Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                        JL. Le Roux, Ed.
Expires: May 19, August 14, 2008                                  France Telecom
                                                       November 16, 2007
                                                       February 11, 2008

      Path Computation Element (PCE) communication Communication Protocol (PCEP)
                       draft-ietf-pce-pcep-09.txt
                       draft-ietf-pce-pcep-10.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007). (2008).

Abstract

   This document specifies the Path Computation Element communication Communication
   Protocol (PCEP) for communications between a Path Computation Client
   (PCC) and a Path Computation Element (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 (GMPLS) Traffic Engineering.  The  PCEP protocol
   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.

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].

Table of Contents

   1.  Terminology  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Architectural Protocol Overview (Model)  . . . . . . . . . . .  5
     4.1.  Problem  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Architectural Protocol Overview  . . . . . . . . . . . . .  6
       4.2.1.  Initialization Phase . . . . . . . . . . . . . . . . .  7
       4.2.2.  Path computation request sent by Computation Request Sent By a PCC to a PCE  . . .  8
       4.2.3.  Path computation reply sent by the Computation Reply Sent By The PCE to a PCC  . . .  9
       4.2.4.  Notification . . . . . . . . . . . . . . . . . . . . . 11
       4.2.5.  Error  . . . . . . . . . . . . . . . . . . . . . . . . 12 13
       4.2.6.  Termination of the PCEP Session  . . . . . . . . . . . 13
       4.2.7.  Intermitent versus Permanent PCEP Session  . . . . . . 14
   5.  Transport protocol Protocol . . . . . . . . . . . . . . . . . . . . . . 13 14
   6.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Common header  . . . . . . . . . . . . . . . . . . . . . . 14 15
     6.2.  Open message Message . . . . . . . . . . . . . . . . . . . . . . . 15
     6.3.  Keepalive message Message  . . . . . . . . . . . . . . . . . . . . 16
     6.4.  Path Computation Request (PCReq) message Message . . . . . . . . . 17
     6.5.  Path Computation Reply (PCRep) message Message . . . . . . . . . . 18
     6.6.  Notification (PCNtf) message Message . . . . . . . . . . . . . . . 20
     6.7.  Error (PCErr) Message  . . . . . . . . . . . . . . . . . . 21
     6.8.  Close message Message  . . . . . . . . . . . . . . . . . . . . . . 21 22
   7.  Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 22
     7.1.  PCE TLV Format . . . . . . . . . . . . . . . . . . . . . . 22
     7.2.  Common object header Object Header . . . . . . . . . . . . . . . . . . . 22 23
     7.3.  OPEN object Object  . . . . . . . . . . . . . . . . . . . . . . . 24
     7.4.  RP Object  . . . . . . . . . . . . . . . . . . . . . . . . 25
       7.4.1.  Object definition Definition  . . . . . . . . . . . . . . . . . . 25 26
       7.4.2.  Handling of the RP object Object  . . . . . . . . . . . . . . 28
     7.5.  NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 28
     7.6.  END-POINT Object . . . . . . . . . . . . . . . . . . . . . 31
     7.7.  BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 32
     7.8.  METRIC Object  . . . . . . . . . . . . . . . . . . . . . . 33
     7.9.  Explicit Route Object  . . . . . . . . . . . . . . . . . . 36
     7.10. Reported Route Record Object  . . . . . . . . . . . . . . . . . . . 36 37
     7.11. LSPA Object  . . . . . . . . . . . . . . . . . . . . . . . 37
     7.12. Include Route Object Object  . . . . . . . . . . . . . . . 39
     7.13. SVEC Object  . . . . . . . . . . . . . . . . . . . . . . . 39
       7.13.1. Notion of Dependent and Synchronized path
               computation requests Path
               Computation Requests . . . . . . . . . . . . . . . . . 39
       7.13.2. SVEC Object  . . . . . . . . . . . . . . . . . . . . . 41
       7.13.3. Handling of the SVEC Object  . . . . . . . . . . . . . 42
     7.14. NOTIFICATION Object  . . . . . . . . . . . . . . . . . . . 43
     7.15. PCEP-ERROR Object  . . . . . . . . . . . . . . . . . . . . 46
     7.16. LOAD-BALANCING Object  . . . . . . . . . . . . . . . . . . 50
     7.17. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 51
   8.  Manageability Considerations . . . . . . . . . . . . . . . . . 52
     8.1.  Control of Function and Policy . . . . . . . . . . . . . . 52
     8.2.  Information and Data Models  . . . . . . . . . . . . . . . 54
     8.3.  Liveness Detection and Monitoring  . . . . . . . . . . . . 54
     8.4.  Verifying Correct Operation  . . . . . . . . . . . . . . . 54
     8.5.  Requirements on Other Protocols and Functional
           Componentssection
           Components . . . . . . . . . . . . . . . . . . . . . . . . 55
     8.6.  Impact on Network Operation  . . . . . . . . . . . . . . . 55
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 55
     9.1.  TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 55
     9.2.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . 55
     9.3.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . . . 55 56
     9.4.  Notification  RP Object  . . . . . . . . . . . . . . . . . . . . . . . . 57
     9.5.  PCEP Error  Notification Object  . . . . . . . . . . . . . . . . . . . . 57 58
     9.6.  CLOSE  PCEP-ERROR Object  . . . . . . . . . . . . . . . . . . . . . . . 58
     9.7.  PCEP TLV format  CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 59
     9.8.  NO-PATH-VECTOR TLV  NO-PATH Object . . . . . . . . . . . . . . . . . . . . 59
   10. . . 60
     9.9.  METRIC Object  . . . . . . . . . . . . . . . . . . . . . . 60
     9.10. PCEP Finite State Machine (FSM) TLV Type Indicators . . . . . . . . . . . . . . . 59
   11. . . 61
     9.11. NO-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . . . 61
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 66
     11.1. 61
     10.1. PCEP Authentication and Integrity  . . . . . . . . . . . . 66
     11.2. 62
     10.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 67
     11.3. 62
     10.3. Protection against Against Denial of Service attacks Attacks . . . . . . . 67
     11.4. Request input shaping/policing 62
       10.3.1. Protection Against TCP DoS Attacks . . . . . . . . . . 62
       10.3.2. Request Input Shaping/Policing . . . . 67
   12. . . . . . . . . 63
   11. Authors' addresses Addresses . . . . . . . . . . . . . . . . . . . . . . 68
   13. 63
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 69
   14. 65
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 69
     14.1. 65
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 69
     14.2. 65
     13.2. Informative References . . . . . . . . . . . . . . . . . . 69 65
   Appendix A.  PCEP Finite State Machine (FSM) . . . . . . . . . . . 67
   Appendix B.  PCEP Variables  . . . . . . . . . . . . . . . . . . . 71 74
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 72 74
   Intellectual Property and Copyright Statements . . . . . . . . . . 73 76

1.  Terminology

   Terminology used in this document

   AS: Autonomous System.

   Explicit path: full explicit path from start to destination made of  Introduction

   [RFC4655] describes the motivations and architecture for a Path
   Compuation Element (PCE) based model for the computation of
   Multiprotocol Label Switching (MPLS) and Generalized (GMPLS) Traffic
   Engineering Label Swtich 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 the requirement
   for using the same protocol 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],
   [I-D.ietf-pce-interas-pcecp-reqs] and [I-D.ietf-pce-inter-layer-req].

   This document specifies the Path Computation Element Communication
   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.

2.  Terminology

   Terminology 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.

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

   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: mix of strict and loose hops comprising of 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.

2.  Introduction

3.  Assumptions

   [RFC4655] describes the motivations and architecture for a PCE-based
   model for the computation of MPLS and GMPLS TE LSPs.  The model
   allows for the separation of PCE from 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 protocol including the requirement for using
   the same protocol 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],
   [I-D.ietf-pce-interas-pcecp-reqs] and [I-D.ietf-pce-inter-layer-req].

   This document specifies the Path Computation Element communication
   Protocol (PCEP) for communications between a Path Computation Client
   (PCC) and a Path Computation Element (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.

