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RFC 5810 - Forwarding and Control Element Separation (ForCES) Pr


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Internet Engineering Task Force (IETF)                     A. Doria, Ed.
Request for Comments: 5810                Lulea University of Technology
Category: Standards Track                             J. Hadi Salim, Ed.
ISSN: 2070-1721                                                     Znyx
                                                            R. Haas, Ed.
                                                                     IBM
                                                        H. Khosravi, Ed.
                                                                   Intel
                                                            W. Wang, Ed.
                                                                 L. Dong
                                           Zhejiang Gongshang University
                                                                R. Gopal
                                                                   Nokia
                                                              J. Halpern
                                                              March 2010

           Forwarding and Control Element Separation (ForCES)
                         Protocol Specification

Abstract

   This document specifies the Forwarding and Control Element Separation
   (ForCES) protocol.  The ForCES protocol is used for communications
   between Control Elements(CEs) and Forwarding Elements (FEs) in a
   ForCES Network Element (ForCES NE).  This specification is intended
   to meet the ForCES protocol requirements defined in RFC 3654.
   Besides the ForCES protocol, this specification also defines the
   requirements for the Transport Mapping Layer (TML).

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc5810.

Copyright Notice

   Copyright (c) 2010 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.

Table of Contents

   1. Introduction ....................................................5
   2. Terminology and Conventions .....................................6
      2.1. Requirements Language ......................................6
      2.2. Other Notation .............................................6
      2.3. Integers ...................................................6
   3. Definitions .....................................................6
   4. Overview .......................................................10
      4.1. Protocol Framework ........................................11
           4.1.1. The PL .............................................13
           4.1.2. The TML ............................................14
           4.1.3. The FEM/CEM Interface ..............................14
      4.2. ForCES Protocol Phases ....................................15
           4.2.1. Pre-association ....................................16
           4.2.2. Post-association ...................................18
      4.3. Protocol Mechanisms .......................................19
           4.3.1. Transactions, Atomicity, Execution, and Responses ..19
           4.3.2. Scalability ........................................25
           4.3.3. Heartbeat Mechanism ................................26
           4.3.4. FE Object and FE Protocol LFBs .....................27
      4.4. Protocol Scenarios ........................................27
           4.4.1. Association Setup State ............................27
           4.4.2. Association Established State or Steady State ......29
   5. TML Requirements ...............................................31
      5.1. TML Parameterization ......................................34
   6. Message Encapsulation ..........................................35
      6.1. Common Header .............................................35
      6.2. Type Length Value (TLV) Structuring .......................40
           6.2.1. Nested TLVs ........................................41
           6.2.2. Scope of the T in TLV ..............................41
      6.3. ILV .......................................................41
      6.4. Important Protocol Encapsulations .........................42
           6.4.1. Paths ..............................................42
           6.4.2. Keys ...............................................42
           6.4.3. DATA TLVs ..........................................43
           6.4.4. Addressing LFB Entities ............................43
   7. Protocol Construction ..........................................44
      7.1. Discussion on Encoding ....................................48
           7.1.1. Data Packing Rules .................................48
           7.1.2. Path Flags .........................................49
           7.1.3. Relation of Operational Flags with Global
                  Message Flags ......................................49
           7.1.4. Content Path Selection .............................49
           7.1.5. LFBselect-TLV ......................................49
           7.1.6. OPER-TLV ...........................................50
           7.1.7. RESULT TLV .........................................52
           7.1.8. DATA TLV ...........................................55

           7.1.9. SET and GET Relationship ...........................56
      7.2. Protocol Encoding Visualization ...........................56
      7.3. Core ForCES LFBs ..........................................59
           7.3.1. FE Protocol LFB ....................................60
           7.3.2. FE Object LFB ......................................63
      7.4. Semantics of Message Direction ............................63
      7.5. Association Messages ......................................64
           7.5.1. Association Setup Message ..........................64
           7.5.2. Association Setup Response Message .................66
           7.5.3. Association Teardown Message .......................68
      7.6. Configuration Messages ....................................69
           7.6.1. Config Message .....................................69
           7.6.2. Config Response Message ............................71
      7.7. Query Messages ............................................73
           7.7.1. Query Message ......................................73
           7.7.2. Query Response Message .............................75
      7.8. Event Notification Message ................................77
      7.9. Packet Redirect Message ...................................79
      7.10. Heartbeat Message ........................................82
   8. High Availability Support ......................................83
      8.1. Relation with the FE Protocol .............................83
      8.2. Responsibilities for HA ...................................86
   9. Security Considerations ........................................87
      9.1. No Security ...............................................87
           9.1.1. Endpoint Authentication ............................88
           9.1.2. Message Authentication .............................88
      9.2. ForCES PL and TML Security Service ........................88
           9.2.1. Endpoint Authentication Service ....................88
           9.2.2. Message Authentication Service .....................89
           9.2.3. Confidentiality Service ............................89
   10. Acknowledgments ...............................................89
   11. References ....................................................89
      11.1. Normative References .....................................89
      11.2. Informative References ...................................90
   Appendix A.  IANA Considerations ..................................91
     A.1.  Message Type Namespace ....................................91
     A.2.  Operation Selection .......................................92
     A.3.  Header Flags ..............................................93
     A.4.  TLV Type Namespace ........................................93
     A.5.  RESULT-TLV Result Values ..................................94
     A.6.  Association Setup Response ................................94
     A.7.  Association Teardown Message ..............................95
   Appendix B.  ForCES Protocol LFB Schema ...........................96
     B.1.  Capabilities .............................................102
     B.2.  Components ...............................................102
   Appendix C.  Data Encoding Examples ..............................103
   Appendix D.  Use Cases ...........................................107

1.  Introduction

   Forwarding and Control Element Separation (ForCES) defines an
   architectural framework and associated protocols to standardize
   information exchange between the control plane and the forwarding
   plane in a ForCES Network Element (ForCES NE).  RFC 3654 has defined
   the ForCES requirements, and RFC 3746 has defined the ForCES
   framework.  While there may be multiple protocols used within the
   overall ForCES architecture, the terms "ForCES protocol" and
   "protocol" as used in this document refer to the protocol used to
   standardize the information exchange between Control Elements (CEs)
   and Forwarding Elements (FEs) only.

   The ForCES FE model [RFC5812] presents a formal way to define FE
   Logical Function Blocks (LFBs) using XML.  LFB configuration
   components, capabilities, and associated events are defined when the
   LFB is formally created.  The LFBs within the FE are accordingly
   controlled in a standardized way by the ForCES protocol.

   This document defines the ForCES protocol specifications.  The ForCES
   protocol works in a master-slave mode in which FEs are slaves and CEs
   are masters.  The protocol includes commands for transport of LFB
   configuration information, association setup, status, event
   notifications, etc.

   Section 3 provides a glossary of terminology used in the
   specification.

   Section 4 provides an overview of the protocol, including a
   discussion on the protocol framework and descriptions of the Protocol
   Layer (PL), a Transport Mapping Layer (TML), and the ForCES protocol
   mechanisms.  Section 4.4 describes several protocol scenarios and
   includes message exchange descriptions.

   While this document does not define the TML, Section 5 details the
   services that a TML MUST provide (TML requirements).

   The ForCES protocol defines a common header for all protocol
   messages.  The header is defined in Section 6.1, while the protocol
   messages are defined in Section 7.

   Section 8 describes the protocol support for high-availability
   mechanisms including redundancy and fail over.

   Section 9 defines the security mechanisms provided by the PL and TML.

2.  Terminology and Conventions

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.2.  Other Notation

   In Table 1 and Table 2, the following notation is used to indicate
   multiplicity:

      (value)+ .... means "1 or more instances of value"

      (value)* .... means "0 or more instances of value"

2.3.  Integers

   All integers are to be coded as unsigned binary integers of
   appropriate length.

3.  Definitions

   This document follows the terminology defined by the ForCES
   requirements in [RFC3654] and by the ForCES framework in [RFC3746].
   The definitions be are repeated below for clarity.

   Addressable Entity (AE):

   A physical device that is directly addressable given some
   interconnect technology.  For example, on IP networks, it is a device
   that can be reached using an IP address; and on a switch fabric, it
   is a device that can be reached using a switch fabric port number.

   Control Element (CE):

   A logical entity that implements the ForCES protocol and uses it to
   instruct one or more FEs on how to process packets.  CEs handle
   functionality such as the execution of control and signaling
   protocols.

   CE Manager (CEM):

   A logical entity responsible for generic CE management tasks.  It is
   particularly used during the pre-association phase to determine with
   which FE(s) a CE should communicate.  This process is called FE
   discovery and may involve the CE manager learning the capabilities of
   available FEs.

   Data Path:

   A conceptual path taken by packets within the forwarding plane inside
   an FE.

   Forwarding Element (FE):

   A logical entity that implements the ForCES protocol.  FEs use the
   underlying hardware to provide per-packet processing and handling as
   directed/controlled by one or more CEs via the ForCES protocol.

   FE Model:

   A model that describes the logical processing functions of an FE.
   The FE model is defined using Logical Function Blocks (LFBs).

   FE Manager (FEM):

   A logical entity responsible for generic FE management tasks.  It is
   used during the pre-association phase to determine with which CE(s)
   an FE should communicate.  This process is called CE discovery and
   may involve the FE manager learning the capabilities of available
   CEs.  An FE manager may use anything from a static configuration to a
   pre-association phase protocol (see below) to determine which CE(s)
   to use.  Being a logical entity, an FE manager might be physically
   combined with any of the other logical entities such as FEs.

   ForCES Network Element (NE):

   An entity composed of one or more CEs and one or more FEs.  To
   entities outside an NE, the NE represents a single point of
   management.  Similarly, an NE usually hides its internal organization
   from external entities.

   High Touch Capability:

   This term will be used to apply to the capabilities found in some
   forwarders to take action on the contents or headers of a packet
   based on content other than what is found in the IP header.  Examples
   of these capabilities include quality of service (QoS) policies,
   virtual private networks, firewall, and L7 content recognition.

   Inter-FE Topology:

   See FE Topology.

   Intra-FE Topology:

   See LFB Topology.

   LFB (Logical Function Block):

   The basic building block that is operated on by the ForCES protocol.
   The LFB is a well-defined, logically separable functional block that
   resides in an FE and is controlled by the CE via the ForCES protocol.
   The LFB may reside at the FE's data path and process packets or may
   be purely an FE control or configuration entity that is operated on
   by the CE.  Note that the LFB is a functionally accurate abstraction
   of the FE's processing capabilities, but not a hardware-accurate
   representation of the FE implementation.

   FE Topology:

   A representation of how the multiple FEs within a single NE are
   interconnected.  Sometimes this is called inter-FE topology, to be
   distinguished from intra-FE topology (i.e., LFB topology).

   LFB Class and LFB Instance:

   LFBs are categorized by LFB classes.  An LFB instance represents an
   LFB class (or type) existence.  There may be multiple instances of
   the same LFB class (or type) in an FE.  An LFB class is represented
   by an LFB class ID, and an LFB instance is represented by an LFB
   instance ID.  As a result, an LFB class ID associated with an LFB
   instance ID uniquely specifies an LFB existence.

   LFB Meta Data:

   Meta data is used to communicate per-packet state from one LFB to
   another, but is not sent across the network.  The FE model defines
   how such meta data is identified, produced, and consumed by the LFBs.
   It defines the functionality but not how meta data is encoded within
   an implementation.

   LFB Component:

   Operational parameters of the LFBs that must be visible to the CEs
   are conceptualized in the FE model as the LFB components.  The LFB
   components include, for example, flags, single parameter arguments,
   complex arguments, and tables that the CE can read and/or write via
   the ForCES protocol (see below).

   LFB Topology:

   Representation of how the LFB instances are logically interconnected
   and placed along the data path within one FE.  Sometimes it is also
   called intra-FE topology, to be distinguished from inter-FE topology.

   Pre-association Phase:

   The period of time during which an FE manager and a CE manager are
   determining which FE(s) and CE(s) should be part of the same network
   element.

   Post-association Phase:

   The period of time during which an FE knows which CE is to control it
   and vice versa.  This includes the time during which the CE and FE
   are establishing communication with one another.

   ForCES Protocol:

   While there may be multiple protocols used within the overall ForCES
   architecture, the terms "ForCES protocol" and "protocol" refer to the
   Fp reference points in the ForCES framework in [RFC3746].  This
   protocol does not apply to CE-to-CE communication, FE-to-FE
   communication, or communication between FE and CE managers.
   Basically, the ForCES protocol works in a master-slave mode in which
   FEs are slaves and CEs are masters.  This document defines the
   specifications for this ForCES protocol.

   ForCES Protocol Layer (ForCES PL):

   A layer in the ForCES protocol architecture that defines the ForCES
   protocol messages, the protocol state transfer scheme, and the ForCES
   protocol architecture itself (including requirements of ForCES TML as
   shown below).  Specifications of ForCES PL are defined by this
   document.

   ForCES Protocol Transport Mapping Layer (ForCES TML):

   A layer in ForCES protocol architecture that uses the capabilities of
   existing transport protocols to specifically address protocol message
   transportation issues, such as how the protocol messages are mapped
   to different transport media (like TCP, IP, ATM, Ethernet, etc.), and
   how to achieve and implement reliability, multicast, ordering, etc.
   The ForCES TML specifications are detailed in separate ForCES
   documents, one for each TML.

4.  Overview

   The reader is referred to the framework document [RFC3746], and in
   particular, Sections 3 and 4, for an architectural overview and an
   explanation of how the ForCES protocol fits in.  There may be some
   content overlap between the framework document and this section in
   order to provide clarity.  This document is authoritative on the
   protocol, whereas [RFC3746] is authoritative on the architecture.

4.1.  Protocol Framework

   Figure 1 below is reproduced from the framework document for clarity.
   It shows an NE with two CEs and two FEs.

                            ---------------------------------------
                            | ForCES Network Element              |
     --------------   Fc    | --------------      --------------  |
     | CE Manager |---------+-|     CE 1   |------|    CE 2    |  |
     --------------         | |            |  Fr  |            |  |
           |                | --------------      --------------  |
           | Fl             |         |  |    Fp       /          |
           |                |       Fp|  |----------| /           |
           |                |         |             |/            |
           |                |         |             |             |
           |                |         |     Fp     /|----|        |
           |                |         |  /--------/      |        |
     --------------     Ff  | --------------      --------------  |
     | FE Manager |---------+-|     FE 1   |  Fi  |     FE 2   |  |
     --------------         | |            |------|            |  |
                            | --------------      --------------  |
                            |   |  |  |  |          |  |  |  |    |
                            ----+--+--+--+----------+--+--+--+-----
                                |  |  |  |          |  |  |  |
                                |  |  |  |          |  |  |  |
                                  Fi/f                   Fi/f

          Fp: CE-FE interface
          Fi: FE-FE interface
          Fr: CE-CE interface
          Fc: Interface between the CE manager and a CE
          Ff: Interface between the FE manager and an FE
          Fl: Interface between the CE manager and the FE manager
          Fi/f: FE external interface

                  Figure 1: ForCES Architectural Diagram

   The ForCES protocol domain is found in the Fp reference points.  The
   Protocol Element configuration reference points, Fc and Ff, also play
   a role in the booting up of the ForCES protocol.  The protocol
   element configuration (indicated by reference points Fc, Ff, and Fl
   in [RFC3746]) is out of scope of the ForCES protocol but is touched
   on in this document in discussion of FEM and CEM since it is an
   integral part of the protocol pre-association phase.

   Figure 2 below shows further breakdown of the Fp interfaces by means
   of the example of an MPLS QoS-enabled Network Element.

         -------------------------------------------------
         |       |       |       |       |       |       |
         |OSPF   |RIP    |BGP    |RSVP   |LDP    |. . .  |
         |       |       |       |       |       |       |
         -------------------------------------------------    CE
         |               ForCES Interface                |
         -------------------------------------------------
                                 ^   ^
                                 |   |
                         ForCES  |   |data
                         control |   |packets
                         messages|   |(e.g., routing packets)
                                 |   |
                                 v   v
         -------------------------------------------------
         |               ForCES Interface                |
         -------------------------------------------------    FE
         |       |       |       |       |       |       |
         |LPM Fwd|Meter  |Shaper |MPLS   |Classi-|. . .  |
         |       |       |       |       |fier   |       |
         -------------------------------------------------

                 Figure 2: Examples of CE and FE Functions

   The ForCES interface shown in Figure 2 constitutes two pieces: the PL
   and the TML.

   This is depicted in Figure 3 below.

         +------------------------------------------------
         |               CE PL                           |
         +------------------------------------------------
         |              CE TML                           |
         +------------------------------------------------
                                   ^
                                   |
                      ForCES       |   (i.e.,  ForCES data + control
                      PL           |    packets )
                      messages     |
                      over         |
                      specific     |
                      TML          |
                      encaps       |
                      and          |
                      transport    |
                                   |
                                   v
         +------------------------------------------------
         |              FE TML                           |
         +------------------------------------------------
         |               FE PL                           |
         +------------------------------------------------

                        Figure 3: ForCES Interface

   The PL is in fact the ForCES protocol.  Its semantics and message
   layout are defined in this document.  The TML layer is necessary to
   connect two ForCES PLs as shown in Figure 3 above.  The TML is out of
   scope for this document but is within scope of ForCES.  This document
   defines requirements the PL needs the TML to meet.

   Both the PL and the TML are standardized by the IETF.  While only one
   PL is defined, different TMLs are expected to be standardized.  To
   interoperate, the TML at the CE and FE are expected to conform to the
   same definition.

   On transmit, the PL delivers its messages to the TML.  The local TML
   delivers the message to the destination TML.  On receive, the TML
   delivers the message to its destination PL.

4.1.1.  The PL

   The PL is common to all implementations of ForCES and is standardized
   by the IETF as defined in this document.  The PL is responsible for
   associating an FE or CE to an NE.  It is also responsible for tearing

   down such associations.  An FE uses the PL to transmit various
   subscribed-to events to the CE PL as well as to respond to various
   status requests issued from the CE PL.  The CE configures both the FE
   and associated LFBs' operational parameters using the PL.  In
   addition, the CE may send various requests to the FE to activate or
   deactivate it, reconfigure its HA parameterization, subscribe to
   specific events, etc.  More details can be found in Section 7.

4.1.2.  The TML

   The TML transports the PL messages.  The TML is where the issues of
   how to achieve transport-level reliability, congestion control,
   multicast, ordering, etc. are handled.  It is expected that more than
   one TML will be standardized.  The various possible TMLs could vary
   their implementations based on the capabilities of underlying media
   and transport.  However, since each TML is standardized,
   interoperability is guaranteed as long as both endpoints support the
   same TML.  All ForCES protocol layer implementations MUST be portable
   across all TMLs, because all TMLs MUST have the top-edge semantics
   defined in this document.

4.1.3.  The FEM/CEM Interface

   The FEM and CEM components, although valuable in the setup and
   configurations of both the PL and TML, are out of scope of the ForCES
   protocol.  The best way to think of them is as configurations/
   parameterizations for the PL and TML before they become active (or
   even at runtime based on implementation).  In the simplest case, the
   FE or CE reads a static configuration file.  RFC 3746 has a more
   detailed description on how the FEM and CEM could be used.  The pre-
   association phase, where the CEM and FEM can be used, are described
   briefly in Section 4.2.1.

   An example of typical things the FEM/CEM could configure would be
   TML-specific parameterizations such as:

   a.  How the TML connection should happen (for example, what IP
       addresses to use, transport modes, etc.)

   b.  The ID for the FE (FEID) or CE (CEID) (which would also be issued
       during the pre-association phase)

   c.  Security parameterization such as keys, etc.

   d.  Connection association parameters

   An example of connection association parameters might be:

   o  simple parameters: send up to 3 association messages every 1
      second

   o  complex parameters: send up to 4 association messages with
      increasing exponential timeout

4.2.  ForCES Protocol Phases

   ForCES, in relation to NEs, involves two phases: the pre-association
   phase where configuration/initialization/bootup of the TML and PL
   layer happens, and the post-association phase where the ForCES
   protocol operates to manipulate the parameters of the FEs.

                       CE sends Association Setup
           +---->--->------------>---->---->---->------->----+
           |                                                 Y
           ^                                                 |
           |                                                 Y
       +---+-------+                                     +-------------+
       |FE pre-    |                                     | FE post-    |
       |association|    CE sends Association Teardown    | association |
       |phase      |<------- <------<-----<------<-------+ phase       |
       |           |                                     |             |
       +-----------+                                     +-------------+
             ^                                               Y
             |                                               |
             +-<---<------<-----<------<----<---------<------+
                           FE loses association

                     Figure 4: The FE Protocol Phases

   In the mandated case, once associated, the FE may forward packets
   depending on the configuration of its specific LFBs.  An FE that is
   associated to a CE will continue sending packets until it receives an
   Association Teardown Message or until it loses association.  An
   unassociated FE MAY continue sending packets when it has a high
   availability capability.  The extra details are explained in
   Section 8 and not discussed here to allow for a clear explanation of
   the basics.

