path: root/doc/rfc/rfc5440.txt

Network Working Group                                   JP. Vasseur, Ed.
Request for Comments: 5440                                 Cisco Systems
Category: Standards Track                               JL. Le Roux, Ed.
                                                          France Telecom
                                                              March 2009


      Path Computation Element (PCE) Communication Protocol (PCEP)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

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   document authors.  All rights reserved.

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   it for publication as an RFC or to translate it into languages other
   than English.












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Abstract

   This document specifies the Path Computation Element (PCE)
   Communication Protocol (PCEP) for communications between a Path
   Computation Client (PCC) and a PCE, or between two PCEs.  Such
   interactions include path computation requests and path computation
   replies as well as notifications of specific states related to the
   use of a PCE in the context of Multiprotocol Label Switching (MPLS)
   and Generalized MPLS (GMPLS) Traffic Engineering.  PCEP is designed
   to be flexible and extensible so as to easily allow for the addition
   of further messages and objects, should further requirements be
   expressed in the future.







































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Table of Contents

   1. Introduction ....................................................5
      1.1. Requirements Language ......................................5
   2. Terminology .....................................................5
   3. Assumptions .....................................................6
   4. Architectural Protocol Overview (Model) .........................7
      4.1. Problem ....................................................7
      4.2. Architectural Protocol Overview ............................7
           4.2.1. Initialization Phase ................................8
           4.2.2. Session Keepalive ...................................9
           4.2.3. Path Computation Request Sent by a PCC to a PCE ....10
           4.2.4. Path Computation Reply Sent by The PCE to a PCC ....11
           4.2.5. Notification .......................................12
           4.2.6. Error ..............................................14
           4.2.7. Termination of the PCEP Session ....................14
           4.2.8. Intermittent versus Permanent PCEP Session .........15
   5. Transport Protocol .............................................15
   6. PCEP Messages ..................................................15
      6.1. Common Header .............................................16
      6.2. Open Message ..............................................16
      6.3. Keepalive Message .........................................18
      6.4. Path Computation Request (PCReq) Message ..................19
      6.5. Path Computation Reply (PCRep) Message ....................20
      6.6. Notification (PCNtf) Message ..............................21
      6.7. Error (PCErr) Message .....................................22
      6.8. Close Message .............................................23
      6.9. Reception of Unknown Messages .............................23
   7. Object Formats .................................................23
      7.1. PCEP TLV Format ...........................................24
      7.2. Common Object Header ......................................24
      7.3. OPEN Object ...............................................25
      7.4. RP Object .................................................27
           7.4.1. Object Definition ..................................27
           7.4.2. Handling of the RP Object ..........................30
      7.5. NO-PATH Object ............................................31
      7.6. END-POINTS Object .........................................34
      7.7. BANDWIDTH Object ..........................................35
      7.8. METRIC Object .............................................36
      7.9. Explicit Route Object .....................................39
      7.10. Reported Route Object ....................................39
      7.11. LSPA Object ..............................................40
      7.12. Include Route Object .....................................42
      7.13. SVEC Object ..............................................42
           7.13.1. Notion of Dependent and Synchronized Path
                   Computation Requests ..............................42
           7.13.2. SVEC Object .......................................44
           7.13.3. Handling of the SVEC Object .......................45



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      7.14. NOTIFICATION Object ......................................46
      7.15. PCEP-ERROR Object ........................................49
      7.16. LOAD-BALANCING Object ....................................54
      7.17. CLOSE Object .............................................55
   8. Manageability Considerations ...................................56
      8.1. Control of Function and Policy ............................56
      8.2. Information and Data Models ...............................57
      8.3. Liveness Detection and Monitoring .........................57
      8.4. Verifying Correct Operation ...............................58
      8.5. Requirements on Other Protocols and Functional
           Components ................................................58
      8.6. Impact on Network Operation ...............................58
   9. IANA Considerations ............................................59
      9.1. TCP Port ..................................................59
      9.2. PCEP Messages .............................................59
      9.3. PCEP Object ...............................................59
      9.4. PCEP Message Common Header ................................61
      9.5. Open Object Flag Field ....................................61
      9.6. RP Object .................................................61
      9.7. NO-PATH Object Flag Field .................................62
      9.8. METRIC Object .............................................63
      9.9. LSPA Object Flag Field ....................................63
      9.10. SVEC Object Flag Field ...................................64
      9.11. NOTIFICATION Object ......................................64
      9.12. PCEP-ERROR Object ........................................65
      9.13. LOAD-BALANCING Object Flag Field .........................67
      9.14. CLOSE Object .............................................67
      9.15. PCEP TLV Type Indicators .................................68
      9.16. NO-PATH-VECTOR TLV .......................................68
   10. Security Considerations .......................................69
      10.1. Vulnerability ............................................69
      10.2. TCP Security Techniques ..................................70
      10.3. PCEP Authentication and Integrity ........................70
      10.4. PCEP Privacy .............................................71
      10.5. Key Configuration and Exchange ...........................71
      10.6. Access Policy ............................................73
      10.7. Protection against Denial-of-Service Attacks .............73
           10.7.1. Protection against TCP DoS Attacks ................73
           10.7.2. Request Input Shaping/Policing ....................74
   11. Acknowledgments ...............................................75
   12. References ....................................................75
      12.1. Normative References .....................................75
      12.2. Informative References ...................................76
   Appendix A.  PCEP Finite State Machine (FSM) ......................79
   Appendix B.  PCEP Variables .......................................85
   Appendix C.  Contributors .........................................86





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1.  Introduction

   [RFC4655] describes the motivations and architecture for a Path
   Computation Element (PCE) based model for the computation of
   Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
   Traffic Engineering Label Switched Paths (TE LSPs).  The model allows
   for the separation of PCE from Path Computation Client (PCC), and
   allows for the cooperation between PCEs.  This necessitates a
   communication protocol between PCC and PCE, and between PCEs.
   [RFC4657] states the generic requirements for such a protocol
   including that the same protocol be used between PCC and PCE, and
   between PCEs.  Additional application-specific requirements (for
   scenarios such as inter-area, inter-AS, etc.) are not included in
   [RFC4657], but there is a requirement that any solution protocol must
   be easily extensible to handle other requirements as they are
   introduced in application-specific requirements documents.  Examples
   of such application-specific requirements are [RFC4927], [RFC5376],
   and [INTER-LAYER].

   This document specifies the Path Computation Element Protocol (PCEP)
   for communications between a PCC and a PCE, or between two PCEs, in
   compliance with [RFC4657].  Such interactions include path
   computation requests and path computation replies as well as
   notifications of specific states related to the use of a PCE in the
   context of MPLS and GMPLS Traffic Engineering.

   PCEP is designed to be flexible and extensible so as to easily allow
   for the addition of further messages and objects, should further
   requirements be expressed in the future.

1.1.  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.  Terminology

   The following terminology is used in this document.

   AS:  Autonomous System.

   Explicit path:  Full explicit path from start to destination; made of
      a list of strict hops where a hop may be an abstract node such as
      an AS.

   IGP area:  OSPF area or IS-IS level.




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   Inter-domain TE LSP:  A TE LSP whose path transits at least two
      different domains where a domain can be an IGP area, an Autonomous
      System, or a sub-AS (BGP confederation).

   PCC:  Path Computation Client; any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element; an entity (component, application, or
      network node) that is capable of computing a network path or route
      based on a network graph and applying computational constraints.

   PCEP Peer:  An element involved in a PCEP session (i.e., a PCC or a
      PCE).

   TED:  Traffic Engineering Database that contains the topology and
      resource information of the domain.  The TED may be fed by IGP
      extensions or potentially by other means.

   TE LSP:  Traffic Engineering Label Switched Path.

   Strict/loose path:  A mix of strict and loose hops comprising at
      least one loose hop representing the destination where a hop may
      be an abstract node such as an AS.

   Within this document, when describing PCE-PCE communications, the
   requesting PCE fills the role of a PCC.  This provides a saving in
   documentation without loss of function.

   The message formats in this document are specified using Backus-Naur
   Format (BNF) encoding as specified in [RBNF].

3.  Assumptions

   [RFC4655] describes various types of PCE.  PCEP does not make any
   assumption about, and thus does not impose any constraint on, the
   nature of the PCE.

   Moreover, it is assumed that the PCE has the required information
   (usually including network topology and resource information) so as
   to perform the computation of a path for a TE LSP.  Such information
   can be gathered by routing protocols or by some other means.  The way
   in which the information is gathered is out of the scope of this
   document.

   Similarly, no assumption is made about the discovery method used by a
   PCC to discover a set of PCEs (e.g., via static configuration or
   dynamic discovery) and on the algorithm used to select a PCE.  For




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   reference, [RFC4674] defines a list of requirements for dynamic PCE
   discovery and IGP-based solutions for such PCE discovery are
   specified in [RFC5088] and [RFC5089].

4.  Architectural Protocol Overview (Model)

   The aim of this section is to describe the PCEP model in the spirit
   of [RFC4101].  An architectural protocol overview (the big picture of
   the protocol) is provided in this section.  Protocol details can be
   found in further sections.

4.1.  Problem

   The PCE-based architecture used for the computation of paths for MPLS
   and GMPLS TE LSPs is described in [RFC4655].  When the PCC and the
   PCE are not collocated, a communication protocol between the PCC and
   the PCE is needed.  PCEP is such a protocol designed specifically for
   communications between a PCC and a PCE or between two PCEs in
   compliance with [RFC4657]: a PCC may use PCEP to send a path
   computation request for one or more TE LSPs to a PCE, and the PCE may
   reply with a set of computed paths if one or more paths can be found
   that satisfies the set of constraints.

4.2.  Architectural Protocol Overview

   PCEP operates over TCP, which fulfills the requirements for reliable
   messaging and flow control without further protocol work.

   Several PCEP messages are defined:

   o  Open and Keepalive messages are used to initiate and maintain a
      PCEP session, respectively.

   o  PCReq: a PCEP message sent by a PCC to a PCE to request a path
      computation.

   o  PCRep: a PCEP message sent by a PCE to a PCC in reply to a path
      computation request.  A PCRep message can contain either a set of
      computed paths if the request can be satisfied, or a negative
      reply if not.  The negative reply may indicate the reason why no
      path could be found.

   o  PCNtf: a PCEP notification message either sent by a PCC to a PCE
      or sent by a PCE to a PCC to notify of a specific event.

   o  PCErr: a PCEP message sent upon the occurrence of a protocol error
      condition.




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   o  Close message: a message used to close a PCEP session.

   The set of available PCEs may be either statically configured on a
   PCC or dynamically discovered.  The mechanisms used to discover one
   or more PCEs and to select a PCE are out of the scope of this
   document.

   A PCC may have PCEP sessions with more than one PCE, and similarly a
   PCE may have PCEP sessions with multiple PCCs.

   Each PCEP message is regarded as a single transmission unit and parts
   of messages MUST NOT be interleaved.  So, for example, a PCC sending
   a PCReq and wishing to close the session, must complete sending the
   request message before starting to send a Close message.

4.2.1.  Initialization Phase

   The initialization phase consists of two successive steps (described
   in a schematic form in Figure 1):

   1)  Establishment of a TCP connection (3-way handshake) between the
       PCC and the PCE.

   2)  Establishment of a PCEP session over the TCP connection.

   Once the TCP connection is established, the PCC and the PCE (also
   referred to as "PCEP peers") initiate PCEP session establishment
   during which various session parameters are negotiated.  These
   parameters are carried within Open messages and include the Keepalive
   timer, the DeadTimer, and potentially other detailed capabilities and
   policy rules that specify the conditions under which path computation
   requests may be sent to the PCE.  If the PCEP session establishment
   phase fails because the PCEP peers disagree on the session parameters
   or one of the PCEP peers does not answer after the expiration of the
   establishment timer, the TCP connection is immediately closed.
   Successive retries are permitted but an implementation should make
   use of an exponential back-off session establishment retry procedure.

   Keepalive messages are used to acknowledge Open messages, and are
   used once the PCEP session has been successfully established.

   Only one PCEP session can exist between a pair of PCEP peers at any
   one time.  Only one TCP connection on the PCEP port can exist between
   a pair of PCEP peers at any one time.

   Details about the Open message and the Keepalive message can be found
   in Sections 6.2 and 6.3, respectively.




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               +-+-+                 +-+-+
               |PCC|                 |PCE|
               +-+-+                 +-+-+
                 |                     |
                 | Open msg            |
                 |--------             |
                 |        \   Open msg |
                 |         \  ---------|
                 |          \/         |
                 |          /\         |
                 |         /  -------->|
                 |        /            |
                 |<------     Keepalive|
                 |             --------|
                 |Keepalive   /        |
                 |--------   /         |
                 |        \/           |
                 |        /\           |
                 |<------   ---------->|
                 |                     |

   Figure 1: PCEP Initialization Phase (Initiated by a PCC)

   (Note that once the PCEP session is established, the exchange of
   Keepalive messages is optional.)

4.2.2.  Session Keepalive

   Once a session has been established, a PCE or PCC may want to know
   that its PCEP peer is still available for use.

   It can rely on TCP for this information, but it is possible that the
   remote PCEP function has failed without disturbing the TCP
   connection.  It is also possible to rely on the mechanisms built into
   the TCP implementations, but these might not provide failure
   notifications that are sufficiently timely.  Lastly, a PCC could wait
   until it has a path computation request to send and could use its
   failed transmission or the failure to receive a response as evidence
   that the session has failed, but this is clearly inefficient.

   In order to handle this situation, PCEP includes a keepalive
   mechanism based on a Keepalive timer, a DeadTimer, and a Keepalive
   message.

   Each end of a PCEP session runs a Keepalive timer.  It restarts the
   timer every time it sends a message on the session.  When the timer
   expires, it sends a Keepalive message.  Other traffic may serve as
   Keepalive (see Section 6.3).



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   The ends of the PCEP session also run DeadTimers, and they restart
   the timers whenever a message is received on the session.  If one end
   of the session receives no message before the DeadTimer expires, it
   declares the session dead.

   Note that this means that the Keepalive message is unresponded and
   does not form part of a two-way keepalive handshake as used in some
   protocols.  Also note that the mechanism is designed to reduce to a
   minimum the amount of keepalive traffic on the session.

   The keepalive traffic on the session may be unbalanced according to
   the requirements of the session ends.  Each end of the session can
   specify (on an Open message) the Keepalive timer that it will use
   (i.e., how often it will transmit a Keepalive message if there is no
   other traffic) and a DeadTimer that it recommends its peer to use
   (i.e., how long the peer should wait before declaring the session
   dead if it receives no traffic).  The session ends may use different
   Keepalive timer values.

   The minimum value of the Keepalive timer is 1 second, and it is
   specified in units of 1 second.  The recommended default value is 30
   seconds.  The timer may be disabled by setting it to zero.

   The recommended default for the DeadTimer is 4 times the value of the
   Keepalive timer used by the remote peer.  This means that there is
   never any risk of congesting TCP with excessive Keepalive messages.

4.2.3.  Path Computation Request Sent by a PCC to a PCE

                     +-+-+                  +-+-+
                     |PCC|                  |PCE|
                     +-+-+                  +-+-+
   1) Path computation |                      |
      event            |                      |
   2) PCE Selection    |                      |
   3) Path computation |---- PCReq message--->|
      request sent to  |                      |
      the selected PCE |                      |

               Figure 2: Path Computation Request

   Once a PCC has successfully established a PCEP session with one or
   more PCEs, if an event is triggered that requires the computation of
   a set of paths, the PCC first selects one or more PCEs.  Note that
   the PCE selection decision process may have taken place prior to the
   PCEP session establishment.





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   Once the PCC has selected a PCE, it sends a path computation request
   to the PCE (PCReq message) that contains a variety of objects that
   specify the set of constraints and attributes for the path to be
   computed.  For example, "Compute a TE LSP path with source IP
   address=x.y.z.t, destination IP address=x'.y'.z'.t', bandwidth=B
   Mbit/s, Setup/Holding priority=P, ...".  Additionally, the PCC may
   desire to specify the urgency of such request by assigning a request
   priority.  Each request is uniquely identified by a request-id number
   and the PCC-PCE address pair.  The process is shown in a schematic
   form in Figure 2.

   Note that multiple path computation requests may be outstanding from
   a PCC to a PCE at any time.

   Details about the PCReq message can be found in Section 6.4.

