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

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.

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

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
   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.

   (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.

   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.

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.

   (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:

   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.

   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>.

   [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
   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