architecture can be used for coordinating control
   system and application requests to compute paths, enforce policies,
   and manage network resources for the benefit of the applications that
   use the network.  The examination of the use cases shows the ABNO
   architecture as a toolkit comprising many existing components and
   protocols and so this document looks like a cookbook.  ABNO is
   compatible with pre-existing Network Management System (NMS) and
   Operations Support System (OSS) deployments as well as with more
   recent developments in programmatic networks such as Software Defined
   Networking (SDN).

1.1  Scope

   This document describes a toolkit.  It shows how existing functional
   components described in a large number of separate documents can be
   brought together within a single architecture to provide the function
   necessary for ABNO.

   In many cases, existing protocols are known to be good enough or
   almost good enough to satisfy the requirements of interfaces between
   the components.  In these cases the protocols are called out as
   suitable candidates for use within an implementation of ABNO.

   In other cases it is clear that further work will be required, and in
   those cases a pointer to on-going work that may be of use is
   provided.  Where there is no current work that can be identified by
   the authors, a short description of the missing interface protocol is
   given in the Appendix.

   Thus, this document may be seen as providing an applicability
   statement for existing protocols, and guidance for developers of new
   protocols or protocol extensions.

2. Application Based Network Operations (ABNO)

2.1  Assumptions

   The principal assumption underlying this document is that existing
   technologies should be used where they are adequate for the task.
   Furthermore, when an existing technology is almost sufficient, it is
   assumed to be preferable to make minor extensions rather than to
   invent a whole new technology.

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   Note that this document describes an architecture.  Functional
   components are architectural concepts and have distinct and clear
   responsibilities.  Pairs of functional components interact over
   functional interfaces that are, themselves, architectural concepts.

2.2  Implementation of the Architecture

   It needs to be strongly emphasized that this document describes a
   functional architecture.  It is not a software design.  Thus, it is
   not intended that this architecture constrain implementations.
   However, the separation of the ABNO functions into separate
   functional components with clear interfaces between them enables
   implementations to choose which features to include and allows
   different functions to be distributed across distinct processes or
   even processors.

   An implementation of this architecture may make several important
   decisions about the functional components:

   - Multiple functional components may be grouped together into one
     software component such that all of the functions are bundled
     and only the external interfaces are exposed.  This may have
     distinct advantages for fast paths within the software, and can
     reduce inter-process communication overhead.

     For example, an active, stateful PCE could be implemented as a
     single server combining the ABNO components of the PCE, the
     Traffic Engineering Database, the LSP Database, and the
     Provisioning Manager (see Section 2.3).

   - The functional components could be distributed across separate
     processes, processors, or servers so that the interfaces are
     exposed as external protocols.

     For example, the OAM Handler (see Section could be
     presented on a dedicated server in the network that consumes all
     status reports from the network, aggregates them, correlates them,
     and then dispatches notifications to other servers that need to
     understand what has happened.

   - There could be multiple instances of any or each of the
     components.  That is, the function of a functional component could
     be partitioned across multiple software components with each
     responsible for handling a specific feature or a partition of the

     For example, there may be multiple Traffic Engineering Databases
     (see Section in an implementation with each holding the

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     topology information of a separate network domain (such as a
     network layer or an Autonomous System).  Similarly there could be
     multiple PCE instances each processing on a different Traffic
     Engineering Database, and potentially distributed on different
     servers under different management control.  As a final example,
     there could be multiple ABNO Controllers each with capability to
     support different classes of application or application service.

   The purpose of the description of this architecture is to facilitate
   different implementations while offering interoperability between
   implementations of key components and easy interaction with the
   applications and with the network devices.

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2.3  Generic ABNO Architecture

   The following diagram illustrates the ABNO architecture.  The
   components and functional interfaces are discussed in Sections 2.3.1
   2.3.2 respectively.  The use cases described in Section 3 show how
   different components are used selectively to provide different

    |          OSS / NMS / Application Service Coordinator           |
      |   |   |    |           |                                 |
   :  |   |   |    |      +----+----------------------+          |     :
   :  |   |   | +--+---+  |                           |      +---+---+ :
   :  |   |   | |Policy+--+     ABNO Controller       +------+       | :
   :  |   |   | |Agent |  |                           +--+   |  OAM  | :
   :  |   |   | +-+--+-+  +-+------------+----------+-+  |   |Handler| :
   :  |   |   |   |  |      |            |          |    |   |       | :
   :  |   | +-+---++ | +----+-+  +-------+-------+  |    |   +---+---+ :
   :  |   | |ALTO  | +-+ VNTM |--+               |  |    |       |     :
   :  |   | |Server|   +--+-+-+  |               |  | +--+---+   |     :
   :  |   | +--+---+      | |    |      PCE      |  | | I2RS |   |     :
   :  |   |    |  +-------+ |    |               |  | |Client|   |     :
   :  |   |    |  |         |    |               |  | +-+--+-+   |     :
   :  | +-+----+--+-+       |    |               |  |   |  |     |     :
   :  | | Databases +-------:----+               |  |   |  |     |     :
   :  | |   TED     |       |    +-+---+----+----+  |   |  |     |     :
   :  | |  LSP-DB   |       |      |   |    |       |   |  |     |     :
   :  | +-----+--+--+     +-+---------------+-------+-+ |  |     |     :
   :  |       |  |        |    Provisioning Manager   | |  |     |     :
   :  |       |  |        +-----------------+---+-----+ |  |     |     :
      |       |  |                 |   |    |   |       |  |     |
      |     +-+--+-----------------+--------+-----------+----+   |
      +----/               Client Network Layer               \--+
      |   +----------------------------------------------------+ |
      |      |                         |        |          |     |
    /                      Server Network Layers                    \

                  Figure 1 : Generic ABNO Architecture

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2.3.1 ABNO Components

  This section describes the functional components shown as boxes in
  Figure 1.  The interactions between those components, the functional
  interfaces, are described in Section 2.3.2. NMS and OSS

   A Network Management System (NMS) or an Operations Support System
   (OSS) can be used to control, operate, and manage a network.  Within
   the ABNO architecture, an NMS or OSS may issue high-level service
   requests to the ABNO Controller.  It may also establish policies for
   the activities of the components within the architecture.

   The NMS and OSS can be consumers of network events reported through
   the OAM Handler and can act on these reports as well as displaying
   them to users and raising alarms.  The NMS and OSS can also access
   the Traffic Engineering Database (TED) and Label Switched Path
   Database (LSP-DB) to show the users the current state of the network.

   Lastly, the NMS and OSS may utilize a direct programmatic or
   configuration interface to interact with the network elements within
   the network. Application Service Coordinator

   In addition to the NMS and OSS, services in the ABNO architecture
   may be requested by or on behalf of applications.  In this context
   the term "application" is very broad.  An application may be a
   program that runs on a host or server and that provides services to a
   user, such as a video conferencing application.  Alternatively, an
   application may be a software tool with which a user makes requests
   of the network to set up specific services such as end-to-end
   connections or scheduled bandwidth reservations.  Finally, an
   application may be a sophisticated control system that is responsible
   for arranging the provision of a more complex network service such as
   a virtual private network.

   For the sake of this architecture, all of these concepts of an
   application are grouped together and are shown as the Application
   Service Coordinator since they are all in some way responsible for
   coordinating the activity of the network to provide services for use
   by applications.  In practice, the function of the Application
   Service Coordinator may be distributed across multiple applications
   or servers.

   The Application Service Coordinator communicates with the ABNO
   Controller to request operations on the network.

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   The ABNO Controller is the main gateway to the network for the NMS,
   OSS, and Application Service Coordinator for the provision of
   advanced network coordination and functions.  The ABNO Controller
   governs the behavior of the network in response to changing network
   conditions and in accordance with application network requirements
   and policies.  It is the point of attachment, and invokes the right
   components in the right order.

   The use cases in Section 3 provide a clearer picture of how the
   ABNO Controller interacts with the other components in the ABNO
   architecture. Policy Agent

   Policy plays a very important role in the control and management of
   the network.  It is, therefore, significant in influencing how the
   key components of the ABNO architecture operate.

   Figure 1 shows the Policy Agent as a component that is configured
   by the NMS/OSS with the policies that it applies.  The Policy Agent
   is responsible for propagating those policies into the other
   components of the system.

   Simplicity in the figure necessitates leaving out many of the policy
   interactions that will take place.  Although the Policy Agent is only
   shown interacting with the ABNO Controller, the Alto Server, and the
   Virtual Network Topology Manager (VNTM), it will also interact with a
   number of other components and the network elements themselves.  For
   example, the Path Computation Element (PCE) will be a Policy
   Enforcement Point (PEP) [RFC2753] as described in [RFC5394], and the
   Interface to the Routing System (I2RS) Client will also be a PEP as
   noted in [I-D.ietf-i2rs-architecture]. Interface to the Routing System (I2RS) Client

   The Interface to the Routing System (I2RS) is described in
   [I-D.ietf-i2rs-architecture].  The interface provides a programmatic
   way to access (for read and write) the routing state and policy
   information on routers in the network.

   The I2RS Client is introduced in [I-D.ietf-i2rs-problem-statement].
   Its purpose is to manage information requests across a number of
   routers (each of which runs an I2RS Agent) and coordinate setting or
   gathering state to/from those routers.

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   Operations, Administration, and Maintenance (OAM) plays a critical
   role in understanding how a network is operating, detecting faults,
   and taking the necessary action to react to problems in the network.

   Within the ABNO architecture, the OAM Handler is responsible for
   receiving notifications (often called alerts) from the network about
   potential problems, for correlating them, and for triggering other
   components of the system to take action to preserve or recover the
   services that were established by the ABNO Controller.  The OAM
   Handler also reports network problems and, in particular, service-
   affecting problems to the NMS, OSS, and Application Service

   Additionally, the OAM Handler interacts with the devices in the
   network to initiate OAM actions within the data plane such as
   monitoring and testing. Path Computation Element (PCE)

   The Path Computation Element (PCE) is introduced in [RFC4655].  It is
   a functional component that services requests to compute paths across
   a network graph.  In particular, it can generate traffic engineered
   routes for MPLS-TE and GMPLS Label Switched Paths (LSPs).  The PCE
   may receive these requests from the ABNO Controller, from the Virtual
   Network Topology Manager, or from network elements themselves.

   The PCE operates on a view of the network topology stored in the
   Traffic Engineering Database (TED).  A more sophisticated computation
   may be provided by a Stateful PCE that enhances the TED with
   information about the LSPs that are provisioned and operational
   within the network as described in [RFC4655] and

   Additional function in an Active PCE allows a functional component
   that includes a Stateful PCE to make provisioning requests to set up
   new services or to modify in-place services as described in
   [I-D.ietf-pce-stateful-pce] and [I-D.ietf-pce-pce-initiated-lsp].
   This function may directly access the network elements, or may be
   channelled through the Provisioning Manager.

   Coordination between multiple PCEs operating on different TEDs can
   prove useful for performing path computation in multi-domain (for
   example, inter-AS) or multi-layer networks.

   Since the PCE is a key component of the ABNO architecture, a better
   view of its role can be gained by examining the use cases described

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   in Section 3. Databases

   The ABNO Architecture includes a number of databases that contain
   information stores for use by the system.  The two main databases are
   the Traffic Engineering Database (TED) and the LSP Database (LSP-DB),
   but there may be a number of other databases to contain information
   about topology (ALTO Server), policy (Policy Agent), services (ABNO
   Controller), etc.

   In the text that follows specific key components that are consumers
   of the databases are highlighted.  It should be noted that the
   databases are available for inspection by any of the ABNO components.
   Updates to the databases should handled with some care since allowing
   multiple components to write to a database can be the cause of a
   number of contention and sequencing problems. Traffic Engineering Database (TED)

   The Traffic Engineering Database (TED) is a data store of topology
   information about a network that may be enhanced with capability
   data (such as metrics or bandwidth capacity) and active status
   information (such as up/down status or residual unreserved

   The TED may be built from information supplied by the network or
   from data (such as inventory details) sourced through the NMS/OSS.

   The principal use of the TED in the ABNO architecture is to provide
   the raw data on which the Path Computation Element operates.  But
   the TED may also be inspected by users at the NMS/OSS to view the
   current status of the network, and may provide information to
   application services such as Application Layer Traffic Optimization
   (ALTO) [RFC5693]. LSP Database

   The LSP Database (LSP-DB) is a data store of information about LSPs
   that have been set up in the network, or that could be established.
   The information stored includes the paths and resource usage of the

   The LSP-DB may be built from information generated locally.  For
   example, when LSPs are provisioned, the LSP-DB can be updated.  The
   database can also be constructed from information gathered from the
   network by polling or reading the state of LSPs that have already
   been set up.

