



PCE Working Group                                          H. Zheng, Ed.
Internet-Draft                             Huawei Technologies Co., Ltd.
Intended status: Standards Track                                  Y. Lee
Expires: 16 October 2026                                         Samsung
                                                             R. Casellas
                                                                    CTTC
                                                           D. Ceccarelli
                                                                   Cisco
                                                              April 2026


               PCEP Extension for Flexible Grid Networks
                    draft-ietf-pce-flexible-grid-14

Abstract

   This document provides the Path Computation Element Communication
   Protocol (PCEP) extensions for the support of Routing and Spectrum
   Assignment (RSA) in Flexible Grid networks.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 3 October 2026.

Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.










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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Spectrum Assignment (SA) Object . . . . . . . . . . . . . . .   5
     4.1.  Frequency Slot Selection TLV  . . . . . . . . . . . . . .   6
     4.2.  Frequency Slot Restriction Constraint TLV . . . . . . . .   7
       4.2.1.  Frequency Slot Restriction Field  . . . . . . . . . .   9
   5.  Encoding of an RSA Path Reply . . . . . . . . . . . . . . . .   9
     5.1.  Error Indicator . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  NO-PATH Indicator . . . . . . . . . . . . . . . . . . . .  10
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .  11
     6.1.  Control of Function and Policy  . . . . . . . . . . . . .  11
     6.2.  Information and Data Models . . . . . . . . . . . . . . .  11
     6.3.  Verifying Correct Operation . . . . . . . . . . . . . . .  11
     6.4.  Requirements on Other Protocols and Functional
           Components  . . . . . . . . . . . . . . . . . . . . . . .  12
     6.5.  Impact on Network Operation . . . . . . . . . . . . . . .  12
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Huawei Technologies . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  New PCEP Object . . . . . . . . . . . . . . . . . . . . .  13
     9.2.  New PCEP TLV: Frequency Slot Selection TLV  . . . . . . .  13
     9.3.  New PCEP TLV: Frequency Slot Restriction Constraint
           TLV . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.4.  New PCEP TLV: Spectrum Allocation TLV . . . . . . . . . .  14
     9.5.  New No-Path Reasons . . . . . . . . . . . . . . . . . . .  14
     9.6.  New Error-Types and Error-Values  . . . . . . . . . . . .  15
     9.7.  New Error-Values for Existing Error Type (24) . . . . . .  15
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   11. Contributors' Address . . . . . . . . . . . . . . . . . . . .  15
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     12.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18





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1.  Terminology

   This document uses the terminology defined in [RFC4655], [RFC5440],
   and [RFC7698].

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Introduction

   [RFC4655] defines a Path Computation Element (PCE)-based path
   computation architecture and explains how a Path Computation Element
   (PCE) may compute Label Switched Paths (LSP) in Multiprotocol Label
   Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
   networks at the request of Path Computation Clients (PCCs).  A PCC is
   said 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 communications Protocol (PCEP) is the communication protocol
   used between a PCC and a PCE, and can 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.

   [RFC8780] provides the PCEP extensions for the support of Routing and
   Wavelength Assignment (RWA) in Wavelength Switched Optical Networks
   (WSON) based on the requirements specified in [RFC6163] and
   [RFC7449].














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   To allow efficient allocation of optical spectral bandwidth for
   systems that have high bit-rates, the International Telecommunication
   Union Telecommunication Standardization Sector (ITU-T) has extended
   its Recommendations [ITU-T_G.694.1] to include an enhanced Dense
   Wavelength Division Multiplexing (DWDM) grid by defining a set of
   nominal central frequencies, channel spacings, and the concept of the
   "frequency slot".  In such an environment, a data-plane connection is
   switched based on allocated, variable-sized frequency ranges within
   the optical spectrum, creating what is known as a flexible grid
   (flexi-grid).  [RFC7698] provides Framework and Requirements for
   GMPLS-Based Control of Flexi-Grid Dense Wavelength Division
   Multiplexing (DWDM) Networks.

   The terms "Routing and Spectrum Assignment" (RSA) is introduced in
   [RFC7698] to refer to the process determines a route and frequency
   slot for an LSP.  Hence, when a path is computed, the spectrum
   assignment process determines the central frequency and slot width.
   The term "Spectrum Switched Optical Networks" is also introduced in
   [RFC7698] to refer to a flexi-grid enabled DWDM network, which can be
   controlled by a GMPLS or PCE control plane.

