    Internet Engineering Task Force (IETF)                       Y. Lee, Ed.
    Request for Comments: 7449                                        Huawei
    Category: Informational                                G. Bernstein, Ed.
    ISSN: 2070-1721                                        Grotto Networking
                                                               J. Martensson
                                                                       Acreo
                                                                   T. Takeda
                                                                         NTT
                                                                T. Tsuritani
                                                                        KDDI
                                                         O. Gonzalez de Dios
                                                                  Telefonica
                                                               February 2015

      Path Computation Element Communication Protocol (PCEP) Requirements
                 for Wavelength Switched Optical Network (WSON)
                       Routing and Wavelength Assignment

    Abstract

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

    Status of This Memo

       This document is not an Internet Standards Track specification; it is
       published for informational purposes.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Not all documents
       approved by the IESG are a candidate for any level of Internet
       Standard; see Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc7449.

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    Copyright Notice

       Copyright (c) 2015 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 Simplified BSD License.

    Table of Contents

       1. Introduction ....................................................3
       2. WSON RWA Processes and Architecture .............................4
       3. Requirements ....................................................5
          3.1. Path Computation Type Option ...............................5
          3.2. RWA Processing .............................................6
          3.3. Bulk RWA Path Request/Reply ................................6
          3.4. RWA Path Reoptimization Request/Reply ......................7
          3.5. Wavelength Range Constraint ................................7
          3.6. Wavelength Assignment Preference ...........................7
          3.7. Signal-Processing Capability Restriction ...................8
       4. Manageability Considerations ....................................8
          4.1. Control of Function and Policy .............................8
          4.2. Information and Data Models (e.g., MIB Module) .............9
          4.3. Liveness Detection and Monitoring ..........................9
          4.4. Verifying Correct Operation ................................9
          4.5. Requirements on Other Protocols and Functional Components ..9
          4.6. Impact on Network Operation ................................9
       5. Security Considerations .........................................9
       6. References .....................................................10
          6.1. Normative References ......................................10
          6.2. Informative References ....................................10
       Acknowledgments....................................................11
       Authors' Addresses.................................................11

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    1.  Introduction

       [RFC4655] defines the PCE-based architecture and explains how a Path
       Computation Element (PCE) may compute Label Switched Paths (LSPs) in
       networks controlled by Multiprotocol Label Switching Traffic
       Engineering (MPLS-TE) and Generalized MPLS (GMPLS) 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; it may be within an optical switching element, a Network
       Management System (NMS), or an Operational Support System (OSS), or
       it may be an independent network server.

       The Path Computation Element Communication Protocol (PCEP) is the
       communication protocol used between a PCC and PCE; it 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 (WSONs).  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 cases,
       the lightpath is said to satisfy the wavelength-continuity
       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

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       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].

       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 [RFC2119].

    2.  WSON RWA Processes and Architecture

       In [RFC6163], three alternative process architectures were given for
       performing routing and wavelength assignment.  These are shown
       schematically in Figure 1, where R stands for Routing, WA for
       Wavelength Assignment, and DWA for Distributed Wavelength Assignment.

         +-------------------+
         |  +-------+  +--+  |    +-------+    +--+     +-------+    +---+
         |  |   R   |  |WA|  |    |   R   |--->|WA|     |   R   |--->|DWA|
         |  +-------+  +--+  |    +-------+    +--+     +-------+    +---+
         |   Combined        |     Separate Processes   Separate Processes
         |   Process         |                          WA performed in a
         +-------------------+                          distributed manner
               (a)                       (b)                    (b')

                        Figure 1: RWA Process Alternatives

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

       (a)  Combined Process (R&WA)

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

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

            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)

            A standard path computation (unaware of detailed wavelength
            availability) takes place, and 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
            should be covered by GMPLS PCEP extensions; it does not present
            new WSON-specific requirements.

       The various process architectures for implementing RWA have been
       reviewed above.  Figure 2 shows one typical PCE-based implementation,
       which is referred to as the 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

    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 MAY include the path computation type.  This can be:

       (a)  Both RWA, or

       (b)  Routing only.

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

    3.2.  RWA Processing

       As discussed in Section 2, various RWA processing options should be
       supported in a PCEP request/reply.

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

            (i)  Explicit Label Control (ELC) [RFC3473]

            (ii) A set of recommended labels for each hop.  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 an 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., network disconnected,
            wavelength not found, both, etc.).  Note that 'wavelength not
            found' may include several sub-cases such as wavelength
            continuity not met, unsupported FEC/Modulation type, etc.

    3.3.  Bulk RWA Path Request/Reply

       Sending simultaneous path requests for "routing only" computation is
       supported by the 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 requests.  A bulk path request provides an ability to
            request a number of simultaneous RWA path requests.

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

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    3.4.  RWA Path Reoptimization Request/Reply

       This section provides a number of requirements concerning RWA path
       reoptimization processing in PCEP.

