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Versions: (draft-vasseur-pce-pcep) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 RFC 5440

Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                        JL. Le Roux, Ed.
Expires: August 17, 2007                                  France Telecom
                                                       February 13, 2007


      Path Computation Element (PCE) communication Protocol (PCEP)
                       draft-ietf-pce-pcep-06.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   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.
   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  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 a PCC to a PCE  . . .  8
       4.2.3.  Path computation reply sent by the PCE to a PCC  . . .  9
       4.2.4.  Notification . . . . . . . . . . . . . . . . . . . . . 11
       4.2.5.  Error  . . . . . . . . . . . . . . . . . . . . . . . . 12
       4.2.6.  Termination of the PCEP Session  . . . . . . . . . . . 13
   5.  Transport protocol . . . . . . . . . . . . . . . . . . . . . . 13
   6.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Common header  . . . . . . . . . . . . . . . . . . . . . . 14
     6.2.  Open message . . . . . . . . . . . . . . . . . . . . . . . 15
     6.3.  Keepalive message  . . . . . . . . . . . . . . . . . . . . 16
     6.4.  Path Computation Request (PCReq) message . . . . . . . . . 17
     6.5.  Path Computation Reply (PCRep) message . . . . . . . . . . 18
     6.6.  Notification (PCNtf) message . . . . . . . . . . . . . . . 19
     6.7.  Error (PCErr) Message  . . . . . . . . . . . . . . . . . . 20
     6.8.  Close message  . . . . . . . . . . . . . . . . . . . . . . 20
   7.  Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  Common object header . . . . . . . . . . . . . . . . . . . 21
     7.2.  OPEN object  . . . . . . . . . . . . . . . . . . . . . . . 22
     7.3.  RP Object  . . . . . . . . . . . . . . . . . . . . . . . . 24
       7.3.1.  Object definition  . . . . . . . . . . . . . . . . . . 24
       7.3.2.  Handling of the RP object  . . . . . . . . . . . . . . 26
     7.4.  NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 26
     7.5.  END-POINT Object . . . . . . . . . . . . . . . . . . . . . 29
     7.6.  BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 30
     7.7.  METRIC Object  . . . . . . . . . . . . . . . . . . . . . . 31
     7.8.  Explicit Route Object  . . . . . . . . . . . . . . . . . . 34
     7.9.  Route Record Object  . . . . . . . . . . . . . . . . . . . 34
     7.10. LSPA Object  . . . . . . . . . . . . . . . . . . . . . . . 35



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     7.11. IRO Object . . . . . . . . . . . . . . . . . . . . . . . . 36
     7.12. SVEC Object  . . . . . . . . . . . . . . . . . . . . . . . 37
       7.12.1. Notion of Dependent and Synchronized path
               computation requests . . . . . . . . . . . . . . . . . 37
       7.12.2. SVEC Object  . . . . . . . . . . . . . . . . . . . . . 38
       7.12.3. Handling of the SVEC Object  . . . . . . . . . . . . . 40
     7.13. NOTIFICATION Object  . . . . . . . . . . . . . . . . . . . 40
     7.14. PCEP-ERROR Object  . . . . . . . . . . . . . . . . . . . . 43
     7.15. LOAD-BALANCING Object  . . . . . . . . . . . . . . . . . . 47
     7.16. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 48
   8.  Manageability Considerations . . . . . . . . . . . . . . . . . 49
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 49
     9.1.  TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 49
     9.2.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . 50
     9.3.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . . . 50
     9.4.  Notification . . . . . . . . . . . . . . . . . . . . . . . 51
     9.5.  PCEP Error . . . . . . . . . . . . . . . . . . . . . . . . 52
     9.6.  NO-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . . . 53
   10. PCEP Finite State Machine (FSM)  . . . . . . . . . . . . . . . 54
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 59
     11.1. PCEP Authentication and Integrity  . . . . . . . . . . . . 60
     11.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 60
     11.3. Protection against Denial of Service attacks . . . . . . . 60
     11.4. Request input shaping/policing . . . . . . . . . . . . . . 61
   12. Authors' addresses . . . . . . . . . . . . . . . . . . . . . . 61
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 62
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 63
     14.2. Informative References . . . . . . . . . . . . . . . . . . 63
   Appendix A.  Compliance with the PCECP Requirement Document  . . . 65
   Appendix B.  PCEP Variables  . . . . . . . . . . . . . . . . . . . 65
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 66
   Intellectual Property and Copyright Statements . . . . . . . . . . 67


















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1.  Terminology

   Terminology used in this document

   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 the
   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

   [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



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   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 [I-D.ietf-pce-pcecp-interarea-reqs],
   [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 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 the required information so
   as to perform the computation of TE LSP that usually requires network
   topology and resource information.  Such information can be gathered
   by routing protocols or by some other means, the gathering of which
   is out of the scope of this document.