4.2.4.  Path Computation Reply Sent by The PCE to a PCC

                 +-+-+                  +-+-+
                 |PCC|                  |PCE|
                 +-+-+                  +-+-+
                   |                      |
                   |---- PCReq message--->|
                   |                      |1) Path computation
                   |                      |   request received
                   |                      |
                   |                      |2) Path successfully
                   |                      |   computed
                   |                      |
                   |                      |3) Computed paths
                   |                      |   sent to the PCC
                   |                      |
                   |<--- PCRep message ---|
                   |    (Positive reply)  |

       Figure 3a: Path Computation Request With Successful
                       Path Computation














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                 +-+-+                  +-+-+
                 |PCC|                  |PCE|
                 +-+-+                  +-+-+
                   |                      |
                   |                      |
                   |---- PCReq message--->|
                   |                      |1) Path computation
                   |                      |   request received
                   |                      |
                   |                      |2) No Path found that
                   |                      |   satisfies the request
                   |                      |
                   |                      |3) Negative reply sent to
                   |                      |   the PCC (optionally with
                   |                      |   various additional
                   |                      |   information)
                   |<--- PCRep message ---|
                   |   (Negative reply)   |

       Figure 3b: Path Computation Request With Unsuccessful
                       Path Computation

   Upon receiving a path computation request from a PCC, the PCE
   triggers a path computation, the result of which can be either:

   o  Positive (Figure 3a): the PCE manages to compute a path that
      satisfies the set of required constraints.  In this case, the PCE
      returns the set of computed paths to the requesting PCC.  Note
      that PCEP supports the capability to send a single request that
      requires the computation of more than one path (e.g., computation
      of a set of link-diverse paths).

   o  Negative (Figure 3b): no path could be found that satisfies the
      set of constraints.  In this case, a PCE may provide the set of
      constraints that led to the path computation failure.  Upon
      receiving a negative reply, a PCC may decide to resend a modified
      request or take any other appropriate action.

   Details about the PCRep message can be found in Section 6.5.

4.2.5.  Notification

   There are several circumstances in which a PCE may want to notify a
   PCC of a specific event.  For example, suppose that the PCE suddenly
   gets overloaded, potentially leading to unacceptable response times.
   The PCE may want to notify one or more PCCs that some of their
   requests (listed in the notification) will not be satisfied or may
   experience unacceptable delays.  Upon receiving such notification,



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   the PCC may decide to redirect its path computation requests to
   another PCE should an alternate PCE be available.  Similarly, a PCC
   may desire to notify a PCE of a particular event such as the
   cancellation of pending requests.

                       +-+-+                  +-+-+
                       |PCC|                  |PCE|
                       +-+-+                  +-+-+
   1) Path computation   |                      |
      event              |                      |
   2) PCE Selection      |                      |
   3) Path computation   |---- PCReq message--->|
      request X sent to  |                      |4) Path computation
      the selected PCE   |                      |   request queued
                         |                      |
                         |                      |
   5) Path computation   |                      |
      request X cancelled|                      |
                         |---- PCNtf message -->|
                         |                      |6) Path computation
                         |                      |   request X cancelled

      Figure 4: Example of PCC Notification (Cancellation Notification)
                             Sent to a PCE

                       +-+-+                  +-+-+
                       |PCC|                  |PCE|
                       +-+-+                  +-+-+
   1) Path computation   |                      |
      event              |                      |
   2) PCE Selection      |                      |
   3) Path computation   |---- PCReq message--->|
      request X sent to  |                      |4) Path computation
      the selected PCE   |                      |   request queued
                         |                      |
                         |                      |
                         |                      |5) PCE gets overloaded
                         |                      |
                         |                      |
                         |                      |6) Path computation
                         |                      |   request X cancelled
                         |                      |
                         |<--- PCNtf message----|

     Figure 5: Example of PCE Notification (Cancellation Notification)
                            Sent to a PCC

   Details about the PCNtf message can be found in Section 6.6.



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4.2.6.  Error

   The PCEP Error message (also referred to as a PCErr message) is sent
   in several situations: when a protocol error condition is met or when
   the request is not compliant with the PCEP specification (e.g.,
   capability not supported, reception of a message with a mandatory
   missing object, policy violation, unexpected message, unknown request
   reference).

                      +-+-+                  +-+-+
                      |PCC|                  |PCE|
                      +-+-+                  +-+-+
   1) Path computation  |                      |
      event             |                      |
   2) PCE Selection     |                      |
   3) Path computation  |---- PCReq message--->|
      request X sent to |                      |4) Reception of a
      the selected PCE  |                      |   malformed object
                        |                      |
                        |                      |5) Request discarded
                        |                      |
                        |<-- PCErr message  ---|
                        |                      |

     Figure 6: Example of Error Message Sent by a PCE to a PCC
          in Reply to the Reception of a Malformed Object

   Details about the PCErr message can be found in Section 6.7.

4.2.7.  Termination of the PCEP Session

   When one of the PCEP peers desires to terminate a PCEP session it
   first sends a PCEP Close message and then closes the TCP connection.
   If the PCEP session is terminated by the PCE, the PCC clears all the
   states related to pending requests previously sent to the PCE.
   Similarly, if the PCC terminates a PCEP session, the PCE clears all
   pending path computation requests sent by the PCC in question as well
   as the related states.  A Close message can only be sent to terminate
   a PCEP session if the PCEP session has previously been established.

   In case of TCP connection failure, the PCEP session is immediately
   terminated.

   Details about the Close message can be found in Section 6.8.







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4.2.8.  Intermittent versus Permanent PCEP Session

   An implementation may decide to keep the PCEP session alive (and thus
   the corresponding TCP connection) for an unlimited time.  (For
   instance, this may be appropriate when path computation requests are
   sent on a frequent basis so as to avoid opening a TCP connection each
   time a path computation request is needed, which would incur
   additional processing delays.)  Conversely, in some other
   circumstances, it may be desirable to systematically open and close a
   PCEP session for each PCEP request (for instance, when sending a path
   computation request is a rare event).

5.  Transport Protocol

   PCEP operates over TCP using a registered TCP port (4189).  This
   allows the requirements of reliable messaging and flow control to be
   met without further protocol work.  All PCEP messages MUST be sent
   using the registered TCP port for the source and destination TCP
   port.

6.  PCEP Messages

   A PCEP message consists of a common header followed by a variable-
   length body made of a set of objects that can either be mandatory or
   optional.  In the context of this document, an object is said to be
   mandatory in a PCEP message when the object MUST be included for the
   message to be considered valid.  A PCEP message with a missing
   mandatory object MUST trigger an Error message (see Section 7.15).
   Conversely, if an object is optional, the object may or may not be
   present.

   A flag referred to as the P flag is defined in the common header of
   each PCEP object (see Section 7.2).  When this flag is set in an
   object in a PCReq, the PCE MUST take the information carried in the
   object into account during the path computation.  For example, the
   METRIC object defined in Section 7.8 allows a PCC to specify a
   bounded acceptable path cost.  The METRIC object is optional, but a
   PCC may set a flag to ensure that the constraint is taken into
   account.  In this case, if the constraint cannot be taken into
   account by the PCE, the PCE MUST trigger an Error message.

   For each PCEP message type, rules are defined that specify the set of
   objects that the message can carry.  We use the Backus-Naur Form
   (BNF) (see [RBNF]) to specify such rules.  Square brackets refer to
   optional sub-sequences.  An implementation MUST form the PCEP
   messages using the object ordering specified in this document.





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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Ver |  Flags  |  Message-Type |       Message-Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 7: PCEP Message Common Header

   Ver (Version - 3 bits):  PCEP version number.  Current version is
      version 1.

   Flags (5 bits):  No flags are currently defined.  Unassigned bits are
      considered as reserved.  They MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Message-Type (8 bits):  The following message types are currently
      defined:

         Value    Meaning
           1        Open
           2        Keepalive
           3        Path Computation Request
           4        Path Computation Reply
           5        Notification
           6        Error
           7        Close

   Message-Length (16 bits):  total length of the PCEP message including
      the common header, expressed in bytes.

6.2.  Open Message

   The Open message is a PCEP message sent by a PCC to a PCE and by a
   PCE to a PCC in order to establish a PCEP session.  The Message-Type
   field of the PCEP common header for the Open message is set to 1.

   Once the TCP connection has been successfully established, the first
   message sent by the PCC to the PCE or by the PCE to the PCC MUST be
   an Open message as specified in Appendix A.

   Any message received prior to an Open message MUST trigger a protocol
   error condition causing a PCErr message to be sent with Error-Type
   "PCEP session establishment failure" and Error-value "reception of an
   invalid Open message or a non Open message" and the PCEP session
   establishment attempt MUST be terminated by closing the TCP
   connection.



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   The Open message is used to establish a PCEP session between the PCEP
   peers.  During the establishment phase, the PCEP peers exchange
   several session characteristics.  If both parties agree on such
   characteristics, the PCEP session is successfully established.

   The format of an Open message is as follows:

   <Open Message>::= <Common Header>
                     <OPEN>

   The Open message MUST contain exactly one OPEN object (see
   Section 7.3).

   Various session characteristics are specified within the OPEN object.
   Once the TCP connection has been successfully established, the sender
   MUST start an initialization timer called OpenWait after the
   expiration of which, if no Open message has been received, it sends a
   PCErr message and releases the TCP connection (see Appendix A for
   details).

   Once an Open message has been sent to a PCEP peer, the sender MUST
   start an initialization timer called KeepWait after the expiration of
   which, if neither a Keepalive message has been received nor a PCErr
   message in case of disagreement of the session characteristics, a
   PCErr message MUST be sent and the TCP connection MUST be released
   (see Appendix A for details).

   The OpenWait and KeepWait timers have a fixed value of 1 minute.

   Upon the receipt of an Open message, the receiving PCEP peer MUST
   determine whether the suggested PCEP session characteristics are
   acceptable.  If at least one of the characteristics is not acceptable
   to the receiving peer, it MUST send an Error message.  The Error
   message SHOULD also contain the related OPEN object and, for each
   unacceptable session parameter, an acceptable parameter value SHOULD
   be proposed in the appropriate field of the OPEN object in place of
   the originally proposed value.  The PCEP peer MAY decide to resend an
   Open message with different session characteristics.  If a second
   Open message is received with the same set of parameters or with
   parameters that are still unacceptable, the receiving peer MUST send
   an Error message and it MUST immediately close the TCP connection.
   Details about error messages can be found in Section 7.15.
   Successive retries are permitted, but an implementation SHOULD make
   use of an exponential back-off session establishment retry procedure.

   If the PCEP session characteristics are acceptable, the receiving
   PCEP peer MUST send a Keepalive message (defined in Section 6.3) that
   serves as an acknowledgment.



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   The PCEP session is considered as established once both PCEP peers
   have received a Keepalive message from their peer.

6.3.  Keepalive Message

   A Keepalive message is a PCEP message sent by a PCC or a PCE in order
   to keep the session in active state.  The Keepalive message is also
   used in response to an Open message to acknowledge that an Open
   message has been received and that the PCEP session characteristics
   are acceptable.  The Message-Type field of the PCEP common header for
   the Keepalive message is set to 2.  The Keepalive message does not
   contain any object.

   PCEP has its own keepalive mechanism used to ensure the liveness of
   the PCEP session.  This requires the determination of the frequency
   at which each PCEP peer sends Keepalive messages.  Asymmetric values
   may be chosen; thus, there is no constraint mandating the use of
   identical keepalive frequencies by both PCEP peers.  The DeadTimer is
   defined as the period of time after the expiration of which a PCEP
   peer declares the session down if no PCEP message has been received
   (Keepalive or any other PCEP message); thus, any PCEP message acts as
   a Keepalive message.  Similarly, there are no constraints mandating
   the use of identical DeadTimers by both PCEP peers.  The minimum
   Keepalive timer value is 1 second.  Deployments SHOULD consider
   carefully the impact of using low values for the Keepalive timer as
   these might not give rise to the expected results in periods of
   temporary network instability.

   Keepalive messages are sent at the frequency specified in the OPEN
   object carried within an Open message according to the rules
   specified in Section 7.3.  Because any PCEP message may serve as
   Keepalive, an implementation may either decide to send Keepalive
   messages at fixed intervals regardless of whether other PCEP messages
   might have been sent since the last sent Keepalive message, or may
   decide to differ the sending of the next Keepalive message based on
   the time at which the last PCEP message (other than Keepalive) was
   sent.

   Note that sending Keepalive messages to keep the session alive is
   optional, and PCEP peers may decide not to send Keepalive messages
   once the PCEP session is established; in which case, the peer that
   does not receive Keepalive messages does not expect to receive them
   and MUST NOT declare the session as inactive.

   The format of a Keepalive message is as follows:

   <Keepalive Message>::= <Common Header>




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6.4.  Path Computation Request (PCReq) Message

   A Path Computation Request message (also referred to as a PCReq
   message) is a PCEP message sent by a PCC to a PCE to request a path
   computation.  A PCReq message may carry more than one path
   computation request.  The Message-Type field of the PCEP common
   header for the PCReq message is set to 3.

   There are two mandatory objects that MUST be included within a PCReq
   message: the RP and the END-POINTS objects (see Section 7).  If one
   or both of these objects is missing, the receiving PCE MUST send an
   error message to the requesting PCC.  Other objects are optional.

   The format of a PCReq message is as follows:

   <PCReq Message>::= <Common Header>
                      [<svec-list>]
                      <request-list>

   where:

      <svec-list>::=<SVEC>[<svec-list>]
      <request-list>::=<request>[<request-list>]

      <request>::= <RP>
                   <END-POINTS>
                   [<LSPA>]
                   [<BANDWIDTH>]
                   [<metric-list>]
                   [<RRO>[<BANDWIDTH>]]
                   [<IRO>]
                   [<LOAD-BALANCING>]

   where:

   <metric-list>::=<METRIC>[<metric-list>]

   The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, RRO, IRO, and
   LOAD-BALANCING objects are defined in Section 7.  The special case of
   two BANDWIDTH objects is discussed in detail in Section 7.7.

   A PCEP implementation is free to process received requests in any
   order.  For example, the requests may be processed in the order they
   are received, reordered and assigned priority according to local
   policy, reordered according to the priority encoded in the RP object
   (Section 7.4.1), or processed in parallel.





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6.5.  Path Computation Reply (PCRep) Message

   The PCEP Path Computation Reply message (also referred to as a PCRep
   message) is a PCEP message sent by a PCE to a requesting PCC in
   response to a previously received PCReq message.  The Message-Type
   field of the PCEP common header for the PCRep message is set to 4.

   The bundling of multiple replies to a set of path computation
   requests within a single PCRep message is supported by PCEP.  If a
   PCE receives non-synchronized path computation requests by means of
   one or more PCReq messages from a requesting PCC, it MAY decide to
   bundle the computed paths within a single PCRep message so as to
   reduce the control plane load.  Note that the counter side of such an
   approach is the introduction of additional delays for some path
   computation requests of the set.  Conversely, a PCE that receives
   multiple requests within the same PCReq message MAY decide to provide
   each computed path in separate PCRep messages or within the same
   PCRep message.  A PCRep message may contain positive and negative
   replies.

   A PCRep message may contain a set of computed paths corresponding to
   either a single path computation request with load-balancing (see
   Section 7.16) or multiple path computation requests originated by a
   requesting PCC.  The PCRep message may also contain multiple
   acceptable paths corresponding to the same request.

   The PCRep message MUST contain at least one RP object.  For each
   reply that is bundled into a single PCReq message, an RP object MUST
   be included that contains a Request-ID-number identical to the one
   specified in the RP object carried in the corresponding PCReq message
   (see Section 7.4 for the definition of the RP object).

   If the path computation request can be satisfied (i.e., the PCE finds
   a set of paths that satisfy the set of constraints), the set of
   computed paths specified by means of Explicit Route Objects (EROs) is
   inserted in the PCRep message.  The ERO is defined in Section 7.9.
   The situation where multiple computed paths are provided in a PCRep
   message is discussed in detail in Section 7.13.  Furthermore, when a
   PCC requests the computation of a set of paths for a total amount of
   bandwidth by means of a LOAD-BALANCING object carried within a PCReq
   message, the ERO of each computed path may be followed by a BANDWIDTH
   object as discussed in section Section 7.16.

   If the path computation request cannot be satisfied, the PCRep
   message MUST include a NO-PATH object.  The NO-PATH object (described
   in Section 7.5) may also contain other information (e.g, reasons for
   the path computation failure).