3.  Assumptions

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

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

   Similarly, no assumption is made on about the discovery method used by a
   PCC to discover a set of PCEs (e.g. (e.g., via static configuration or
   dynamic discovery) and on the algorithm used to select a PCE.  For
   the sake of reference
   reference, [RFC4674] defines a list of requirements for dynamic PCE
   discovery and IGP-based solutions for such PCE discovery are
   specified in [I-D.ietf-pce-disco-proto-ospf] [RFC5088] and
   [I-D.ietf-pce-disco-proto-isis]. [RFC5089].

4.  Architectural Protocol Overview (Model)

   The aim of this section is to describe the PCEP model in the spirit
   of [RFC4101].  An architecture 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 path for MPLS
   and GMPLS TE LSP 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 LSP(s) LSPs to a PCE and the PCE may
   reply with a set of computed path(s) paths if one or more path(s) can be
   found that
   satisfy satisfies the set of constraints can be found. constraints.

4.2.  Architectural Protocol Overview

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

   Several PCEP messages are defined:

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

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

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

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

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

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

   The set of available PCE(s) may either be either statically configured on a
   PCC or dynamically discovered.  The mechanisms used to discover one
   or more PCE(s) 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.

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 a 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 messages, and once
   the PCEP session has been successfully established, Keepalive
   messages may be exchanged between PCEP peers to ensure the liveness
   of the PCEP session.

   A single

   Only one PCEP session can exist between a pair a PCEP peers. peers at any
   one time.

   Details about the Open message and the Keepalive messages message can be found
   inSection 6.2 and Section 6.3 respectively.

               +-+-+                 +-+-+
               |PCC|                 |PCE|
               +-+-+                 +-+-+
                 |                     |
              |----
                 | Open message --->| msg            |
                 |--------             |
              |<---
                 |        \   Open message ----| msg |
                 |         \  ---------|
                 |          \/         |
                 |          /\         |
              |<--- Keepalive -------|
                 |         /  -------->|
                 |        /            |
                 |<------     Keepalive|
                 |             --------|
                 |Keeplaive   /        |
                 |--------   /         |
                 |        \/           |
                 |        /\           |
                 |<------   ---------->|
                 |                     |
                 :                     :
                 :                     :
                 |                     |
                 |---- 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.  Path computation request sent by 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 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 path(s), paths, the PCC first selects one or more PCE(s). PCE.  Note that the
   PCE selection decision process may have taken place prior to the PCEP
   session establishment.

   Once the PCC has selected a PCE, it sends the PCE 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/Hold 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 Figure 2.

   Details about the PCReq message can be found in Section 6.4

4.2.3.  Path computation reply sent by the Computation Reply Sent By The PCE to a PCC
                 +-+-+                  +-+-+
                 |PCC|                  |PCE|
                 +-+-+                  +-+-+
                   |                      |
                   |---- PCReq message--->|
                   |                      |1) Path computation
                   |                      |request received
                   |                      |
                   |                      |2)Path successfully
                   |                      |computed
                   |                      |
                   |                      |3) Computed path(s) sent
                   |                      |sent
                   |                      |to the PCC
                   |<--- PCRep message ---|
                   |    (Positive reply)  |

    Figure 3a: Path computation request with successful path computation Computation Request With Successful
               Path Computation

                 +-+-+                  +-+-+
                 |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 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 either be:

   o  Positive (Figure 3-a): the PCE manages to compute a path that
      satisfies the set of required constraints, in which case the PCE
      returns the set of computed path(s) 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. (e.g., computation
      of a set of link-diverse paths).

   o  Negative (Figure 3-b): 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.

4.2.4.  Notification

   There are several circumstances whereby in which a PCE may want to notify a
   PCC of a specific event.  For example, suppose that the PCE suddenly
   gets overloaded thus 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,
   the PCC may decide to redirect it(s) its path computation
   request(s) 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 request(s). 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   |                      |triggered                      |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 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   |                      |triggered                      |request queued
                      |                      |
                      |                      |
                      |                      |5) PCE gets overloaded
                      |                      |
                      |                      |
                      |                      |6) Path computation
                      |                      |request X cancelled
                      |                      |
                      |<--- PCNtf message----|

   Figure 5: Example of PCE notification (cancellation notification) sent to Notification (Cancellation
   Notification) Sent To a PCC

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

4.2.5.  Error

   The PCEP Error messages are message (also referred to as a PCErr message) is sent
   in several situations: when a protocol error condition is met
   (e.g. unknown object, non supported 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, ...).

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

   Figure 6: Example of Error message (policy violation) sent by 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.

4.2.6.  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.

5.  Transport protocol

4.2.7.  Intermitent versus Permanent PCEP operates over TCP using a well-known TCP port (to be assigned by
   IANA).  This allows the requirements of reliable messaging and flow
   control to be met without further protocol work. Session

   An implementation may decide to keep the TCP connection PCEP session alive (and thus
   the corresponding TCP connection) for an unlimited time (this may for
   instance be appropriate when path computation requests are sent on a
   frequent basis so as to avoid to open 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 the TCP connection a PCEP session for each
   PCEP request (for instance when sending a path computation request is
   a rare event).

6.

5.  Transport Protocol

   PCEP operates over TCP using a well-known TCP port (to be assigned by
   IANA).  This allows the requirements of reliable messaging and flow
   control to be met without further protocol work.

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 as 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) that can be 7.2).  When this flag is set by a PCEP peer to
   enforce in an
   object in a PCReq, the PCE to MUST take into account the related 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 optional, but a
   PCC may set a flag to ensure that
   such the constraint is taken into
   account.  Similarly to the previous  In this case, if such 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 [RFC4234]) to specify such rules.  Square brackets refer
   to optional sub-
   sequences. sub-sequences.  An implementation MUST form the PCEP
   messages using the object ordering specified in this document.

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-Lenght       Message-Length          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 7: PCEP message common header 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 and MUST be set to zero on transmission.

   Message-Type (8 bits):

   The following message types are currently defined (to be confirmed by
   IANA).
   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 expressed
   in bytes including the common header.

6.2.  Open message Message

   The Open message is a PCEP message sent by a PCC to a PCE and 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 (To
   be confirmed by IANA).

   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 Section 10. Appendix A.  Any message received
   prior to an Open message MUST trigger a protocol error condition and
   the PCEP session MUST be terminated.  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.  TOTO
   Open message
   <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 Section 10 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 Section 10 Appendix A for details).

   The KeepWait timer has 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 characteristic(s) is not
   acceptable by the receiving peer, it MUST send an Error message.  The
   Error message SHOULD also contain the related Open object: 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 message can be found in Section 7.15.

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

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

6.3.  Keepalive message 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 (To be confirmed by IANA).  The
   Keepalive message does not contain any object.

   PCEP has its own keepalive mechanism used to ensure of the liveness
   of the PCEP session.  This requires the determination of the
   frequency at which each PCEP peer sends keepalive 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 (Keepalive or any other PCEP message: thus,
   any PCEP message acts as a keepalive Keepalive message).  Similarly, there is
   no constraints mandating the use of identical DeadTimers by both PCEP
   peers.  The minimum KeepAlive timer value is 1 second.

   Keepalive messages are used to acknowledge an Open message if the
   receiving PCEP peer agrees on the session characteristics and to
   ensure the liveness of the PCEP session.  Keepalive messages are sent at the frequency specified in the OPEN
   object carried within an Open
   message. message according to the rules
   speciifed in Section 7.3.  Because any PCEP message may serve as Keepalive
   Keepalive, an implementation may either decide to send Keepalive
   messages at fixed intervals regardless on whether other PCEP messages
   might have been sent since the last sent Keepalive message 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) has been was
   sent.

   Note that sending Keepalive messages to maintain keep the session alive is
   optional and PCEP peers may decide to not send Keepalive messages
   once the PCEP session is established. 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.

   Keepalive message
   <Keepalive Message>::= <Common Header>

6.4.  Path Computation Request (PCReq) message Message

   A Path Computation Request message (also referred to as a PCReq
   message) is a PCEP message sent by a PCC to a PCE so as 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 (To be confirmed by IANA).