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


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.



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4.1.  Problem

   The PCE-based architecture used for the computation of MPLS and GMPLS
   TE LSP 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) to a PCE and the PCE
   may reply with a set of computed path(s) if one or more path(s) that
   satisfy the set of constraints can be found.

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) if the request can be satisfied or a negative reply
   otherwise.

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

   The establishment of a PCEP session is always initiated by the PCC.




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

   A single PCEP session can exist between a pair a PCEP peers.

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



















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            +-+-+                  +-+-+
            |PCC|                  |PCE|
            +-+-+                  +-+-+
              |                      |
              |---- Open message --->|
              |                      |
              |<--- Open message ----|
              |                      |
              |                      |
              |                      |
              |<--- Keepalive -------|
              |                      |
              |---- Keepalive ------>|

   Figure 1: PCEP Initialization phase without parameter
             negotiation(initiated by a PCC)


4.2.2.  Path computation request sent by a PCC to a PCE



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

                  Figure 2: Path computation request

   Once a PCC has successfully established a PCEP session with one or
   more PCEs, if an event is triggered that requires the computation of
   a set of path(s), the PCC first selects one or more PCE(s) to send
   the request to.  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 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



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   and the PCC-PCE address pair.  The process is shown in a schematic
   form in figure 2.

   Details about the PCReq message can be found in Section 6.4

4.2.3.  Path computation reply sent by the PCE to a PCC













































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

  Figure 3a: Path 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
   Upon receiving a path computation request from a PCC, the PCE
   triggers a path computation, the result of which can either be:

   - 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) to the requesting PCC.  Note that
   PCEP supports the capability to send a single request which requires
   the computation of more than one path (e.g. computation of a set of
   link-diverse paths).




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   - 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 a PCE may want to notify a
   PCC of a specific event.  For example, suppose that the PCE suddenly
   experiences some congestion that would lead 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) path computation
   request(s) 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).































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                 +-+-+                  +-+-+
                 |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
                   |                      |
                   |                      |
5) Path computation|                      |
request X cancelled|                      |
                   |---- PCNtf message -->|
                   |                      |6) Path computation
                   |                      |request X cancelled

Figure 4: Example of PCC notification (cancellation notification) sent to a PCE


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


Figure 5: Example of PCE notification (cancellation notification) sent to a PCC

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

4.2.5.  Error

   PCEP Error messages are sent when a protocol error condition is met
   (e.g. unknown object, non supported object, policy violation, ...).



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                    +-+-+                  +-+-+
                    |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 => Policy
                      |                      |violation !
                      |                      |5) Request discarded
                      |                      |
                      |<-- PCErr message  ---|
                      |                      |

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

   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 close 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 immediatly
   terminated.

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


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.

   An implementation may decide to keep the TCP session alive 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 session 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



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   close the TCP connection for each PCEP request (for instance when
   sending a path computation request is a rare event).


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 7.14).
   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 7.1) that can be set by a PCEP peer to
   enforce a PCE to take into account the related information during the
   path computation.  For example, the METRIC object defined in
   Section 7.7allows a PCC to specify a bounded acceptable path cost.
   The METRIC object is optional but a PCC may set a flag to ensure that
   such constraint is taken into account.  Similarly to the previous
   case, if such constraint cannot be taken into account by the PCE,
   this should 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) to specify such rules.  Square brackets refer to optional sub-
   sequences.  An implementation MUST form the PCEP messages using the
   object ordering specified in this document.

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

                Figure 7: PCEP message common header
   Ver (Version - 3 bits): PCEP version number.  Current version is
   version 1.

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

   Message-Type (8 bits):




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   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
   Reserved: This field MUST be set to zero on transmission and MUST be
   ignored on receipt.

   Message Length (32 bits): total length of the PCEP message expressed
   in bytes including the common header.

6.2.  Open 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.  Any message received prior to an Open message
   (other than a Keepalive 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.

   Open message
   <Open Message>::= <Common Header>
                     <OPEN>
   The Open message MUST contain exactly one OPEN object (see
   Section 7.2).  Various session characteristics are specified within
   the OPEN object.

   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 an Open message has been received nor a PCErr
   message in case of disagreement of the session characteristics, the
   TCP connection MUST be released (see Section 10 for details).

   The KeepWait timer has a fixed value of 1 minute.




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   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 7.14.

   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 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

   A Keepalive message is a PCEP message sent by a PCC or a PCE in order
   to keep the session in active state.  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 messages.
   Asymmetric values may be chosen; thus there is no constraints
   mandating the use of identical keepalive frequencies by both PCEP
   peers.  The DeadTimer is defined as the period of time after the
   expiration of which a PCEP peer declares the session down if no PCEP
   message has been received (keepalive or any other PCEP message: thus,
   any PCEP message acts as a keepalive message).  Similarly, there is
   no constraints mandating the use of identical DeadTimers by both PCEP
   peers.  The minimum KeepAliveTimer value is 1 second.