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   The format of a PCRep message is as follows:


   <PCRep Message> ::= <Common Header>
                       <response-list>

   where:

      <response-list>::=<response>[<response-list>]

      <response>::=<RP>
                  [<NO-PATH>]
                  [<attribute-list>]
                  [<path-list>]

      <path-list>::=<path>[<path-list>]

      <path>::= <ERO><attribute-list>

   where:

    <attribute-list>::=[<LSPA>]
                       [<BANDWIDTH>]
                       [<metric-list>]
                       [<IRO>]

    <metric-list>::=<METRIC>[<metric-list>]

6.6.  Notification (PCNtf) Message

   The PCEP Notification message (also referred to as the PCNtf message)
   can be sent either by a PCE to a PCC, or by a PCC to a PCE, to notify
   of a specific event.  The Message-Type field of the PCEP common
   header for the PCNtf message is set to 5.

   The PCNtf message MUST carry at least one NOTIFICATION object and MAY
   contain several NOTIFICATION objects should the PCE or the PCC intend
   to notify of multiple events.  The NOTIFICATION object is defined in
   Section 7.14.  The PCNtf message MAY also contain RP objects (see
   Section 7.4) when the notification refers to particular path
   computation requests.

   The PCNtf message may be sent by a PCC or a PCE in response to a
   request or in an unsolicited manner.







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   The format of a PCNtf message is as follows:

   <PCNtf Message>::=<Common Header>
                     <notify-list>

   <notify-list>::=<notify> [<notify-list>]

   <notify>::= [<request-id-list>]
                <notification-list>

   <request-id-list>::=<RP>[<request-id-list>]

   <notification-list>::=<NOTIFICATION>[<notification-list>]

6.7.  Error (PCErr) Message

   The PCEP Error message (also referred to as a PCErr message) is sent
   in several situations: when a protocol error condition is met or when
   the request is not compliant with the PCEP specification (e.g.,
   reception of a malformed message, reception of a message with a
   mandatory missing object, policy violation, unexpected message,
   unknown request reference).  The Message-Type field of the PCEP
   common header for the PCErr message is set to 6.

   The PCErr message is sent by a PCC or a PCE in response to a request
   or in an unsolicited manner.  If the PCErr message is sent in
   response to a request, the PCErr message MUST include the set of RP
   objects related to the pending path computation requests that
   triggered the error condition.  In the latter case (unsolicited), no
   RP object is inserted in the PCErr message.  For example, no RP
   object is inserted in a PCErr when the error condition occurred
   during the initialization phase.  A PCErr message MUST contain a
   PCEP-ERROR object specifying the PCEP error condition.  The PCEP-
   ERROR object is defined in Section 7.15.

   The format of a PCErr message is as follows:

   <PCErr Message> ::= <Common Header>
                       ( <error-obj-list> [<Open>] ) | <error>
                       [<error-list>]

   <error-obj-list>::=<PCEP-ERROR>[<error-obj-list>]

   <error>::=[<request-id-list>]
              <error-obj-list>

   <request-id-list>::=<RP>[<request-id-list>]




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   <error-list>::=<error>[<error-list>]

   The procedure upon the receipt of a PCErr message is defined in
   Section 7.15.

6.8.  Close Message

   The Close message is a PCEP message that is either sent by a PCC to a
   PCE or by a PCE to a PCC in order to close an established PCEP
   session.  The Message-Type field of the PCEP common header for the
   Close message is set to 7.

   The format of a Close message is as follows:

   <Close Message>::= <Common Header>
                      <CLOSE>

   The Close message MUST contain exactly one CLOSE object (see
   Section 6.8).  If more than one CLOSE object is present, the first
   MUST be processed and subsequent objects ignored.

   Upon the receipt of a valid Close message, the receiving PCEP peer
   MUST cancel all pending requests, it MUST close the TCP connection
   and MUST NOT send any further PCEP messages on the PCEP session.

6.9.  Reception of Unknown Messages

   A PCEP implementation that receives an unrecognized PCEP message MUST
   send a PCErr message with Error-value=2 (capability not supported).

   If a PCC/PCE receives unrecognized messages at a rate equal or
   greater than MAX-UNKNOWN-MESSAGES unknown message requests per
   minute, the PCC/PCE MUST send a PCEP CLOSE message with close
   value="Reception of an unacceptable number of unknown PCEP message".
   A RECOMMENDED value for MAX-UNKNOWN-MESSAGES is 5.  The PCC/PCE MUST
   close the TCP session and MUST NOT send any further PCEP messages on
   the PCEP session.

7.  Object Formats

   PCEP objects have a common format.  They begin with a common object
   header (see Section 7.2).  This is followed by object-specific fields
   defined for each different object.  The object may also include one
   or more type-length-value (TLV) encoded data sets.  Each TLV has the
   same structure as described in Section 7.1.






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7.1.  PCEP TLV Format

   A PCEP object may include a set of one or more optional TLVs.

   All PCEP TLVs have the following format:

   Type:   2 bytes
   Length: 2 bytes
   Value:  variable

   A PCEP object TLV is comprised of 2 bytes for the type, 2 bytes
   specifying the TLV length, and a value field.

   The Length field defines the length of the value portion in bytes.
   The TLV is padded to 4-bytes alignment; padding is not included in
   the Length field (so a 3-byte value would have a length of 3, but the
   total size of the TLV would be 8 bytes).

   Unrecognized TLVs MUST be ignored.

   IANA management of the PCEP Object TLV type identifier codespace is
   described in Section 9.

7.2.  Common Object Header

   A PCEP object carried within a PCEP message consists of one or more
   32-bit words with a common header that has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Object body)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 8: PCEP Common Object Header

   Object-Class (8 bits):  identifies the PCEP object class.

   OT (Object-Type - 4 bits):  identifies the PCEP object type.

      The Object-Class and Object-Type fields are managed by IANA.

      The Object-Class and Object-Type fields uniquely identify each
      PCEP object.



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   Res flags (2 bits):  Reserved field.  This field MUST be set to zero
      on transmission and MUST be ignored on receipt.

   P flag (Processing-Rule - 1-bit):  the P flag allows a PCC to specify
      in a PCReq message sent to a PCE whether the object must be taken
      into account by the PCE during path computation or is just
      optional.  When the P flag is set, the object MUST be taken into
      account by the PCE.  Conversely, when the P flag is cleared, the
      object is optional and the PCE is free to ignore it.

   I flag (Ignore - 1 bit):  the I flag is used by a PCE in a PCRep
      message to indicate to a PCC whether or not an optional object was
      processed.  The PCE MAY include the ignored optional object in its
      reply and set the I flag to indicate that the optional object was
      ignored during path computation.  When the I flag is cleared, the
      PCE indicates that the optional object was processed during the
      path computation.  The setting of the I flag for optional objects
      is purely indicative and optional.  The I flag has no meaning in a
      PCRep message when the P flag has been set in the corresponding
      PCReq message.

   If the PCE does not understand an object with the P flag set or
   understands the object but decides to ignore the object, the entire
   PCEP message MUST be rejected and the PCE MUST send a PCErr message
   with Error-Type="Unknown Object" or "Not supported Object" along with
   the corresponding RP object.  Note that if a PCReq includes multiple
   requests, only requests for which an object with the P flag set is
   unknown/unrecognized MUST be rejected.

   Object Length (16 bits):  Specifies the total object length including
      the header, in bytes.  The Object Length field MUST always be a
      multiple of 4, and at least 4.  The maximum object content length
      is 65528 bytes.

7.3.  OPEN Object

   The OPEN object MUST be present in each Open message and MAY be
   present in a PCErr message.  There MUST be only one OPEN object per
   Open or PCErr message.

   The OPEN object contains a set of fields used to specify the PCEP
   version, Keepalive frequency, DeadTimer, and PCEP session ID, along
   with various flags.  The OPEN object may also contain a set of TLVs
   used to convey various session characteristics such as the detailed
   PCE capabilities, policy rules, and so on.  No TLVs are currently
   defined.





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   OPEN Object-Class is 1.

   OPEN Object-Type is 1.

   The format of the OPEN object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ver |   Flags |   Keepalive   |  DeadTimer    |      SID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                       Optional TLVs                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 9: OPEN Object Format

   Ver (3 bits):  PCEP version.  Current version is 1.

   Flags (5 bits):  No flags are currently defined.  Unassigned bits are
      considered as reserved.  They MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Keepalive (8 bits):  maximum period of time (in seconds) between two
      consecutive PCEP messages sent by the sender of this message.  The
      minimum value for the Keepalive is 1 second.  When set to 0, once
      the session is established, no further Keepalive messages are sent
      to the remote peer.  A RECOMMENDED value for the keepalive
      frequency is 30 seconds.

   DeadTimer (8 bits):  specifies the amount of time after the
      expiration of which the PCEP peer can declare the session with the
      sender of the Open message to be down if no PCEP message has been
      received.  The DeadTimer SHOULD be set to 0 and MUST be ignored if
      the Keepalive is set to 0.  A RECOMMENDED value for the DeadTimer
      is 4 times the value of the Keepalive.

   Example:

   A sends an Open message to B with Keepalive=10 seconds and
   DeadTimer=40 seconds.  This means that A sends Keepalive messages (or
   any other PCEP message) to B every 10 seconds and B can declare the
   PCEP session with A down if no PCEP message has been received from A
   within any 40-second period.






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   SID (PCEP session ID - 8 bits):  unsigned PCEP session number that
      identifies the current session.  The SID MUST be incremented each
      time a new PCEP session is established.  It is used for logging
      and troubleshooting purposes.  Each increment SHOULD have a value
      of 1 and may cause a wrap back to zero.

      The SID is used to disambiguate instances of sessions to the same
      peer.  A PCEP implementation could use a single source of SIDs
      across all peers, or one source for each peer.  The former might
      constrain the implementation to only 256 concurrent sessions.  The
      latter potentially requires more states.  There is one SID number
      in each direction.

   Optional TLVs may be included within the OPEN object body to specify
   PCC or PCE characteristics.  The specification of such TLVs is
   outside the scope of this document.

   When present in an Open message, the OPEN object specifies the
   proposed PCEP session characteristics.  Upon receiving unacceptable
   PCEP session characteristics during the PCEP session initialization
   phase, the receiving PCEP peer (PCE) MAY include an OPEN object
   within the PCErr message so as to propose alternative acceptable
   session characteristic values.

7.4.  RP Object

   The RP (Request Parameters) object MUST be carried within each PCReq
   and PCRep messages and MAY be carried within PCNtf and PCErr
   messages.  The RP object is used to specify various characteristics
   of the path computation request.

   The P flag of the RP object MUST be set in PCReq and PCRep messages
   and MUST be cleared in PCNtf and PCErr messages.  If the RP object is
   received with the P flag set incorrectly according to the rules
   stated above, the receiving peer MUST send a PCErr message with
   Error-Type=10 and Error-value=1.  The corresponding path computation
   request MUST be cancelled by the PCE without further notification.

7.4.1.  Object Definition

   RP Object-Class is 2.

   RP Object-Type is 1.








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   The format of the RP object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Flags                    |O|B|R| Pri |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Request-ID-number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLVs                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 10: RP Object Body Format

   The RP object body has a variable length and may contain additional
   TLVs.  No TLVs are currently defined.

   Flags (32 bits)

   The following flags are currently defined:

   o  Pri (Priority - 3 bits): the Priority field may be used by the
      requesting PCC to specify to the PCE the request's priority from 1
      to 7.  The decision of which priority should be used for a
      specific request is a local matter; it MUST be set to 0 when
      unused.  Furthermore, the use of the path computation request
      priority by the PCE's scheduler is implementation specific and out
      of the scope of this document.  Note that it is not required for a
      PCE to support the priority field: in this case, it is RECOMMENDED
      that the PCC set the priority field to 0 in the RP object.  If the
      PCE does not take into account the request priority, it is
      RECOMMENDED to set the priority field to 0 in the RP object
      carried within the corresponding PCRep message, regardless of the
      priority value contained in the RP object carried within the
      corresponding PCReq message.  A higher numerical value of the
      priority field reflects a higher priority.  Note that it is the
      responsibility of the network administrator to make use of the
      priority values in a consistent manner across the various PCCs.
      The ability of a PCE to support request prioritization MAY be
      dynamically discovered by the PCCs by means of PCE capability
      discovery.  If not advertised by the PCE, a PCC may decide to set
      the request priority and will learn the ability of the PCE to
      support request prioritization by observing the Priority field of
      the RP object received in the PCRep message.  If the value of the
      Pri field is set to 0, this means that the PCE does not support




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      the handling of request priorities: in other words, the path
      computation request has been honored but without taking the
      request priority into account.

   o  R (Reoptimization - 1 bit): when set, the requesting PCC specifies
      that the PCReq message relates to the reoptimization of an
      existing TE LSP.  For all TE LSPs except zero-bandwidth LSPs, when
      the R bit is set, an RRO (see Section 7.10) MUST be included in
      the PCReq message to show the path of the existing TE LSP.  Also,
      for all TE LSPs except zero-bandwidth LSPs, when the R bit is set,
      the existing bandwidth of the TE LSP to be reoptimized MUST be
      supplied in a BANDWIDTH object (see Section 7.7).  This BANDWIDTH
      object is in addition to the instance of that object used to
      describe the desired bandwidth of the reoptimized LSP.  For zero-
      bandwidth LSPs, the RRO and BANDWIDTH objects that report the
      characteristics of the existing TE LSP are optional.

   o  B (Bi-directional - 1 bit): when set, the PCC specifies that the
      path computation request relates to a bi-directional TE LSP that
      has the same traffic engineering requirements including fate
      sharing, protection and restoration, LSRs, TE links, and resource
      requirements (e.g., latency and jitter) in each direction.  When
      cleared, the TE LSP is unidirectional.

   o  O (strict/loose - 1 bit): when set, in a PCReq message, this
      indicates that a loose path is acceptable.  Otherwise, when
      cleared, this indicates to the PCE that a path exclusively made of
      strict hops is required.  In a PCRep message, when the O bit is
      set this indicates that the returned path is a loose path;
      otherwise (when the O bit is cleared), the returned path is made
      of strict hops.

   Unassigned bits are considered reserved.  They MUST be set to zero on
   transmission and MUST be ignored on receipt.

   Request-ID-number (32 bits):  The Request-ID-number value combined
      with the source IP address of the PCC and the PCE address uniquely
      identify the path computation request context.  The Request-ID-
      number is used for disambiguation between pending requests, and
      thus it MUST be changed (such as by incrementing it) each time a
      new request is sent to the PCE, and may wrap.

      The value 0x00000000 is considered invalid.

      If no path computation reply is received from the PCE (e.g., the
      request is dropped by the PCE because of memory overflow), and the
      PCC wishes to resend its request, the same Request-ID-number MUST
      be used.  Upon receiving a path computation request from a PCC



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      with the same Request-ID-number, the PCE SHOULD treat the request
      as a new request.  An implementation MAY choose to cache path
      computation replies in order to quickly handle retransmission
      without having to process a path computation request twice (in the
      case that the first request was dropped or lost).  Upon receiving
      a path computation reply from a PCE with the same Request-ID-
      number, the PCC SHOULD silently discard the path computation
      reply.

      Conversely, different Request-ID-numbers MUST be used for
      different requests sent to a PCE.

      The same Request-ID-number MAY be used for path computation
      requests sent to different PCEs.  The path computation reply is
      unambiguously identified by the IP source address of the replying
      PCE.

7.4.2.  Handling of the RP Object

   If a PCReq message is received that does not contain an RP object,
   the PCE MUST send a PCErr message to the requesting PCC with Error-
   Type="Required Object missing" and Error-value="RP Object missing".

   If the O bit of the RP message carried within a PCReq message is
   cleared and local policy has been configured on the PCE to not
   provide explicit paths (for instance, for confidentiality reasons), a
   PCErr message MUST be sent by the PCE to the requesting PCC and the
   pending path computation request MUST be discarded.  The Error-Type
   is "Policy Violation" and Error-value is "O bit cleared".

   When the R bit of the RP object is set in a PCReq message, this
   indicates that the path computation request relates to the
   reoptimization of an existing TE LSP.  In this case, the PCC MUST
   also provide the strict/loose path by including an RRO object in the
   PCReq message so as to avoid/limit double-bandwidth counting if and
   only if the TE LSP is a non-zero-bandwidth TE LSP.  If the PCC has
   not requested a strict path (O bit set), a reoptimization can still
   be requested by the PCC, but this requires that the PCE either be
   stateful (keep track of the previously computed path with the
   associated list of strict hops), or have the ability to retrieve the
   complete required path segment.  Alternatively, the PCC MUST inform
   the PCE about the working path and the associated list of strict hops
   in PCReq.  The absence of an RRO in the PCReq message for a non-zero-
   bandwidth TE LSP (when the R bit of the RP object is set) MUST
   trigger the sending of a PCErr message with Error-Type="Required
   Object Missing" and Error-value="RRO Object missing for
   reoptimization".




