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Versions: 00 01 02 03 04 05 draft-ietf-pce-wson-routing-wavelength

Network Working Group                                          Y. Lee
Internet Draft                                                 Huawei
Intended status: Standard Track
Expires: August 2008                                      G. Bernstein
                                                     Grotto Networking

                                                     February 18, 2008


      PCEP Requirements and Extensions for WSON Routing and Wavelength
                                Assignment


               draft-lee-pce-wson-routing-wavelength-01.txt


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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This memo provides application-specific requirements and protocol
   enhancements for the Path Computation Element communication Protocol
   (PCEP) for the support of Wavelength Switched Optical Networks (WSON).



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   Lightpath provisioning in WSONs requires a routing and wavelength
   assignment (RWA) process.  From a path computation perspective,
   wavelength assignment is the process of determining which wavelength
   can be used on each hop of a path and forms an additional routing
   constraint to optical light path computation. Different computational
   architectures for the RWA process are given and the PCEP extensions
   needed to support these architectures are defined.





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 0.

Table of Contents


   1. Introduction................................................3
   2. Background: RWA Computation Architectures....................4
   3. PCECP Requirements..........................................5
      3.1. RWA Computation Options.................................5
      3.2. Optimization Degree.....................................6
      3.3. Wavelength Assignment and Wavelength Set Information.....7
      3.4. Lightpath Route Parameters..............................7
      3.5. Timeliness Characteristics of Lightpath.................7
      3.6. Duration of Lightpath...................................8
      3.7. Wavelength Selection Preference.........................8
   4. Protocol Extensions for Support of WSON RWA..................9
      4.1. RWA Computation Options.................................9
      4.2. Lightpath Route Parameter TLV..........................10
      4.3. Wavelength Selection Preferences.......................11
      4.4. Wavelength Suggestion/Restriction TLV..................12
      4.5. Error Indicator........................................13
      4.6. NO-PATH Indicator......................................13
   5. Manageability Considerations................................13
      5.1. Control of Function and Policy.........................14
      5.2. Information and Data Models, e.g. MIB module...........14
      5.3. Liveness Detection and Monitoring......................14
      5.4. Verifying Correct Operation............................14
      5.5. Requirements on Other Protocols and Functional Components15
      5.6. Impact on Network Operation............................15
   6. Security Considerations.....................................15
   7. IANA Considerations........................................15


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   8. Acknowledgments............................................15
   9. References.................................................16
      9.1. Normative References...................................16
      9.2. Informative References.................................16
   Authors' Addresses............................................17
   Intellectual Property Statement................................17
   Disclaimer of Validity........................................18



1. Introduction

   [RFC4655] defines the PCE based Architecture and explains how a Path
   Computation Element (PCE) may compute Label Switched Paths (LSP) in
   Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and
   Generalized MPLS (GMPLS) networks at the request of Path Computation
   Clients (PCCs).  A PCC is shown to be any network component that
   makes such a request and may be for instance an Optical Switching
   Element with a Wavelength Division Multiplexing (WDM) network.  The
   PCE, itself, can be located anywhere within the network, and may be
   within an optical switching element, a Network Management System (NMS)
   or Operational Support System (OSS), or may be an independent network
   server.

   The PCE communications Protocol (PCEP) is the communication protocol
   used between PCC and PCE, and may also be used between cooperating
   PCEs.  [RFC4657] sets out the common protocol requirements for PCEP.
   Additional application-specific requirements for PCEP are deferred to
   separate documents.

   This document provides a set of application-specific PCEP
   requirements and protocol enhancements for support of path
   computation in Wavelength Switched Optical Networks (WSON).  WSON
   refers to WDM based optical networks in which switching is performed
   selectively based on the wavelength of an optical signal.

   The path in WSON is referred to as a lightpath.  A lightpath may span
   multiple fiber links and the path should be assigned a wavelength for
   each link.  A transparent optical network is made up of optical
   devices that can switch but not convert wavelengths. In a transparent
   optical network, a lightpath operates on the same wavelength across
   all fiber links that it traverses. In such case, the lightpath is
   said to satisfy the wavelength-continuity constraint. Two lightpaths
   that share a common fiber link should not be assigned the same
   wavelength otherwise blocking will occur during lightpath
   provisioning.  Therefore, assigning the proper wavelength on a



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   lightpath is an essential requirement in the optical path computation
   process.