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   The main use of the LSP-DB within the ABNO architecture is to enhance
   the planning and optimization of LSPs.  New LSPs can be established
   to be path-disjoint from other LSPs in order to offer protected
   services; LSPs can be rerouted in order to put them on more optimal
   paths or to make network resources available for other LSPs; LSPs can
   be rapidly repaired when a network failure is reported; LSPs can be
   moved onto other paths in order to avoid resources that have planned
   maintenance outages. Shared Risk Link Group (SRLG) Databases

   The TED may, itself, be supplemented by SRLG information that assigns
   to each network resource one or more identifiers that associates the
   resource with other resources in the same TED that share the same
   risk of failure.

   While this information can be highly useful, it may be supplemented
   by additional detailed information maintained in a separate database
   and indexed using the SRLG identifier from the TED.  Such a database
   can interpret SRLG information provided by other networks (such as
   server networks), can provide failure probabilities associated with
   each SRLG, can offer prioritization when SRLG-disjoint paths can't be
   found, and can correlate SRLGs between different server networks or
   between different peer networks. Other Databases

   There may be other databases that are built within the ABNO system
   and which are referenced when operating the network.  These databases
   might include information about, for example, traffic flows and
   demands, predicted or scheduled traffic demands, links and node
   failure and repair history, network resources such as packet labels
   and physical labels (i.e., MPLS and GMPLS labels), etc.

   As mentioned in Section, the TED may be enhanced by
   inventory information.  It is quite likely in many networks that such
   an inventory is held in a separate database (the Inventory Database)
   that includes details of manufacturer, model, installation date, etc. ALTO Server

   The ALTO server provides network information to the application
   layer based on abstract maps of a network region.  This information
   provides a simplified view, but it is useful to steer application
   layer traffic.  ALTO services enable Service Providers to share
   information about network locations and the costs of paths between
   them.  The selection criteria to choose between two locations may
   depend on information such as maximum bandwidth, minimum cross-

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   domain traffic, lower cost to the user, etc.

   The ALTO server generates ALTO views to share information with the
   Application Service Coordinator so that it can better select paths
   in the network to carry application-layer traffic.  The ALTO views
   are computed based on information from the network databases, from
   policies configured by the Policy Agent, and through the algorithms
   used by the PCE.

   Specifically, the base ALTO protocol [I-D.ietf-alto-protocol] defines
   a single-node abstract view of a network to the Application Service
   Coordinator.  Such a view consists of two maps: a network map and a
   cost map.  A network map defines multiple provider-defined
   Identifiers (PIDs), which represent entrance points to the network.
   Each node in the application layer is known as an End Point (EP),
   and each EP is assigned to a PID, because PIDs are the entry points
   of the application in the network.  As defined in [I-D.ietf-alto-
   protocol], a PID can denote a subnet, a set of subnets, a
   metropolitan area, a PoP, etc.  Each such network region can be a
   single domain or multiple networks, it is just the view that the ALTO
   server is exposing to the application layer.  A cost map provides
   costs between EPs and/or PIDs.  The criteria that Application Service
   Coordinator uses to choose application routes between two locations
   may depend on attributes such as maximum bandwidth, minimum cross-
   domain traffic, lower cost to the user, etc. Virtual Network Topology Manager (VNTM)

   A Virtual Network Topology (VNT) is defined in [RFC5212] as a set of
   one or more LSPs in one or more lower-layer networks that provides
   information for efficient path handling in an upper-layer network.
   For instance, a set of LSPs in a wavelength division multiplexed
   (WDM) network can provide connectivity as virtual links in a higher-
   layer packet switched network.

   The VNT enhances the physical/dedicated links that are available in
   the upper-layer network and is configured by setting up or tearing
   down the lower-layer LSPs and by advertising the changes into the
   higher-layer network.  The VNT can be adapted to traffic demands
   so that capacity in the higher-layer network can be created or
   released as needed.  Releasing unwanted VNT resources makes them
   available in the lower-layer network for other uses.

   The creation of virtual topology for inclusion in a network is not a
   simple task.  Decisions must be made about which nodes in the upper-
   layer it is best to connect, in which lower-layer network to
   provision LSPs to provide the connectivity, and how to route the LSPs
   in the lower-layer network.  Furthermore, some specific actions have

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   to be taken to cause the lower-layer LSPs to be provisioned and the
   connectivity in the upper-layer network to be advertised.

   [RFC5623] describes how the VNTM may instantiate connections in the
   server-layer in support of connectivity in the client-layer.  Within
   the ABNO  architecture, the creation of new connections may be
   delegated to the Provisioning Manager as discussed in Section

   All of these actions and decisions are heavily influenced by policy,
   so the VNTM component that coordinates them takes input from the
   Policy Agent.  The VNTM is also closely associated with the PCE for
   the upper-layer network and each of the PCEs for the lower-layer
   networks. Provisioning Manager

   The Provisioning Manager is responsible for making or channelling
   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].

   See Section for more details of the interactions between the
   Provisioning Manager and the network. Client and Server Network Layers

   The client and server networks are shown in Figure 1 as illustrative
   examples of the fact that the ABNO architecture may be used to
   coordinate services across multiple networks where lower-layer
   networks provide connectivity in upper-layer networks.

   Section 3.2 describes a set of use cases for multi-layer networking.

2.3.2 Functional Interfaces

   This section describes the interfaces between functional components
   that might be externalized in an implementation allowing the
   components to be distributed across platforms.  Where existing
   protocols might provide all or most of the necessary capabilities
   they are noted.  Appendix A notes the interfaces where more protocol
   specification may be needed. Configuration and Programmatic Interfaces

   The network devices may be configured or programmed direct from the
   NMS/OSS.  Many protocols already exist to perform these functions

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   - SNMP [RFC3412]
   - Netconf [RFC6241]
   - ForCES [RFC5810]
   - OpenFlow [ONF]
   - PCEP [I-D.ietf-pce-pce-initiated-lsp].

   The TeleManagement Forum (TMF) Multi-Technology Operations System
   Interface (MTOSI) standard [TMF-MTOSI] was developed to facilitate
   application-to-application interworking and provides network level
   management capabilities to discover, configure and activate
   resources.  Initially the MTOSI information model was only capable of
   representing connection oriented networks and resources.  In later
   releases, support is added for connection less networks.  MTOSI is
   from NMS perspective a north bound interface and is based on SOAP
   web services.

   From the ABNO perspective, network configuration is a pass-through
   function.  It can be seen represented on the left hand side of
   Figure 1. TED Construction from the Networks

   As described in Section, the TED provides details of the
   capabilities and state of the network for use by the ABNO system and
   the PCE in particular.

   The TED can be constructed by participating in the IGP-TE protocols
   run by the networks (for example, OSPF-TE [RFC3630] and ISIS-TE
   [RFC5305]).  Alternatively, the TED may be fed using link-state
   distribution extensions to BGP [I-D.ietf-idr-ls-distribution].

   The ABNO system may maintain a single TED unified across multiple
   networks, or may retain a separate TED for each network.

   Additionally, an ALTO Server [RFC5693] may provide an abstracted
   topology from a network to build an application-level TED that can
   be used by a PCE to compute paths between servers and application-
   layer entities for the provision of application services. TED Enhancement

   The TED may be enhanced by inventory information supplied from the
   NMS/OSS.  This may supplement the data collected as described in
   Section with information that is not normally distributed
   within the network such as node types and capabilities, or the
   characteristics of optical links.

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   No protocol is currently identified for this interface, but the
   protocol developed or adopted to satisfy the requirements of the
   Interface to the Routing System (I2RS) [I-D.ietf-i2rs-architecture]
   may be a suitable candidate because it is required to be able to
   distribute bulk routing state information in a well-defined encoding
   language.  Another candidate protocol may be Netconf [RFC6241]
   passing data encoded using YANG [RFC6020].

   Note that, in general, any protocol and encoding that is suitable
   for presenting the TED as described in Section will likely be
   suitable (or could be made suitable) for enabling write-access to the
   TED as described in this section. TED Presentation

   The TED may be presented north-bound from the ABNO system for use by
   an NMS/OSS or by the Application Service Coordinator.  This allows
   users and applications to get a view of the network topology and the
   status of the network resources.  It also allows planning and
   provisioning of application services.

   There are several protocols available for exporting the TED north-

   - The ALTO protocol [I-D.ietf-alto-protocol] is designed to
     distribute the abstracted topology used by an ALTO Server and may
     prove useful for exporting the TED.  ALTO server provides the cost
     between EPs or between PIDs, so the application layer can select
     which is the most appropriate connection for the information
     exchange between its application end points.

   - The same protocol used to export topology information from the
     network can be used to export the topology from the TED.

   - The Interface to the Routing System (I2RS)
     [I-D.ietf-i2rs-architecture] will require a protocol that is
     capable of handling bulk routing information exchanges that would
     be suitable for exporting the TED.  In this case it would make
     sense to have a standardized representation of the TED in a formal
     data modelling language such as YANG [RFC6020] so that an existing
     protocol could be used such as Netconf [RFC6241] or XMPP [RFC6120].

   Note that export from the TED can be a full dump of the content
   (expressed in a suitable abstraction language) as described above, or
   it could be an aggregated or filtered set of data based on policies
   or specific requirements.  Thus, the relationships shown in Figure 1
   may be a little simplistic in that the ABNO Controller may also be

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   involved in preparing and presenting the TED information over a
   north-bound interface. Path Computation Requests from the Network

   As originally specified in the PCE architecture [RFC4655], network
   elements can make path computation requests to a PCE using the PCE
   protocol (PCEP) [RFC5440].  This facilitates the network setting up
   LSPs in response to simple connectivity requests, and it allows the
   network to re-optimize or repair LSPs. Provisioning Manager Control of Networks

   As described in Section, the Provisioning Manager makes or
   channels requests to provision resources in the network.  These
   operations can take place at two levels: there can be requests to
   program/configure specific resources in the data or forwarding
   planes; and there can be requests to trigger a set of actions to be
   programmed with the assistance of a control plane.

   A number of protocols already exist to provision network resources as

   - Program/configure specific network resources

     - ForCES [RFC5810] defines a protocol for separation of the control
       element (the Provisioning Manager) from the forwarding elements
       in each node in the network.

     - The Generic Switch Management Protocol (GSMP) [RFC3292] is an
       asymmetric protocol that allows one or more external switch
       controllers (such as the Provisioning Manager) to establish and
       maintain the state of a label switch such as an MPLS switch.

     - OpenFlow [ONF] is a communications protocol that gives an
       OpenFlow Controller (such as the Provisioning Manager) access to
       the forwarding plane of a network switch or router in the

     - Historically, other configuration-based mechanisms have been used
       to set up the forwarding/switching state at individual nodes
       within networks.  Such mechanisms have ranged from non-standard
       command line interfaces (CLIs) to various standards-based options
       such as TL1 [TL1] and SNMP [RFC3412].  These mechanisms are not
       designed for rapid operation of a network and are not easily
       programmatic.  They are not proposed for use by the Provisioning
       Manager as part of the ABNO architecture.

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     - Netconf [RFC6241] provides a more active configuration protocol
       that may be suitable for bulk programming of network resources.
       Its use in this way is dependent on suitable YANG modules being
       defined for the necessary options.  Early work in the IETF's
       Netmod working group is focused on a higher level of routing
       function more comparable with the function discussed in Section [I-D.ietf-netmod-routing-cfg].

     - The [TMF-MTOSI] specification provides provisioning, activation
       and deactivation and release of resources via the Service
       Activation Interface (SAI).  The Common Communication Vehicle
       (CCV) is the middleware required to implement MTOSI.  CCV is then
       used to provide middleware abstraction in combination with Web
       Services Description Language (WSDL) to allow MTOSI interfaces to
       be bound to different middleware technologies as needed.

   - Trigger actions through the control plane

     - LSPs can be requested using a management system interface to the
       head end of the LSP using tools such as CLIs, TL1 [TL1] or SNMP
       [RFC3412].  Configuration at this granularity is not as time-
       critical as when individual network resources are programmed
       because the main task of programming end-to-end connectivity is
       devolved to the control plane.  Nevertheless, these mechanisms
       remain unsuitable for programmatic control of the network and are
       not proposed for use by the Provisioning Manager as part of the
       ABNO architecture.