   There are two mandatory objects that MUST be included within a PCReq
   message: the RP and the END-POINTS objects (see section 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>]
                   [<BANDWIDTH>]
                   [<metric-list>]
                   [<RRO>]
                   [<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 details detail in Section 7.7.

6.5.  Path Computation Reply (PCRep) message 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 is set to 4 (To be confirmed by
   IANA).

   The bundling of multiple replies to a set of path computation
   requests within a single 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).

   A PCRep message may contain a set of computed path(s) 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 bundling of multiple replies to a set of path computation
   requests within a single PCRep message is supported by PCEP.  If 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 path(s) 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 (the PCE finds a set
   of path(s) paths that satisfy the set of constraint(s)), constraints), the set of computed path(s)
   paths specified by means of ERO object(s) objects is inserted in the PCRep
   message.  The ERO object is defined in Section 7.9.  Such a  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 of X 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 comprise contain other information (e.g (e.g, reasons for
   the path computation failure).

   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 Message

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

   The PCNtf message MUST carry at least one NOTIFICATION object and may 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 an RP object objects (see
   Section 7.4 when the notification refers to a particular path
   computation request. requests.

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

   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>

   <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.  The Message-Type 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 is set to 6 (To be confirmed by IANA).

   The PCErr message is either sent by a PCC or a PCE in response to a request
   or in an unsolicited manner.  In  If the former case, 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 request(s) requests that
   triggered the protocol error condition.  In the later case (unsolicited), no
   RP object is inserted in the PCErr message.  No  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 PCEP-
   ERROR object is defined in section Section 7.15.

   The format of a PCErr message is as follows:
   <PCErr Message> ::= <Common Header>
                       <error-list>
                       ( <error-object-list> [<Open>]

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

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

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

6.8.  Close message 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 (To be confirmed by IANA).

   Close message
   <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 vlaid Close message, the receiving PCEP peer
   MUST cancel all pending requests and requests, it MUST close the TCP connection. connection
   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.

7.1.  PCE TLV Format

   A PCEP object may include a set of one or more optional TLV(s). TLVs.

   All PCEP TLVs have the following format:

   Type: 2 bytes
   Lenght:
   Length: 2 bytes
   Value
   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 three bytes byte value would have a length of three,
   but the total size of the TLV would be eight bytes).

   Unrecognized TLVs MUST be ignored.

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

7.2.  Common object header Object Header

   A PCEP object carried within a PCEP message consists of one or more
   32-bit words with a common header which 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.

   Res flags (2 bits).  Reserved field.  This field MUST be set to zero
   on transmission and MUST be ignored on receipt.  Unassigned bits are
   considered as reserved.  They MUST be set to zero on transmission and
   MUST be ignored on receipt.

   o  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 if not
      supported. it.

   o  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 had has been set in the corresponding
      PCRep
      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 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, 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.

   OPEN Object-Class is to be assigned by IANA (recommended value=1)

   OPEN Object-Type is to be assigned by IANA (recommended value=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  DeadTimer    |      SID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         Optional TLV(s)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    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 and MUST be set to zero on transmission.

   Keepalive (8 bits): maximum period of time (in seconds) between two
   consecutive PCEP messages sent by the
   sending sender of PCEP messages. this message.  The
   minimum value for the Keepalive is 1 second.  When set to 0, once the
   session is established, no further Keepalive messages need to be 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 down if no PCEP message has been received.  The
   DeadTimer MUST 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

   Example:

   A sends an Open message to B with Keepalive=10 seconds and
   Deadtimer=30 seconds.  This means that A sends Keepalive messages (or
   ay other PCEP message) to B every 30 10 seconds and B can declare the
   PCEP session with A down if no PCEP message has been received from A. A
   within any 30 second period.

   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 and is mainly used for logging and
   troubleshooting purposes.  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 PCReq messages
   and MUST be cleared in PCNtf and PCErr messages.  If the RP objet is
   received with the P flag set incorrectely according to the rules
   states 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 Definition

   RP Object-Class is to be assigned by IANA (recommended value=2)

   RP Object-Type is to be assigned by IANA (recommended value=1)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |                          Flags                    |O|B|R| Pri |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Request-ID-number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLV(s)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 10: RP object body format

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

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

   Flags (24 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 of a local matter and 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
      to
      that the PCC set the priority field to 0 by the PCC 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 PCC(s). PCCs.
      The ability of a PCE to support requests request prioritization may MAY be
      dynamically discovered by the PCC(s) 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
      the handling of request priorities: in other words, the path
      computation request has been honoured 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 in which case, in addition to the TE LSP
      attributes, the current path of the existing TE LSP to be
      reoptimized MUST be provided in the PCReq (except for 0-bandwidth
      TE LSP) LSPs) message by means of an RRO object defined in Section 7.10. 7.10
      and (again except in the case of 0-bandwidth TE LSPs) the existing
      bandwidth of the LSP to be reoptimized MUST be supplied in an
      additional BANDWIDTH object as described in Section 7.7.

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

   o  O (strict/lOose (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 (the O bit is cleared), the returned path is made of
      strict hops.

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

   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
   MUST be incremented each time a new request is sent to the PCE.  The
   value 0x0000000 is considered as invalid.  If no path computation
   reply is received from the PCE, and the PCC wishes to resend its
   request, the same Request-ID-number MUST be used.  Conversely,
   different Request-ID-number MUST be used for different requests sent
   to a PCE.  The same Request-ID-number may 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 Object

   If a PCReq message is received without containing 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 path(s) 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".

   R bit: 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 0-bandwidth non-0-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 implies for requires that the PCE to be either be
   stateful (keep track of the previously computed path with the
   associated list of strict hops) hops), or to have the ability to retrieve the
   complete required path segment.  Alternatively the PCC MUST be
   able to inform
   the PCE of the working path with the associated list of strict hops
   in PCReq.  The absence of an RRO in the PCReq message for a non
   0-bandwidth non-0-
   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".

   If the PCC receives a PCRep message that contains a RP object
   referring to an unknown Request-ID-Number, the PCC MUST send a PCErr
   message with Error-Type="Unknown request reference".

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.  The NO-PATH object is used to report the
   impossibility to find a path that satisfies the set of constraints.

   There are potentially several categories of issues 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
   and the 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 object(s) 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. found (in which case the value
   differs from the value in the original request).

   NO-PATH Object-Class is to be assigned by IANA (recommended value=3)

   NO-PATH Object-Type is to be assigned by IANA (recommended value=1)

   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 TLV(s)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 11: NO-PATH object format 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:

   0x00: No path satisfying the set of constraints could be found

   0x01: PCE chain broken

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

   Flags (16 bits).

   The following flag is currently defined:

   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
   reason is
   failing constraints are specified.  When the  The C bit flag has no meaning and is set,
   ignored unless the NI field value MUST
   be is set to 0x00.

   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 MBits/s.  Suppose that PCE cannot
   find a path for X MBits/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
   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
   path(s) is/are
   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 fix fixed
length value field of 32-bits 32-bit flags field.

TYPE: To be assigned by IANA (suggested value=1)
LENGTH: 1
VALUE: 32-bits 32-bit flags field

   IANA is requested to manage the space of flags carried in the NO-
   PATH-VECTOR TLV (see Section 9).

   The following flags are currently defined:

   o  0x01:  Bit number: 1 - PCE currently unavailable

   o  0x02:  Bit number: 2 - Unknown destination

   o  0x03:  Bit number: 3 - Unknown source

7.6.  END-POINT 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-POINT
   object MUST be set.  If the END-POINT objet 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 or may not correspond to the source and destination
   IP address of the TE LSP but rather to a path segment.  Two END-
   POINTS objects (for IPv4 and IPv6) are defined.

   END-POINTS Object-Class is to be assigned by IANA (recommended
   value=4)

   END-POINTS Object-Type is to be assigned by IANA (recommended value=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 Object Body Format for IPv4

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 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.

