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Versions: (draft-leroux-pce-of) 00 01 02 03 04 05 06 RFC 5541

Network Working Group                                       J.L. Le Roux
Internet Draft                                            France Telecom
Category: Standard Track
Expires: August 2008                                        J.P. Vasseur
                                                       Cisco System Inc.

                                                                  Y. Lee
                                                                  Huawei





                                                              March 2008


       Encoding of Objective Functions in Path Computation Element
                    communication Protocol (PCEP)

                     draft-ietf-pce-of-02.txt


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Abstract

   The computation of one or a series of Traffic Engineering Label
   Switched Paths (TE LSPs) in MultiProtocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks, is subject to a set of one or more
   specific optimization criteria(s), referred to as an objective
   function (e.g. minimum cost path, widest path, etc.). A Path
   Computation Element (PCE) may support one or multiple objective
   functions, and it is desired for a Path Computation Client (PCC) to
   automatically discover the set of objective functions supported by a
   PCE. Furthermore, it may be useful for a PCC to specify in a path
   computation request the required objective function to be used by the
   PCE to compute a TE LSP or a set of TE LSPs. Thus the aim of this
   document is to define extensions to the PCE communication Protocol
   (PCEP) in order to allow a PCC to discover the set of objective
   functions supported by a PCE as well as to allow a PCC to indicate in
   a path computation request the required objective function and a PCE
   to indicate in a path computation reply the objective function that
   was used for path computation.

Conventions used in this document

   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.

Table of Contents

   1.      Terminology.................................................3
   2.      Introduction................................................3
   3.      Discovery of PCE Objective Functions........................5
   3.1.    OF-List TLV.................................................5
   3.2.    Elements of procedure.......................................6
   4.      Objective Function in PCEP Path Computation request and
             reply messages............................................6
   4.1.    OF Object...................................................6
   4.1.1.  Elements of Procedure.......................................7
   4.2.    Carrying the OF object in a PCEP message....................8
   4.3.    New RP object flag.........................................10
   4.3.1.  Elements of procedure......................................10
   5.      Objective Functions definition.............................10
   6.      IANA Considerations........................................12
   6.1.    PCE Objective Function registry............................12
   6.2.    PCEP code points...........................................13
   6.2.1.  OF Object..................................................13
   6.2.2.  OF-List TLV................................................13
   6.2.3.  PCEP Error values..........................................13
   6.2.4.  RP Object flag.............................................14
   7.      Security Considerations....................................14
   8.      Manageability Considerations...............................14
   8.1.    Control of Function and Policy.............................14

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   8.2.    Information and Data Models................................14
   8.3.    Liveness Detection and Monitoring..........................15
   8.4.    Verify Correct Operations..................................15
   8.5.    Requirements on other protocols............................15
   8.6.    Impact on network operations...............................15
   9.      Acknowledgments............................................15
   10.     References.................................................15
   10.1.   Normative references.......................................15
   10.2.   Informative references.....................................16
   11.     Author's Addresses:........................................16
   12.     Intellectual Property Statement............................17


 1. Terminology

   Terminology used in this document

      LSR: Label Switching Router.

      OF: Objective Function: A set of one or more optimization
      criteria(s) used for the computation of a single path (e.g. path
      cost minimization), or the synchronized computation of a set of
      paths (e.g. aggregate bandwidth consumption minimization, etc.).

      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: Path Computation Element communication Protocol.

      TE LSP: Traffic Engineered Label Switched Path.

 2. Introduction

   The PCE-based network architecture [RFC4655] defines a Path
   Computation Element (PCE) as an entity capable of computing TE LSP
   paths based on a network graph, and applying computational
   constraints.  A PCE serves path computation requests sent by Path
   Computation Clients (PCC).

   The PCE communication Protocol (PCEP), defined in [PCEP], allows for
   communication between a PCC and a PCE or between two PCEs, in
   compliance with requirements and guidelines set forth in [RFC4657].
   Such interactions include path computation requests and path
   computation replies.