     - As noted above, Netconf [RFC6241] provides a more active
       configuration protocol.  This may be particularly suitable for
       requesting the establishment of LSPs.  Work would be needed to
       complete a suitable YANG module.

     - The PCE protocol (PCEP) [RFC5440] has been proposed as a suitable
       protocol for requesting the establishment of LSPs
       [I-D.ietf-pce-pce-initiated-lsp].  This works well because the
       protocol elements necessary are exactly the same as used to
       respond to a path computation request.

       The functional element that issues PCEP requests to establish
       LSPs is known as an "Active PCE", however it should be noted that
       the ABNO functional component responsible for requesting LSPs is
       the Provisioning Manager.  Other controllers like the the VNTM
       and the ABNO Controller use the services of the Provisioning
       Manager to isolate the twin functions of computing and requesting
       paths from the provisioning mechanisms in place with any given

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   Note that I2RS does not provide a mechanism for control of network
   resources at this level as it is designed to provide control of
   routing state in routers, not forwarding state in the data plane. Auditing the Network

   Once resources have been provisioned or connections established in
   the network, it is important that the ABNO system can determine the
   state of the network.  Similarly, when provisioned resources are
   modified or taken out of service, the changes in the network need to
   be understood by the ABNO system.  This function falls into four

   - Updates to the TED are gathered as described in Section

   - Explicit notification of the successful establishment and the
     subsequent state of LSP can be provided through extensions to PCEP
     as described in [I-D.ietf-pce-stateful-pce] and

   - OAM can be commissioned and the results inspected by the OAM
     Handler as described in Section

   - A number of ABNO components may make inquiries and inspect network
     state through a variety of techniques including I2RS, Netconf, or
     SNMP. Controlling The Routing System

   As discussed in Section, the Interface to the Routing System
   (I2RS) provides a programmatic way to access (for read and write) the
   routing state and policy information on routers in the network.  The
   I2RS Client issues requests to routers in the network to establish or
   retrieve routing state.  Those requests utilize the I2RS protocol
   which has yet to be selected/designed by the IETF. ABNO Controller Interface to PCE

   The ABNO Controller needs to be able to consult the PCE to determine
   what services can be provisioned in the network.  There is no reason
   why this interface cannot be based on the standard PCE protocol as
   defined in [RFC5440]. VNTM Interface to and from PCE

   There are two interactions between the Virtual Network Topology
   Manager and the PCE.

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   The first interaction is used when VNTM wants to determine what LSPs
   can be set up in a network: in this case it uses the standard PCEP
   interface [RFC5440] to make path computation requests.

   The second interaction arises when a PCE determines that it cannot
   compute a requested path or notices that (according to some
   configured policy) a network is short of resources (for example, the
   capacity on some key link is close to exhausted).  In this case, the
   PCE may notify the VNTM which may (again according to policy) act to
   construct more virtual topology.  This second interface is not
   currently specified although it may be that the protocol selected or
   designed to satisfy I2RS will provide suitable features (see Section or an extension could be made to the PCEP Notify message
   (PCNtf) [RFC5440]. ABNO Control Interfaces

   The north-bound interface from the ABNO Controller is used by the
   NMS, OSS, and Application Service Coordinator to request services in
   the network in support of applications.  The interface will also need
   to be able to report the asynchronous completion of service requests
   and convey changes in the status of services.

   This interface will also need strong capabilities for security,
   authentication, and policy.

   This interface is not currently specified.  It needs to be a
   transactional interface that supports the specification of abstract
   services with adequate flexibility to facilitate easy extension and
   yet be concise and easily parsable.

   It is possible that the protocol selected or designed to satisfy I2RS
   will provide suitable features (see Section ABNO Provisioning Requests

   Under some circumstances the ABNO Controller may make requests direct
   to the Provisioning Manager.  For example, if the Provisioning
   Manager is acting as an SDN Controller then the ABNO Controller may
   use one of the APIs defined to allow requests to me made to the SDN
   Controller (such as the Floodlight REST API [Flood]).  Alternatively,
   since the Provisioning Manager may also receive instructions from a
   stateful PCE, the use of PCEP extensions might be appropriate in
   some cases [I-D.ietf-pce-pce-initiated-lsp].

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   As described in Section and throughout this document, policy
   forms a critical component of the ABNO architecture.  The role of
   policy will include enforcing the following rules and requirements:

   - Adding resources on demand should be gated by the authorized

   - Client microflows should not trigger server-layer setup or

   - Accounting capabilities should be supported.

   - Security mechanisms for authorization of requests and capabilities
     are required.

   Other policy-related function in the system might include the policy
   behavior of the routing and forwarding system such as:

   - ECMP behavior

   - Classification of packets onto LSPs or QoS catgories.

   Various policy-capable architectures have been defined including a
   framework for using policy with a PCE-enabled system [RFC5394].
   However, the take-up of the IETF's Common Open Policy Service
   protocol (COPS) [RFC2748] has been poor.
   New work will be needed to define all of the policy interfaces within
   the ABNO architecture and to determine which are internal interfaces
   and which may be external and so in need of a protocol specification.
   There is some discussion that the I2RS protocol may support the
   configuration and manipulation of policies. OAM and Reporting

   The OAM Handler must interact with the networks to perform several

   - Enabling OAM function within the network.

   - Performing proactive OAM operations in the network.

   - Receiving notifications of network events.

   Any of the configuration and programmatic interfaces described in
   Section may serve this purpose.  Netconf notifications are
   described in [RFC5277], and OpenFlow supports a number of

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   asynchronous event notifications [ONF].  Additionally Syslog
   [RFC5424] is a protocol for reporting events from the network, and
   IPFIX [RFC7011] is designed to allow network statistics to be
   aggregated and reported.

   The OAM Handler also correlates events reported from the network and
   reports them onward to the ABNO Controller (which can apply the
   information to the recovery of services that it has provisioned) and
   to the NMS, OSS, and Application Service Coordinator.  The reporting
   mechanism used here can be essentially the same as used when events
   are reported from the network and no new protocol is needed although
   new data models for technology-independent OAM reporting.

3. ABNO Use Cases

   This section provides a number of examples of how the ABNO
   architecture can be applied to provide application-driven and
   NMS/OSS-driven network operations.

3.1 Inter-AS Connectivity

   The following use case describes how the ABNO framework can be used
   set up an end-to-end MPLS service across multiple Autonomous Systems
   (ASes).  Consider the simple network topology shown in Figure 2.  The
   three ASes (ASa, ASb, and ASc) are connected at ASBRs a1, a2, b1
   through b4, c1, and c2.  A source node (s) located in ASa is to be
   connected to a destination node (d) located in ASc.  The optimal path
   for the LSP from s to d must be computed, and then the network must
   be triggered to set up the LSP.

          +--------------+ +-----------------+ +--------------+
          |ASa           | |       ASb       | |          ASc |
          |         +--+ | | +--+       +--+ | | +--+         |
          |         |a1|-|-|-|b1|       |b3|-|-|-|c1|         |
          | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
          | |s|          | |                 | |          |d| |
          | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
          |         |a2|-|-|-|b2|       |b4|-|-|-|c2|         |
          |         +--+ | | +--+       +--+ | | +--+         |
          |              | |                 | |              |
          +--------------+ +-----------------+ +--------------+

      Figure 2 : Inter-AS Domain Topology with H-PCE (Parent PCE)

   The following steps are performed to deliver the service within the
   ABNO architecture.

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   1. Request Management

      As shown in Figure 3, the NMS/OSS issues a request to the ABNO
      Controller for a path between s and d.  The ABNO Controller
      verifies that the NMS/OSS has sufficient rights to make the
      service request.

                           |       NMS/OSS       |
            +--------+    +-----------+-------------+
            | Policy +-->-+     ABNO Controller     |
            | Agent  |    |                         |
            +--------+    +-------------------------+

               Figure 3 : ABNO Request Management

   2. Service Path Computation with Hierarchical PCE

      The ABNO Controller needs to determine an end-to-end path for the
      LSP.  Since the ASes will want to maintain a degree of
      confidentiality about their internal resources and topology, they
      will not share a TED and each will have its own PCE.  In such a
      situation, the Hierarchical PCE (H-PCE) architecture described in
      [RFC6805] is applicable.

      As shown in Figure 4, the ABNO Controller sends a request to the
      parent PCE for an end-to-end path.  As described in [RFC6805], the
      parent PCE consults its TED that shows the connectivity between
      ASes.  This helps it understand that the end-to-end path must
      cross each of ASa, ASb, and ASc, so it is sends individual path
      computation requests to each of PCE a, b, and c to determine the
      best options for crossing the ASes.

      Each child PCE applies policy to the requests it receives to
      determine whether the request is to be allowed and to select the
      type of network resources that can be used in the computation
      result.  For confidentiality reasons, each child PCE may supply
      its computation responses using a path key [RFC5520] to hide the
      details of the path segment it has computed.

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                        | ABNO Controller |
                             |       A
                             V       |
                          +--+-------+--+   +--------+
            +--------+    |             |   |        |
            | Policy +-->-+ Parent PCE  +---+ AS TED |
            | Agent  |    |             |   |        |
            +--------+    +-+----+----+-+   +--------+
                           /     |     \
                          /      |      \
                   +-----+-+ +---+---+ +-+-----+
                   |       | |       | |       |
                   | PCE a | | PCE b | | PCE c |
                   |       | |       | |       |
                   +---+---+ +---+---+ +---+---+
                       |         |         |
                    +--+--+   +--+--+   +--+--+
                    | TEDa|   | TEDb|   | TEDc|
                    +-----+   +-----+   +-----+

      Figure 4 : Path Computation Request with Hierarchical PCE

      The parent PCE collates the responses from the children and
      applies its own policy to stitch them together into the best end-
      to-end path which it returns as a response to the ABNO Controller.

    3. Provisioning the End-to-End LSP

      There are several options for how the end-to-end LSP gets
      provisioned in the ABNO architecture.  Some of these are described

      3a. Provisioning from the ABNO Controller With a Control Plane

          Figure 5 shows how the ABNO Controller makes a request through
          the Provisioning Manager to establish the end-to-end LSP.  As
          described in Section these interactions can use the
          Netconf protocol [RFC6241] or the extensions to PCEP described
          in [I-D.ietf-pce-pce-initiated-lsp].  In either case, the
          provisioning request is sent to the head end Label Switching
          Router (LSR) and it signals in the control plane (using a
          protocol such as RSVP-TE [RFC3209]) to cause the LSP to be

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                         | ABNO Controller |
                           | Provisioning |
                           | Manager      |
            /                  Network                      \

                Figure 5 : Provisioning the End-to-End LSP

      3b. Provisioning through Programming Network Resources

          Another option is that the LSP is provisioned hop by hop from
          the Provisioning Manager using a mechanism such as ForCES
          [RFC5810] or OpenFlow [ONF] as described in Section
          In this case, the picture is the same as shown in Figure 5.
          The interaction between the ABNO Controller and the

          Provisioning Manager will be PCEP or Netconf as described in
          option 3a., and the Provisioning Manager will have the
          responsibility to fan out the requests to the individual
          network elements.

      3c. Provisioning with an Active Parent PCE

          The active PCE is described in Section based on the
          concepts expressed in [I-D.ietf-pce-pce-initiated-lsp].  In
          this approach, the process described in 3a is modified such
          that the PCE issues a PCEP command to the network direct
          without a response being first returned to the ABNO

          This situation is shown in Figure 6, and could be modified so
          that the Provisioning Manager still programs the individual
          network elements as described in 3b.