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   If a PCC/PCE receives a PCRep/PCReq message that contains an RP
   object referring to an unknown Request-ID-number, the PCC/PCE MUST
   send a PCErr message with Error-Type="Unknown request reference".
   This is used for debugging purposes.  If a PCC/PCE receives PCRep/
   PCReq messages with unknown requests at a rate equal or greater than
   MAX-UNKNOWN-REQUESTS unknown requests per minute, the PCC/PCE MUST
   send a PCEP CLOSE message with close value="Reception of an
   unacceptable number of unknown requests/replies".  A RECOMMENDED
   value for MAX-UNKNOWN-REQUESTS is 5.  The PCC/PCE MUST close the TCP
   session and MUST NOT send any further PCEP messages on the PCEP
   session.

   The reception of a PCEP message that contains an RP object referring
   to a Request-ID-number=0x00000000 MUST be treated in similar manner
   as an unknown request.

7.5.  NO-PATH Object

   The NO-PATH object is used in PCRep messages in response to an
   unsuccessful path computation request (the PCE could not find a path
   satisfying the set of constraints).  When a PCE cannot find a path
   satisfying a set of constraints, it MUST include a NO-PATH object in
   the PCRep message.

   There are several categories of issue that can lead to a negative
   reply.  For example, the PCE chain might be broken (should there be
   more than one PCE involved in the path computation) or no path
   obeying the set constraints could be found.  The "NI (Nature of
   Issue)" field in the NO-PATH object is used to report the error
   category.

   Optionally, if the PCE supports such capability, the NO-PATH object
   MAY contain an optional NO-PATH-VECTOR TLV defined below and used to
   provide more information on the reasons that led to a negative reply.
   The PCRep message MAY also contain a list of objects that specify the
   set of constraints that could not be satisfied.  The PCE MAY just
   replicate the set of objects that was received that was the cause of
   the unsuccessful computation or MAY optionally report a suggested
   value for which a path could have been found (in which case, the
   value differs from the value in the original request).

   NO-PATH Object-Class is 3.

   NO-PATH Object-Type is 1.







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   The format of the NO-PATH object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Nature of Issue|C|          Flags              |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLVs                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 11: NO-PATH Object Format

   NI - Nature of Issue (8 bits):  The NI field is used to report the
      nature of the issue that led to a negative reply.  Two values are
      currently defined:

         0: No path satisfying the set of constraints could be found

         1: PCE chain broken

      The Nature of Issue field value can be used by the PCC for various
      purposes:

      *  Constraint adjustment before reissuing a new path computation
         request,

      *  Explicit selection of a new PCE chain,

      *  Logging of the error type for further action by the network
         administrator.

      IANA management of the NI field codespace is described in
      Section 9.

   Flags (16 bits).

   The following flag is currently defined:

   o  C flag (1 bit): when set, the PCE indicates the set of unsatisfied
      constraints (reasons why a path could not be found) in the PCRep
      message by including the relevant PCEP objects.  When cleared, no
      failing constraints are specified.  The C flag has no meaning and
      is ignored unless the NI field is set to 0x00.

   Unassigned bits are considered as reserved.  They MUST be set to zero
   on transmission and MUST be ignored on receipt.



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   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   The NO-PATH object body has a variable length and may contain
   additional TLVs.  The only TLV currently defined is the NO-PATH-
   VECTOR TLV defined below.

   Example: consider the case of a PCC that sends a path computation
   request to a PCE for a TE LSP of X Mbit/s.  Suppose that PCE cannot
   find a path for X Mbit/s.  In this case, the PCE must include in the
   PCRep message a NO-PATH object.  Optionally, the PCE may also include
   the original BANDWIDTH object so as to indicate that the reason for
   the unsuccessful computation is the bandwidth constraint (in this
   case, the NI field value is 0x00 and C flag is set).  If the PCE
   supports such capability, it may alternatively include the BANDWIDTH
   object and report a value of Y in the bandwidth field of the
   BANDWIDTH object (in this case, the C flag is set) where Y refers to
   the bandwidth for which a TE LSP with the same other characteristics
   (such as Setup/Holding priorities, TE LSP attribute, local
   protection, etc.) could have been computed.

   When the NO-PATH object is absent from a PCRep message, the path
   computation request has been fully satisfied and the corresponding
   paths are provided in the PCRep message.

   An optional TLV named NO-PATH-VECTOR MAY be included in the NO-PATH
   object in order to provide more information on the reasons that led
   to a negative reply.

   The NO-PATH-VECTOR TLV is compliant with the PCEP TLV format defined
   in Section 7.1 and is comprised of 2 bytes for the type, 2 bytes
   specifying the TLV length (length of the value portion in bytes)
   followed by a fixed-length 32-bit flags field.

   Type:   1
   Length: 4 bytes
   Value:  32-bit flags field

   IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
   (see Section 9).

   The following flags are currently defined:

   o  Bit number: 31 - PCE currently unavailable

   o  Bit number: 30 - Unknown destination

   o  Bit number: 29 - Unknown source



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7.6.  END-POINTS Object

   The END-POINTS object is used in a PCReq message to specify the
   source IP address and the destination IP address of the path for
   which a path computation is requested.  The P flag of the END-POINTS
   object MUST be set.  If the END-POINTS object is received with the P
   flag cleared, the receiving peer MUST send a PCErr message with
   Error-Type=10 and Error-value=1.  The corresponding path computation
   request MUST be cancelled by the PCE without further notification.

   Note that the source and destination addresses specified in the END-
   POINTS object may correspond to the source and destination IP address
   of the TE LSP or to those of a path segment.  Two END-POINTS objects
   (for IPv4 and IPv6) are defined.

   END-POINTS Object-Class is 4.

   END-POINTS Object-Type is 1 for IPv4 and 2 for IPv6.

   The format of the END-POINTS object body for IPv4 (Object-Type=1) 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Source IPv4 address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Destination IPv4 address                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 12: END-POINTS Object Body Format for IPv4




















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   The format of the END-POINTS object for IPv6 (Object-Type=2) 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                Source IPv6 address (16 bytes)                 |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |              Destination IPv6 address (16 bytes)              |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 13: END-POINTS Object Body Format for IPv6

   The END-POINTS object body has a fixed length of 8 bytes for IPv4 and
   32 bytes for IPv6.

   If more than one END-POINTS object is present, the first MUST be
   processed and subsequent objects ignored.

7.7.  BANDWIDTH Object

   The BANDWIDTH object is used to specify the requested bandwidth for a
   TE LSP.  The notion of bandwidth is similar to the one used for RSVP
   signaling in [RFC2205], [RFC3209], and [RFC3473].

   If the requested bandwidth is equal to 0, the BANDWIDTH object is
   optional.  Conversely, if the requested bandwidth is not equal to 0,
   the PCReq message MUST contain a BANDWIDTH object.

   In the case of the reoptimization of a TE LSP, the bandwidth of the
   existing TE LSP MUST also be included in addition to the requested
   bandwidth if and only if the two values differ.  Consequently, two
   Object-Type values are defined that refer to the requested bandwidth
   and the bandwidth of the TE LSP for which a reoptimization is being
   performed.

   The BANDWIDTH object may be carried within PCReq and PCRep messages.

   BANDWIDTH Object-Class is 5.






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   Two Object-Type values are defined for the BANDWIDTH object:

   o  Requested bandwidth: BANDWIDTH Object-Type is 1.

   o  Bandwidth of an existing TE LSP for which a reoptimization is
      requested.  BANDWIDTH Object-Type is 2.

   The format of the BANDWIDTH object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Bandwidth                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 14: BANDWIDTH Object Body Format

   Bandwidth (32 bits):  The requested bandwidth is encoded in 32 bits
      in IEEE floating point format (see [IEEE.754.1985]), expressed in
      bytes per second.  Refer to Section 3.1.2 of [RFC3471] for a table
      of commonly used values.

   The BANDWIDTH object body has a fixed length of 4 bytes.

7.8.  METRIC Object

   The METRIC object is optional and can be used for several purposes.

   In a PCReq message, a PCC MAY insert one or more METRIC objects:

   o  To indicate the metric that MUST be optimized by the path
      computation algorithm (IGP metric, TE metric, hop counts).
      Currently, three metrics are defined: the IGP cost, the TE metric
      (see [RFC3785]), and the number of hops traversed by a TE LSP.

   o  To indicate a bound on the path cost that MUST NOT be exceeded for
      the path to be considered as acceptable by the PCC.

   In a PCRep message, the METRIC object MAY be inserted so as to
   provide the cost for the computed path.  It MAY also be inserted
   within a PCRep with the NO-PATH object to indicate that the metric
   constraint could not be satisfied.

   The path computation algorithmic aspects used by the PCE to optimize
   a path with respect to a specific metric are outside the scope of
   this document.





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   It must be understood that such path metrics are only meaningful if
   used consistently: for instance, if the delay of a computed path
   segment is exchanged between two PCEs residing in different domains,
   consistent ways of defining the delay must be used.

   The absence of the METRIC object MUST be interpreted by the PCE as a
   path computation request for which no constraints need be applied to
   any of the metrics.

   METRIC Object-Class is 6.

   METRIC Object-Type is 1.

   The format of the METRIC object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |    Flags  |C|B|       T       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          metric-value                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 15: METRIC Object Body Format

   The METRIC object body has a fixed length of 8 bytes.

   Reserved (16 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   T (Type - 8 bits):  Specifies the metric type.

      Three values are currently defined:
      *  T=1: IGP metric
      *  T=2: TE metric
      *  T=3: Hop Counts

   Flags (8 bits):  Two flags are currently defined:

      *  B (Bound - 1 bit): When set in a PCReq message, the metric-
         value indicates a bound (a maximum) for the path metric that
         must not be exceeded for the PCC to consider the computed path
         as acceptable.  The path metric must be less than or equal to
         the value specified in the metric-value field.  When the B flag
         is cleared, the metric-value field is not used to reflect a
         bound constraint.





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      *  C (Computed Metric - 1 bit): When set in a PCReq message, this
         indicates that the PCE MUST provide the computed path metric
         value (should a path satisfying the constraints be found) in
         the PCRep message for the corresponding metric.

      Unassigned flags MUST be set to zero on transmission and MUST be
      ignored on receipt.

   Metric-value (32 bits):  metric value encoded in 32 bits in IEEE
      floating point format (see [IEEE.754.1985]).

   Multiple METRIC objects MAY be inserted in a PCRep or a PCReq message
   for a given request (i.e., for a given RP).  For a given request,
   there MUST be at most one instance of the METRIC object for each
   metric type with the same B flag value.  If, for a given request, two
   or more instances of a METRIC object with the same B flag value are
   present for a metric type, only the first instance MUST be considered
   and other instances MUST be ignored.

   For a given request, the presence of two METRIC objects of the same
   type with a different value of the B flag is allowed.  Furthermore,
   it is also allowed to insert, for a given request, two METRIC objects
   with different types that have both their B flag cleared: in this
   case, an objective function must be used by the PCE to solve a multi-
   parameter optimization problem.

   A METRIC object used to indicate the metric to optimize during the
   path computation MUST have the B flag cleared and the C flag set to
   the appropriate value.  When the path computation relates to the
   reoptimization of an exiting TE LSP (in which case, the R flag of the
   RP object is set), an implementation MAY decide to set the metric-
   value field to the computed value of the metric of the TE LSP to be
   reoptimized with regards to a specific metric type.

   A METRIC object used to reflect a bound MUST have the B flag set, and
   the C flag and metric-value field set to the appropriate values.

   In a PCRep message, unless not allowed by PCE policy, at least one
   METRIC object MUST be present that reports the computed path metric
   if the C flag of the METRIC object was set in the corresponding path
   computation request (the B flag MUST be cleared).  The C flag has no
   meaning in a PCRep message.  Optionally, the PCRep message MAY
   contain additional METRIC objects that correspond to bound
   constraints; in which case, the metric-value MUST be equal to the
   corresponding computed path metric (the B flag MUST be set).  If no
   path satisfying the constraints could be found by the PCE, the METRIC
   objects MAY also be present in the PCRep message with the NO-PATH
   object to indicate the constraint metric that could be satisfied.



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   Example: if a PCC sends a path computation request to a PCE where the
   metric to optimize is the IGP metric and the TE metric must not
   exceed the value of M, two METRIC objects are inserted in the PCReq
   message:

   o  First METRIC object with B=0, T=1, C=1, metric-value=0x0000

   o  Second METRIC object with B=1, T=2, metric-value=M

   If a path satisfying the set of constraints can be found by the PCE
   and there is no policy that prevents the return of the computed
   metric, the PCE inserts one METRIC object with B=0, T=1, metric-
   value= computed IGP path cost.  Additionally, the PCE may insert a
   second METRIC object with B=1, T=2, metric-value= computed TE path
   cost.

7.9.  Explicit Route Object

   The ERO is used to encode the path of a TE LSP through the network.
   The ERO is carried within a PCRep message to provide the computed TE
   LSP if the path computation was successful.

   The contents of this object are identical in encoding to the contents
   of the Resource Reservation Protocol Traffic Engineering Extensions
   (RSVP-TE) Explicit Route Object (ERO) defined in [RFC3209],
   [RFC3473], and [RFC3477].  That is, the object is constructed from a
   series of sub-objects.  Any RSVP-TE ERO sub-object already defined or
   that could be defined in the future for use in the RSVP-TE ERO is
   acceptable in this object.

   PCEP ERO sub-object types correspond to RSVP-TE ERO sub-object types.

   Since the explicit path is available for immediate signaling by the
   MPLS or GMPLS control plane, the meanings of all of the sub-objects
   and fields in this object are identical to those defined for the ERO.

   ERO Object-Class is 7.

   ERO Object-Type is 1.

7.10.  Reported Route Object

   The RRO is exclusively carried within a PCReq message so as to report
   the route followed by a TE LSP for which a reoptimization is desired.

   The contents of this object are identical in encoding to the contents
   of the Route Record Object defined in [RFC3209], [RFC3473], and
   [RFC3477].  That is, the object is constructed from a series of sub-



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   objects.  Any RSVP-TE RRO sub-object already defined or that could be
   defined in the future for use in the RSVP-TE RRO is acceptable in
   this object.

   The meanings of all of the sub-objects and fields in this object are
   identical to those defined for the RSVP-TE RRO.

   PCEP RRO sub-object types correspond to RSVP-TE RRO sub-object types.

   RRO Object-Class is 8.

   RRO Object-Type is 1.

7.11.  LSPA Object

   The LSPA (LSP Attributes) object is optional and specifies various TE
   LSP attributes to be taken into account by the PCE during path
   computation.  The LSPA object can be carried within a PCReq message,
   or a PCRep message in case of unsuccessful path computation (in this
   case, the PCRep message also contains a NO-PATH object, and the LSPA
   object is used to indicate the set of constraints that could not be
   satisfied).  Most of the fields of the LSPA object are identical to
   the fields of the SESSION-ATTRIBUTE object (C-Type = 7) defined in
   [RFC3209] and [RFC4090].  When absent from the PCReq message, this
   means that the Setup and Holding priorities are equal to 0, and there
   are no affinity constraints.  See Section 4.7.4 of [RFC3209] for a
   detailed description of the use of resource affinities.

   LSPA Object-Class is 9.

   LSPA Object-Types is 1.




















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   The format of the LSPA object body is:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Exclude-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-all                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Setup Prio   |  Holding Prio |     Flags   |L|   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLVs                           //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 16: LSPA Object Body Format

   Setup Prio (Setup Priority - 8 bits):  The priority of the TE LSP
      with respect to taking resources, in the range of 0 to 7.  The
      value 0 is the highest priority.  The Setup Priority is used in
      deciding whether this session can preempt another session.

   Holding Prio (Holding Priority - 8 bits):  The priority of the TE LSP
      with respect to holding resources, in the range of 0 to 7.  The
      value 0 is the highest priority.  Holding Priority is used in
      deciding whether this session can be preempted by another session.

   Flags (8 bits)

      L flag:  Corresponds to the "Local Protection Desired" bit
         ([RFC3209]) of the SESSION-ATTRIBUTE Object.  When set, this
         means that the computed path must include links protected with
         Fast Reroute as defined in [RFC4090].

      Unassigned flags MUST be set to zero on transmission and MUST be
      ignored on receipt.

   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Note that optional TLVs may be defined in the future to carry
   additional TE LSP attributes such as those defined in [RFC5420].






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7.12.  Include Route Object

   The IRO (Include Route Object) is optional and can be used to specify
   that the computed path MUST traverse a set of specified network
   elements.  The IRO MAY be carried within PCReq and PCRep messages.
   When carried within a PCRep message with the NO-PATH object, the IRO
   indicates the set of elements that cause the PCE to fail to find a
   path.

