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rfc:rfc7491

Internet Engineering Task Force (IETF) D. King Request for Comments: 7491 Old Dog Consulting Category: Informational A. Farrel ISSN: 2070-1721 Juniper Networks

                                                            March 2015
 A PCE-Based Architecture for Application-Based Network Operations

Abstract

 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.  An environment that operates to meet these types of
 requirements is said to have Application-Based Network Operations
 (ABNO).  ABNO brings together many existing technologies and may be
 seen as the use of a toolbox of existing components enhanced with a
 few new elements.
 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.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7491.

King & Farrel Informational [Page 1] RFC 7491 PCE-Based Architecture for ABNO March 2015

Copyright Notice

 Copyright (c) 2015 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

King & Farrel Informational [Page 2] RFC 7491 PCE-Based Architecture for ABNO March 2015

Table of Contents

 1. Introduction ....................................................4
    1.1. Scope ......................................................5
 2. Application-Based Network Operations (ABNO) .....................6
    2.1. Assumptions ................................................6
    2.2. Implementation of the Architecture .........................6
    2.3. Generic ABNO Architecture ..................................7
         2.3.1. ABNO Components .....................................8
         2.3.2. Functional Interfaces ..............................15
 3. ABNO Use Cases .................................................24
    3.1. Inter-AS Connectivity .....................................24
    3.2. Multi-Layer Networking ....................................30
         3.2.1. Data Center Interconnection across
                Multi-Layer Networks ...............................34
    3.3. Make-before-Break .........................................37
         3.3.1. Make-before-Break for Reoptimization ...............37
         3.3.2. Make-before-Break for Restoration ..................38
         3.3.3. Make-before-Break for Path Test and Selection ......40
    3.4. Global Concurrent Optimization ............................42
         3.4.1. Use Case: GCO with MPLS LSPs .......................43
    3.5. Adaptive Network Management (ANM) .........................45
         3.5.1. ANM Trigger ........................................46
         3.5.2. Processing Request and GCO Computation .............46
         3.5.3. Automated Provisioning Process .....................47
    3.6. Pseudowire Operations and Management ......................48
         3.6.1. Multi-Segment Pseudowires ..........................48
         3.6.2. Path-Diverse Pseudowires ...........................50
         3.6.3. Path-Diverse Multi-Segment Pseudowires .............51
         3.6.4. Pseudowire Segment Protection ......................52
         3.6.5. Applicability of ABNO to Pseudowires ...............52
    3.7. Cross-Stratum Optimization (CSO) ..........................53
         3.7.1. Data Center Network Operation ......................53
         3.7.2. Application of the ABNO Architecture ...............56
    3.8. ALTO Server ...............................................58
    3.9. Other Potential Use Cases .................................61
         3.9.1. Traffic Grooming and Regrooming ....................61
         3.9.2. Bandwidth Scheduling ...............................62
 4. Survivability and Redundancy within the ABNO Architecture ......62
 5. Security Considerations ........................................63
 6. Manageability Considerations ...................................63
 7. Informative References .........................................64
 Appendix A. Undefined Interfaces ..................................69
 Acknowledgements ..................................................70
 Contributors ......................................................71
 Authors' Addresses ................................................71

King & Farrel Informational [Page 3] RFC 7491 PCE-Based Architecture for ABNO March 2015

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 Operations
 (ABNO).
 The Path Computation Element (PCE) [RFC4655] was developed to provide
 path computation services for GMPLS- and MPLS-controlled networks.
 The applicability of PCEs 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:
  1. 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].
  1. 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)
   [I2RS-Arch], or through the control plane coordinated through the
   PCE Communication Protocol (PCEP) [PCE-Init-LSP].
  1. 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.

King & Farrel Informational [Page 4] RFC 7491 PCE-Based Architecture for ABNO March 2015

  1. Network resource coordination to automate provisioning, and to

facilitate traffic grooming and regrooming, bandwidth scheduling,

   and Global Concurrent Optimization using PCEP [RFC5557].
  1. 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 ongoing 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 Appendix A.
 Thus, this document may be seen as providing an applicability
 statement for existing protocols, and guidance for developers of new
 protocols or protocol extensions.

King & Farrel Informational [Page 5] RFC 7491 PCE-Based Architecture for ABNO March 2015

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.
 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:
  1. 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
   interprocess 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 Label Switched Path Database, and the
   Provisioning Manager (see Section 2.3).
  1. The functional components could be distributed across separate

processes, processors, or servers so that the interfaces are

   exposed as external protocols.

King & Farrel Informational [Page 6] RFC 7491 PCE-Based Architecture for ABNO March 2015

   For example, the Operations, Administration, and Maintenance (OAM)
   Handler (see Section 2.3.1.6) 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.
  1. 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
   network.
   For example, there may be multiple Traffic Engineering Databases
   (see Section 2.3.1.8) in an implementation, with each holding the
   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 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.

2.3. Generic ABNO Architecture

 Figure 1 illustrates the ABNO architecture.  The components and
 functional interfaces are discussed in Sections 2.3.1 and 2.3.2,
 respectively.  The use cases described in Section 3 show how
 different components are used selectively to provide different
 services.  It is important to understand that the relationships and
 interfaces shown between components in this figure are illustrative
 of some of the common or likely interactions; however, this figure
 does not preclude other interfaces and relationships as necessary to
 realize specific functionality.

King & Farrel Informational [Page 7] RFC 7491 PCE-Based Architecture for ABNO March 2015

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

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.

King & Farrel Informational [Page 8] RFC 7491 PCE-Based Architecture for ABNO March 2015

2.3.1.1. 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.

2.3.1.2. 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 that a user uses to make requests
 to 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.

King & Farrel Informational [Page 9] RFC 7491 PCE-Based Architecture for ABNO March 2015

2.3.1.3. ABNO Controller

 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 it 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.

2.3.1.4. 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 [I2RS-Arch].

2.3.1.5. Interface to the Routing System (I2RS) Client

 The Interface to the Routing System (I2RS) is described in
 [I2RS-Arch].  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 [I2RS-PS].  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.

King & Farrel Informational [Page 10] RFC 7491 PCE-Based Architecture for ABNO March 2015

2.3.1.6. OAM Handler

 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
 Coordinator.
 Additionally, the OAM Handler interacts with the devices in the
 network to initiate OAM actions within the data plane, such as
 monitoring and testing.

