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A PCE-based Architecture for Application-based Network Operations

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This is an older version of an Internet-Draft that was ultimately published as RFC 7491.
Authors Daniel King , Adrian Farrel
Last updated 2012-12-01
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Internet Engineering Task Force                                  D. King
Internet-Draft                                        Old Dog Consulting
Intended status: Informational                                 A. Farrel
Expires: June 2, 2013                                   Juniper Networks
                                                        December 2, 2012

   A PCE-based Architecture for Application-based Network Operations



   Services such as content distribution, distributed databases, or
   inter-data center connectivity place a set of new requirements on the
   operation of networks.  They need on-demand and application-specific
   reservation of network connectivity, reliability, and resources (such
   as bandwidth).  An environment that operates to meet this type of
   requirement is said to have Application-Based Network Operations

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

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

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 5, 2013.

King & Farrel                                                   [Page 1]
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Copyright Notice

   Copyright (c) 2012 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
   ( in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction ................................................ 2
    1.1  Scope ..................................................... 4
   2. Application-based Network Operations (ABNO) .................. 4
    2.1  Assumptions and Requirements .............................. 4
    2.2  Generic Architecture ...................................... 5
      2.2.1 ABNO Components ........................................ 6
      2.2.2 ABNO Functional Interfaces ............................ 10
   3. ABNO Use Cases .............................................. 16
    3.1 Inter-AS Connectivity ..................................... 16
    3.2 Multi-Layer Networking .................................... 22
    3.3 Bandwidth Scheduling ...................................... 25
    3.4 Grooming and Regrooming ................................... 26
    3.5 Global Concurrent Optimization ............................ 26
    3.6 Adaptive Network Planning ................................. 26
   4. Security Consideration ...................................... 26
   5. IANA Considerations ......................................... 26
   6. References .................................................. 26
     6.1 Informative References ................................... 26
   7. Authors' Addresses .......................................... 29
   A. Undefined Interfaces ........................................ 30

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.

King & Farrel                                                   [Page 2]
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   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).  An
   environment that operates to meet this type of application-aware
   requirement is said to have Application-Based Network Operation

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

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

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

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

   - Interconnection of Content Delivery Networks (CDNi) [RFC6707]
     through the establishment and resizing of connections between
     content distribution networks.

   - Network resource coordination to facilitate grooming and
     regrooming, bandwidth scheduling, and global concurrent
     optimization [RFC5557].

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

   This document outlines the architecture and use cases for ABNO, and
   shows how the ABNO architecture can be used for co-ordinating 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.

King & Farrel                                                   [Page 3]
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1.1  Scope

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

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

   In other cases it is clear that further work will be required, and in
   those cases a pointer to on-going work that may be of use will be

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

2. Application Based Network Operations (ABNO)

2.1  Assumptions

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

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

   It is not intended that this architecture constrains implementations.
   For example, a stateful and active PCE could be implemented as a
   single a server combining the ABNO components of the PCE, the Traffic
   Engineering Database, and the Resource Manager (see Section 2.2).
   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.

King & Farrel                                                   [Page 4]
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2.2  Generic ABNO Architecture

   The following diagram illustrates the ABNO architecture.  The
   components and functional interfaces are discussed in Sections 2.2.1
   2.2.2 respectively.  The use cases described in Section 3 show how
   different components are used selectively to provide different

     |                        OSS / NMS                             |
       |     |    |           |                  |                |
       |     |    |           |   +--------------+--------------+ |
       |     |    |           |   |     Application Service     | |
       |     |    |           |   |         Coordinator         | |
       |     |    |           |   +-----------+---------------+-+ |
       |     |    |           |               |               |   |
    |  |     |    |      +----+---------------+------+        |   |   |
    |  |     | +--+---+  |                           |      +-+---+-+ |
    |  |     | |Policy+--+     ABNO Controller       +------+       | |
    |  |     | |Agent |  |                           +--+   |  OAM  | |
    |  |     | +--+---+  +-+------------+----------+-+  |   |Handler| |
    |  |     |    |        |            |          |    |   |       | |
    |  |     |    |   +----+-+  +-------+-------+  |    |   +---+---+ |
    |  |     |    +---+ VNTM |--+               |  |    |       |     |
    |  |     |        +--+-+-+  |               |  | +--+---+   |     |
    |  |     |           | |    |      PCE      |  | | I2RS |   |     |
    |  |  +--+---+       | |    |               |  | |Client|   |     |
    |  |  |      +-------+ |    |               |  | +-+--+-+   |     |
    |  |  | TEDs +---------:----+               |  |   |  |     |     |
    |  |  |      |         |    +-+-----+-------+  |   |  |     |     |
    |  |  +-+--+-+         |      |     |          |   |  |     |     |
    |  |    |  |         +-+------------+----------+-+ |  |     |     |
    |  |    |  |         |      Resource Manager     | |  |     |     |
    |  |    |  |         +-----------------+---+-----+ |  |     |     |
       |    |  |                  |        |   |       |  |     |
       |   +---+------------------+--------+-----------+----+   |
       +--/               Client Network Layer               \--+
       | +----------------------------------------------------+ |
       |    |                                  |          |     |
    /                     Server Network Layers                    \