   The FE state transitions are controlled by means of the FE Object LFB
   FEState component, which is defined in [RFC5812], Section 5.1, and
   also explained in Section 7.3.2.

   The FE initializes in the FEState OperDisable.  When the FE is ready
   to process packets in the data path, it transitions itself to the
   OperEnable state.

   The CE may decide to pause the FE after it already came up as
   OperEnable.  It does this by setting the FEState to AdminDisable.
   The FE stays in the AdminDisable state until it is explicitly
   configured by the CE to transition to the OperEnable state.

   When the FE loses its association with the CE, it may go into the
   pre-association phase depending on the programmed policy.  For the FE
   to properly complete the transition to the AdminDisable state, it
   MUST stop packet forwarding and this may impact multiple LFBS.  How
   this is achieved is outside the scope of this specification.

4.2.1.  Pre-association

   The ForCES interface is configured during the pre-association phase.
   In a simple setup, the configuration is static and is typically read
   from a saved configuration file.  All the parameters for the
   association phase are well known after the pre-association phase is
   complete.  A protocol such as DHCP may be used to retrieve the
   configuration parameters instead of reading them from a static
   configuration file.  Note, this will still be considered static pre-
   association.  Dynamic configuration may also happen using the Fc, Ff,
   and Fl reference points (refer to [RFC3746]).  Vendors may use their
   own proprietary service discovery protocol to pass the parameters.
   Essentially, only guidelines are provided here and the details are
   left to the implementation.

   The following are scenarios reproduced from the framework document to
   show a pre-association example.

      <----Ff ref pt--->              <--Fc ref pt------->
      FE Manager      FE                CE Manager    CE
       |              |                 |             |
       |              |                 |             |
    (security exchange)               (security exchange)
      1|<------------>| authentication 1|<----------->|authentication
       |              |                 |             |
     (FE ID, components)              (CE ID, components)
      2|<-------------| request        2|<------------|request
       |              |                 |             |
      3|------------->| response       3|------------>|response
      (corresponding CE ID)          (corresponding FE ID)
       |              |                 |             |
       |              |                 |             |

        Figure 5: Examples of a Message Exchange over the Ff and Fc
                             Reference Points

      <-----------Fl ref pt-------------->            |

      FE Manager      FE               CE Manager     CE
       |              |                 |             |
       |              |                 |             |
      (security exchange)               |             |
      1|<------------------------------>|             |
       |              |                 |             |
      (a list of CEs and their components)            |
      2|<-------------------------------|             |
       |              |                 |             |
      (a list of FEs and their components)            |
      3|------------------------------->|             |
       |              |                 |             |
       |              |                 |             |

    Figure 6: Example of a Message Exchange over the Fl Reference Point

   Before the transition to the association phase, the FEM will have
   established contact with a CEM component.  Initialization of the
   ForCES interface will have completed, and authentication as well as
   capability discovery may be complete.  Both the FE and CE would have
   the necessary information for connecting to each other for
   configuration, accounting, identification, and authentication
   purposes.  To summarize, at the completion of this stage both sides
   have all the necessary protocol parameters such as timers, etc.  The
   Fl reference point may continue to operate during the association
   phase and may be used to force a disassociation of an FE or CE.  The
   specific interactions of the CEM and the FEM that are part of the

   pre-association phase are out of scope; for this reason, these
   details are not discussed any further in this specification.  The
   reader is referred to the framework document [RFC3746] for a slightly
   more detailed discussion.

4.2.2.  Post-association

   In this phase, the FE and CE components communicate with each other
   using the ForCES protocol (PL over TML) as defined in this document.
   There are three sub-phases:

   o  Association Setup Stage

   o  Established Stage

   o  Association Lost Stage

4.2.2.1.  Association Setup Stage

   The FE attempts to join the NE.  The FE may be rejected or accepted.
   Once granted access into the NE, capabilities exchange happens with
   the CE querying the FE.  Once the CE has the FE capability
   information, the CE can offer an initial configuration (possibly to
   restore state) and can query certain components within either an LFB
   or the FE itself.

   More details are provided in Section 4.4.

   On successful completion of this stage, the FE joins the NE and is
   moved to the Established Stage.

4.2.2.2.  Established Stage

   In this stage, the FE is continuously updated or queried.  The FE may
   also send asynchronous event notifications to the CE or synchronous
   heartbeat notifications if programmed to do so.  This stage continues
   until a termination occurs, either due to loss of connectivity or due
   to a termination initiated by either the CE or the FE.

   Refer to the section on protocol scenarios, Section 4.4, for more
   details.

4.2.2.3.  Association Lost Stage

   In this stage, both or either the CE or FE declare the other side is
   no longer associated.  The disconnection could be initiated by either
   party for administrative purposes but may also be driven by
   operational reasons such as loss of connectivity.

   A core LFB known as the FE Protocol Object (FEPO) is defined (refer
   to Appendix B and Section 7.3.1).  FEPO defines various timers that
   can be used in conjunction with a traffic-sensitive heartbeat
   mechanism (Section 4.3.3) to detect loss of connectivity.

   The loss of connectivity between TMLs does not indicate a loss of
   association between respective PL layers.  If the TML cannot repair
   the transport loss before the programmed FEPO timer thresholds
   associated with the FE is exceeded, then the association between the
   respective PL layers will be lost.

   FEPO defines several policies that can be programmed to define
   behavior upon a detected loss of association.  The FEPO's programmed
   CE failover policy (refer to Sections 8, 7.3.1, 4.3.3, and B) defines
   what takes place upon loss of association.

   For this version of the protocol (as defined in this document), the
   FE, upon re-association, MUST discard any state it has as invalid and
   retrieve new state.  This approach is motivated by a desire for
   simplicity (as opposed to efficiency).

4.3.  Protocol Mechanisms

   Various semantics are exposed to the protocol users via the PL header
   including transaction capabilities, atomicity of transactions, two-
   phase commits, batching/parallelization, high availability, and
   failover as well as command pipelines.

   The EM (Execution Mode) flag, AT (Atomic Transaction) flag, and TP
   (Transaction Phase) flag as defined in the common header
   (Section 6.1) are relevant to these mechanisms.

4.3.1.  Transactions, Atomicity, Execution, and Responses

   In the master-slave relationship, the CE instructs one or more FEs on
   how to execute operations and how to report the results.

   This section details the different modes of execution that a CE can
   order the FE(s) to perform, as defined in Section 4.3.1.1.  It also
   describes the different modes a CE can ask the FE(s) to use for
   formatting the responses after processing the operations as
   requested.  These modes relate to the transactional two-phase commit
   operations.

4.3.1.1.  Execution

   There are 3 execution modes that can be requested for a batch of
   operations spanning one or more LFB selectors (refer to
   Section 7.1.5) in one protocol message.  The EM flag defined in the
   common header (Section 6.1) selects the execution mode for a protocol
   message, as below:

   a.  execute-all-or-none

   b.  continue-execute-on-failure

   c.  execute-until-failure

4.3.1.1.1.  execute-all-or-none

   When set to this mode of execution, independent operations in a
   message MAY be targeted at one or more LFB selectors within an FE.
   All these operations are executed serially, and the FE MUST have no
   execution failure for any of the operations.  If any operation fails
   to execute, then all the previous ones that have been executed prior
   to the failure will need to be undone.  That is, there is rollback
   for this mode of operation.

   Refer to Section 4.3.1.2.2 for how this mode is used in cases of
   transactions.  In such a case, no operation is executed unless a
   commit is issued by the CE.

   Care should be taken on how this mode is used because a mis-
   configuration could result in traffic losses.  To add certainty to
   the success of an operation, one should use this mode in a
   transactional operation as described in Section 4.3.1.2.2

4.3.1.1.2.  continue-execute-on-failure

   If several independent operations are targeted at one or more LFB
   selectors, execution continues for all operations at the FE even if
   one or more operations fail.

4.3.1.1.3.  execute-until-failure

   In this mode, all operations are executed on the FE sequentially
   until the first failure.  The rest of the operations are not executed
   but operations already completed are not undone.  That is, there is
   no rollback in this mode of operation.

4.3.1.2.  Transaction and Atomicity

4.3.1.2.1.  Transaction Definition

   A transaction is defined as a collection of one or more ForCES
   operations within one or more PL messages that MUST meet the ACIDity
   properties [ACID], defined as:

   Atomicity:   In a transaction involving two or more discrete pieces
                of information, either all of the pieces are committed
                or none are.

   Consistency: A transaction either creates a new and valid state of
                data or, if any failure occurs, returns all data to the
                state it was in before the transaction was started.

   Isolation:   A transaction in process and not yet committed MUST
                remain isolated from any other transaction.

   Durability:  Committed data is saved by the system such that, even in
                the event of a failure and a system restart, the data is
                available in its correct state.

   There are cases where the CE knows exact memory and implementation
   details of the FE such as in the case of an FE-CE pair from the same
   vendor where the FE-CE pair is tightly coupled.  In such a case, the
   transactional operations may be simplified further by extra
   computation at the CE.  This view is not discussed further other than
   to mention that it is not disallowed.

   As defined above, a transaction is always atomic and MAY be

   a.  Within an FE alone
       Example: updating multiple tables that are dependent on each
       other.  If updating one fails, then any that were already updated
       MUST be undone.

   b.  Distributed across the NE
       Example: updating table(s) that are inter-dependent across
       several FEs (such as L3 forwarding-related tables).

4.3.1.2.2.  Transaction Protocol

   By use of the execution mode, as defined in Section 4.3.1.1, the
   protocol has provided a mechanism for transactional operations within
   one stand-alone message.  The 'execute-all-or-none' mode can meet the
   ACID requirements.

   For transactional operations of multiple messages within one FE or
   across FEs, a classical transactional protocol known as two-phase
   commit (2PC) [2PCREF] is supported by the protocol to achieve the
   transactional operations utilizing Config messages (Section 7.6.1).

   The COMMIT and TRCOMP operations in conjunction with the AT and the
   TP flags in the common header (Section 6.1) are provided for 2PC-
   based transactional operations spanning multiple messages.

   The AT flag, when set, indicates that this message belongs to an
   Atomic Transaction.  All messages for a transaction operation MUST
   have the AT flag set.  If not set, it means that the message is a
   stand-alone message and does not participate in any transaction
   operation that spans multiple messages.

   The TP flag indicates the Transaction Phase to which this message
   belongs.  There are 4 possible phases for a transactional operation
   known as:

      SOT (Start of Transaction)

      MOT (Middle of Transaction)

      EOT (End of Transaction)

      ABT (Abort)

   The COMMIT operation is used by the CE to signal to the FE(s) to
   commit a transaction.  When used with an ABT TP flag, the COMMIT
   operation signals the FE(s) to roll back (i.e., un-COMMIT) a
   previously committed transaction.

   The TRCOMP operation is a small addition to the classical 2PC
   approach.  TRCOMP is sent by the CE to signal to the FE(s) that the
   transaction they have COMMITed is now over.  This allows the FE(s) an
   opportunity to clear state they may have kept around to perform a
   roll back (if it became necessary).

   A transaction operation is started with a message in which the TP
   flag is set to Start of Transaction (SOT).  Multi-part messages,
   after the first one, are indicated by the Middle of Transaction (MOT)
   flag.  All messages from the CE MUST set the AlwaysACK flag
   (Section 6) to solicit responses from the FE(s).

   Before the CE issues a commit (described further below), the FE MUST
   only validate that the operation can be executed but not execute it.

      Any failure notified by an FE causes the CE to abort the
      transaction on all FEs involved in the transaction.  This is
      achieved by sending a Config message with an ABT flag and a COMMIT
      operation.

      If there are no failures by any participating FE, the transaction
      commitment phase is signaled from the CE to the FE by an End of
      Transaction (EOT) configuration message with a COMMIT operation.

   The FE MUST respond to the CE's EOT message.  There are two possible
   failure scenarios in which the CE MUST abort the transaction (as
   described above):

   a.  If any participating FE responds with a failure message in
       relation to the transaction.

   b.  If no response is received from a participating FE within a
       specified timeout.

   If all participating FEs respond with a success indicator within the
   expected time, then the CE MUST issue a TRCOMP operation to all
   participating FEs.  An FE MUST NOT respond to a TRCOMP.

   Note that a transactional operation is generically atomic; therefore,
   it requires that the execution modes of all messages in a transaction
   operation should always be kept the same and be set to 'execute-all-
   or-none'.  If the EM flag is set to other execution modes, it will
   result in a transaction failure.

   As noted above, a transaction may span multiple messages.  It is up
   to the CE to keep track of the different outstanding messages making
   up a transaction.  As an example, the correlator field could be used
   to mark transactions and a sequence field to label the different
   messages within the same atomic transaction, but this is out of scope
   and up to implementations.

4.3.1.2.3.  Recovery

   Any of the participating FEs or the CE or the associations between
   them may fail after the EOT Response message has been sent by the FE
   but before the CE has received all the responses, e.g., if the EOT
   response never reaches the CE.

   In this protocol revision, as indicated in Section 4.2.2.3, an FE
   losing an association would be required to get entirely new state
   from the newly associated CE upon a re-association.  Although this
   approach is simplistic and provides likeliness of losing data path

   traffic, it is a design choice to avoid the additional complexity of
   managing graceful restarts.  The HA mechanisms (Section 8) are
   provided to allow for a continuous operation in case of FE failures.

   Flexibility is provided on how to react when an FE loses association.
   This is dictated by the CE failover policy (refer to Section 8 and
   Section 7.3).

4.3.1.2.4.  Transaction Messaging Example

   This section illustrates an example of how a successful two-phase
   commit between a CE and an FE would look in the simple case.

         FE PL                                                  CE PL

           |                                                      |
           | (1) Config, SOT,AT, EM=All-or-None, OP= SET/DEL,etc  |
           |<-----------------------------------------------------|
           |                                                      |
           | (2) ACKnowledge                                      |
           |----------------------------------------------------->|
           |                                                      |
           | (3) Config, MOT,AT, EM=All-or-None, OP= SET/DEL,etc  |
           |<-----------------------------------------------------|
           |                                                      |
           | (4) ACKnowledge                                      |
           |----------------------------------------------------->|
           |                                                      |
           | (5) Config, MOT,AT, EM=All-or-None, OP= SET/DEL,etc  |
           |<-----------------------------------------------------|
           |                                                      |
           | (6) ACKnowledge                                      |
           |----------------------------------------------------->|
           .                                                      .
           .                                                      .
           .                                                      .
           .                                                      .
           |                                                      |
           | (N) Config, EOT,AT, EM=All-or-None, OP= COMMIT       |
           |<-----------------------------------------------------|
           |                                                      |
           | (N+1)Config-response, ACKnowledge, OP=COMMIT-RESPONSE|
           |----------------------------------------------------->|
           |                                                      |
           | (N+2) Config, OP=TRCOMP                              |
           |<-----------------------------------------------------|

                  Figure 7: Example of a Two-Phase Commit

   For the scenario illustrated above:

   o  In step 1, the CE issues a Config message with an operation of
      choice like a DEL or SET.  The transaction flags are set to
      indicate a Start of Transaction (SOT), Atomic Transaction (AT),
      and execute-all-or-none.

   o  The FE validates that it can execute the request successfully and
      then issues an acknowledgment back to the CE in step 2.

   o  In step 3, the same sort of construct as in step 1 is repeated by
      the CE with the transaction flag changed to Middle of Transaction
      (MOT).

   o  The FE validates that it can execute the request successfully and
      then issues an acknowledgment back to the CE in step 4.

   o  The CE-FE exchange continues in the same manner until all the
      operations and their parameters are transferred to the FE.  This
      happens in step (N-1).

   o  In step N, the CE issues a commit.  A commit is a Config message
      with an operation of type COMMIT.  The transaction flag is set to
      End of Transaction (EOT).  Essentially, this is an "empty" message
      asking the FE to execute all the operations it has gathered since
      the beginning of the transaction (message #1).

   o  The FE at this point executes the full transaction.  It then
      issues an acknowledgment back to the CE in step (N+1) that
      contains a COMMIT-RESPONSE.

   o  The CE in this case has the simple task of issuing a TRCOMP
      operation to the FE in step (N+2).

4.3.2.  Scalability

   It is desirable that the PL not become the bottleneck when larger
   bandwidth pipes become available.  To pick a hypothetical example in
   today's terms, if a 100-Gbps pipe is available and there is
   sufficient work, then the PL should be able to take advantage of this
   and use all of the 100-Gbps pipe.  Two mechanisms have been provided
   to achieve this.  The first one is batching and the second one is a
   command pipeline.

   Batching is the ability to send multiple commands (such as Config) in
   one Protocol Data Unit (PDU).  The size of the batch will be affected
   by, among other things, the path MTU.  The commands may be part of
   the same transaction or may be part of unrelated transactions that
   are independent of each other.

   Command pipelining allows for pipelining of independent transactions
   that do not affect each other.  Each independent transaction could
   consist of one or more batches.

4.3.2.1.  Batching

   There are several batching levels at different protocol hierarchies.

   o  Multiple PL PDUs can be aggregated under one TML message.

   o  Multiple LFB classes and instances (as indicated in the LFB
      selector) can be addressed within one PL PDU.

   o  Multiple operations can be addressed to a single LFB class and
      instance.

4.3.2.2.  Command Pipelining

   The protocol allows any number of messages to be issued by the CE
   before the corresponding acknowledgments (if requested) have been
   returned by the FE.  Hence, pipelining is inherently supported by the
   protocol.  Matching responses with requests messages can be done
   using the correlator field in the message header.

4.3.3.  Heartbeat Mechanism

   Heartbeats (HBs) between FEs and CEs are traffic sensitive.  An HB is
   sent only if no PL traffic is sent between the CE and FE within a
   configured interval.  This has the effect of reducing the amount of
   HB traffic in the case of busy PL periods.

   An HB can be sourced by either the CE or FE.  When sourced by the CE,
   a response can be requested (similar to the ICMP ping protocol).  The
   FE can only generate HBs in the case of being configured to do so by
   the CE.  Refer to Section 7.3.1 and Section 7.10 for details.

4.3.4.  FE Object and FE Protocol LFBs

   All PL messages operate on LFB constructs, as this provides more
   flexibility for future enhancements.  This means that maintenance and
   configurability of FEs, NE, and the ForCES protocol itself MUST be
   expressed in terms of this LFB architecture.  For this reason,
   special LFBs are created to accommodate this need.

   In addition, this shows how the ForCES protocol itself can be
   controlled by the very same type of structures (LFBs) it uses to
   control functions such as IP forwarding, filtering, etc.

   To achieve this, the following specialized LFBs are introduced:

   o  FE Protocol LFB, which is used to control the ForCES protocol.

   o  FE Object LFB, which is used to control components relative to the
      FE itself.  Such components include FEState [RFC5812], vendor,
      etc.

   These LFBs are detailed in Section 7.3.

4.4.  Protocol Scenarios

   This section provides a very high level description of sample message
   sequences between a CE and an FE.  For protocol message encoding
   refer to Section 6.1, and for the semantics of the protocol refer to
   Section 4.3.

4.4.1.  Association Setup State

   The associations among CEs and FEs are initiated via the Association
   Setup message from the FE.  If a Setup Request is granted by the CE,
   a successful Setup Response message is sent to the FE.  If CEs and
   FEs are operating in an insecure environment, then the security
   associations have to be established between them before any
   association messages can be exchanged.  The TML MUST take care of
   establishing any security associations.

   This is typically followed by capability query, topology query, etc.
   When the FE is ready to start processing the data path, it sets the
   FEO FEState component to OperEnable (refer to [RFC5812] for details)
   and reports it to the CE as such when it is first queried.
   Typically, the FE is expected to be ready to process the data path
   before it associates, but there may be rare cases where it needs time
   do some pre-processing -- in such a case, the FE will start in the
   OperDisable state and when it is ready will transition to the
   OperEnable state.  An example of an FE starting in OperDisable then

   transitioning to OperEnable is illustrated in Figure 8.  The CE could
   at any time also disable the FE's data path operations by setting the
   FEState to AdminDisable.  The FE MUST NOT process packets during this
   state unless the CE sets the state back to OperEnable.  These
   sequences of messages are illustrated in Figure 8 below.

