Network Working Group                                            Y. Lee
Internet Draft                                                   Huawei
Intended status: Informational                             G. Bernstein
Expires: February 2015                                Grotto Networking
                                                       Jonas Martensson
                                                              T. Takeda
                                                           T. Tsuritani
                                                          O. G. de Dios

                                                         August 1, 2014

       PCEP Requirements for WSON Routing and Wavelength Assignment



   This memo provides application-specific requirements for the Path
   Computation Element communication Protocol (PCEP) for the support of
   Wavelength Switched Optical Networks (WSON). 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. Requirements for optical impairments will be
   addressed in a separate document.

Status of this Memo

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Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

Table of Contents

   1. Introduction...................................................3
   2. WSON RWA Processes & Architecture..............................4
   3. Requirements...................................................6
      3.1. Path Computation Type Option..............................6
      3.2. RWA Processing............................................6
      3.3. Bulk RWA Path Request/Reply...............................7
      3.4. RWA Path Re-optimization Request/Reply....................7
      3.5. Wavelength Range Constraint...............................7
      3.6. Wavelength Assignment Preference..........................8
      3.7. Signal Processing Capability Restriction..................8
   4. Manageability Considerations...................................8
      4.1. Control of Function and Policy............................9
      4.2. Information and Data Models, e.g. MIB module..............9
      4.3. Liveness Detection and Monitoring.........................9
      4.4. Verifying Correct Operation...............................9

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      4.5. Requirements on Other Protocols and Functional Components10
      4.6. Impact on Network Operation..............................10
   5. Security Considerations.......................................10
   6. IANA Considerations...........................................10
   7. Acknowledgments...............................................10
   8. References....................................................10
      8.1. Normative References.....................................10
      8.2. Informative References...................................11
   Authors' Addresses...............................................12
   Intellectual Property Statement..................................12
   Disclaimer of Validity...........................................13

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)-controlled 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). 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 cannot 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 path from origin to destination. It is, however, to be noted
   that wavelength converters may be limited for cost reasons, 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 computations.

   In this document we first review the processes for routing and
   wavelength assignment (RWA) used when wavelength continuity
   constraints are present and then specify requirements for PCEP to
   support RWA. Requirements for optical impairments will be addressed
   in a separate document.

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

2. WSON RWA Processes & Architecture

   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)                    (b')

                    Figure 1. RWA process alternatives

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

   (a)   Combined Processes (R&WA)

         Here path selection and wavelength assignment are performed as
         a single process. The requirements for PCC-PCE interaction
         with such a combined RWA process PCE is addressed in this

   (b)   Routing separate from Wavelength Assignment (R+WA)

         Here the routing process furnishes one or more potential paths
         to the wavelength assignment process that then performs final
         path selection and wavelength assignment. The requirements for
         PCE-PCE interaction with one PCE implementing the routing
         process and another implementing the wavelength assignment
         process are not addressed in this document.

   (b')  Routing and distributed Wavelength Assignment (R+DWA)

         Here a standard path computation (unaware of detailed
         wavelength availability) takes place, then wavelength
         assignment is performed along this path in a distributed
         manner via signaling (RSVP-TE). This alternative is a
         particular case of R+WA and it should be covered by GMPLS PCEP
         extensions and does not present new WSON-specific

   In the previous section various process architectures for
   implementing RWA have been reviewed. Figure 2 shows one typical PCE-
   based implementation, which is referred to as Combined Process
   (R&WA). With this architecture, the two processes of routing and
   wavelength assignment are accessed via a single PCE. This
   architecture is the base architecture from which the requirements
   are specified in this document.

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

              Figure 2. Combined Process (R&WA) architecture

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3. Requirements

   The requirements for the PCC to PCE interface of Figure 2 are
   specified in this section.

   3.1.  Path Computation Type Option

   A PCEP request MUST include the path computation type. This can be:

     (i)    Both Routing and Wavelength Assignment (RWA),

     (ii)   Routing only.

   This requirement is needed to differentiate between the currently
   supported routing with distributed wavelength assignment option and
   combined RWA. In case of distributed wavelength assignment option,
   wavelength assignment will be performed at each node of the route.

   3.2. RWA Processing

   (a)   When the request is a RWA path computation type, the request
      MUST further include the wavelength assignment options. At the
      minimum, the following option should be supported:

         (i)    Explicit Label Control (ELC) [RFC4003]

         (ii)   A set of recommended labels. The PCC can select the
                label based on local policy.

     Note that option (ii) may also be used in R+WA or R+DWA.

   (b)   In case of a RWA computation type, the response MUST include
      the wavelength(s) assigned to the path and an indication of which
      label assignment option has been applied (ELC or label set).

   (c)   In the case where a valid path is not found, the response MUST
      include why the path is not found (e.g., no path, wavelength not
      found, optical quality check failed, etc.)