       (a)  For a reoptimization request, the request MUST provide both the
            path and current wavelength to be reoptimized and MAY include
            the following options:

           (i)   Reoptimize the path keeping the same wavelength(s)

           (ii)  Reoptimize wavelength(s) keeping the same path

           (iii) Reoptimize allowing both the wavelength and the path to
                 change

       (b)  The corresponding response to the reoptimized request MUST
            provide the reoptimized path and wavelengths even when the
            request asked for the path or the wavelength to remain
            unchanged.

       (c)  In the case that the new path is not found, the response MUST
            include why the path is not found (e.g., network disconnected,
            wavelength not found, both, etc.).  Note that 'wavelength not
            found' may include several sub-cases such as wavelength
            continuity not met, unsupported FEC/Modulation type, etc.

    3.5.  Wavelength Range Constraint

       For any RWA computation type request, the requester (PCC) MUST be
       allowed to specify a restriction on the wavelengths to be used.  The
       requester MAY use this option to restrict the assigned wavelength for
       explicit labels or label sets.  This restriction may, for example,
       come from the tuning ability of a laser transmitter, any optical
       element, or a policy-based restriction.

       Note that the requester (e.g., PCC) is not required to furnish any
       range restrictions.

    3.6.  Wavelength Assignment Preference

       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.

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       (a)  An RWA computation type request MAY include the requester
            preference for random assignment, descending order, ascending
            order, etc.  A response SHOULD follow the requester preference
            unless it conflicts with the operator's policy.

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

    3.7.  Signal-Processing Capability Restriction

       Signal-processing compatibility is an important constraint for
       optical path computation.  The signal type for an end-to-end optical
       path must match at the source and at the destination.

       The PCC MUST be allowed to specify the signal type at the endpoints
       (i.e., at the source and at the destination).  The following signal-
       processing capabilities should be supported at a minimum:

       o  Modulation Type List

       o  FEC Type List

       The PCC MUST also be allowed to state whether transit modification is
       acceptable for the above signal-processing capabilities.

    4.  Manageability Considerations

       Manageability of WSON RWA with PCE must address the following
       considerations.

    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:

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       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

       As this document only concerns the requirements to support WSON RWA,
       no additional MIB module is defined in this document.  However, the
       corresponding solution document will list the information that should
       be added to the PCE MIB module defined in [RFC7420].

    4.3.  Liveness Detection and Monitoring

       This document does not define any new mechanisms that 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

       This document does not define any new mechanisms that imply any new
       verification requirements in addition to those already listed in
       Section 8.4 of [RFC5440]

    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

       This document does not define any new mechanisms that 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.

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       Solutions that address the requirements in this document need to
       verify that existing PCEP security mechanisms adequately protect the
       additional network capabilities and must include new mechanisms as
       necessary.

    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,
                  <http://www.rfc-editor.org/info/rfc2119>.

       [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
                  Computation Element (PCE)-Based Architecture", RFC 4655,
                  August 2006, <http://www.rfc-editor.org/info/rfc4655>.

       [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
                  Element (PCE) Communication Protocol (PCEP)", RFC 5440,
                  March 2009, <http://www.rfc-editor.org/info/rfc5440>.

    6.2.  Informative References

       [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Resource ReserVation Protocol-
                  Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
                  January 2003, <http://www.rfc-editor.org/info/rfc3473>.

       [RFC4657]  Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
                  Element (PCE) Communication Protocol Generic
                  Requirements", RFC 4657, September 2006,
                  <http://www.rfc-editor.org/info/rfc4657>.

       [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,
                  <http://www.rfc-editor.org/info/rfc5088>.

       [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,
                  <http://www.rfc-editor.org/info/rfc5089>.

       [RFC6163]  Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
                  "Framework for GMPLS and Path Computation Element (PCE)
                  Control of Wavelength Switched Optical Networks (WSONs)",
                  RFC 6163, April 2011,
                  <http://www.rfc-editor.org/info/rfc6163>.

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       [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
                  Hardwick, "Path Computation Element Communication Protocol
                  (PCEP) Management Information Base (MIB) Module", RFC
                  7420, December 2014,
                  <http://www.rfc-editor.org/info/rfc7420>.

    Acknowledgments

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

    Authors' Addresses

       Young Lee (editor)
       Huawei Technologies
       5340 Legacy Drive, Building 3
       Plano, TX 75245
       United States

       Phone: (469) 277-5838
       EMail: leeyoung@huawei.com

       Greg Bernstein (editor)
       Grotto Networking
       Fremont, CA
       United States

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

       Jonas Martensson
       Acreo
       Isafjordsgatan 22
       164 40 Kista
       Sweden

       EMail: Jonas.Martensson@acreo.se

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    RFC 7449             PCEP Requirements for WSON RWA        February 2015

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

       EMail: tomonori.takeda@ntt.com

       Takehiro Tsuritani
       KDDI R&D Laboratories, Inc.
       2-1-15 Ohara Kamifukuoka Saitama, 356-8502
       Japan

       Phone: +81-49-278-7806
       EMail: tsuri@kddilabs.jp

       Oscar Gonzalez de Dios
       Telefonica
       Distrito Telefonica, ed. Sur 3, Pta 3, Ronda de la Comunicacion
       Madrid, 28050
       Spain

       Phone: +34 913129647
       EMail: oscar.gonzalezdedios@telefonica.com

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