   Keepalive messages are used either 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.  Because any PCEP message may serve as Keepalive an
   implementation may either decide to send Keepalive messages at fixed
   intervals regardless on whether other PCEP messages might have been



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   sent since the last sent Keepalive message or may decide to differ
   the sending of the next Keepalive message based on the time at which
   the last PCEP message (other than Keepalive) has been sent.

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

6.4.  Path Computation Request (PCReq) message

   A Path Computation Request message (also referred to as a PCReq
   message) is a PCEP message sent by a PCC to a PCE so as to request a
   path computation.  The Message-Type field of the PCEP common header
   for the PCReq message is set to 3 (To be confirmed by IANA).

   There is 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 of these objects is missing, the receiving PCE
   MUST send an error message to the requesting PCC.  Other objects are
   optional.

   The format of a PCReq message is as follows:
   <PCReq Message>::= <Common Header>
                      [<SVEC-list>]
                      <request-list>

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

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

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


   The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, ERO, IRO and LOAD-
   BALANCING objects are defined in Section 7.  The special case of two
   BANDWIDTH objects is discussed in details in Section 7.6.






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6.5.  Path Computation Reply (PCRep) message

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

   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 7.3for 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 7.15) 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 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, it MAY decide to
   provide each computed path in separate PCRep messages.

   If the path computation request can be satisfied (the PCE finds a set
   of path(s) that satisfy the set of constraint(s)), the set of
   computed path(s) specified by means of ERO object(s) is inserted in
   the PCRep message.  The ERO object is defined in Section 7.8.  Such a
   situation where multiple computed paths are provided in a PCRep
   message is discussed in detail in Section 7.12.  Furthermore, when a
   PCC requests the computation 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 7.15.

   If the path computation request cannot be satisfied, the PCRep
   message MUST include a NO-PATH object.  The NO-PATH object (described
   in Section 7.4) may also comprise other information (e.g reasons for
   the path computation failure).





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   The format of a PCRep message is as follows:
   <PCRep Message> ::= <Common Header>
                       <response-list>

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


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

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

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

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


6.6.  Notification (PCNtf) message

   The PCEP Notification message (also referred to as the PCNtf message)
   can either be sent by a PCE to a PCC or by a PCC to a PCE so as 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
   contain several NOTIFICATION objects should the PCE or the PCC intend
   to notify of multiple events.  The NOTIFICATION object is defined in
   Section 7.13.  The PCNtf message MAY also contain an RP object (see
   Section 7.3 when the notification refers to a particular path
   computation request.

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











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   The format of a PCNtf message is as follows:
   <PCNtf Message>::=<Common Header>
                     <notify-list>

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

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

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

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

6.7.  Error (PCErr) Message

   The PCEP Error message (also referred to as a PCErr message) is sent
   when a protocol error condition is met.  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 the former case, the PCErr
   message MUST include the set of RP objects related to the pending
   path computation request(s) that triggered the protocol error
   condition.  In the later case (unsolicited), no RP object is inserted
   in the PCErr message.  No RP object is inserted in a PCErr when the
   error condition occurred during the initialization phase.  A PCErr
   message MUST contain a PCEP-ERROR object specifying the PCEP error
   condition.  The PCEP-ERROR object is defined in section Section 7.14.

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

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

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

   <error-obj-list>:==<PCEP-ERROR>[<error-obj-list>]
   The procedure upon the reception of a PCErr message is defined in
   Section 7.14.

6.8.  Close message

   The Close message is a PCEP message that is either sent by a PCC to a
   PCE or by a PCE to a PCC in order to close a PCEP session.  The



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   Message-Type field of the PCEP common header for the Open 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).

   Upon the receipt of a Close message, the receiving PCEP peer MUST
   cancel all pending requests and MUST close the TCP connection.


7.  Object Formats

7.1.  Common 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.

   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



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   and the PCE is free to ignore it if not supported.

   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 been set in the corresponding PCRep
   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".

   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.

7.2.  OPEN object

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

   The OPEN object contains a set of fields used to specify the PCEP
   version, Keepalive frequency, DeadTimer, 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 such TLV is 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)












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   The format of the OPEN object body is as follows:
    0             1               2               3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Ver  | Flags |   Keepalive   |  Deadtimer    |      SID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         Optional TLV(s)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 9: OPEN Object format
   Ver (Ver - 4 bits): PCEP version.  Current version is 1.

   Flags (4 bits): No Flags are currently defined.  Unassigned bits are
   considered as reserved and MUST be set to zero on transmission.