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                        | ABNO Controller |
                          +--+----------+         +--------------+
            +--------+    |             |         | Provisioning |
            | Policy +-->-+ Parent PCE  +---->----+ Manager      |
            | Agent  |    |             |         |              |
            +--------+    +-+----+----+-+         +-----+--------+
                           /     |     \                |
                          /      |      \               |
                   +-----+-+ +---+---+ +-+-----+        V
                   |       | |       | |       |        |
                   | PCE a | | PCE b | | PCE c |        |
                   |       | |       | |       |        |
                   +-------+ +-------+ +-------+        |
                      /                  Network                      \

            Figure 6 : LSP Provisioning with an Active PCE

      3d. Provisioning with Active Child PCEs and Segment Stitching

          A mixture of the approaches described in 3b and 3c can result
          in a combination of mechanisms to program the network to
          provide the end-to-end LSP.  Figure 7 shows how each child PCE
          can be an active PCE responsible for setting up an edge-to-
          edge LSP segment across one of the ASes.  The ABNO Controller
          then uses the Provisioning Manager to program the inter-AS
          connections using ForCES or OpenFlow and the LSP segments are
          stitched together following the ideas described in [RFC5150].
          Philosophers may debate whether the Parent PCE in this model
          is active (instructing the children to provision LSP segments)
          or passive (requesting path segments that the children

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                           | ABNO Controller +-------->--------+
                           +----+-------+----+                 |
                                |       A                      |
                                V       |                      |
                             +--+-------+--+                   |
               +--------+    |             |                   |
               | Policy +-->-+ Parent PCE  |                   |
               | Agent  |    |             |                   |
               +--------+    ++-----+-----++                   |
                             /      |      \                   |
                            /       |       \                  |
                       +---+-+   +--+--+   +-+---+             |
                       |     |   |     |   |     |             |
                       |PCE a|   |PCE b|   |PCE c|             |
                       |     |   |     |   |     |             V
                       +--+--+   +--+--+   +---+-+             |
                          |         |          |               |
                          V         V          V               |
               +----------+-+ +------------+ +-+----------+    |
               |Provisioning| |Provisioning| |Provisioning|    |
               |Manager     | |Manager     | |Manager     |    |
               +-+----------+ +-----+------+ +-----+------+    |
                 |                  |              |           |
                 V                  V              V           |
              +--+-----+       +----+---+       +--+-----+     |
             /   AS a   \=====/   AS b   \=====/   AS c   \    |
            +------------+ A +------------+ A +------------+   |
                           |                |                  |
                     +-----+----------------+-----+            |
                     |    Provisioning Manager    +----<-------+

       Figure 7 : LSP Provisioning With Active Child PCEs and Stitching

   4. Verification of Service

      The ABNO Controller will need to ascertain that the end-to-end LSP
      has been set up as requested.  In the case of a control plane
      being used to establish the LSP, the head end LSR may send a
      notification (perhaps using PCEP) to report successful setup, but
      to be sure that the LSP is up, the ABNO Controller will request
      the OAM Handler to perform Continuity Check OAM in the Data Plane
      and report back that the LSP is ready to carry traffic.

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   5. Notification of Service Fulfillment

      Finally, when the ABNO Controller is satisfied that the requested
      service is ready to carry traffic, it will notify the NMS/OSS.
      The delivery of the service may be further checked through
      auditing the network as described in

3.2 Multi-Layer Networking

   Networks are typically constructed using multiple layers.  These
   layers represent separations of administrative regions or of
   technologies, and may also represent a distinction between client
   and server networking roles.

   It is preferable to coordinate network resource control and
   utilization (i.e., consideration and control of multiple layers),
   rather than controlling and optimizing resources at each layer
   independently.  This facilitates network efficiency and network
   automation, and may be defined as inter-layer traffic engineering.

   The PCE architecture supports inter-layer traffic engineering
   [RFC5623] and, in combination with the ABNO architecture, provides a
   suite of capabilities for network resource coordination across
   multiple layers.

   The following use case demonstrates ABNO used to coordinate
   allocation of server-layer network resources to create virtual
   topology in a client-layer network in order to satisfy a request for
   end-to-end client-layer connectivity.  Consider the simple multi-
   layer network in Figure 8.

      +--+   +--+   +--+                    +--+   +--+   +--+
      |P1|---|P2|---|P3|                    |P4|---|P5|---|P6|
      +--+   +--+   +--+                    +--+   +--+   +--+
                        \                  /
                         \                /
                          +--+  +--+  +--+
                          +--+  +--+  +--+

                   Figure 8 : A Multi-Layer Network

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   There are six packet layer routers (P1 through P6) and three optical
   layer lambda switches (L1 through L3).  There is connectivity in the
   packet layer between routers P1, P2, and P3, and also between routers
   P4, P5, and P6, but there is no packet-layer connectivity between
   these two islands of routers perhaps because of a network failure or
   perhaps because all existing bandwidth between the islands has
   already been used up.  However, there is connectivity in the optical
   layer between switches L1, L2, and L3, and the optical network is
   connected out to routers P3 and P4 (they have optical line cards).
   In this example, a packet layer connection (an MPLS LSP) is desired
   between P1 and P6.

   In the ABNO architecture, the following steps are performed to
   deliver the service.

   1. Request Management

      As shown in Figure 9, the Application Service Coordinator issues a
      request for connectivity from P1 to P6 in the packet layer
      network.  That is, the Application Service Coordinator requests an
      MPLS LSP with a specific bandwidth to carry traffic for its
      application.  The ABNO Controller verifies that the Application
      Service Coordinator has sufficient rights to make the service

                  |    Application Service    |
                  |        Coordinator        |
        +------+   +------------+------------+
        |Policy+->-+     ABNO Controller     |
        |Agent |   |                         |
        +------+   +-------------------------+

       Figure 9 : Application Service Coordinator Request Management

   2. Service Path Computation in the Packet Layer

      The ABNO Controller sends a path computation request to the
      packet layer PCE to compute a suitable path for the requested LSP
      as shown in Figure 10.  The PCE uses the appropriate policy for
      the request and consults the TED for the packet layer.  It
      determines that no path is immediately available.

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                         | ABNO Controller |
            +--------+     +--+-----------+   +--------+
            | Policy +-->--+ Packet Layer +---+ Packet |
            | Agent  |     |      PCE     |   |   TED  |
            +--------+     +--------------+   +--------+

                Figure 10 : Path Computation Request

   3. Invocation of VNTM and Path Computation in the Optical Layer

      After the path computation failure in step 2, instead of notifying
      ABNO Controller of the failure, the PCE invokes the VNTM to see
      whether it can create the necessary link in the virtual network
      topology to bridge the gap.

      As shown in Figure 11, the packet layer PCE reports the
      connectivity problem to the VNTM, and the VNTM consults policy to
      determine what it is allowed to do in this case.  Assuming that
      the policy allows it, VNTM asks the optical layer PCE to see
      whether it can find a path across the optical network that could
      be provisioned to provide a virtual link for the packet layer.  In
      addressing this request, the optical layer PCE consults a TED for
      the optical layer network.

               +--------+     |      |     +--------------+
               | Policy +-->--+ VNTM +--<--+ Packet Layer |
               | Agent  |     |      |     |      PCE     |
               +--------+     +---+--+     +--------------+
                            +---------------+   +---------+
                            | Optical Layer +---+ Optical |
                            |      PCE      |   |   TED   |
                            +---------------+   +---------+

       Figure 11 : Invocation of VNTM and Optical Layer Path Computation

   4. Provisioning in the Optical Layer

      Once a path has been found across the optical layer network it
      needs to be provisioned.  The options follow those in step 3 of

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      Section 3.1.  That is, provisioning can be initiated by the
      optical layer PCE or by its user, the VNTM.  The command can be
      sent to the head end of the optical LSP (P3) so that the control
      plane (for example, GMPLS [RFC3473]) can be used to provision the
      LSP.  Alternatively, the network resources can be provisioned
      direct using any of the mechanisms described in Section

   5. Creation of Virtual Topology in the Packet Layer

      Once the LSP has been set up in the optical layer it can be made
      available in the packet layer as a virtual link.  If the GMPLS
      signaling used the mechanisms described in [RFC6107] this process
      can be automated within the control plane, otherwise it may
      require a specific instruction to the head end router of the
      optical LSP (for example, through the Interface to the Routing

      Once the virtual link is created as shown in Figure 12, it is
      advertised in the IGP for the packet layer network and the link
      will appear in the TED for the packet layer network.

              | Packet |
              |   TED  |
                    +--+                    +--+
                    +--+                    +--+
                        \                  /
                         \                /
                          +--+  +--+  +--+
                          +--+  +--+  +--+

           Figure 12 : Advertisement of a New Virtual Link

   6. Path Computation Completion and Provisioning in the Packet Layer

      Now there are sufficient resources in the packet layer network.
      The PCE for the packet layer can complete its work and the MPLS
      LSP can be provisioned as described in Section 3.1.
   7. Verification and Notification of Service Fulfillment

      As discussed in Section 3.1, the ABNO Controller will need to
      verify that the end-to-end LSP has been correctly established

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      before reporting service fulfillment to the Application
      Service Coordinator.

      Furthermore, it is highly likely that service verification will be
      necessary before the optical layer LSP can be put into service as
      a virtual link.  Thus, the VNTM will need to coordinate with the
      OAM Handler to ensure that the LSP is ready for use.

3.2.1 Data Center Interconnection across Multi-Layer Networks

   In order to support new and emerging cloud-based applications, such
   as real-time data backup, virtual machine migration, server
   clustering or load reorganization, the dynamic provisioning and
   allocation of IT resources and the interconnection of multiple,
   remote Data Centers (DC) is a growing requirement.

   These operations require traffic being delivered between data
   centers, and, typically, the connections providing such inter-DC
   connectivity are provisioned using static circuits or dedicated
   leased lines, leading to an inefficiency in terms of resource
   utilization.  Moreover, a basic requirement is that such a group of
   remote DCs can be operated logically as one.

   In such environments, the data plane technology is operator and
   provider dependent. Their customers may rent LSC, PSC or TDM
   services, and the application and usage of the ABNO architecture and
   Controller enables the required dynamic end to end network service
   provisioning, regardless of underlying service and transport layers.

   Consequently, the interconnection of DCs may involve the operation,
   control, and management of heterogeneous environments.  Each DC site
   and the metro-core network segment used to interconnect them, with
   regard to not only the underlying data plane technology, but also the
   control plane.  For example, each DC site or domain could be
   controlled locally in a centralized way (e.g., via OpenFlow [ONF]),
   whereas the metro-core transport infrastructure is controlled by
   GMPLS.  Although OpenFlow is specially adapted to single domain
   intra-DC networks (packet level control, lots of routing exceptions),
   a standardized GMPLS based architecture would enable dynamic optical
   resource allocation and restoration in multi-domain (e.g., multi-
   vendor) core networks interconnecting distributed data centers.

   The application of an ABNO architecture and related procedures would
   involve the following aspects:

   1. Request Application Service Coordinator or NMS

   As shown in Figure 13, the ABNO Controller receives a request from

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   the Application Service Coordinator or from the NMS, in order to
   create a new end-to-end connection between two end points.  The
   actual addressing of these end points is discussed in the next
   section.  The ABNO Controller asks the PCE for a path between these
   two endpoints, after considering any applicable policy as defined by
   the Policy Agent (see Figure 1).

                     |    Application Service    |
                     |     Coordinator or NMS    |
           +------+   +------------+------------+
           |Policy+->-+     ABNO Controller     |
           |Agent |   |                         |
           +------+   +-------------------------+

       Figure 13 : Application Service Coordinator Request Management

   2. Cross-Stratum Addressing Mapping

   In order to compute an end to end path, the PCE needs to have a
   unified view of the overall topology, which means that it has to
   consider and identify the actual endpoints with regard to the client
   network addresses.  The ABNO Controller and/or the PCE may need to
   translate or map addresses from different address spaces.  Depending
   on how the topological information is disseminated and gathered,
   there are two possible scenarios:

   a. The Application Layer knows Client Network Layer.  Entities
      belonging to the application layer may have an interface with the
      TED or with an ALTO server, allowing the mapping of the high level
      endpoints to network addresses.  The Application Layer may have an
      interface with TEDs or with ALTO server, it may know which are the
      client network layer addresses, where DCs are connected.  The
      mechanism used to enable this address correlation is out of the
      scope of this document but could be achieved via manual
      configuration, for example.  In this scenario, the request from
      the NMS or Application layer contains addresses in the client
      layer network.  Therefore, when the ABNO Controller requests the
      PCE to compute a path between these two end points: the PCE can
      compute the path and continue the work-flow in communication with
      the Provisioning Manager.

   b. Application Layer knows Server Network Layer.  In this case, when
      the ABNO Controller asks the PCE for a path, there is no route

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      between two end points.  Similarly to the use case in section 3.1,
      the PCE asks the VNTM to create a new connection between two
      addresses in the Server Network Layer.  As the VNTM has access to
      TED information and this mapping has to exist, the VNTM can
      determine the corresponding Client Layer addresses and continue
      with the provisioning process.