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   The computation of one or a set of TE LSPs is subject to a set of one
   or more optimization criteria(s), called an objective function. An
   objective function is used by the PCE, when it computes a path or a
   set of paths, in order to select the "best" candidate path(s). There
   is a variety of objective functions: an objective function could
   apply either to a set of non synchronized path computation requests,
   or to a set of synchronized path computation requests. In the former
   case, the objective function refers to an individual path computation
   request (e.g. computation of the shortest constrained path where the
   metric is the IGP metric, computation of the least loaded constrained
   path, etc.). Conversely in the latter case, the objective function
   refers to a set of path computation requests the computation of which
   is synchronized (e.g. minimize the aggregate bandwidth consumption of
   all LSPs, minimize the sum of the delays for two diverse paths, or
   the delta between those delays, etc.). Moreover, some objective
   functions relate to the optimization of a single metric and others to
   the optimization of a set of metrics (organized in a hierarchical
   manner, using a weighted function, etc.).

   As spelled out in [RFC4674], it may be useful for a PCC to discover
   the set of objective functions supported by a PCE. Furthermore,
   [RFC4657] requires the ability for a PCC to indicate in a path
   computation request a required/desired objective function, as well as
   optional function parameters.

   For these purposes, this document extends the PCE communication
   Protocol (PCEP). It defines PCEP extensions allowing a PCE
   advertising a list of supported objective functions, as well as
   extensions so as to carry the objective function in PCEP request and
   reply messages. It thus complements the PCEP base specification
   [PCEP].

   Note that IS-IS and OSPF based PCE Discovery mechanisms are defined
   in ([RFC5089], [RFC5088]). These mechanisms are dedicated to the
   discovery of a few generic parameters while more detailed PCE
   parameters should rather be discovered using the PCE communication
   Protocol. Objective functions pertain to this second category; thus
   the Objective Function discovery procedure is handled by PCEP.

   A new PCEP TLV, named the OF-List TLV is defined in section 3. The
   OF-List TLV is carried in the PCEP OPEN object and allows a PCE
   advertising to a PCEP peer, during PCEP session setup phase, the list
   of objective functions that it supports.

   A new PCEP object, the OF object, is defined in section 4. The OF
   object is carried within a PCReq message to indicate the
   required/desired objective function to be applied by a PCE or in a
   PCRep message to indicate the objective function that was used for
   path computation.



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   Six mandatory objective functions that must be supported by PCEP are
   listed in [RFC4657]. This document provides a definition of these six
   mandatory objective functions. Additional objective functions may be
   defined in other documents. Note that additional objective functions
   are defined for PCE Global Concurrent Optimization (GCO) application,
   in [PCE-GCO].


 3. Discovery of PCE Objective Functions

   This section defines PCEP extensions (see [PCEP]) so as to support
   the advertisement of the objective functions supported by a PCE.

   A new PCEP OF-List (Objective Function list) TLV is defined. The PCEP
   OF-List TLV is carried within an OPEN object, in order for a PCE to
   advertise to a PCEP peer the list of objective functions it supports,
   during PCEP session setup phase.

 3.1. OF-List TLV

   The PCEP OF-List TLV is optional. It MAY be carried within an OPEN
   object sent by a PCE in an Open message to a PCEP peer, so as to
   indicate the list of supported objective functions.

   The OF-List TLV format is compliant with the PCEP TLV format defined
   in [PCEP]. That is, the TLV is composed of 2 octets for the type, 2
   octets specifying the TLV length, and a value field. The Length field
   defines the length of the value portion in octets. The TLV is padded
   to four-octet alignment and padding is not included in the Length
   field (e.g. a three octet value would have a length of three, but the
   total size of the TLV would be eight octets).