                  Figure 1: Generic ABNO Architecture

King & Farrel                                                   [Page 5]
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2.2.1 ABNO Components

  This section describes the functional components shown as boxes in
  Figure 1.  The interactions between those components, that is the
  functional interfaces, are described in Section 2.2.2. NMS and OSS

   A Network Management Station (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) to show the users the current
   state of the network.

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

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

   For the sake of this architecture, all of these concepts of an
   application are grouped together and are shown as the Application
   Service Coordinator since they are all in some way responsible for
   coordinating the activity of the network to provide services for use
   by applications.

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

King & Farrel                                                   [Page 6]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012 ABNO Controller

   The ABNO Controller is the main gateway to the network for the NMS,
   OSS, and the 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.

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

   Policy plays a very important role in the control and management of
   the network.  It is therefore significant in influencing how the key
   components of the ANBO 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 possible 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 and the Virtual Network
   Topology Manager (VNTM), it will also interact with the Path
   Computation Element (PCE), the Interface to the Routing System (I2RS)
   Client, and the network elements themselves. Interface to the Routing System (I2RS) Client

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

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

King & Farrel                                                   [Page 7]
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   Within the ABNO architecture, the OAM Handler is responsible for
   receiving notifications (often called alerts) from the network about
   potential problems, for correlating them, and for triggering other
   components of the system to take action to preserve or recover the
   services that were established by the ABNO Controller.  The OAM
   Handler also reports network problems and, in particular, service-
   affecting problems to the NMS, OSS, and Application Service

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

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

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

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

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

   Since the PCE is a key component of the ABNO architecture, a better
   view of its role can be gained by examining the use cases described
   in Section 3.

King & Farrel                                                   [Page 8]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012 Traffic Engineering Database (TED)

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

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

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

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

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

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

   All of these actions and decisions are heavily influenced by policy,
   so the Virtual Network Topology Manager (VNTM) [RFC5623] 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.

King & Farrel                                                   [Page 9]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012 Resource Manager

   The Resource Manager is responsible for making or channelling
   requests for the establishment of LSPs.  This may be instructions to
   the control plane running in the networks, or may involve the
   programming of individual network devices.  In the latter case, the
   Resource Manager may act as an OpenFlow Controller [ONF].

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

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

   Section 3.2 describes a use case for multi-layer networking.

2.2.2 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. Configuration and Programmatic Interfaces

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

   - SNMP [RFC3412]

   - Netconf [RFC6241]

   - ForCES [RFC5810]

   - OpenFlow [ONF].

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

King & Farrel                                                  [Page 10]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012 TED Construction from the Networks

   As described in Section, the Traffic Engineering Database
   (TED) provides details of the capabilities of the network for use by the ABNO system and the PCE in particular.

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

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

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

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

   No protocol is currently identified for this interface, but the
   Interface to the Routing System (I2RS) protocol
   [I-D.ward-irs-framework] may be a suitable candidate because it is
   designed 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]. TED Presentation

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

   There are several protocols available for exporting the TED north-

   - The ALTO protocol [I-D.ietf-alto-protocol] is deigned to distribute
     the abstracted topology used by an ALTO Server and may prove useful
     for exporting the TED.

King & Farrel                                                  [Page 11]
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   - The same protocol used to export topology information from the
     network can be used to export the topology from the TED.

   - The Interface to the Routing System (I2RS) [I-D.ward-irs-framework]
     will require a protocol that is capable of handling bulk routing
     information exchanges that would be suitable for exporting the TED. Network Making Path Computation Requests

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

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

   A number of protocols already exist to provision network resources as

   - Program/configure specific network resources

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

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

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

     - Historically, other configuration-based mechanisms have been used
       to set up the forwarding/switching state at individual nodes
       within networks.  Such mechanisms have ranged from non-standard
       command line interfaces (CLIs) to various standards-based options
       such as TL1 [TL1] and SNMP [RFC3412].  These mechanisms are not

King & Farrel                                                  [Page 12]
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       designed for rapid operation of a network and are not easily
       programmatic.  They are not proposed for use by the Resource
       Controller as part of the ABNO architecture.

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

   - Trigger actions through the control plane

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

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

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

       The functional element that issues PCEP requests to establish
       LSPs is known as an "Active PCE", however it should be noted that
       the ABNO functional components responsible for requesting LSPs
       are more likely to be the Resource Manager, the Virtual Network
       Topology Manager, and the ABNO Controller itself.