   3. Provisioning Process

   Once the path has been obtained, the provisioning manager receives a
   high level provisioning request to provision the service.  Since, in
   the considered use case, the network elements are not necessarily
   configured using the same protocol, the end to end path is split into
   segments, and the ABNO Controller coordinates or orchestrates the
   establishment by adapting and/or translating the abstract
   provisioning request to concrete segment requests, by means of a VNTM
   or PCE, which issue the corresponding commands or instructions.  The
   provisioning may involve configuring the data plane elements directly
   or delegating the establishment of the underlying connection to a
   dedicated control plane instance, responsible for that segment.

   The Provisioning Manager could use a number of mechanisms to program
   the network elements as shown in Figure 14.  It learns which
   technology is used for the actual provisioning at each segment either
   by manual configuration or discovery.

                     | ABNO Controller |
         +------+     +------+-------+
         | VNTM +--<--+     PCE      |
         +---+--+     +------+-------+
             |               |
             V               V
       |       Provisioning Manager       |
         |       |       |       |       |
         V       |       V       |       V
       OpenFlow  V    ForCes     V      PCEP
              NetConf          SNMP

       Figure 14 : Provisioning Process

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   4. Verification and Notification of Service Fulfillment

   Once the end-to-end connectivity service has been provisioned, and
   after the verification of the correct operation of the service, the
   ABNO Controller needs to notify the Application Service Coordinator
   or NMS.

3.3 Make-Before-Break

   A number of different services depend on the establishment of a new
   LSP so that traffic supported by an existing LSP can be switched
   without disruption.  This section describes those use cases, presents
   a generic model for make-before-break within the ABNO architecture,
   and shows how each use case can be supported by using elements of the
   generic model.

3.3.1 Make-Before-Break for Re-optimization

   Make-before-break is a mechanism supported in RSVP-TE signaling where
   a new LSP is set up before the LSP it replaces is torn down
   [RFC3209].  This process has several benefits in situations such as
   re-optimization of in-service LSPs.

   The process is simple, and the example shown in Figure 15 utilizes a
   stateful PCE [I-D.ietf-pce-stateful-pce] to monitor the network and
   take re-optimization actions when necessary.  In this process a
   service request is made to the ABNO Controller by a requester such as
   the OSS.  The service request indicates that the LSP should be re-
   optimized under specific conditions according to policy.  This allows
   the ABNO Controller to manage the sequence and prioritization of re-
   optimizing multiple LSPs using elements of Global Concurrent
   Optimization (GCO) as described in Section 3.4, and applying policies
   across the network so that, for instance, LSPs for delay-sensitive
   services are re-optimized first.

   The ABNO Controller commissions the PCE to compute and set up the
   initial path.

   Over time, the PCE monitors the changes in the network as reflected
   in the TED, and according to the configured policy may compute and
   set up a replacement path, using make-before-break within the

   Once the new path has been set up and the Network reports that it is
   in use correctly, PCE tears down the old path and may report the
   re-optimization event to the ABNO Controller.

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             | OSS / NMS / Application Service Coordinator |
                       |     ABNO Controller     |
               +------+     +-------+-------+     +-----+
               |Policy+-----+      PCE      +-----+ TED |
               |Agent |     +-------+-------+     +-----+
               +------+             |
            /                    Network                    \

              Figure 15 : The Make-Before-Break Process

3.3.2 Make-Before-Break for Restoration

   Make-before-break may also be used to repair a failed LSP where
   there is a desire to retain resources along some of the path, and
   where there is the potential for other LSPs to "steal" the resources
   if the failed LSP is torn down first.  Unlike the example in Section
   3.3.1, this case is service-interrupting, but that arises from the
   break in service introduced by the network failure.  Obviously, in
   the case of a point-to-multipoint LSP, the failure might only affect
   part of the tree and the disruption will only be to a subset of the
   destination leaves so that a make-before-break restoration approach
   will not cause disruption to the leaves that were not affected by
   the original failure.

   Figure 16 shows the components that interact for this use case.  A
   service request is made to the ABNO Controller by a requester such as
   the OSS.  The service request indicates that the LSP may be restored
   after failure and should attempt to reuse as much of the original
   path as possible.

   The ABNO Controller commissions the PCE to compute and set up the
   initial path.  The ABNO Controller also requests the OAM Handler to
   initiate OAM on the LSP and to monitor the results.

   At some point the network reports a fault to the OAM Handler which
   notifies the ABNO Controller.

   The ABNO Controller commissions the PCE to compute a new path, re-

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   using as much of the original path as possible, and PCE sets up the
   new LSP.

   Once the new path has been set up and the Network reports that it is
   in use correctly, the ABNO Controller instructs the PCE to tear down
   the old path.

             | OSS / NMS / Application Service Coordinator |
                       +------------+------------+   +-------+
                       |     ABNO Controller     +---+  OAM  |
                       +------------+------------+   |Handler|
                                    |                +---+---+
                            +-------+-------+            |
                            |      PCE      |            |
                            +-------+-------+            |
                                    |                    |
            /                    Network                    \

          Figure 16 : The Make-Before-Break Restoration Process

3.3.3 Make-Before-Break for Path Test and Selection

   In a more complicated use case, an LSP may be monitored for a number
   of attributes such as delay and jitter.  When the LSP falls below a
   threshold, the traffic may be moved to another LSP that offers the
   desired (or at least a better) quality of service.  To achieve this,
   it is necessary to establish the new LSP and test it, and because the
   traffic must not be interrupted, make-before-break must be used.

   Moreover, it may be the case that no new LSP can provide the desired
   attributes, and that a number of LSPs need to be tested so that the
   best can be selected.  Furthermore, even when the original LSP is set
   up, it could be desirable to test a number of LSPs before deciding
   which should be used to carry the traffic.

   Figure 17 shows the components that interact for this use case.
   Because multiple LSPs might exist at once, a distinct action is
   needed to coordinate which one carries the traffic, and this is the
   job of the I2RS Client acting under the control of the ABNO

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   The OAM Handler is responsible for initiating tests on the LSPs and
   for reporting the results back to the ABNO Controller.  The OAM
   Handler can also check end-to-end connectivity test results across a
   multi-domain network even when each domain runs a different
   technology.  For example, an end-to-end might be achieved by
   stitching together an MPLS segment, an Ethernet/VLAN segment, and an
   IP etc.

   Otherwise, the process is similar to that for re-optimization
   discussed in Section 3.3.1.

             | OSS / NMS / Application Service Coordinator |
            +------+   +------------+------------+    +-------+
            |Policy+---+     ABNO Controller     +----+  OAM  |
            |Agent |   |                         +--+ |Handler|
            +------+   +------------+------------+  | +---+---+
                                    |               |     |
                            +-------+-------+    +--+---+ |
                            |      PCE      |    | I2RS | |
                            +-------+-------+    |Client| |
                                    |            +--+---+ |
                                    |               |     |
           /                     Network                     \

      Figure 17 : The Make-Before-Break Path Test and Selection Process

   The pseudo-code that follows gives an indication of the interactions
   between ABNO components.

      OSS requests quality-assured service


      DoWhile not enough LSPs (ABNO Controller)
        Instruct PCE to compute and provision the LSP (ABNO Controller)
        Create the LSP (PCE)


      DoFor each LSP (ABNO Controller)
        Test LSP (OAM Handler)

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        Report results to ABNO Controller (OAM Handler)

      Evaluate results of all tests (ABNO Controller)
      Select preferred LSP and instruct I2RS client (ABNO Controller)
      Put traffic on preferred LSP (I2RS Client)

      DoWhile too many LSPs (ABNO Controller)
        Instruct PCE to tear down unwanted LSP (ABNO Controller)
        Tear down unwanted LSP (PCE)

      DoUntil trigger (OAM controller, ABNO Controller, Policy Agent)
        keep sending traffic (Network)
        Test LSP (OAM Handler)

      If there is already a suitable LSP (ABNO Controller)
        GoTo Label2
        GoTo Label1

3.4 Global Concurrent Optimization

   Global Concurrent Optimization (GCO) is defined in [RFC5557] and
   represents a key technology for maximizing network efficiency by
   computing a set of traffic engineered paths concurrently.  A GCO path
   computation request will simultaneously consider the entire topology
   of the network, and the complete set of new LSPs together with their
   respective constraints.  Similarly, GCO may be applied to recompute
   the paths of a set of existing LSPs.

   GCO may be requested in a number of scenarios.  These include:

   o Routing of new services where the PCE should consider other
     services or network topology.

   o A reoptimization of existing services due to fragmented network
     resources or sub-optimized placement of sequentially computed

   o Recovery of connectivity for bulk services in the event of a
     catastrophic network failure.

   A service provider may also want to compute and deploy new bulk
   services based on a predicted traffic matrix. The GCO

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   functionality and capability to perform concurrent computation
   provides a significant network optimization advantage, thus utilizing
   network resources optimally and avoiding blocking.

   The following use case shows how the ABNO architecture and components
   are used to achieve concurrent optimization across a set of services.

3.4.1 Use Case: GCO with MPLS LSPs

   When considering the GCO path computation problem, we can split the
   GCO objective functions into three optimization categories, these

   o Minimize aggregate Bandwidth Consumption (MBC).

   o Minimize the load of the Most Loaded Link (MLL).

   o Minimize Cumulative Cost of a set of paths (MCC).

   This use case assumes the GCO request will be offline and be
   initiated from an NMS/OSS, that is it may take significant time to
   compute the service, and the paths reported in the response may
   want to be verified by the user before being provisioned within
   the network.

   1. Request Management

      The NMS/OSS issues a request for new service connectivity for bulk
      services. The ABNO Controller verifies that the NMS/OSS has
      sufficient rights to make the service request and apply a GCO
      attribute with a request to Minimize aggregate Bandwidth
      Consumption (MBC) as shown in Figure 18.

                           |       NMS/OSS       |
            +--------+    +-----------+-------------+
            | Policy +-->-+     ABNO Controller     |
            | Agent  |    |                         |
            +--------+    +-------------------------+

            Figure 18 : NMS Request to ABNO Controller

      1a. Each service request has a source, destination and bandwidth

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          request. These service requests are sent to the ABNO
          Controller and categorized as a GCO. The PCE uses the
          appropriate policy for the request and consults the TED for
          the packet layer.

   2. Service Path Computation in the Packet Layer

      To compute a set of services for the GCO application, PCEP
      supports synchronization vector (SVEC) lists for synchronized
      dependent path computations as defined in [RFC5440] and described
      in [RFC6007].

      2a. The ABNO Controller sends the bulk service request to the
          GCO-capable packet layer PCE using PCEP messaging.  The PCE
          uses the appropriate policy for the request and consults the
          TED for the packet layer as shown in Figure 19.

                         | ABNO Controller |
            +--------+     +--+-----------+   +--------+
            |        |     |              |   |        |
            | Policy +-->--+ GCO-capable  +---+ Packet |
            | Agent  |     | Packet Layer |   |  TED   |
            |        |     |     PCE      |   |        |
            +--------+     +--------------+   +--------+

         Figure 19 : Path Computation Request from GCO-capable PCE

      2b. Upon receipt of the bulk (GCO) service requests, the PCE
          applies the MBC objective function and computes the services

      2c. Once the requested GCO service path computation completes, the
          PCE sends the resulting paths back to the ABNO Controller as a
          PCEP response as shown in Figure 20. The response includes a
          fully computed explicit path for each service (TE LSP).

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                     |       NMS/OSS       |
                     |    ABNO Controller  |
                     |                     |

         Figure 20 : ABNO Sends Solution to the NMS/OSS

   3. The concurrently computed solution received from the PCE is sent
      back to the NMS/OSS by the ABNO Controller. The NMS/OSS user can
      then check the candidate paths and either provision the new
      services, or save the solution for deployment in the future.

3.5 Adaptive Network Management (ANM)

   The ABNO architecture provides the capability for reactive network
   control of resources based on classification, profiling and
   prediction based on current demands and resource utilization.
   Server-layer transport network resources, such as Optical Transport
   Network (OTN) time-slicing [G.709], or the fine granularity grid of
   wavelengths with variable spectral bandwidth (flexi-grid) [G.694.1],
   can be manipulated to meet current and projected demands in a model
   called Elastic Optical Networks (EON).

   EON provides spectrum-efficient and scalable transport by
   introducing flexible granular grooming in the optical frequency
   domain. This is achieved using arbitrary contiguous
   concatenation of optical spectrum that allows creation of custom-
   sized bandwidth.  This bandwidth is defined in slots of 12,5GHz.