   The OSPF OF-List TLV has the following format:

         TYPE: To be assigned by IANA  (suggested value = 4 )
         LENGTH: N * 2 (where N is the number of objective functions)
         VALUE: list of 2-bytes objective function code points,
                identifying the objective functions supported by the
                sender of the Open message.

      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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             OF Code #1        |      OF Code #2               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                                                             //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             OF Code #N        |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   OF Code (2 bytes): Objective Function code point identifier.

   IANA is requested to manage the PCE objective function code point
   registry (see IANA section).


 3.2. Elements of procedure

   A PCE MAY include and OF-List TLV within an OPEN object in an Open
   message sent to a PCEP peer, to advertise a set of one or more
   objective functions. The OF-List TLV MUST NOT appear more than once
   in an OPEN object. The absence of the OF-List TLV in an OPEN object
   must be interpreted as an absence of information on the list of
   supported objective functions by the PCE.

   As specified in [PCEP], a PCEP peer that does not recognize the OF-
   List TLV will silently ignore it.


 4. Objective Function in PCEP Path Computation request and reply
    messages

   This section defines PCEP extensions ([PCEP]) so as to support the
   communication of objective functions in PCEP path computation request
   and reply messages. A new PCEP OF (Objective Function) object is
   defined, to be carried within a PCReq message in order for the PCC to
   indicate the required/desired objective function.

   The PCEP OF Object may also be carried within a PCRep message in
   order for the PCE to indicate the objective function that was used by
   the PCE.

   A new flag is defined in the RP object, so as to indicate in a PCReq
   message that the PCE MUST provide in the PCRep message the objective
   function that was used during path computation.

   Also new PCEP error type and value are defined.

 4.1. OF Object

   The PCEP OF (Objective Function) object is optional. It MAY be
   carried within a PCReq message so as to indicate the desired/required
   objective function to be applied by the PCE during path computation,
   or within a PCRep message so as to indicate the objective function
   that was used by the PCE during path computation.

   The OF object format is compliant with the PCEP object format defined
   in [PCEP].

   The OF Object-Class is to be assigned by IANA (recommended value=21).

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   The OF Object-Types is to be assigned by IANA (recommended value=1).


   The format of the OF 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Objective Function Code(IANA)  |     Reserved                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //              Optional TLV(s)                                //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Objective Function Code (2 bytes): The identifier of the Objective
   Function. The IANA is requested to manage the PCE objective function
   code point registry (see IANA section).

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

   Optional TLVs may be defined so as to encode objective function
   parameters.

 4.1.1. Elements of Procedure

   To request the use of a specific objective function to be used by the
   PCE a PCC MUST include an OF object in the PCReq message.

   [PCEP] specifies a bit flag referred to as the P bit in a PCEP
   common header that can be set by a PCC to enforce a PCE to take into
   account the related information during the path computation. If the
   objective function is mandatory (required objective function), the P
   bit in the OF object MUST be set, else if it is optional (desired
   objective function) the P bit MUST be cleared.

   On receipt of a PCReq message with an OF object, a PCE MUST proceed
   as follows:

        - If the OF object is unknown/unsupported, the PCE MUST follow
          procedures defined in [PCEP], that is if the P bit is set, it
          sends a PCErr message with error type unknown/unsupported
          object (type 3 and 4) and the related path computation request
          MUST be discarded. If the P bit is cleared it is free
          to ignore the object.

        - If the objective function is unknown / unsupported and the P
          bit is set, the PCE MUST send a PCErr message with a new PCEP
          error type "objective function error" and error value
          "unknown/unsupported objective function" (defined in this

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          document), and the related path computation request MUST be
          discarded.

        - If the objective function is unknown / unsupported and the P
          bit is cleared, the PCE SHOULD apply another (default)
          objective function.

        - If the objective function is supported but policy does not
          permit applying it, and the P bit is set, the PCE MUST send a
          PCErr message with the PCEP error type "policy-violation"
          (type 5) and a new error value "objective function not
          allowed" (defined in this document).