   IRO Object-Class is 10.

   IRO Object-Type is 1.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Sub-objects)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 17: IRO Body Format

   Sub-objects:  The IRO is made of sub-objects identical to the ones
      defined in [RFC3209], [RFC3473], and [RFC3477], where the IRO sub-
      object type is identical to the sub-object type defined in the
      related documents.

      The following sub-object types are supported.

          Type   Sub-object
           1     IPv4 prefix
           2     IPv6 prefix
           4     Unnumbered Interface ID
           32    Autonomous system number

   The L bit of such sub-object has no meaning within an IRO.

7.13.  SVEC Object

7.13.1.  Notion of Dependent and Synchronized Path Computation Requests

   Independent versus dependent path computation requests: path
   computation requests are said to be independent if they are not
   related to each other.  Conversely, a set of dependent path
   computation requests is such that their computations cannot be
   performed independently of each other (a typical example of dependent
   requests is the computation of a set of diverse paths).



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   Synchronized versus non-synchronized path computation requests: a set
   of path computation requests is said to be non-synchronized if their
   respective treatment (path computations) can be performed by a PCE in
   a serialized and independent fashion.

   There are various circumstances where the synchronization of a set of
   path computations may be beneficial or required.

   Consider the case of a set of N TE LSPs for which a PCC needs to send
   path computation requests to a PCE.  The first solution consists of
   sending N separate PCReq messages to the selected PCE.  In this case,
   the path computation requests are non-synchronized.  Note that the
   PCC may chose to distribute the set of N requests across K PCEs for
   load balancing purposes.  Considering that M (with M<N) requests are
   sent to a particular PCEi, as described above, such M requests can be
   sent in the form of successive PCReq messages destined to PCEi or
   bundled within a single PCReq message (since PCEP allows for the
   bundling of multiple path computation requests within a single PCReq
   message).  That said, even in the case of independent requests, it
   can be desirable to request from the PCE the computation of their
   paths in a synchronized fashion that is likely to lead to more
   optimal path computations and/or reduced blocking probability if the
   PCE is a stateless PCE.  In other words, the PCE should not compute
   the corresponding paths in a serialized and independent manner, but
   it should rather "simultaneously" compute their paths.  For example,
   trying to "simultaneously" compute the paths of M TE LSPs may allow
   the PCE to improve the likelihood to meet multiple constraints.

   Consider the case of two TE LSPs requesting N1 Mbit/s and N2 Mbit/s,
   respectively, and a maximum tolerable end-to-end delay for each TE
   LSP of X ms.  There may be circumstances where the computation of the
   first TE LSP, irrespectively of the second TE LSP, may lead to the
   impossibility to meet the delay constraint for the second TE LSP.

   A second example is related to the bandwidth constraint.  It is quite
   straightforward to provide examples where a serialized independent
   path computation approach would lead to the impossibility to satisfy
   both requests (due to bandwidth fragmentation), while a synchronized
   path computation would successfully satisfy both requests.

   A last example relates to the ability to avoid the allocation of the
   same resource to multiple requests, thus helping to reduce the call
   setup failure probability compared to the serialized computation of
   independent requests.

   Dependent path computations are usually synchronized.  For example,
   in the case of the computation of M diverse paths, if such paths are
   computed in a non-synchronized fashion, this seriously increases the



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   probability of not being able to satisfy all requests (sometimes also
   referred to as the well-known "trapping problem").

   Furthermore, this would not allow a PCE to implement objective
   functions such as trying to minimize the sum of the TE LSP costs.  In
   such a case, the path computation requests must be synchronized: they
   cannot be computed independently of each other.

   Conversely, a set of independent path computation requests may or may
   not be synchronized.

   The synchronization of a set of path computation requests is achieved
   by using the SVEC object that specifies the list of synchronized
   requests that can either be dependent or independent.

   PCEP supports the following three modes:

   o  Bundle of a set of independent and non-synchronized path
      computation requests,

   o  Bundle of a set of independent and synchronized path computation
      requests (requires the SVEC object defined below),

   o  Bundle of a set of dependent and synchronized path computation
      requests (requires the SVEC object defined below).

7.13.2.  SVEC Object

   Section 7.13.1 details the circumstances under which it may be
   desirable and/or required to synchronize a set of path computation
   requests.  The SVEC (Synchronization VECtor) object allows a PCC to
   request the synchronization of a set of dependent or independent path
   computation requests.  The SVEC object is optional and may be carried
   within a PCReq message.

   The aim of the SVEC object carried within a PCReq message is to
   request the synchronization of M path computation requests.  The SVEC
   object is a variable-length object that lists the set of M path
   computation requests that must be synchronized.  Each path
   computation request is uniquely identified by the Request-ID-number
   carried within the respective RP object.  The SVEC object also
   contains a set of flags that specify the synchronization type.

   SVEC Object-Class is 11.

   SVEC Object-Type is 1.





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   The format of the SVEC object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |                   Flags                 |S|N|L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Request-ID-number #1                      |
   //                                                             //
   |                     Request-ID-number #M                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 18: SVEC Body Object Format

   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Flags (24 bits):  Defines the potential dependency between the set of
      path computation requests.

      *  L (Link diverse) bit: when set, this indicates that the
         computed paths corresponding to the requests specified by the
         following RP objects MUST NOT have any link in common.

      *  N (Node diverse) bit: when set, this indicates that the
         computed paths corresponding to the requests specified by the
         following RP objects MUST NOT have any node in common.

      *  S (SRLG diverse) bit: when set, this indicates that the
         computed paths corresponding to the requests specified by the
         following RP objects MUST NOT share any SRLG (Shared Risk Link
         Group).

      In case of a set of M synchronized independent path computation
      requests, the bits L, N, and S are cleared.

   Unassigned flags MUST be set to zero on transmission and MUST be
   ignored on receipt.

   The flags defined above are not exclusive.

7.13.3.  Handling of the SVEC Object

   The SVEC object allows a PCC to specify a list of M path computation
   requests that MUST be synchronized along with a potential dependency.
   The set of M path computation requests may be sent within a single
   PCReq message or multiple PCReq messages.  In the latter case, it is
   RECOMMENDED for the PCE to implement a local timer (called the



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   SyncTimer) activated upon the receipt of the first PCReq message that
   contains the SVEC object after the expiration of which, if all the M
   path computation requests have not been received, a protocol error is
   triggered.  When a PCE receives a path computation request that
   cannot be satisfied (for example, because the PCReq message contains
   an object with the P bit set that is not supported), the PCE sends a
   PCErr message for this request (see Section 7.2), the PCE MUST cancel
   the whole set of related path computation requests and MUST send a
   PCErr message with Error-Type="Synchronized path computation request
   missing".

   Note that such PCReq messages may also contain non-synchronized path
   computation requests.  For example, the PCReq message may comprise N
   synchronized path computation requests that are related to RP 1, ...,
   RP N and are listed in the SVEC object along with any other path
   computation requests that are processed as normal.

7.14.  NOTIFICATION Object

   The NOTIFICATION object is exclusively carried within a PCNtf message
   and can either be used in a message sent by a PCC to a PCE or by a
   PCE to a PCC so as to notify of an event.

   NOTIFICATION Object-Class is 12.

   NOTIFICATION Object-Type is 1.

   The format of the NOTIFICATION body object 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |     Flags     |      NT       |     NV        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLVs                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 19: NOTIFICATION Body Object Format

   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Flags (8 bits):  No flags are currently defined.  Unassigned flags
      MUST be set to zero on transmission and MUST be ignored on
      receipt.




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   NT (Notification Type - 8 bits):  The Notification-type specifies the
      class of notification.

   NV (Notification Value - 8 bits):  The Notification-value provides
      addition information related to the nature of the notification.

   Both the Notification-type and Notification-value are managed by
   IANA.

   The following Notification-type and Notification-value values are
   currently defined:

   o  Notification-type=1: Pending Request cancelled

      *  Notification-value=1: PCC cancels a set of pending requests.  A
         Notification-type=1, Notification-value=1 indicates that the
         PCC wants to inform a PCE of the cancellation of a set of
         pending requests.  Such an event could be triggered because of
         external conditions such as the receipt of a positive reply
         from another PCE (should the PCC have sent multiple requests to
         a set of PCEs for the same path computation request), a network
         event such as a network failure rendering the request obsolete,
         or any other events local to the PCC.  A NOTIFICATION object
         with Notification-type=1, Notification-value=1 is carried
         within a PCNtf message sent by the PCC to the PCE.  The RP
         object corresponding to the cancelled request MUST also be
         present in the PCNtf message.  Multiple RP objects may be
         carried within the PCNtf message; in which case, the
         notification applies to all of them.  If such a notification is
         received by a PCC from a PCE, the PCC MUST silently ignore the
         notification and no errors should be generated.

      *  Notification-value=2: PCE cancels a set of pending requests.  A
         Notification-type=1, Notification-value=2 indicates that the
         PCE wants to inform a PCC of the cancellation of a set of
         pending requests.  A NOTIFICATION object with Notification-
         type=1, Notification-value=2 is carried within a PCNtf message
         sent by a PCE to a PCC.  The RP object corresponding to the
         cancelled request MUST also be present in the PCNtf message.
         Multiple RP objects may be carried within the PCNtf message; in
         which case, the notification applies to all of them.  If such
         notification is received by a PCE from a PCC, the PCE MUST
         silently ignore the notification and no errors should be
         generated.

   o  Notification-type=2: Overloaded PCE

      *  Notification-value=1: A Notification-type=2, Notification-



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         value=1 indicates to the PCC that the PCE is currently in an
         overloaded state.  If no RP objects are included in the PCNtf
         message, this indicates that no other requests SHOULD be sent
         to that PCE until the overloaded state is cleared: the pending
         requests are not affected and will be served.  If some pending
         requests cannot be served due to the overloaded state, the PCE
         MUST also include a set of RP objects that identifies the set
         of pending requests that are cancelled by the PCE and will not
         be honored.  In this case, the PCE does not have to send an
         additional PCNtf message with Notification-type=1 and
         Notification-value=2 since the list of cancelled requests is
         specified by including the corresponding set of RP objects.  If
         such notification is received by a PCE from a PCC, the PCE MUST
         silently ignore the notification and no errors should be
         generated.

      *  A PCE implementation SHOULD use a dual-threshold mechanism used
         to determine whether it is in a congestion state with regards
         to specific resource monitoring (e.g.  CPU, memory).  The use
         of such thresholds is to avoid oscillations between overloaded/
         non-overloaded state that may result in oscillations of request
         targets by the PCCs.

      *  Optionally, a TLV named OVERLOADED-DURATION may be included in
         the NOTIFICATION object that specifies the period of time
         during which no further request should be sent to the PCE.
         Once this period of time has elapsed, the PCE should no longer
         be considered in a congested state.

         The OVERLOADED-DURATION TLV is compliant with the PCEP TLV
         format defined in Section 7.1 and is comprised of 2 bytes for
         the type, 2 bytes specifying the TLV length (length of the
         value portion in bytes), followed by a fixed-length value field
         of a 32-bit flags field.

         Type:   2
         Length: 4 bytes
         Value:  32-bit flags field indicates the estimated PCE
                 congestion duration in seconds.

      *  Notification-value=2: A Notification-type=2, Notification-
         value=2 indicates that the PCE is no longer in an overloaded
         state and is available to process new path computation
         requests.  An implementation SHOULD make sure that a PCE sends
         such notification to every PCC to which a Notification message
         (with Notification-type=2, Notification-value=1) has been sent
         unless an OVERLOADED-DURATION TLV has been included in the
         corresponding message and the PCE wishes to wait for the



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         expiration of that period of time before receiving new
         requests.  If such notification is received by a PCE from a
         PCC, the PCE MUST silently ignore the notification and no
         errors should be generated.  It is RECOMMENDED to support some
         dampening notification procedure on the PCE so as to avoid too
         frequent congestion state and congestion state release
         notifications.  For example, an implementation could make use
         of an hysteresis approach using a dual-threshold mechanism that
         triggers the sending of congestion state notifications.
         Furthermore, in case of high instabilities of the PCE
         resources, an additional dampening mechanism SHOULD be used
         (linear or exponential) to pace the notification frequency and
         avoid oscillation of path computation requests.

   When a PCC receives an overload indication from a PCE, it should
   consider the impact on the entire network.  It must be remembered
   that other PCCs may also receive the notification, and so many path
   computation requests could be redirected to other PCEs.  This may, in
   turn, cause further overloading at PCEs in the network.  Therefore,
   an application at a PCC receiving an overload notification should
   consider applying some form of back-off (e.g., exponential) to the
   rate at which it generates path computation requests into the
   network.  This is especially the case as the number of PCEs reporting
   overload grows.

7.15.  PCEP-ERROR Object

   The PCEP-ERROR object is exclusively carried within a PCErr message
   to notify of a PCEP error.

   PCEP-ERROR Object-Class is 13.

   PCEP-ERROR Object-Type is 1.

   The format of the PCEP-ERROR object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |      Flags    |   Error-Type  |  Error-value  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLVs                           //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 20: PCEP-ERROR Object Body Format




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   A PCEP-ERROR object is used to report a PCEP error and is
   characterized by an Error-Type that specifies the type of error and
   an Error-value that provides additional information about the error
   type.  Both the Error-Type and the Error-value are managed by IANA
   (see the IANA section).

   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Flags (8 bits):  no flag is currently defined.  This flag MUST be set
      to zero on transmission and MUST be ignored on receipt.

   Error-Type (8 bits):  defines the class of error.

   Error-value (8 bits):  provides additional details about the error.

   Optionally, the PCEP-ERROR object may contain additional TLVs so as
   to provide further information about the encountered error.

   A single PCErr message may contain multiple PCEP-ERROR objects.































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   For each PCEP error, an Error-Type and an Error-value are defined.

   Error-Type    Meaning
      1          PCEP session establishment failure
                 Error-value=1: reception of an invalid Open message or
                                a non Open message.
                 Error-value=2: no Open message received before the
                                expiration of the OpenWait timer
                 Error-value=3: unacceptable and non-negotiable session
                                characteristics
                 Error-value=4: unacceptable but negotiable session
                                characteristics
                 Error-value=5: reception of a second Open message with
                                still unacceptable session
                                characteristics
                 Error-value=6: reception of a PCErr message proposing
                                unacceptable session characteristics
                 Error-value=7: No Keepalive or PCErr message received
                                before the expiration of the KeepWait
                                timer
      2          Capability not supported
      3          Unknown Object
                  Error-value=1: Unrecognized object class
                  Error-value=2: Unrecognized object Type
      4          Not supported object
                  Error-value=1: Not supported object class
                  Error-value=2: Not supported object Type
      5          Policy violation
                  Error-value=1: C bit of the METRIC object set
                                 (request rejected)
                  Error-value=2: O bit of the RP object set
                                 (request rejected)
      6          Mandatory Object missing
                  Error-value=1: RP object missing
                  Error-value=2: RRO object missing for a reoptimization
                                 request (R bit of the RP object set)
                                 when bandwidth is not equal to 0.
                  Error-value=3: END-POINTS object missing
      7          Synchronized path computation request missing
      8          Unknown request reference
      9          Attempt to establish a second PCEP session
      10         Reception of an invalid object
                  Error-value=1: reception of an object with P flag not
                  set although the P flag must be set according to this
                  specification.






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   The error types listed above are described below.

   Error-Type=1: PCEP session establishment failure.

      If a malformed message is received, the receiving PCEP peer MUST
      send a PCErr message with Error-Type=1, Error-value=1.

      If no Open message is received before the expiration of the
      OpenWait timer, the receiving PCEP peer MUST send a PCErr message
      with Error-Type=1, Error-value=2 (see Appendix A for details).

      If one or more PCEP session characteristics are unacceptable by
      the receiving peer and are not negotiable, it MUST send a PCErr
      message with Error-Type=1, Error-value=3.

      If an Open message is received with unacceptable session
      characteristics but these characteristics are negotiable, the
      receiving PCEP peer MUST send a PCErr message with Error-Type-1,
      Error-value=4 (see Section 6.2 for details).

      If a second Open message is received during the PCEP session
      establishment phase and the session characteristics are still
      unacceptable, the receiving PCEP peer MUST send a PCErr message
      with Error-Type-1, Error-value=5 (see Section 6.2 for details).

      If a PCErr message is received during the PCEP session
      establishment phase that contains an Open message proposing
      unacceptable session characteristics, the receiving PCEP peer MUST
      send a PCErr message with Error-Type=1, Error-value=6.

      If neither a Keepalive message nor a PCErr message is received
      before the expiration of the KeepWait timer during the PCEP
      session establishment phase, the receiving PCEP peer MUST send a
      PCErr message with Error-Type=1, Error-value=7.