2.3.1.7. Path Computation Element (PCE)

 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 a
 database (the LSP-DB -- see Section 2.3.1.8.2) containing information
 about the LSPs that are provisioned and operational within the
 network as described in [RFC4655] and [Stateful-PCE].
 Additional functionality 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
 [Stateful-PCE] and [PCE-Init-LSP].  This function may directly access
 the network elements or may be channeled through the Provisioning
 Manager.
 Coordination between multiple PCEs operating on different TEDs can
 prove useful for performing path computation in multi-domain or
 multi-layer networks.  A domain in this case might be an Autonomous
 System (AS), thus enabling inter-AS path computation.

King & Farrel Informational [Page 11] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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
 in Section 3.

2.3.1.8. Databases

 The ABNO architecture includes a number of databases that contain
 information stored for use by the system.  The two main databases are
 the TED and the LSP Database (LSP-DB), but there may be a number of
 other databases used 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 be 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.

2.3.1.8.1. Traffic Engineering Database (TED)

 The 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 bandwidth).
 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].

2.3.1.8.2. LSP Database

 The 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 LSPs.
 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.

King & Farrel Informational [Page 12] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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.  A Stateful PCE (see Section 2.3.1.7) is a
 primary consumer of the LSP-DB.

2.3.1.8.3. 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 associate 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 cannot
 be found, and can correlate SRLGs between different server networks
 or between different peer networks.

2.3.1.8.4. Other Databases

 There may be other databases that are built within the ABNO system
 and that are referenced when operating the network.  These databases
 might include information about, for example, traffic flows and
 demands, predicted or scheduled traffic demands, link 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 2.3.1.8.1, 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 the manufacturer, model, installation date,
 etc.

2.3.1.9. 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

King & Farrel Informational [Page 13] RFC 7491 PCE-Based Architecture for ABNO March 2015

 them.  The selection criteria to choose between two locations may
 depend on information such as maximum bandwidth, minimum cross-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 [RFC7285] 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 [RFC7285], a PID can
 denote a subnet, a set of subnets, a metropolitan area, a Point of
 Presence (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 the 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.

2.3.1.10. 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.

King & Farrel Informational [Page 14] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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
 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 2.3.1.11.
 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.

2.3.1.11. Provisioning Manager

 The Provisioning Manager is responsible for making or channeling
 requests for the establishment of LSPs.  This may be instructions to
 the control plane running in the networks or may involve the
 programming of individual network devices.  In the latter case, the
 Provisioning Manager may act as an OpenFlow Controller [ONF].
 See Section 2.3.2.6 for more details of the interactions between the
 Provisioning Manager and the network.

2.3.1.12. 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.

King & Farrel Informational [Page 15] RFC 7491 PCE-Based Architecture for ABNO March 2015

 As noted at the top of Section 2.3, it is important to understand
 that the relationships and interfaces shown between components in
 Figure 1 are illustrative of some of the common or likely
 interactions; however, this figure and the descriptions in the
 subsections below do not preclude other interfaces and relationships
 as necessary to realize specific functionality.  Thus, some of the
 interfaces described below might not be visible as specific
 relationships in Figure 1, but they can nevertheless exist.

2.3.2.1. Configuration and Programmatic Interfaces

 The network devices may be configured or programmed directly from the
 NMS/OSS.  Many protocols already exist to perform these functions,
 including the following:
  1. SNMP [RFC3412]
  1. The Network Configuration Protocol (NETCONF) [RFC6241]
  1. RESTCONF [RESTCONF]
  1. The General Switch Management Protocol (GSMP) [RFC3292]
  1. ForCES [RFC5810]
  1. OpenFlow [ONF]
  1. PCEP [PCE-Init-LSP]
 The TeleManagement Forum (TMF) Multi-Technology Operations Systems
 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 was added for connectionless networks.  MTOSI is,
 from the 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.

2.3.2.2. TED Construction from the Networks

 As described in Section 2.3.1.8, the TED provides details of the
 capabilities and state of the network for use by the ABNO system and
 the PCE in particular.

King & Farrel Informational [Page 16] RFC 7491 PCE-Based Architecture for ABNO March 2015

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

2.3.2.3. 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 2.3.2.2 with information that is not normally distributed
 within the network, such as node types and capabilities, or the
 characteristics of optical links.
 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) [I2RS-Arch] 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 combination of protocol and encoding that
 is suitable for presenting the TED as described in Section 2.3.2.4
 will likely be suitable (or could be made suitable) for enabling
 write-access to the TED as described in this section.

2.3.2.4. 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-
 bound:
  1. The ALTO protocol [RFC7285] is designed to distribute the

abstracted topology used by an ALTO Server and may prove useful for

   exporting the TED.  The ALTO Server provides the cost between EPs

King & Farrel Informational [Page 17] RFC 7491 PCE-Based Architecture for ABNO March 2015

   or between PIDs, so the application layer can select which is the
   most appropriate connection for the information exchange between
   its application end points.
  1. The same protocol used to export topology information from the

network can be used to export the topology from the TED [BGP-LS].

  1. The I2RS [I2RS-Arch] 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 modeling
   language such as YANG [RFC6020] so that an existing protocol such
   as NETCONF [RFC6241] or the Extensible Messaging and Presence
   Protocol (XMPP) [RFC6120] could be used.
 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
 involved in preparing and presenting the TED information over a
 north-bound interface.

2.3.2.5. 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 PCEP
 [RFC5440].  This facilitates the network setting up LSPs in response
 to simple connectivity requests, and it allows the network to
 reoptimize or repair LSPs.

2.3.2.6. Provisioning Manager Control of Networks

 As described in Section 2.3.1.11, 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.

King & Farrel Informational [Page 18] RFC 7491 PCE-Based Architecture for ABNO March 2015

 A number of protocols already exist to provision network resources,
 as follows:
 o  Program/configure specific network resources
  1. ForCES [RFC5810] defines a protocol for separation of the

control element (the Provisioning Manager) from the forwarding

      elements in each node in the network.
  1. The General 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.
  1. 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
      network.
  1. 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 Transaction Language 1 (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.
  1. 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 2.3.2.8; see [YANG-Rtg].
  1. The [TMF-MTOSI] specification provides provisioning, activation,

deactivation, and release of resources via the Service

      Activation Interface (SAI).  The Common Communication Vehicle
      (CCV) is the middleware required to implement MTOSI.  The CCV is
      then used to provide middleware abstraction in combination with
      the Web Services Description Language (WSDL) to allow MTOSIs to
      be bound to different middleware technologies as needed.

King & Farrel Informational [Page 19] RFC 7491 PCE-Based Architecture for ABNO March 2015

 o  Trigger actions through the control plane
  1. 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.
  1. 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.
  1. The PCE Communication Protocol (PCEP) [RFC5440] has been

proposed as a suitable protocol for requesting the establishment

      of LSPs [PCE-Init-LSP].  This works well, because the protocol
      elements necessary are exactly the same as those 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
      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 network.
 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.