   If the requested bandwidth is equal to 0, the BANDWIDTH object is
   optional.  Conversely, if the requested bandwidth is non 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 to be assigned by IANA (recommended
   value=5)

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

   o  Requested bandwidth: BANDWIDTH Object-Type is to be assigned by
      IANA (recommended value=1)

   o  Bandwidth of an existing TE LSP for which a reoptimization is
      requested.  BANDWIDTH Object-Type is to be assigned by IANA
      (recommended value=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 Object Body Format

   Bandwidth: 32 bits.  The requested bandwidth is encoded in 32 bits in
   IEEE floating point format, 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 a one of more METRIC object: 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.

   It must be understood that such path metric is metrics are only meaningful if
   used consistently: for instance, if the delay of a computed path computation
   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 the PCE may choose the metric to no constraints need be used. applied to
   any of the metrics.

   METRIC Object-Class is to be assigned by IANA (recommended value=6)

   METRIC Object-Type is to be assigned by IANA (recommended value=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 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:

   o  T=1: IGP metric

   o  T=2: TE metric
   o  T=3: Hop Counts

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

   o  B (Bound - 1 bit): When set in a PCReq message, the metric-value
      indicates a bound (a maximum) for the path cost 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.

   o  C (Cost (Computed Metric - 1 bit): When set in a PCReq message, this
      indicates that the PCE MUST provide the computed path cost 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.

   Multiple METRIC Objects MAY be inserted in a PCRep or the PCReq
   message.  There MUST be at most one instance of the METRIC object for
   each metric type with the same B flag value.  If 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.

   In a PCReq message the

   The presence of multiple two METRIC objects can be
   used to specify a multi-parameters (e.g. a metric may be a constraint
   or of the same type with a parameter to minimize/maximize) objective function or multiple
   bounds for different constraints where at most one METRIC object must
   be used to indicate
   value of the metric to optimize (B-flag B-Flag in a PCEReq message is cleared): the
   other METRIC object MUST be used to reflect bound constraints (B-Flag allowed.  Furthermore, it
   is set).  If also allowed to insert in a PCReq message is received that contains two METRIC objects with
   the B flag set, same type that have both their B-Flag cleared: in this case, an
   objective function must be used by the receiving peer MUST send PCE to solve a PCErr
   message with Error-type=10 and Error-value=2. multi-parameter
   constraint problem.

   A METRIC object used to indicate the metric to optimize during the
   path computation MUST have the B-Flag cleared and the T-Flag C-Flag set to
   the appropriate value.  When the path computation relates to the
   reoptimization of an exiting TE LSP (in which case R-Flag of the RP
   object is set) an implementation MAY decide to set the metric-value
   field to the cost 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, the
   T-Flag
   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 cost in
   particular metric
   if the C bit of the METRIC object was set in the corresponding path
   computation request (the B-flag MUST be cleared);
   optionally 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 cost (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.

   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 object 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 preventing to provide that prevents the path cost is in place, return of the computed
   metric, the PCE inserts one METRIC object with B=0, T=1, metric-value= 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. LSP through the network.
   The ERO is carried within a PCRep message to provide the computed TE
   LSP should have the path computation have been 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.
   sub-objects.  Any RSVP 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 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 to be assigned by IANA (recommended value=7)
   ERO Object-Type is to be assigned by IANA (recommended value=1)

7.10.  Reported Route Record Object

   The RRO is used to record the route followed by a TE LSP.  The PCEP
   RRO is exclusively carried within a PCReq message so as to specify 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-
   objects.  Any RSVP 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 RSVP-TE RRO sub-object types.

   RRO Object-Class is to be assigned by IANA (recommended value=8)

   RRO Object-Type is to be assigned by IANA (recommended value=1)

7.11.  LSPA Object

   The LSPA object is optional and specifies various TE LSP attributes
   to be taken into account by the PCE during path computation.  The
   LSPA (LSP Attributes) object can either be carried within a PCReq
   message 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 constraint(s) constraints that could not be
   satisfied).  Most of the fields of the LSPA object are identical to
   the fields of the SESSION-ATTRIBUTE (C-Type = 7) object 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.

   LSPA Object-Class is to be assigned by IANA (recommended value=9)

   LSPA Object-Types is to be assigned by IANA (recommended value=1)
   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 TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 16: LSPA object body format Object Body Format
   Setup Prio (Setup Priority - 8 bits).  The priority of the session 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
   session 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)

   The flag L corresponds to the "Local protection desired" bit
   ([RFC3209]) of the SESSION-ATTRIBUTE Object.

   L Flag (Local protection desired).  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 [RFC4420].

7.12.  Include Route Object 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 fail the cause de PCE to fail to find a
   path.

   IRO Object-Class is to be assigned by IANA (recommended value=10)

   IRO Object-Type is to be assigned by IANA (recommended value=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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Subobjects)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 17: IRO body format
   Subobjects Body Format

   Subobjects: The IRO is made of sub-object(s) subobjects identical to the ones
   defined in [RFC3209], [RFC3473] and [RFC3477] for use where the IRO subobject
   type is identical to the subobject type defined in EROs. the related
   documents.

   The following subobject types are supported.

   Type   Subobject
        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 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).

   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. non-synchronized.  Note that the
   PCC may chose to distribute the set of N requests across K PCEs for
   load balancing purpose. 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 MBits/s and N2 MBits/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
   set up failure probability compared to the serialized computation of
   independent requests.

   Dependent path computation 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
   probability of not being able to satisfy all requests (sometimes also
   referred to as the well-know "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 (SVEC object defined below required),

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

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 to be assigned by IANA (recommended value=11)

   SVEC Object-Type is to be assigned by IANA (recommended value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 1.

   The format of the SVEC
   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 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.

   o  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.

   o  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.

   o  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 message. messages.  In the later case, it is
   RECOMMENDED for the PCE to implement a local timer 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 (this timer is
   called the SyncTimer).  When a PCE receives a path computation
   request that cannot be satisfied (for example 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 message may also contain non-synchronized path
   computation requests.  For example, the PCReq message may comprise N
   synchronized path computation requests related to RP 1, ... , RP N
   listed in the SVEC object along with any other path computation
   requests.
   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 to be assigned by IANA (recommended
   value=12)

   NOTIFICATION Object-Type is to be assigned by IANA (recommended
   value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 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 TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 19: NOTIFICATION body object format 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.

   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 should be 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 request(s). 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 request(s). 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 obsolete,
         or any other event(s) 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 request(s). 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 request(s).  Such event could be triggered because of
         PCE overloaded state or because of missing path computation
         requests that are part the set of synchronized path computation requests.  A NOTIFICATION object with Notification-type=1, 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-
         value=1 indicates to the PCC(s) that the PCE is currently in an
         overloaded state.  If no RP objects are comprised 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 object(s) 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 object(s).
         If such notification is received by a PCE from a PCC, the PCE
         MUST silently ignore the notification and no errors should be
         generated.

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 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 fix length value field of 32-bits flags field.

TYPE: To be assigned by IANA (suggested value=2)
LENGTH: 4
VALUE: 32-bits 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 congested state
         and is available to process new path computation requests.  An
         implementation MUST 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
         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-thresholds mechanism
         triggering 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 path computation requests oscillation.

      *  Alternatively, PCE may decide to signal its (non) overloaded
         state using a IGP-based notification mechanism as defined in
         [I-D.ietf-pce-disco-proto-isis]and
         [I-D.ietf-pce-disco-proto-ospf].  A PCE may also decide to
         signal its overloaded state using PCEP and its no longer
         overloaded state using an IGP-based notification and vice-
         versa.

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 to be assigned by IANA (recommended
   value=13)

   PCEP-ERROR Object-Type is to be assigned by IANA (recommended
   value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 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 TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 20: PCEP-ERROR object body format Object Body Format

   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 should be 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 TLV so as to
   provide further information about the encountered error.

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

   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 a malformed 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 a malformed 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.
               Error-value=2: reception of a PCReq message with two METRIC objects
               with B-flag set.

   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 Section 10 Appendix A for details).

   If one or more PCEP session characteristic(s) 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.

   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 TLV(s) 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 TLV(s) TLVs (defined below) that identifies the
   missing request(s).

   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 fix length value field of 4 bytes.

   TYPE: To be assigned by IANA (suggested value=3)
   LENGTH: 4
   VALUE: 4 bytes that indicates 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.