   This document provides PCEP extensions to support RSA in Flexi-grid
   networks.

   Figure 1 shows one typical PCE-based implementation, which is
   referred to as the Combined Routing and Spectrum Assignment (RSA)
   [RFC7698].  With this architecture, the two processes of routing and
   spectrum assignment are accessed via a single PCE.  This architecture
   is the base architecture from which the PCEP extensions are specified
   in this document.


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


      Figure 1: Combined Routing and Spectrum Assignment Architecture









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4.  Spectrum Assignment (SA) Object

   This document aligns with GMPLS extensions for PCEP [RFC8779] for
   generic property such as label, label-set and label assignment noting
   that frequency is a type of label.  Frequency restrictions and
   constraints are also formulated in terms of labels per [RFC7579].

   Spectrum allocation can be performed by the PCE by different means:

   a.  By means of Explicit Label Control (ELC) where the PCE allocates
       which label to use for each interface/node along the path.

   b.  By means of a Label Set where the PCE provides a range of
       potential frequency slots to allocate by each node along the
       path.

   Option b. allows distributed spectrum allocation (performed during
   signaling) to complete spectrum assignment.  Additionally, given a
   range of potential spectrums to allocate, a PC Request SHOULD convey
   the heuristic / mechanism to the allocation.

   The format Routing Backus-Naur Form (RBNF) [RFC5511] of a PCReq
   message per [RFC5440] after incorporating the Spectrum Assignment
   (SA) Object is as follows:


                      <PCReq Message> ::= <Common Header>
                                             [<svec-list>]
                                             <request-list>
                         Where:
                      <request-list>::=<request>[<request-list>]
                      <request>::= <RP>
                                   <GENERALIZED ENDPOINTS>
                                      [<SA>]
                                      [other optional objects...]


   If the SA Object is present in the PCReq message, it MUST be encoded
   after the GENERALIZED ENDPOINTS Object.

   The SA Object-Class is TBD1 (to be assigned by IANA).  The SA Object-
   Type is 1.

   The format of the Spectrum Assignment (SA) Object body is as shown in
   Figure 2.






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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Reserved             |           Flags             |M|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                      Optional TLVs                          //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                            Figure 2: SA Object

   Reserved (16 bits)

   Flags (16 bits)

   One Flag bit is allocated as follows:

   M (Mode - 1 bit): M bit is used to indicate the mode of spectrum
   assignment.  When the M bit is set to 1, this indicates that the
   spectrum assigned by the PCE must be explicit.  That is, the selected
   way to convey the allocated spectrum is by means of Explicit Label
   Control (ELC) [RFC3472] for each hop of a computed LSP.  Otherwise,
   when the M bit is set to 0, the spectrum assigned by the PCE needs
   not be explicit (i.e., it can be suggested in the form of Label Set
   Objects in the corresponding response, to allow distributed SA).  In
   such case, the PCE MUST return a Label Set Field as described in
   Section 2.6 of [RFC7579] in the response.  See Section 5 of this
   document for the encoding discussion of a Label Set Field in a PCRep
   message.

4.1.  Frequency Slot Selection TLV

   The Frequency Slot Selection TLV is used to indicate the frequency
   slot selection constraint in regard to the order of frequency slot
   assignment to be returned by the PCE.  This TLV is only applied when
   the M bit is set in the SA Object specified in Section 4.  This TLV
   SHOULD NOT be present and MUST be ignored when the M bit is set to 0.

   The Frequency Slot Selection TLV value field is defined as:


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S|  FSA Method  |                   Reserved                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Frequency Slot Assignment (FSA) Method (7 bits):

   *  0: unspecified (any); This does not constrain the SA method used
      by a PCC This value is implied when the Frequency Slot Selection
      TLV is absent.

   *  1: First-Fit.  All the feasible frequency slots are numbered
      (based on 'n' parameter), and this SA method chooses the available
      frequency slot with the lowest index, where 'n' is the parameter
      in f = 193.1 THz + n x 0.00625 THz where 193.1THz is the ITU-T
      'anchor frequency' and 'n' is a positive integer including 0
      [RFC7698].