           FE PL                  CE PL

             |                       |
             |   Asso Setup Req      |
             |---------------------->|
             |                       |
             |   Asso Setup Resp     |
             |<----------------------|
             |                       |
             | LFBx Query capability |
             |<----------------------|
             |                       |
             | LFBx Query Resp       |
             |---------------------->|
             |                       |
             | FEO Query (Topology)  |
             |<----------------------|
             |                       |
             | FEO Query Resp        |
             |---------------------->|
             |                       |
             | FEO OperEnable Event  |
             |---------------------->|
             |                       |
             |  Config FEO Adminup   |
             |<----------------------|
             |                       |
             | FEO Config-Resp       |
             |---------------------->|
             |                       |

   Figure 8: Message Exchange between CE and FE to Establish
   an NE Association

   On successful completion of this state, the FE joins the NE.

4.4.2.  Association Established State or Steady State

   In this state, the FE is continuously updated or queried.  The FE may
   also send asynchronous event notifications to the CE, synchronous
   Heartbeat messages, or Packet Redirect message to the CE.  This
   continues until a termination (or deactivation) is initiated by
   either the CE or FE.  Figure 9 below, helps illustrate this state.

           FE PL                          CE PL

             |                              |
             |    Heartbeat                 |
             |<---------------------------->|
             |                              |
             |   Heartbeat                  |
             |----------------------------->|
             |                              |
             | Config-set LFBy (Event sub.) |
             |<-----------------------------|
             |                              |
             |     Config Resp LFBy         |
             |----------------------------->|
             |                              |
             |  Config-set LFBx Component   |
             |<-----------------------------|
             |                              |
             |     Config Resp  LFBx        |
             |----------------------------->|
             |                              |
             |Config-Query LFBz (Stats)     |
             |<--------------------------- -|
             |                              |
             |    Query Resp LFBz           |
             |----------------------------->|
             |                              |
             |    FE Event Report           |
             |----------------------------->|
             |                              |
             |  Config-Del LFBx Component   |
             |<-----------------------------|
             |                              |
             |     Config Resp LFBx         |
             |----------------------------->|
             |                              |
             |    Packet Redirect LFBx      |
             |----------------------------->|
             |                              |
             |    Heartbeat                 |
             |<-----------------------------|
             .                              .
             .                              .
             |                              |

   Figure 9: Message Exchange between CE and FE during
   Steady-State Communication

   Note that the sequence of messages shown in the figure serve only as
   examples and the message exchange sequences could be different from
   what is shown in the figure.  Also, note that the protocol scenarios
   described in this section do not include all the different message
   exchanges that would take place during failover.  That is described
   in the HA section (Section 8).

5.  TML Requirements

   The requirements below are expected to be met by the TML.  This text
   does not define how such mechanisms are delivered.  As an example,
   the mechanisms to meet the requirements could be defined to be
   delivered via hardware or between 2 or more TML software processes on
   different CEs or FEs in protocol-level schemes.

   Each TML MUST describe how it contributes to achieving the listed
   ForCES requirements.  If for any reason a TML does not provide a
   service listed below, a justification needs to be provided.

   Implementations that support the ForCES protocol specification MUST
   implement [RFC5811].  Note that additional TMLs might be specified in
   the future, and if a new TML defined in the future that meets the
   requirements listed here proves to be better, then the "MUST
   implement TML" may be redefined.

   1.  Reliability

       Various ForCES messages will require varying degrees of reliable
       delivery via the TML.  It is the TML's responsibility to provide
       these shades of reliability and describe how the different ForCES
       messages map to reliability.

       The most common level of reliability is what we refer to as
       strict or robust reliability in which we mean no losses,
       corruption, or re-ordering of information being transported while
       ensuring message delivery in a timely fashion.

       Payloads such as configuration from a CE and its response from an
       FE are mission critical and must be delivered in a robust
       reliable fashion.  Thus, for information of this sort, the TML
       MUST either provide built-in protocol mechanisms or use a
       reliable transport protocol for achieving robust/strict
       reliability.

       Some information or payloads, such as redirected packets or
       packet sampling, may not require robust reliability (can tolerate
       some degree of losses).  For information of this sort, the TML
       could define to use a mechanism that is not strictly reliable
       (while conforming to other TML requirements such as congestion
       control).

       Some information or payloads, such as heartbeat packets, may
       prefer timeliness over reliable delivery.  For information of
       this sort, the TML could define to use a mechanism that is not
       strictly reliable (while conforming to other TML requirements
       such as congestion control).

   2.  Security

       TML provides security services to the ForCES PL.  Because a
       ForCES PL is used to operate an NE, attacks designed to confuse,
       disable, or take information from a ForCES-based NE may be seen
       as a prime objective during a network attack.

       An attacker in a position to inject false messages into a PL
       stream can affect either the FE's treatment of the data path (for
       example, by falsifying control data reported as coming from the
       CE) or the CE itself (by modifying events or responses reported
       as coming from the FE).  For this reason, CE and FE node
       authentication and TML message authentication are important.

       The PL messages may also contain information of value to an
       attacker, including information about the configuration of the
       network, encryption keys, and other sensitive control data, so
       care must be taken to confine their visibility to authorized
       users.

       *  The TML MUST provide a mechanism to authenticate ForCES CEs
          and FEs, in order to prevent the participation of unauthorized
          CEs and unauthorized FEs in the control and data path
          processing of a ForCES NE.

       *  The TML SHOULD provide a mechanism to ensure message
          authentication of PL data transferred from the CE to FE (and
          vice versa), in order to prevent the injection of incorrect
          data into PL messages.

       *  The TML SHOULD provide a mechanism to ensure the
          confidentiality of data transferred from the ForCES PL, in
          order to prevent disclosure of PL-level information
          transported via the TML.

       The TML SHOULD provide these services by employing TLS or IPsec.

   3.  Congestion control

       The transport congestion control scheme used by the TML needs to
       be defined.  The congestion control mechanism defined by the TML
       MUST prevent transport congestive collapse [RFC2914] on either
       the FE or CE side.

   4.  Uni/multi/broadcast addressing/delivery, if any

       If there is any mapping between PL- and TML-level uni/multi/
       broadcast addressing, it needs to be defined.

   5.  HA decisions

       It is expected that availability of transport links is the TML's
       responsibility.  However, based upon its configuration, the PL
       may wish to participate in link failover schemes and therefore
       the TML MUST support this capability.

       Please refer to Section 8 for details.

   6.  Encapsulations used

       Different types of TMLs will encapsulate the PL messages on
       different types of headers.  The TML needs to specify the
       encapsulation used.

   7.  Prioritization

       It is expected that the TML will be able to handle up to 8
       priority levels needed by the PL and will provide preferential
       treatment.

       While the TML needs to define how this is achieved, it should be
       noted that the requirement for supporting up to 8 priority levels
       does not mean that the underlying TML MUST be capable of
       providing up to 8 actual priority levels.  In the event that the
       underlying TML layer does not have support for 8 priority levels,
       the supported priority levels should be divided between the
       available TML priority levels.  For example, if the TML only
       supports 2 priority levels, 0-3 could go in one TML priority
       level, while 4-7 could go in the other.

       The TML MUST NOT re-order config packets with the same priority.

   8.  Node Overload Prevention

       The TML MUST define mechanisms it uses to help prevent node
       overload.

       Overload results in starvation of node compute cycles and/or
       bandwidth resources, which reduces the operational capacity of a
       ForCES NE.  NE node overload could be deliberately instigated by
       a hostile node to attack a ForCES NE and create a denial of
       service (DoS).  It could also be created by a variety of other
       reasons such as large control protocol updates (e.g., BGP flaps),
       which consequently cause a high frequency of CE to FE table
       updates, HA failovers, or component failures, which migrate an FE
       or CE load overwhelming the new CE or FE, etc.  Although the
       environments under which SIP and ForCES operate are different,
       [RFC5390] provides a good guide to generic node requirements one
       needs to guard for.

       A ForCES node CPU may be overwhelmed because the incoming packet
       rate is higher than it can keep up with -- in such a case, a
       node's transport queues grow and transport congestion
       subsequently follows.  A ForCES node CPU may also be adversely
       overloaded with very few packets, i.e., no transport congestion
       at all (e.g., a in a DoS attack against a table hashing algorithm
       that overflows the table and/or keeps the CPU busy so it does not
       process other tasks).  The TML node overload solution specified
       MUST address both types of node overload scenarios.

5.1.  TML Parameterization

   It is expected that it should be possible to use a configuration
   reference point, such as the FEM or the CEM, to configure the TML.

   Some of the configured parameters may include:

   o  PL ID

   o  Connection Type and associated data.  For example, if a TML uses
      IP/TCP/UDP, then parameters such as TCP and UDP port and IP
      addresses need to be configured.

   o  Number of transport connections

   o  Connection capability, such as bandwidth, etc.

   o  Allowed/supported connection QoS policy (or congestion control
      policy)

6.  Message Encapsulation

   All PL PDUs start with a common header Section 6.1 followed by one or
   more TLVs Section 6.2, which may nest other TLVs Section 6.2.1.  All
   fields are in network byte order.

6.1.  Common Header

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |version| rsvd  | Message Type  |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Source ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Destination ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Correlator[63:32]                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Correlator[31:0]                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Flags                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 10: Common Header

   The message is 32-bit aligned.

   Version (4 bits):
      Version number.  Current version is 1.

   rsvd (4 bits):
      Unused at this point.  A receiver should not interpret this field.
      Senders MUST set it to zero and receivers MUST ignore this field.

   Message Type (8 bits):
      Commands are defined in Section 7.

   Length (16 bits):
      length of header + the rest of the message in DWORDS (4-byte
      increments).

   Source ID  (32 bits):

   Dest ID (32 bits):

      *   Each of the source and destination IDs are 32-bit IDs that are
          unique NE-wide and that identify the termination points of a
          ForCES PL message.

      *   IDs allow multi/broad/unicast addressing with the following
          approach:

          a.  A split address space is used to distinguish FEs from CEs.
              Even though in a large NE there are typically two or more
              orders of magnitude of more FEs than CEs, the address
              space is split uniformly for simplicity.

          b.  The address space allows up to 2^30 (over a billion) CEs
              and the same amount of FEs.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |TS |                           sub-ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 11: ForCES ID Format

           c.  The 2 most significant bits called Type Switch (TS) are
             used to split the ID space as follows:

   TS        Corresponding ID range       Assignment
   --        ----------------------       ----------
   0b00      0x00000000 to 0x3FFFFFFF     FE IDs (2^30)
   0b01      0x40000000 to 0x7FFFFFFF     CE IDs (2^30)
   0b10      0x80000000 to 0xBFFFFFFF     reserved
   0b11      0xC0000000 to 0xFFFFFFEF     multicast IDs (2^30 - 16)
   0b11      0xFFFFFFF0 to 0xFFFFFFFC     reserved
   0b11      0xFFFFFFFD                   all CEs broadcast
   0b11      0xFFFFFFFE                   all FEs broadcast
   0b11      0xFFFFFFFF                   all FEs and CEs (NE) broadcast

             Figure 12: Type Switch ID Space

      *   Multicast or broadcast IDs are used to group endpoints (such
          as CEs and FEs).  As an example, one could group FEs in some
          functional group, by assigning a multicast ID.  Likewise,
          subgroups of CEs that act, for instance, in a back-up mode may
          be assigned a multicast ID to hide them from the FE.

          +   Multicast IDs can be used for both source or destination
              IDs.

          +   Broadcast IDs can be used only for destination IDs.

      *   This document does not discuss how a particular multicast ID
          is associated to a given group though it could be done via
          configuration process.  The list of IDs an FE owns or is part
          of are listed on the FE Object LFB.

   Correlator (64 bits):

      This field is set by the CE to correlate ForCES Request messages
      with the corresponding Response messages from the FE.
      Essentially, it is a cookie.  The correlator is handled
      transparently by the FE, i.e., for a particular Request message
      the FE MUST assign the same correlator value in the corresponding
      Response message.  In the case where the message from the CE does
      not elicit a response, this field may not be useful.

      The correlator field could be used in many implementations in
      specific ways by the CE.  For example, the CE could split the
      correlator into a 32-bit transactional identifier and 32-bit
      message sequence identifier.  Another example is a 64-bit pointer
      to a context block.  All such implementation-specific uses of the
      correlator are outside the scope of this specification.

      It should be noted that the correlator is transmitted on the
      network as if it were a 64-bit unsigned integer with the leftmost
      or most significant octet (bits 63-56) transmitted first.

      Whenever the correlator field is not relevant, because no message
      is expected, the correlator field is set to 0.

   Flags (32 bits):
   Identified so far:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |     |     |   | |   |                                     |
   |ACK| Pri |Rsr  |EM |A|TP |     Reserved                        |
   |   |     | vd. |   |T|   |                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 13: Header Flags

   - ACK: ACK indicator (2 bits)

   The ACK indicator flag is only used by the CE when sending a Config
   message (Section 7.6.1) or an HB message (Section 7.10) to indicate
   to the message receiver whether or not a response is required by the
   sender.  Note that for all other messages than the Config message or
   the HB message this flag MUST be ignored.

   The flag values are defined as follows:

      'NoACK' (0b00) - to indicate that the message receiver MUST NOT
      send any Response message back to this message sender.

      'SuccessACK'(0b01) - to indicate that the message receiver MUST
      send a Response message back only when the message has been
      successfully processed by the receiver.

      'FailureACK'(0b10) - to indicate that the message receiver MUST
      send a Response message back only when there is failure by the
      receiver in processing (executing) the message.  In other words,
      if the message can be processed successfully, the sender will not
      expect any response from the receiver.

      'AlwaysACK' (0b11) - to indicate that the message receiver MUST
      send a Response message.

   Note that in above definitions, the term success implies a complete
   execution without any failure of the message.  Anything else than a
   complete successful execution is defined as a failure for the message
   processing.  As a result, for the execution modes (defined in
   Section 4.3.1.1) like execute-all-or-none, execute-until-failure, and
   continue-execute-on-failure, if any single operation among several
   operations in the same message fails, it will be treated as a failure
   and result in a response if the ACK indicator has been set to
   'FailureACK' or 'AlwaysACK'.

   Also note that, other than in Config and HB messages, requirements
   for responses of messages are all given in a default way rather than
   by ACK flags.  The default requirements of these messages and the
   expected responses are summarized below.  Detailed descriptions can
   be found in the individual message definitions:

           +   Association Setup message always expects a response.

           +   Association Teardown Message, and Packet Redirect
               message, never expect responses.

           +   Query message always expects a response.

           +   Response message never expects further responses.

   - Pri: Priority (3 bits)

   ForCES protocol defines 8 different levels of priority (0-7).  The
   priority level can be used to distinguish between different protocol
   message types as well as between the same message type.  The higher
   the priority value, the more important the PDU is.  For example, the
   REDIRECT packet message could have different priorities to
   distinguish between routing protocol packets and ARP packets being
   redirected from FE to CE.  The normal priority level is 1.  The
   different priorities imply messages could be re-ordered; however,
   re-ordering is undesirable when it comes to a set of messages within
   a transaction and caution should be exercised to avoid this.

   - EM: Execution Mode (2 bits)

   There are 3 execution modes; refer to Section 4.3.1.1 for details.

      Reserved..................... (0b00)

      `execute-all-or-none` ....... (0b01)

      `execute-until-failure` ..... (0b10)

      `continue-execute-on-failure` (0b11)

   - AT:  Atomic Transaction (1 bit)

   This flag indicates if the message is a stand-alone message or one of
   multiple messages that belong to 2PC transaction operations.  See
   Section 4.3.1.2.2 for details.

      Stand-alone message ......... (0b0)

      2PC transaction message ..... (0b1)

   - TP: Transaction Phase (2 bits)

   A message from the CE to the FE within a transaction could be
   indicative of the different phases the transaction is in.  Refer to
   Section 4.3.1.2.2 for details.

      SOT (start of transaction) ..... (0b00)

      MOT (middle of transaction) .... (0b01)

      EOT (end of transaction) ........(0b10)

      ABT (abort) .....................(0b11)

6.2.  Type Length Value (TLV) Structuring

   TLVs are extensively used by the ForCES protocol.  TLVs have some
   very nice properties that make them a good candidate for encoding the
   XML definitions of the LFB class model.  These are:

   o  Providing for binary type-value encoding that is close to the XML
      string tag-value scheme.

   o  Allowing for fast generalized binary-parsing functions.

   o  Allowing for forward and backward tag compatibility.  This is
      equivalent to the XML approach, i.e., old applications can ignore
      new TLVs and newer applications can ignore older TLVs.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | TLV Type                    | TLV Length                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Value (Essentially the TLV Data)                   |
   ~                                                               ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 14: TLV Representation

   TLV Type (16):

   The TLV type field is 2 octets, and semantically indicates the type
   of data encapsulated within the TLV.

   TLV Length (16):

   The TLV length field is 2 octets, and includes the length of the TLV
   type (2 octets), TLV Length (2 octets), and the length of the TLV
   data found in the value field, in octets.  Note that this length is
   the actual length of the value, before any padding for alignment is
   added.

   TLV Value (variable):

   The TLV value field carries the data.  For extensibility, the TLV
   value may in fact be a TLV.  Padding is required when the length is
   not a multiple of 32 bits, and is the minimum number of octets
   required to bring the TLV to a multiple of 32 bits.  The length of
   the value before padding is indicated by the TLV Length field.

   Note: The value field could be empty, which implies the minimal
   length a TLV could be is 4 (length of "T" field and length of "L"
   field).

6.2.1.  Nested TLVs

   TLV values can be other TLVs.  This provides the benefits of protocol
   flexibility (being able to add new extensions by introducing new TLVs
   when needed).  The nesting feature also allows for a conceptual
   optimization with the XML LFB definitions to binary PL representation
   (represented by nested TLVs).

6.2.2.  Scope of the T in TLV

   There are two global name scopes for the "Type" in the TLV.  The
   first name scope is for OPER-TLVs and is defined in A.4 whereas the
   second name scope is outside OPER-TLVs and is defined in section A.2.

6.3.  ILV

   The ILV is a slight variation of the TLV.  This sets the type ("T")
   to be a 32-bit local index that refers to a ForCES component ID
   (refer to Section 6.4.1).

   The ILV length field is a 4-octet integer, and includes the length of
   the ILV type (4 octets), ILV Length (4 octets), and the length of the
   ILV data found in the value field, in octets.  Note that, as in the
   case of the TLV, this length is the actual length of the value,
   before any padding for alignment is added.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Identifier                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Length                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Value                                  |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 15: ILV Representation

   It should be noted that the "I" values are of local scope and are
   defined by the data declarations from the LFB definition.  Refer to
   Section 7.1.8 for discussions on usage of ILVs.

6.4.  Important Protocol Encapsulations

   In this section, we review a few encapsulation concepts that are used
   by the ForCES protocol for its operations.

   We briefly re-introduce two concepts, paths, and keys, from the
   ForCES model [RFC5812] in order to provide context.  The reader is
   referred to [RFC5812] for a lot of the finer details.

   For readability reasons, we introduce the encapsulation schemes that
   are used to carry content in a protocol message, namely, FULLDATA-
   TLV, SPARSEDATA-TLV, and RESULT-TLV.

6.4.1.  Paths

   The ForCES model [RFC5812] defines an XML-based language that allows
   for a formal definition of LFBs.  This is similar to the relationship
   between ASN.1 and SNMP MIB definition (MIB being analogous to the LFB
   and ASN.1 being analogous to the XML model language).  Any entity
   that the CE configures on an FE MUST be formally defined in an LFB.
   These entities could be scalars (e.g., a 32-bit IPv4 address) or
   vectors (such as a nexthop table).  Each entity within the LFB is
   given a numeric 32-bit identifier known as a "component id".  This
   scheme allows the component to be "addressed" in a protocol
   construct.

   These addressable entities could be hierarchical (e.g., a table
   column or a cell within a table row).  In order to address
   hierarchical data, the concept of a path is introduced by the model
   [RFC5812].  A path is a series of 32-bit component IDs that are
   typically presented in a dot-notation (e.g., 1.2.3.4).  Section 7
   formally defines how paths are used to reference data that is being
   encapsulated within a protocol message.

6.4.2.  Keys

   The ForCES model [RFC5812] defines two ways to address table rows.
   The standard/common mechanism is to allow table rows to be referenced
   by a 32-bit index.  The secondary mechanism is via keys that allow
   for content addressing.  An example key is a multi-field content key
   that uses the IP address and prefix length to uniquely reference an
   IPv4 routing table row.  In essence, while the common scheme to
   address a table row is via its table index, a table row's path could
   be derived from a key.  The KEYINFO-TLV (Section 7) is used to carry
   the data that is used to do the lookup.

6.4.3.  DATA TLVs

   Data from or to the FE is carried in two types of TLVs: FULLDATA-TLV
   and SPARSEDATA-TLV.  Responses to operations executed by the FE are
   carried in RESULT-TLVs.