   Keepalive (8 bits): minimum period of time (in seconds) between the
   sending of PCEP messages.  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 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 a PCEP peer declares the session with the sender of the Open
   message down if no PCEP message has been received.  The DeadTimer
   MUST be set to 0 if the Keepalive is set to 0.  A RECOMMENDED value
   for the DeadTimer is 4 times the value of the Keepalive.

   SID (PCEP session-ID - 8 bits): specifies a 2 octet 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.

   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 session
   characteristic values.







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7.3.  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 P flag of the RP object MUST be set in PCReq and PCReq
   messages and MUST be cleared in PCNtf and PCErr messages.  The RP
   object is used to specify various characteristics of the path
   computation request.

7.3.1.  Object 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: 18 bits - The following flags are currently defined:

   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 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



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   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).  The ability of a PCE to support requests
   prioritization may be dynamically discovered by the PCC(s) 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 the 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.

   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) message by
   means of an RRO object defined in Section 7.9.

   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, and resource requirements (e.g.
   latency and jitter) in each direction.  When cleared, the TE LSP is
   unidirectional.

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



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

7.3.2.  Handling of the RP object

   If a PCReq message is received without containing 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 set
   and local policy has been configured on the PCE to not provide
   explicit path(s) (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 set".

   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 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 the PCE to be either
   stateful (keep track of the previously computed path with the
   associated list of strict hops) or to have the ability to retrieve
   the complete required path segment.  Alternatively the PCC MUST be
   able to inform PCE of the working path with associated list of strict
   hops in PCReq.  The absence of an RRO in the PCReq message for a 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".

7.4.  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



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   impossibility to find a path that satisfies the set of constraints.
   Optionally, if the PCE supports such capability, the NO-PATH object
   MAY contain an optional NO-PATH-VECTOR TLV defined below and 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) 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.

   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)







































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   The format of the NO-PATH object body is as follows:
0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|       Flags                 |          Reserved             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
//                      Optional TLV(s)                        //
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 11: NO-PATH object format

Optionally, a TLV named NO-PATH-VECTOR MAY be included in the
NO-PATH object that specifies the reason that led to unsuccessful path computation.

The NO-PATH-VECTOR TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, followed by
a fix length value field of 32-bits flags field used to report the reason(s)
that led to unsuccessful path computation The NO-PATH-VECTOR TLV is padded
to eight-octet alignment.

TYPE: To be assigned by IANA
LENGTH: 4
VALUE: 32-bits flags field

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

The following flags are currently defined:

0x01: PCE currently unavailable
0x02: Unknown destination
   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.

   Flags (16 bits).  The following flags are currently defined:

   Reserved: This field MUST be set to zero on transmission and MUST be
   ignored on receipt.

   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 specified.

   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



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   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 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 provided in the PCRep message.

7.5.  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.  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)






















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   The format of the END-POINTS object body for IPv4 (Object-Type=1) is
   as follows:

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Source IPv4 address                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Destination IPv4 address                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 12: END-POINTS object body format for IPv4

The format of the END-POINTS object for IPv6 (Object-Type=2) is as follows:

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                Source IPv6 address (16 bytes)                 |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|              Destination IPv6 address (16 bytes)              |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 13: END-POINTS object body format for IPv6

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

7.6.  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 are defined that refer to the requested bandwidth and the
   bandwidth of the TE LSP for which a reoptimization is being



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   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 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
   Bandwidth: 32 bits.  The requested bandwidth is encoded in 32 bits in
   IEEE floating point format, expressed in bytes per second.

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

7.7.  METRIC Object

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

   In a PCReq message, a PCC MAY insert a METRIC object:

   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 and the TE
      metric (see [RFC3785]) and the number of hops traversed by a TE
      LSP.

   o  To indicate a bound on the path cost than 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.



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   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 only meaningful if
   used consistently: for instance, if the delay of a 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
   be used.

   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

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

   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

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



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

   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.  In two or more instances of a METRIC object are
   present for a metric type, only the first instance MUST be considered
   and other instances MUST be ignored.

   In a PCReq message the presence of multiple METRIC object can be used
   to specify a multi-parameters (e.g. a metric may be a constraint or a
   parameter to minimize/maximize) objective function or multiple bounds
   for different constraints where at most one METRIC object must be
   used to indicate the metric to optimize (B-flag is cleared): the
   other METRIC object MUST be used to reflect bound constraints (B-Flag
   is set).

   A METRIC object used to indicate the metric to optimize during the
   path computation MUST have the B-Flag cleared and the T-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 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 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 if
   the C bit of the METRIC object was set in the corresponding path
   computation request (the B-flag MUST be cleared); 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 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:



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   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 no policy preventing to provide the path cost is in place, the
   PCE inserts one METRIC object with B=0, T=1, metric-value= computed
   IGP path cost.  Additionally, the PCE may insert a second METRIC
   object with B=1, T=2, metric-value= computed TE path cost.