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 bandwidth requirement could be satisfied
   by a set of TE LSPs such that the sum of their bandwidths is equal to
   X. Thus 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 MBits/s, with
   potentially some constraints on the number of TE LSPs and the minimum
   bandwidth of each of these TE LSPs.  Such 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 to be assigned by IANA (recommended
   value=14)

   LOAD-BALANCING Object-Type is to be assigned by IANA (recommended
   value=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 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 Flag field MUST be
   set to zero on transmission and MUST be ignored on receipt). 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, expressed in bytes per second.

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

   If a PCC requests the computation of a set of TE LSP(s) LSPs so that the sum
   of their bandwidth is X, the maximum number of TE LSP 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 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 object(s) MUST
   be silently ignored.

   CLOSE Object-Class is to be assigned by IANA (recommended value=15)

   CLOSE Object-Type is to be assigned by IANA (recommended value=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 TLV(s)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 22: CLOSE Object format
   Reason (4 bits): specifies the reason for closing the PCEP session.
   The setting of this field is optional.  The following values are
   currently defined.

   Reasons
    Value        Meaning
      1          No explanation provided
      2          DeadTimer expired
      3          Reception of a malformed PCEP message Format

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

   Flags (4 (8 bits): No Flags are currently defined.  The Flag field MUST
   be set to zero on transmission and MUST be ignored on receipt.

   Optional TLVs may be included within

   Reason (8 bits): specifies the CLOSE object body.  The
   specification of such reason for closing the PCEP session.
   The setting of this field is optional.  IANA is requested to manage
   the codespace of the Reason field.  The following values are
   currently defined (To be confirmed by IANA).

   Reasons
    Value        Meaning
      1          No explanation provided
      2          DeadTimer expired
      3          Reception of a malformed PCEP message

   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
   [I-D.ietf-pce-manageability-requirements].

8.1.  Control of Function and Policy

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

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

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

   o  Negotiation enabled or disabled,

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

   o  The SyncTimer,

   o  The maximum number of sessions that can be setup,

   o  Request timer: amount of time a PCC waits for a reply before
      resending its path computation requests (potentially to an
      alternate PCE).

   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 a specific group of sessions 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. (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 [I-D.kkoushik-pce-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, allowing checking mechanism to check the liveliness of a PCEP
   peer and a notification procedure allowing a PCE to advertise its
   congestion 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
   [I-D.vasseur-pce-monitoring].
   [I-D.ietf-pce-monitoring].

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 a
      returned path fit in with the requested TE parameters.

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

8.5.  Requirements on Other Protocols and Functional Componentssection 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 ([I-D.ietf-pce-disco-proto-isis],
   [I-D.ietf-pce-disco-proto-ospf]) ([RFC5088], [RFC5089]) may have an
   impact on PCEP.  To avoid that a high frequency of PCE Discovery/Disappearance Discovery/
   Disappearance trigger high frequency of PCEP session setup/deletion,
   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 limiting a limit to be placed on the number of
   session that can be setup set up on a PCEP speaker, and MAY allow limiting 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.

9.  IANA Considerations

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

   IANA is requested to establish 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
   [RFC2434]).  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 will use a well-known TCP port to be assigned by IANA.

9.2.  PCEP Messages

   IANA is requested to create 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 is requested to create 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

         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

        14             LOAD-BALANCING                      This document
                       Object-Type
                           1

        15             CLOSE                               This document
                       Object-Type
                           1

9.4.  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

   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

     1-3       Priority              This document
      4        Reoptimization        This document
      5        Bi-directional        This document
      6        Strict/Loose          This document

9.5.  Notification Object

   A NOTIFICATION object

   IANA is characterized by requested to create a Notification-type that
   specifies registry for the class of notification Notification-type and a
   Notification-value that
   provides additional information related to the nature of the
   notification.  Both Notification Object and manage the Notification-type and Notification-value are
   managed by IANA (see IANA section). code
   space.

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

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

9.5.  PCEP Error Object

9.6.  PCEP-ERROR objects are used Object

   IANA is requested to report create a PCEP error and are
   characterized by an Error-Type which specifies registry for the type of error Error-type and
   an Error-value that provides additional information about the error
   type.  Both Error-
   value of the Error-Type PCEP Error Object and manage the Error-Value are managed by IANA. code space.

   For each PCEP error, an Error-type and an Error-value are defined.
Error-Type  Meaning                                                    Reference
   1        PCEP session establishment failure                         This document
            Error-value=1: reception of a malformed 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 a malformed an invalid object                         This document
               Error-value=1: reception of an object with P flag not set although   This document
               the P-flag must be set according to this specification.
               Error-value=2: reception of a PCReq message with two METRIC objects
               with B-flag set.

9.6.

9.7.  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

9.7.

9.8.  NO-PATH Object

   IANA is requested to create a registry to manage the codespace of NI
   field present in 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 docuement

9.9.  METRIC Object

   IANA is requested to create a registry to manage the codespace of 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

   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

      1       Bound              This document
      2       Computed metric    This document

9.10.  PCEP TLV format Type Indicators

   IANA is requested to create 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

9.8.

9.11.  NO-PATH-VECTOR TLV

   IANA is requested to manage the space of flags carried in the NO-
   PATH-VECTOR TLV defined in this document, numbering them in the usual
   IETF notation starting at zero and continuing through 31.

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

   Each bit should be tracked with the following qualities: - Bit number
   - Name flag - Reference

   Bits

    Bit Number     Name Flag                         Reference
     1             PCE currently Unavailable    This document
     2             Unknown Destination          This document
     3             Unknown Source               This document

10.  Security Considerations

   PCEP Finite State Machine (FSM)

   The section describes could be 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 target of the following set attacks:

   o  Spoofing (PCC or PCE impersonation)

   o  Snooping (message interception)

   o  Falsification

   o  Denial of variables:

   Connect: timer (in seconds) started after having initialized a TCP
   connection using the Service

   A PCEP well-known TCP port.  The value of the
   TCPConnect timer is 60 seconds.

   ConnectRetry: specifies the number of times the system has tried to
   establish a TCP connection with a attack may have significant impact, particularly in an
   inter-AS context as PCEP peer without success.

   ConnectMaxRetry: Maximum number facilitates inter-AS path establishment.

   Several mechanisms are proposed below, so as to ensure
   authentication, integrity and privacy of times the system tries PCEP Communications, and
   also to
   establish a TCP connection using the protect against DoS attacks.

10.1.  PCEP well-known TCP port before
   going back Authentication and Integrity

   It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option to
   provide for the Idle state.  The value of the ConnectMaxRetry is 5.

   OpenWait: timer that corresponds to the amount authenticity and integrity of time a PCEP peer messages.  This
   will wait to receive an Open allow protecting against PCE or PCC impersonation and also
   against message from the PCEP peer after content falsification.

   This requires the
   expiration maintenance, exchange and configuration of which the system releases the PCEP resource MD-5
   keys on PCCs and go back PCEs.  Note that such maintenance may be especially
   onerous to the Idle state.  The OpenWait timer has a fixed value of 60
   seconds.

   KeepWait: timer that corresponds operators as pointed out in
   [I-D.ietf-rpsec-bgpsecrec].  Hence it is important to limit the amount
   number of time keys while ensuring the required level of security.

   MD-5 signature faces some limitations, as explained in [RFC2385].
   Note that when a digest technique stronger than MD5 is specified and
   implemented, PCEP peer
   will wait could be easily upgraded to receive a KeepAlive or a PCErr message from the use it.

10.2.  PCEP
   peer after the expiration of which the system releases the Privacy

   Ensuring PCEP
   resource and go back to the Idle state.  The KeepWait timer has a
   fixed value of 60 seconds.

   OpenRetry: specifies the number communication privacy is of times the system has received key importance, especially
   in an
   Open message with unacceptable inter-AS context, where PCEP session characteristics.

   The following two states variable are defined:

   RemoteOK: the RemoteOK variable is a Boolean set to 1 if communication end-points do not
   reside in the system
   has received same AS, as an acceptable Open message.