   In FULLDATA-TLV, the data is encoded in such a way that a receiver of
   such data, by virtue of being armed with knowledge of the path and
   the LFB definition, can infer or correlate the TLV "Value" contents.
   This is essentially an optimization that helps reduce the amount of
   description required for the transported data in the protocol
   grammar.  Refer to Appendix C for an example of FULLDATA-TLVs.

   A number of operations in ForCES will need to reference optional data
   within larger structures.  The SPARSEDATA-TLV encoding is provided to
   make it easier to encapsulate optionally appearing data components.
   Refer to Appendix C for an example of SPARSEDATA-TLV.

   RESULT-TLVs carry responses back from the FE based on a config issued
   by the CE.  Refer to Appendix C for examples of RESULT-TLVs and
   Section 7.1.7 for layout.

6.4.4.  Addressing LFB Entities

   Section 6.4.1 and Section 6.4.2 discuss how to target an entity
   within an LFB.  However, the addressing mechanism used requires that
   an LFB type and instance are selected first.  The LFB selector is
   used to select an LFB type and instance being targeted.  Section 7
   goes into more details; for our purpose, we illustrate this concept
   using Figure 16 below.  More examples of layouts can be found reading
   further into the text (example: Figure 22).

      main hdr (Message type: example "config")
       |
       |
       |
       +- T = LFBselect
              |
              +-- LFBCLASSID (unique per LFB defined)
              |
              |
              +-- LFBInstance  (runtime configuration)
              |
              +-- T = An operation TLV describes what we do to an entity
                  |   //Refer to the OPER-TLV values enumerated below
                  |   //the TLVs that can be used for operations
                  |
                  |
                  +--+-- one or more path encodings to target an entity
                     | // Refer to the discussion on keys and paths
                     |
                     |
                     +-- The associated data, if any, for the entity
                        // Refer to discussion on FULL/SPARSE DATA TLVs

                       Figure 16: Entity Addressing

7.  Protocol Construction

   A protocol layer PDU consists of a common header (defined in
   Section 6.1 ) and a message body.  The common header is followed by a
   message-type-specific message body.  Each message body is formed from
   one or more top-level TLVs.  A top-level TLV may contain one or more
   sub-TLVs; these sub-TLVs are described in this document as OPER-TLVs,
   because they describe an operation to be done.

   +-------------+---------------+---------------------+---------------+
   |   Message   | Top-Level TLV |     OPER-TLV(s)     |   Reference   |
   |     Name    |               |                     |               |
   +-------------+---------------+---------------------+---------------+
   | Association |  (LFBselect)* |        REPORT       | Section 7.5.1 |
   |    Setup    |               |                     |               |
   | Association | ASRresult-TLV |         none        | Section 7.5.2 |
   |    Setup    |               |                     |               |
   |   Response  |               |                     |               |
   | Association | ASTreason-TLV |         none        | Section 7.5.3 |
   |   Teardown  |               |                     |               |
   |    Config   |  (LFBselect)+ |  (SET | SET-PROP |  | Section 7.6.1 |
   |             |               |    DEL | COMMIT |   |               |
   |             |               |       TRCOMP)+      |               |
   |    Config   |  (LFBselect)+ |   (SET-RESPONSE |   | Section 7.6.2 |
   |   Response  |               | SET-PROP-RESPONSE | |               |
   |             |               |    DEL-RESPONSE |   |               |
   |             |               |  COMMIT-RESPONSE)+  |               |
   |    Query    |  (LFBselect)+ |  (GET | GET-PROP)+  | Section 7.7.1 |
   |    Query    |  (LFBselect)+ |   (GET-RESPONSE |   | Section 7.7.2 |
   |   Response  |               | GET-PROP-RESPONSE)+ |               |
   |    Event    |   LFBselect   |        REPORT       |  Section 7.8  |
   |   Notifi-   |               |                     |               |
   |    cation   |               |                     |               |
   |    Packet   |  REDIRECT-TLV |         none        |  Section 7.9  |
   |   Redirect  |               |                     |               |
   |  Heartbeat  |      none     |         none        |  Section 7.10 |
   +-------------+---------------+---------------------+---------------+

                                  Table 1

   The different messages are illustrated in Table 1.  The different
   message type numerical values are defined in Appendix A.1.  All the
   TLV values are defined in Appendix A.2.

   An LFBselect TLV (refer to Section 7.1.5) contains the LFB Classid
   and LFB instance being referenced as well as the OPER-TLV(s) being
   applied to that reference.

   Each type of OPER-TLV is constrained as to how it describes the paths
   and selectors of interest.  The following BNF describes the basic
   structure of an OPER-TLV and Table 2 gives the details for each type.

       OPER-TLV := 1*PATH-DATA-TLV
       PATH-DATA-TLV := PATH  [DATA]
       PATH := flags IDcount IDs [SELECTOR]
       SELECTOR :=  KEYINFO-TLV
       DATA := FULLDATA-TLV / SPARSEDATA-TLV / RESULT-TLV /
               1*PATH-DATA-TLV
       KEYINFO-TLV := KeyID FULLDATA-TLV
       FULLDATA-TLV := encoded data component which may nest
                      further FULLDATA-TLVs
       SPARSEDATA-TLV := encoded data that may have optionally
                        appearing components
       RESULT-TLV := Holds result code and optional FULLDATA-TLV

                        Figure 17: BNF of OPER-TLV

   o  PATH-DATA-TLV identifies the exact component targeted and may have
      zero or more paths associated with it.  The last PATH-DATA-TLV in
      the case of nesting of paths via the DATA construct in the case of
      SET, SET-PROP requests, and GET-RESPONSE/GET-PROP-RESPONSE is
      terminated by encoded data or response in the form of either
      FULLDATA-TLV or SPARSEDATA-TLV or RESULT-TLV.

   o  PATH provides the path to the data being referenced.

      *  flags (16 bits) are used to further refine the operation to be
         applied on the path.  More on these later.

      *  IDcount (16 bits): count of 32-bit IDs

      *  IDs: zero or more 32-bit IDs (whose count is given by IDcount)
         defining the main path.  Depending on the flags, IDs could be
         field IDs only or a mix of field and dynamic IDs.  Zero is used
         for the special case of using the entirety of the containing
         context as the result of the path.

   o  SELECTOR is an optional construct that further defines the PATH.
      Currently, the only defined selector is the KEYINFO-TLV, used for
      selecting an array entry by the value of a key field.  The
      presence of a SELECTOR is correct only when the flags also
      indicate its presence.

   o  A KEYINFO-TLV contains information used in content keying.

      *  A 32-bit KeyID is used in a KEYINFO-TLV.  It indicates which
         key for the current array is being used as the content key for
         array entry selection.

      *  The key's data is the data to look for in the array, in the
         fields identified by the key field.  The information is encoded
         according to the rules for the contents of a FULLDATA-TLV, and
         represents the field or fields that make up the key identified
         by the KeyID.

   o  DATA may contain a FULLDATA-TLV, SPARSEDATA-TLV, a RESULT-TLV, or
      1 or more further PATH-DATA selections.  FULLDATA-TLV and
      SPARSEDATA-TLV are only allowed on SET or SET-PROP requests, or on
      responses that return content information (GET-RESPONSE, for
      example).  PATH-DATA may be included to extend the path on any
      request.

      *  Note: Nested PATH-DATA-TLVs are supported as an efficiency
         measure to permit common subexpression extraction.

      *  FULLDATA-TLV and SPARSEDATA-TLV contain "the data" whose path
         has been selected by the PATH.  Refer to Section 7.1 for
         details.

      *  The following table summarizes the applicability and
         restrictions of the FULL/SPARSEDATA-TLVs and the RESULT-TLV to
         the OPER-TLVs.

   +-------------------+-------------------------------+---------------+
   |      OPER-TLV     |            DATA TLV           |   RESULT-TLV  |
   +-------------------+-------------------------------+---------------+
   |        SET        |                               |      none     |
   |      SET-PROP     |        (FULLDATA-TLV |        |      none     |
   |                   |        SPARSEDATA-TLV)+       |               |
   |    SET-RESPONSE   |              none             | (RESULT-TLV)+ |
   | SET-PROP-RESPONSE |              none             | (RESULT-TLV)+ |
   |        DEL        |                               |      none     |
   |    DEL-RESPONSE   |              none             | (RESULT-TLV)+ |
   |        GET        |              none             |      none     |
   |      GET-PROP     |              none             |      none     |
   |    GET-RESPONSE   |        (FULLDATA-TLV)+        | (RESULT-TLV)* |
   | GET-PROP-RESPONSE |        (FULLDATA-TLV)+        | (RESULT-TLV)* |
   |       REPORT      |        (FULLDATA-TLV)+        |      none     |
   |       COMMIT      |              none             |      none     |
   |  COMMIT-RESPONSE  |              none             | (RESULT-TLV)+ |
   |       TRCOMP      |              none             |      none     |
   +-------------------+-------------------------------+---------------+

                                     Table 2

   o  RESULT-TLV contains the indication of whether the individual SET
      or SET-PROP succeeded.  RESULT-TLV is included on the assumption
      that individual parts of a SET request can succeed or fail
      separately.

   In summary, this approach has the following characteristics:

   o  There can be one or more LFB class ID and instance ID combinations
      targeted in a message (batch).

   o  There can one or more operations on an addressed LFB class ID/
      instance ID combination (batch).

   o  There can be one or more path targets per operation (batch).

   o  Paths may have zero or more data values associated (flexibility
      and operation specific).

   It should be noted that the above is optimized for the case of a
   single LFB class ID and instance ID targeting.  To target multiple
   instances within the same class, multiple LFBselects are needed.

7.1.  Discussion on Encoding

   Section 6.4.3 discusses the two types of DATA encodings (FULLDATA-TLV
   and SPARSEDATA-TLV) and the justifications for their existence.  In
   this section, we explain how they are encoded.

7.1.1.  Data Packing Rules

   The scheme for encoding data used in this document adheres to the
   following rules:

   o  The Value ("V" of TLV) of FULLDATA-TLV will contain the data being
      transported.  This data will be as was described in the LFB
      definition.

   o  Variable-sized data within a FULLDATA-TLV will be encapsulated
      inside another FULLDATA-TLV inside the V of the outer TLV.  For an
      example of such a setup, refer to Appendices C and D.

   o  In the case of FULLDATA-TLVs:

      *  When a table is referred to in the PATH (IDs) of a PATH-DATA-
         TLV, then the FULLDATA-TLV's "V" will contain that table's row
         content prefixed by its 32-bit index/subscript.  On the other

         hand, the PATH may contain an index pointing to a row in table;
         in such a case, the FULLDATA-TLV's "V" will only contain the
         content with the index in order to avoid ambiguity.

7.1.2.  Path Flags

   Only bit 0, the SELECTOR Bit, is currently used in the path flags as
   illustrated in Figure 18.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | |                           |
      |S|   Reserved                |
      | |                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 18: Path Flags

      The semantics of the flag are defined as follows:

   o  SELECTOR Bit: F_SELKEY(set to 1) indicates that a KEY Selector is
      present following this path information, and should be considered
      in evaluating the path content.

7.1.3.  Relation of Operational Flags with Global Message Flags

   Global flags, such as the execution mode and the atomicity indicators
   defined in the header, apply to all operations in a message.  Global
   flags provide semantics that are orthogonal to those provided by the
   operational flags, such as the flags defined in path-data.  The scope
   of operational flags is restricted to the operation.

7.1.4.  Content Path Selection

   The KEYINFO-TLV describes the KEY as well as associated KEY data.
   KEYs, used for content searches, are restricted and described in the
   LFB definition.

7.1.5.  LFBselect-TLV

   The LFBselect TLV is an instance of a TLV as defined in Section 6.2.
   The definition is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Type = LFBselect       |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          LFB Class ID                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        LFB Instance ID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        OPER-TLV                               |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                           ...                                 ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        OPER-TLV                               |
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 19: PL PDU Layout

   Type:

   The type of the TLV is "LFBselect"

   Length:

   Length of the TLV including the T and L fields, in octets.

   LFB Class ID:

   This field uniquely recognizes the LFB class/type.

   LFB Instance ID:

   This field uniquely identifies the LFB instance.

   OPER-TLV:

   It describes an operation nested in the LFBselect TLV.  Note that
   usually there SHOULD be at least one OPER-TLV present for an LFB
   select TLV.

7.1.6.  OPER-TLV

   The OPER-TLV is a place holder in the grammar for TLVs that define
   operations.  The different types are defined in Table 3, below.

   +-------------------+--------+--------------------------------------+
   |      OPER-TLV     |   TLV  |               Comments               |
   |                   | "Type" |                                      |
   +-------------------+--------+--------------------------------------+
   |        SET        | 0x0001 |   From CE to FE.  Used to create or  |
   |                   |        |       add or update components       |
   |      SET-PROP     | 0x0002 |   From CE to FE.  Used to create or  |
   |                   |        |  add or update component properties  |
   |    SET-RESPONSE   | 0x0003 |     From FE to CE.  Used to carry    |
   |                   |        |           response of a SET          |
   | SET-PROP-RESPONSE | 0x0004 |     From FE to CE.  Used to carry    |
   |                   |        |        response of a SET-PROP        |
   |        DEL        | 0x0005 |   From CE to FE.  Used to delete or  |
   |                   |        |          remove an component         |
   |    DEL-RESPONSE   | 0x0006 |     From FE to CE.  Used to carry    |
   |                   |        |           response of a DEL          |
   |        GET        | 0x0007 |  From CE to FE.  Used to retrieve an |
   |                   |        |               component              |
   |      GET-PROP     | 0x0008 |  From CE to FE.  Used to retrieve an |
   |                   |        |          component property          |
   |    GET-RESPONSE   | 0x0009 |     From FE to CE.  Used to carry    |
   |                   |        |           response of a GET          |
   | GET-PROP-RESPONSE | 0x000A |     From FE to CE.  Used to carry    |
   |                   |        |        response of a GET-PROP        |
   |       REPORT      | 0x000B |   From FE to CE.  Used to carry an   |
   |                   |        |          asynchronous event          |
   |       COMMIT      | 0x000C |    From CE to FE.  Used to issue a   |
   |                   |        |      commit in a 2PC transaction     |
   |  COMMIT-RESPONSE  | 0x000D |   From FE to CE.  Used to confirm a  |
   |                   |        |      commit in a 2PC transaction     |
   |       TRCOMP      | 0x000E |   From CE to FE.  Used to indicate   |
   |                   |        |  NE-wide success of 2PC transaction  |
   +-------------------+--------+--------------------------------------+

                                  Table 3

   Different messages use OPER-TLV and define how they are used (refer
   to Table 1 and Table 2).

   SET, SET-PROP, and GET/GET-PROP requests are issued by the CE and do
   not carry RESULT-TLVs.  On the other hand, SET-RESPONSE, SET-PROP-
   RESPONSE, and GET-RESPONSE/GET-PROP-RESPONSE carry RESULT-TLVs.

   A GET-RESPONSE in response to a successful GET will have FULLDATA-
   TLVs added to the leaf paths to carry the requested data.  For GET
   operations that fail, instead of the FULLDATA-TLV there will be a
   RESULT-TLV.

   For a SET-RESPONSE/SET-PROP-RESPONSE, each FULLDATA-TLV or
   SPARSEDATA-TLV in the original request will be replaced with a
   RESULT-TLV in the response.  If the request set the FailureACK flag,
   then only those items that failed will appear in the response.  If
   the request was for AlwaysACK, then all components of the request
   will appear in the response with RESULT-TLVs.

   Note that if a SET/SET-PROP request with a structure in a FULLDATA-
   TLV is issued, and some field in the structure is invalid, the FE
   will not attempt to indicate which field was invalid, but rather will
   indicate that the operation failed.  Note further that if there are
   multiple errors in a single leaf PATH-DATA/FULLDATA-TLB, the FE can
   select which error it chooses to return.  So if a FULLDATA-TLV for a
   SET/SET-PROP of a structure attempts to write one field that is read
   only, and attempts to set another field to an invalid value, the FE
   can return indication of either error.

   A SET/SET-PROP operation on a variable-length component with a length
   of 0 for the item is not the same as deleting it.  If the CE wishes
   to delete, then the DEL operation should be used whether the path
   refers to an array component or an optional structure component.

7.1.7.  RESULT TLV

   The RESULT-TLV is an instance of TLV defined in Section 6.2.  The
   definition is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Type = RESULT-TLV          |               Length          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Result Value  |                  Reserved                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 20: RESULT-TLV

                           Defined Result Values

   +-----------------------------+-----------+-------------------------+
   |         Result Value        |   Value   |        Definition       |
   +-----------------------------+-----------+-------------------------+
   |          E_SUCCESS          |    0x00   |         Success         |
   |       E_INVALID_HEADER      |    0x01   |  Unspecified error with |
   |                             |           |         header.         |
   |      E_LENGTH_MISMATCH      |    0x02   |   Header length field   |
   |                             |           |  does not match actual  |
   |                             |           |      packet length.     |
   |      E_VERSION_MISMATCH     |    0x03   |  Unresolvable mismatch  |
   |                             |           |       in versions.      |
   |  E_INVALID_DESTINATION_PID  |    0x04   |    Destination PID is   |
   |                             |           | invalid for the message |
   |                             |           |        receiver.        |
   |        E_LFB_UNKNOWN        |    0x05   |   LFB Class ID is not   |
   |                             |           |    known by receiver.   |
   |       E_LFB_NOT_FOUND       |    0x06   |  LFB Class ID is known  |
   |                             |           |   by receiver but not   |
   |                             |           |    currently in use.    |
   | E_LFB_INSTANCE_ID_NOT_FOUND |    0x07   |  LFB Class ID is known  |
   |                             |           |    but the specified    |
   |                             |           |  instance of that class |
   |                             |           |     does not exist.     |
   |        E_INVALID_PATH       |    0x08   |  The specified path is  |
   |                             |           |       impossible.       |
   |  E_COMPONENT_DOES_NOT_EXIST |    0x09   |  The specified path is  |
   |                             |           |     possible but the    |
   |                             |           |    component does not   |
   |                             |           | exist (e.g., attempt to |
   |                             |           | modify a table row that |
   |                             |           |  has not been created). |
   |           E_EXISTS          |    0x0A   |   The specified object  |
   |                             |           |   exists but it cannot  |
   |                             |           | exist for the operation |
   |                             |           |    to succeed (e.g.,    |
   |                             |           |    attempt to add an    |
   |                             |           |  existing LFB instance  |
   |                             |           |   or array subscript).  |
   |         E_NOT_FOUND         |    0x0B   |   The specified object  |
   |                             |           |  does not exist but it  |
   |                             |           |    MUST exist for the   |
   |                             |           |   operation to succeed  |
   |                             |           |    (e.g., attempt to    |
   |                             |           |  delete a non-existing  |
   |                             |           |  LFB instance or array  |
   |                             |           |       subscript).       |

   |         E_READ_ONLY         |    0x0C   |   Attempt to modify a   |
   |                             |           |     read-only value.    |
   |   E_INVALID_ARRAY_CREATION  |    0x0D   |   Attempt to create an  |
   |                             |           | array with an unallowed |
   |                             |           |        subscript.       |
   |     E_VALUE_OUT_OF_RANGE    |    0x0E   |     Attempt to set a    |
   |                             |           |   parameter to a value  |
   |                             |           |      outside of its     |
   |                             |           |     allowable range.    |
   |     E_CONTENTS_TOO_LONG     |    0x0D   |     Attempt to write    |
   |                             |           |   contents larger than  |
   |                             |           | the target object space |
   |                             |           |    (i.e., exceeding a   |
   |                             |           |         buffer).        |
   |     E_INVALID_PARAMETERS    |    0x10   |   Any other error with  |
   |                             |           |     data parameters.    |
   |    E_INVALID_MESSAGE_TYPE   |    0x11   |   Message type is not   |
   |                             |           |       acceptable.       |
   |       E_INVALID_FLAGS       |    0x12   |  Message flags are not  |
   |                             |           |    acceptable for the   |
   |                             |           |   given message type.   |
   |        E_INVALID_TLV        |    0x13   | A TLV is not acceptable |
   |                             |           |  for the given message  |
   |                             |           |          type.          |
   |        E_EVENT_ERROR        |    0x14   | Unspecified error while |
   |                             |           |    handling an event.   |
   |       E_NOT_SUPPORTED       |    0x15   |   Attempt to perform a  |
   |                             |           |  valid ForCES operation |
   |                             |           |  that is unsupported by |
   |                             |           |  the message receiver.  |
   |        E_MEMORY_ERROR       |    0x16   | A memory error occurred |
   |                             |           |    while processing a   |
   |                             |           |    message (no error    |
   |                             |           | detected in the message |
   |                             |           |         itself).        |
   |       E_INTERNAL_ERROR      |    0x17   |   An unspecified error  |
   |                             |           |      occurred while     |
   |                             |           |   processing a message  |
   |                             |           |  (no error detected in  |
   |                             |           |   the message itself).  |
   |              -              | 0x18-0xFE |         Reserved        |
   |     E_UNSPECIFIED_ERROR     |    0xFF   |  Unspecified error (for |
   |                             |           |    when the FE cannot   |
   |                             |           |     decide what went    |
   |                             |           |         wrong).         |
   +-----------------------------+-----------+-------------------------+

                                  Table 4

7.1.8.  DATA TLV

   A FULLDATA-TLV has "T"= FULLDATA-TLV and a 16-bit length followed by
   the data value/contents.  Likewise, a SPARSEDATA-TLV has "T" =
   SPARSEDATA-TLV, a 16-bit length, followed by the data value/contents.
   In the case of the SPARSEDATA-TLV, each component in the Value part
   of the TLV will be further encapsulated in an ILV.