        - If the objective function is supported but policy does not
           allow applying it, and the P bit is cleared, the PCE SHOULD
           apply another (default) objective function.

        - If the objective function is supported and policy allows
          applying it, then if the P bit is set the PCE MUST apply the
          requested objective function, else if the P bit is cleared the
          PCE is free to apply any other objective function.

        The default objective function may be locally configured.


 4.2. Carrying the OF object in a PCEP message

   The OF object MAY be carried within a PCReq message. An OF object
   specifying an objective function that applies to a set of
   synchronized path computation requests MUST be carried just after the
   corresponding SVEC object, and MUST NOT be repeated for each
   elementary request.

   An OF object specifying an objective function that applies to an
   individual path computation request (non synchronized case) MUST
   follow the RP object for which it applies.

   The format of the PCReq message is updated as follows:

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

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

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

         <request>::= <RP>
                      <END-POINTS>

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                      [<OF>]
                      [<LSPA>]
                      [<BANDWIDTH>]
                      [<metric-list>]
                      [<RRO>]
                      [<IRO>]
                      [<LOAD-BALANCING>]
      where:

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


   The OF object MAY be carried within a PCRep message to indicate the
   objective function used by the PCE during path computation.

   When the PCE wants to indicate to the PCC the objective function that
   was used for the synchronized computation of a set of paths, the
   PCRep message MUST include the corresponding SVEC object directly
   followed by the OF object, which MUST NOT be repeated for each
   elementary request.
   An OF object specifying an objective function used for an individual
   path computation (non synchronized case) MUST follow the RP object
   for which it applies.

   The format of the PCRep message is updated as follows:

   <PCRep Message> ::= <Common Header>
                      [<SVEC-list>]
                       <response-list>

      where:

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

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

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

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

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

    where:

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

    Note: The OF object MUST NOT be associated to a negative reply, i.e.
    a reply with a NO-PATH object.

 4.3. New RP object flag

   In some cases, where no objective function is specified in the
   request, or an optional objective function is desired (P flag cleared
   in the OF object common header) but the PCE does not follow the
   recommendation, the PCC may desire to know the objective function
   that was used by the PCE during path computation. To that end, a new
   flag is defined in the RP object, named the OF flag, allowing a PCC
   to request for the inclusion in the path computation reply of the
   objective function that was used by the PCE during path computation.

   The following new bit flag of the RP object is defined:

   Objective Function (OF) flag (1 bit): 0x200 (bit number 16)
   (suggested value, to be assigned by IANA).  When set in a PCReq
   message, this indicates that the PCE has to provide the applied
   objective function (should a path satisfying the constraints be found)
   in the PCRep message. When set in a PCRep message this indicates that
   the Objective Function that was used during path computation is
   included.


 4.3.1. Elements of procedure

   If the PCC wants to know the objective function used by the PCE
   during path computation for a given request, it MUST set the OF flag
   in the RP object.

   On receipt of a PCReq message with the OF flag in the RP object set,
   the PCE has to proceed as follows:

        - If policy permits it MUST include in the PCRep message an OF
          object indicating the objective function it used during path
          computation.

        - If policy does not permit, it MUST send a PCErr message with
          the PCEP error code "policy-violation" (type 5) and a new
          error value "objective function indication not allowed"
          (defined in this document).

 5. Objective Functions definition

   Six objective functions that must be supported by PCEP are listed in
   [RFC4657]. Objective function codes should be assigned by IANA and
   are suggested below.

   Objective functions are formulated using the following terminology:

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        - a network comprises a set of N links {Li, (i=1...N)}
        - a path P is a list of K links {Lpi,(i=1...K)}
        - metric of link L is noted M(L), this can be the IGP metric the
          TE metric or any other metric.
        - the cost of a path P is noted C(P),
          C(P) = sum {M(Lpi), (i=1...K)}.
        - residual bandwidth on link L is noted r(L)
        - maximum reservable bandwidth on link L is noted R(L).