7.8.  Explicit Route Object

   The ERO is used to encode a TE LSP.  The ERO is carried within a
   PCRep message to provide the computed TE LSP should have the path
   computation been successful.

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

   PCEP ERO sub-object types correspond to RSVP 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)

7.9.  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
   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 RRO sub-object already defined or that could be
   defined in the future for use in the 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 RRO.



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   PCEP RRO sub-object types correspond to RSVP 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)

7.10.  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 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) that
   could not be satisfied).  Most of the fields of the LSPA object are
   identical to the fields of the SESSION-ATTRIBUTE 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
   Setup Prio (Setup Priority - 8 bits).  The priority of the session
   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.




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   Holding Prio (Holding Priority - 8 bits).  The priority of the
   session 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

   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].

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

   Note that the Optional TLV field may contain additional TE LSP
   attributes as defined in [RFC4420].

7.11.  IRO Object

   The IRO (Include Route Object) object is optional and can be used to
   specify that the computed path MUST traverse a set of specified
   network elements.  The IRO object 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 PCE 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 object body format
   Subobjects The IRO object is made of sub-object(s) identical to the
   ones defined in [RFC3209], [RFC3473] and [RFC3477] for use in EROs.

   The following subobject types are supported.






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   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 object.

7.12.  SVEC Object

7.12.1.  Notion of Dependent and Synchronized path computation requests

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

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

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

   Consider the case of a set of N TE LSPs for which a PCC needs to send
   path computation requests to a PCE.  The first solution consists of
   sending N separate PCReq messages to the selected PCE.  In this case,
   the path computation requests are non synchronized.  Note that the
   PCC may chose to distribute the set of N requests across K PCEs for
   load balancing purpose.  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 PCRep
   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



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   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).

7.12.2.  SVEC Object

   Section 7.12.1 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



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   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 object body is as follows:
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Reserved    |                   Flags                 |S|N|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Request-ID-number #1                      |                                                               |
//                                                             //
|                     Request-ID-number #M                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 18: SVEC body object format

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

   Flags: Defines the potential dependency between the set of path
   computation requests.

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

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

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

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




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   The flags defined above are not exclusive.

7.12.3.  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.  In the later case, it is
   RECOMMENDED for the PCE to implement a local timer 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).  In this case the PCE MUST cancel the whole set of
   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.

7.13.  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.















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   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

   Reserved (8 bits): This field 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.

   Flags: no flags are currently defined.

   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).
         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).  Such event could be triggered because of
         external conditions such as the receipt of a positive reply
         from another PCE (should the PCC have sent multiple requests to
         a set of PCEs for the same path computation request), a network
         event such as a network failure rendering the request obsolete
         or any other event(s) 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 notification is received by a
         PCC from a PCE, the PCC MUST silently ignore the notification



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         and no errors should be generated.

      *  Notification-value=2: PCE cancels a set of pending request(s).
         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 congested 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-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: PCE congestion

      *  Notification-value=1.  A Notification-type=2, Notification-
         value=1 indicates to the PCC(s) that the PCE is currently in a
         congested state.  If no RP objects are comprised in the PCNtf
         message, this indicates that no other requests SHOULD be sent
         to that PCE until the congested state is cleared: the pending
         requests are not affected and will be served.  If some pending
         requests cannot be served due to the congested state, the PCE
         MUST also include a set of RP object(s) 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.
















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Optionally, a TLV named CONGESTION-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 CONGESTION-DURATION TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, 2 octets
for an "Unused" field (the value of which MUST be set to 0), followed by
a fix length value field of 4 octets specifying the estimated PCE
congestion duration in seconds. The CONGESTION-DURATION TLV is padded
to eight-octet alignment.

TYPE: To be assigned by IANA
LENGTH: 4
VALUE: estimated congestion duration in seconds

      *  If a new PCEP session is established while the PCE is in
         congested state, the PCE MUST immediately send a PCNtf with
         Notification-type=2, Notification-value=1 along with the
         optional CONGESTION-DURATION TLV.

      *  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 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
         a CONGESTION-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.

7.14.  PCEP-ERROR Object

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




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   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
   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.

   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.  No TLV is
   currently defined.

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










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   For each PCEP error, an Error-type and an Error-value are defined.
Error-Type    Meaning
   1          PCEP session establishment failure
               Error-value=1: reception of a malformed 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)
               Error-value=3: END-POINTS object missing
   7          Synchronized path computation request missing
   8          Unknown request reference
   9          DeadTimer expired
   10         Attempt to establish a second PCEP session

   Error-Type=1: PCEP session establishment failure.

   If a malformed Open 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 for details).

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



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   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=2 and 3 respectively).
   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) 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



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   computation requests listed within the corresponding SVEC object
   after the expiration of the timer SyncTimer defined in
   Section 7.12.3, 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) (defined below) that identifies the
   missing request(s).