King & Farrel Informational [Page 20] RFC 7491 PCE-Based Architecture for ABNO March 2015

2.3.2.7. 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
 categories:
  1. Updates to the TED are gathered as described in Section 2.3.2.2.
  1. Explicit notification of the successful establishment and the

subsequent state of the LSP can be provided through extensions to

   PCEP as described in [Stateful-PCE] and [PCE-Init-LSP].
  1. OAM can be commissioned and the results inspected by the OAM

Handler as described in Section 2.3.2.14.

  1. A number of ABNO components may make inquiries and inspect network

state through a variety of techniques, including I2RS, NETCONF, or

   SNMP.

2.3.2.8. Controlling the Routing System

 As discussed in Section 2.3.1.5, 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 will be based on a combination of NETCONF [RFC6241] and
 RESTCONF [RESTCONF] with some additional features.

2.3.2.9. 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 standard PCEP as defined in
 [RFC5440].

2.3.2.10. VNTM Interface to and from PCE

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

King & Farrel Informational [Page 21] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 low on resources (for example, the
 capacity on some key link is nearly 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 2.3.2.8); alternatively, an extension to the PCEP Notify
 message (PCNtf) [RFC5440] could be made.

2.3.2.11. 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 designed to satisfy I2RS will
 provide suitable features (see Section 2.3.2.8).

2.3.2.12. ABNO Provisioning Requests

 Under some circumstances, the ABNO Controller may make requests
 directly 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 be
 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 [PCE-Init-LSP].

King & Farrel Informational [Page 22] RFC 7491 PCE-Based Architecture for ABNO March 2015

2.3.2.13. Policy Interfaces

 As described in Section 2.3.1.4 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:
  1. Adding resources on demand should be gated by the authorized

capability.

  1. Client microflows should not trigger server-layer setup or

allocation.

  1. Accounting capabilities should be supported.
  1. Security mechanisms for authorization of requests and capabilities

are required.

 Other policy-related functionality in the system might include the
 policy behavior of the routing and forwarding system, such as:
  1. ECMP behavior
  1. Classification of packets onto LSPs or QoS categories.
 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.  Work will also be needed 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.

2.3.2.14. OAM and Reporting

 The OAM Handler must interact with the network to perform several
 actions:
  1. Enabling OAM function within the network.
  1. Performing proactive OAM operations in the network.
  1. Receiving notifications of network events.

King & Farrel Informational [Page 23] RFC 7491 PCE-Based Architecture for ABNO March 2015

 Any of the configuration and programmatic interfaces described in
 Section 2.3.2.1 may serve this purpose.  NETCONF notifications are
 described in [RFC5277], and OpenFlow supports a number of
 asynchronous event notifications [ONF].  Additionally, Syslog
 [RFC5424] is a protocol for reporting events from the network, and IP
 Flow Information Export (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 the mechanism used
 when events are reported from the network; no new protocol is needed,
 although new data models may be required 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.  The purpose of these examples is
 to give some concrete material to demonstrate the architecture so
 that it may be more easily comprehended, and to illustrate that the
 application of the architecture is achieved by "profiling" and by
 selecting only the relevant components and interfaces.
 Similarly, it is not the intention that this section contain a
 complete list of all possible applications of ABNO.  The examples are
 intended to broadly cover a number of applications that are commonly
 discussed, but this does not preclude other use cases.
 The descriptions in this section are not fully detailed applicability
 statements for ABNO.  It is anticipated that such applicability
 statements, for the use cases described and for other use cases,
 could be suitable material for separate documents.

3.1. Inter-AS Connectivity

 The following use case describes how the ABNO framework can be used
 to 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 AS
 Border Routers (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.

King & Farrel Informational [Page 24] RFC 7491 PCE-Based Architecture for ABNO March 2015

        +--------------+ +-----------------+ +--------------+
        |ASa           | |       ASb       | |          ASc |
        |         +--+ | | +--+       +--+ | | +--+         |
        |         |a1|-|-|-|b1|       |b3|-|-|-|c1|         |
        | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
        | |s|          | |                 | |          |d| |
        | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
        |         |a2|-|-|-|b2|       |b4|-|-|-|c2|         |
        |         +--+ | | +--+       +--+ | | +--+         |
        |              | |                 | |              |
        +--------------+ +-----------------+ +--------------+
 Figure 2: Inter-AS Domain Topology with Hierarchical PCE (Parent PCE)
 The following steps are performed to deliver the service within the
 ABNO architecture:
 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       |
                               +----------+----------+
                                          |
                                          V
                +--------+    +-----------+-------------+
                | 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, which shows the connectivity between

King & Farrel Informational [Page 25] RFC 7491 PCE-Based Architecture for ABNO March 2015

    ASes.  This helps it understand that the end-to-end path must
    cross each of ASa, ASb, and ASc, so it sends individual path
    computation requests to each of PCEs 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
    types 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.
                         +-----------------+
                         | 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.

King & Farrel Informational [Page 26] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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
    below.
    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 2.3.2.6, these interactions can use the
        NETCONF protocol [RFC6241] or the extensions to PCEP described
        in [PCE-Init-LSP].  In either case, the provisioning request
        is sent to the head-end Label Switching Router (LSR), and that
        LSR signals in the control plane (using a protocol such as
        RSVP-TE [RFC3209]) to cause the LSP to be established.
                          +-----------------+
                          | ABNO Controller |
                          +--------+--------+
                                   |
                                   V
                            +------+-------+
                            | Provisioning |
                            | Manager      |
                            +------+-------+
                                   |
                                   V
              +--------------------+------------------------+
             /                  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 2.3.2.6.
        In this case, the picture is the same as that 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 be responsible
        for fanning out the requests to the individual network
        elements.

King & Farrel Informational [Page 27] RFC 7491 PCE-Based Architecture for ABNO March 2015

    3c. Provisioning with an Active Parent PCE
        The Active PCE is described in Section 2.3.1.7, based on the
        concepts expressed in [PCE-Init-LSP].  In this approach, the
        process described in option 3a is modified such that the PCE
        issues a direct PCEP command to the network, without a
        response being first returned to the ABNO Controller.
        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 option 3b.
                +-----------------+
                | ABNO Controller |
                +----+------------+
                     |
                     V
                  +--+----------+         +--------------+
    +--------+    |             |         | 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 options 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

King & Farrel Informational [Page 28] RFC 7491 PCE-Based Architecture for ABNO March 2015

        in this model is active (instructing the children to provision
        LSP segments) or passive (requesting path segments that the
        children provision).
                         +-----------------+
                         | 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 Section 2.3.2.7.

