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Network Working Group                                            Y. Lee
Internet Draft                                                   Huawei
Intended status: Standard Track
Expires: July 2012                                         G. Bernstein
                                                      Grotto Networking

                                                       Jonas Martensson
                                                                  Acreo

                                                              T. Takeda
                                                                    NTT

                                                           T. Tsuritani
                                                                   KDDI



                                                        January 6, 2012


                   PCEP Extensions for WSON Impairments


                   draft-lee-pce-wson-impairments-03.txt


Status of this Memo

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   This Internet-Draft will expire on July 6, 2012.





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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Abstract

   As an optical signal progresses along its path it may be altered by
   the various physical processes in the optical fibers and devices it
   encounters. When such alterations result in signal degradation,
   these processes are usually referred to as "impairments". These
   physical characteristics may be important constraints to consider in
   path computation process in wavelength switched optical networks.

   This document provides PCEP extensions to support Impairment Aware
   Routing and Wavelength Assignment (IA-RWA) in wavelength switched
   optical networks.





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
      1.1. WSON RWA Processes (no impairments).......................5
      1.2. WSON IA-RWA Processes.....................................6
   2. WSON PCE Architectures and Requirements........................7


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      2.1. RWA PCC to PCE Interface..................................8
         2.1.1. A new RWA path request...............................8
            2.1.1.1. Signal Quality Measure TLV......................9
         2.1.2. A new RWA path reply................................10
            2.1.2.1. Signal Quality Measure TLV.....................10
      2.2. RWA-PCE to IV-PCE Interface..............................12
         2.2.1. A new impairment-validated (IV) path request........13
         2.2.2. A new impairment-validated (IV) path reply..........13
   3. Manageability Considerations..................................13
      3.1. Control of Function and Policy...........................13
      3.2. Information and Data Models, e.g. MIB module.............14
      3.3. Liveness Detection and Monitoring........................14
      3.4. Verifying Correct Operation..............................14
      3.5. Requirements on Other Protocols and Functional Components14
      3.6. Impact on Network Operation..............................15
   4. Security Considerations.......................................15
   5. IANA Considerations...........................................15
   6. References....................................................15
      6.1. Normative References.....................................15
      6.2. Informative References...................................16
   Authors' Addresses...............................................16
   7. Acknowledgments...............................................17



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 within 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 communication 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 for support of path computation in Wavelength Switched


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   Optical Networks (WSON) with impairments.  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 from one
   wavelength to another. 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 can not be assigned the same wavelength.  To do otherwise
   would result in both signals interfering with each other. Note that
   advanced additional multiplexing techniques such as polarization
   based multiplexing are not addressed in this document since the
   physical layer aspects are not currently standardized. Therefore,
   assigning the proper wavelength on a lightpath is an essential
   requirement in the optical path computation process.

   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 relatively
   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.

   One of the most basic questions in communications is whether one can
   successfully transmit information from a transmitter to a receiver
   within a prescribed error tolerance, usually specified as a maximum
   permissible bit error ratio (BER). This generally depends on the
   nature of the signal transmitted between the sender and receiver and
   the nature of the communications channel between the sender and
   receiver. The optical path utilized (along with the wavelength)
   determines the communications channel.

   The optical impairments incurred by the signal along the fiber and
   at each optical network element along the path determine whether the
   BER performance or any other measure of signal quality can be met
   for this particular signal on this particular path. Given the
   existing standards covering optical characteristics (impairments)
   and the knowledge of how the impact of impairments may be estimated


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   along a path, [WSON-IMP] provides a framework for impairment aware
   path computation and establishment utilizing GMPLS protocols and the
   PCE architecture.

   Some transparent optical subnetworks are designed such that over any
   path the degradation to an optical signal due to impairments never
   exceeds prescribed bounds. This may be due to the limited geographic
   extent of the network, the network topology, and/or the quality of
   the fiber and devices employed. In such networks the path selection
   problem reduces to determining a continuous wavelength from source
   to destination (the Routing and Wavelength Assignment problem).
   These networks are discussed in [RFC6163]. In other optical
   networks, impairments are important and the path selection process
   must be impairment-aware.

   In this document we first review the processes for routing and
   wavelength assignment (RWA) used when wavelength continuity
   constraints are present. We then review the processes for optical
   impairment aware RWA (IA-RWA). Based on selected process models we
   then specify requirements for PCEP to support IA-RWA. Note that
   requirements for PCEP to support RWA are specified in a separate
   document [PCEP-RWA].