The REQ-MISSING TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, 2 octets
for an "Unused" field (the value of which MUST be set to 0), followed by
a fix length value field of 4 octets specifying the request-id-number
that correspond to the missing request. The REQ-MISSING TLV is padded
to eight-octet alignment.

TYPE: To be assigned by IANA
LENGTH: 4
VALUE: 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=7).  In addition, the PCC MUST include
   in the PCErr message the unknown RP object.

   Error-Type=9: If a PCEP peer does not receive any PCEP message
   (Keepalive, PCReq, PCRep, PCNtf) during the DeadTimer period, the
   PCEP peer MUST send a PCErr message with a PCEP-ERROR object (Error-
   type=9, Error-value=1).  The PCEP session MUST be terminated
   according to the procedure defined in Section 6.8.

   Error-Type=10: 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.

7.15.  LOAD-BALANCING Object

   There are situations where no TE LSP with a bandwidth of X could be
   found by a PCE while such bandwidth requirement could be satisfied by
   a set of TE LSPs such that the sum of their bandwidths is equal to X.
   Thus it might be useful for a PCC to request a set of TE LSPs so that
   the sum of their bandwidth is equal to X 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.



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   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

   Reserved : This field MUST be set to zero on transmission and MUST be
   ignored on receipt.

   Flags ()

   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 octets.

   If a PCC requests the computation of a set of TE LSP(s) 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 object with the Max-LSP and Min-Bandwidth fields set to N
   and B respectively.

7.16.  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)



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   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.  Three values are currently
   defined.

   Reasons
    Value        Meaning
      1          No explanation provided
      2          DeadTimer expired
      3          PCEP session characteristics negotiation failure
      4          Reception of a malformed PCEP message

   Reserved: This field MUST be set to zero on transmission and MUST be
   ignored on receipt.

   Flags (4 bits): No Flags are currently defined.

   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

   It is expected and required to specify a MIB for the PCEP
   communication protocol (in a separate document).  Furthermore,
   additional tools related to performance, fault and diagnostic
   detection are required which will also be specified in separate
   documents.


9.  IANA Considerations

9.1.  TCP Port

   PCEP will use a well-known TCP port to be assigned by IANA.





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9.2.  PCEP Messages

   Each PCEP message has a Message-Type.

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

9.3.  PCEP Object

   IANA assigns value to PCEP parameters.  Each PCEP object has an
   Object-Class and an Object-Type.

 Object-Class      Name

        1                 OPEN
                          Object-Type
                             1

        2                 RP
                          Object-Type
                             1

        3                 NO-PATH
                          Object-Type
                             1

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

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

        6                 METRIC
                          Object-Type
                             1

        7                 ERO



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                          Object-Type
                             1

        8                 RRO
                          Object-Type
                             1

        9                 LSPA
                          Object-Type
                             1

       10                 IRO
                          Object-Type
                             1

       11                 SVEC
                          Object-Type
                             1

       12                 NOTIFICATION
                          Object-Type
                             1

       13                 PCEP-ERROR
                          Object-Type
                             1

       14                 LOAD-BALANCING
                          Object-Type
                             1

       15                 CLOSE
                          Object-Type
                             1

9.4.  Notification

   A NOTIFICATION object is characterized by a Notification-type that
   specifies the class of notification and a Notification-value that
   provides additional information related to the nature of the
   notification.  Both the Notification-type and Notification-value are
   managed by IANA (see IANA section).









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Notification-type     Name
         1                    Pending Request cancelled
                               Notification-value
                                        1: PCC cancels a set of pending request(s)
                                        2: PCE cancels a set of pending request(s)
         2                    PCE Congestion
                               Notification-value
                                        1: PCE in congested state
                                        2: PCE no longer in congested state

9.5.  PCEP Error

   PCEP-ERROR objects are used to report a PCEP error and are
   characterized by an Error-Type which specifies the type of error and
   an Error-value that provides additional information about the error
   type.  Both the Error-Type and the Error-Value are managed by IANA.



































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   For each PCEP error, an Error-type and an Error-value are defined.
Error-Type    Meaning
   1          PCEP session establishment failure
               Error-value=1: reception of a malformed 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)
               Error-value=3: END-POINTS object missing
   7          Synchronized path computation request missing
   8          Unknown request reference
   9          DeadTimer expired
   10         Attempt to establish a second PCEP session

9.6.  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
   - Defining RFC - Name of bit





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   Currently two bits are defined.

   Here are the suggested values:

   0x01: PCE currently Unavailable
   0x02: Unknown Destination.


