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Network Working Group                                            Y. Lee
Internet Draft                                                   Huawei
Intended status: Standard Track
Expires: June 2010                                         G. Bernstein
                                                      Grotto Networking

                                                        Jonas Martensson
                                                                   Acreo

                                                              T. Takeda
                                                                    NTT

                                                           T. Tsuritani
                                                                   KDDI



                                                      December 15, 2009


                  PCEP Requirements for WSON Impairments


                   draft-lee-pce-wson-impairments-01.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 15, 2009.

Copyright Notice



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   Copyright (c) 2009 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.



Abstract

   This memo provides application-specific requirements for the Path
   Computation Element communication Protocol (PCEP) for the support of
   Impairments in Wavelength Switched Optical Networks (WSON). From a
   path computation perspective, optical impairments are additional
   constraints on the process of determining an optical light path.



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.....................................5
   2. WSON PCE Architectures and Requirements........................7
      2.1. RWA PCC to PCE Interface..................................8
         2.1.1. A new RWA path request...............................8
         2.1.2. An RWA path re-optimization request..................8
      2.2. RWA-PCE to IV-PCE Interface...............................9
   3. Manageability Considerations..................................10
      3.1. Control of Function and Policy...........................10
      3.2. Information and Data Models, e.g. MIB module.............11
      3.3. Liveness Detection and Monitoring........................11
      3.4. Verifying Correct Operation..............................11


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      3.5. Requirements on Other Protocols and Functional Components11
      3.6. Impact on Network Operation..............................11
   4. Security Considerations.......................................12
   5. IANA Considerations...........................................12
   6. Acknowledgments...............................................12
   7. References....................................................12
      7.1. Normative References.....................................12
      7.2. Informative References...................................13
   Authors' Addresses...............................................14
   Intellectual Property Statement..................................14
   Disclaimer of Validity...........................................15



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
   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


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   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 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).


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   These networks are discussed in [WSON-Frame]. 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 [WSON-Frame] 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 [WSON-FRAME].



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.





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                  +-----------------------------------+
                  |   +--+     +-------+     +--+     |
                  |   |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.

   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.






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   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.

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

                                   (a)


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

                                   (b)
                    Figure 3 PCE architectures for RWA.



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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/reply

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

   o  The BER limit

   o  Q factor

   o  OSNR + Margin

   o  PMD

   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.

   Margin" means "insurance" (e.g. 3~6dB) for suppliers and operators
   against unpredictable degradation and unestimatable degradation due
   to fiber nonlinearity and mismatched wavelength along the path.



   2. 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.  An RWA path re-optimization request/reply

   1. If a BER limit was required in the original path request then a
      BER limit MUST be furnished in the re-optimization request.
      Otherwise, furnishing a BER limit is optional. 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.)



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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-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-PCE to the IV-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.

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
   [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.




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   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.


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 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 [PCEP].


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
   [PCEP]


3.5. Requirements on Other Protocols and Functional Components

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


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 [PCEP].







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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. 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.



7. References

7.1. 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.





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   [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.



7.2. Informative References

   [WSON-Frame] Bernstein, G. and Lee, Y. (Editors), and W. Imajuku, "A
             Framework for the Control and Measurement of Wavelength
             Switched Optical Networks (WSON) with Impairments
             draft-bernstein-ccamp-wson-impairments-02.txt, work in
             progress.

   [WSON-IMP] Bernstein, G. and Lee, Y. (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.














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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

   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

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   users of this specification can be obtained from the IETF on-line IPR
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