   Adaptive Network Management (ANM) with EON allows appropriately-
   sized optical bandwidth to be allocated to an end-to-end optical
   path.  In flexi-grid, the allocation is performed according to the
   traffic volume or following user requests, and can be achieved in a
   highly spectrum-efficient and scalable manner.  Similarly, OTN
   provides an adaptive and elastic provisioning of bandwidth on top of
   wavelength switched optical networks (WSON).

   To efficiently use optical resources, a system is required which can
   monitor network resources, and decide the optimal network
   configuration based on the status, bandwidth availability and user
   service. We call this ANM.

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3.5.1. ANM Trigger

   There are different reasons to trigger an adaptive network
   management process, these include:

   o  Measurement: traffic measurements can be used in order to cause
      spectrum allocations that fit the traffic needs as efficiently as
      possible.  This function may be influenced by measuring the IP
      router traffic flows, by examining traffic engineering or link
      state databases, by usage thresholds for critical links in the
      network, or by requests from external entities.  Nowadays, network
      operators have active monitoring probes in the network, which
      store their results in the OSS.  The OSS or OAM Handler components
      activate this measurement-based trigger, so the ABNO Controller
      would not be directly involved in this case.

   o  Human: operators may request ABNO to run an adaptive network
      planning process via a NMS.

   o  Periodic: adaptive network planning process can be run
      periodically to find an optimum configuration.

   An ABNO Controller would receive a request from OSS or NMS to run an
   adaptive network manager process.

3.5.2. Processing request and GCO computation

   Based on the human or periodic trigger requests described in the
   previous Section, the OSS or NMS will send a request to the ABNO
   Controller to perform EON-based GCO.  The ABNO Controller will
   select a set of services to be reoptimized and choose an objective
   function that will deliver the best use of network resources.  In
   making these choices, the ABNO Controller is guided by network-wide
   policy on the use of resources, the definition of optimization, and
   the level of perturbation to existing services that is tolerable.

   Much as in Section 3.5, this request for GCO is passed to the PCE.
   The PCE can then consider the end-to-end paths and every channel's
   optimal spectrum assignment in order to satisfy traffic demands and
   optimize the optical spectrum consumption within the network.

   The PCE will operate on the TED, but is likely to also be stateful so
   that it knows which LSPs correspond to which waveband allocations on
   which links in the network.  Once PCE arrives at an answer, it
   returns a set of potential paths to the ABNO Controller which passes
   them on to the NMS or OSS to supervise/select the subsequent path
   set-up/modification process.

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   This exchange is shown in Figure 21.  Note that the figure does not
   show the interactions used by the OSS/NMS for establishing or
   modifying LSPs in the network.

                     |        OSS or NMS         |
                                 |   ^
                                 V   |
           +------+   +----------+---+----------+
           |Policy+->-+     ABNO Controller     |
           |Agent |   |                         |
           +------+   +----------+---+----------+
                                 |   ^
                                 V   |
                           +      PCE     |

        Figure 21 : Adaptive Network Management with human intervention

3.5.3.  Automated Provisioning Process

   Although most of network operations are supervised by the operator,
   there are some actions, which may not require supervision, like a
   simple modification of a modulation format in a Bit-rate Variable
   Transponder (BVT) (to increase the optical spectrum efficiency or
   reduce energy consumption).  In this processes, where human
   intervention is not required, the PCE sends the Provisioning Manager
   new configuration to configure the network elements as shown in
   Figure 22.

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                     |       OSS or NMS       |
           +------+   +----------+------------+
           |Policy+->-+     ABNO Controller   |
           |Agent |   |                       |
           +------+   +----------+------------+
                          +     PCE     |
                 |       Provisioning Manager       |

      Figure 22 : Adaptive Network Management without human intervention

3.6 Pseudowire Operations and Management

   Pseudowires in an MPLS network [RFC3985] operate as a form of layered
   network over the connectivity provided by the MPLS network.  The
   pseudowires are carried by LSPs operating as transport tunnels, and
   planning is necessary to determine how those tunnels are placed in
   the network and which tunnels are used by any pseudowire.

   This section considers four use cases: multi-segment pseudowires,
   path-diverse pseudowires, path-diverse multi-segment pseudowires, and
   pseudowire segment protection.  Section 3.6.5 describes the
   applicability of the ABNO architecture to these four use cases.

3.6.1 Multi-Segment Pseudowires

   [RFC5254] described the architecture for multi-segment pseudowires.
   An end-to-end service, as shown in Figure 23, can consist of a
   series of stitched segments shown on the figure as AC, PW1, PW2, PW3,
   and AC.  Each pseudowire segment is stitched at a 'stitching PE' (S-
   PE): for example, PW1 is stitched to PW2 at S-PE1.  Each access
   circuit (AC) is stitched to a pseudowire segment at a 'terminating
   PE' (T-PE): for example, PW1 is stitched to the AC at T-PE1.

   Each pseudowire segment is carried across the MPLS network in an LSP
   operating as a transport tunnel: for example, PW1 is carried in LSP1.
   The LSPs between provider edge nodes (PEs) may traverse different

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   MPLS networks with the PEs as border nodes, or the PEs may lie within
   the network such that the LSPs each only span part of the network.

             -----         -----         -----         -----
    ---     |T-PE1|  LSP1 |S-PE1|  LSP2 |S-PE3|  LSP3 |T-PE2|    +---+
   |   | AC |     |=======|     |=======|     |=======|     | AC |   |
   |   |    |     |=======|     |=======|     |=======|     |    |   |
    ---     |     |       |     |       |     |       |     |    +---+
             -----         -----         -----         -----

                Figure 23 : Multi-Segment Pseudowire

   While the topology shown in Figure 23 is easy to navigate, the
   reality of a deployed network can be considerably more complex.  The
   topology in Figure 24 shows a small mesh of PEs.  The links between
   the PEs are not physical links but represent the potential of MPLS
   LSPs between the PEs.

   When establishing the end-to-end service between customer edge nodes
   (CEs) CE1 and CE2, some choice must be made about which PEs to use.
   In other words, a path computation must be made to determine the
   pseudowire segment 'hops', and then the necessary LSP tunnels must be
   established to carry the pseudowire segments that will be stitched

   Of course, each LSP may itself require a path computation decision to
   route it through the MPLS network between PEs.

   The choice of path for the multi-segment pseudowire will depend on
   such issues as:
   - MPLS connectivity
   - MPLS bandwidth availability
   - pseudowire stitching capability and capacity at PEs
   - policy and confidentiality considerations for use of PEs.

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

             Figure 24 : Multi-Segment Pseudowire Network Topology

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3.6.2 Path-Diverse Pseudowires

   The connectivity service provided by a pseudowire may need to be
   resilient to failure.  In many cases, this function is provided by
   provisioning a pair of pseudowires carried by path-diverse LSPs
   across the network as shown in Figure 25 (the terminology is
   inherited directly from [RFC3985]).  Clearly, in this case, the
   challenge is to keep the two LSPs (LSP1 and LSP2) disjoint within the
   MPLS network.  This problem is not different from the normal MPLS
   path-diversity problem.

                 -------                         -------
                |  PE1  |          LSP1         |  PE2  |
           AC   |       |=======================|       |   AC
    --- -  /    |       |=======================|       |    \  -----
   |     |/     |       |                       |       |     \|     |
   | CE1 +      |       |      MPLS Network     |       |      + CE2 |
   |     |\     |       |                       |       |     /|     |
    --- -  \    |       |=======================|       |    /  -----
           AC   |       |=======================|       |   AC
                |       |          LSP2         |       |
                 -------                         -------

                 Figure 25 : Path-Diverse Pseudowires

                 -------                         -------
                |  PE1  |          LSP1         |  PE2  |
            AC  |       |=======================|       |  AC
            /   |       |=======================|       |   \
    -----  /    |       |                       |       |    \  -----
   |     |/      -------                         -------      \|     |
   | CE1 +                     MPLS Network                    + CE2 |
   |     |\      -------                         -------      /|     |
    -----  \    |  PE3  |                       |  PE4  |    /  -----
            \   |       |=======================|       |   /
            AC  |       |=======================|       |  AC
                |       |          LSP2         |       |
                 -------                         -------

            Figure 26 : Path-Diverse Pseudowires With Disjoint PEs

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   The path-diverse pseudowire is developed in Figure 26 by the "dual-
   homing" of each CE through more than one PE.  The requirement for LSP
   path diversity is exactly the same, but it is complicated by the LSPs
   having distinct end points.  In this case, the head-end router (e.g.,
   PE1) cannot be relied upon to maintain the path diversity through the
   signaling protocol because it is aware of the path of the only one of
   the LSPs.  Thus some form of coordinated path computation approach is

3.6.3 Path-Diverse Multi-Segment Pseudowires

   Figure 27 shows how the services in the previous two sections may be
   combined to offer end-to-end diverse paths in a multi-segment
   environment.  To offer end-to-end resilience to failure, two entirely
   diverse, end-to-end multi-segment pseudowires may be needed.

                                  -----                -----
                                 /-----\               ----- \
             -----         -----/       \-----         -----  \ ---
      ---  / -----\        -----\        -----        /-----    ---
     |CE1|<        -------   |   -------   |         /
      ---  \ -----        \-----        \-----      /
             -----         -----         -----

      Figure 27 : Path-Diverse Multi-Segment Pseudowire Network Topology

   Just as in any diverse-path computation, the selection of the first
   path needs to be made with awareness of the fact that a second,
   fully-diverse path is also needed.  If a sequential computation was
   applied to the topology in Figure 27, the first path CE1,T-PE1,S-PE1,
   S-PE3,T-PE2,CE2 would make it impossible to find a second path that
   was fully diverse from the first.

   But the problem is complicated by the multi-layer nature of the
   network.  It is not enough that the PEs are chosen to diverse because
   the LSP tunnels between them might share links within the MPLS
   network.  Thus, a multi-layer planning solution is needed to achieve
   the desired level of service.

3.6.4 Pseudowire Segment Protection

   An alternative to the end-to-end pseudowire protection service
   described in Section 3.6.3 can be achieved by protecting individual
   pseudowire segments or PEs.  For example, in Figure 27, the
   pseudowire between S-PE1 and S-PE5 may be protected by a pair of

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   stitched segments running between S-PE1 and S-PE5, and between S-PE5
   and S-PE3.  This is shown in detail in Figure 28.

             -------              -------              -------
            | S-PE1 |    LSP1    | S-PE5 |    LSP3    | S-PE3 |
            |       |============|       |============|       |
            |   .........PW1..................PW3..........   | Outgoing
   Incoming |  :    |============|       |============|    :  | segment
   segment  |  :    |             -------             |    :..........
    ...........:    |                                 |    :  |
            |  :    |                                 |    :  |
            |  :    |=================================|    :  |
            |   .........PW2...............................   |
            |       |=================================|       |
            |       |    LSP2                         |       |
             -------                                   -------

   Figure 28 : Fragment of a Segment-Protected Multi-Segment Pseudowire

   The determination of pseudowire protection segments requires
   coordination and planning, and just as in Section 3.6.5, this
   planning must be cognizant of the paths taken by LSPs through the
   underlying MPLS networks.

3.6.5 Applicability of ABNO to Pseudowires

   The ABNO architecture lends itself well to the planning and control
   pseudowires in the use cases described above.  The user or
   application needs a single point at which it requests services: the
   ABNO Controller.  The ABNO Controller can ask a PCE to draw on the
   topology of pseudowire stitching-capable PEs as well as additional
   information regarding PE capabilities, such as load on PEs and
   administrative policies, and the PCE can use a series of TEDs or
   other PCEs for the underlying MPLS networks to determine the paths of
   the LSP tunnels.  Then a number of different provisioning systems can
   be used to instantiate the LSPs and provision the pseudowires under
   the control of the Provisioning Manager.  The ABNO Controller will
   use the I2RS Client to instruct the network devices about what
   traffic should be placed on which pseudowires, and in conjunction
   with the OAM Handler can ensure that failure events are handled
   correctly, that service quality levels are appropriate, and that
   service protection levels are maintained.

   In many respects, the pseudowire network forms an overlay network
   (with its own TED and provisioning mechanisms) carried by underlying
   packet networks.  Further client networks (the pseudowire payloads)
   may be carried by the pseduowire network.  Thus, the problem space

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   being addressed by ABNO in this case is a classic multi-layer

3.7.  Cross-Stratum Optimization (CSO)

   Considering the term "stratum" to broadly differentiate the layers of
   most concern to the application and to the network in general, the
   need for Cross Stratum optimization (CSO) arises when the application
   stratum and network stratum need to be coordinated to achieve
   operational efficiency as well as resource optimization in both
   application and network strata.