   On the other hand, when a switching node has the ability to perform
   wavelength conversion the wavelength-continuity constraint can be
   relaxed, and a lightpath may use different wavelengths on different
   links along its route from origin to destination. It is, however, to
   be noted that wavelength converters may be limited due to their high
   cost, while the number of WDM channels that can be supported in a
   fiber is also limited. As a WSON can be composed of network nodes
   that cannot perform wavelength conversion, nodes with limited
   wavelength conversion, and nodes with full wavelength conversion
   abilities, wavelength assignment is an additional routing constraint
   to be considered in all lightpath computation.

   The remainder of this document uses terminology from [RFC4655].



2. Background: RWA Computation Architectures

   The WSON framework [WSON-FRAME] document defines the following RWA
   computation architectures.

   o Combined RWA --- Both routing and wavelength assignment are
      performed at a single computational entity.  This choice assumes
      that computational entity has sufficient WSON network link/nodal
      and topology information to be able to compute RWA.

   o Separate Routing and WA --- Separate entities perform routing and
      wavelength assignment.  The path(s) obtained from the routing
      computational entity must be furnished to the entity performing
      wavelength assignment.

   o Routing with Distributed WA --- Routing is performed at a
      computational entity while wavelength assignment is performed in a
      distributed fashion across the nodes along the path.


   For the Combined RWA architecture, there are two possible computing
   entities: (i) the NE is the computational entity -- in this case,
   there is no separate PCE as the NE assumes PCE function; (ii) a
   separate PCE is the computational entity.  This document is only
   concerned with case (ii). In this case, the PCE should perform both
   routing (R) and wavelength assignment (WA) upon request of the PCC.




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   For the Separate Routing and Wavelength architecture, there can be
   two variations:


   o A separate PCE will perform only wavelength assignment (WA) while
      the NE performs the route calculation based on its local knowledge.
      In this case, the NE should furnish the route list to the PCE so
      that the PCE would be able to assign wavelength to the route.

   o One PCE performs the routing (R) function while another PCE
      performs the Wavelength Assignment (WA) function in a tandem
      fashion.  The fact that two PCEs are involved (one for Routing and
      one for Wavelength Assignment (WA)) could be invisible to the
      original PCC.

   For the Routing with Distributed WA architecture, the PCE is only
   responsible for routing (i.e., path computation), not for exact
   wavelength assignment. The exact assignment of wavelengths would be
   performed at the NEs along the path in a distributed fashion. However,
   the PCE may choose to limit the wavelengths that can be used (i.e.,
   by specifying a wavelength set to the NEs).

3. PCECP Requirements

   This section provides the PCECP requirements to support WSON routing
   and wavelength assignment (RWA) applications.  The requirements
   specified in this section are detailed requirements based on high-
   level specification in [WSON-FRAME].



    3.1. RWA Computation Options

   The following RWA computation options should be conveyed in the PC
   Request:



   o The request is for both Routing and Wavelength Assignment (R+WA).
      This case may arise when the NE is not capable of either route
      calculation or wavelength assignment at the node level, or when a
      more optimal RWA is desired.

   o The request is for Routing (R) only.  This case may arise when the
      NE is not capable of route calculation at the node level while
      wavelength assignment is done at the node level in a distributed
      fashion.


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   o The request is for Wavelength Assignment (WA) only.  This case may
      arise when the NE is capable of route calculation at the node
      level (e.g., via an IGP-TE) but with no wavelength information
      is available at the node level, or when two PCEs work in tandem
      with one performing the routing (R) function and another
      wavelength assignment (WA).  In either case, the calculated route
      list at one computing entity should be supplied in the request
      message to the other computing entity where WA is applied.

   o The request is for Routing (R) with the suggested/restricted
      wavelength set. This is a variation from the Routing only option.
      With this option, the PCE computes the route and the candidate
      wavelengths associated with the route. In this case, the exact
      wavelength assignment is to be performed at the NE level.


   The corresponding PC Reply message should include the following
   information:

   o An indicator that conveys the original request was for (i) WA only;
      (ii) R+WA; (iii) R only; (iv) R with the suggested/restricted
      wavelength set

   o The route list and the recommended wavelengths to be used for the
      route.

   o In the case of failure to find a proper route or wavelengths
      assigned to the route, proper reasons for the failure should be
      conveyed: (i) route not found; (ii) wavelength not found (i.e.,
      wavelength blocking); (iii) both route and wavelength not found.