   There are three objective functions that apply to the computation of
   a single path:

   Objective Function Code: 1 (suggested value, to be assigned by IANA)
   Name: Minimum Cost Path (MCP)
   Description: Find a path P such that C(P) is minimized.

   Objective Function Code: 2 (suggested value, to be assigned by IANA)
   Name: Minimum Load Path (MLP)
   Description: Find a path P such that ( Max {(R(Lpi) - r(Lpi)) /
   R(Lpi), i=1...K } ) is minimized

   Objective Function Code: 3 (suggested value, to be assigned by IANA)
   Name: Maximum residual Bandwidth Path (MBP)
   Description: Find a path P such that ( Min { r(Lpi)), i=1...K } )  is
   maximized.

   There are three objective functions that apply to a set of path
   computation requests the computation of which is synchronized:

   Objective Function Code: 4 (suggested value, to be assigned by IANA)
   Name: Minimize aggregate Bandwidth Consumption (MBC)
   Description: Find a set of paths such that ( Sum {R(Li) - r(Li),
   i=1...N} ) is minimized.

   Objective Function Code: 5 (suggested value, to be assigned by IANA)
   Name: Minimize the Load of the most loaded Link (MLL)
   Description: Find a set of paths such that ( Max { (R(Li) - r(Li)) /
   R(Li), i=1...N}) is minimized.

   Objective Function Code: 6 (suggested value, to be assigned by IANA)
   Name: Minimize the Cumulative Cost of a set of paths (MCC)
   Description: Find a set of paths {P1...Pm} such that (Sum { C(Pi),
   i=1...m}) is minimized.

   Other objective functions may be defined in separate documents.








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 6. IANA Considerations

 6.1. PCE Objective Function registry

   This document defines a 16-bit PCE Objective Function identifier to
   be carried within the PCEP OF object, as well as the PCEP OF-List TLV.

   IANA is requested to create and manage the 16-bit "PCE Objective
   Function" code point registry, starting from 1 and continuing through
   32767, as follows:

   - Objective Function code point value
   - Objective Function name
   - Defining RFC

   The same registry is applicable to the OF object and the OF-List TLV
   defined in this document.

   The guidelines (using terms defined in [RFC2434]) for the
   assignment of objective function code point values are as follows:

      - Function code value 0 is reserved.
      - Function code value in the range 1-32767 are to be assigned as
        follows:
            - Function code values 1 through 1023 are to be assigned by
              IANA using the "IETF Consensus" policy.
            - Function code values 1024 through 32767 are to be
              assigned by IANA, using the "First Come First Served"
              policy.
       - Function code values in the range 32768-65535 are for
         "Private Use".

   Six objective functions are defined in section 5 of this document and
   should be assigned by IANA:

   Code Point           Name                    Defining RFC

       1                MCP                       this doc
       2                MLP                       this doc
       3                MBP                       this doc
       4                MBC                       this doc
       5                MLL                       this doc
       6                MCC                       this doc






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 6.2. PCEP code points

 6.2.1. OF Object

     The IANA has been requested to manage the PCEP Objects code point
     registry (see [PCEP]).

     This document defines a new PCEP object, the OF object, to be
     carried in PCReq and PCRep messages. The IANA is requested to make
     the following allocation (suggested value):

      Object    Name     Object    Name         Reference
      Class              Type

        21       OF        1       Objective    (this document)
                                   Function

 6.2.2. OF-List TLV

   IANA is requested to manage the PCEP TLV code point registry (see
   [PCEP]).
   This document defines a new PCEP TLV, the OF-List TLV, to be carried
   in the OPEN object. The IANA is requested to make the following
   allocation (suggested value):

      Type      TLV name                   References
      -----     --------                   ----------
       4         OF-List                   (This document)


 6.2.3. PCEP Error values

   A new PCEP Error-Type is defined in this document, with two error
   values (Error-Type and Error-value to be assigned by IANA):