10.  PCEP Finite State Machine (FSM)

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

   PCEP Finite State Machine


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

   Figure 23: PCEP Finite State Machine for the PCC

   PCEP defines the following set of variables:



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

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

   TCPMaxRetry: Maximum number of times the system tries to establish a
   TCP connection using the PCEP well-known TCP port before going back
   to the Idle state.  The value of the TCPMaxRetry is 5.

   OpenWait: timer (in seconds) that corresponds to the amount of time a
   PCEP peer will wait to receive an Open message from the PCEP peer
   after the expiration of which the system releases the PCEP resource
   and go back to the Idle state.

   KeepWait: timer that corresponds to the amount of time a PCEP peer
   will wait to receive a KeepAlive or a PCErr message from the PCEP
   peer after the expiration of which the system releases the PCEP
   resource and go back to the Idle state.  The KeepWait timer has a
   fixed value of 1 minute.

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

   The following two states variable are defined:

   RemoteOK: the 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 message acknowledging 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,




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   LocalOK=0,

   RemoteOK=0,

   OpenRetry=0.

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

   o  Starts the TCPConnect timer,

   o  Initiates of a TCP connection with the PCEP peer,

   o  Increments the TCPRetry variable,

   o  Moves to the TCPPending state.

   Upon receiving a TCP connection on the well-known PCEP TCP port, if
   the PCE is in congested state, the PCE MUST immediately send a PCErr
   with Notification-type=2, Notification-value=1 along with the
   optional CONGESTION-DURATION TLV (see Section 7.13).

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

   o  Sends an Open message,

   o  Starts the OpenWait timer,

   o  Stars the KeepWait timer,

   o  Moves to the OpenWait state.

   It is expected that an implementation will 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,





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   o  Starts the KeepWait timer,

   o  Moves to the OpenWait state.

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

   If TCPRetry =TCPMaxRetry the system moves to the Idle State

   If TCPRetry < TCPMaxRetry the system:

   o  Starts the TCPConnect timer,

   o  Initiates of a TCP connection with the PCEP peer,

   o  Increments the TCPRetry variable,

   o  Stays in the TPCPending state.

   If the system detects that the PCEP peer tries to simultaneously
   establish a TCP connection, it stops the TCP connection establishment
   if and only if the PCEP peer has a higher IP address and moves to the
   Idle state.  This guarantees that in case of "collision" a single TCP
   connection is established.

   OpenWait State:

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

   If the system receives an Open message from the PCEP peer before the
   expiration of the OpenWait timer, PCEP checks the PCEP session
   attributes (Keepalive frequency, DeadTimer, ...).

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

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

   If OpenRetry=2, the PCEP peer sends a PCErr with Error-Type=1 and
   Error-value=5, the system releases the PCEP resources for that peer,
   and moves back to the Idle state.

   If no errors are detected and the session characteristics are



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   acceptable to the local system, the system:

   o  Sends a Keepalive message to the PCEP peer,

   o  Starts the Keepalive timer,

   o  Sets the RemoteOK variable to 1.

   If LocalOK=1 the system moves to the UP state.

   If LocalOK=0 the system moves to the KeepWait state.

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

   If no errors are detected, OpenRetry=1, the session characteristics
   are unacceptable but negotiable (such as the Keepalive frequency or
   the DeadTimer), the system:

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

   o  If LocalOK=1, the system stays in the OpenWait state

   o  If LocalOK=0, the system moves to the KeepWait state

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

   KeepWait State

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

   If a Keepalive message is received before the expiration of the
   KeepWait timer, LocalOK=1

   If RemoteOK=1, the system moves to the UP state.

   If RemoteOK=0, the system moves to the OpenWait State.

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



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   timer:

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

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

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

   If no PCEP message (Keepalive, PCReq, PCRep, PCNtf) is received from
   the PCEP peer after the expiration of the DeadTimer, the systems
   sends a PCErr message with a PCEP-ERROR object (Error-type=9, Error-
   value=1), terminates PCEP session according to the procedure defined
   in Section 6.8, releases the PCEP resources for that PCEP peer,
   closes the TCP connection and moves to the Idle State.

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

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


11.  Security Considerations

   PCEP could be the target of the following attacks:




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   o  Spoofing (PCC or PCE impersonation)

   o  Snooping (message interception)

   o  Falsification

   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 to ensure
   authentication, integrity and privacy of PCEP Communications, and
   also to protect against DoS attacks.

11.1.  PCEP Authentication and Integrity

   It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option to
   provide for the authenticity and integrity of PCEP messages.  This
   will allow protecting against PCE or PCC impersonation and also
   against message content falsification.

   This requires the maintenance, exchange and configuration of MD-5
   keys on PCCs and PCEs.  Note that such maintenance may be especially
   onerous to the operators as pointed out in
   [I-D.ietf-rpsec-bgpsecrec].  Hence it is important to limit the
   number of keys while ensuring 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
   and implemented, PCEP could be easily upgraded to use it.

