PCEP Extension for Flexible Grid Networks
draft-ietf-pce-flexible-grid-05

Document Type Active Internet-Draft (pce WG)
Authors Young Lee  , Haomian Zheng  , Ramon Casellas  , Ricard Vilalta  , Daniele Ceccarelli  , Francesco Lazzeri 
Last updated 2021-02-22
Replaces draft-lee-pce-flexible-grid
Stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Formats plain text pdf htmlized bibtex
Stream WG state WG Document
Document shepherd No shepherd assigned
IESG IESG state I-D Exists
Consensus Boilerplate Unknown
Telechat date
Responsible AD (None)
Send notices to (None)
PCE Working Group                                               Y. Lee  
Internet Draft                                                 Samsung 
Intended status: Standard Track                      H. Zheng (Editor) 
Expires: August 22, 2021                           Huawei Technologies 
                                                           R. Casellas 
                                                            R. Vilalta 
                                                                  CTTC 
                                                         D. Ceccarelli 
                                                            F. Lazzeri 
                                                              Ericsson 
                                   
                                                     February 22, 2021 
 
                                      
                 PCEP Extension for Flexible Grid Networks 

                      draft-ietf-pce-flexible-grid-05 

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 to IETF in full conformance with 
   the provisions of BCP 78 and BCP 79.        

   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups.  Note that 
   other groups may also distribute working documents as Internet-
   Drafts. 

   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." 

   The list of current Internet-Drafts can be accessed at 
   http://www.ietf.org/ietf/1id-abstracts.txt 

   The list of Internet-Draft Shadow Directories can be accessed at 
   http://www.ietf.org/shadow.html. 

   This Internet-Draft will expire on August 22, 2021. 

 
 
 
Lee, et al               Expires August 2021                   [Page 1] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

Copyright Notice 

   Copyright (c) 2021 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. Terminology ................................................. 3 
   2. Requirements Language ....................................... 3 
   3. Introduction ................................................ 3 
   4. Spectrum Assignment (SA) Object ............................. 5 
      4.1. Frequency-Slot Selection TLV ........................... 7 
      4.2. Frequency-slot Restriction Constraint TLV .............. 8 
         4.2.1. Frequency-Slot Restriction Field ................. 10 
   5. Encoding of a RSA Path Reply ............................... 10 
      5.1. Error Indicator........................................ 11 
      5.2. NO-PATH Indicator ..................................... 11 
   6. Manageability Considerations ............................... 12 
      6.1. Control of Function and Policy ........................ 12 
      6.2. Information and Data Models ........................... 12 
      6.3. Verifying Correct Operation ........................... 13 
      6.4. Requirements on Other Protocols and Functional Components13 
      6.5. Impact on Network Operation ........................... 13 
   7. Implementation Status ...................................... 13 
   8. Security Considerations .................................... 14 
   9. IANA Considerations ........................................ 14 
      9.1. New PCEP Object........................................ 14 
      9.2. New PCEP TLV: Frequency Slot Selection TLV ............ 14 
      9.3. New PCEP TLV: Frequency Slot Restriction Constraint TLV. 15 
      9.4. New PCEP TLV: Spectrum Allocation TLV ................. 15 
      9.5. New No-Path Reasons ................................... 15 
      9.6. New Error-Types and Error-Values ...................... 16 
      9.7. New Error-Values for Existing Error Type (24) ......... 16 
   10. References ................................................ 16 

 
 
Lee et al.               Expires August 2021                   [Page 2] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

      10.1. Normative References ................................. 16 
      10.2. Informative References ............................... 17 
   11. Contributors .............................................. 18 
   Authors' Addresses ............................................ 19 
    
    

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].   

 
 
Lee et al.               Expires August 2021                   [Page 3] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   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 [G.694.1] and [G.872] to 
   include a new 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 route 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 2 shows one typical PCE based implementation, which is 
   referred to as the Combined Routing and Spectrum Assignment (R&SA) 
   [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 Process (R&SA) architecture 

    

 
 
Lee et al.               Expires August 2021                   [Page 4] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

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 request, it MUST be encoded after 
   the GENERALIZED ENDPOINTS object.    
 
 
Lee et al.               Expires August 2021                   [Page 5] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   SA Object-Class is (TBD1) (To be assigned by IANA). 

   SA Object-Type is 1.               

   The format of the Spectrum Assignment (SA) object body is as 
   follows: 

   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| 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                Frequency-Slot Selection TLV                   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         Frequency-Slot Restriction Constraint TLV             | 
   .                                                               . 
   .                                                               . 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   //                      Optional TLVs                          // 
   |                                                               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                            Figure 2 SA Object 

   o  Reserved (16 bits) 

   o  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 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) [RFC4003] for each hop of a 
         computed LSP. Otherwise, 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.  

 
 
Lee et al.               Expires August 2021                   [Page 6] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

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 
   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 cleared.  

   The Frequency-Slot Selection sub-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                   | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
  Where: 
     
      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 sub-TLV is absent. 
    
      1: First-Fit.  All the feasible frequency slots are numbered3  
         (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 193.1  
         THz 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 (see [RFC5440]). 
 