   Below are the encoding rules for the FULLDATA-TLV and SPARSEDATA-
   TLVs.  Appendix C is very useful in illustrating these rules:

   1.  Both ILVs and TLVs MUST be 32-bit aligned.  Any padding bits used
       for the alignment MUST be zero on transmission and MUST be
       ignored upon reception.

   2.  FULLDATA-TLVs may be used at a particular path only if every
       component at that path level is present.  In example 1(c) of
       Appendix C, this concept is illustrated by the presence of all
       components of the structure S in the FULLDATA-TLV encoding.  This
       requirement holds regardless of whether the fields are fixed or
       variable length, mandatory or optional.

       *   If a FULLDATA-TLV is used, the encoder MUST lay out data for
           each component in the same order in which the data was
           defined in the LFB specification.  This ensures the decoder
           is able to retrieve the data.  To use the example 1 again in
           Appendix C, this implies the encoder/decoder is assumed to
           have knowledge of how structure S is laid out in the
           definition.

       *   In the case of a SPARSEDATA-TLV, it does not need to be
           ordered since the "I" in the ILV uniquely identifies the
           component.  Examples 1(a) and 1(b) in Appendix C illustrate
           the power of SPARSEDATA-TLV encoding.

   3.  Inside a FULLDATA-TLV

       *   The values for atomic, fixed-length fields are given without
           any TLV encapsulation.

       *   The values for atomic, variable-length fields are given
           inside FULLDATA-TLVs.

       *   The values for arrays are in the form of index/subscript,
           followed by value as stated in "Data Packing Rules"
           (Section 7.1.1) and demonstrated by the examples in the
           appendices.

   4.  Inside a SPARSEDATA-TLV

       *   The values of all fields MUST be given with ILVs (32-bit
           index, 32-bit length).

   5.  FULLDATA-TLVs cannot contain an ILV.

   6.  A FULLDATA-TLV can also contain a FULLDATA-TLV for variable-sized
       components.  The decoding disambiguation is assumed from rule #3
       above.

7.1.9.  SET and GET Relationship

   It is expected that a GET-RESPONSE would satisfy the following:

   o   It would have exactly the same path definitions as those sent in
       the GET.  The only difference is that a GET-RESPONSE will contain
       FULLDATA-TLVs.

   o   It should be possible to take the same GET-RESPONSE and convert
       it to a SET successfully by merely changing the T in the
       operational TLV.

   o   There are exceptions to this rule:

       1.  When a KEY selector is used with a path in a GET operation,
           that selector is not returned in the GET-RESPONSE; instead,
           the cooked result is returned.  Refer to the examples using
           KEYS to see this.

       2.  When dumping a whole table in a GET, the GET-RESPONSE that
           merely edits the T to be SET will end up overwriting the
           table.

7.2.  Protocol Encoding Visualization

   The figure below shows a general layout of the PL PDU.  A main header
   is followed by one or more LFB selections each of which may contain
   one or more operations.

   main hdr (Config in this case)
        |
        |
        +--- T = LFBselect
        |        |
        |        +-- LFBCLASSID
        |        |
        |        |
        |        +-- LFBInstance
        |        |
        |        +-- T = SET
        |        |   |
        |        |   +--  // one or more path targets
        |        |        // with their data here to be added
        |        |
        |        +-- T  = DEL
        |        .   |
        |        .   +--  // one or more path targets to be deleted
        |
        |
        +--- T = LFBselect
        |        |
        |        +-- LFBCLASSID
        |        |
        |        |
        |        +-- LFBInstance
        |        |
        |        + -- T= SET
        |        |    .
        |        |    .
        |        + -- T= DEL
        |        |    .
        |        |    .
        |        |
        |        + -- T= SET
        |        |    .
        |        |    .
        |
        |
        +--- T = LFBselect
                |
                +-- LFBCLASSID
                |
                +-- LFBInstance
                .
                .
                .
                     Figure 21: PL PDU Logical Layout

   The figure below shows a more detailed example of the general layout
   of the operation within a targeted LFB selection.  The idea is to
   show the different nesting levels a path could take to get to the
   target path.

        T = SET
        |  |
        |  +- T = Path-data
        |       |
        |       + -- flags
        |       + -- IDCount
        |       + -- IDs
        |       |
        |       +- T = Path-data
        |          |
        |          + -- flags
        |          + -- IDCount
        |          + -- IDs
        |          |
        |          +- T = Path-data
        |             |
        |             + -- flags
        |             + -- IDCount
        |             + -- IDs
        |             + -- T = KEYINFO-TLV
        |             |    + -- KEY_ID
        |             |    + -- KEY_DATA
        |             |
        |             + -- T = FULLDATA-TLV
        |                  + -- data
        |
        |
        T = SET
        |  |
        |  +- T = Path-data
        |  |  |
        |  |  + -- flags
        |  |  + -- IDCount
        |  |  + -- IDs
        |  |  |
        |  |  + -- T = FULLDATA-TLV
        |  |          + -- data
        |  +- T = Path-data
        |     |

        |     + -- flags
        |     + -- IDCount
        |     + -- IDs
        |     |
        |     + -- T = FULLDATA-TLV
        |             + -- data
        T = DEL
           |
           +- T = Path-data
                |
                + -- flags
                + -- IDCount
                + -- IDs
                |
                +- T = Path-data
                   |
                   + -- flags
                   + -- IDCount
                   + -- IDs
                   |
                   +- T = Path-data
                      |
                      + -- flags
                      + -- IDCount
                      + -- IDs
                      + -- T = KEYINFO-TLV
                      |    + -- KEY_ID
                      |    + -- KEY_DATA
                      +- T = Path-data
                           |
                           + -- flags
                           + -- IDCount
                           + -- IDs

                    Figure 22: Sample Operation Layout

   Appendix D shows a more concise set of use cases on how the data
   encoding is done.

7.3.  Core ForCES LFBs

   There are two LFBs that are used to control the operation of the
   ForCES protocol and to interact with FEs and CEs:

   o  FE Protocol LFB

   o  FE Object LFB

   Although these LFBs have the same form and interface as other LFBs,
   they are special in many respects.  They have fixed well-known LFB
   Class and Instance IDs.  They are statically defined (no dynamic
   instantiation allowed), and their status cannot be changed by the
   protocol: any operation to change the state of such LFBs (for
   instance, in order to disable the LFB) MUST result in an error.
   Moreover, these LFBs MUST exist before the first ForCES message can
   be sent or received.  All components in these LFBs MUST have pre-
   defined default values.  Finally, these LFBs do not have input or
   output ports and do not integrate into the intra-FE LFB topology.

7.3.1.  FE Protocol LFB

   The FE Protocol LFB is a logical entity in each FE that is used to
   control the ForCES protocol.  The FE Protocol LFB Class ID is
   assigned the value 0x2.  The FE Protocol LFB Instance ID is assigned
   the value 0x1.  There MUST be one and only one instance of the FE
   Protocol LFB in an FE.  The values of the components in the FE
   Protocol LFB have pre-defined default values that are specified here.
   Unless explicit changes are made to these values using Config
   messages from the CE, these default values MUST be used for correct
   operation of the protocol.

   The formal definition of the FE Protocol Object LFB can be found in
   Appendix B.

7.3.1.1.  FE Protocol Capabilities

   FE Protocol capabilities are read-only.

7.3.1.1.1.  SupportableVersions

   ForCES protocol version(s) supported by the FE.

7.3.1.1.2.  FE Protocol Components

   FE Protocol components (can be read and set).

7.3.1.1.2.1.  CurrentRunningVersion

   Current running version of the ForCES protocol.

7.3.1.1.2.2.  FEID

   FE unicast ID.

7.3.1.1.2.3.  MulticastFEIDs

   FE multicast ID(s) list - This is a list of multicast IDs to which
   the FE belongs.  These IDs are configured by the CE.

7.3.1.1.2.4.  CEHBPolicy

   CE heartbeat policy - This policy, along with the parameter 'CE
   Heartbeat Dead Interval (CE HDI)' as described below, defines the
   operating parameters for the FE to check the CE liveness.  The policy
   values with meanings are listed as follows:

   o  0 (default) - This policy specifies that the CE will send a
      Heartbeat message to the FE(s) whenever the CE reaches a time
      interval within which no other PL messages were sent from the CE
      to the FE(s); refer to Section 4.3.3 and Section 7.10 for details.
      The CE HDI component as described below is tied to this policy.

   o  1 - The CE will not generate any HB messages.  This actually means
      that the CE does not want the FE to check the CE liveness.

   o  Others - Reserved.

7.3.1.1.2.5.  CEHDI

   CE Heartbeat Dead Interval (CE HDI) - The time interval the FE uses
   to check the CE liveness.  If FE has not received any messages from
   CE within this time interval, FE deduces lost connectivity, which
   implies that the CE is dead or the association to the CE is lost.
   Default value is 30 s.

7.3.1.1.2.6.  FEHBPolicy

   FE heartbeat policy - This policy, along with the parameter 'FE
   Heartbeat Interval (FE HI)', defines the operating parameters for how
   the FE should behave so that the CE can deduce its liveness.  The
   policy values and the meanings are:

   o  0 (default) - The FE should not generate any Heartbeat messages.
      In this scenario, the CE is responsible for checking FE liveness
      by setting the PL header ACK flag of the message it sends to
      AlwaysACK.  The FE responds to the CE whenever the CE sends such
      Heartbeat Request messages.  Refer to Section 7.10 and
      Section 4.3.3 for details.

   o  1 - This policy specifies that the FE MUST actively send a
      Heartbeat message if it reaches the time interval assigned by the
      FE HI as long as no other messages were sent from the FE to the CE
      during that interval as described in Section 4.3.3.

   o  Others - Reserved.

7.3.1.1.2.7.  FEHI

   FE Heartbeat Interval (FE HI) - The time interval the FE should use
   to send HB as long as no other messages were sent from the FE to the
   CE during that interval as described in Section 4.3.3.  The default
   value for an FE HI is 500 ms.

7.3.1.1.2.8.  CEID

   Primary CEID - The CEID with which the FE is associated.

7.3.1.1.2.9.  LastCEID

   Last Primary CEID - The CEID of the last CE with which the FE
   associated.  This CE ID is reported to the new Primary CEID.

7.3.1.1.2.10.  BackupCEs

   The list of backup CEs an FE can use as backups.  Refer to Section 8
   for details.

7.3.1.1.2.11.  CEFailoverPolicy

   CE failover policy - This specifies the behavior of the FE when the
   association with the CE is lost.  There is a very tight relation
   between CE failover policy and Section 7.3.1.1.2.8,
   Section 7.3.1.1.2.10, Section 7.3.1.1.2.12, and Section 8.  When an
   association is lost, depending on configuration, one of the policies
   listed below is activated.

   o  0 (default) - The FE should stop functioning immediately and
      transition to FE OperDisable.

   o  1 - The FE should continue running and do what it can even without
      an associated CE.  This basically requires that the FE support CE
      Graceful restart (and defines such support in its capabilities).
      If the CEFTI expires before the FE re-associates with either the
      primary CEID (Section 7.3.1.1.2.8) or one of possibly several
      backup CEs (Section 7.3.1.1.2.10), the FE will go operationally
      down.

   o  Others - Reserved.

7.3.1.1.2.12.  CEFTI

   CE Failover Timeout Interval (CEFTI) - The time interval associated
   with the CE failover policy case '0' and '1'.  The default value is
   set to 300 seconds.  Note that it is advisable to set the CEFTI value
   much higher than the CE Heartbeat Dead Interval (CE HDI) since the
   effect of expiring this parameter is devastating to the operation of
   the FE.

7.3.1.1.2.13.  FERestartPolicy

   FE restart policy - This specifies the behavior of the FE during an
   FE restart.  The restart may be from an FE failure or other reasons
   that have made the FE down and then need to restart.  The values are
   defined as follows:

   o  0(default)- Restart the FE from scratch.  In this case, the FE
      should start from the pre-association phase.

   o  Others - Reserved for future use.

7.3.2.  FE Object LFB

   The FE Object LFB is a logical entity in each FE and contains
   components relative to the FE itself, and not to the operation of the
   ForCES protocol.

   The formal definition of the FE Object LFB can be found in [RFC5812].
   The model captures the high-level properties of the FE that the CE
   needs to know to begin working with the FE.  The class ID for this
   LFB class is also assigned in [RFC5812].  The singular instance of
   this class will always exist, and will always have instance ID 0x1
   within its class.  It is common, although not mandatory, for a CE to
   fetch much of the component and capability information from this LFB
   instance when the CE begins controlling the operation of the FE.

7.4.  Semantics of Message Direction

   Recall: The PL provides a master(CE)-slave(FE) relationship.  The
   LFBs reside at the FE and are controlled by CE.

   When messages go from the CE, the LFB selector (class and instance)
   refers to the destination LFB selection that resides in the FE.

   When messages go from the FE to the CE, the LFB selector (class and
   instance) refers to the source LFB selection that resides in the FE.

7.5.  Association Messages

   The ForCES Association messages are used to establish and tear down
   associations between FEs and CEs.

7.5.1.  Association Setup Message

   This message is sent by the FE to the CE to set up a ForCES
   association between them.

   Message transfer direction:
      FE to CE

   Message header:
      The Message Type in the header is set to MessageType=
      'AssociationSetup'.  The ACK flag in the header MUST be ignored,
      and the Association Setup message always expects to get a response
      from the message receiver (CE), whether or not the setup is
      successful.  The correlator field in the header is set, so that FE
      can correlate the response coming back from the CE correctly.  The
      FE may set the source ID to 0 in the header to request that the CE
      should assign an FE ID for the FE in the Setup Response message.

   Message body:
      The Association Setup message body optionally consists of zero,
      one, or two LFBselect TLVs, as described in Section 7.1.5.  The
      Association Setup message only operates on the FE Object and FE
      Protocol LFBs; therefore, the LFB class ID in the LFBselect TLV
      only points to these two kinds of LFBs.

      The OPER-TLV in the LFBselect TLV is defined as a 'REPORT'
      operation.  More than one component may be announced in this
      message using the REPORT operation to let the FE declare its
      configuration parameters in an unsolicited manner.  These may
      contain components suggesting values such as the FE HB Interval or
      the FEID.  The OPER-TLV used is defined below.

   OPER-TLV for Association Setup:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type = REPORT              |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    PATH-DATA-TLV for REPORT                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Figure 23: OPER-TLV

   Type:
      Only one operation type is defined for the Association Setup
      message:

      Type = "REPORT" - This type of operation is for the FE to report
             something to the CE.

   PATH-DATA-TLV for REPORT:
      This is generically a PATH-DATA-TLV format that has been defined
      in Section 7 in the PATH-DATA BNF definition.  The PATH-DATA-TLV
      for the REPORT operation MAY contain FULLDATA-TLV(s) but SHALL NOT
      contain any RESULT-TLV in the data format.  The RESULT-TLV is
      defined in Section 7.1.7 and the FULLDATA-TLV is defined in
      Section 7.1.8.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type =  Association Setup)
        |
        |
        +--- T = LFBselect
        |        |
        |        +-- LFBCLASSID = FE object
        |        |
        |        |
        |        +-- LFBInstance = 0x1
        |
        +--- T = LFBselect
                 |
                 +-- LFBCLASSID = FE Protocol object
                 |
                 |
                 +-- LFBInstance = 0x1
                       |
                       +---OPER-TLV = REPORT
                           |
                           +-- Path-data to one or more components

            Figure 24: PDU Format for Association Setup Message

7.5.2.  Association Setup Response Message

   This message is sent by the CE to the FE in response to the Setup
   message.  It indicates to the FE whether or not the setup is
   successful, i.e., whether an association is established.

   Message transfer direction:

   CE to FE

   Message header:

   The Message Type in the header is set to MessageType=
   'AssociationSetupResponse'.  The ACK flag in the header MUST be
   ignored, and the Setup Response message never expects to get any more
   responses from the message receiver (FE).  The destination ID in the
   header will be set to the source ID in the corresponding Association
   Setup message, unless that source ID was 0.  If the corresponding
   source ID was 0, then the CE will assign an FE ID value and use that
   value for the destination ID.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Type = ASRresult       |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Association Setup Result                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 25: ASResult OPER-TLV

   Type (16 bits):

   The type of the TLV is "ASResult".

   Length (16 bits):

   Length of the TLV including the T and L fields, in octets.

   Association Setup result (32 bits):

   This indicates whether the Setup message was successful or whether
   the FE request was rejected by the CE.  The defined values are:

       0 = success

       1 = FE ID invalid

       2 = permission denied

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type =  Association Setup Response)
    |
    |
    +--- T = ASResult-TLV

      Figure 26: PDU Format for Association Setup Response Message

7.5.3.  Association Teardown Message

   This message can be sent by the FE or CE to any ForCES element to end
   its ForCES association with that element.

   Message transfer direction:

   CE to FE, or FE to CE (or CE to CE)

   Message Header:

   The Message Type in the header is set to MessageType=
   "AssociationTeardown".  The ACK flag MUST be ignored.  The correlator
   field in the header MUST be set to zero and MUST be ignored by the
   receiver.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Type = ASTreason       |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Teardown Reason                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 27: ASTreason-TLV

   Type (16 bits):

   The type of the TLV is "ASTreason".

   Length (16 bits):

   Length of the TLV including the T and L fields, in octets.

   Teardown reason (32 bits):

   This indicates the reason why the association is being terminated.
   Several reason codes are defined as follows.

       0 - normal teardown by administrator

       1 - error - loss of heartbeats

       2 - error - out of bandwidth

       3 - error - out of memory

       4 - error - application crash

       255 - error - other or unspecified

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type =  Association Teardown)
    |
    |
    +--- T = ASTreason-TLV

      Figure 28: PDU Format for Association Teardown Message

7.6.  Configuration Messages

   The ForCES Configuration messages are used by CE to configure the FEs
   in a ForCES NE and report the results back to the CE.

7.6.1.  Config Message

   This message is sent by the CE to the FE to configure LFB components
   in the FE.  This message is also used by the CE to subscribe/
   unsubscribe to LFB events.

   As usual, a Config message is composed of a common header followed by
   a message body that consists of one or more TLV data formats.
   Detailed description of the message is as follows:

   Message transfer direction:

   CE to FE

   Message header:

   The Message Type in the header is set to MessageType= 'Config'.  The
   ACK flag in the header can be set to any value defined in
   Section 6.1, to indicate whether or not a response from the FE is
   expected by the message.

   OPER-TLV for Config:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Type                 |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        PATH-DATA-TLV                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 29: OPER-TLV for Config

   Type:

   The operation type for Config message.  Two types of operations for
   the Config message are defined:

       Type = "SET" - This operation is to set LFB components

       Type = "SET-PROP" - This operation is to set LFB component
              properties.

       Type = "DEL" - This operation is to delete some LFB components.

       Type = "COMMIT" - This operation is sent to the FE to commit in a
              2pc transaction.  A COMMIT TLV is an empty TLV, i.e., it
              has no "V"alue.  In other words, there is a length of 4
              (which is for the header only).

       Type = "TRCOMP" - This operation is sent to the FE to mark the
              success from an NE perspective of a 2pc transaction.  A
              TRCOMP TLV is an empty TLV, i.e., it has no "V"alue.  In
              other words, there is a length of 4 (which is for the
              header only).

   PATH-DATA-TLV:

   This is generically a PATH-DATA-TLV format that has been defined in
   Section 7 in the PATH-DATA-TLV BNF definition.  The restriction on
   the use of PATH-DATA-TLV for SET/SET-PROP operation is that it MUST
   contain either FULLDATA-TLV or SPARSEDATA-TLV(s), but MUST NOT
   contain any RESULT-TLV.  The restriction on the use of PATH-DATA-TLV
   for DEL operation is it MAY contain FULLDATA-TLV or
   SPARSEDATA-TLV(s), but MUST NOT contain any RESULT-TLV.  The
   RESULT-TLV is defined in Section 7.1.7 and FULLDATA-TLVs and
   SPARSEDATA-TLVs are defined in Section 7.1.8.