   Note that the 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                                                  [Page 13]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012 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.  This function falls into four categories:

   - Updates to the TED are gathered as described in Section

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

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

   - ABNO components can may make enquiries and inspect network state
     through I2RS or using Netconf. Controlling The Routing System

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

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

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

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

   The second interaction arises when a PCE determines that it cannot   
   compute a requested path or notices that (according to some
   configured policy) a network is short of resources (for example, the
   capacity on some key link is close to exhausted).  In this case, the

King & Farrel                                                  [Page 14]
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   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 I2RS protocol
   provides suitable features. 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 I2RS protocol (see Section will
   support the necessary features. Policy Interfaces

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

   - Adding resources on demand should be gated by the authorized

   - Client microflows should not trigger server-layer setup or

   - Accounting capabilities should be supported.

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

   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.  There is some discussion that the I2RS

King & Farrel                                                  [Page 15]
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   protocol may support the configuration and manipulation of policies. OAM and Reporting

   The OAM Handler must interact with the networks to perform several

   - Enabling OAM function within the network.

   - Performing proactive OAM operations in the network.

   - Receiving notifications of network events.

   Any of the configuration and programmatic interfaces described in
   Section may serve this purpose, although neither Netconf nor
   OpenFlow currently supports asynchronous notifications.  Additionally
   Syslog [RFC5424] is a protocol for reporting events from the network,
   and IPFIX [RFC5101] is designed to allow network statistics to be
   aggregated and reported.

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

3. ABNO Use Case

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

3.1 Inter-AS Connectivity

   The following use case describes how the ABNO framework can be used
   set up an end-to-end service across multiple Autonomous Systems
   (ASes).  Consider the simple network topology shown in Figure 2.  The
   three ASes (ASa, ASb, and ASc) are connected as 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                                                  [Page 16]
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          +--------------+ +-----------------+ +--------------+
          |ASa           | |ASb              | |ASc           |
          |              | |                 | |              |
          |         +--+ | | +--+       +--+ | | +--+         |
          |         |a1|-|-|-|b1|       |b3|-|-|-|c1|         |
          | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
          | |s|          | |                 | |          |d| |
          | +-+     +--+ | | +--+       +--+ | | +--+     +-+ |
          |         |a2|-|-|-|b2|       |b4|-|-|-|c2|         |
          |         +--+ | | +--+       +--+ | | +--+         |
          |              | |                 | |              |
          +--------------+ +-----------------+ +--------------+

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

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

   1. Request Management

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

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

               Figure 3: ABNO Request Management

   2. Service Path Computation with Hierarchical PCE

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

      As shown in Figure 4, the ABNO Controller sends a request to the

King & Farrel                                                  [Page 17]
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      parent PCE for an end-to-end path.  As described in [RFC6805], the
      parent PCE consults is TED that shows the connectivity between
      ASes.  This helps it understand that the end-to-end path must
      cross each of ASa, ASb, and ASc, so it is sends individual path
      computation requests to each of PCE a, b, and c to determine the
      best options for crossing the ASes.

                        | 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

      Each child PCE applies policy to the requests is receives to
      determine whether the request is to be allowed and to select the
      type of networks 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.

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

    3. Provisioning the End-to-End LSP

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

King & Farrel                                                  [Page 18]
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      3a. Provisioning from the ABNO Controller With a Control Plane

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

                         | ABNO Controller |
                            | Resource  |
                            | Manager   |
            /                  Network                      \

                Figure 5: Provisioning the End-to-End LSP

      3b. Provisioning through Programming Network Resources

          Another option is that the LSP is provisioned hop by hop from
          the Resource Manager using ForCES [RFC5810] or OpenFlow [ONF]
          as described in Section  In this case, the picture is
          the same as shown in Figure 5.  The interaction between the
          ABNO Controller and the Resource Manager will be PCEP or
          Netconf as described in option 3a., and the Resource Manager
          will have the responsibility to fan out the requests to the
          individual network elements.

      3c. Provisioning with an Active PCE

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

King & Farrel                                                  [Page 19]
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          This situation is shown in Figure 6, and could be modified so
          that the Resource Manager still programs the individual
          network elements as described in 3b.

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

            Figure 6: LSP Provisioning with an Active PCE

      3d. Provisioning with Active Child PCEs and Segment Stitching

          A mixture of the approaches described in 3b and 3c can result
          in a combination of mechanisms to program the network to
          provide the end-to-end LSP.  Figure 7 shows how each child PCE
          can be an active PCE responsible for setting up an edge-to-
          edge LSP segment across one of the ASes.  The ABNO Controller
          then uses the Resource Manager to program the inter-AS
          connections using ForCES or OpenFlow and the LSP segments are
          stitched together following the ideas described in [RFC5150].