   LocalOK: the LocalOK variable is attacker that intercept a Boolean set PCE message
   could obtain sensitive information related to 1 if the system has
   received a Keepalive message acknowledging that the Open message sent computed paths and
   resources.  Privacy can be ensured thanks to the peer was valid.

   Idle State:

   The idle state is the initial PCEP state where encryption.  To ensure
   privacy of PCEP (also referred to
   as "the system") waits for an initialization event that can either communication, IPsec [RFC4303] tunnels MAY be
   manually triggered by the user (configuration) used
   between PCC and PCEs or automatically
   triggered by various events.  In Idle state, PCEP resources are
   allocated (memory, potential process, ...) but no PCEP messages are
   accepted from any PCEP peer.  The system listens the well-known PCEP between PCEs.  Note that this could also be
   used to ensure Authentication and Integrity, in which case, TCP port.

   The following set of variable are initialized:

   TCPRetry=0,

   LocalOK=0,

   RemoteOK=0,

   OpenRetry=0.

   Upon detection MD-5
   option would not be required.

10.3.  Protection Against Denial of a local initialization event (e.g. user
   configuration to establish a PCEP session with a particular Service Attacks

10.3.1.  Protection Against TCP DoS Attacks

   PCEP
   peer, local event triggering can be the establishment target of a PCEP session with
   a PCEP peer TCP DoS attacks, such as the automatic detection of a PCEP peer, ...), the
   system:

   o  Initiates for instance SYN
   attacks, as all protocols running on top of a TCP connection with the TCP.  PCEP peer,

   o  Starts can use the Connect timer,

   o  Moves
   same mechanisms as defined in [RFC5036] to mitigate the TCPPending state.

   Upon receiving a threat of
   such attacks:

   o  A PCE should avoid promiscuous TCP connection on the well-known listens for PCEP 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.
      establishment.  It is expected should use only listens that an implementation will are specific to
      authorized PCCs.

   o  The use an exponentially
   increase timer between automatically generated Initialization events
   and between retrials of TCP connection establishments.

   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 MD5 option helps somewhat since it prevents a SYN
      from being accepted unless the TCP connection establishment fails (an error MD5 segment checksum is detected
   during the TCP connection establishment) or valid.

      However, the Connect timer
   expires:

   If ConnectRetry =ConnectMaxRetry receiver must compute the system moves checksum before it can
      decide to the Idle State

   If ConnectRetry < ConnectMaxRetry the system: discard an otherwise acceptable SYN segment.

   o  Initiates  The use of a TCP connection with access-list on the PCE so as to restrict access to
      authorized PCCs.

10.3.2.  Request Input Shaping/Policing

   A PCEP peer,

   o  Increments the ConnectRetry variable,

   o  Restarts the Connect timer,
   o  Stays in the TPCPending state.

   In response implementation may be subject to any other event the system releases the Denial Of Service attacks
   consisting of sending a very large number of PCEP resources
   for that peer and moves back messages (e.g.
   PCReq messages).  Thus, especially in multi-Service Provider
   environments, a PCE implementation should implement request input
   shaping/policing so as to throttle the Idle state.

   OpenWait State:

   In the OpenWait state, amount of received PCEP
   messages without compromising the system waits implementation behavior.

11.  Authors' Addresses

   The content of this document was contributed by the editors and the
   co-authors listed below:

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

   Email: arthi@juniper.net

   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

   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

12.  Acknowledgements

   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.  Special thank to Adrian Farrel for his very valuable
   suggestions.  The authors would also like to thank Fabien Verhaeghe
   for an Open message from its
   PCEP peer.

   If the system receives very fruitful discussions and useful suggestions.

13.  References

13.1.  Normative References

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

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an Open message from the PCEP peer before
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 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.

13.2.  Informative References

   [I-D.ietf-pce-inter-layer-req]
              Oki, E., "PCC-PCE Communication and PCE Discovery
              Requirements for Inter-Layer Traffic  Engineering",
              draft-ietf-pce-inter-layer-req-06 (work in progress),
              November 2007.

   [I-D.ietf-pce-interas-pcecp-reqs]
              Bitar, N., "Inter-AS Requirements for the
   expiration Path Computation
              Element Communication  Protocol (PCECP)",
              draft-ietf-pce-interas-pcecp-reqs-03 (work in progress),
              July 2007.

   [I-D.ietf-pce-manageability-requirements]
              Farrel, A., "Inclusion of the OpenWait timer, the system first examines all Manageability Sections in PCE
              Working Group Drafts",
              draft-ietf-pce-manageability-requirements-02 (work in
              progress), August 2007.

   [I-D.ietf-pce-monitoring]
              Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
   its sessions that are
              monitoring tools for Path Computation Element based
              Architecture", draft-ietf-pce-monitoring-01 (work in
              progress), February 2008.

   [I-D.ietf-rpsec-bgpsecrec]
              Christian, B. and T. Tauber, "BGP Security Requirements",
              draft-ietf-rpsec-bgpsecrec-09 (work in progress),
              November 2007.

   [I-D.kkoushik-pce-pcep-mib]
              Stephan, E. and K. Koushik, "PCE communication
              protocol(PCEP) Management Information Base",
              draft-kkoushik-pce-pcep-mib-01 (work in progress),
              July 2007.

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

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

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

   [RFC3785]  Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P., and has
              T. Telkamp, "Use of Interior Gateway Protocol (IGP) Metric
              as a lower IP
      address than the PCEP Peer, the system closes the TCP connection,
      releases the PCEP resources second MPLS Traffic Engineering (TE) Metric", BCP 87,
              RFC 3785, May 2004.

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

   [RFC4101]  Rescorla, E. and moves back
      to the Idle state.

   o  If the session was initiated by the PCEP peer IAB, "Writing Protocol Models", RFC 4101,
              June 2005.

   [RFC4234]  Crocker, D., Ed. 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, P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

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

   [RFC4420]  Farrel, A., Papadimitriou, D., Vasseur, J., and moves back to the Idle state.

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

   If an error is detected (e.g. malformed Open message, presence A.
              Ayyangar, "Encoding of two
   Open objects, ...), PCEP generates an error notification, the PCEP
   peer sends a PCErr message with Error-Type=1 Attributes for Multiprotocol Label
              Switching (MPLS) Label Switched Path (LSP) Establishment
              Using Resource ReserVation Protocol-Traffic Engineering
              (RSVP-TE)", RFC 4420, February 2006.

   [RFC4655]  Farrel, A., Vasseur, J., and Error-value=1.  The
   system releases the PCEP resources 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.

   [RFC4927]  Le Roux, J., "Path Computation Element Communication
              Protocol (PCECP) Specific Requirements for the PCEP peer, closes the TCP
   connection Inter-Area MPLS
              and moves to the Idle state.

   If no errors are detected, PCEP increments the OpenRetry variable.

   If no errors are detected, OpenRetry=1 GMPLS Traffic Engineering", RFC 4927, June 2007.

   [RFC5036]  Andersson, L., Minei, I., and the session
   characteristics are unacceptable, the PCEP peer sends a PCErr with
   Error-Type=1 B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5088]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and Error-value=5, the system releases the PCEP
   resources R. Zhang,
              "OSPF Protocol Extensions for that peer Path Computation Element
              (PCE) Discovery", RFC 5088, January 2008.

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

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 state.

   If no errors are detected and the session characteristics are
   acceptable to  |-------+  |
   |+----->|       |----------+
   +------>+-+-+-+-+

   Figure 23: PCEP Finite State Machine for the local system, PCC

   PCEP defines the system:

   o  Sends following set of variables:

   Connect: timer (in seconds) started after having initialized a Keepalive message to TCP
   connection using the PCEP peer,

   o  Starts the Keepalive timer,

   o  Sets the RemoteOK variable to 1.

   If LocalOK=1 the system clears well-known TCP port.  The value of the OpenWait
   TCPConnect timer and moves to is 60 seconds.

   ConnectRetry: specifies the UP
   state.

   If LocalOK=0 number of times the system clears the OpenWait timer, starts the
   KeepWait timer and moves has tried to the KeepWait state.