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|
    +--+   +--+   +--+                    +--+   +--+   +--+
                      \                  /
                       \                /
                        +--+  +--+  +--+
                        |L1|--|L2|--|L3|
                        +--+  +--+  +--+
                     Figure 8: Multi-Layer Network
 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

King & Farrel Informational [Page 30] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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
    request.
                           +---------------------------+
                           |    Application Service    |
                           |        Coordinator        |
                           +-------------+-------------+
                                         |
                                         V
                 +------+   +------------+------------+
                 |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.

King & Farrel Informational [Page 31] RFC 7491 PCE-Based Architecture for ABNO March 2015

                           +-----------------+
                           | ABNO Controller |
                           +----+------------+
                                |
                                V
              +--------+     +--+-----------+   +--------+
              | 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
    the 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.  Assuming that the policy
    allows it, the VNTM asks the optical-layer PCE to 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     |
                +--------+     +---+--+     +--------------+
                                   |
                                   V
                             +---------------+   +---------+
                             | 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
    Section 3.1.  That is, provisioning can be initiated by the
    optical-layer PCE or by its user, the VNTM.  The command can be

King & Farrel Informational [Page 32] RFC 7491 PCE-Based Architecture for ABNO March 2015

    sent to the head end of the optical LSP (P3) so that the control
    plane (for example, GMPLS RSVP-TE [RFC3473]) can be used to
    provision the LSP.  Alternatively, the network resources can be
    provisioned directly, using any of the mechanisms described in
    Section 2.3.2.6.
 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 I2RS).
    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  |
                   +------+-+
                          A
                          |
                         +--+                    +--+
                         |P3|....................|P4|
                         +--+                    +--+
                             \                  /
                              \                /
                               +--+  +--+  +--+
                               |L1|--|L2|--|L3|
                               +--+  +--+  +--+
              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
    before reporting service fulfillment to the Application Service
    Coordinator.

King & Farrel Informational [Page 33] RFC 7491 PCE-Based Architecture for ABNO March 2015

    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 (DCs) 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 lambda switch capable
 (LSC), packet switch capable (PSC), or time division multiplexing
 (TDM) services, and the application and usage of the ABNO
 architecture and Controller enable 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.

King & Farrel Informational [Page 34] RFC 7491 PCE-Based Architecture for ABNO March 2015

 The application of an ABNO architecture and related procedures would
 involve the following aspects:
 1. Request from the Application Service Coordinator or NMS
    As shown in Figure 13, the ABNO Controller receives a request from
    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 end points, after considering any applicable policy as
    defined by the Policy Agent (see Figure 1).
                           +---------------------------+
                           |    Application Service    |
                           |     Coordinator or NMS    |
                           +-------------+-------------+
                                         |
                                         V
                 +------+   +------------+------------+
                 |Policy+->-+     ABNO Controller     |
                 |Agent |   |                         |
                 +------+   +-------------------------+
      Figure 13: Application Service Coordinator Request Management
 2. Address 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 end points 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 topology information is disseminated and
    gathered, there are two possible scenarios:
    2a. The Application Layer Knows the Client Network Layer
        Entities belonging to the application layer may have an
        interface with the TED or with an ALTO Server allowing those
        entities to map the high-level end points to network
        addresses.  The mechanism used to enable this address
        correlation is out of scope for this document but relies on
        direct interfaces to other ABNO components in addition to the
        interface to the ABNO Controller.

King & Farrel Informational [Page 35] RFC 7491 PCE-Based Architecture for ABNO March 2015

        In this scenario, the request from the NMS or Application
        Service Coordinator contains addresses in the client-layer
        network.  Therefore, when the ABNO Controller requests the PCE
        to compute a path between two end points, the PCE is able to
        use the supplied addresses, compute the path, and continue the
        workflow in communication with the Provisioning Manager.
    2b. The Application Layer Does Not Know the Client Network Layer
        In this case, when the ABNO Controller receives a request from
        the NMS or Application Service Coordinator, the request
        contains only identifiers from the application-layer address
        space.  In order for the PCE to compute an end-to-end path,
        these identifiers must be converted to addresses in the
        client-layer network.  This translation can be performed by
        the ABNO Controller, which can access the TED and ALTO
        databases allowing the path computation request that it sends
        to the PCE to simply be contained within one network and TED.
        Alternatively, the computation request could use the
        application-layer identifiers, leaving the job of address
        mapping to the PCE.
        Note that in order to avoid any confusion both approaches in
        this scenario require clear identification of the address
        spaces that are in use.
 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 that issues 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.

King & Farrel Informational [Page 36] RFC 7491 PCE-Based Architecture for ABNO March 2015

    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 by either manual configuration or discovery.
                                +-----------------+
                                | ABNO Controller |
                                +-------+---------+
                                        |
                                        |
                                        V
                    +------+     +------+-------+
                    | VNTM +--<--+     PCE      |
                    +---+--+     +------+-------+
                        |               |
                        V               V
                  +-----+---------------+------------+
                  |       Provisioning Manager       |
                  +----------------------------------+
                    |       |       |       |       |
                    V       |       V       |       V
                  OpenFlow  V    ForCES     V      PCEP
                         NETCONF          SNMP
                     Figure 14: Provisioning Process
 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 with
 little or no 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 Reoptimization

 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
 reoptimization of in-service LSPs.

King & Farrel Informational [Page 37] RFC 7491 PCE-Based Architecture for ABNO March 2015

 The process is simple, and the example shown in Figure 15 utilizes a
 Stateful PCE [Stateful-PCE] to monitor the network and take
 reoptimization 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
 reoptimized under specific conditions according to policy.  This
 allows the ABNO Controller to manage the sequence and prioritization
 of reoptimizing 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 reoptimized 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
 network.
 Once the new path has been set up and the network reports that it is
 being used correctly, the PCE tears down the old path and may report
 the reoptimization event to the ABNO Controller.
           +---------------------------------------------+
           | 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

King & Farrel Informational [Page 38] RFC 7491 PCE-Based Architecture for ABNO March 2015

 failed LSP is torn down first.  Unlike the example in Section 3.3.1,
 this case addresses a situation where the service is interrupted, but
 this interruption 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,
 reusing as much of the original path as possible, and the PCE sets up
 the new LSP.
 Once the new path has been set up and the network reports that it is
 being used 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

King & Farrel Informational [Page 39] RFC 7491 PCE-Based Architecture for ABNO March 2015

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
 Controller.
 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 path might be achieved by
 stitching together an MPLS segment, an Ethernet/VLAN segment, another
 IP segment, etc.
 Otherwise, the process is similar to that for reoptimization as
 discussed in Section 3.3.1.