    Error-type      Meaning and error values                Reference

        14           Objective Function Error                (this doc)
                     Error-value=1: unknown objective function
                     (request rejected)
                     Error-value=2: unsupported objective function
                     (request rejected)

   Two new error values are defined for the error type "policy
   violation" (type 5):

   Error-type      Meaning and error values                  Reference

       5         Policy violation
                 Error-value=3: objective function not allowed (this doc)
                  (request rejected)

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                 Error-value=4: OF bit of the RP object set    (this doc)
                  (request rejected)


 6.2.4. RP Object flag

   A new flag of the RP object (specified in [PCEP]) is defined in this
   document. The IANA is requested to make the following allocation
   (suggested value):

   Bit      Hex     Name      Reference
   Number

    16      0x200   OF       (this document)


 7.                    Security Considerations

Mechanisms discussed in [PCEP] to secure a PCEP session can be used to
secure the PCEP OF object and OF list TLV as well.

 8. Manageability Considerations

 8.1. Control of Function and Policy

   It MUST be possible to configure the activation/deactivation of
   Objective Function Discovery in PCEP.

   In addition to the parameters already listed in section 8.1 of [PCEP],
   a PCEP implementation SHOULD allow configuring on a PCE a list of
   authorized objective functions. This may apply to any session the
   PCEP speaker participates in, to a specific session with a given PCEP
   peer or to a specific group of sessions with a specific group of PCEP
   peers.

   Note that it is not mandatory for an implementation to support all
   objective functions defined in section 5.

   It MUST be possible to configure a default objective function used
   for path computation when a path request is received that requests to
   use an optional objective function.

 8.2. Information and Data Models

   The PCEP MIB Module defined in [PCEP-MIB] MUST be extended to include
   Objective Functions.






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 8.3. Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [PCEP].

 8.4. Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [PCEP].

 8.5. Requirements on other protocols

   Mechanisms defined in this document do not imply any requirements on
   other protocols in addition to those already listed in [PCEP].

 8.6. Impact on network operations

   Mechanisms defined in this document do not have any impact on network
   operations in addition to those already listed in [PCEP].


 9. Acknowledgments

   The authors would like to thank Jerry Ash and Fabien Verhaeghe for
   their useful comments.

 10. References

 10.1. Normative references

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

   [RFC2740] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
   RFC 2740, December 1999.

   [RFC3630] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
   Extensions to OSPF Version 2", RFC 3630, September 2003.

   [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic
   Engineering", RFC 3784, June 2004.

   [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
   Element (PCE)-based Architecture", RFC4655, august 2006.

   [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE)
   communication Protocol (PCEP)", draft-ietf-pce-pcep, work in
   progress.



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 10.2. Informative references

   [RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
   Generic Requirements", RFC4657, September 2006.

   [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
   RFC4674, October 2006.

   [RFC5089] Le Roux, Vasseur, et al. "IS-IS protocol extensions for
   Path Computation Element (PCE) Discovery", RFC5089,
   January 2008.

   [RFC5088] Le Roux, Vasseur, et al. "OSPF protocol extensions for
   Path Computation Element (PCE) Discovery", RFC5088,
   January 2008.

   [PCE-GCO] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
   Computation Element Communication Protocol (PCECP) Requirements and
   Protocol Extensions In Support of Global Concurrent Optimization",
   draft-ietf-pce-global-concurrent-optimization, work in
   progress



 11. Author's Addresses:

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   Email: jeanlouis.leroux@orange-ftgroup.com

   Jean-Philippe Vasseur
   Cisco Systems, Inc.
   1414 Massachusetts avenue
   Boxborough , MA - 01719
   USA
   Email: jpv@cisco.com

   Young Lee
   Huawei Technologies, LTD.
   1700 Alma Drive, Suite 100
   Plano, TX  75075
   USA
   Email: ylee@huawei.com






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