    0 denotes requiring the same frequency-slot in both directions;  
      1 denotes that different spectrums on both directions are   
      allowed. 
 
 
Lee et al.               Expires August 2021                   [Page 7] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

    
   IANA is to allocate a new PCEP TLV type, Frequency-Slot Selection 
   TLV (TBD2) in the "PCEP TLV Type Indicators" subregistry 
   (http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-tlv-type-
   indicators).  
      

   The processing rules for this TLV are as follows: 

    
      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.  

   The format of the Frequency-Slot Restriction Constraint TLV is as 
   follows: 

   <Frequency-lot Restriction Constraint> ::= 

                  (<Action> 

                  <Link Identifiers> <Freq-slot Restriction>)... 

   Where 

   <Link Identifiers> ::= <Link Identifier> [<Link Identifiers>] 

   See Section 4.3.1 in [RFC8780] for the encoding of the Link     
   Identifiers Field.  
 
 
Lee et al.               Expires August 2021                   [Page 8] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   

   IANA is to allocate a new PCEP TLV, the Frequency slot Restriction 
   Constraint TLV type (TBD5). This TLV MAY appear more than once to be 
   able to specify multiple restrictions.   

   The TLV data is defined as follows: 

 

    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 

   o  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.  

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

   Note that 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.  
 
 
Lee et al.               Expires August 2021                   [Page 9] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   Note that all link identifiers in the same list must be of the same  
   type.  
 
   o  Reserved: Reserved for future use (16 bits)  

 
   o  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. 

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 a RSA Path Reply 

   This section provides the encoding of a RSA Path Reply, in the 
   PCRep/PCUpd message, for frequency slot allocation as discussed in 
   Section 4. Spectrum Allocation TLV IANA is to allocate a new PCEP 
   TLV type, the Spectrum Allocation TLV type (TBD6). The TLV data is 
   defined as follows: 

    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(s)                      | 
   //                        . . . .                              // 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 
                 Figure 4 Spectrum Allocation TLV Encoding 

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

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

   o  M (Mode): 1 bit  

 
 
Lee et al.               Expires August 2021                  [Page 10] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

      -  0 indicates the allocation is under Explicit Label Control. 

      -  1 indicates the allocation is expressed in Label Sets.   

   Note that all link identifiers in the same list must be of the same  
   type.  
   o  Link Identifier (variable): Identifies the interface to which 
   assignment spectrum(s) is applied. See Section 3.3 for Link 
   Identifier encoding.   

   o  Allocated Spectrum(s) (variable): Indicates the allocated 
   spectrum(s) to the link identifier. See Section 3.3.1 for encoding 
   details.  

   This TLV is encoded as an attributes TLV, per [RFC5420], which is 
   carried in the ERO LSP Attribute Subobjects per [RFC7570].  
 
5.1. Error Indicator 

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

   A new Error-Type (TBD7) and subsequent error-values are defined as 
   follows: 

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

         Error-Type=TBD7; Error-value=2: if a PCE receives a 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=TDB) and an Error-value (Error-value=2). The PCE stops 
         processing the request.  The corresponding RSA computation 
         MUST be cancelled at the PCC.  

5.2. NO-PATH Indicator 

   To communicate the reason(s) 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 

 
 
Lee et al.               Expires August 2021                  [Page 11] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   [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. 

         Bit TBD8: When set, the PCE indicates no feasible route 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]. 

 
 
 
Lee et al.               Expires August 2021                  [Page 12] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

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]. 

6.4. Requirements on Other Protocols and Functional Components 

   The PCE Discovery mechanisms ([RFC5089] and [RFC5088]) may be used 
   to advertise Flexi-Grid RSA path computation capabilities to PCCs. 
   This draft has requirements on other protocols (ERO objects, etc. 
   which are under TEAS or CCAMP.) 

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". 

 
 
Lee et al.               Expires August 2021                  [Page 13] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   At the time of posting the -05 version of this document, there are 
   no known implementations of this mechanism.  It is believed that two   
   vendors are considering prototype implementations, but these plans   
   are too vague to make any further assertions. 

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 

   IANA is requested to make allocations from the sub-registries as 
   described in the following sections. 
    
9.1. New PCEP Object 

   As described in Section 4.1, a new PCEP Object is defined to carry 
   frequency-slot assignment related constraints. IANA is 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 Sections 4.2, a new PCEP TLV is defined to indicate 
   spectrum selection constraints. IANA is 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 
   --------------------------------------------------------- 
   TBD2         Spectrum Selection     [This.I-D] 
                      

 
 
Lee et al.               Expires August 2021                  [Page 14] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

9.3. New PCEP TLV: Frequency Slot Restriction Constraint TLV 

   As described in Section 4.3, a new PCEP TLV is defined to indicate 
   wavelength restriction constraints. IANA is 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 freq-slots(s) by the PCE in response to a request by 
   the PCC. IANA is 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 4.3, 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 
   route was found that meets all the RSA constraints (e.g., spectrum 
   restriction, signal compatibility, etc.) associated with a RSA path 
   computation request. 