King & Farrel Informational [Page 40] RFC 7491 PCE-Based Architecture for ABNO March 2015

           +---------------------------------------------+
           | 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 pseudocode that follows gives an indication of the interactions
 between ABNO components.
    OSS requests quality-assured service
    :Label1
    DoWhile not enough LSPs (ABNO Controller)
      Instruct PCE to compute and provision the LSP (ABNO Controller)
      Create the LSP (PCE)
    EndDo
    :Label2
    DoFor each LSP (ABNO Controller)
      Test LSP (OAM Handler)
      Report results to ABNO Controller (OAM Handler)
    EndDo
    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)
    EndDo

King & Farrel Informational [Page 41] RFC 7491 PCE-Based Architecture for ABNO March 2015

    DoUntil trigger (OAM Handler, ABNO Controller, Policy Agent)
      keep sending traffic (Network)
      Test LSP (OAM Handler)
    EndDo
    If there is already a suitable LSP (ABNO Controller)
      GoTo Label2
    Else
      GoTo Label1
    EndIf

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 suboptimized placement of sequentially computed
    services.
 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 functionality
 and capability to perform concurrent computation provide 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.

King & Farrel Informational [Page 42] RFC 7491 PCE-Based Architecture for ABNO March 2015

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:
 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 that 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       |
                               +----------+----------+
                                          |
                                          V
                +--------+    +-----------+-------------+
                | Policy +-->-+     ABNO Controller     |
                | Agent  |    |                         |
                +--------+    +-------------------------+
                Figure 18: NMS Request to ABNO Controller
    1a. Each service request has a source, destination, and bandwidth
        request.  These service requests are sent to the ABNO
        Controller and categorized as GCO requests.  The PCE uses the
        appropriate policy for each request and consults the TED for
        the packet layer.

King & Farrel Informational [Page 43] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 |
                             +----+------------+
                                  |
                                  V
                +--------+     +--+-----------+   +--------+
                |        |     |              |   |        |
                | 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
        concurrently.
    2c. Once the requested GCO service path computation completes, the
        PCE sends the resulting paths back to the ABNO Controller.
        The response includes a fully computed explicit path for each
        service (TE LSP).

King & Farrel Informational [Page 44] RFC 7491 PCE-Based Architecture for ABNO March 2015

 3. The concurrently computed solution received from the PCE is sent
    back to the NMS/OSS by the ABNO Controller as a PCEP response, as
    shown in Figure 20.  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.
                       +---------------------+
                       |       NMS/OSS       |
                       +----------+----------+
                                  ^
                                  |
                       +----------+----------+
                       |    ABNO Controller  |
                       |                     |
                       +---------------------+
             Figure 20: ABNO Sends Solution to the NMS/OSS

3.5. Adaptive Network Management (ANM)

 The ABNO architecture provides the capability for reactive network
 control of resources relying 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].
 EON provides spectrum-efficient and scalable transport by introducing
 flexible granular traffic grooming in the optical frequency domain.
 This is achieved using arbitrary contiguous concatenation of the
 optical spectrum that allows the creation of custom-sized bandwidth.
 This bandwidth is defined in slots of 12.5 GHz.
 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, optical modulation format, and associated reach, or following
 user requests, and can be achieved in a highly spectrum-efficient and
 scalable manner.  Similarly, OTN provides for flexible and granular
 provisioning of bandwidth on top of Wavelength Switched Optical
 Networks (WSONs).
 To efficiently use optical resources, a system is required that can
 monitor network resources and decide the optimal network
 configuration based on the status, bandwidth availability, and user
 service.  We call this ANM.

King & Farrel Informational [Page 45] RFC 7491 PCE-Based Architecture for ABNO March 2015

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 that 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 an NMS.
 o  Periodic: An adaptive network planning process can be run
    periodically to find an optimum configuration.
 An ABNO Controller would receive a request from an 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.
 This request for GCO is passed to the PCE, along the lines of the
 description in Section 3.4.  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 the 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
 setup/modification process.

King & Farrel Informational [Page 46] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 network operations are supervised by the operator,
 there are some actions that 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 process, where human
 intervention is not required, the PCE sends the Provisioning Manager
 a new configuration to configure the network elements, as shown in
 Figure 22.

King & Farrel Informational [Page 47] RFC 7491 PCE-Based Architecture for ABNO March 2015

                       +------------------------+
                       |       OSS or NMS       |
                       +-----------+------------+
                                   |
                                   V
             +------+   +----------+------------+
             |Policy+->-+     ABNO Controller   |
             |Agent |   |                       |
             +------+   +----------+------------+
                                   |
                                   V
                            +------+------+
                            +     PCE     |
                            +------+------+
                                   |
                                   V
                   +----------------------------------+
                   |       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] describes 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 in the figure as AC, PW1, PW2, PW3, and
 AC.  Each pseudowire segment is stitched at a "stitching Provider
 Edge" (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.

King & Farrel Informational [Page 48] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 PE nodes may traverse different MPLS networks with
 the PEs as border nodes, or the PEs may lie within the network such
 that each LSP spans only part of the network.
  1. —- —– —– —–
  2. – |T-PE1| LSP1 |S-PE1| LSP2 |S-PE3| LSP3 |T-PE2| +—+

| | AC | |=======| |=======| |=======| | AC | |

  |CE1|----|........PW1........|..PW2........|..PW3........|----|CE2|
  |   |    |     |=======|     |=======|     |=======|     |    |   |
   ---     |     |       |     |       |     |       |     |    +---+
            -----         -----         -----         -----
                  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
 together.
 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:
  1. MPLS connectivity
  1. MPLS bandwidth availability
  1. pseudowire stitching capability and capacity at PEs
  1. policy and confidentiality considerations for use of PEs

King & Farrel Informational [Page 49] RFC 7491 PCE-Based Architecture for ABNO March 2015

  1. —-

|S-PE5|

                                /-----\
   ---      -----         -----/       \-----         -----      ---
  |CE1|----|T-PE1|-------|S-PE1|-------|S-PE3|-------|T-PE2|----|CE2|
   ---      -----\        -----\        -----        /-----      ---
                  \         |   -------   |         /
                   \      -----        \-----      /
                    -----|S-PE2|-------|S-PE4|-----
                          -----         -----
         Figure 24: Multi-Segment Pseudowire Network Topology

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.
  1. —— ——-

| PE1 | LSP1 | PE2 |

          AC   |       |=======================|       |   AC
           ----...................PW1...................----
   --- -  /    |       |=======================|       |    \  -----
  |     |/     |       |                       |       |     \|     |
  | CE1 +      |       |      MPLS Network     |       |      + CE2 |
  |     |\     |       |                       |       |     /|     |
   --- -  \    |       |=======================|       |    /  -----
           ----...................PW2...................----
          AC   |       |=======================|       |   AC
               |       |          LSP2         |       |
                -------                         -------
                  Figure 25: Path-Diverse Pseudowires
 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 only one of the LSPs.  Thus, some form of coordinated path
 computation approach is needed.