   Error-Type=2:  the PCE indicates that the path computation request
      cannot be honored because it does not support one or more required
      capability.  The corresponding path computation request MUST be
      cancelled.

   Error-Type=3 or Error-Type=4:  if a PCEP message is received that
      carries a PCEP object (with the P flag set) not recognized by the
      PCE or recognized but not supported, then the PCE MUST send a
      PCErr message with a PCEP-ERROR object (Error-Type=3 and 4,
      respectively).  In addition, the PCE MAY include in the PCErr
      message the unknown or not supported object.  The corresponding
      path computation request MUST be cancelled by the PCE without
      further notification.



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   Error-Type=5:  if a path computation request is received that is not
      compliant with an agreed policy between the PCC and the PCE, the
      PCE MUST send a PCErr message with a PCEP-ERROR object (Error-
      Type=5).  The corresponding path computation MUST be cancelled.
      Policy-specific TLVs carried within the PCEP-ERROR object may be
      defined in other documents to specify the nature of the policy
      violation.

   Error-Type=6:  if a path computation request is received that does
      not contain a mandatory object, the PCE MUST send a PCErr message
      with a PCEP-ERROR object (Error-Type=6).  If there are multiple
      mandatory objects missing, the PCErr message MUST contain one
      PCEP-ERROR object per missing object.  The corresponding path
      computation MUST be cancelled.

   Error-Type=7:  if a PCC sends a synchronized path computation request
      to a PCE and the PCE does not receive all the synchronized path
      computation requests listed within the corresponding SVEC object
      after the expiration of the timer SyncTimer defined in
      Section 7.13.3, the PCE MUST send a PCErr message with a PCEP-
      ERROR object (Error-Type=7).  The corresponding synchronized path
      computation MUST be cancelled.  It is RECOMMENDED for the PCE to
      include the REQ-MISSING TLVs (defined below) that identify the
      missing requests.

      The REQ-MISSING TLV is compliant with the PCEP TLV format defined
      in section 7.1 and is comprised of 2 bytes for the type, 2 bytes
      specifying the TLV length (length of the value portion in bytes),
      followed by a fixed-length value field of 4 bytes.

         Type:   3
         Length: 4 bytes
         Value:  4 bytes that indicate the Request-ID-number that
                 corresponds to the missing request.

   Error-Type=8:  if a PCC receives a PCRep message related to an
      unknown path computation request, the PCC MUST send a PCErr
      message with a PCEP-ERROR object (Error-Type=8).  In addition, the
      PCC MUST include in the PCErr message the unknown RP object.

   Error-Type=9:  if a PCEP peer detects an attempt from another PCEP
      peer to establish a second PCEP session, it MUST send a PCErr
      message with Error-Type=9, Error-value=1.  The existing PCEP
      session MUST be preserved and all subsequent messages related to
      the tentative establishment of the second PCEP session MUST be
      silently ignored.





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   Error-Type=10:  if a PCEP peers receives an object with the P flag
      not set although the P flag must be set according to this
      specification, it MUST send a PCErr message with Error-Type=10,
      Error-value=1.

7.16.  LOAD-BALANCING Object

   There are situations where no TE LSP with a bandwidth of X could be
   found by a PCE although such a bandwidth requirement could be
   satisfied by a set of TE LSPs such that the sum of their bandwidths
   is equal to X.  Thus, it might be useful for a PCC to request a set
   of TE LSPs so that the sum of their bandwidth is equal to X Mbit/s,
   with potentially some constraints on the number of TE LSPs and the
   minimum bandwidth of each of these TE LSPs.  Such a request is made
   by inserting a LOAD-BALANCING object in a PCReq message sent to a
   PCE.

   The LOAD-BALANCING object is optional.

   LOAD-BALANCING Object-Class is 14.

   LOAD-BALANCING Object-Type is 1.

   The format of the LOAD-BALANCING object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Reserved            |     Flags     |     Max-LSP   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Min-Bandwidth                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 21: LOAD-BALANCING Object Body Format

   Reserved (16 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Flags (8 bits):  No flag is currently defined.  The Flags field MUST
      be set to zero on transmission and MUST be ignored on receipt.

   Max-LSP (8 bits):  maximum number of TE LSPs in the set.

   Min-Bandwidth (32 bits):  Specifies the minimum bandwidth of each
      element of the set of TE LSPs.  The bandwidth is encoded in 32
      bits in IEEE floating point format (see [IEEE.754.1985]),
      expressed in bytes per second.




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   The LOAD-BALANCING object body has a fixed length of 8 bytes.

   If a PCC requests the computation of a set of TE LSPs so that the sum
   of their bandwidth is X, the maximum number of TE LSPs is N, and each
   TE LSP must at least have a bandwidth of B, it inserts a BANDWIDTH
   object specifying X as the required bandwidth and a LOAD-BALANCING
   object with the Max-LSP and Min-Bandwidth fields set to N and B,
   respectively.

7.17.  CLOSE Object

   The CLOSE object MUST be present in each Close message.  There MUST
   be only one CLOSE object per Close message.  If a Close message is
   received that contains more than one CLOSE object, the first CLOSE
   object is the one that must be processed.  Other CLOSE objects MUST
   be silently ignored.

   CLOSE Object-Class is 15.

   CLOSE Object-Type is 1.

   The format of the CLOSE object body 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |      Flags    |    Reason     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         Optional TLVs                       //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 22: CLOSE Object Format

   Reserved (16 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Flags (8 bits):  No flags are currently defined.  The Flag field MUST
      be set to zero on transmission and MUST be ignored on receipt.

   Reason (8 bits):  specifies the reason for closing the PCEP session.
      The setting of this field is optional.  IANA manages the codespace
      of the Reason field.  The following values are currently defined:







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       Reasons
        Value        Meaning
          1          No explanation provided
          2          DeadTimer expired
          3          Reception of a malformed PCEP message
          4          Reception of an unacceptable number of unknown
                     requests/replies
          5          Reception of an unacceptable number of unrecognized
                     PCEP messages

   Optional TLVs may be included within the CLOSE object body.  The
   specification of such TLVs is outside the scope of this document.

8.  Manageability Considerations

   This section follows the guidance of [PCE-MANAGE].

8.1.  Control of Function and Policy

   A PCEP implementation SHOULD allow configuring the following PCEP
   session parameters on the implementation:

   o  The local Keepalive and DeadTimer (i.e., parameters sent by the
      PCEP peer in an Open message),

   o  The maximum acceptable remote Keepalive and DeadTimer (i.e.,
      parameters received from a peer in an Open message),

   o  Whether negotiation is enabled or disabled,

   o  If negotiation is allowed, the minimum acceptable Keepalive and
      DeadTimer timers received from a PCEP peer,

   o  The SyncTimer,

   o  The maximum number of sessions that can be set up,

   o  The request timer, the amount of time a PCC waits for a reply
      before resending its path computation requests (potentially to an
      alternate PCE),

   o  The MAX-UNKNOWN-REQUESTS,

   o  The MAX-UNKNOWN-MESSAGES.

   These parameters may be configured as default parameters for any PCEP
   session the PCEP speaker participates in, or may apply to a specific
   session with a given PCEP peer or to a specific group of sessions



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   with a specific group of PCEP peers.  A PCEP implementation SHOULD
   allow configuring the initiation of a PCEP session with a selected
   subset of discovered PCEs.  Note that PCE selection is a local
   implementation issue.  A PCEP implementation SHOULD allow configuring
   a specific PCEP session with a given PCEP peer.  This includes the
   configuration of the following parameters:

   o  The IP address of the PCEP peer,

   o  The PCEP speaker role: PCC, PCE, or both,

   o  Whether the PCEP speaker should initiate the PCEP session or wait
      for initiation by the peer,

   o  The PCEP session parameters, as listed above, if they differ from
      the default parameters,

   o  A set of PCEP policies including the type of operations allowed
      for the PCEP peer (e.g., diverse path computation,
      synchronization, etc.).

   A PCEP implementation MUST allow restricting the set of PCEP peers
   that can initiate a PCEP session with the PCEP speaker (e.g., list of
   authorized PCEP peers, all PCEP peers in the area, all PCEP peers in
   the AS).

8.2.  Information and Data Models

   A PCEP MIB module is defined in [PCEP-MIB] that describes managed
   objects for modeling of PCEP communication including:

   o  PCEP client configuration and status,

   o  PCEP peer configuration and information,

   o  PCEP session configuration and information,

   o  Notifications to indicate PCEP session changes.

8.3.  Liveness Detection and Monitoring

   PCEP includes a keepalive mechanism to check the liveliness of a PCEP
   peer and a notification procedure allowing a PCE to advertise its
   overloaded state to a PCC.  Also, procedures in order to monitor the
   liveliness and performances of a given PCE chain (in case of
   multiple-PCE path computation) are defined in [PCE-MONITOR].





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8.4.  Verifying Correct Operation

   Verifying the correct operation of a PCEP communication can be
   performed by monitoring various parameters.  A PCEP implementation
   SHOULD provide the following parameters:

   o  Response time (minimum, average, and maximum), on a per-PCE-peer
      basis,

   o  PCEP session failures,

   o  Amount of time the session has been in active state,

   o  Number of corrupted messages,

   o  Number of failed computations,

   o  Number of requests for which no reply has been received after the
      expiration of a configurable timer and by verifying that at least
      one path exists that satisfies the set of constraints.

   A PCEP implementation SHOULD log error events (e.g., corrupted
   messages, unrecognized objects).

8.5.  Requirements on Other Protocols and Functional Components

   PCEP does not put any new requirements on other protocols.  As PCEP
   relies on the TCP transport protocol, PCEP management can make use of
   TCP management mechanisms (such as the TCP MIB defined in [RFC4022]).

   The PCE Discovery mechanisms ([RFC5088], [RFC5089]) may have an
   impact on PCEP.  To avoid that a high frequency of PCE Discoveries/
   Disappearances triggers a high frequency of PCEP session setups/
   deletions, it is RECOMMENDED to introduce some dampening for
   establishment of PCEP sessions.

8.6.  Impact on Network Operation

   In order to avoid any unacceptable impact on network operations, an
   implementation SHOULD allow a limit to be placed on the number of
   sessions that can be set up on a PCEP speaker, and MAY allow a limit
   to be placed on the rate of messages sent by a PCEP speaker and
   received from a peer.  It MAY also allow sending a notification when
   a rate threshold is reached.







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9.  IANA Considerations

   IANA assigns values to the PCEP protocol parameters (messages,
   objects, TLVs).

   IANA established a new top-level registry to contain all PCEP
   codepoints and sub-registries.

   The allocation policy for each new registry is by IETF Consensus: new
   values are assigned through the IETF consensus process (see
   [RFC5226]).  Specifically, new assignments are made via RFCs approved
   by the IESG.  Typically, the IESG will seek input on prospective
   assignments from appropriate persons (e.g., a relevant Working Group
   if one exists).

9.1.  TCP Port

   PCEP has been registered as TCP port 4189.

9.2.  PCEP Messages

   IANA created a registry for PCEP messages.  Each PCEP message has a
   message type value.


   Value     Meaning                          Reference
     1        Open                          This document
     2        Keepalive                     This document
     3        Path Computation Request      This document
     4        Path Computation Reply        This document
     5        Notification                  This document
     6        Error                         This document
     7        Close                         This document

9.3.  PCEP Object

   IANA created a registry for PCEP objects.  Each PCEP object has an
   Object-Class and an Object-Type.

   Object-Class Value   Name                               Reference

          1             OPEN                               This document
                        Object-Type
                            1

          2             RP                                 This document
                        Object-Type
                            1



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          3             NO-PATH                            This document
                        Object-Type
                            1

          4             END-POINTS                         This document
                        Object-Type
                            1: IPv4 addresses
                            2: IPv6 addresses

          5             BANDWIDTH                          This document
                        Object-Type
                          1: Requested bandwidth
                          2: Bandwidth of an existing TE LSP
                             for which a reoptimization is performed.

          6             METRIC                             This document
                        Object-Type
                            1

          7             ERO                                This document
                        Object-Type
                            1

          8             RRO                                This document
                        Object-Type
                            1

          9             LSPA                               This document
                        Object-Type
                            1

         10             IRO                                This document
                        Object-Type
                            1

         11             SVEC                               This document
                        Object-Type
                            1

         12             NOTIFICATION                       This document
                        Object-Type
                            1

         13             PCEP-ERROR                         This document
                        Object-Type
                            1





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         14             LOAD-BALANCING                     This document
                        Object-Type
                            1

         15             CLOSE                              This document
                        Object-Type
                            1

9.4.  PCEP Message Common Header

   IANA created a registry to manage the Flag field of the PCEP Message
   Common Header.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently defined for the PCEP message common header.

9.5.  Open Object Flag Field

   IANA created a registry to manage the Flag field of the OPEN object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently for the OPEN Object flag field.

9.6.  RP Object

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description




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   o  Defining RFC

   Several bits are defined for the RP Object flag field in this
   document.  The following values have been assigned:

   Codespace of the Flag field (RP Object)

     Bit      Description              Reference

      26      Strict/Loose          This document
      27      Bi-directional        This document
      28      Reoptimization        This document
     29-31    Priority              This document


9.7.  NO-PATH Object Flag Field

   IANA created a registry to manage the codespace of the NI field and
   the Flag field of the NO-PATH object.


    Value       Meaning                        Reference

      0    No path satisfying the set        This document
           of constraints could be found
      1    PCE chain broken                  This document

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   One bit is defined for the NO-PATH Object flag field in this
   document:

   Codespace of the Flag field (NO-PATH Object)

     Bit      Description                      Reference

      0    Unsatisfied constraint indicated    This document







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9.8.  METRIC Object

   IANA created a registry to manage the codespace of the T field and
   the Flag field of the METRIC Object.

   Codespace of the T field (Metric Object)

    Value      Meaning          Reference

      1        IGP metric      This document
      2        TE metric       This document
      3        Hop Counts      This document

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Several bits are defined in this document.  The following values have
   been assigned:

   Codespace of the Flag field (Metric Object)

     Bit      Description         Reference

      6       Computed metric    This document
      7       Bound              This document

9.9.  LSPA Object Flag Field

   IANA created a registry to manage the Flag field of the LSPA object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   One bit is defined for the LSPA Object flag field in this document:





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   Codespace of the Flag field (LSPA Object)

     Bit      Description             Reference

      7    Local Protection Desired   This document


9.10.  SVEC Object Flag Field

   IANA created a registry to manage the Flag field of the SVEC object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Three bits are defined for the SVEC Object flag field in this
   document:

   Codespace of the Flag field (SVEC Object)

     Bit      Description      Reference

      21      SRLG Diverse     This document
      22      Node Diverse     This document
      23      Link Diverse     This document

9.11.  NOTIFICATION Object

   IANA created a registry for the Notification-type and Notification-
   value of the NOTIFICATION object and manages the code space.

   Notification-type  Name                                 Reference
         1            Pending Request cancelled            This document
                      Notification-value
                        1: PCC cancels a set of pending requests
                        2: PCE cancels a set of pending requests

         2            Overloaded PCE                       This document
                      Notification-value
                        1: PCE in congested state
                        2: PCE no longer in congested state





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   IANA created a registry to manage the Flag field of the NOTIFICATION
   object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently for the Flag Field of the NOTIFICATION object.

9.12.  PCEP-ERROR Object

   IANA created a registry for the Error-Type and Error-value of the
   PCEP Error Object and manages the code space.

































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   For each PCEP error, an Error-Type and an Error-value are defined.

Error-  Meaning                                           Reference
Type
  1     PCEP session establishment failure                This document
        Error-value=1: reception of an invalid Open message or
                       a non Open message.
        Error-value=2: no Open message received before the expiration
                       of the OpenWait timer
        Error-value=3: unacceptable and non-negotiable session
                       characteristics
        Error-value=4: unacceptable but negotiable session
                       characteristics
        Error-value=5: reception of a second Open message with
                       still unacceptable session characteristics
        Error-value=6: reception of a PCErr message proposing
                       unacceptable session characteristics
        Error-value=7: No Keepalive or PCErr message received
                       before the expiration of the KeepWait timer
        Error-value=8: PCEP version not supported
  2     Capability not supported                          This document
  3     Unknown Object                                    This document
         Error-value=1: Unrecognized object class
         Error-value=2: Unrecognized object Type
  4     Not supported object                              This document
         Error-value=1: Not supported object class
         Error-value=2: Not supported object Type
  5     Policy violation                                  This document
         Error-value=1: C bit of the METRIC object set
                        (request rejected)
         Error-value=2: O bit of the RP object cleared
                        (request rejected)
  6     Mandatory Object missing                          This document
         Error-value=1: RP object missing
         Error-value=2: RRO missing for a reoptimization
                        request (R bit of the RP object set)
         Error-value=3: END-POINTS object missing
  7     Synchronized path computation request missing     This document
  8     Unknown request reference                         This document
  9     Attempt to establish a second PCEP session        This document
 10     Reception of an invalid object                    This document
         Error-value=1: reception of an object with P flag
                        not set although the P flag must be
                        set according to this specification.