   Data center based applications can provide a wide variety of services
   such as video gaming, cloud computing, and grid applications.  High-
   bandwidth video applications are also emerging, such as remote
   medical surgery, live concerts, and sporting events.

   This use-case for the ABNO architecture is mainly concerned with data
   center applications that make substantial bandwidth demands either in
   aggregate or individually.  In addition these applications may need
   specific bounds on QoS related parameters such as latency and jitter.

3.7.1.  Data Center Network Operation

   Data centers come in a wide variety of sizes and configurations, but
   all contain compute servers, storage, and application control.  Data
   centers offer application services to end-users such as video gaming,
   cloud computing and others.  Since the data centers used to provide
   application services may be distributed around a network, the
   decisions about the control and management of application services,
   such as where to instantiate another service instance or to which
   data center a new client is assigned, can have a significant impact
   on the state of the network.  Conversely the capabilities and state
   of the network can have a major impact on application performance.

   These decisions are typically made by applications with very little
   or no information concerning the underlying network.  Hence, such
   decisions may be sub-optimal from the application's point of view or
   considering network resource utilization and quality of service.

   Cross-stratum optimization is the process of optimizing both the
   application experience and the network utilization by coordinating
   decisions in the application stratum and the network stratum.
   Application resources can be roughly categorized into computing
   resources, (i.e., servers of various types and granularities such as
   VMs, memory, and storage) and content (e.g., video, audio, databases,
   and large data sets).  By network stratum we mean the IP layer and
   below (e.g., MPLS, SDH, OTN, WDM).  The network stratum has resources

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   that include routers, switches, and links.  We are particularly
   interested in further unleashing the potential presented by MPLS and
   GMPLS control planes at the lower network layers in response to the
   high aggregate or individual demands from the application layer.

   This use-case demonstrates that the ABNO architecture can allow
   cross-stratum application/network optimization for the data center
   use case.  Other forms of cross-stratum optimization (for example,
   for peer-to-peer applications) are out of scope.  Virtual Machine Migration

   A key enabler for data center cost savings, consolidation,
   flexibility and application scalability has been the technology of
   compute virtualization provided through Virtual Machines (VMs).  To
   the software application a VM looks like a dedicated processor with
   dedicated memory and a dedicated operating system.

   VMs offer not only a unit of compute power but also provide an
   "application environment" that can be replicated, backed up, and
   moved.  Different VM configurations may be offered that are optimized
   for different types of processing (e.g., memory intensive, throughput

   VMs may be moved between compute resources in a data center and could
   be moved between data centers.  VM migration serves to balance load
   across data center resources and has several modes:
     (i) scheduled vs. dynamic;
     (ii) bulk vs. sequential;
     (iii) point-to-point vs. point-to-multi-point

   While VM migration may solve problems of load or planned maintenance
   within a data center it can also be effective to reduce network load
   around the data center.  But the act of migrating VMs especially
   between data centers can impact the network and other services that
   are offered.

   For certain applications such as disaster recovery, bulk migration is
   required on the fly, which may necessitate concurrent computation and
   path setup dynamically.

   Thus, application stratum operations must also take account of the
   situation in the network stratum even as the application stratum
   actions may be driven by the status of the network stratum. Load Balancing

   Application servers may be instantiated in many data centers located

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   in different parts of the network.  When an end-user makes a request
   an application request, a decision has to be made about which data
   center should host the processing and storage required to meet the
   request.  One of the major drivers for operating multiple data
   centers (rather than one very large data center) is so that the
   application will run on a machine that is closer to the end-users and
   thus improve the user experience by reducing network latency.
   However, if the network is congested or the data center is overloaded
   this strategy can backfire.

   Thus, among the key factors to be considered in choosing the server
   on which to instantiate a VM for an application include:

     - The utilization of the servers in the data center

     - The network loading conditions within a data center

     - The network loading conditions between data centers

     - The network conditions between the end-user and data center

   Again, the choices made in the application stratum need to consider
   the situation in the network stratum.

3.7.2.  Application of the ABNO Architecture

   This section shows how the ABNO architecture is applicable to the
   cross-stratum data center issues described in Section 3.7.1.

   Figure 29 shows a diagram of an example data center based
   application.  A carrier network provides access for an and-user
   through PE4. Three data centers (DC1, DC2, and DC3) are accessed
   through different parts of the network via PE1, PE2, and PE3.

   The Application Service Coordinator receives information from the
   end-user about the services it wants, and converts this to service
   requests that it passes to the the ABNO Controller.   The end-user
   may already know which data center it wishes to use, the Application
   Service Controller may be able to make this determination, or the
   task of selecting the data center may be left to the ABNO Controller.

   The ABNO controller examines the network resources using information
   gathered from the other ABNO components and uses those components to
   configure the network to support the end-user's needs.

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   +----------+    +---------------------------------+
   | End-user |--->| Application Service Coordinator |
   +----------+    +---------------------------------+
         |                          |
         |                          v
         |                 +-----------------+
         |                 | ABNO Controller |
         |                 +-----------------+
         |                          |
         |                          v
         |               +---------------------+       +--------------+
         |               |Other ABNO Components|       | o o o   DC 1 |
         |               +---------------------+       |  \|/         |
         |                          |            ------|---O          |
         |                          v           |      |              |
         |            --------------------------|--    +--------------+
         |           / Carrier Network      PE1 |  \
         |          /      .....................O   \   +--------------+
         |         |      .                          |  | o o o   DC 2 |
         |         | PE4 .                      PE2  |  |  \|/         |
          ---------|----O........................O---|--|---O          |
                   |     .                           |  |              |
                   |      .                    PE3   |  +--------------+
                    \      .....................O   /
                     \                          |  /   +--------------+
                      --------------------------|--    | o o o   DC 3 |
                                                |      |  \|/         |
                                                 ------|---O          |
                                                       |              |

           Figure 29 : The ABNO Architecture in the Context of
               Cross-Stratum Optimization for Data Centers Deployed Applications, Services, and Products

   The ABNO controller will need to utilize a number of components to
   realize the CSO functions described in Section 3.7.1.

   The ALTO server provides information about topological proximity and
   appropriate geographical locations servers with respect to the
   underlying networks.  This information can be used to optimize the
   selection of peer location which will help reduce the path of IP
   traffic or can contain it within specific service providers'
   networks.  ALTO in conjunction with the ABNO Controller and the
   Application Service Coordinator can address general problems such as
   the selection of application servers based on resource availability
   and usage of the underlying networks.

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   The ABNO Controller can also formulate a view of current network load
   from the TED and from the OAM Handler (for example, by running
   diagnostic tools that measure latency, jitter, and packet loss).
   This view obviously influences not just how paths from end-user to
   data center are provisioned, but can also guide the selection of
   which data center should provide the service and possibly even the
   points of attachment to be used by the end-user and to reach the
   chosen data center.  A view of how PCE can fit in with CSO is
   provided in [I-D.dhody-pce-cso-enabled-path-computation] on which the
   content of Figure 29 is based.

   As already discussed, the combination of the ABNO Controller and the
   Application Service Coordinator will need to be able to select (and
   possibly migrate) the location of the VM that provides the service
   for the end-user.  Since a common technique used to direct the end-
   user to the correct VM/server is to employ DNS redirection, an
   important capability of the ABNO controller will be to be able to
   program the DNS servers accordingly.

   Furthermore, as already noted in other sections of this document, the
   ABNO Controller can coordinate the placement of traffic within the
   network to achieve load-balancing and to provide resilience to
   failures.  These features can be used in conjunction with the
   functions discussed above, to ensure that the placement of new VMs,
   the traffic that they generate, and the load caused by VM migration
   can be carried by the network and do not disrupt existing services.

3.8 Other Potential Use Cases

   This section serves as a place-holder for other potential use cases
   that might get documented in a future revision of this document.

3.8.1 Grooming and Regrooming

   This use case could cover the following scenarios:

   - Nested LSPs
   - Packet Classification (IP flows into LSPs at edge routers)
   - Bucket Stuffing
   - IP Flows into ECMP Hash Bucket

3.8.2 Bandwidth Scheduling

   Bandwidth Scheduling consist of configuring LSPs based on a given
   time schedule. This can be used to support maintenance or
   operational schedules or to adjust network capacity based on
   traffic pattern detection.

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   The ABNO framework provides the components to enable bandwidth
   scheduling solutions.

3.8.3 ALTO Server

   The ABNO architecture allows use cases with joint network and
   application-layer optimization.  In such a use case, an application
   is presented with an abstract network topology containing only
   information relevant to the application.  The application computes
   its application-layer routing according to its application objective.
   The application may interact with the ABNO Controller to set up
   explicit LSPs to support its application-layer routing.

   The following steps are performed to illustrate such a use case.

   1. Application Request of Application-layer Topology

      Consider the network shown in Figure 30.  The network consists of
      5 nodes and 6 links.

            +----+       L0 Wt=10 BW=50       +----+
            | N0 |............................| N3 |
            +----+                            +----+
              |   \    L4                        |
              |    \   Wt=7                      |
              |     \  BW=40                     |
              |      \                           |
        L1    |       +----+                     |
        Wt=10 |       | N4 |               L2    |
        BW=45 |       +----+               Wt=12 |
              |      /                     BW=30 |
              |     /  L5                        |
              |    /   Wt=10                     |
              |   /    BW=45                     |
            +----+                            +----+
            | N1 |............................| N2 |
            +----+       L3 Wt=15 BW=35       +----+

               Figure 30 : Raw Network Topology

     The application, which has endpoints hosted at N0, N1, and N2,
     requests network topology so that it can compute its application
     layer routing, for example, to maximize the throughput of content
     replication among endpoints at the three sites.

     The request arrives at the ABNO Controller, which forwards the
     request to the ALTO Server component.  The ALTO Server consults the

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     Policy Agent, the TED, and the PCE to return an abstract,
     application-layer topology.  Figure 31 shows a possible reduced,
     topology for the application.  For example, the policy may specify
     that the bandwidth exposed to an application may not exceed 40.
     The network has precomputed that the route from N0 to N2 should use
     the path of N0->N3-> N2, according to goals such as GCO (see
     Section 3.4).

                | N0 |............
                +----+            \
                  |   \            \
                  |    \            \
                  |     \            \
                  |      |            \   AL0M2
            L1    |      | AL4M5       \  Wt=22
            Wt=10 |      | Wt=17        \ BW=30
            BW=40 |      | BW=40         \
                  |      |                \
                  |     /                  \
                  |    /                    \
                  |   /                      \
                +----+                        +----+
                | N1 |........................| N2 |
                +----+   L3 Wt=15 BW=35       +----+

        Figure 31 : Reduced Graph for a Particular Application

      The ALTO Server uses the topology and existing routing to compute
      an abstract network map consisting of 3 PIDs.  The pair-wise
      bandwidth as well as shared bottlenecks will be computed from the
      internal network topology and reflected in cost maps.

   2. Application Computes Application Overlay

      Using the abstract topology, the application computes an
      application-layer routing.  For concreteness, the application may
      compute a spanning tree to maximize the total bandwidth from N0 to
      N2.  Figure 32 shows an example application-layer routing using a
      route of N0->N1-> N2 for 35 Mbps and N0->N2 for 30 Mbps, for a
      total of 65 Mbps.

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             | N0 |----------------------------------+
             +----+        AL0M2 BW=30               |
               |                                     |
               |                                     |
               |                                     |
               |                                     |
               | L1                                  |
               |                                     |
               | BW=35                               |
               |                                     |
               |                                     |
               |                                     |
               V                                     V
             +----+        L3 BW=35                +----+
             | N1 |...............................>| N2 |
             +----+                                +----+

             Figure 32 : Application-layer Spanning Tree

   3. ABNO Controller Setup Application Path

      The application may submit its application routes to the ABNO
      Controller to set up explicit LSPs to support its operation.  The
      ABNO Controller consults the ALTO maps to map the application
      layer routing back to internal network topology and then instructs
      the provisioning manager to set up the paths.  The ABNO Controller
      may re-trigger GCO to re-optimize network traffic engineering.

4. Survivability and Redundancy within the ABNO Architecture

   The ABNO architecture described in this document is presented in
   terms of functional units.  Each unit could be implemented separately
   or bundled with other units into single programs or products.
   Furthermore, each implemented unit or bundle could be deployed on a
   separate device (for example, a network server), on a separate
   virtual machine (for example, in data center), or groups of programs
   could be deployed on the same processor.  From the point of view of
   the architecutral model, these implementation and deployment choices
   are entirely unimportant.