11.2.  PCEP Privacy

   Ensuring PCEP communication privacy is of key importance, especially
   in an inter-AS context, where PCEP communication end-points do not
   reside in the same AS, as an attacker that intercept a PCE message
   could obtain sensitive information related to computed paths and
   resources.  Privacy can be ensured thanks to encryption.  To ensure
   privacy of PCEP communication, IPSec [RFC2406] tunnels MAY be used
   between PCC and PCEs or between PCEs.  Note that this could also be
   used to ensure Authentication and Integrity, in which case, TCP MD-5
   option would not be required.

11.3.  Protection against Denial of Service attacks

   PCEP can be the target of TCP DoS attacks, such as for instance SYN
   attacks, as all protocols running on top of TCP.  PCEP can use the
   same mechanisms as defined in [RFC3036] to mitigate the threat of



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   such attacks:

   o  A PCE should avoid promiscuous TCP listens for PCEP TCP session
      establishment.  It should use only listens that are specific to
      authorized PCCs.

   o  The use of the MD5 option helps somewhat since it prevents a SYN
      from being accepted unless the MD5 segment checksum is valid.
      However, the receiver must compute the checksum before it can
      decide to discard an otherwise acceptable SYN segment.

   o  The use of access-list on the PCE so as to restrict access to
      authorized PCCs.

11.4.  Request input shaping/policing

   A PCEP implementation may be subject 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, a PCE implementation should implement request input
   shaping/policing so as to throttle the amount of received PCEP
   messages without compromising the implementation behavior.


12.  Authors' addresses

   This document was the collective work of several authors.  The
   content of this document was contributed by the editors 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



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   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 and Jon Parker for their very valuable input.  Special thank
   to Adrian Farrel for his very valuable suggestions.


14.  References







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14.1.  Normative References

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

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

   [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.

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

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

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

14.2.  Informative References

   [I-D.ietf-ccamp-inter-domain-rsvp-te]
              Ayyangar, A. and J. Vasseur, "Inter domain MPLS and GMPLS
              Traffic Engineering - RSVP-TE extensions",
              draft-ietf-ccamp-inter-domain-rsvp-te-04 (work in
              progress), January 2007.

   [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-01 (work in progress),
              December 2006.



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   [I-D.ietf-pce-disco-proto-ospf]
              Roux, J., "OSPF protocol extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-ospf-01 (work in progress),
              December 2006.

   [I-D.ietf-pce-inter-layer-req]
              Oki, E., "PCC-PCE Communication Requirements for Inter-
              Layer Traffic Engineering",
              draft-ietf-pce-inter-layer-req-03 (work in progress),
              October 2006.

   [I-D.ietf-pce-interas-pcecp-reqs]
              Bitar, N., "Inter-AS Requirements for the Path Computation
              Element Communication  Protocol (PCECP)",
              draft-ietf-pce-interas-pcecp-reqs-01 (work in progress),
              October 2006.

   [I-D.ietf-pce-pcecp-interarea-reqs]
              Roux, J., "PCE Communication Protocol (PCECP) Specific
              Requirements for Inter-Area  Multi Protocol Label
              Switching (MPLS) and Generalized MPLS (GMPLS) Traffic
              Engineering", draft-ietf-pce-pcecp-interarea-reqs-05 (work
              in progress), December 2006.

   [I-D.ietf-rpsec-bgpsecrec]
              Christian, B. and T. Tauber, "BGP Security Requirements",
              draft-ietf-rpsec-bgpsecrec-06 (work in progress),
              June 2006.

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

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

   [RFC2406]  Kent, S. and R. Atkinson, "IP Encapsulating Security
              Payload (ESP)", RFC 2406, November 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., and
              T. Telkamp, "Use of Interior Gateway Protocol (IGP) Metric
              as a second MPLS Traffic Engineering (TE) Metric", BCP 87,
              RFC 3785, May 2004.

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



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              June 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.


Appendix A.  Compliance with the PCECP Requirement Document

   The aim of this section is to list the set of requirements set forth
   in [RFC4657] that are not satisfied by the current revision of this
   document.  This only concerns the requirements listed as MUST
   according to [RFC2119].

   Here is the list of currently unsatisfied requirements:

   o  Allow to select/prefer from advertised list of standard objective
      functions/options

   o  Allow to customize objective function/options

   o  Support "unsynchronized" & "synchronized" objective functions

   PCEP is a flexible protocol allowing for the addition of new message
   and objects type.  With regards to the requirement liste above, the
   Working Group has decided to cover those requirements in a separate
   document.


Appendix B.  PCEP Variables

   PCEP defines the following configurable variables:

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

   DeadTimer: period of timer after the expiration of which a PCEP peer
   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 7.12.3.
   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



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   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, Inc
   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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Full Copyright Statement

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