King & Farrel Informational [Page 50] RFC 7491 PCE-Based Architecture for ABNO March 2015

  1. —— ——-

| PE1 | LSP1 | PE2 |

           AC  |       |=======================|       |  AC
            ---...................PW1...................---
           /   |       |=======================|       |   \
   -----  /    |       |                       |       |    \  -----
  |     |/      -------                         -------      \|     |
  | CE1 +                     MPLS Network                    + CE2 |
  |     |\      -------                         -------      /|     |
   -----  \    |  PE3  |                       |  PE4  |    /  -----
           \   |       |=======================|       |   /
            ---...................PW2...................---
           AC  |       |=======================|       |  AC
               |       |          LSP2         |       |
                -------                         -------
         Figure 26: Path-Diverse Pseudowires with Disjoint PEs

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.
  1. —- —–

|S-PE5|————–|T-PE4|

                                /-----\               ----- \
            -----         -----/       \-----         -----  \ ---
           |T-PE1|-------|S-PE1|-------|S-PE3|-------|T-PE2|--|CE2|
     ---  / -----\        -----\        -----        /-----    ---
    |CE1|<        -------   |   -------   |         /
     ---  \ -----        \-----        \-----      /
           |T-PE3|-------|S-PE2|-------|S-PE4|-----
            -----         -----         -----
   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.

King & Farrel Informational [Page 51] RFC 7491 PCE-Based Architecture for ABNO March 2015

 But the problem is complicated by the multi-layer nature of the
 network.  It is not enough that the PEs are chosen to be 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
 enabled by the mechanism 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 stitched segments running between S-PE1 and S-PE5, and
 between S-PE5 and S-PE3.  This is shown in detail in Figure 28.
  1. —— ——- ——-

| 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
 of 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.  At the time of this writing, PCEP does not support

King & Farrel Informational [Page 52] RFC 7491 PCE-Based Architecture for ABNO March 2015

 path computation requests and responses concerning pseudowires, but
 the concepts are very similar to existing uses and the necessary
 extensions would be very small.
 Once the paths have been computed, 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 pseudowire network.  Thus, the problem space
 being addressed by ABNO in this case is a classic multi-layer
 network.

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

King & Farrel Informational [Page 53] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 suboptimal 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
 Virtual Machines (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, Synchronous Digital
 Hierarchy (SDH), OTN, WDM).  The network stratum has resources 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.

3.7.1.1. 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 not only offer 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
 intensive).

King & Farrel Informational [Page 54] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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-multipoint
 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 into account the
 situation in the network stratum, even as the application stratum
 actions may be driven by the status of the network stratum.

3.7.1.2. Load Balancing

 Application servers may be instantiated in many data centers located
 in different parts of the network.  When an end-user makes 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, the key factors to be considered in choosing the server on
 which to instantiate a VM for an application include:
  1. The utilization of the servers in the data center
  1. The network load conditions within a data center
  1. The network load conditions between data centers
  1. The network conditions between the end-user and data center

King & Farrel Informational [Page 55] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 end-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 desired services and converts this information to
 service requests that it passes to the ABNO Controller.  The
 end-users may already know which data center they wish to use, or the
 Application Service Coordinator may be able to make this
 determination; otherwise, the task of selecting the data center must
 be performed by the ABNO Controller, and this may utilize a further
 database (see Section 2.3.1.8) to contain information about server
 loads and other data center parameters.
 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.

King & Farrel Informational [Page 56] RFC 7491 PCE-Based Architecture for ABNO March 2015

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

3.7.2.1. 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 location to 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.

King & Farrel Informational [Page 57] RFC 7491 PCE-Based Architecture for ABNO March 2015

 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 the end-user
 to the 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 the PCE can fit in with CSO is
 provided in [CSO-PCE], 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 the ability 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. 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
    five nodes and six links.
    The application, which has end points 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 end points at the three sites.

King & Farrel Informational [Page 58] RFC 7491 PCE-Based Architecture for ABNO March 2015

               +----+       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 request arrives at the ABNO Controller, which forwards the
    request to the ALTO Server component.  The ALTO Server consults
    the Policy Agent, the TED, and the PCE to return an abstract,
    application-layer topology.
    For example, the policy may specify that the bandwidth exposed to
    an application may not exceed 40 Mbps.  The network has
    precomputed that the route from N0 to N2 should use the path
    N0->N3->N2, according to goals such as GCO (see Section 3.4).  The
    ALTO Server can then produce a reduced topology for the
    application, such as the topology shown in Figure 31.

King & Farrel Informational [Page 59] RFC 7491 PCE-Based Architecture for ABNO March 2015

                    +----+
                    | 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 three 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 of 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.

King & Farrel Informational [Page 60] RFC 7491 PCE-Based Architecture for ABNO March 2015

             +----+
             | N0 |----------------------------------+
             +----+        AL0M2 BW=30               |
               |                                     |
               |                                     |
               |                                     |
               |                                     |
               | L1                                  |
               |                                     |
               | BW=35                               |
               |                                     |
               |                                     |
               |                                     |
               V                                     V
             +----+        L3 BW=35                +----+
             | N1 |...............................>| N2 |
             +----+                                +----+
              Figure 32: Application-Layer Spanning Tree
 3. Application Path Set Up by the ABNO Controller
    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 reoptimize network traffic engineering.

3.9. Other Potential Use Cases

 This section serves as a placeholder for other potential use cases
 that might get documented in future documents.