   *  2: Random.  This SA method chooses a feasible frequency slot value
      of 'n' randomly.

   *  3-127: Unassigned.

   S (Symmetry, 1 bit): This flag is only meaningful when the request is
   for a bidirectional LSP, i.e., when the B (Bi-directional) flag is
   set in the RP Object (see Section 7.4.1 of [RFC5440]). 0 denotes
   requiring the same frequency slot in both directions; 1 denotes that
   different spectrums on both directions are allowed.

   The Frequency Slot Selection TLV type is TBD2 (to be assigned by
   IANA).

   If a PCE does not support the attribute(s), its behavior is specified
   below:

   *  S bit clear not supported: a PathErr MUST be generated with the
      Error Code "Routing Problem" (24) with error sub-code "Unsupported
      Frequency Slot Selection Symmetry value" (TBD3).

   *  FSA method not supported: a PathErr MUST be generated with the
      Error Code "Routing Problem" (24) with error sub-code "Unsupported
      Frequency Slot Assignment value" (TBD4).

4.2.  Frequency Slot Restriction Constraint TLV

   For any request that contains a frequency slot assignment, the
   requester (PCC) must be able to specify a restriction on the
   frequency slots to be used.  This restriction is to be interpreted by
   the PCE as a constraint on the tuning ability of the origination
   laser transmitter or on any other maintenance related constraints.






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   The Frequency Slot Restriction Constraint TLV type is TBD5 (to be
   assigned by IANA).  This TLV MAY appear more than once to be able to
   specify multiple restrictions.  The TLV data is defined as shown in
   Figure 3.


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Action          |    Count      |          Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Link Identifiers                          |
       |                          . . .                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Frequency Slot Restriction Field               |
       //                        . . . .                              //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 3: Spectrum Restriction Constraint TLV Encoding

   The fields in the TLV are as follows:

   *  Action: 8 bits.

      -  0 - Inclusive List indicates that one or more link identifiers
         are included in the Link Set. Each identifies a separate link
         that is part of the set.

      -  1 - Inclusive Range indicates that the Link Set defines a range
         of links.  It contains two link identifiers.  The first
         identifier indicates the start of the range (inclusive).  The
         second identifier indicates the end of the range (inclusive).
         All links with numeric values between the bounds are considered
         to be part of the set.  A value of zero in either position
         indicates that there is no bound on the corresponding portion
         of the range.  Note that the Action field can be set to 0 when
         unnumbered link identifier is used.

   *  Count: The number of the link identifiers (8 bits).

   *  Reserved: Reserved for future use (16 bits).

   *  Link Identifiers: Identifies each link ID for which restriction is
      applied.  The length is dependent on the link format and the Count
      field.  See Section 4.3.1 in [RFC8780] for Link Identifier
      encoding.




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   A PCC MAY add a frequency slot restriction that applies to all links
   by setting the Count field to zero and specifying just a set of
   frequency slots.

   Note that all link identifiers in the same list must be of the same
   type.

4.2.1.  Frequency Slot Restriction Field

   The Frequency Slot Restriction Field of the Frequency slot
   restriction TLV is encoded as defined in Section 4.2 of [RFC8363].

5.  Encoding of an RSA Path Reply

   This section provides the encoding of an RSA Path Reply, in the
   PCRep/PCUpd message, for frequency slot allocation as discussed in
   Section 4.  The Spectrum Allocation TLV type is TBD6 (to be assigned
   by IANA).  The TLV data is defined as shown in Figure 4.

   [RFC7570] describes how an attribute TLV ([RFC5420]) can be carried
   in an ERO as a TLV within an LSP Attribute Subobject to provide a
   per-hop description of an LSP attribute.  The Spectrum Assignment TLV
   can be carried in the LSP Attribute Subobject to indicate the
   spectrum to be assigned on the identified link.


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Type             |        Length               |M|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Link Identifier                           |
       |                          . . .                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Allocated Spectrum                         |
       //                        . . . .                              //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 4: Spectrum Allocation TLV Encoding

   *  Type (16 bits): The type of the TLV (TBD6).

   *  Length (15 bits): The length of the TLV including the Type and
      Length fields.