       Note:  For Event subscription, the events will be defined by the
              individual LFBs.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type = Config)
    |
    |
    +--- T = LFBselect
    .        |
    .        +-- LFBCLASSID = target LFB class
    .        |
             |
             +-- LFBInstance = target LFB instance
             |
             |
             +-- T = operation { SET }
             |   |
             |   +--  // one or more path targets
             |      // associated with FULLDATA-TLV or SPARSEDATA-TLV(s)
             |
             +-- T = operation { DEL }
             |   |
             |   +--  // one or more path targets
             |
             +-- T = operation { COMMIT } //A COMMIT TLV is an empty TLV
                      .
                      .

              Figure 30: PDU Format for Configuration Message

7.6.2.  Config Response Message

   This message is sent by the FE to the CE in response to the Config
   message.  It indicates whether or not the Config was successful on
   the FE and also gives a detailed response regarding the configuration
   result of each component.

   Message transfer direction:

   FE to CE

   Message header:

   The Message Type in the header is set to MessageType= 'Config
   Response'.  The ACK flag in the header is always ignored, and the
   Config Response message never expects to get any further response
   from the message receiver (CE).

   OPER-TLV for Config Response:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Type                 |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        PATH-DATA-TLV                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 31: OPER-TLV for Config Response

   Type:
          The operation type for Config Response message.  Two types of
          operations for the Config Response message are defined:

       Type = "SET-RESPONSE" - This operation is for the response of the
              SET operation of LFB components.

       Type = "SET-PROP-RESPONSE" - This operation is for the response
              of the SET-PROP operation of LFB component properties.

       Type = "DEL-RESPONSE" - This operation is for the response of the
              DELETE operation of LFB components.

       Type = "COMMIT-RESPONSE" - This operation is sent to the CE to
              confirm a commit success in a 2pc transaction.  A
              COMMIT-RESPONSE TLV MUST contain a RESULT-TLV indicating
              success or failure.

   PATH-DATA-TLV:

   This is generically a PATH-DATA-TLV format that has been defined in
   Section 7 in the PATH-DATA-TLV BNF definition.  The restriction on
   the use of PATH-DATA-TLV for SET-RESPONSE operation is that it MUST
   contain RESULT-TLV(s).  The restriction on the use of PATH-DATA-TLV
   for DEL-RESPONSE operation is it also MUST contain RESULT-TLV(s).
   The RESULT-TLV is defined in Section 7.1.7.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

    main hdr (type = ConfigResponse)
     |
     |
     +--- T = LFBselect
     .        |
     .        +-- LFBCLASSID = target LFB class
     .        |
              |
              +-- LFBInstance = target LFB instance
              |
              |
              +-- T = operation { SET-RESPONSE }
              |   |
              |   +--  // one or more path targets
              |        // associated with FULL or SPARSEDATA-TLV(s)
              |
              +-- T = operation { DEL-RESPONSE }
              |   |
              |   +--  // one or more path targets
              |
              +-- T = operation { COMMIT-RESPONSE }
              |           |
              |           +--  RESULT-TLV

             Figure 32: PDU Format for Config Response Message

7.7.  Query Messages

   The ForCES Query messages are used by the CE to query LFBs in the FE
   for information like LFB components, capabilities, statistics, etc.
   Query messages include the Query message and the Query Response
   message.

7.7.1.  Query Message

   A Query message is composed of a common header and a message body
   that consists of one or more TLV data formats.  Detailed description
   of the message is as follows:

   Message transfer direction:

   from CE to FE

   Message header:

   The Message Type in the header is set to MessageType= 'Query'.  The
   ACK flag in the header is always ignored, and a full response for a
   Query message is always expected.  The Correlator field in the header
   is set, so that the CE can locate the response back from FE
   correctly.

   OPER-TLV for Query:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type = GET/GET-PROP        |               Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    PATH-DATA-TLV for GET/GET-PROP             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 33: TLV for Query

   Type:

   The operation type for query.  Two operation types are defined:

       Type = "GET" - This operation is to request to get LFB
              components.

       Type = "GET-PROP" - This operation is to request to get LFB
              component properties.

   PATH-DATA-TLV for GET/GET-PROP:

   This is generically a PATH-DATA-TLV format that has been defined in
   Section 7 in the PATH-DATA-TLV BNF definition.  The restriction on
   the use of PATH-DATA-TLV for GET/GET-PROP operation is it MUST NOT
   contain any SPARSEDATA-TLV or FULLDATA- TLV and RESULT-TLV in the
   data format.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type = Query)
    |
    |
    +--- T = LFBselect
    .        |
    .        +-- LFBCLASSID = target LFB class
    .        |
             |
             +-- LFBInstance = target LFB instance
             |
             |
             +-- T = operation { GET }
             |   |
             |   +--  // one or more path targets
             |
             +-- T = operation { GET }
             .   |
             .   +--  // one or more path targets
             .

                  Figure 34: PDU Format for Query Message

7.7.2.  Query Response Message

   When receiving a Query message, the receiver should process the
   message and come up with a query result.  The receiver sends the
   query result back to the message sender by use of the Query Response
   message.  The query result can be the information being queried if
   the query operation is successful, or can also be error codes if the
   query operation fails, indicating the reasons for the failure.

   A Query Response message is also composed of a common header and a
   message body consisting of one or more TLVs describing the query
   result.  Detailed description of the message is as follows:

   Message transfer direction:

   from FE to CE

   Message header:

   The Message Type in the header is set to MessageType=
   'QueryResponse'.  The ACK flag in the header is ignored.  As a
   response itself, the message does not expect a further response.

   OPER-TLV for Query Response:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Type = GET-RESPONSE/GET-PROP-RESPONSE|    Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        PATH-DATA-TLV for GET-RESPONSE/GET-PROP-RESPONSE       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 35: TLV for Query Response

   Type:

   The operation type for query response.  One operation type is
   defined:

       Type = "GET-RESPONSE" - This operation is for the response of the
              GET operation of LFB components.

       Type = "GET-PROP-RESPONSE" - This operation is for the response
              of the GET-PROP operation of LFB components.

   PATH-DATA-TLV for GET-RESPONSE/GET-PROP-RESPONSE:

   This is generically a PATH-DATA-TLV format that has been defined in
   Section 7 in the PATH-DATA-TLV BNF definition.  The PATH-DATA- TLV
   for the GET-RESPONSE operation MAY contain SPARSEDATA-TLV,
   FULLDATA-TLV, and/or RESULT-TLV(s) in the data encoding.  The
   RESULT-TLV is defined in Section 7.1.7 and the SPARSEDATA-TLVs and
   FULLDATA-TLVs are defined in Section 7.1.8.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type = QueryResponse)
     |
     |
     +--- T = LFBselect
     .        |
     .        +-- LFBCLASSID = target LFB class
     .        |
              |
              +-- LFBInstance = target LFB instance
              |
              |
              +-- T = operation { GET-RESPONSE }
              |   |
              |   +--  // one or more path targets
              |
              +-- T = operation { GET-PROP-RESPONSE }
              .   |
              .   +--  // one or more path targets
              .

             Figure 36: PDU Format for Query Response Message

7.8.  Event Notification Message

   Event Notification message is used by the FE to asynchronously notify
   the CE of events that happen in the FE.

   All events that can be generated in an FE are subscribable by the CE.
   The CE can subscribe to an event via a Config message with the SET-
   PROP operation, where the included path specifies the event, as
   defined by the LFB Library and described by the FE Model.

   As usual, an Event Notification message is composed of a common
   header and a message body that consists of one or more TLV data
   formats.  Detailed description of the message is as follows:

   Message transfer direction:

   FE to CE

   Message header:

   The Message Type in the message header is set to
   MessageType = 'EventNotification'.  The ACK flag in the header MUST
   be ignored by the CE, and the Event Notification message does not
   expect any response from the receiver.

   OPER-TLV for Event Notification:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type = REPORT              |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    PATH-DATA-TLV for REPORT                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 37: TLV for Event Notification

   Type:

   Only one operation type is defined for the Event Notification
   message:

      Type = "REPORT" - This type of operation is for the FE to report
             something to the CE.

   PATH-DATA-TLV for REPORT:

   This is generically a PATH-DATA-TLV format that has been defined in
   Section 7 in the PATH-DATA-TLV BNF definition.  The PATH-DATA- TLV
   for the REPORT operation MAY contain FULLDATA-TLV or
   SPARSEDATA-TLV(s) but MUST NOT contain any RESULT-TLV in the data
   format.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type = Event Notification)
     |
     |
     +--- T = LFBselect
                |
                +-- LFBCLASSID = target LFB class
                |
                |
                +-- LFBInstance = target LFB instance
                |
                |
                +-- T = operation { REPORT }
                |   |
                |   +--  // one or more path targets
                |        // associated with FULL/SPARSE DATA TLV(s)
                +-- T = operation { REPORT }
                .   |
                .   +--  // one or more path targets
                .        // associated with FULL/SPARSE DATA TLV(s)

           Figure 38: PDU Format for Event Notification Message

7.9.  Packet Redirect Message

   A Packet Redirect message is used to transfer data packets between
   the CE and FE.  Usually, these data packets are control packets, but
   they may be just data path packets that need further (exception or
   high-touch) processing.  It is also feasible that this message
   carries no data packets and rather just meta data.

   The Packet Redirect message data format is formatted as follows:

   Message transfer direction:

   CE to FE or FE to CE

   Message header:

   The Message Type in the header is set to MessageType=
   'PacketRedirect'.

   Message body:

   This consists of one or more TLVs that contain or describe the packet
   being redirected.  The TLV is specifically a Redirect TLV (with the
   TLV Type="Redirect").  Detailed data format of a Redirect TLV for a
   Packet Redirect message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Type = Redirect        |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Meta Data TLV                          |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Redirect Data TLV                      |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 39: Redirect_Data TLV

   Meta Data TLV:

   This is a TLV that specifies meta data associated with followed
   redirected data.  The TLV is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type = METADATA-TLV        |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Meta Data ILV                          |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                           ...                                 ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Meta Data ILV                          |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 40: METADATA-TLV

   Meta Data ILV:

   This is an Identifier-Length-Value format that is used to describe
   one meta data.  The ILV has the format as:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Meta Data ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Length                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Meta Data Value                        |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 41: Meta Data ILV

   where Meta Data ID is an identifier for the meta data, which is
   statically assigned by the LFB definition.

   Redirect Data TLV:

   This is a TLV describing one packet of data to be directed via the
   redirect operation.  The TLV format is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type = REDIRECTDATA-TLV    |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Redirected Data                        |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 42: Redirect Data TLV

   Redirected Data:

   This field contains the packet that is to be redirected in network
   byte order.  The packet should be 32 bits aligned as is the data for
   all TLVs.  The meta data infers what kind of packet is carried in
   value field and therefore allows for easy decoding of data
   encapsulated.

   To better illustrate the above PDU format, a tree structure for the
   format is shown below:

   main hdr (type = PacketRedirect)
           |
           |
           +--- T = Redirect
           .        |
           .        +-- T = METADATA-TLV
                    |          |
                    |          +--  Meta Data ILV
                    |          |
                    |          +--  Meta Data ILV
                    |          .
                    |          .
                    |
                    +-- T = REDIRECTDATA-TLV
                        |
                        +--  // Redirected Data

             Figure 43: PDU Format for Packet Redirect Message

7.10.  Heartbeat Message

   The Heartbeat (HB) message is used for one ForCES element (FE or CE)
   to asynchronously notify one or more other ForCES elements in the
   same ForCES NE on its liveness.  Section 4.3.3 describes the traffic-
   sensitive approach used.

   A Heartbeat message is sent by a ForCES element periodically.  The
   parameterization and policy definition for heartbeats for an FE are
   managed as components of the FE Protocol Object LFB, and can be set
   by CE via a Config message.  The Heartbeat message is a little
   different from other protocol messages in that it is only composed of
   a common header, with the message body left empty.  A detailed
   description of the message is as follows:

   Message transfer direction:

   FE to CE or CE to FE

   Message header:

   The Message Type in the message header is set to MessageType =
   'Heartbeat'.  Section 4.3.3 describes the HB mechanisms used.  The
   ACK flag in the header MUST be set to either 'NoACK' or 'AlwaysACK'
   when the HB is sent.

       *   When set to 'NoACK', the HB is not soliciting for a response.

       *   When set to 'AlwaysACK', the HB Message sender is always
           expecting a response from its receiver.  According to the HB
           policies defined in Section 7.3.1, only the CE can send such
           an HB message to query FE liveness.  For simplicity and
           because of the minimal nature of the HB message, the response
           to an HB message is another HB message, i.e., no specific HB
           Response message is defined.  Whenever an FE receives an HB
           message marked with 'AlwaysACK' from the CE, the FE MUST send
           an HB message back immediately.  The HB message sent by the
           FE in response to the 'AlwaysACK' MUST modify the source and
           destination IDs so that the ID of the FE is the source ID and
           the CE ID of the sender is the destination ID, and MUST
           change the ACK information to 'NoACK'.  A CE MUST NOT respond
           to an HB message with 'AlwaysACK' set.

       *   When set to anything else other than 'NoACK' or 'AlwaysACK',
           the HB message is treated as if it was a 'NoACK'.

   The correlator field in the HB message header SHOULD be set
   accordingly when a response is expected so that a receiver can
   correlate the response correctly.  The correlator field MAY be
   ignored if no response is expected.

   Message body:

   The message body is empty for the Heartbeat message.

8.  High Availability Support

   The ForCES protocol provides mechanisms for CE redundancy and
   failover, in order to support High Availability as defined in
   [RFC3654].  FE redundancy and FE to FE interaction is currently out
   of scope of this document.  There can be multiple redundant CEs and
   FEs in a ForCES NE.  However, at any one time only one primary CE can
   control the FEs though there can be multiple secondary CEs.  The FE
   and the CE PL are aware of the primary and secondary CEs.  This
   information (primary, secondary CEs) is configured in the FE and in
   the CE PLs during pre-association by the FEM and the CEM
   respectively.  Only the primary CE sends control messages to the FEs.

8.1.  Relation with the FE Protocol

   High Availability parameterization in an FE is driven by configuring
   the FE Protocol Object LFB (refer to Appendix B and Section 7.3.1).
   The FE Heartbeat Interval, CE Heartbeat Dead Interval, and CE

   Heartbeat policy help in detecting connectivity problems between an
   FE and CE.  The CE failover policy defines the reaction on a detected
   failure.

   Figure 44 extends the state machine illustrated in Figure 4 to allow
   for new states that facilitate connection recovery.

       (CE issues Teardown ||    +-----------------+
          Lost association) &&   | Pre-association |
         CE failover policy = 0  | (Association    |
             +------------>-->-->|   in            +<----+
             |                   | progress)       |     |
             |     CE issues     +--------+--------+     |
             |     Association        |                  | CFTI
             |       Setup            V                  | timer
             |     ___________________+                  | expires
             |     |                                     |
             |     V                                     ^
           +-+-----------+                          +-------+-----+
           |             |                          |  Not        |
           |             |  (CE issues Teardown ||  |  Associated |
           |             |    Lost association) &&  |             |
           | Associated  |  CE failover policy = 1  | (May        |
           |             |                          | Continue    |
           |             |---------->------->------>|  Forwarding)|
           |             |                          |             |
           +-------------+                          +-------------+
                ^                                         V
                |                                         |
                |            CE issues                    |
                |            Association                  |
                |            Setup                        |
                +_________________________________________+

                Figure 44: FE State Machine Considering HA

   Section 4.2 describes transitions between the pre-association,
   associated, and not associated states.

   When communication fails between the FE and CE (which can be caused
   by either the CE or link failure but not FE related), either the TML
   on the FE will trigger the FE PL regarding this failure or it will be
   detected using the HB messages between FEs and CEs.  The
   communication failure, regardless of how it is detected, MUST be
   considered as a loss of association between the CE and corresponding
   FE.

   If the FE's FEPO CE failover policy is configured to mode 0 (the
   default), it will immediately transition to the pre-association
   phase.  This means that if association is again established, all FE
   state will need to be re-established.

   If the FE's FEPO CE failover policy is configured to mode 1, it
   indicates that the FE is capable of HA restart recovery.  In such a
   case, the FE transitions to the not associated state and the CEFTI
   timer is started.  The FE MAY continue to forward packets during this
   state.  It MAY also recycle through any configured secondary CEs in a
   round-robin fashion.  It first adds its primary CE to the tail of
   backup CEs and sets its primary CE to be the first secondary.  It
   then attempts to associate with the CE designated as the new primary
   CE.  If it fails to re-associate with any CE and the CEFTI expires,
   the FE then transitions to the pre-association state.

   If the FE, while in the not associated state, manages to reconnect to
   a new primary CE before CEFTI expires, it transitions to the
   associated state.  Once re-associated, the FE tries to recover any
   state that may have been lost during the not associated state.  How
   the FE achieves this is out of scope for this document.

   Figure 45 below illustrates the ForCES message sequences that the FE
   uses to recover the connection.

         FE                   CE Primary        CE Secondary
         |                       |                    |
         |  Asso Estb,Caps exchg |                    |
       1 |<--------------------->|                    |
         |                       |                    |
         |       All msgs        |                    |
       2 |<--------------------->|                    |
         |                       |                    |
         |                       |                    |
         |                   FAILURE                  |
         |                                            |
         |         Asso Estb,Caps exchange            |
       3 |<------------------------------------------>|
         |                                            |
         |              Event Report (pri CE down)    |
       4 |------------------------------------------->|
         |                                            |
         |                   All Msgs                 |
       5 |<------------------------------------------>|

              Figure 45: CE Failover for Report Primary Mode

   A CE-to-CE synchronization protocol would be needed to support fast
   failover as well as to address some of the corner cases; however,
   this will not be defined by the ForCES protocol as it is out of scope
   for this specification.

   An explicit message (a Config message setting primary CE component in
   the FE Protocol Object) from the primary CE can also be used to
   change the primary CE for an FE during normal protocol operation.

   Also note that the FEs in a ForCES NE could also use a multicast CE
   ID, i.e., they could be associated with a group of CEs (this assumes
   the use of a CE-CE synchronization protocol, which is out of scope
   for this specification).  In this case, the loss of association would
   mean that communication with the entire multicast group of CEs has
   been lost.  The mechanisms described above will apply for this case
   as well during the loss of association.  If, however, the secondary
   CE was also using the multicast CE ID that was lost, then the FE will
   need to form a new association using a different CE ID.  If the
   capability exists, the FE MAY first attempt to form a new association
   with the original primary CE using a different non-multicast CE ID.

8.2.  Responsibilities for HA

   TML level:

   1.  The TML controls logical connection availability and failover.

   2.  The TML also controls peer HA management.

   At this level, control of all lower layers, for example, transport
   level (such as IP addresses, MAC addresses, etc.) and associated
   links going down are the role of the TML.

   PL level:

   All other functionality, including configuring the HA behavior during
   setup, the CE IDs used to identify primary and secondary CEs,
   protocol messages used to report CE failure (Event Report), Heartbeat
   messages used to detect association failure, messages to change the
   primary CE (Config), and other HA-related operations described
   before, are the PL responsibility.

   To put the two together, if a path to a primary CE is down, the TML
   would take care of failing over to a backup path, if one is
   available.  If the CE is totally unreachable, then the PL would be
   informed and it would take the appropriate actions described earlier.

9.  Security Considerations

   The ForCES framework document [RFC3746], Section 8, goes into
   extensive detail on a variety of security threats, the possible
   effects of those threats on the protocol, and responses to those
   threats.  This document does not repeat that discussion; the reader
   is referred to the ForCES framework document [RFC3746] for those
   details and how the ForCES architecture addresses them.

   ForCES PL uses security services provided by the ForCES TML.  The TML
   provides security services such as endpoint authentication service,
   message authentication service, and confidentiality service.
   Endpoint authentication service is invoked at the time of the pre-
   association connection establishment phase and message authentication
   is performed whenever the FE or CE receives a packet from its peer.

   The following are the general security mechanisms that need to be in
   place for ForCES PL.

   o  Security mechanisms are session controlled -- that is, once the
      security is turned on depending upon the chosen security level (No
      Security, Authentication, Confidentiality), it will be in effect
      for the entire duration of the session.

   o  An operator should configure the same security policies for both
      primary and backup FEs and CEs (if available).  This will ensure
      uniform operations and avoid unnecessary complexity in policy
      configuration.

9.1.  No Security

   When "No Security" is chosen for ForCES protocol communication, both
   endpoint authentication and message authentication service needs to
   be performed by ForCES PL.  Both these mechanism are weak and do not
   involve cryptographic operation.  An operator can choose "No
   Security" level when the ForCES protocol endpoints are within a
   single box, for example.