   If no errors are detected but the session characteristics are
   unacceptable and non-negotiable, the PCEP peer sends
   establish a PCErr TCP connection with
   Error-Type=1 and Error-value=3, a PCEP peer without success.

   ConnectMaxRetry: Maximum number of times the system releases tries to
   establish a TCP connection using the PCEP
   resources for that peer, and moves well-known TCP port before
   going back to the Idle state.

   If no errors are detected, OpenRetry=0, the session characteristics
   are unacceptable but negotiable (such as the Keepalive period or the
   DeadTimer),  The value of the system:

   o  Increments ConnectMaxRetry is 5.

   OpenWait: timer that corresponds to the OpenRetry variable,

   o  Sends amount of time a PCErr PCEP peer
   will wait to receive an Open message with Error-Type=1 and Error-value=4 that
      contains proposed acceptable session characteristics,

   o  If LocalOK=1, the system restarts from the OpenWait timer and stays in PCEP peer after the OpenWait state

   o  If LocalOK=0,
   expiration of which the system clears the OpenWait timer, starts releases the
      KeepWait timer PCEP resource and moves go back
   to the KeepWait state

   If no Open message is received before Idle state.  The OpenWait timer has a fixed value of 60
   seconds.

   KeepWait: timer that corresponds to the expiration amount of the OpenWait
   timer, the time a PCEP peer sends
   will wait to receive a KeepAlive or a PCErr message with Error-Type=1 and
   Error-value=2, the system releases the PCEP resources for from the PCEP
   peer, closes the TCP connection and moves to
   peer after the Idle state.

   In response to any other event expiration of which the system releases the PCEP resources
   for that peer
   resource and moves go back to the Idle state.  The KeepWait State

   In timer has a
   fixed value of 60 seconds.

   OpenRetry: specifies the Keepwait state, number of times the system waits for has received an
   Open message with unacceptable PCEP session characteristics.

   The following two states variable are defined:

   RemoteOK: the receipt of RemoteOK variable is a Boolean set to 1 if the system
   has received an acceptable Open message.

   LocalOK: the LocalOK variable is a Boolean set to 1 if the system has
   received a Keepalive from its PCEP peer message acknowledging its that the Open message sent
   to the peer was valid.

   Idle State:

   The idle state is the initial PCEP state where 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, ...) but no PCEP messages are
   accepted from any PCEP peer.  The system listens the well-known PCEP
   TCP port.

   The following set of variable are initialized:

   TCPRetry=0,

   LocalOK=0,

   RemoteOK=0,

   OpenRetry=0.

   Upon detection of a
   PCErr message in response local initialization event (e.g. user
   configuration to unacceptable establish a PCEP session
   characteristics proposed in the Open message.

   If an error is detected (e.g. malformed Keepalive message), with a particular PCEP
   generates an error notification,
   peer, local event triggering the PCEP peer sends establishment of a PCErr message PCEP session with Error-Type=1 and Error-value=1.  The system releases the
   a PCEP
   resources for peer such as the automatic detection of a PCEP peer, closes ...), the
   system:

   o  Initiates of a TCP connection and moves with the PCEP peer,

   o  Starts the Connect timer,

   o  Moves to the Idle TCPPending state.

   If

   Upon receiving a Keepalive message is received before TCP connection on the expiration of well-known PCEP TCP port, if
   the
   KeepWait timer, then TCP connection establishment succeeds, the system sets LocalOK=1 and: system:

   o  If RemoteOK=1, the system clears  Sends an Open message,

   o  Starts the KeepWait timer and moves OpenWait timer,

   o  Moves to the UP OpenWait state.

   o

   If RemoteOK=0, the connection establishment fails, the system clears remains in the KeepWait timer, starts Idle
   state.  Any other event received in the
      OpenWait Idle state is ignored.

   It is expected that an implementation will use an exponentially
   increasing timer between automatically generated Initialization
   events and moves 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. state.

   If a PCErr message the TCP connection establishment fails (an error is received before detected
   during the expiration of TCP connection establishment) or the KeepWait
   timer:

   1. Connect timer
   expires:

   o  If ConnectRetry =ConnectMaxRetry the proposed values are unacceptable, system moves to the PCEP peer sends Idle
      State

   o  If ConnectRetry < ConnectMaxRetry the system:

      1.  Initiates of a
       PCErr message TCP connection with Error-Type=1 and Error-value=6 and the PCEP peer,

      2.  Increments the ConnectRetry variable,
      3.  Restarts the Connect timer,

      4.  Stays in the TPCPending state.

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

   2.  If

   OpenWait State:

   In the proposed values are acceptable, OpenWait state, the system adjusts waits for an Open message from its
   PCEP session characteristics according to the proposed values
       received in the PCErr message restarts the KeepWait timer and
       sends a new Open message. peer.

   If RemoteOK=1, the system restarts the
       KeepWait timer and stays in receives an Open message from the KeepWait state.  If RemoteOK=0, PCEP peer before the system clears
   expiration of the KeepWait OpenWait timer, start the OpenWait timer
       and moves to system first examines all of
   its sessions that are in the OpenWait or KeepWait state.  If neither a Keepalive nor a PCErr is received after the expiration
   of the KeepWait timer, another
   session with the same PCEP peer sends a PCErr message with
   Error-Type=1 and Error-value=7 and, already exists (same IP address),
   then the system releases performs the PCEP
   resources for that PCEP peer, closes following collision resolution
   procedure:

   o  If the TCP connection system has initiated the current session and moves to it has a lower
      IP address than the Idle State.

   In response to any other event PCEP Peer, the system closes the TCP
      connection, releases the PCEP resources for that peer the pending session
      and moves back to the Idle state.

   UP State

   In

   o  If the UP state, session was initiated by the PCEP peer starts exchanging PCEP messages
   according to the session characteristics.

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

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

   If a malformed message is received, state.

   o  Otherwise, the system terminates checks the PCEP session according to attributes
      (Keepalive frequency, DeadTimer, ...).

   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 procedure defined in Section 6.8, PCEP peer sends a
   PCErr message with Error-Type=1 and Error-value=1.  The system
   releases the PCEP resources for that the PCEP peer, closes the TCP
   connection and moves to the Idle State. state.

   If no errors are detected, PCEP increments the system detects that OpenRetry variable.

   If no errors are detected, OpenRetry=1 and the session
   characteristics are unacceptable, the PCEP peer tries to setup a second TCP
   connection, it stops the TCP connection establishment and sends a PCErr with Error-Type=9.

   If the TCP connection fails,
   Error-Type=1 and Error-value=5, the system releases the PCEP
   resources for that PCEP peer, closes the TCP connection peer and moves back to the Idle
   State.

11.  Security Considerations

   PCEP could be state.

   If no errors are detected, and the target of session characteristics are
   acceptable to the following attacks:

   o  Spoofing (PCC or PCE impersonation) local system, the system:

   o  Snooping (message interception)  Sends a Keepalive message to the PCEP peer,

   o  Falsification  Starts the Keepalive timer,

   o  Denial of Service

   A PCEP attack may have significant impact, particularly in an
   inter-AS context as PCEP facilitates inter-AS path establishment.
   Several mechanisms are proposed below, so as  Sets the RemoteOK variable to ensure
   authentication, integrity 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 privacy of non-negotiable, the PCEP Communications, peer sends a PCErr with
   Error-Type=1 and
   also to protect against DoS attacks.

11.1. Error-value=3, the system releases the PCEP Authentication
   resources for that peer, and Integrity

   It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option moves back to
   provide for the authenticity Idle state.

   If no errors are detected, and integrity of PCEP messages.  This
   will allow protecting against PCE or PCC impersonation OpenRetry is 0, and also
   against message content falsification.

   This requires the maintenance, exchange and configuration of MD-5
   keys on PCCs 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 PCEs.  Note Error-value=4 that such maintenance may be especially
   onerous to
      contains proposed acceptable session characteristics,

   o  If LocalOK=1, the operators as pointed out system restarts the OpenWait timer and stays in
   [I-D.ietf-rpsec-bgpsecrec].  Hence it is important to limit
      the
   number of keys while ensuring OpenWait state

   o  If LocalOK=0, the required level of security.