3.9.1. Traffic Grooming and Regrooming

 This use case could cover the following scenarios:
  1. Nested LSPs
  1. Packet Classification (IP flows into LSPs at edge routers)
  1. Bucket Stuffing
  1. IP Flows into ECMP Hash Bucket

King & Farrel Informational [Page 61] RFC 7491 PCE-Based Architecture for ABNO March 2015

3.9.2. Bandwidth Scheduling

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

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) or on a separate
 virtual machine (for example, in a data center), or groups of
 programs could be deployed on the same processor.  From the point of
 view of the architectural model, these implementation and deployment
 choices are entirely unimportant.
 Similarly, the realization of a functional component of the ABNO
 architecture could be supported by more than one instance of an
 implementation, or by different instances 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 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, synchronization between
 instances of components may be needed in order to facilitate seamless
 resiliency.
 How these features are achieved in an ABNO implementation or
 deployment is outside the scope of this document.

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5. Security Considerations

 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
 manage 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 managed.  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.
 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 mechanism to gather and collate information about the
 network, reporting it to management applications, storing it for
 future inspection, and triggering actions according to configured
 policies.

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

7. Informative References

 [BGP-LS]   Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
            Ray, "North-Bound Distribution of Link-State and TE
            Information using BGP", Work in Progress, draft-ietf-idr-
            ls-distribution-10, January 2015.
 [CSO-PCE]  Dhody, D., Lee, Y., Contreras, LM., Gonzalez de Dios, O.,
            and N. Ciulli, "Cross Stratum Optimization enabled Path
            Computation", Work in Progress, draft-dhody-pce-cso-
            enabled-path-computation-07, January 2015.
 [EON]      Gerstel, O., Jinno, M., Lord, A., and S.J.B. Yoo, "Elastic
            optical networking: a new dawn for the optical layer?",
            IEEE Communications Magazine, Volume 50, Issue 2,
            ISSN 0163-6804, February 2012.
 [Flood]    Project Floodlight, "Floodlight REST API",
            <http://www.projectfloodlight.org>.
 [G.694.1]  ITU-T Recommendation G.694.1, "Spectral grids for WDM
            applications: DWDM frequency grid", February 2012.
 [G.709]    ITU-T Recommendation G.709, "Interface for the optical
            transport network", February 2012.
 [I2RS-Arch]
            Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
            Nadeau, "An Architecture for the Interface to the Routing
            System", Work in Progress, draft-ietf-i2rs-
            architecture-09, March 2015.
 [I2RS-PS]  Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Interface
            to the Routing System Problem Statement", Work in
            Progress, draft-ietf-i2rs-problem-statement-06,
            January 2015.

King & Farrel Informational [Page 64] RFC 7491 PCE-Based Architecture for ABNO March 2015

 [ONF]      Open Networking Foundation, "OpenFlow Switch Specification
            Version 1.4.0 (Wire Protocol 0x05)", October 2013.
 [PCE-Init-LSP]
            Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
            Extensions for PCE-initiated LSP Setup in a Stateful PCE
            Model", Work in Progress, draft-ietf-pce-pce-initiated-
            lsp-03, March 2015.
 [RESTCONF] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
            Protocol", Work in Progress, draft-ietf-netconf-
            restconf-04, January 2015.
 [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,
            <http://www.rfc-editor.org/info/rfc2748>.
 [RFC2753]  Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
            for Policy-based Admission Control", RFC 2753,
            January 2000, <http://www.rfc-editor.org/info/rfc2753>.
 [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
            and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
            Tunnels", RFC 3209, December 2001,
            <http://www.rfc-editor.org/info/rfc3209>.
 [RFC3292]  Doria, A., Hellstrand, F., Sundell, K., and T. Worster,
            "General Switch Management Protocol (GSMP) V3", RFC 3292,
            June 2002, <http://www.rfc-editor.org/info/rfc3292>.
 [RFC3412]  Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
            "Message Processing and Dispatching for the Simple Network
            Management Protocol (SNMP)", STD 62, RFC 3412,
            December 2002, <http://www.rfc-editor.org/info/rfc3412>.
 [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
            Switching (GMPLS) Signaling Resource ReserVation Protocol-
            Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
            January 2003, <http://www.rfc-editor.org/info/rfc3473>.
 [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
            (TE) Extensions to OSPF Version 2", RFC 3630,
            September 2003, <http://www.rfc-editor.org/info/rfc3630>.

King & Farrel Informational [Page 65] RFC 7491 PCE-Based Architecture for ABNO March 2015

 [RFC3746]  Yang, L., Dantu, R., Anderson, T., and R. Gopal,
            "Forwarding and Control Element Separation (ForCES)
            Framework", RFC 3746, April 2004,
            <http://www.rfc-editor.org/info/rfc3746>.
 [RFC3985]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
            Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005,
            <http://www.rfc-editor.org/info/rfc3985>.
 [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
            Computation Element (PCE)-Based Architecture", RFC 4655,
            August 2006, <http://www.rfc-editor.org/info/rfc4655>.
 [RFC5150]  Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
            "Label Switched Path Stitching with Generalized
            Multiprotocol Label Switching Traffic Engineering (GMPLS
            TE)", RFC 5150, February 2008,
            <http://www.rfc-editor.org/info/rfc5150>.
 [RFC5212]  Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
            M., and D. Brungard, "Requirements for GMPLS-Based Multi-
            Region and Multi-Layer Networks (MRN/MLN)", RFC 5212,
            July 2008, <http://www.rfc-editor.org/info/rfc5212>.
 [RFC5254]  Bitar, N., Ed., Bocci, M., Ed., and L. Martini, Ed.,
            "Requirements for Multi-Segment Pseudowire Emulation Edge-
            to-Edge (PWE3)", RFC 5254, October 2008,
            <http://www.rfc-editor.org/info/rfc5254>.
 [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
            Notifications", RFC 5277, July 2008,
            <http://www.rfc-editor.org/info/rfc5277>.
 [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
            Engineering", RFC 5305, October 2008,
            <http://www.rfc-editor.org/info/rfc5305>.
 [RFC5394]  Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
            "Policy-Enabled Path Computation Framework", RFC 5394,
            December 2008, <http://www.rfc-editor.org/info/rfc5394>.
 [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009,
            <http://www.rfc-editor.org/info/rfc5424>.
 [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
            Element (PCE) Communication Protocol (PCEP)", RFC 5440,
            March 2009, <http://www.rfc-editor.org/info/rfc5440>.