   Similarly, the realisation of a functional component of the ABNO
   architecture could be supported by more than one instance of an
   implementation, or by different intances of different implementations
   that provide the same or similar function.  For example, the PCE
   component might have multiple instantiations for sharing the
   processing load of a large number of computation requests, and
   different instances might have different algorithmic capabilities so

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   that one instance might serve parallel computation requests for
   disjoint paths, while another instance might have the capability to
   compute optimal point-to-multipoint paths.

   This ability to have multiple instances of ABNO components also
   enables resiliency within the model since, in the event of the
   failure of one instance of one component (because of software
   failure, hardware failure, or connectivity problems) other instances
   can take over.  In some circumstances state synchronization between
   instances of components may be needed in order to facilitate seamless

   How these features are achieved in an ABNO implementation or
   deployment is outside the scope of this document.  It is worth
   noting that the VNFpool effort in the IETF is examining how instances
   of network functions may be "pooled" for resilence and potentially
   for load-balancing.

5. Security Consideration

   The ABNO architecture describes a network system and security must
   play an important part.

   The first consideration is that the external protocols (those shown
   as entering or leaving the big box in Figure 1) must be appropriately
   secured.  This security will include authentication and authorization
   to control access to the different functions that the ABNO system can
   perform, to enable different policies based on identity, and to
   regulate the control of the network devices.

   Secondly, the internal protocols that are used between ABNO
   components must also have appropriate security particularly when the
   components are implemented on separate network nodes.

   Considering that the ABNO system contains a lot of data about the
   network, the services carried by the network, and the services
   delivered to customers, access to information held in the system must
   be carefully regulated.  Since such access will be largely through
   the external protocols, the policy-based controls enabled by
   authentication will be powerful.  But it should also be noted that
   any data sent from the databases in the ABNO system can reveal
   details of the network and should, therefore, be considered as a
   candidate for encryption.  Furthermore, since ABNO components can
   access the information stored in the database, care is required to
   ensure that all such components are genuine, and to consider
   encrypting data that flows between components when they are
   implemented at remote nodes.

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   The conclusion is that all protocols used to realize the ABNO
   architecture should have rich security features.

6. Manageability Considerations

   The whole of the ABNO architecture is essentially about managing the
   network.  In this respect there is very little extra to say.  ABNO
   provides a mechanisms to gather and collate information about the
   network, reporting it to management applications, storing it for
   future inspection, and triggering actions according to configured

   The ABNO system will, itself, need monitoring and management.  This
   can be seen as falling into several categories:
   - Management of external protocols
   - Management of internal protocols
   - Management and monitoring of ABNO components
   - Configuration of policy to be applied across the ABNO system.

7. IANA Considerations

   This document makes no requests for IANA action.

8. Acknowledgements

   Thanks for discussions and review are due to Ken Gray, Jan Medved,
   Nitin Bahadur, Diego Caviglia, Joel Halpern, Brian Field, Ori
   Gerstel, Daniele Ceccarelli, Diego Caviglia Cyril Margaria, Jonathan
   Hardwick, Nico Wauters, Tom Taylor, Qin Wu, and Luis Contreras.
   Thanks to George Swallow for suggesting the existence of the SRLG

   This work received funding from the European Union's Seventh
   Framework Programme for research, technological development and
   demonstration through the PACE project under grant agreement
   number 619712 and through the IDEALIST project under grant agreement
   number 317999.

9. References

9.1. Informative References

   [Flood]   Project Floodlight, "Floodlight REST API",

   [G.694.2] ITU-T Recommendation G.694.2, "Spectral grids for WDM
             applications: CWDM wavelength grid", December 2003.

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   [G.709]   ITU-T, "Interface for the Optical Transport Network
             (OTN)", G.709 Recommendation, October 2009.

            "Dhody, D., Lee, Y., Contreras, LM., Gonzalez de Dios, O,
            and N. Ciulli, "Cross Stratum Optimization enabled Path
            Computation", draft-dhody-pce-cso-enabled-path-computation,
            work in progress.

             Alimi, R., Penno, R., and Yang, Y., "ALTO Protocol",
             draft-ietf-alto-protocol, work in progress.

             Atlas, A., Halpern, J., Hares, S., Ward, D., and T. Nadeau,
             "An Architecture for the Interface to the Routing System",
             draft-ietf-i2rs-architecture, work in progress.

             Atlas, A., Nadeau, T., and D. Ward, "Interface to the
             Routing System Problem Statement",
             draft-ietf-i2rs-problem-statement, work in progress.

             Gredler, H., Medved, J., Previdi, S., Farrel, A., and
             Ray, S., "North-Bound Distribution of Link-State and TE
             Information using BGP", draft-ietf-idr-ls-distribution,
             work in progress.

             Lhotka, L., "A YANG Data Model for Routing Management",
             draft-ietf-netmod-routing-cfg, work in progress.

             Crabbe, E., Minei, I., Sivabalan, S., and Varga, R., "PCEP
             Extensions for PCE-initiated LSP Setup in a Stateful PCE
             Model", draft-ietf-pce-pce-initiated-lsp, work in

             Crabbe, E., Medved, J., Minei, I., and R. Varga, "PCEP
             Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
             work in progress.

   [ONF]     Open Networking Foundation, "OpenFlow Switch Specification
             Version 1.4.0 (Wire Protocol 0x05)", October 2013.

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   [RFC2748] Durham, D., Ed., Boyle, J., Cohen, R., Herzog, S., Rajan,
             R., and A. Sastry, "The COPS (Common Open Policy Service)
             Protocol", RFC 2748, January 2000.

   [RFC2753] Yavatkar, R., Pendarakis, D. and R. Guerin, "A
             Framework for Policy-based Admission Control", RFC2753,
             January 2000.

   [RFC3209] D. Awduche et al., "RSVP-TE: Extensions to RSVP for LSP
             Tunnels", RFC 3209, December 2001.

   [RFC3292] Doria, A., Hellstrand, F., Sundell, K., and Worster, T.,
             "General Switch Management Protocol (GSMP) V3", RFC 3292,
             June 2002.

   [RFC3412] Case, J., Harrington, D., Preshun, R., and Wijnen, B.,
             "Message Processing and Dispatching for the Simple Network
             Management Protocol (SNMP)", RFC 3412, December 2002.

   [RFC3473] L. Berger et al., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Resource ReserVation Protocol-
             Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
             January 2003.

   [RFC3630] Katz, D., Kmpella, K., and Yeung, D., "Traffic Engineering
             (TE) Extensions to OSPF Version 2", RFC 3630, September

   [RFC3746] Yang, L., Dantu, R., Anderson, T., and Gopal, R.,
             "Forwarding and Control Element Separation (ForCES)
             Framework", RFC 3746, April 2004.

   [RFC3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
             Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.

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

   [RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP. and Farrel, A.,
             "Label Switched Path Stitching with Generalized
             Multiprotocol Label Switching Traffic Engineering (GMPLS
             TE)", RFC 5150, February 2008.

   [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
             M., and Brungard, D., "Requirements for GMPLS-Based Multi-
             Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July

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   [RFC5254] Bitar, N., Bocci, M. and L. Martini, "Requirements for
             Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)",
             RFC 5254, October 2008

   [RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications",
             RFC 5277, July 2008.

   [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
             Engineering", RFC 5305, October 2008.

   [RFC5394] Bryskin, I., Papadimitriou, D., Berger, L. and Ash, J.,
             "Policy-Enabled Path Computation Framework", RFC 5394,
             December 2008.

   [RFC5424] R. Gerhards, "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5440] Vasseur, JP. and Le Roux, JL., "Path Computation Element
             (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009.

   [RFC5520] Bradford, R., Vasseur, JP., and Farrel, A., "Preserving
             Topology Confidentiality in Inter-Domain Path Computation
             Using a Path-Key-Based Mechanism", RC 5520, April 2009.

   [RFC5557] Lee, Y., Le Roux, JL., King, D., and Oki, E., "Path
             Computation Element Communication Protocol (PCEP)
             Requirements and Protocol Extensions in Support of Global
             Concurrent Optimization", RFC 5557, July 2009.

   [RFC5623] Oki, E., Takeda, T., Le Roux, JL., and Farrel, A.,
             "Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic
             Engineering", RFC 5623, September 2009.

   [RFC5693] Seedorf, J., and Burger, E., "Application-Layer Traffic
             Optimization (ALTO) Problem Statement", RFC 5693, October

   [RFC5810] A. Doria, et al., "Forwarding and Control Element
             Separation (ForCES) Protocol Specification", RFC 5810,
             March 2010.

   [RFC6007] I. Nishioka. and D. King., "Use of the Synchronization
             VECtor (SVEC) List for Synchronized Dependent Path
             Computations", RFC 6007, September 2010.

   [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
             Network Configuration Protocol (NETCONF)", RFC 6020,
             October 2010.

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   [RFC6107] Shiomoto, K. and A. Farrel, "Procedures for Dynamically
             Signaled Hierarchical Label Switched Paths", RFC 6107,
             February 2011.

   [RFC6120] P. Saint-Andre, "Extensible Messaging and Presence Protocol
             (XMPP): Core", RFC 6120, March 2011.

   [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and Bierman,
             A., "Network Configuration Protocol (NETCONF)", RFC 6241,
             June 2011.

   [RFC6707] Niven-Jenkins, B., Le Faucheur, F., and Bitar, N., "Content
             Distribution Network Interconnection (CDNI) Problem
             Statement", RFC 6707, September 2012.

   [RFC6805] King, D. and Farrel, A., "The Application of the Path
             Computation Element Architecture to the Determination of a
             Sequence of Domains in MPLS and GMPLS", RFC 6805, November

   [RFC7011] Claise, B., Trammell, B., and Paitken, "Specification of
             the IP Flow Information Export (IPFIX) Protocol for the
             Exchange of IP Traffic Flow Information", STD 77, RFC 7011,
             Spetember 2013.

   [RFC7297] Boucadair, M., Jacquenet, c., and N. Wang, "IP/MPLS
             Connectivity Provisioning Profile (CPP)", RFC 7297, July

   [TL1]     Telcorida, "Operations Application Messages - Language For
             Operations Application", GR-831, November 1996.

             TeleManagement Forum "Multi-Technology Operations Systems
             Interface (MTOSI)",

10. Contributors' Addresses

   Quintin Zhao
   Huawei Technologies
   125 Nagog Technology Park
   Acton, MA  01719

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   Victor Lopez
   Telefonica I+D

   Ramon Casellas

   Yuji Kamite
   NTT Communications Corporation

   Yosuke Tanaka
   NTT Communications Corporation

   Young Lee
   Huawei Technologies

   Y. Richard Yang
   Yale University

11. Authors' Addresses

   Daniel King
   Old Dog Consulting

   Adrian Farrel
   Juniper Networks

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Appendix A.  Undefined Interfaces

   This Appendix provides a brief list of interfaces that are not yet
   defined at the time of writing.  Interfaces where there is a choice
   of existing protocols are not listed.

   - An interface for adding additional information to the Traffic
     Engineering Database is described in Section  No protocol
     is currently identified for this interface, but candidates include:

     - The protocol developed or adopted to satisfy the requirements of
       I2RS [I-D.ietf-i2rs-architecture]

     - Netconf [RFC6241]

   - The protocol or protocols to be used by the Interface to the
     Routing System described in Section have yet to be
     determined.  The I2RS working group will make this decision after
     use cases and protocol requirements have been agreed.  Various
     candidate protocols have been identified although none appears to
     be suitable without some extensions to the currently-specified
     protocol elements.  The list of protocols supplied here is
     illustrative and not intended to constrain the work of the I2RS
     working group.  The order of the list is not significant.

     - OpenFlow [ONF]
     - Netconf [RFC6241]
     - ForCES [RFC3746]

   - As described in Section, the Virtual Network Topology
     Manager needs an interface that can be used by a PCE or the ABNO
     Controller to inform it that a client layer needs more virtual
     topology.  It is possible that the protocol identified for use
     with I2RS will satisfy this requirement.

   - The north-bound interface from the ABNO Controller is used by the
     NMS, OSS, and Application Service Coordinator to request services
     in the network in support of applications as described in Section

     - It is possible that the protocol selected or designed to satisfy

     - A potential approach for this type of interface is described in
       [RFC7297] for a simple use case.

   - As noted in Section there may be layer-independent data
     models for offering common interfaces to control, configure, and
     report OAM.

King & Farrel                                                  [Page 66]