   IANA created a registry to manage the Flag field of the PCEP-ERROR
   object.




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   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently for the Flag Field of the PCEP-ERROR Object.

9.13.  LOAD-BALANCING Object Flag Field

   IANA created a registry to manage the Flag field of the LOAD-
   BALANCING object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently for the Flag Field of the LOAD-BALANCING
   Object.

9.14.  CLOSE Object

   The CLOSE object MUST be present in each Close message in order to
   close a PCEP session.  The reason field of the CLOSE object specifies
   the reason for closing the PCEP session.  The reason field of the
   CLOSE object is managed by IANA.

   Reasons

    Value        Meaning
      1          No explanation provided
      2          DeadTimer expired
      3          Reception of a malformed PCEP message
      4          Reception of an unacceptable number of unknown
                 requests/replies
      5          Reception of an unacceptable number of unrecognized
                 PCEP messages

   IANA created a registry to manage the flag field of the CLOSE object.




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   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   No bits are currently for the Flag Field of the CLOSE Object.

9.15.  PCEP TLV Type Indicators

   IANA created a registry for the PCEP TLVs.

    Value         Meaning                    Reference

      1          NO-PATH-VECTOR TLV         This document
      2          OVERLOAD-DURATION TLV      This document
      3          REQ-MISSING TLV            This document

9.16.  NO-PATH-VECTOR TLV

   IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
   defined in this document, numbering them from 0 as the least
   significant bit.

   New bit numbers may be allocated only by an IETF Consensus action.

   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Name flag

   o  Reference

   Bit Number       Name                         Reference
     31             PCE currently unavailable    This document
     30             Unknown destination          This document
     29             Unknown source               This document










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10.  Security Considerations

10.1.  Vulnerability

   Attacks on PCEP may result in damage to active networks.  If path
   computation responses are changed, the PCC may be encouraged to set
   up inappropriate LSPs.  Such LSPs might deviate to parts of the
   network susceptible to snooping, or might transit congested or
   reserved links.  Path computation responses may be attacked by
   modification of the PCRep message, by impersonation of the PCE, or by
   modification of the PCReq to cause the PCE to perform a different
   computation from that which was originally requested.

   It is also possible to damage the operation of a PCE through a
   variety of denial-of-service attacks.  Such attacks can cause the PCE
   to become congested with the result that path computations are
   supplied too slowly to be of value for PCCs.  This could lead to
   slower-than-acceptable recovery times or delayed LSP establishment.
   In extreme cases, it may be that service requests are not satisfied.

   PCEP could be the target of the following attacks:

   o  Spoofing (PCC or PCE impersonation)

   o  Snooping (message interception)

   o  Falsification

   o  Denial of Service

   In inter-AS scenarios when PCE-to-PCE communication is required,
   attacks may be particularly significant with commercial as well as
   service-level implications.

   Additionally, snooping of PCEP requests and responses may give an
   attacker information about the operation of the network.  Simply by
   viewing the PCEP messages someone can determine the pattern of
   service establishment in the network and can know where traffic is
   being routed, thereby making the network susceptible to targeted
   attacks and the data within specific LSPs vulnerable.

   The following sections identify mechanisms to protect PCEP against
   security attacks.








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10.2.  TCP Security Techniques

   At the time of writing, TCP-MD5 [RFC2385] is the only available
   security mechanism for securing the TCP connections that underly PCEP
   sessions.

   As explained in [RFC2385], the use of MD5 faces some limitations and
   does not provide as high a level of security as was once believed.  A
   PCEP implementation supporting TCP-MD5 SHOULD be designed so that
   stronger security keying techniques or algorithms that may be
   specified for TCP can be easily integrated in future releases.

   The TCP Authentication Option [TCP-AUTH] (TCP-AO) specifies new
   security procedures for TCP, but is not yet complete.  Since it is
   believed that [TCP-AUTH] will offer significantly improved security
   for applications using TCP, implementers should expect to update
   their implementation as soon as the TCP Authentication Option is
   published as an RFC.

   Implementations MUST support TCP-MD5 and should make the security
   function available as a configuration option.

   Operators will need to observe that some deployed PCEP
   implementations may pre-date the completion of [TCP-AUTH], and it
   will be necessary to configure policy for secure communication
   between PCEP speakers that support the TCP Authentication Option, and
   those that don't.

   An alternative approach for security over TCP transport is to use the
   Transport Layer Security (TLS) protocol [RFC5246].  This provides
   protection against eavesdropping, tampering, and message forgery.
   But TLS doesn't protect the TCP connection itself, because it does
   not authenticate the TCP header.  Thus, it is vulnerable to attacks
   such as TCP reset attacks (something against which TCP-MD5 does
   protect).  The use of TLS would, however, require the specification
   of how PCEP initiates TLS handshaking and how it interprets the
   certificates exchanged in TLS.  That specification is out of the
   scope of this document, but could be the subject of future work.

10.3.  PCEP Authentication and Integrity

   Authentication and integrity checks allow the receiver of a PCEP
   message to know that the message genuinely comes from the node that
   purports to have sent it and to know whether the message has been
   modified.






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   The TCP-MD5 mechanism [RFC2385] described in the previous section
   provides such a mechanism subject to the concerns listed in [RFC2385]
   and [RFC4278].  These issues will be addressed and resolved by
   [TCP-AUTH].

10.4.  PCEP Privacy

   Ensuring PCEP communication privacy is of key importance, especially
   in an inter-AS context, where PCEP communication end-points do not
   reside in the same AS, as an attacker that intercepts a PCE message
   could obtain sensitive information related to computed paths and
   resources.

   PCEP privacy can be ensured by encryption.  TCP MAY be run over IPsec
   [RFC4303] tunnels to provide the required encryption.  Note that
   IPsec can also ensure authentication and integrity; in which case,
   TCP-MD5 or TCP-AO would not be required.  However, there is some
   concern that IPsec on this scale would be hard to configure and
   operate.  Use of IPSec with PCEP is out of the scope of this document
   and may be addressed in a separate document.

10.5.  Key Configuration and Exchange

   Authentication, tamper protection, and encryption all require the use
   of keys by sender and receiver.

   Although key configuration per session is possible, it may be
   particularly onerous to operators (in the same way as for the Border
   Gateway Protocol (BGP) as discussed in [BGP-SEC]).  If there is a
   relatively small number of PCCs and PCEs in the network, manual key
   configuration MAY be considered a valid choice by the operator,
   although it is important to be aware of the vulnerabilities
   introduced by such mechanisms (i.e., configuration errors, social
   engineering, and carelessness could all give rise to security
   breaches).  Furthermore, manually configured keys are less likely to
   be regularly updated which also increases the security risk.  Where
   there is a large number of PCCs and PCEs, the operator could find
   that key configuration and maintenance is a significant burden as
   each PCC needs to be configured to the PCE.

   An alternative to individual keys is the use of a group key.  A group
   key is common knowledge among all members of a trust domain.  Thus,
   since the routers in an IGP area or an AS are part of a common trust
   domain [MPLS-SEC], a PCEP group key MAY be shared among all PCCs and
   PCEs in an IGP area or AS.  The use of a group key will considerably
   simplify the operator's configuration task while continuing to secure





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   PCEP against attack from outside the network.  However, it must be
   noted that the more entities that have access to a key, the greater
   the risk of that key becoming public.

   With the use of a group key, separate keys would need to be
   configured for the PCE-to-PCE communications that cross trust domain
   (e.g., AS) boundaries, but the number of these relationships is
   likely to be very small.

   PCE discovery ([RFC5088] and [RFC5089]) is a significant feature for
   the successful deployment of PCEP in large networks.  This mechanism
   allows a PCC to discover the existence of suitable PCEs within the
   network without the necessity of configuration.  It should be obvious
   that, where PCEs are discovered and not configured, the PCC cannot
   know the correct key to use.  There are three possible approaches to
   this problem that retain some aspect of security:

   o  The PCCs may use a group key as previously discussed.

   o  The PCCs may use some form of secure key exchange protocol with
      the PCE (such as the Internet Key Exchange protocol v2 (IKE)
      [RFC4306]).  The drawback to this is that IKE implementations on
      routers are not common and this may be a barrier to the deployment
      of PCEP.  Details are out of the scope of this document and may be
      addressed in a separate document.

   o  The PCCs may make use of a key server to determine the key to use
      when talking to the PCE.  To some extent, this is just moving the
      problem, since the PCC's communications with the key server must
      also be secure (for example, using Kerberos [RFC4120]), but there
      may some (minor) benefit in scaling if the PCC is to learn about
      several PCEs and only needs to know one key server.  Note that key
      servers currently have very limited implementation.  Details are
      out of the scope of this document and may be addressed in a
      separate document.

   PCEP relationships are likely to be long-lived even if the PCEP
   sessions are repeatedly closed and re-established.  Where protocol
   relationships persist for a large number of protocol interactions or
   over a long period of time, changes in the keys used by the protocol
   peers is RECOMMENDED [RFC4107].  Note that TCP-MD5 does not allow the
   key to be changed without closing and reopening the TCP connection
   which would result in the PCEP session being terminated and needing
   to be restarted.  That might not be a significant issue for PCEP.
   Note also that the plans for the TCP Authentication Option [TCP-AUTH]
   will allow dynamic key change (roll-over) for an active TCP
   connection.




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   If key exchange is used (for example, through IKE), then it is
   relatively simple to support dynamic key updates and apply these to
   PCEP.

   Note that in-band key management for the TCP Authentication Option
   [TCP-AUTH] is currently unresolved.

   [RFC3562] sets out some of the issues for the key management of
   secure TCP connections.

10.6.  Access Policy

   Unauthorized access to PCE function represents a variety of potential
   attacks.  Not only may this be a simple denial-of-service attack (see
   Section 10.7), but it would be a mechanism for an intruder to
   determine important information about the network and operational
   network policies simply by inserting bogus computation requests.
   Furthermore, false computation requests could be used to predict
   where traffic will be placed in the network when real requests are
   made, allowing the attacker to target specific network resources.

   PCEs SHOULD be configurable for access policy.  Where authentication
   is used, access policy can be achieved through the exchange or
   configuration of keys as described in Section 10.5.  More simple
   policies MAY be configured on PCEs in the form of access lists where
   the IP addresses of the legitimate PCCs are listed.  Policies SHOULD
   also be configurable to limit the type of computation requests that
   are supported from different PCCs.

   It is RECOMMENDED that access policy violations are logged by the PCE
   and are available for inspection by the operator to determine whether
   attempts have been made to attack the PCE.  Such mechanisms MUST be
   lightweight to prevent them from being used to support denial-of-
   service attacks (see Section 10.7).

10.7.  Protection against Denial-of-Service Attacks

   Denial-of-service (DoS) attacks could be mounted at the TCP level or
   at the PCEP level.  That is, the PCE could be attacked through
   attacks on TCP or through attacks within established PCEP sessions.

10.7.1.  Protection against TCP DoS Attacks

   PCEP can be the target of TCP DoS attacks, such as for instance SYN
   attacks, as is the case for all protocols that run over TCP.  Other
   protocol specifications have investigated this problem and PCEP can
   share their experience.  The reader is referred to the specification




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   of the Label Distribution Protocol (LDP) [RFC5036] for example.  In
   order to protect against TCP DoS attacks, PCEP implementations can
   support the following techniques.

   o  PCEP uses a single registered port for all communications.  The
      PCE SHOULD listen for TCP connections only on ports where
      communication is expected.

   o  The PCE MAY implement an access list to immediately reject (or
      discard) TCP connection attempts from unauthorized PCCs.

   o  The PCE SHOULD NOT allow parallel TCP connections from the same
      PCC on the PCEP-registered port.

   o  The PCE MAY require the use of the MD5 option on all TCP
      connections, and MAY reject (or discard) any connection setup
      attempt that does not use MD5.  A PCE MUST NOT accept any SYN
      packet for which the MD5 segment checksum is invalid.  Note,
      however, that the use of MD5 requires that the receiver use CPU
      resources to compute the checksum before it can decide to discard
      an otherwise acceptable SYN segment.

10.7.2.  Request Input Shaping/Policing

   A PCEP implementation may be subject to DoS attacks within a
   legitimate PCEP session.  For example, a PCC might send a very large
   number of PCReq messages causing the PCE to become congested or
   causing requests from other PCCs to be queued.

   Note that the direct use of the Priority field on the RP object to
   prioritize received requests does not provide any protection since
   the attacker could set all requests to be of the highest priority.

   Therefore, it is RECOMMENDED that PCE implementations include input
   shaping/policing mechanisms that either throttle the requests
   received from any one PCC, or apply queuing or priority-degradation
   techniques to over-communicative PCCs.

   Such mechanisms MAY be set by default, but SHOULD be available for
   configuration.  Such techniques may be considered particularly
   important in multi-service-provider environments to protect the
   resources of one service provider from unwarranted, over-zealous, or
   malicious use by PCEs in another service provider.








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11.  Acknowledgments

   The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash,
   Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard
   Douville, Jon Parker, Martin German, and Dennis Aristow for their
   very valuable input.  The authors would also like to thank Fabien
   Verhaeghe for the very fruitful discussions and useful suggestions.
   David McGrew and Brian Weis provided valuable input to the Security
   Considerations section.

   Ross Callon, Magnus Westerlund, Lars Eggert, Pasi Eronen, Tim Polk,
   Chris Newman, and Russ Housley provided important input during IESG
   review.

12.  References

12.1.  Normative References

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

   [RFC2205]        Braden, B., Zhang, L., Berson, S., Herzog, S., and
                    S. Jamin, "Resource ReSerVation Protocol (RSVP) --
                    Version 1 Functional Specification", RFC 2205,
                    September 1997.

   [RFC2385]        Heffernan, A., "Protection of BGP Sessions via the
                    TCP MD5 Signature Option", RFC 2385, August 1998.

   [RFC3209]        Awduche, D., Berger, L., Gan, D., Li, T.,
                    Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions
                    to RSVP for LSP Tunnels", RFC 3209, December 2001.

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

   [RFC3477]        Kompella, K. and Y. Rekhter, "Signalling Unnumbered
                    Links in Resource ReSerVation Protocol - Traffic
                    Engineering (RSVP-TE)", RFC 3477, January 2003.

   [RFC4090]        Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
                    Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
                    May 2005.






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

12.2.  Informative References

   [BGP-SEC]        Christian, B. and T. Tauber, "BGP Security
                    Requirements", Work in Progress, November 2008.

   [IEEE.754.1985]  IEEE Standard 754, "Standard for Binary Floating-
                    Point Arithmetic", August 1985.

   [INTER-LAYER]    Oki, E., Roux, J., Kumaki, K., Farrel, A., and T.
                    Takeda, "PCC-PCE Communication and PCE Discovery
                    Requirements for Inter-Layer Traffic Engineering",
                    Work in Progress, January 2009.

   [MPLS-SEC]       Fang, L. and M. Behringer, "Security Framework for
                    MPLS and GMPLS Networks", Work in Progress,
                    November 2008.

   [PCE-MANAGE]     Farrel, A., "Inclusion of Manageability Sections in
                    PCE Working Group Drafts", Work in Progress,
                    January 2009.

   [PCE-MONITOR]    Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
                    monitoring tools for Path Computation Element based
                    Architecture", Work in Progress, November 2008.

   [PCEP-MIB]       Stephan, E. and K. Koushik, "PCE communication
                    protocol (PCEP) Management Information Base",
                    Work in Progress, November 2008.

   [RBNF]           Farrel, A., "Reduced Backus-Naur Form (RBNF) A
                    Syntax Used in Various Protocol Specifications",
                    Work in Progress, November 2008.

   [RFC1321]        Rivest, R., "The MD5 Message-Digest Algorithm",
                    RFC 1321, April 1992.

   [RFC3471]        Berger, L., "Generalized Multi-Protocol Label
                    Switching (GMPLS) Signaling Functional Description",
                    RFC 3471, January 2003.

   [RFC3562]        Leech, M., "Key Management Considerations for the
                    TCP MD5 Signature Option", RFC 3562, July 2003.