King & Farrel Informational [Page 66] RFC 7491 PCE-Based Architecture for ABNO March 2015

 [RFC5520]  Bradford, R., Ed., Vasseur, JP., and A. Farrel,
            "Preserving Topology Confidentiality in Inter-Domain Path
            Computation Using a Path-Key-Based Mechanism", RFC 5520,
            April 2009, <http://www.rfc-editor.org/info/rfc5520>.
 [RFC5557]  Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
            Computation Element Communication Protocol (PCEP)
            Requirements and Protocol Extensions in Support of Global
            Concurrent Optimization", RFC 5557, July 2009,
            <http://www.rfc-editor.org/info/rfc5557>.
 [RFC5623]  Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
            "Framework for PCE-Based Inter-Layer MPLS and GMPLS
            Traffic Engineering", RFC 5623, September 2009,
            <http://www.rfc-editor.org/info/rfc5623>.
 [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
            Optimization (ALTO) Problem Statement", RFC 5693,
            October 2009, <http://www.rfc-editor.org/info/rfc5693>.
 [RFC5810]  Doria, A., Ed., Hadi Salim, J., Ed., Haas, R., Ed.,
            Khosravi, H., Ed., Wang, W., Ed., Dong, L., Gopal, R., and
            J.  Halpern, "Forwarding and Control Element Separation
            (ForCES) Protocol Specification", RFC 5810, March 2010,
            <http://www.rfc-editor.org/info/rfc5810>.
 [RFC6007]  Nishioka, I. and D. King, "Use of the Synchronization
            VECtor (SVEC) List for Synchronized Dependent Path
            Computations", RFC 6007, September 2010,
            <http://www.rfc-editor.org/info/rfc6007>.
 [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
            the Network Configuration Protocol (NETCONF)", RFC 6020,
            October 2010, <http://www.rfc-editor.org/info/rfc6020>.
 [RFC6107]  Shiomoto, K., Ed., and A. Farrel, Ed., "Procedures for
            Dynamically Signaled Hierarchical Label Switched Paths",
            RFC 6107, February 2011,
            <http://www.rfc-editor.org/info/rfc6107>.
 [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
            Protocol (XMPP): Core", RFC 6120, March 2011,
            <http://www.rfc-editor.org/info/rfc6120>.
 [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
            and A. Bierman, Ed., "Network Configuration Protocol
            (NETCONF)", RFC 6241, June 2011,
            <http://www.rfc-editor.org/info/rfc6241>.

King & Farrel Informational [Page 67] RFC 7491 PCE-Based Architecture for ABNO March 2015

 [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
            Distribution Network Interconnection (CDNI) Problem
            Statement", RFC 6707, September 2012,
            <http://www.rfc-editor.org/info/rfc6707>.
 [RFC6805]  King, D., Ed., and A. Farrel, Ed., "The Application of the
            Path Computation Element Architecture to the Determination
            of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
            November 2012, <http://www.rfc-editor.org/info/rfc6805>.
 [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
            "Specification of the IP Flow Information Export (IPFIX)
            Protocol for the Exchange of Flow Information", STD 77,
            RFC 7011, September 2013,
            <http://www.rfc-editor.org/info/rfc7011>.
 [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
            Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
            "Application-Layer Traffic Optimization (ALTO) Protocol",
            RFC 7285, September 2014,
            <http://www.rfc-editor.org/info/rfc7285>.
 [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
            Connectivity Provisioning Profile (CPP)", RFC 7297,
            July 2014, <http://www.rfc-editor.org/info/rfc7297>.
 [Stateful-PCE]
            Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
            Extensions for Stateful PCE", Work in Progress,
            draft-ietf-pce-stateful-pce-10, October 2014.
 [TL1]      Telcorida, "Operations Application Messages - Language For
            Operations Application Messages", GR-831, November 1996.
 [TMF-MTOSI]
            TeleManagement Forum, "Multi-Technology Operations Systems
            Interface (MTOSI)",
            <https://www.tmforum.org/MTOSI/2319/home.html>.
 [YANG-Rtg] Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
            Management", Work in Progress, draft-ietf-netmod-routing-
            cfg-17, March 2015.

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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 this writing.  Interfaces where there is a
 choice of existing protocols are not listed.
 o  An interface for adding additional information to the Traffic
    Engineering Database is described in Section 2.3.2.3.  No protocol
    is currently identified for this interface, but candidates
    include:
  1. The protocol developed or adopted to satisfy the requirements of

I2RS [I2RS-Arch]

  1. NETCONF [RFC6241]
 o  The protocol to be used by the Interface to the Routing System is
    described in Section 2.3.2.8.  The I2RS working group has
    determined that this protocol will be based on a combination of
    NETCONF [RFC6241] and RESTCONF [RESTCONF] with further additions
    and modifications as deemed necessary to deliver the desired
    function.  The details of the protocol are still to be determined.
 o  As described in Section 2.3.2.10, 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, or this could be achieved
    using extensions to the PCEP Notify message (PCNtf).
 o  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 2.3.2.11.
  1. It is possible that the protocol selected or designed to satisfy

I2RS will address the requirement.

  1. A potential approach for this type of interface is described in

[RFC7297] for a simple use case.

 o  As noted in Section 2.3.2.14, there may be layer-independent data
    models for offering common interfaces to control, configure, and
    report OAM.

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 o  As noted in Section 3.6, the ABNO model could be applied to
    placing multi-segment pseudowires in a network topology made up of
    S-PEs and MPLS tunnels.  The current definition of PCEP [RFC5440]
    and associated extensions that are works in progress do not
    include all of the details to request such paths, so some work
    might be necessary, although the general concepts will be easily
    reusable.  Indeed, such work may be necessary for the wider
    applicability of PCEs in many networking scenarios.

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, Cyril Margaria, Jonathan Hardwick, Nico
 Wauters, Tom Taylor, Qin Wu, and Luis Contreras.  Thanks to George
 Swallow for suggesting the existence of the SRLG database.  Tomonori
 Takeda and Julien Meuric provided valuable comments as part of their
 Routing Directorate reviews.  Tina Tsou provided comments as part of
 her Operational Directorate review.
 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.

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Contributors

 Quintin Zhao
 Huawei Technologies
 125 Nagog Technology Park
 Acton, MA  01719
 United States
 EMail: qzhao@huawei.com
 Victor Lopez
 Telefonica I+D
 EMail: vlopez@tid.es
 Ramon Casellas
 CTTC
 EMail: ramon.casellas@cttc.es
 Yuji Kamite
 NTT Communications Corporation
 EMail: y.kamite@ntt.com
 Yosuke Tanaka
 NTT Communications Corporation
 EMail: yosuke.tanaka@ntt.com
 Young Lee
 Huawei Technologies
 EMail: leeyoung@huawei.com
 Y. Richard Yang
 Yale University
 EMail: yry@cs.yale.edu

Authors' Addresses

 Daniel King
 Old Dog Consulting
 EMail: daniel@olddog.co.uk
 Adrian Farrel
 Juniper Networks
 EMail: adrian@olddog.co.uk

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