King & Farrel                                                  [Page 20]
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                           | ABNO Controller +-------->--------+
                           +----+-------+----+                 |
                                |       A                      |
                                V       |                      |
                             +--+-------+--+                   |
               +--------+    |             |                   |
               | Policy +-->-+ Parent PCE  |                   |
               | Agent  |    |             |                   |
               +--------+    ++-----+-----++                   |
                             /      |      \                   |
                            /       |       \                  |
                       +---+-+   +--+--+   +-+---+             |
                       |     |   |     |   |     |             |
                       |PCE a|   |PCE b|   |PCE c|             |
                       |     |   |     |   |     |             V
                       +--+--+   +--+--+   +--+--+             |
                          |         |         |                |
                          V         V         V                |
                   +--------+   +--------+  +--------+         |
                   |Resource|   |Resource|  |Resource|         |
                   |Manager |   |Manager |  |Manager |         |
                   +-+------+   +---+----+  +------+-+         |
                     |              |              |           |
                     V              V              V           |
              +------+-+       +----+---+       +--+-----+     |
             /   AS a   \=====/   AS b   \=====/   AS c   \    |
            +------------+ A +------------+ A +------------+   |
                           |                |                  |
                     +-----+----------------+-----+            |
                     |      Resource 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.

3.2 Multi-Layer Networking

   Networks typically comprise of multiple layers.  These layers
   represent separations of administrative regions, technology, and may
   also represent a distinction between client and server networking

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

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

                   Figure 8: A Multi-Layer Network

King & Farrel                                                  [Page 22]
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   In the ABNO architecture, the following steps are performed to
   deliver the service.

   1. Request Management

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

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

       Figure 9: Application Service Coordinator Request Management

   2. Service Path Computation in the Packet Layer

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

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

                Figure 10: Path Computation Request

King & Farrel                                                  [Page 23]
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   3. Invocation of VNTM and Path Computation in the Optical Layer

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

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

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

       Figure 11: Invocation of VNTM and Optical Layer Path Computation

   5. 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
      sent to the head end of the optical LSP (P3) so that the control
      plane (for example, GMPLS [RFC3473]) can be used to provision the
      LSP.  Alternatively, the network resources can be provisioned
      direct using any of the mechanisms described in Section

   6. 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

King & Farrel                                                  [Page 24]
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      require a specific instruction to the head end router of the
      optical LSP (for example, through the Interface to the Routing

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

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

           Figure 12: Advertisement of a New Virtual Link

   7. 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.

   9. 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 the Application
      Service Coordinator.

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

3.3 Bandwidth Scheduling

   This section to be completed in a future revision of this document.

King & Farrel                                                  [Page 25]
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3.4 Grooming and Regrooming

   This section to be completed in a future revision of this document.

   This use case will cover the following scenarios:

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

3.5 Global Concurrent Optimization

   This section to be completed in a future revision of this document.

3.6 Adaptive Network Planning

   The ABNO architecture provides the capability for reactive network
   control of resources based on classification, profiling and
   prediction based on current demands and resource utilization.  ABNO
   would then manipulate server-layer transport network resources,
   including OTN and Flexi-grid to meet current and projected demands.

   This section to be completed in a future revision of this document.

4. Security Consideration

   To be discussed.

5. IANA Considerations

   This document makes no requests for IANA action.

6. References

6.1. Informative References

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

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

King & Farrel                                                  [Page 26]
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             Alimi, R., Penno, R., and Yang, Y., "ALTO Protocol",
             draft-ietf-alto-protocol, work in progress.

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

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

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

             Atlas, A., Nadeau, T. and Ward, D., "Interface to the
             Routing System Framework", draft-ward-irs-framework, work
             in progress.

   [ONF]     Open Networking Foundation, "OpenFlow Switch Specification
             Version 1.1.0 Implemented (Wire Protocol 0x02)", February

   [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.

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

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

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

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

King & Farrel                                                  [Page 27]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012

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

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

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

   [RFC5101] B. Claise, "Specification of the IP Flow Information Export
             (IPFIX) Protocol for the Exchange of IP Traffic Flow
             Information", RFC 5101, January 2008.

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

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

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

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

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

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

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

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

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draft-farrkingel-pce-abno-architecture-00.txt              December 2012

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

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

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

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

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

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

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

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

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

7. Authors' Addresses

   Daniel King
   Old Dog Consulting


   Adrian Farrel
   Juniper Networks


King & Farrel                                                  [Page 29]
draft-farrkingel-pce-abno-architecture-00.txt              December 2012

Appendix A.  Undefined Interfaces

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

   To be completed in future release of this document.

King & Farrel                                                  [Page 30]