    3.2. Optimization Degree

   The PC Request Message should indicate the degree of optimization
   associated with lightpath computation.


   o Concurrent Optimization: multiple lightpaths requested at once.

   o Lightpath and backup lightpath requested at once.

   o Sequential Optimization: single lightpath requested.

   The PC Reply Message should include the original optimization degree
   associated with the request when replying the path computation
   results.



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    3.3. Wavelength Assignment and Wavelength Set Information

   The PCE MUST specify the wavelength assignment and/or wavelength set
   information in response to the wavelength assignment/wavelength set
   Request made by the PCC in the PCReq message.

   If the original request is either for both Routing and Wavelength
   Assignment or for Wavelength Assignment only, the exact wavelength
   assignment result can be conveyed to the PCC using the ERO object and
   ERO Label subobject within the ERO. Note that this is not a new
   requirement. [PCEP] allows this mechanism, which is defined as the
   Label Set mechanism in [RFC3471].

   If the original request is for Routing with wavelength
   suggested/restricted wavelength set, then the Wavelength Set
   information must be provided to the PCC.



    3.4. Lightpath Route Parameters

   The request MAY indicate the specific lightpath route parameters in
   the PCReq message:

   o Bidirectional Assignment of wavelengths for a bidirectional LSP
      request. This means that the same wavelength should be assigned in
      both directions on each hop.

   o Simultaneous assignment of the same wavelength to primary and
      backup paths.

   The PCRep message should include the original lightpath route
   parameters associated with the request when replying with the path
   computation results.



    3.5. Timeliness Characteristics of Lightpath

   The request MAY indicate the specific timeliness of the computation
   request for a lightpath. This will likely be related to the use to
   which the lightpath will be put:

   o Time Critical: this type of request is useful for those lightpath
      establishment requests used for restoration of service or other
      high priority real time services.



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   o Soft Time Bounds: this type of request is a more typical new
      connection request.  While expected to be responsive, there should
      be more time to take into account network optimization.

   o Scheduled: this type of request is useful when the requested
      lightpath connections are not time critical (i.e., the request is
      significantly ahead of their intended "in-service" time.  It is to
      be noted that we will not explicitly deal with scheduled case in
      this document but the optimization can be handled via [PCE-GCO].

   The reply should indicate the original timeliness characteristics of
   the lightpath request with path computation results.



    3.6. Duration of Lightpath

   The request MAY indicate specific lightpath duration information
   associated with the request. This may be useful to the PCE since it
   is not worthwhile to optimize lightpaths with relatively short
   duration as compared to pseudo-static paths.


    3.7. Wavelength Selection Preference

   The PC Request MAY indicate computation objective functions that
   specify the Wavelength Selection Preference to which a path
   computation request is applied.

   The Wavelength Selection Preference to be supported at the minimum is:

   o Random

   o First Fit

   o Most Used

   o Least Loaded

   o Don't care: default

   Note that the objective functions to be supported for a single LSP
   request are listed in [PCEP] and [PCE-OF] and that the objective
   functions to be supported for a concurrent LSP request are listed in
   [PCE-GCO] and [PCE-OF].




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   The PCRep should indicate which wavelength selection preference has
   actually been applied.



4. Protocol Extensions for Support of WSON RWA

   This section describes PCEP extension necessary to meet the
   requirements set out in the previous section.

    4.1. RWA Computation Options

   The PCC has to include the RWA computation option in the PCReq
   message in order to convey a particular computation option.  To
   support such indication a new flag, the RC flag, is defined in the RP
   (Request Parameter) Object.


   The RC flag is defined in the Flags field of the RP (Request
   Parameter) object as follows. Bit number assignment to be confirmed
   by IANA (see Section 8).

      Bit     Name    Description                          Reference

   10-11   RC-bits Routing Wavelength Computation       This document


   RC bits (Routing wavelength Computation bits - 2 bits):

   o 11: Request is for both R (Routing) and Wavelength Assignment (WA).

   o 01: Request is for Wavelength Assignment (WA) only.

   o 10: Request is for Routing (R) with suggested/restricted
      Wavelength Set

   o 00: Request is for Routing (R) only.

   When the RC bits are set to 11 in a PCReq message, the requesting PCC
   requires the PCE to provide in the PCRep message the assigned
   wavelength associated with the computed path.  This request is for
   both Routing (R) and Wavelength Assignment (WA).