   *  M (Mode): 1 bit




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      -  1 indicates the allocation is under Explicit Label Control.

      -  0 indicates the allocation is expressed in Label Sets.

   *  Link Identifiers: Identifies each link ID for which restriction is
      applied.  The length is dependent on the link format and the Count
      field.  See Section 4.3.1 in [RFC8780] for Link Identifier
      encoding.

   *  Allocated Spectrum (variable): Indicates the spectrum allocated to
      the link identifier.  See Section 4.3 of [RFC7699] for encoding
      details.

   Note that all link identifiers in the same list must be of the same
   type.

5.1.  Error Indicator

   To indicate errors associated with the RSA request, a new Error Type
   and subsequent error-values are defined as follows for inclusion in
   the PCEP-ERROR Object:

   A new Error-Type (TBD7) and subsequent error-value is defined as
   follows:

   *  Error-Type=TBD7; Error-value=1: if a PCE receives an RSA request
      and the PCE is not capable of RSA computation, the PCE MUST send a
      PCErr message with a PCEP-ERROR Object (Error-Type=TBD7) and an
      Error-value (Error-value=1).  The PCE stops processing the
      request.  The corresponding RSA computation MUST be cancelled at
      the PCC.

   Note that generic resource exhaustion at the PCE (e.g., insufficient
   memory) is not signaled via this Error-Type; the PCEP overload
   mechanism (see Section 7.15 of [RFC5440]) applies.

5.2.  NO-PATH Indicator

   To communicate the reasons for not being able to find RSA for the
   path request, the NO-PATH Object can be used in the corresponding
   response.  The format of the NO-PATH Object body is defined in
   [RFC5440].  The object may contain a NO-PATH-VECTOR TLV to provide
   additional information about why a path computation has failed.

   One new bit flag is defined to be carried in the Flags field in the
   NO-PATH-VECTOR TLV carried in the NO-PATH Object.





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   *  Bit TBD8: When set, the PCE indicates no feasible path was found
      that meets all the constraints (e.g., spectrum restriction, etc.)
      associated with RSA.

6.  Manageability Considerations

   Manageability of flexi-grid Routing and Spectrum Assignment (RSA)
   with PCE must address the following considerations:

6.1.  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:

   *  The ability to send a Flexi-Grid RSA 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:

   *  The support for Flexi-Grid RSA.

   *  A set of Flexi-Grid RSA specific policies (authorized sender,
      request rate limiter, etc).

   These parameters may be configured as default parameters for any PCEP
   session the PCEP speaker participates in, or may apply to a specific
   session with a given PCEP peer or a specific group of sessions with a
   specific group of PCEP peers.

6.2.  Information and Data Models

   Extensions to the PCEP YANG module may include to cover the Flexi-
   Grid RSA information introduced in this document.  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].

6.3.  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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6.4.  Requirements on Other Protocols and Functional Components

   The PCE Discovery mechanisms ([RFC5088] and [RFC5089]) may be used to
   advertise Flexi-Grid RSA path computation capabilities to PCCs.

6.5.  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].

7.  Implementation Status

   [NOTE TO RFC EDITOR: This whole section and the reference to
   [RFC7942] is to be removed before publication as an RFC]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].

   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942]], "this will allow reviewers and working
   groups to assign due consideration to documents that have the benefit
   of running code, which may serve as evidence of valuable
   experimentation and feedback that have made the implemented protocols
   more mature.  It is up to the individual working groups to use this
   information as they see fit".

7.1.  Huawei Technologies

   At the time of posting the -10 version of this document, Huawei has
   implemented some of the features specified in this document, on the
   WDM network.  Details are as follow:









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                Organization: Huawei Technologies Co.,Ltd.
                Implementation: Huawei's WDM systems
                Description: supporting PCE Protocol with WDM extensions
                Maturity Level: supported features
                Coverage: Partial
                Contact: zhenghaomian@huawei.com


8.  Security Considerations

   This document has no requirement for a change to the security models
   within PCEP.  However, the additional information distributed in
   order to address the RSA problem represents a disclosure of network
   capabilities that an operator may wish to keep private.
   Consideration should be given to securing this information.

9.  IANA Considerations

   This document requests IANA actions to allocate code points for the
   objects and sub-registries defined in this document.