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   3.3. Bulk RWA Path Request/Reply

   Sending simultaneous path requests for "routing only" computation is
   supported by PCEP specification [RFC5440]. To remain consistent the
   following requirements are added.

   (a)   A PCEP request MUST be able to specify an option for bulk RWA
      path request. Bulk path request is an ability to request a number
      of simultaneous RWA path requests.

   (b)   The PCEP response MUST include the path and the assigned
      wavelength assigned for each RWA path request specified in the
      original bulk request.

   3.4. RWA Path Re-optimization Request/Reply

   1. For a re-optimization request, the request MUST provide both the
      path and current wavelength to be re-optimized and MAY include
      the following options:

       a. Re-optimize the path keeping the same wavelength(s)

       b. Re-optimize wavelength(s) keeping the same path

       c. Re-optimize allowing both the wavelength and the path to

   2. The corresponding response to the re-optimized request MUST
      provide the re-optimized path and wavelengths.

   3. In case that the path is not found, the response MUST include why
      the path is not found (e.g., no path, wavelength not found, both
      path and wavelength not found, etc.)

   3.5. Wavelength Range Constraint

   For any RWA computation type request, the requester (PCC) MAY
   specify a restriction on the wavelengths to be used. The requester
   MAY use this option to restrict the assigned wavelength for explicit
   label or label set.

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   Note that the requestor (e.g., PCC) is not required to furnish any
   range restrictions. This restriction may for example come from the
   tuning ability of a laser transmitter, any optical element, or an
   policy-based restriction.

   3.6. Wavelength Assignment Preference

   1. A RWA computation type request MAY include the requestor
     preference for, e.g., random assignment, descending order,
     ascending order, etc. A response SHOULD follow the requestor
     preference unless it conflicts with operator's policy.

   2. A request for two or more paths MUST be able to include an option
     constraining the paths to have the same wavelength(s) assigned.
     This is useful in the case of protection with single transponder
     (e.g., 1+1 link disjoint paths).

   In a network with wavelength conversion capabilities (e.g. sparse 3R
   regenerators), a request SHOULD be able to indicate whether a
   single, continuous wavelength should be allocated or not. In other
   words, the requesting PCC SHOULD be able to specify the precedence
   of wavelength continuity even if wavelength conversion is available.

   3.7. Signal Processing Capability Restriction

   A request MUST be able to specify restrictions for signal
   compatibility either on the endpoints or on any given links. The
   following signal processing capabilities should be supported at a

      o  Modulation Type List

      o  FEC Type List

4. Manageability Considerations

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

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   4.1. 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 RWA request.

   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 RWA.

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

   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.

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

   As this document only concerns the requirements to support WSON RWA,
   no additional MIB module is defined in this document. However, the
   corresponding solution draft will list the information that should
   be added to the PCE MIB module defined in [PCEP-MIB].

   4.3. 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].

   4.4. 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]

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   4.5. Requirements on Other Protocols and Functional Components

   If PCE discovery mechanisms ([RFC5089] and [RFC5088]) were to be
   extended for technology-specific capabilities, advertising WSON RWA
   path computation capability should be considered.

   4.6. 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].

5. Security Considerations

   This document has no requirement for a change to the security models
   within PCEP [RFC5440]. 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.

6. IANA Considerations

   This informational document does not make any requests for IANA

7. Acknowledgments

   The authors would like to thank Adrian Farrel, Cycil Margaria and
   Ramon Casellas for many helpful comments that greatly improved the
   contents of this draft.

   This document was prepared using

8. References

   8.1. Normative References

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

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

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

   8.2. Informative References

   [RFC4003] L. Berger, "GMPLS Signaling Procedure for Egress Control",
             RFC 4003, February 2005.

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

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

   [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.

   [PCEP-MIB] Koushik, K, et al., "PCE communication protocol(PCEP)
             Management Information Base", draft-ietf-pce-pcep-mib,
             work in progress.

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Authors' Addresses

   Young Lee (Ed.)
   Huawei Technologies
   5340 Legacy Drive, Building 3
   Plano, TX 75245, USA
   Phone: (469)277-5838

   Greg Bernstein (Ed.)
   Grotto Networking
   Fremont, CA, USA
   Phone: (510) 573-2237

   Jonas Martensson

   Tomonori Takeda
   NTT Corporation
   3-9-11, Midori-Cho
   Musashino-Shi, Tokyo 180-8585, Japan

   Takehiro Tsuritani
   KDDI R&D Laboratories, Inc.
   2-1-15 Ohara Kamifukuoka Saitama, 356-8502. Japan
   Phone:  +81-49-278-7357

   Oscar Gonzalez de Dios
   Telefonica Investigacion y Desarrollo
   C/ Emilio Vargas 6
   Madrid,   28043
   Phone: +34 91 3374013

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