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

1.1. WSON RWA Processes (no impairments)

   In [RFC6163] three alternative process architectures were given for
   performing routing and wavelength assignment. These are shown
   schematically in Figure 1.

     +-------------------+
     |  +-------+  +--+  |    +-------+    +--+     +-------+    +---+
     |  |Routing|  |WA|  |    |Routing|--->|WA|     |Routing|--->|DWA|
     |  +-------+  +--+  |    +-------+    +--+     +-------+    +---+
     |   Combined        |     Separate Processes   Separate Processes
     |   Processes       |                          WA performed in a
     +-------------------+                          Distributed manner
           (a)                       (b)                    (c)

                      Figure 1                                  RWA process alternatives.

   Detail description of each alternative can be found in [RFC6163].






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1.2. WSON IA-RWA Processes

   In [WSON-IMP] impairments were addressed by adding an "impairment
   validation" (IV) process. For approximate impairment validation
   three process alternatives were given in [WSON-IMP] and are shown in
   Figure 2. Since there are many possible alternative combinations,
   these are just three examples. Please note that the requirements for
   all possible architectures can be reduced to the cases in Figure 3
   in section 2.


                  +-----------------------------------+
                  |   +--+     +-------+     +--+     |
                  |   |IV|     |Routing|     |WA|     |
                  |   +--+     +-------+     +--+     |
                  |                                   |
                  |        Combined Processes         |
                  +-----------------------------------+
                                  (a)

           +--------------+      +----------------------+
           | +----------+ |      | +-------+    +--+    |
           | |    IV    | |      | |Routing|    |WA|    |
           | |candidates| |----->| +-------+    +--+    |
           | +----------+ |      |  Combined Processes  |
           +--------------+      +----------------------+
                                  (b)

            +-----------+        +----------------------+
            | +-------+ |        |    +--+    +--+      |
            | |Routing| |------->|    |WA|    |IV|      |
            | +-------+ |        |    +--+    +--+      |
            +-----------+        | Distributed Processes|
                                 +----------------------+
                                  (c)
       Figure 2                   Process flows for the three main approximate impairment
                        architectural alternatives.

   These alternatives have the following properties and impact on PCEP
   requirements in this document.

   1. Combined IV and RWA Process - Here the processes of impairment
      validation, routing and wavelength assignment are aggregated into
      a single PCE. The requirements for PCC-PCE interaction with such
      a combined IV-RWA process PCE is addressed in this document.




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   2. IV-Candidates + RWA Process - As explained in [WSON-IMP]
      separating the impairment validation process from the RWA process
      maybe necessary to deal with impairment sharing constraints. In
      this architecture one PCE computes impairment candidates and
      another PCE uses this information while performing RWA. The
      requirements for PCE-to-PCE interaction of this architecture will
      be addressed in this document.

   3. Routing + Distributed WA and IV - Here a standard path
      computation (unaware of detailed wavelength availability or
      optical impairments) takes place, then wavelength assignment and
      impairment validation is performed along this path in a
      distributed manner via signaling (RSVP-TE). This alternative
      should be covered by existing or emerging GMPLS PCEP extensions
      and does not present new WSON specific requirements.

2. WSON PCE Architectures and Requirements

   In the previous section we reviewed various process architectures
   for implementing RWA with and without regard for optical impairment.
   In Figure 3 we reduce these alternatives to two PCE based
   implementations. In Figure 3(a) we show the three processes of
   routing, wavelength assignment and impairment validation accessed
   via a single PCE. The implementation details of the interactions of
   the processes are not subject to standardization in this case only
   the PCC to PCE communications.

   In Figure 3(b) the impairment validation process is implemented in a
   separate PCE. Here the RWA-PCE acts as a coordinator and the PCC to
   RWA-PCE interface will be the same as in Figure 3(a), however in
   this case we have additional requirements for the RWA-PCE to IV-PCE
   interface.

















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                          +-----------------------------------+
            +-----+       |   +--+     +-------+     +--+     |
            |     |       |   |IV|     |Routing|     |WA|     |
            | PCC |<----->|   +--+     +-------+     +--+     |
            |     |       |                                   |
            +-----+       |               PCE                 |
                          +-----------------------------------+

                                   (a)


                       +----------------------+     +--------------+
         +-----+       | +-------+    +--+    |     |              |
         |     |       | |Routing|    |WA|    |     |      IV      |
         | PCC |<----->| +-------+    +--+    |<--->|  candidates  |
         |     |       |                      |     |              |
         +-----+       | RWA-PCE (coordinator)|     |    IV-PCE    |
                       +----------------------+     +--------------+

                                   (b)
                     Figure 3                                 PCE architectures for RWA.