   In order to have interoperable and uniform implementation across
   various security levels, each CE and FE endpoint MUST implement this
   level.

   What is described below (in Section 9.1.1 and Section 9.1.2) are
   error checks and not security procedures.  The reader is referred to
   Section 9.2 for security procedures.

9.1.1.  Endpoint Authentication

   Each CE and FE PL maintains a list of associations as part of its
   configuration.  This is done via the CEM and FEM interfaces.  An FE
   MUST connect to only those CEs that are configured via the FEM;
   similarly, a CE should accept the connection and establish
   associations for the FEs which are configured via the CEM.  The CE
   should validate the FE identifier before accepting the connections
   during the pre-association phase.

9.1.2.  Message Authentication

   When a CE or FE initiates a message, the receiving endpoint MUST
   validate the initiator of the message by checking the common header
   CE or FE identifiers.  This will ensure proper protocol functioning.
   This extra processing step is recommended even when the underlying
   TML layer security services exist.

9.2.  ForCES PL and TML Security Service

   This section is applicable if an operator wishes to use the TML
   security services.  A ForCES TML MUST support one or more security
   services such as endpoint authentication service, message
   authentication service, and confidentiality service, as part of TML
   security layer functions.  It is the responsibility of the operator
   to select an appropriate security service and configure security
   policies accordingly.  The details of such configuration are outside
   the scope of the ForCES PL and are dependent on the type of transport
   protocol and the nature of the connection.

   All these configurations should be done prior to starting the CE and
   FE.

   When certificates-based authentication is being used at the TML, the
   certificate can use a ForCES-specific naming structure as certificate
   names and, accordingly, the security policies can be configured at
   the CE and FE.

   The reader is asked to refer to specific TML documents for details on
   the security requirements specific to that TML.

9.2.1.  Endpoint Authentication Service

   When TML security services are enabled, the ForCES TML performs
   endpoint authentication.  Security association is established between
   CE and FE and is transparent to the ForCES PL.

9.2.2.  Message Authentication Service

   This is a TML-specific operation and is transparent to the ForCES PL.
   For details, refer to Section 5.

9.2.3.  Confidentiality Service

   This is a TML-specific operation and is transparent to the ForCES PL.
   For details, refer to Section 5.

10.  Acknowledgments

   The authors of this document would like to acknowledge and thank the
   ForCES Working Group and especially the following: Furquan Ansari,
   Alex Audu, Steven Blake, Shuchi Chawla, Alan DeKok, Ellen M.
   Deleganes, Xiaoyi Guo, Yunfei Guo, Evangelos Haleplidis, Zsolt
   Haraszti, Fenggen Jia, John C. Lin, Alistair Munro, Jeff Pickering,
   T. Sridhlar, Guangming Wang, Chaoping Wu, and Lily L. Yang, for their
   contributions.  We would also like to thank David Putzolu and Patrick
   Droz for their comments and suggestions on the protocol and for their
   infinite patience.  We would also like to thank Sue Hares and Alia
   Atlas for extensive reviews of the document.

   Alia Atlas did a wonderful job of shaping the document to make it
   more readable by providing the IESG feedback.

   Ross Callon was instrumental in getting us over major humps to
   getting this document published.

   The editors have used the xml2rfc [RFC2629] tools in creating this
   document and are very grateful for the existence and quality of these
   tools.  The editor is also grateful to Elwyn Davies for his help in
   correcting the XML source of this document.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
              RFC 2914, September 2000.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5390]  Rosenberg, J., "Requirements for Management of Overload in
              the Session Initiation Protocol", RFC 5390, December 2008.

   [RFC5811]  Hadi Salim, J. and K. Ogawa, "SCTP-Based Transport Mapping
              Layer (TML) for the Forwarding and Control Element
              Separation (ForCES) Protocol", RFC 5811, March 2010.

   [RFC5812]  Halpern, J. and J. Hadi Salim, "Forwarding and Control
              Element Separation (ForCES) Forwarding Element Model",
              RFC 5812, March 2010.

11.2.  Informative References

   [2PCREF]   Gray, J., "Notes on database operating systems", in
              "Operating Systems: An Advanced Course" Lecture Notes in
              Computer Science, Vol. 60, pp. 394-481, Springer-Verlag,
              1978.

   [ACID]     Haerder, T. and A. Reuter, "Principles of Transaction-
              Orientated Database Recovery", 1983.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3654]  Khosravi, H. and T. Anderson, "Requirements for Separation
              of IP Control and Forwarding", RFC 3654, November 2003.

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

Appendix A.  IANA Considerations

   Following the policies outlined in "Guidelines for Writing an IANA
   Considerations Section in RFCs" (RFC 5226 [RFC5226]), the following
   namespaces are defined in ForCES.

   o  Message Type Namespace, Section 7

   o  Operation Type Namespace, Section 7.1.6

   o  Header Flags, Section 6.1

   o  TLV Type, Section 7

   o  TLV Result Values, Section 7.1.7

   o  LFB Class ID, Section 7.1.5 (resolved by model document,
      [RFC5812].

   o  Result: Association Setup Response, Section 7.5.2

   o  Reason: Association Teardown Message, Section 7.5.3

A.1.  Message Type Namespace

   The Message Type is an 8-bit value.  The following is the guideline
   for defining the Message Type namespace:

   Message Types 0x00 - 0x1F
      Message Types in this range are part of the base ForCES protocol.
      Message Types in this range are allocated through an IETF
      consensus action [RFC5226].

      Values assigned by this specification:

       0x00               Reserved
       0x01               AssociationSetup
       0x02               AssociationTeardown
       0x03               Config
       0x04               Query
       0x05               EventNotification
       0x06               PacketRedirect
       0x07 - 0x0E        Reserved
       0x0F               Hearbeat
       0x11               AssociationSetupResponse
       0x12               Reserved
       0x13               ConfigResponse
       0x14               QueryResponse

   Message Types 0x20 - 0x7F
      Message Types in this range are Specification Required [RFC5226].
      Message Types using this range MUST be documented in an RFC or
      other permanent and readily available reference.

   Message Types 0x80 - 0xFF
      Message Types in this range are reserved for vendor private
      extensions and are the responsibility of individual vendors.  IANA
      management of this range of the Message Type namespace is
      unnecessary.

A.2.  Operation Selection

   The Operation Selection (OPER-TLV) namespace is 16 bits long.  The
   following is the guideline for managing the OPER-TLV namespace.

   OPER-TLV Type 0x0000-0x0FF
      OPER-TLV Types in this range are allocated through an IETF
      consensus process [RFC5226].

      Values assigned by this specification:

                 0x0000           Reserved
                 0x0001           SET
                 0x0002           SET-PROP
                 0x0003           SET-RESPONSE
                 0x0004           SET-PROP-RESPONSE
                 0x0005           DEL
                 0x0006           DEL-RESPONSE
                 0x0007           GET
                 0x0008           GET-PROP
                 0x0009           GET-RESPONSE
                 0x000A           GET-PROP-RESPONSE
                 0x000B           REPORT
                 0x000C           COMMIT
                 0x000D           COMMIT-RESPONSE
                 0x000E           TRCOMP

   OPER-TLV Type 0x0100-0x7FFF
      OPER-TLV Types using this range MUST be documented in an RFC or
      other permanent and readily available reference [RFC5226].

   OPER-TLV Type 0x8000-0xFFFF
      OPER-TLV Types in this range are reserved for vendor private
      extensions and are the responsibility of individual vendors.  IANA
      management of this range of the OPER-TLV Type namespace is
      unnecessary.

A.3.  Header Flags

      The Header flag field is 32 bits long.  Header flags are part of
      the ForCES base protocol.  Header flags are allocated through an
      IETF consensus action [RFC5226].

A.4.  TLV Type Namespace

   The TLV Type namespace is 16 bits long.  The following is the
   guideline for managing the TLV Type namespace.

   TLV Type 0x0000-0x01FF
      TLV Types in this range are allocated through an IETF consensus
      process [RFC5226].

      Values assigned by this specification:

                 0x0000           Reserved
                 0x0001           REDIRECT-TLV
                 0x0010           ASResult-TLV
                 0x0011           ASTreason-TLV
                 0x1000           LFBselect-TLV
                 0x0110           PATH-DATA-TLV
                 0x0111           KEYINFO-TLV
                 0x0112           FULLDATA-TLV
                 0x0113           SPARSEDATA-TLV
                 0x0114           RESULT-TLV
                 0x0115           METADATA-TLV
                 0x0116           REDIRECTDATA-TLV

   TLV Type 0x0200-0x7FFF
      TLV Types using this range MUST be documented in an RFC or other
      permanent and readily available reference [RFC5226].

   TLV Type 0x8000-0xFFFF
      TLV Types in this range are reserved for vendor private extensions
      and are the responsibility of individual vendors.  IANA management
      of this range of the TLV Type namespace is unnecessary.

A.5.  RESULT-TLV Result Values

   The RESULT-TLV RTesult Value is an 8-bit value.

                0x00        E_SUCCESS
                0x01        E_INVALID_HEADER
                0x02        E_LENGTH_MISMATCH
                0x03        E_VERSION_MISMATCH
                0x04        E_INVALID_DESTINATION_PID
                0x05        E_LFB_UNKNOWN
                0x06        E_LFB_NOT_FOUND
                0x07        E_LFB_INSTANCE_ID_NOT_FOUND
                0x08        E_INVALID_PATH
                0x09        E_COMPONENT_DOES_NOT_EXIST
                0x0A        E_EXISTS
                0x0B        E_NOT_FOUND
                0x0C        E_READ_ONLY
                0x0D        E_INVALID_ARRAY_CREATION
                0x0E        E_VALUE_OUT_OF_RANGE
                0x0F        E_CONTENTS_TOO_LONG
                0x10        E_INVALID_PARAMETERS
                0x11        E_INVALID_MESSAGE_TYPE
                0x12        E_E_INVALID_FLAGS
                0x13        E_INVALID_TLV
                0x14        E_EVENT_ERROR
                0x15        E_NOT_SUPPORTED
                0x16        E_MEMORY_ERROR
                0x17        E_INTERNAL_ERROR
                0x18-0xFE   Reserved
                0xFF        E_UNSPECIFIED_ERROR

   All values not assigned in this specification are designated as
   Assignment by Expert Review.

A.6.  Association Setup Response

   The Association Setup Response namespace is 32 bits long.  The
   following is the guideline for managing the Association Setup
   Response namespace.

   Association Setup Response 0x0000-0x00FF
      Association Setup Responses in this range are allocated through an
      IETF consensus process [RFC5226].

      Values assigned by this specification:

          0x0000   Success
          0x0001   FE ID Invalid
          0x0002   Permission Denied

   Association Setup Response 0x0100-0x0FFF
      Association Setup Responses in this range are Specification
      Required [RFC5226].  Values using this range MUST be documented in
      an RFC or other permanent and readily available reference
      [RFC5226].

   Association Setup Response 0x1000-0xFFFF
      Association Setup Responses in this range are reserved for vendor
      private extensions and are the responsibility of individual
      vendors.  IANA management of this range of the Association Setup
      Response namespace is unnecessary.

A.7.  Association Teardown Message

   The Association Teardown Message namespace is 32 bits long.  The
   following is the guideline for managing the Association Teardown
   Message namespace.

   Association Teardown Message 0x00000000-0x0000FFFF
      Association Teardown Messages in this range are allocated through
      an IETF consensus process [RFC5226].

      Values assigned by this specification:

           0x00000000        Normal - teardown by administrator
           0x00000001        Error  - loss of heartbeats
           0x00000002        Error  - loss of bandwidth
           0x00000003        Error  - out of Memory
           0x00000004        Error  - application crash
           0x000000FF        Error  - unspecified

   Association Teardown Message 0x00010000-0x7FFFFFFF
      Association Teardown Messages in this range are Specification
      Required [RFC5226].  Association Teardown Messages using this
      range MUST be documented in an RFC or other permanent and readily
      available references.  [RFC5226].

   Association Teardown Message 0x80000000-0xFFFFFFFFF
      Association Teardown Messages in this range are reserved for
      vendor private extensions and are the responsibility of individual

      vendors.  IANA management of this range of the Association
      Teardown Message namespace is unnecessary.

Appendix B.  ForCES Protocol LFB Schema

   The schema described below conforms to the LFB schema described in
   the ForCES model [RFC5812].

   Section 7.3.1 describes the details of the different components
   defined in this definition.

   <LFBLibrary xmlns="urn:ietf:params:xml:ns:forces:lfbmodel:1.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       provides="FEPO">
   <!-- XXX  -->
     <dataTypeDefs>
        <dataTypeDef>
           <name>CEHBPolicyValues</name>
                  <synopsis>
                      The possible values of CE heartbeat policy
                  </synopsis>
              <atomic>
              <baseType>uchar</baseType>
              <specialValues>
                 <specialValue value="0">
                   <name>CEHBPolicy0</name>
                   <synopsis>
                        The CE heartbeat policy 0
                   </synopsis>
                   </specialValue>
                 <specialValue value="1">
                    <name>CEHBPolicy1</name>
                    <synopsis>
                         The CE heartbeat policy 1
                    </synopsis>
                 </specialValue>
               </specialValues>
               </atomic>
         </dataTypeDef>

         <dataTypeDef>
            <name>FEHBPolicyValues</name>
                 <synopsis>
                     The possible values of FE heartbeat policy
                </synopsis>
              <atomic>
              <baseType>uchar</baseType>
              <specialValues>

                <specialValue value="0">
                  <name>FEHBPolicy0</name>
                  <synopsis>
                       The FE heartbeat policy 0
                  </synopsis>
                </specialValue>
                <specialValue value="1">
                   <name>FEHBPolicy1</name>
                   <synopsis>
                        The FE heartbeat policy 1
                   </synopsis>
                  </specialValue>
               </specialValues>
               </atomic>
         </dataTypeDef>

         <dataTypeDef>
         <name>FERestartPolicyValues</name>
               <synopsis>
                   The possible values of FE restart policy
               </synopsis>
              <atomic>
              <baseType>uchar</baseType>
              <specialValues>
                 <specialValue value="0">
                   <name>FERestartPolicy0</name>
                   <synopsis>
                        The FE restart policy 0
                   </synopsis>
                   </specialValue>
               </specialValues>
               </atomic>
         </dataTypeDef>

         <dataTypeDef>
         <name>CEFailoverPolicyValues</name>
               <synopsis>
                   The possible values of CE failover policy
               </synopsis>
              <atomic>
              <baseType>uchar</baseType>
              <specialValues>
                <specialValue value="0">
                   <name>CEFailoverPolicy0</name>
                   <synopsis>
                        The CE failover policy 0
                   </synopsis>
                 </specialValue>

               <specialValue value="1">
                  <name>CEFailoverPolicy1</name>
                  <synopsis>
                       The CE failover policy 1
                  </synopsis>
                </specialValue>
               </specialValues>
               </atomic>
         </dataTypeDef>

        <dataTypeDef>
           <name>FEHACapab</name>
                  <synopsis>
                      The supported HA features
                  </synopsis>
              <atomic>
              <baseType>uchar</baseType>
              <specialValues>
                 <specialValue value="0">
                   <name>GracefullRestart</name>
                   <synopsis>
                        The FE supports Graceful Restart
                   </synopsis>
                   </specialValue>
                 <specialValue value="1">
                    <name>HA</name>
                    <synopsis>
                         The FE supports HA
                    </synopsis>
                 </specialValue>
               </specialValues>
               </atomic>
         </dataTypeDef>
     </dataTypeDefs>

     <LFBClassDefs>
       <LFBClassDef LFBClassID="2">
         <name>FEPO</name>
         <synopsis>
            The FE Protocol Object
         </synopsis>
         <version>1.0</version>

     <components>
           <component componentID="1" access="read-only">
               <name>CurrentRunningVersion</name>
               <synopsis>Currently running ForCES version</synopsis>
               <typeRef>uchar</typeRef>

             </component>
           <component componentID="2" access="read-only">
             <name>FEID</name>
             <synopsis>Unicast FEID</synopsis>
             <typeRef>uint32</typeRef>
           </component>
           <component componentID="3" access="read-write">
              <name>MulticastFEIDs</name>
              <synopsis>
                 the table of all multicast IDs
              </synopsis>
              <array type="variable-size">
               <typeRef>uint32</typeRef>
              </array>
           </component>
           <component componentID="4" access="read-write">
             <name>CEHBPolicy</name>
             <synopsis>
              The CE Heartbeat Policy
             </synopsis>
             <typeRef>CEHBPolicyValues</typeRef>
           </component>
           <component componentID="5" access="read-write">
             <name>CEHDI</name>
             <synopsis>
               The CE Heartbeat Dead Interval in millisecs
             </synopsis>
             <typeRef>uint32</typeRef>
           </component>
           <component componentID="6" access="read-write">
             <name>FEHBPolicy</name>
             <synopsis>
               The FE Heartbeat Policy
             </synopsis>
             <typeRef>FEHBPolicyValues</typeRef>
           </component>
           <component componentID="7" access="read-write">
             <name>FEHI</name>
             <synopsis>
               The FE Heartbeat Interval in millisecs
             </synopsis>
             <typeRef>uint32</typeRef>
           </component>
           <component componentID="8" access="read-write">
             <name>CEID</name>
             <synopsis>
                The Primary CE this FE is associated with
             </synopsis>

             <typeRef>uint32</typeRef>
           </component>

           <component componentID="9" access="read-write">
              <name>BackupCEs</name>
              <synopsis>
                 The table of all backup CEs other than the primary
              </synopsis>
              <array type="variable-size">
               <typeRef>uint32</typeRef>
              </array>
           </component>
           <component componentID="10" access="read-write">
             <name>CEFailoverPolicy</name>
             <synopsis>
               The CE Failover Policy
             </synopsis>
             <typeRef>CEFailoverPolicyValues</typeRef>
           </component>

           <component componentID="11" access="read-write">
             <name>CEFTI</name>
             <synopsis>
               The CE Failover Timeout Interval in millisecs
             </synopsis>
             <typeRef>uint32</typeRef>
           </component>
           <component componentID="12" access="read-write">
             <name>FERestartPolicy</name>
             <synopsis>
                The FE Restart Policy
             </synopsis>
             <typeRef>FERestartPolicyValues</typeRef>
           </component>
           <component componentID="13" access="read-write">
             <name>LastCEID</name>
             <synopsis>
                The Primary CE this FE was last associated with
             </synopsis>
             <typeRef>uint32</typeRef>
           </component>
         </components>

        <capabilities>
             <capability componentID="30">
                <name>SupportableVersions</name>
                <synopsis>
                   the table of ForCES versions that FE supports

                </synopsis>
                <array type="variable-size">
                 <typeRef>uchar</typeRef>
                </array>
              </capability>
           <capability componentID="31">
              <name>HACapabilities</name>
              <synopsis>
                 the table of HA capabilities the FE supports
              </synopsis>
              <array type="variable-size">
               <typeRef>FEHACapab</typeRef>
              </array>
           </capability>
         </capabilities>

         <events baseID="61">
           <event eventID="1">
             <name>PrimaryCEDown</name>
             <synopsis>
                 The pimary CE has changed
             </synopsis>
             <eventTarget>
                 <eventField>LastCEID</eventField>
             </eventTarget>
             <eventChanged/>
             <eventReports>
                <eventReport>
                  <eventField>LastCEID</eventField>
                </eventReport>
             </eventReports>
           </event>
         </events>

       </LFBClassDef>
     </LFBClassDefs>
   </LFBLibrary>

B.1.  Capabilities

   Supportable Versions enumerates all ForCES versions that an FE
   supports.

   FEHACapab enumerates the HA capabilities of the FE.  If the FE is not
   capable of graceful restarts or HA, then it will not be able to
   participate in HA as described in Section 8.1.

B.2.  Components

   All components are explained in Section 7.3.1.

Appendix C.  Data Encoding Examples

   In this section a few examples of data encoding are discussed.  These
   example, however, do not show any padding.

   ==========
   Example 1:
   ==========

   Structure with three fixed-lengthof, mandatory fields.

           struct S {
           uint16 a
           uint16 b
           uint16 c
           }

   (a) Describing all fields using SPARSEDATA-TLV

           PATH-DATA-TLV
             Path to an instance of S ...
             SPARSEDATA-TLV
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(b), lengthof(b), valueof(b)
               ComponentIDof(c), lengthof(c), valueof(c)

   (b) Describing a subset of fields

           PATH-DATA-TLV
             Path to an instance of S ...
             SPARSEDATA-TLV
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(c), lengthof(c), valueof(c)

   Note: Even though there are non-optional components in structure S,
   since one can uniquely identify components, one can selectively send
   components of structure S (e.g., in the case of an update from CE to
   FE).