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   [RFC3785]        Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx,
                    P., and T. Telkamp, "Use of Interior Gateway
                    Protocol (IGP) Metric as a second MPLS Traffic
                    Engineering (TE) Metric", BCP 87, RFC 3785,
                    May 2004.

   [RFC4022]        Raghunarayan, R., "Management Information Base for
                    the Transmission Control Protocol (TCP)", RFC 4022,
                    March 2005.

   [RFC4101]        Rescorla, E. and IAB, "Writing Protocol Models",
                    RFC 4101, June 2005.

   [RFC4107]        Bellovin, S. and R. Housley, "Guidelines for
                    Cryptographic Key Management", BCP 107, RFC 4107,
                    June 2005.

   [RFC4120]        Neuman, C., Yu, T., Hartman, S., and K. Raeburn,
                    "The Kerberos Network Authentication Service (V5)",
                    RFC 4120, July 2005.

   [RFC4278]        Bellovin, S. and A. Zinin, "Standards Maturity
                    Variance Regarding the TCP MD5 Signature Option (RFC
                    2385) and the BGP-4 Specification", RFC 4278,
                    January 2006.

   [RFC4303]        Kent, S., "IP Encapsulating Security Payload (ESP)",
                    RFC 4303, December 2005.

   [RFC4306]        Kaufman, C., "Internet Key Exchange (IKEv2)
                    Protocol", RFC 4306, December 2005.

   [RFC5420]        Farrel, A., Ed., Papadimitriou, D., Vasseur, JP.,
                    and A. Ayyangarps, "Encoding of Attributes for MPLS
                    LSP Establishment Using Resource Reservation
                    Protocol Traffic Engineering (RSVP-TE)", RFC 5420,
                    February 2009.

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

   [RFC4657]        Ash, J. and J. Le Roux, "Path Computation Element
                    (PCE) Communication Protocol Generic Requirements",
                    RFC 4657, September 2006.

   [RFC4674]        Le Roux, J., "Requirements for Path Computation
                    Element (PCE) Discovery", RFC 4674, October 2006.



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   [RFC4927]        Le Roux, J., "Path Computation Element Communication
                    Protocol (PCECP) Specific Requirements for Inter-
                    Area MPLS and GMPLS Traffic Engineering", RFC 4927,
                    June 2007.

   [RFC5036]        Andersson, L., Minei, I., and B. Thomas, "LDP
                    Specification", RFC 5036, October 2007.

   [RFC5088]        Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
                    Zhang, "OSPF Protocol Extensions for Path
                    Computation Element (PCE) Discovery", RFC 5088,
                    January 2008.

   [RFC5089]        Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
                    Zhang, "IS-IS Protocol Extensions for Path
                    Computation Element (PCE) Discovery", RFC 5089,
                    January 2008.

   [RFC5246]        Dierks, T. and E. Rescorla, "The Transport Layer
                    Security (TLS) Protocol Version 1.2", RFC 5246,
                    August 2008.

   [RFC5376]        Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
                    Requirements for the Path Computation Element
                    Communication Protocol (PCECP)", RFC 5376,
                    November 2008.

   [TCP-AUTH]       Touch, J., Mankin, A., and R. Bonica, "The TCP
                    Authentication Option", Work in Progress,
                    November 2008.





















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Appendix A.  PCEP Finite State Machine (FSM)

   The section describes the PCEP finite state machine (FSM).  PCEP
   Finite State Machine

                          +-+-+-+-+-+-+<------+
                   +------| SessionUP |<---+  |
                   |      +-+-+-+-+-+-+    |  |
                   |                       |  |
                   |   +->+-+-+-+-+-+-+    |  |
                   |   |  | KeepWait  |----+  |
                   |   +--|           |<---+  |
                   |+-----+-+-+-+-+-+-+    |  |
                   ||          |           |  |
                   ||          |           |  |
                   ||          V           |  |
                   ||  +->+-+-+-+-+-+-+----+  |
                   ||  |  | OpenWait  |-------+
                   ||  +--|           |<------+
                   ||+----+-+-+-+-+-+-+<---+  |
                   |||         |           |  |
                   |||         |           |  |
                   |||         V           |  |
                   ||| +->+-+-+-+-+-+-+    |  |
                   ||| |  |TCPPending |----+  |
                   ||| +--|           |       |
                   |||+---+-+-+-+-+-+-+<---+  |
                   ||||        |           |  |
                   ||||        |           |  |
                   ||||        V           |  |
                   |||+--->+-+-+-+-+       |  |
                   ||+---->| Idle  |-------+  |
                   |+----->|       |----------+
                   +------>+-+-+-+-+

        Figure 23: PCEP Finite State Machine for the PCC

   PCEP defines the following set of variables:

   Connect:  the timer (in seconds) started after having initialized a
      TCP connection using the PCEP-registered TCP port.  The value of
      the Connect timer is 60 seconds.

   ConnectRetry:  the number of times the system has tried to establish
      a TCP connection with a PCEP peer without success.






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   ConnectMaxRetry:  the maximum number of times the system tries to
      establish a TCP connection using the PCEP-registered TCP port
      before going back to the Idle state.  The value of the
      ConnectMaxRetry is 5.

   OpenWait:  the timer that corresponds to the amount of time a PCEP
      peer will wait to receive an Open message from the PCEP peer after
      the expiration of which the system releases the PCEP resource and
      goes back to the Idle state.  The OpenWait timer has a fixed value
      of 60 seconds.

   KeepWait:  the timer that corresponds to the amount of time a PCEP
      peer will wait to receive a Keepalive or a PCErr message from the
      PCEP peer after the expiration of which the system releases the
      PCEP resource and goes back to the Idle state.  The KeepWait timer
      has a fixed value of 60 seconds.

   OpenRetry:  the number of times the system has received an Open
      message with unacceptable PCEP session characteristics.

   The following two state variables are defined:

   RemoteOK:  a boolean that is set to 1 if the system has received an
      acceptable Open message.

   LocalOK:  a boolean that is set to 1 if the system has received a
      Keepalive message acknowledging that the Open message sent to the
      peer was valid.

   Idle State:

   The idle state is the initial PCEP state where the PCEP (also
   referred to as "the system") waits for an initialization event that
   can either be manually triggered by the user (configuration) or
   automatically triggered by various events.  In Idle state, PCEP
   resources are allocated (memory, potential process, etc.) but no PCEP
   messages are accepted from any PCEP peer.  The system listens to the
   PCEP-registered TCP port.

   The following set of variables are initialized:

      TCPRetry=0,

      LocalOK=0,

      RemoteOK=0,

      OpenRetry=0.



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   Upon detection of a local initialization event (e.g., user
   configuration to establish a PCEP session with a particular PCEP
   peer, local event triggering the establishment of a PCEP session with
   a PCEP peer such as the automatic detection of a PCEP peer), the
   system:

   o  Initiates a TCP connection with the PCEP peer,

   o  Starts the Connect timer,

   o  Moves to the TCPPending state.

   Upon receiving a TCP connection on the PCEP-registered TCP port, if
   the TCP connection establishment succeeds, the system:

   o  Sends an Open message,

   o  Starts the OpenWait timer,

   o  Moves to the OpenWait state.

   If the connection establishment fails, the system remains in the Idle
   state.  Any other event received in the Idle state is ignored.

   It is expected that an implementation will use an exponentially
   increasing timer between automatically generated Initialization
   events and between retries of TCP connection establishment.

   TCPPending State:

   If the TCP connection establishment succeeds, the system:

   o  Sends an Open message,

   o  Starts the OpenWait timer,

   o  Moves to the OpenWait state.

   If the TCP connection establishment fails (an error is detected
   during the TCP connection establishment) or the Connect timer
   expires:

   o  If ConnectRetry = ConnectMaxRetry, the system moves to the Idle
      State.







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   o  If ConnectRetry < ConnectMaxRetry, the system:

      1.  Initiates of a TCP connection with the PCEP peer,

      2.  Increments the ConnectRetry variable,

      3.  Restarts the Connect timer,

      4.  Stays in the TCPPending state.

   In response to any other event, the system releases the PCEP
   resources for that peer and moves back to the Idle state.

   OpenWait State:

   In the OpenWait state, the system waits for an Open message from its
   PCEP peer.

   If the system receives an Open message from the PCEP peer before the
   expiration of the OpenWait timer, the system first examines all of
   its sessions that are in the OpenWait or KeepWait state.  If another
   session with the same PCEP peer already exists (same IP address),
   then the system performs the following collision-resolution
   procedure:

   o  If the system has initiated the current session and it has a lower
      IP address than the PCEP peer, the system closes the TCP
      connection, releases the PCEP resources for the pending session,
      and moves back to the Idle state.

   o  If the session was initiated by the PCEP peer and the system has a
      higher IP address that the PCEP peer, the system closes the TCP
      connection, releases the PCEP resources for the pending session,
      and moves back to the Idle state.

   o  Otherwise, the system checks the PCEP session attributes
      (Keepalive frequency, DeadTimer, etc.).

   If an error is detected (e.g., malformed Open message, reception of a
   message that is not an Open message, presence of two OPEN objects),
   PCEP generates an error notification, the PCEP peer sends a PCErr
   message with Error-Type=1 and Error-value=1.  The system releases the
   PCEP resources for the PCEP peer, closes the TCP connection, and
   moves to the Idle state.







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   If no errors are detected, OpenRetry=1, and the session
   characteristics are unacceptable, the PCEP peer sends a PCErr with
   Error-Type=1 and Error-value=5, and the system releases the PCEP
   resources for that peer and moves back to the Idle state.

   If no errors are detected, and the session characteristics are
   acceptable to the local system, the system:

   o  Sends a Keepalive message to the PCEP peer,

   o  Starts the Keepalive timer,

   o  Sets the RemoteOK variable to 1.

   If LocalOK=1, the system clears the OpenWait timer and moves to the
   UP state.

   If LocalOK=0, the system clears the OpenWait timer, starts the
   KeepWait timer, and moves to the KeepWait state.

   If no errors are detected, but the session characteristics are
   unacceptable and non-negotiable, the PCEP peer sends a PCErr with
   Error-Type=1 and Error-value=3, and the system releases the PCEP
   resources for that peer and moves back to the Idle state.

   If no errors are detected, and OpenRetry is 0, and the session
   characteristics are unacceptable but negotiable (such as, the
   Keepalive period or the DeadTimer), then the system:

   o  Increments the OpenRetry variable,

   o  Sends a PCErr message with Error-Type=1 and Error-value=4 that
      contains proposed acceptable session characteristics,

   o  If LocalOK=1, the system restarts the OpenWait timer and stays in
      the OpenWait state.

   o  If LocalOK=0, the system clears the OpenWait timer, starts the
      KeepWait timer, and moves to the KeepWait state.

   If no Open message is received before the expiration of the OpenWait
   timer, the PCEP peer sends a PCErr message with Error-Type=1 and
   Error-value=2, the system releases the PCEP resources for the PCEP
   peer, closes the TCP connection, and moves to the Idle state.

   In response to any other event, the system releases the PCEP
   resources for that peer and moves back to the Idle state.




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   KeepWait State:

   In the Keepwait state, the system waits for the receipt of a
   Keepalive from its PCEP peer acknowledging its Open message or a
   PCErr message in response to unacceptable PCEP session
   characteristics proposed in the Open message.

   If an error is detected (e.g., malformed Keepalive message), PCEP
   generates an error notification, the PCEP peer sends a PCErr message
   with Error-Type=1 and Error-value=1.  The system releases the PCEP
   resources for the PCEP peer, closes the TCP connection, and moves to
   the Idle state.

   If a Keepalive message is received before the expiration of the
   KeepWait timer, then the system sets LocalOK=1 and:

   o  If RemoteOK=1, the system clears the KeepWait timer and moves to
      the UP state.

   o  If RemoteOK=0, the system clears the KeepWait timer, starts the
      OpenWait timer, and moves to the OpenWait State.

   If a PCErr message is received before the expiration of the KeepWait
   timer:

   1.  If the proposed values are unacceptable, the PCEP peer sends a
       PCErr message with Error-Type=1 and Error-value=6, and the system
       releases the PCEP resources for that PCEP peer, closes the TCP
       connection, and moves to the Idle state.

   2.  If the proposed values are acceptable, the system adjusts its
       PCEP session characteristics according to the proposed values
       received in the PCErr message, restarts the KeepWait timer, and
       sends a new Open message.  If RemoteOK=1, the system restarts the
       KeepWait timer and stays in the KeepWait state.  If RemoteOK=0,
       the system clears the KeepWait timer, starts the OpenWait timer,
       and moves to the OpenWait state.

   If neither a Keepalive nor a PCErr is received after the expiration
   of the KeepWait timer, the PCEP peer sends a PCErr message with
   Error-Type=1 and Error-value=7, and the system releases the PCEP
   resources for that PCEP peer, closes the TCP connection, and moves to
   the Idle State.

   In response to any other event, the system releases the PCEP
   resources for that peer and moves back to the Idle state.





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   UP State:

   In the UP state, the PCEP peer starts exchanging PCEP messages
   according to the session characteristics.

   If the Keepalive timer expires, the system restarts the Keepalive
   timer and sends a Keepalive message.

   If no PCEP message (Keepalive, PCReq, PCRep, PCNtf) is received from
   the PCEP peer before the expiration of the DeadTimer, the system
   terminates the PCEP session according to the procedure defined in
   Section 6.8, releases the PCEP resources for that PCEP peer, closes
   the TCP connection, and moves to the Idle State.

   If a malformed message is received, the system terminates the PCEP
   session according to the procedure defined in Section 6.8, releases
   the PCEP resources for that PCEP peer, closes the TCP connection and
   moves to the Idle State.

   If the system detects that the PCEP peer tries to set up a second TCP
   connection, it stops the TCP connection establishment and sends a
   PCErr with Error-Type=9.

   If the TCP connection fails, the system releases the PCEP resources
   for that PCEP peer, closes the TCP connection, and moves to the Idle
   State.

Appendix B.  PCEP Variables

   PCEP defines the following configurable variables:

   Keepalive timer:  minimum period of time between the sending of PCEP
      messages (Keepalive, PCReq, PCRep, PCNtf) to a PCEP peer.  A
      suggested value for the Keepalive timer is 30 seconds.

   DeadTimer:  period of timer after the expiration of which a PCEP peer
      declares the session down if no PCEP message has been received.

   SyncTimer:  timer used in the case of synchronized path computation
      request using the SVEC object defined in Section 7.13.3.  Consider
      the case where a PCReq message is received by a PCE that contains
      the SVEC object referring to M synchronized path computation
      requests.  If after the expiration of the SyncTimer all the M path
      computation requests have not been received, a protocol error is
      triggered and the PCE MUST cancel the whole set of path
      computation requests.  The aim of the SyncTimer is to avoid the
      storage of unused synchronized requests should one of them get
      lost for some reason (e.g., a misbehaving PCC).  Thus, the value



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      of the SyncTimer must be large enough to avoid the expiration of
      the timer under normal circumstances.  A RECOMMENDED value for the
      SyncTimer is 60 seconds.

   MAX-UNKNOWN-REQUESTS:  A RECOMMENDED value is 5.

   MAX-UNKNOWN-MESSAGES:  A RECOMMENDED value is 5.

Appendix C.  Contributors

   The content of this document was contributed by those listed below
   and the editors listed at the end of the document.

   Arthi Ayyangar
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089
   USA

   EMail: arthi@juniper.net


   Adrian Farrel
   Old Dog Consulting
   Phone: +44 (0) 1978 860944

   EMail: adrian@olddog.co.uk


   Eiji Oki
   NTT
   Midori 3-9-11
   Musashino, Tokyo,   180-8585
   JAPAN

   EMail: oki.eiji@lab.ntt.co.jp


   Alia Atlas
   British Telecom

   EMail: akatlas@alum.mit.edu









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RFC 5440                          PCEP                        March 2009


   Andrew Dolganow
   Alcatel
   600 March Road
   Ottawa, ON  K2K 2E6
   CANADA

   EMail: andrew.dolganow@alcatel.com


   Yuichi Ikejiri
   NTT Communications Corporation
   1-1-6 Uchisaiwai-cho, Chiyoda-ku
   Tokyo,   100-819
   JAPAN

   EMail: y.ikejiri@ntt.com


   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower Iidabashi, Chiyoda-ku,
   Tokyo,   102-8460
   JAPAN

   EMail: ke-kumaki@kddi.com

Authors' Addresses

   JP Vasseur (editor)
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   EMail: jpv@cisco.com


   JL Le Roux (editor)
   France Telecom
   2, Avenue Pierre-Marzin
   Lannion  22307
   FRANCE

   EMail: jeanlouis.leroux@orange-ftgroup.com







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