2.1. RWA PCC to PCE Interface

   The PCC to PCE interface of Figure 3(a) and the PCC to RWA-PCE
   (coordinator) interface of Figure 3(b) are the same and we will
   cover both in this section. The following requirements for these
   interfaces are arranged by use cases:

      2.1.1.  A new RWA path request

   The PCReq Message SHOULD include some specific measure of optical
   signal quality to which all feasible paths should conform:

   o  The BER limit

   o  OSNR + Margin

   o  PMD

   o  Q factor

   If the PCReq Message does not include the BER limit and no default
   BER limit is provisioned at the PCE then the PCE will return an
   error specifying that a BER limit must be provided.




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   "Margin" means "insurance" (e.g. 3~6dB) for suppliers and operators
   against unpredictable degradation and other degradation not included
   in the provided estimates such as that due to fiber nonlinearity.

2.1.1.1. Signal Quality Measure TLV

   This TLV represents all impairment constraints that need to be
   considered by the PCE to calculate a path that passes the requested
   measure of signal quality for a signal for a given source and
   destination.

   This TLV is repeated one after another until all signal quality
   types are specified.

   The TLV type is TBD.

   The TLV data is defined as follow:


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |P| Signal Quality Type           |    Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Threshold                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The P bit (1 bit): Indicates if the associated impairment is a path
   level or not.

   The P bit is set to 1 indicates that the associated impairment is a
   path level. This means that the impairment is associated with the
   end-to-end path and the threshold must be satisfied on a path level.

   The P bit is set to 0 indicates that the associated impairment is a
   link level. This means the impairment is associated with the link
   and the threshold must be satisfied on every link of the end-to-end
   path.

   The Signal Quality Type (15 bits): indicates the kind of optical
   signal quality of interest.

      0: reserved




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      1: The BER limit

      2: OSNR + Margin

      3: PMD

      4: Q factor

      5-up: Reserved for future use

   Threshold (32 bits) indicates the threshold (upper or lower) to
   which the specified signal quality measure must satisfy for the
   path/link (depending on the P bit).

   The reserved bits MUST be set to 0 on transmit and MUST be ignored
   on receive.

      2.1.2. A new RWA path reply

   The PCRep Message MUST include the route, wavelengths assigned to
   the route, and an indicator that says if the path conforms to the
   required quality or not. In the case where a valid path is not
   found, the PCRep Message MUST include why the path is not found
   (e.g., no route, wavelength not found, BER failure, etc.)



2.1.2.1. Signal Quality Measure TLV

   This TLV represents the result of the requested measure of signal
   quality for a signal for a given source and destination.

   This TLV is repeated one after another until all signal quality
   types are specified.

   The TLV type is TBD.

   The TLV data is defined as follow:


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |P| Signal Quality Type           |    Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Signal Quality Value                            |


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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The P bit (1 bit): Indicates if the associated signal quality
   measure has passed the threshold or not.

   The P bit is set to 1 indicates that the associated signal quality
   measure has passed the threshold.

   The P bit is set to 0 indicates that the associated signal quality
   measure has failed the threshold.

   The Signal Quality Type (15 bits): indicates the kind of optical
   signal quality of interest.

      0: reserved

      1: The BER limit

      2: OSNR + Margin

      3: PMD

      4: Q factor

      5-up: Reserved for future use

   Signal Quality Value  (32 bits) indicates the actual estimated value
   of the specified signal quality measure for the end-to-end path.

   The reserved bits MUST be set to 0 on transmit and MUST be ignored
   on reception.

















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2.2. RWA-PCE to IV-PCE Interface

   In [WSON-IMP] a sequence diagram for the interaction of the PCC,
   RWA-PCE and IV-PCE of Figure 3(b) was given and is repeated here in
   Figure 4. The interface between the PCC and the RWA-PCE (acting as
   the coordinator) was covered in section 2.1.
     +---+                +-------------+          +-----------------+
     |PCC|                |RWA-Coord-PCE|          |IV-Candidates-PCE|
     +-+-+                +------+------+          +---------+-------+
       ...___     (a)            |                           |
       |     ````---...____      |                           |
       |                   ```-->|                           |
       |                         |                           |
       |                         |--..___    (b)             |
       |                         |       ```---...___        |
       |                         |                   ```---->|
       |                         |                           |
       |                         |                           |
       |                         |           (c)       ___...|
       |                         |       ___....---''''      |
       |                         |<--''''                    |
       |                         |                           |
       |                         |                           |
       |          (d)      ___...|                           |
       |      ___....---'''      |                           |
       |<--'''                   |                           |
       |                         |                           |
       |                         |                           |

       Figure 4                   Sequence diagram for the interactions between PCC, RWA-
                Coordinating-PCE and the IV-Candidates-PCE.