   (c) Describing all fields using a FULLDATA-TLV

           PATH-DATA-TLV
             Path to an instance of S ...
             FULLDATA-TLV
               valueof(a)
               valueof(b)
               valueof(c)

   ==========
   Example 2:
   ==========

   Structure with three fixed-lengthof fields, one mandatory, two
   optional.

           struct T {
           uint16 a
           uint16 b (optional)
           uint16 c (optional)
           }

   This example is identical to example 1, as illustrated below.

   (a) Describing all fields using SPARSEDATA-TLV

           PATH-DATA-TLV
             Path to an instance of S ...
             SPARSEDATA-TLV
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(b), lengthof(b), valueof(b)
               ComponentIDof(c), lengthof(c), valueof(c)

   (b) Describing a subset of fields using SPARSEDATA-TLV

           PATH-DATA-TLV
             Path to an instance of S ...
             SPARSEDATA-TLV
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(c), lengthof(c), valueof(c)

   (c) Describing all fields using a FULLDATA-TLV

           PATH-DATA-TLV
             Path to an instance of S ...
             FULLDATA-TLV
               valueof(a)
               valueof(b)
               valueof(c)

   Note: FULLDATA-TLV _cannot_ be used unless all fields are being
   described.

   ==========
   Example 3:
   ==========

   Structure with a mix of fixed-lengthof and variable-lengthof fields,
   some mandatory, some optional.  Note in this case, b is variable
   sized.

           struct U {
           uint16 a
           string b (optional)
           uint16 c (optional)
           }

   (a) Describing all fields using SPARSEDATA-TLV

           Path to an instance of U ...
           SPARSEDATA-TLV
             ComponentIDof(a), lengthof(a), valueof(a)
             ComponentIDof(b), lengthof(b), valueof(b)
             ComponentIDof(c), lengthof(c), valueof(c)

   (b) Describing a subset of fields using SPARSEDATA-TLV

           Path to an instance of U ...
           SPARSEDATA-TLV
             ComponentIDof(a), lengthof(a), valueof(a)
             ComponentIDof(c), lengthof(c), valueof(c)

   (c) Describing all fields using FULLDATA-TLV

           Path to an instance of U ...
             FULLDATA-TLV
               valueof(a)
               FULLDATA-TLV
                 valueof(b)
               valueof(c)

   Note: The variable-length field requires the addition of a FULLDATA-
   TLV within the outer FULLDATA-TLV as in the case of component b
   above.

   ==========
   Example 4:
   ==========

   Structure containing an array of another structure type.

           struct V {
           uint32 x
           uint32 y
           struct U z[]
           }

   (a) Encoding using SPARSEDATA-TLV, with two instances of z[], also
   described with SPARSEDATA-TLV, assuming only the 10th and 15th
   subscripts of z[] are encoded.

        path to instance of V ...
        SPARSEDATA-TLV
         ComponentIDof(x), lengthof(x), valueof(x)
         ComponentIDof(y), lengthof(y), valueof(y)
         ComponentIDof(z), lengthof(all below)
           ComponentID = 10 (i.e index 10 from z[]), lengthof(all below)
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(b), lengthof(b), valueof(b)
           ComponentID = 15 (index 15 from z[]), lengthof(all below)
               ComponentIDof(a), lengthof(a), valueof(a)
               ComponentIDof(c), lengthof(c), valueof(c)

   Note the holes in the components of z (10 followed by 15).  Also note
   the gap in index 15 with only components a and c appearing but not b.

Appendix D.  Use Cases

   Assume LFB with the following components for the following use cases.

   foo1, type u32, ID = 1

   foo2, type u32, ID = 2

   table1: type array, ID = 3
           components are:
           t1, type u32, ID = 1
           t2, type u32, ID = 2  // index into table2
           KEY: nhkey, ID = 1, V = t2

   table2: type array, ID = 4
           components are:
           j1, type u32, ID = 1
           j2, type u32, ID = 2
           KEY: akey, ID = 1, V = { j1,j2 }

   table3: type array, ID = 5
           components are:
           someid, type u32, ID = 1
           name, type string variable sized, ID = 2

   table4: type array, ID = 6
           components are:
           j1, type u32, ID = 1
           j2, type u32, ID = 2
           j3, type u32, ID = 3
           j4, type u32, ID = 4
           KEY: mykey, ID = 1, V = { j1}

   table5: type array, ID = 7
           components are:
           p1, type u32, ID = 1
           p2, type array, ID = 2, array components of type-X

   Type-X:
           x1, ID 1, type u32
           x2, ID2 , type u32
                   KEY: tkey, ID = 1, V = { x1}

   All examples will use valueof(x) to indicate the value of the
   referenced component x.  In the case where F_SEL** are missing (bits
   equal to 00) then the flags will not show any selection.

   All the examples only show use of FULLDATA-TLV for data encoding;
   although SPARSEDATA-TLV would make more sense in certain occasions,
   the emphasis is on showing the message layout.  Refer to Appendix C
   for examples that show usage of both FULLDATA-TLV and SPARSEDATA-TLV.

   1.   To get foo1

   OPER = GET-TLV
           PATH-DATA-TLV: IDCount = 1, IDs = 1
   Result:
   OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags=0, IDCount = 1, IDs = 1
                   FULLDATA-TLV L = 4+4, V =  valueof(foo1)

   2.   To set foo2 to 10

   OPER = SET-TLV
           PATH-DATA-TLV:
                   flags = 0,  IDCount = 1, IDs = 2
                   FULLDATA-TLV: L = 4+4, V=10

   Result:
   OPER = SET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0,  IDCount = 1, IDs = 2
                   RESULT-TLV

   3.   To dump table2

      OPER = GET-TLV
           PATH-DATA-TLV:
                   IDCount = 1, IDs = 4
      Result:
      OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0, IDCount = 1, IDs = 4
                   FULLDATA-TLV: L = XXX, V=
                        a series of: index, valueof(j1), valueof(j2)
                        representing the entire table

        Note:   One should be able to take a GET-RESPONSE-TLV and
           convert it to a SET-TLV.  If the result in the above example
           is sent back in a SET-TLV (instead of a GET-RESPONSE_TLV),
           then the entire contents of the table will be replaced at
           that point.

   4.   Multiple operations example.  To create entry 0-5 of table2
        (Error conditions are ignored)

   OPER = SET-TLV
           PATH-DATA-TLV:
                   flags = 0 , IDCount = 1, IDs = 4
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 0
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 0
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 1
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 1
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 2
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 2
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 3
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 3
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 4
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 4
                   PATH-DATA-TLV
                     flags = 0, IDCount = 1, IDs = 5
                     FULLDATA-TLV valueof(j1), valueof(j2) of entry 5

   Result:
   OPER = SET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0 , IDCount = 1, IDs = 4
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 0
                       RESULT-TLV
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 1
                       RESULT-TLV
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 2
                       RESULT-TLV
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 3
                       RESULT-TLV
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 4
                       RESULT-TLV
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 5
                       RESULT-TLV

   5.   Block operations (with holes) example.  Replace entry 0,2 of
        table2.

   OPER = SET-TLV
           PATH-DATA-TLV:
                flags =  0 , IDCount = 1, IDs = 4
                PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 0
                   FULLDATA-TLV containing valueof(j1), valueof(j2) of 0
                PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV containing valueof(j1), valueof(j2) of 2

   Result:
   OPER = SET-TLV
           PATH-DATA-TLV:
                flags =  0 , IDCount = 1, IDs = 4
                PATH-DATA-TLV
                    flags = 0, IDCount = 1, IDs = 0
                    RESULT-TLV
                PATH-DATA-TLV
                    flags = 0, IDCount = 1, IDs = 2
                    RESULT-TLV

   6.   Getting rows example.  Get first entry of table2.

   OPER = GET-TLV
           PATH-DATA-TLV:
                   IDCount = 2, IDs = 4.0

   Result:
   OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV:
                   IDCount = 2, IDs = 4.0
                    FULLDATA-TLV containing valueof(j1), valueof(j2)

   7.   Get entry 0-5 of table2.

   OPER = GET-TLV
           PATH-DATA-TLV:
                   flags = 0, IDCount = 1, IDs = 4
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 0
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 1
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 2
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 3
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 4
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 5

   Result:
   OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0, IDCount = 1, IDs = 4
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 0
                       FULLDATA-TLV containing valueof(j1), valueof(j2)
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 1
                       FULLDATA-TLV containing valueof(j1), valueof(j2)
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 2
                       FULLDATA-TLV containing valueof(j1), valueof(j2)
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 3
                       FULLDATA-TLV containing valueof(j1), valueof(j2)
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 4
                       FULLDATA-TLV containing valueof(j1), valueof(j2)
                   PATH-DATA-TLV
                       flags = 0, IDCount = 1, IDs = 5
                       FULLDATA-TLV containing valueof(j1), valueof(j2)

   8.   Create a row in table2, index 5.

   OPER = SET-TLV
           PATH-DATA-TLV:
                flags = 0, IDCount = 2, IDs = 4.5
                FULLDATA-TLV containing valueof(j1), valueof(j2)

   Result:
   OPER = SET-RESPONSE-TLV
           PATH-DATA-TLV:
                flags = 0, IDCount = 1, IDs = 4.5
                RESULT-TLV

   9.   Dump contents of table1.

   OPER = GET-TLV
           PATH-DATA-TLV:
                   flags = 0, IDCount = 1, IDs = 3

   Result:
   OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX
                           (depending on size of table1)
                           index, valueof(t1),valueof(t2)
                           index, valueof(t1),valueof(t2)
                           .
                           .
                           .

   10.  Using keys.  Get row entry from table4 where j1=100.  Recall, j1
        is a defined key for this table and its KeyID is 1.

   OPER = GET-TLV
           PATH-DATA-TLV:
                   flags = F_SELKEY  IDCount = 1, IDs = 6
                   KEYINFO-TLV = KeyID=1, KEY_DATA=100

   Result:
   If j1=100 was at index 10
   OPER = GET-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0, IDCount = 1, IDs = 6.10
                   FULLDATA-TLV containing
                     valueof(j1), valueof(j2),valueof(j3),valueof(j4)

   11.  Delete row with KEY match (j1=100, j2=200) in table2.  Note that
        the j1,j2 pair is a defined key for the table2.

   OPER = DEL-TLV
           PATH-DATA-TLV:
                   flags = F_SELKEY  IDCount = 1, IDs = 4
                   KEYINFO-TLV:  {KeyID =1 KEY_DATA=100,200}

   Result:
   If (j1=100, j2=200) was at entry 15:
   OPER = DELETE-RESPONSE-TLV
           PATH-DATA-TLV:
                   flags = 0  IDCount = 2, IDs = 4.15
                   RESULT-TLV

   12.  Dump contents of table3.  It should be noted that this table has
        a column with a component name that is variable sized.  The
        purpose of this use case is to show how such a component is to
        be encoded.

   OPER = GET-TLV
           PATH-DATA-TLV:
                flags = 0 IDCount = 1, IDs = 5

   Result:
   OPER = GET-RESPONSE-TLV
       PATH-DATA-TLV:
          flags = 0  IDCount = 1, IDs = 5
              FULLDATA-TLV, Length = XXXX
               index, someidv, TLV: T=FULLDATA-TLV, L = 4+strlen(namev),
                      V = valueof(v)
               index, someidv, TLV: T=FULLDATA-TLV, L = 4+strlen(namev),
                      V = valueof(v)
               index, someidv, TLV: T=FULLDATA-TLV, L = 4+strlen(namev),
                      V = valueof(v)
               index, someidv, TLV: T=FULLDATA-TLV, L = 4+strlen(namev),
                      V = valueof(v)
                  .
                  .
                  .

   13.  Multiple atomic operations.

        Note 1:   This emulates adding a new nexthop entry and then
           atomically updating the L3 entries pointing to an old NH to
           point to a new one.  The assumption is that both tables are
           in the same LFB.

        Note:   Observe the two operations on the LFB instance; both are
           SET operations.

   //Operation 1: Add a new entry to table2 index #20.
   OPER = SET-TLV
           Path-TLV:
                   flags = 0, IDCount = 2,  IDs = 4.20
                   FULLDATA-TLV, V= valueof(j1),valueof(j2)

   // Operation 2: Update table1 entry which
   // was pointing with t2 = 10 to now point to 20
   OPER = SET-TLV
           PATH-DATA-TLV:
                   flags = F_SELKEY, IDCount = 1, IDs = 3
                   KEYINFO-TLV = KeyID=1 KEY_DATA=10
                   PATH-DATA-TLV
                           flags = 0  IDCount = 1, IDs = 2
                           FULLDATA-TLV, V= 20

   Result:
   //first operation, SET
   OPER = SET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0 IDCount = 3, IDs = 4.20
                   RESULT-TLV code = success
                           FULLDATA-TLV, V = valueof(j1),valueof(j2)
   // second operation SET - assuming entry 16 was updated
   OPER = SET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0 IDCount = 2, IDs = 3.16
                   PATH-DATA-TLV
                           flags = 0  IDCount = 1, IDs = 2
                           RESULT-TLV code = success
                                   FULLDATA-TLV, Length = XXXX v=20

   14.  Selective setting.  On table4 -- for indices 1, 3, 5, 7, and 9.
        Replace j1 to 100, j2 to 200, j3 to 300.  Leave j4 as is.

   PER = SET-TLV
       PATH-DATA-TLV
           flags = 0, IDCount = 1, IDs = 6
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 1
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   FULLDATA-TLV, Length = XXXX, V = {100}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV, Length = XXXX, V = {200}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX, V = {300}
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 3
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   FULLDATA-TLV, Length = XXXX, V = {100}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV, Length = XXXX, V = {200}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX, V = {300}

           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 5
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   FULLDATA-TLV, Length = XXXX, V = {100}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV, Length = XXXX, V = {200}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX, V = {300}
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 7
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   FULLDATA-TLV, Length = XXXX, V = {100}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV, Length = XXXX, V = {200}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX, V = {300}
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 9
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   FULLDATA-TLV, Length = XXXX, V = {100}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   FULLDATA-TLV, Length = XXXX, V = {200}
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   FULLDATA-TLV, Length = XXXX, V = {300}

   response:

   OPER = SET-RESPONSE-TLV
       PATH-DATA-TLV
           flags = 0, IDCount = 1, IDs = 6
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 1
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   RESULT-TLV

               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   RESULT-TLV
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 3
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   RESULT-TLV
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 5
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   RESULT-TLV
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 7
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   RESULT-TLV
           PATH-DATA-TLV
               flags = 0, IDCount = 1, IDs = 9
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 1
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 2
                   RESULT-TLV
               PATH-DATA-TLV
                   flags = 0, IDCount = 1, IDs = 3
                   RESULT-TLV

   15.  Manipulation of table of table examples.  Get x1 from table10
        row with index 4, inside table5 entry 10.

   operation = GET-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 5, IDs=7.10.2.4.1

   Results:
   operation = GET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 5, IDs=7.10.2.4.1
                   FULLDATA-TLV: L=XXXX, V = valueof(x1)

   16.  From table5's row 10 table10, get X2s based on the value of x1
        equaling 10 (recall x1 is KeyID 1).

   operation = GET-TLV
           PATH-DATA-TLV
                   flag = F_SELKEY, IDCount=3, IDS = 7.10.2
                   KEYINFO-TLV, KeyID = 1, KEYDATA = 10
                   PATH-DATA-TLV
                           IDCount = 1, IDS = 2 //select x2

   Results:
   If x1=10 was at entry 11:
   operation = GET-RESPONSE-TLV
           PATH-DATA-TLV
                   flag = 0, IDCount=5, IDS = 7.10.2.11
                   PATH-DATA-TLV
                           flags = 0  IDCount = 1, IDS = 2
                           FULLDATA-TLV: L=XXXX, V = valueof(x2)

   17.  Further example of manipulating a table of tables

   Consider table6, which is defined as:
   table6: type array, ID = 8
           components are:
           p1, type u32, ID = 1
           p2, type array, ID = 2, array components of type type-A

   type-A:
           a1, type u32, ID 1,
           a2, type array ID2 ,array components of type type-B

   type-B:
           b1, type u32, ID 1
           b2, type u32, ID 2

   If for example one wanted to set by replacing:
   table6.10.p1 to 111
   table6.10.p2.20.a1 to 222
   table6.10.p2.20.a2.30.b1 to 333

   in one message and one operation.

   There are two ways to do this:
      a) using nesting
      b) using a flat path data

   A. Method using nesting
      in one message with a single operation

   operation = SET-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 2, IDs=6.10
                   PATH-DATA-TLV
                           flags = 0, IDCount = 1, IDs=1
                           FULLDATA-TLV: L=XXXX,
                                   V = {111}
                   PATH-DATA-TLV
                           flags = 0  IDCount = 2, IDs=2.20
                           PATH-DATA-TLV
                                   flags = 0, IDCount = 1, IDs=1
                                   FULLDATA-TLV: L=XXXX,
                                           V = {222}
                           PATH-DATA-TLV :
                                   flags = 0, IDCount = 3, IDs=2.30.1
                                   FULLDATA-TLV: L=XXXX,
                                           V = {333}

   Result:
   operation = SET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 2, IDs=6.10
                   PATH-DATA-TLV
                           flags = 0, IDCount = 1, IDs=1
                           RESULT-TLV
                   PATH-DATA-TLV
                           flags = 0  IDCount = 2, IDs=2.20
                           PATH-DATA-TLV
                                   flags = 0, IDCount = 1, IDs=1
                                   RESULT-TLV
                           PATH-DATA-TLV :
                                   flags = 0, IDCount = 3, IDs=2.30.1
                                   RESULT-TLV

   B. Method using a flat path data in
      one message with a single operation

   operation = SET-TLV
           PATH-DATA-TLV :
                   flags = 0, IDCount = 3, IDs=6.10.1
                   FULLDATA-TLV: L=XXXX,
                           V = {111}
           PATH-DATA-TLV :
                   flags = 0, IDCount = 5, IDs=6.10.1.20.1
                   FULLDATA-TLV: L=XXXX,
                           V = {222}
           PATH-DATA-TLV :
                   flags = 0, IDCount = 7, IDs=6.10.1.20.1.30.1
                   FULLDATA-TLV: L=XXXX,
                           V = {333}
   Result:
   operation = SET-TLV
           PATH-DATA-TLV :
                   flags = 0, IDCount = 3, IDs=6.10.1
                   RESULT-TLV
           PATH-DATA-TLV :
                   flags = 0, IDCount = 5, IDs=6.10.1.20.1
                   RESULT-TLV
           PATH-DATA-TLV :
                   flags = 0, IDCount = 7, IDs=6.10.1.20.1.30.1
                   RESULT-TLV

   18.  Get a whole LFB (all its components, etc.).

        For example:   At startup a CE might well want the entire FE
           Object LFB.  So, in a request targeted at class 1, instance
           1, one might find:

   operation = GET-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 0

   result:
   operation = GET-RESPONSE-TLV
           PATH-DATA-TLV
                   flags = 0  IDCount = 0
                   FULLDATA-TLV encoding of the FE Object LFB

Authors' Addresses

   Avri Doria (editor)
   Lulea University of Technology
   Rainbow Way
   Lulea  SE-971 87
   Sweden

   Phone: +46 73 277 1788
   EMail: avri@ltu.se

   Jamal Hadi Salim (editor)
   Znyx
   Ottawa, Ontario
   Canada

   Phone:
   EMail: hadi@mojatatu.com

   Robert Haas (editor)
   IBM
   Saumerstrasse 4
   8803 Ruschlikon
   Switzerland

   Phone:
   EMail: rha@zurich.ibm.com

   Hormuzd M Khosravi (editor)
   Intel
   2111 NE 25th Avenue
   Hillsboro, OR  97124
   USA

   Phone: +1 503 264 0334
   EMail: hormuzd.m.khosravi@intel.com

   Weiming Wang  (editor)
   Zhejiang Gongshang University
   18, Xuezheng Str., Xiasha University Town
   Hangzhou  310018
   P.R. China

   Phone: +86-571-28877721
   EMail: wmwang@zjgsu.edu.cn

   Ligang Dong
   Zhejiang Gongshang University
   18, Xuezheng Str., Xiasha University Town
   Hangzhou  310018
   P.R. China

   Phone: +86-571-28877751
   EMail: donglg@zjgsu.edu.cn

   Ram Gopal
   Nokia
   5, Wayside Road
   Burlington, MA  310035
   USA

   Phone: +1-781-993-3685
   EMail: ram.gopal@nsn.com

   Joel Halpern
   P.O. Box 6049
   Leesburg, VA  20178
   USA

   Phone: +1-703-371-3043
   EMail: jmh@joelhalpern.com

 

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