   IANA is 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 
   ----------------------------------------------------- 
 
 
Lee et al.               Expires August 2021                  [Page 15] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   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 
   WSON RWA errors. IANA is 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: Insufficient     [This.I-D] 
                                Memory 
    
                           2: RSA computation  [This.I-D] 
                             Not supported 

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

   As discussed in Section 4.1, two new PathErr values for the Existing 
   Error Type (24) are to be allocated:  
 
   Meaning                   Error-Value     Reference 
 
   --------------------------------------------------------------- 
   Unsupported Frequency slot  
   Selection Symmetry value        TBD3              [This.I-D] 
    
   Unsupported Frequency Slot  
   Assignment value             TBD4              [This.I-D] 
    

10. References 

10.1. Normative References 

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

   [RFC4003] Berger, L., "GMPLS Signaling Procedure for Egress 
             Control", RFC 4003, February 2005. 
 
 
Lee et al.               Expires August 2021                  [Page 16] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 
             Element (PCE) communication Protocol", RFC 5440, March 
             2009. 

   [RFC5511] A. Farrel, "Routing Backus-Naur Form (RBNF): A Syntax Used 
             to Form Encoding Rules in Various Routing Protocol 
             Specifications", RFC 5511, April 2009.  

   [RFC5088] Le Roux, JL, JP. Vasseur, Y. Ikejiri, and R. Zhang, "OSPF 
             Protocol Extensions for Path Computation Element (PCE) 
             Discovery," RFC 5088, January 2008.  

   [RFC5089] Le Roux, JL, JP. Vasseur, Y. Ikejiri, and R. Zhang, "IS-IS 
             Protocol Extensions for Path Computation Element (PCE) 
             Discovery," RFC 5089, January 2008. 

   [RFC8174] B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119 
             Key Words", RFC 8174, May 2017.  

10.2. Informative References 

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

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

   [RFC5420] Farrel, A. "Encoding of Attributes for MPLS LSP 
             Establishment Using Resource Reservation Protocol Traffic 
             Engineering (RSVP-TE)", RFC 5420, February 2009. 

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

   [RFC7449] Lee, Y., et. al., "PCEP Requirements for WSON Routing and 
             Wavelength Assignment", RFC 7449, February 2015. 

   [RFC7570] Margaria, et al., "Label Switched Path (LSP) Attribute in 
             the Explicit Route Object (ERO)", RFC 7570, July 2015. 

   [RFC7579] Bernstein and Lee, "General Network Element Constraint 
             Encoding for GMPLS Controlled Networks", RFC 7579, June 
             2015.  

 
 
Lee et al.               Expires August 2021                  [Page 17] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

   [RFC7698] O. Gonzalez de Dios, R. Casellas, editors, "Framework and 
             Requirements for GMPLS-Based Control of Flexi-Grid Dense 
             Wavelength Division Multiplexing (DWDM) Networks", RFC 
             7698, November 2015. 

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of 
             Running Code: The Implementation Status Section", BCP 205,         
             RFC 7942, July 2016, 

   [RFC8363] X. Zhang, H. Zheng, R. Casellas, O. Gonzalez de Dios, D. 
             Ceccarelli, "GMPLS OSPF-TE Extensions in Support of Flexi-
             Grid Dense Wavelength Division Multiplexing (DWDM) 
             Networks", RFC8363, May 2018.  

   [RFC8779] Margaria, et al., "PCEP extensions for GMPLS", RFC 8779, 
             July 2020. 

   [RFC8780] Y. Lee (Ed.), and R. Casellas (Ed.), "PCEP Extension for 
             WSON Routing and Wavelength Assignment", RFC8780, July 2020.  

   [G.694.1] "Spectral grids for WDM applications: DWDM frequency 
             grid", ITU-T G.694.1, February 2012.   

   [G.872] "Architecture of optical transport networks", ITU-T G.872, 
             January 2017.  

    

11. Contributors 

 

 
 
Lee et al.               Expires August 2021                  [Page 18] 


Internet-Draft    PCEP Extension for Flexible Grid        February 2021 
    

Authors' Addresses 

   Young Lee 
   Samsung 
   Email: younglee.tx@gmail.com 
     
    
   Haomian Zheng  
   Huawei Technologies 
   Email: zhenghaomian@huawei.com 
    
    
   Ramon Casellas 
   CTTC 
   Av. Carl Friedrich Gauss n7 
   Castelldefels, Barcelona 08860 
   Spain 
    
   Email: ramon.casellas@cttc.es 
 
    
   Ricard Vilalta 
   CTTC 
   Email: ricard.vilalta@cttc.es 
 
 
   Daniele Ceccarelli 
   Ericsson AB 
   Gronlandsgatan 21  
   Kista - Stockholm 
   Email: daniele.ceccarelli@ericsson.com 
 
   Francesco Lazzeri 
   Ericsson 
   Via Melen 77 
   Genova - Italy 
   Email: francesco.lazzeri@ericsson.com  
 
    
    
    

 
 
Lee et al.               Expires August 2021                  [Page 19]