   When the RC bits are set to 01 in a PCReq message, the requesting PCC
   requires the PCE only to provide wavelength assignment (WA).  In such
   case, the PCC must provide the already computed route (as indicated


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   by the ERO and the Bandwidth Object following the RP object) to which
   the PCE would assign the wavelengths.  Note that this option is to
   fulfill one of the RWA computational architectures, namely, the
   Separate Routing and WA option.

   When the RC bits are set to 10, then the PCE is expected to provide
   some suggestive or restrictive wavelength information associated with
   the route.

   When the RC bits are set to 11, 01, or 10, then additional parameters
   associated with the requested lightpath SHOULD be provided in
   optional Lightpath Route Parameter TLV (as specified in Section 3.4)
   within the RP object. See Section 4.2 for the encoding of Lightpath
   Route Parameter TLV.

   The RP object in the PCRep message SHOULD properly indicate the
   original request for the RWA Computation (RC) bit and I bit that have
   actually been applied by the PCE. The actual route list and
   wavelength assignment is to be found in the ERO within ERO Label
   subobjects. ERO Label subobjects can be used to indicate the
   wavelength to be used on particular links. Note that GMPLS signaling
   [RFC3473] supports an explicit route object (ERO) and with ERO Label
   subobjects.



    4.2. Lightpath Route Parameter TLV

   When the RC bit is set to 11, 01, or 10 in the RP object in a PCReq
   message, then the following Lightpath Route Parameter TLV SHOULD be
   included as part of the RP object within the PCReq message.

   The format of the Lightpath Route Parameter TLV is as follows:















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   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |I|S|                                                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Type     To be defined by IANA (suggested value = x)
              Length   2 bits
              Value    I bit: 0 or 1
                 S bit: 0 or 1

   Figure 1    The Lightpath Route Parameter TLV in the RP object in the
                               PCReq Message


   I bit (Bidirectional Assignment of wavelengths - 1 bit):

   o 0: Request is for bidirectional assignment of wavelengths

   o 1: Request is for unidirectional assignment of wavelengths


   S bit (Same Wavelength to primary and backup paths - 1 bit):

   o 0: Request is for assignment of the same wavelength to primary and
      backup paths.

   o 1: Request is for assignment of the different wavelength to
      primary and backup paths.




    4.3. Wavelength Selection Preferences

   When the RC (RWA Computation) flags in the RP object of a PCReq
   indicate computing wavelength assignment, then the following
   Wavelength Selection Preference TLV MAY be included in the RP object
   as an optional TLV.

   The format of the Wavelength Selection Preference TLV is as follows:





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   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Wavelength Selection Preference                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Type     To be defined by IANA (suggested value = x)
              Length   32 bits
              Value    Wavelength Selection Preference

     Figure 2    The Wavelength Selection/Assignment Preferences TLV in
                    the RP object in the PCReq Message


   Five wavelength selection preferences are defined in this document
   and their identifier should be assigned by IANA (suggested value)

      Function
      Code       Description
     --------     ------------
      1             Random
      2              First Fit
      3              Most Used
      4              Least Loaded
     5         Don't Care


   The Wavelength Selection Preference TLV should also be included in
   the RP object in the PCRep message to indicate which wavelength
   selection preference has actually been applied by the PCE in its
   wavelength assignment procedure.





    4.4. Wavelength Suggestion/Restriction TLV

   With the Routing with Distributed Wavelength Assignment option, the
   PCRep should specify the wavelength set information in response to
   the wavelength assignment/wavelength set Request made by the PCC in
   the PCReq message if so requested by the setting of the RC bits in
   the RP object in the PCReq message.



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   We refer to this information as wavelength restriction TLV.

   The encoding of wavelength Suggestion/Restriction TLV is to be
   provided in the next version.


    4.5. Error Indicator

   To indicate errors associated with the RWA request, a new Error-Type
   (15) and subsequent error-values are defined as follows for inclusion
   in the PCEP-ERROR object.

   If a PCE receives a RWA computation request and the PCE is not
   capable of RWA, the PCE MUST send a PCErr message with a PCEP ERROR
   object (Error-Type=15) and an Error-Value (Error-Value=1).  The
   corresponding RWA computation request MUST be cancelled.

   To indicate an error associated with policy violation, a new error
   value "RWA not allowed" is added to the existing error code for
   policy violation (Error-Type=6) as defined in [PCEP].