9.1.  New PCEP Object

   As described in Section 4, a new PCEP Object is defined to carry
   frequency slot assignment-related constraints.  IANA is requested to
   allocate the following from 'PCEP Objects' sub-registry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-objects):


            Object Class    Name    Object                  Reference
            Value                   Type
            -----------------------------------------------------------
            TBD1            SA      1: Spectrum Assignment  [This.I-D]



9.2.  New PCEP TLV: Frequency Slot Selection TLV

   As described in Section 4.1, a new PCEP TLV is defined to indicate
   spectrum selection constraints.  IANA is requested to allocate this
   new TLV from the 'PCEP TLV Type Indicators' subregistry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-tlv-type-
   indicators).








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              Value               Description                 Reference
              ---------------------------------------------------------
              TBD2                Spectrum Selection          [This.I-D]




9.3.  New PCEP TLV: Frequency Slot Restriction Constraint TLV

   As described in Section 4.2, a new PCEP TLV is defined to indicate
   wavelength restriction constraints.  IANA is requested to allocate
   this new TLV from the 'PCEP TLV Type Indicators' subregistry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-tlv-type-
   indicators).


              Value           Description                     Reference
              ---------------------------------------------------------
              TBD5            Frequency Slot Restriction      [This.I-D]
                              Constraint


9.4.  New PCEP TLV: Spectrum Allocation TLV

   As described in Section 5, a new PCEP TLV is defined to indicate the
   allocation of frequency slot(s) by the PCE in response to a request
   by the PCC.  IANA is requested to allocate this new TLV from the
   "PCEP TLV Type Indicators" subregistry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-tlv-type-
   indicators).


               Value           Description             Reference
               ---------------------------------------------------------
               TBD6            Spectrum Allocation     [This.I-D]


9.5.  New No-Path Reasons

   As described in Section 5.2, a new bit flag are defined to be carried
   in the Flags field in the NO-PATH-VECTOR TLV carried in the NO-PATH
   Object.  This flag, when set, indicates that no feasible path was
   found that meets all the RSA constraints (e.g., spectrum restriction,
   signal compatibility, etc.) associated with an RSA path computation
   request.






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   IANA is requested to allocate this new bit flag from the "PCEP NO-
   PATH-VECTOR TLV Flag Field" subregistry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#no-path-vector-tlv).


               Bit             Description                 Reference
               ---------------------------------------------------------
               TBD8            No RSA constraints met      [This.I-D]


9.6.  New Error-Types and Error-Values

   As described in Section 5.1, new PCEP error codes are defined for
   Flexi-Grid RSA errors.  IANA is requested to allocate from the 'PCEP-
   ERROR Object Error Types and Values' sub-registry
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-error-object)


          Error-  Meaning                 Error-Value         Reference
          Type
          -----------------------------------------------------------
          TBD7    Flexi-Grid RSA Error    1: RSA computation  [This.I-D]
                                             Not supported


9.7.  New Error-Values for Existing Error Type (24)

   As discussed in Section 4.1, IANA is requested to allocate two new
   PathErr values for the Existing Error Type (24):


            Meaning                        Error-Value     Reference
            -----------------------------------------------------------
            Unsupported Frequency Slot     TBD3            [This.I-D]
            Selection Symmetry value

            Unsupported Frequency Slot     TBD4            [This.I-D]
            Assignment value


10.  Acknowledgements

   Thanks to Francesco Lazzeri for the technical contribution, and Quan
   Xiong, Dhruv Dhody and Adrian Farrel for useful comments.

11.  Contributors' Address





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   Ricard Vilalta
   CTTC
   Spain

   Email: ricard.vilalta@cttc.es

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3472]  Ashwood-Smith, P., Ed. and L. Berger, Ed., "Generalized
              Multi-Protocol Label Switching (GMPLS) Signaling
              Constraint-based Routed Label Distribution Protocol (CR-
              LDP) Extensions", RFC 3472, DOI 10.17487/RFC3472, January
              2003, <https://www.rfc-editor.org/info/rfc3472>.

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://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, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, DOI 10.17487/RFC5511, April
              2009, <https://www.rfc-editor.org/info/rfc5511>.