   MD-5 signature faces some limitations, as per explained in [RFC2385].
   Note that when one digest technique stronger than MD5 is specified system clears the OpenWait timer, starts the
      KeepWait timer and implemented, PCEP could be easily upgraded moves to use it.

11.2.  PCEP Privacy

   Ensuring PCEP communication privacy the KeepWait state

   If no Open message is received before the expiration of key importance, especially
   in an inter-AS context, where the OpenWait
   timer, the PCEP communication end-points do not
   reside in 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 same AS, as an attacker that intercept a PCE message
   could obtain sensitive information related to computed paths TCP connection and
   resources.  Privacy can be ensured thanks moves to encryption.  To ensure
   privacy of the Idle state.

   In response to any other event the system releases the PCEP communication, IPSec [RFC4303] tunnels MAY be used
   between PCC and PCEs or between PCEs.  Note resources
   for that this could also be
   used to ensure Authentication peer and Integrity, in which case, TCP MD-5
   option would not be required.

11.3.  Protection against Denial of Service attacks

   PCEP can be moves back to the target of TCP DoS attacks, such as Idle state.

   KeepWait State

   In the Keepwait state, the system waits for instance SYN
   attacks, as all protocols running on top the receipt of TCP. a
   Keepalive from its PCEP can use the
   same mechanisms as defined peer acknowledging its Open message or a
   PCErr message in [RFC3036] response to mitigate unacceptable PCEP session
   characteristics proposed in the threat of
   such attacks:

   o  A PCE should avoid promiscuous TCP listens 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
      establishment.  It should use only listens that are specific and moves to
      authorized PCCs.

   o  The use of
   the MD5 option helps somewhat since it prevents Idle state.

   If a SYN
      from being accepted unless the MD5 segment checksum Keepalive message is valid.
      However, received before the expiration of the
   KeepWait timer, then the system sets LocalOK=1 and:

   o  If RemoteOK=1, the receiver must compute system clears the checksum before it can
      decide KeepWait timer and moves to discard an otherwise acceptable SYN segment.
      the UP state.

   o  The use of access-list on  If RemoteOK=0, the PCE so as to restrict access to
      authorized PCCs.

11.4.  Request input shaping/policing

   A PCEP implementation may be subject system clears the KeepWait timer, starts the
      OpenWait timer and moves to Denial Of Service attacks
   consisting of sending a very large number of PCEP messages (e.g.
   PCReq messages).  Thus, especially in multi-Service Providers
   environments, the OpenWait State.

   If a PCE implementation should implement request input
   shaping/policing so as to throttle PCErr message is received before the amount expiration of received PCEP
   messages without compromising the implementation behavior.

12.  Authors' addresses

   This document was KeepWait
   timer:

   1.  If the collective work of several authors.  The
   content of this document was contributed by proposed values are unacceptable, the editors PCEP peer sends a
       PCErr message with Error-Type=1 and Error-value=6 and the co-
   authors listed below:

   Arthi Ayyangar
   Nuova Systems
   2600 San Tomas Expressway
   Santa Clara, CA  95051
   USA

   Email: arthi@nuovasystems.com

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

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

   Alia Atlas
   Google
   1600 Amphitheatre Parkway
   Montain View, CA  94043
   USA

   Email: akatlas@alum.mit.edu

   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

13.  Acknowledgements

   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 system
       releases the PCEP resources for that PCEP peer, closes the TCP
       connection and Dennis Aristow for their very
   valuable input.  Special thank moves to Adrian Farrel for his very valuable
   suggestions.  The authors would also like the Idle state.

   2.  If the proposed values are acceptable, the system adjusts its
       PCEP session characteristics according to thank Fabien Verhaeghe
   for the very fruitfull discussions and useful suggestions.

14.  References

14.1.  Normative References

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

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., the PCErr message restarts the KeepWait timer 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.
       sends a new Open message.  If RemoteOK=1, the system restarts the
       KeepWait timer and Y. Rekhter, "Signalling Unnumbered Links stays in Resource ReSerVation Protocol - Traffic Engineering
              (RSVP-TE)", RFC 3477, January 2003.

   [RFC4090]  Pan, P., Swallow, G., the KeepWait state.  If RemoteOK=0,
       the system clears the KeepWait timer, start the OpenWait timer
       and A. Atlas, "Fast Reroute
              Extensions moves to RSVP-TE for LSP Tunnels", RFC 4090,
              May 2005.

14.2.  Informative References

   [I-D.ietf-pce-disco-proto-isis]
              Roux, J., "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-isis-08 (work in progress),
              September 2007.

   [I-D.ietf-pce-disco-proto-ospf]
              Roux, J., "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-ospf-08 (work in progress),
              September 2007.

   [I-D.ietf-pce-inter-layer-req]
              Oki, E., "PCC-PCE Communication 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 PCE Discovery
              Requirements for Inter-Layer Traffic  Engineering",
              draft-ietf-pce-inter-layer-req-06 (work in progress),
              November 2007.

   [I-D.ietf-pce-interas-pcecp-reqs]
              Bitar, N., "Inter-AS Requirements Error-value=7 and, system releases the PCEP
   resources for that PCEP peer, closes the Path Computation
              Element Communication  Protocol (PCECP)",
              draft-ietf-pce-interas-pcecp-reqs-03 (work in progress),
              July 2007.

   [I-D.ietf-pce-manageability-requirements]
              Farrel, A., "Inclusion of Manageability Sections in PCE
              Working Group Drafts",
              draft-ietf-pce-manageability-requirements-02 (work in
              progress), August 2007.

   [I-D.ietf-rpsec-bgpsecrec]
              Christian, B. TCP connection and T. Tauber, "BGP Security Requirements",
              draft-ietf-rpsec-bgpsecrec-08 (work in progress),
              July 2007.

   [I-D.kkoushik-pce-pcep-mib]
              Stephan, E. moves to
   the Idle State.

   In response to any other event the system releases the PCEP resources
   for that peer and K. Koushik, "PCE communication
              protocol(PCEP) Management Information Base",
              draft-kkoushik-pce-pcep-mib-01 (work in progress),
              July 2007.

   [I-D.vasseur-pce-monitoring]
              Vasseur, J., "A set moves back to the Idle state.

   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 monitoring tools the DeadTimer, the system
   terminates PCEP session according to the procedure defined in
   Section 6.8, releases the PCEP resources for Path
              Computation Element based Architecture",
              draft-vasseur-pce-monitoring-03 (work 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 progress),
              May 2007.

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

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via Section 6.8, releases
   the PCEP resources for that PCEP peer, closes the TCP MD5
              Signature Option", RFC 2385, August 1998.

   [RFC3036]  Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
              B. Thomas, "LDP Specification", RFC 3036, January 2001.

   [RFC3785]  Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P., connection and
              T. Telkamp, "Use of Interior Gateway Protocol (IGP) Metric
              as
   moves to the Idle State.

   If the system detects that the PCEP peer tries to setup a second MPLS Traffic Engineering (TE) Metric", BCP 87,
              RFC 3785, May 2004.

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

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

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

   [RFC4420]  Farrel, A., Papadimitriou, D., Vasseur, J., and A.
              Ayyangar, "Encoding of Attributes for Multiprotocol Label
              Switching (MPLS) Label Switched Path (LSP) Establishment
              Using Resource ReserVation Protocol-Traffic Engineering
              (RSVP-TE)", RFC 4420, February 2006.

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

   [RFC4657]  Ash, J. TCP connection establishment 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.

   [RFC4927]  Le Roux, J., "Path Computation Element Communication
              Protocol (PCECP) Specific Requirements sends a
   PCErr with Error-Type=9.

   If the TCP connection fails, the system releases the PCEP resources
   for Inter-Area MPLS that PCEP peer, closes the TCP connection and GMPLS Traffic Engineering", RFC 4927, June 2007. moves to the Idle
   State.

Appendix A. 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
   declared the session down if no PCEP message has been received.

   SyncTimer: the SYNC timer is 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 SYNC timer 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.  A RECOMMENDED value for the SYNC timer is 60 seconds.

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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