   The interface between the RWA-Coord-PCE and the IV-Candidates-PCE is
   specified by the following requirements:

   1. The PCReq Message from the RWA-Coord-PCE to the IV-Candidate-PCE
      MUST include an indicator that more than one (candidate) path
      between source and destination is desired.

   2. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
      MUST include a limit on the number of optical impairment
      qualified paths to be returned by the IV-PCE.







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   3. The PCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE
      MAY include wavelength constraints. Note that optical impairments
      are wavelength sensitive and hence specifying a wavelength
      constraint may help limit the search for valid paths. This
      requirement has been already covered in [PCEP-RWA] and is
      presented here for an illustration purpose.

   4. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE
      MUST include a set of optical impairment qualified paths along
      with any wavelength constraints on those paths.

   5. The PCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE
      MUST indicate "no path found" in case where a valid path is not
      found.

   6. The PCReq Message from the RWA-Coord-PCE to the IV-Candidate-PCE
      MAY include one or more specified paths and wavelengths that is
      to be verified by the IV-PCE. This requirement is necessary when
      the IV-PCE is allowed to verify specific paths.

   Note that once the Combined RWA Process PCE receives the resulting
   paths from the IV Candidates PCE, then the Combined RWA PCE computes
   RWA for the IV qualified candidate paths and sends the result back
   to the PCC.

      2.2.1. A new impairment-validated (IV) path request

   Details on encoding are TBD.



      2.2.2. A new impairment-validated (IV) path reply

   Details on encoding are TBD.

3. Manageability Considerations

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

3.1. Control of Function and Policy

   In addition to the parameters already listed in Section 8.1 of
   [RFC5440], a PCEP implementation SHOULD allow configuring the
   following PCEP session parameters on a PCC:

   o  The ability to send a WSON IA-RWA request.


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   In addition to the parameters already listed in Section 8.1 of
   [RFC5440], a PCEP implementation SHOULD allow configuring the
   following PCEP session parameters on a PCE:

   o  The support for WSON IA-RWA.

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

   o  A set of WSON IA-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.


3.2. 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 IA-RWA information introduced in
   this document. A future revision of this document will list the
   information that should be added to the MIB module.

3.3. 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 [RFC5440].


3.4. 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 [RFC5440]


3.5. Requirements on Other Protocols and Functional Components

   The PCE Discovery mechanisms ([RFC5089] and [RFC5088]) may be used
   to advertise WSON IA-RWA path computation capabilities to PCCs.





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3.6. 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 [RFC5440].



4. 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.



5. IANA Considerations

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





6. References

6.1. 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.

   [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
             Element (PCE) communication Protocol (PCEP)", RFC 5440,
             March 2009.



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6.2. Informative References

   [RFC6163] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and
             PCE Control of Wavelength Switched Optical Networks", RFC
             6163, April 2011.

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

   [PCEP-RWA] Y. Lee, G. Bernstein, J. Martensson, T. Takeda and T.
             Otani, "PCEP Requirements for WSON Routing and Wavelength
             Assignment", draft-lee-pce-wson-routing-wavelength, work
             in progress.

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

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

   [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.




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





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   Greg Bernstein (Ed.)
   Grotto Networking
   Fremont, CA, USA
   Phone: (510) 573-2237
   Email: gregb@grotto-networking.com

   Jonas Martensson
   Acreo
   Email:Jonas.Martensson@acreo.se

   Tomonori Takeda
   NTT Corporation
   3-9-11, Midori-Cho
   Musashino-Shi, Tokyo 180-8585, Japan
   Email: takeda.tomonori@lab.ntt.co.jp


   Takehiro Tsuritani
   2-1-15 Ohara, Fujimino, Saitama, 356-8502, JAPAN
   KDDI R&D Laboratories Inc.
   Phone: +81-49-278-7806
   Email:  tsuri@kddilabs.jp

7. Acknowledgments

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

   Copyright (c) 2012 IETF Trust and the persons identified as authors
   of the code. All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

   o  Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.

   o  Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the
      distribution.

   o  Neither the name of Internet Society, IETF or IETF Trust, nor the
      names of specific contributors, may be used to endorse or promote
      products derived from this software without specific prior
      written permission.



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