   [RFC7699]  Farrel, A., King, D., Li, Y., and F. Zhang, "Generalized
              Labels for the Flexi-Grid in Lambda Switch Capable (LSC)
              Label Switching Routers", RFC 7699, DOI 10.17487/RFC7699,
              November 2015, <https://www.rfc-editor.org/info/rfc7699>.






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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

12.2.  Informative References

   [ITU-T_G.694.1]
              ITU-, T., "SERIES G: TRANSMISSION SYSTEMS AND MEDIA,
              DIGITAL SYSTEMS AND NETWORKS; Digital networks; Spectral
              grids for WDM applications: DWDM frequency grid", ITU-T
              Rec. G.694.1 , October 2020,
              <https://www.itu.int/rec/T-REC-G.694.1>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC4657]  Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [RFC5420]  Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangar, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, DOI 10.17487/RFC5420,
              February 2009, <https://www.rfc-editor.org/info/rfc5420>.

   [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, DOI 10.17487/RFC6163, April 2011,
              <https://www.rfc-editor.org/info/rfc6163>.

   [RFC7449]  Lee, Y., Ed., Bernstein, G., Ed., Martensson, J., Takeda,
              T., Tsuritani, T., and O. Gonzalez de Dios, "Path
              Computation Element Communication Protocol (PCEP)
              Requirements for Wavelength Switched Optical Network
              (WSON) Routing and Wavelength Assignment", RFC 7449,
              DOI 10.17487/RFC7449, February 2015,
              <https://www.rfc-editor.org/info/rfc7449>.

   [RFC7570]  Margaria, C., Ed., Martinelli, G., Balls, S., and B.
              Wright, "Label Switched Path (LSP) Attribute in the
              Explicit Route Object (ERO)", RFC 7570,
              DOI 10.17487/RFC7570, July 2015,
              <https://www.rfc-editor.org/info/rfc7570>.



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   [RFC7579]  Bernstein, G., Ed., Lee, Y., Ed., Li, D., Imajuku, W., and
              J. Han, "General Network Element Constraint Encoding for
              GMPLS-Controlled Networks", RFC 7579,
              DOI 10.17487/RFC7579, June 2015,
              <https://www.rfc-editor.org/info/rfc7579>.

   [RFC7698]  Gonzalez de Dios, O., Ed., Casellas, R., Ed., Zhang, F.,
              Fu, X., Ceccarelli, D., and I. Hussain, "Framework and
              Requirements for GMPLS-Based Control of Flexi-Grid Dense
              Wavelength Division Multiplexing (DWDM) Networks",
              RFC 7698, DOI 10.17487/RFC7698, November 2015,
              <https://www.rfc-editor.org/info/rfc7698>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC8363]  Zhang, X., Zheng, H., Casellas, R., Gonzalez de Dios, O.,
              and D. Ceccarelli, "GMPLS OSPF-TE Extensions in Support of
              Flexi-Grid Dense Wavelength Division Multiplexing (DWDM)
              Networks", RFC 8363, DOI 10.17487/RFC8363, May 2018,
              <https://www.rfc-editor.org/info/rfc8363>.

   [RFC8779]  Margaria, C., Ed., Gonzalez de Dios, O., Ed., and F.
              Zhang, Ed., "Path Computation Element Communication
              Protocol (PCEP) Extensions for GMPLS", RFC 8779,
              DOI 10.17487/RFC8779, July 2020,
              <https://www.rfc-editor.org/info/rfc8779>.

   [RFC8780]  Lee, Y., Ed. and R. Casellas, Ed., "The Path Computation
              Element Communication Protocol (PCEP) Extension for
              Wavelength Switched Optical Network (WSON) Routing and
              Wavelength Assignment (RWA)", RFC 8780,
              DOI 10.17487/RFC8780, July 2020,
              <https://www.rfc-editor.org/info/rfc8780>.

Authors' Addresses

   Haomian Zheng (editor)
   Huawei Technologies Co., Ltd.
   Email: zhenghaomian@huawei.com


   Young Lee
   Samsung
   Email: younglee.tx@gmail.com




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   Ramon Casellas
   CTTC
   Email: ramon.casellas@cttc.es


   Daniele Ceccarelli
   Cisco
   Email: dceccare@cisco.com











































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