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rfc:rfc7449

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.

Lee, et al. Informational [Page 1] RFC 7449 PCEP Requirements for WSON RWA February 2015

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

Lee, et al. Informational [Page 2] RFC 7449 PCEP Requirements for WSON RWA February 2015

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

Lee, et al. Informational [Page 3] RFC 7449 PCEP Requirements for WSON RWA February 2015

 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.

Lee, et al. Informational [Page 4] RFC 7449 PCEP Requirements for WSON RWA February 2015

 (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.

Lee, et al. Informational [Page 5] RFC 7449 PCEP Requirements for WSON RWA February 2015

 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.

Lee, et al. Informational [Page 6] RFC 7449 PCEP Requirements for WSON RWA February 2015

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.

Lee, et al. Informational [Page 7] RFC 7449 PCEP Requirements for WSON RWA February 2015

 (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:

Lee, et al. Informational [Page 8] RFC 7449 PCEP Requirements for WSON RWA February 2015

 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.

Lee, et al. Informational [Page 9] RFC 7449 PCEP Requirements for WSON RWA February 2015

 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>.

Lee, et al. Informational [Page 10] RFC 7449 PCEP Requirements for WSON RWA February 2015

 [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

Lee, et al. Informational [Page 11] 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

Lee, et al. Informational [Page 12]

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