   If a PCE receives a RWA computation request which is not compliant
   with administrative privileges (i.e., the PCE policy does not support
   RWA), the PCE MUST send a PCErr message with a PCEP-ERROR Object
   (Error-Type=6) and an Error-Value (Error-Value=3).  The corresponding
   RWA computation MUST be cancelled.

    4.6. NO-PATH Indicator

   To communicate the reason(s) for not being able to find RWA
   computation, the NO-PATH object MAY be used in the PCRep message. The
   NO-PATH object is defined in [PCEP].

   As defined in [PCEP], the NO-PATH object carries the NO-PATH_VECTOR
   TLV which has a flags field. One new bit flag is defined in this
   document to indicate RWA-specific computation failures as follows:

   0x10: when set, the PCE indicates that no wavelength was found
   associated with RWA computation in the PCRep message.



5. Manageability Considerations

   Manageability of WSON Routing and Wavelength Assignment (RWA) with
   PCE must address the following considerations:



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    5.1. Control of Function and Policy

   In addition to the parameters already listed in Section 8.1 of [PCEP],
   a PCEP implementation SHOULD allow configuring the following PCEP
   session parameters on a PCC:

   o The ability to send a WSON RWA request.

   In addition to the parameters already listed in Section 8.1 of [PCEP],
   a PCEP implementation SHOULD allow configuring the following PCEP
   session parameters on a PCE:

   o The support for WSON RWA.

   o The maximum number of synchronized path requests associated with
      WSON RWA per request message.

   o A set of WSON RWA specific policies (authorized sender, request
      rate limiter, etc).


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


    5.2. Information and Data Models, e.g. MIB module

   Extensions to the PCEP MIB module defined in [PCEP-MIB] should be
   defined, so as to cover the WSON RWA information introduced in this
   document. A future revision of this document will list the
   information that should be added to the MIB module.

    5.3. 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 section 8.3 of [PCEP].


    5.4. Verifying Correct Operation

   Mechanisms defined in this document do not imply any new verification
   requirements in addition to those already listed in section 8.4 of
   [PCEP]



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    5.5. Requirements on Other Protocols and Functional Components

   The PCE Discovery mechanisms ([ISIS PCED] and [OSPF PCED]) may be
   used to advertise WSON RWA path computation capabilities to PCCs.


    5.6. Impact on Network Operation

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



6. Security Considerations

   This document has no requirement for a change to the security models
   within PCEP [PCEP]. However the additional information distributed in
   order to address the RWA problem represents a disclosure of network
   capabilities that an operator may wish to keep private. Consideration
   should be given to securing this information.



7. IANA Considerations

   A future revision of this document will present requests to IANA for
   codepoint allocation.



8. Acknowledgments

   The authors would like to thank Adrian Farrel for many helpful
   comments that greatly improved the contents of this draft.

   This document was prepared using 2-Word-v2.0.template.dot.










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9. References

    9.1. Normative References

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

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

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

   [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.

   [PCEP]    Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
             Element (PCE) communication Protocol (PCEP) - Version 1",
             draft-ietf-pce-pcep, work in progress.



    9.2. Informative References

   [PCE-OF]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Objective Function
             encoding in Path Computation Element communication and
             discovery protocols", draft-ietf-pce-pce-of, work in
             progress.

   [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.

   [WSON-FRAME] Bernstein, G. and Lee, Y. (Editors), and W. Imajuku,
             "Framework for GMPLS and PCE Control of Wavelength Switched
             Optical Networks", draft-bernstein-ccamp-wavelength-
             switched, work in progress.



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   [ISIS-PCED] Le Roux, J. and JP. Vasseur, "IS-IS protocol extensions
             for Path Computation Element (PCE) Discovery", draft-ietf-
             pce-disco-proto-isis, work in progress.

   [OSPF-PCED] Le Roux, J. and JP. Vasseur, "OSPF protocol extensions
             for Path Computation Element (PCE) Discovery", draft-ietf-
             pce-disco-proto-ospf, work in progress.




Authors' Addresses

   Young Lee (Ed.)
   Huawei Technologies
   1700 Alma Drive, Suite 100
   Plano, TX 75075, USA

   Phone: (972) 509-5599 (x2240)
   Email: ylee@huawei.com


   Greg Bernstein (Ed.)
   Grotto Networking
   Fremont, CA, USA

   Phone: (510) 573-2237
   Email: gregb@grotto-networking.com


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Internet-Draft         PCEP Extension for WSON           February 2008


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