PCE Working Group                                                Y. Lee
Internet-Draft                                                  Samsung
Intended status: Standards Track                               H. Zheng
Expires: December 27, 2022                          Huawei Technologies
                                                          O. G. de Dios
                                                             Telefonica
                                                           Victor Lopez
                                                                  Nokia
                                                                 Z. Ali
                                                          Cisco Systems
                                                          June 27, 2022




  Path Computation Element Communication Protocol (PCEP) Extensions for
             Stateful PCE Usage in GMPLS-controlled Networks

                 draft-ietf-pce-pcep-stateful-pce-gmpls-20


Abstract

   The PCE communication Protocol (PCEP) has been extended to support
   stateful PCE functions where the Stateful PCE maintains information
   about paths and resource usage within a network, but these
   extensions do not cover all requirements for GMPLS networks.

   This document provides the extensions required for PCEP so as to
   enable the usage of a stateful PCE capability in GMPLS-controlled
   networks.

Status of this Memo

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   reference material or to cite them other than as "work in progress."




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Table of Contents


   Table of Contents ............................................... 2
   1. Introduction ................................................. 3
      1.1. Conventions used in this document ....................... 4
   2. Terminology .................................................. 4
   3. General Context of Stateful PCE and PCEP for GMPLS ........... 4
   4. Main Requirements ............................................ 5
   5. Overview of Stateful PCEP Extensions for GMPLS Networks ...... 6
      5.1. Capability Advertisement for Stateful PCEP in GMPLS ..... 6
      5.2. LSP Synchronization ..................................... 7
      5.3. LSP Delegation and Cleanup .............................. 7
      5.4. LSP Operations .......................................... 7
   6. PCEP Object Extensions ....................................... 8
      6.1. Existing Extensions used for Stateful GMPLS ............. 8
      6.2. New Extensions .......................................... 9
         6.2.1. GMPLS-CAPABILITY TLV in OPEN Object ................ 9
         6.2.2. New LSP Exclusion Sub-object in the XRO ............ 9
         6.2.3. New flags in the LSP-EXTENDED-FLAG TLV in LSP Object10
   7. Update to Error Handling .................................... 11
      7.1. Error Handling in PCEP Capabilities Advertisement ...... 11
      7.2. Error Handling in LSP Re-optimization .................. 12


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      7.3. Error Handling in Route Exclusion ...................... 12
      7.4. Error Handling for generalized END-POINTS .............. 12
   8. Implementation .............................................. 13
      8.1. Huawei Technologies .................................... 13
   9. IANA Considerations ......................................... 14
      9.1. New Flags in GMPLS-CAPABILITY TLV ...................... 14
      9.2. New Sub-object for the Exclude Route Object ............ 14
      9.3. Flags Field for LSP exclusion Sub-object ............... 14
      9.4. New  Flags in the LSP-EXTENDED-FLAGS TLV ............... 15
      9.5. New PCEP Error Codes ................................... 15
   10. Manageability Considerations ............................... 16
      10.1. Control of Function through Configuration and Policy .. 16
      10.2. Information and Data Models ........................... 16
      10.3. Liveness Detection and Monitoring ..................... 17
      10.4. Verifying Correct Operation ........................... 17
      10.5. Requirements on Other Protocols and Functional Components17
      10.6. Impact on Network Operation ........................... 17
   11. Security Considerations .................................... 17
   12. Acknowledgement ............................................ 18
   13. References ................................................. 18
      13.1. Normative References .................................. 18
      13.2. Informative References ................................ 19
   14. Contributors' Address ...................................... 21
   Appendix A: PCEP Messages ...................................... 21
      A.1  The PCRpt Message ...................................... 22
      A.2 The PCUpd Message ....................................... 23
      A.3 The PCInitiate Message .................................. 23
   Authors' Addresses ............................................. 25

1. Introduction

   [RFC4655] presents the architecture of a Path Computation Element
   (PCE)-based model for computing Multiprotocol Label Switching (MPLS)
   and Generalized MPLS (GMPLS) Traffic Engineering Label Switched
   Paths (TE LSPs).  To perform such a constrained computation, a PCE
   stores the network topology (i.e., TE links and nodes) and resource
   information (i.e., TE attributes) in its TE Database (TED).  A PCE
   that only maintains TED is referred to as a stateless PCE.  [RFC5440]
   describes the Path Computation Element Communication Protocol (PCEP)
   for interaction between a Path Computation Client (PCC) and a PCE,
   or between two PCEs, enabling computation of TE LSPs.  PCEP is
   further extended to support GMPLS-controlled networks as per
   [RFC8779].

   Stateful PCEs are shown to be helpful in many application scenarios,
   in both MPLS and GMPLS networks, as illustrated in [RFC8051].
   Further discussion of concept of a stateful PCE can be found in
   [RFC7399].  In order for these applications to able to exploit the


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   capability of stateful PCEs, extensions to stateful PCEP for GMPLS
   are required.

   [RFC8051] describes how a stateful PCE can be applicable to solve
   various problems for MPLS-TE and GMPLS networks and the benefits it
   brings to such deployments.

   [RFC8231] specifies a set of extensions to PCEP to enable stateful
   control of TE LSPs where they are configured on the PCC, and control
   over them could be delegated to the PCE. Furthermore, [RFC8281]
   describes the setup and teardown of PCE-initiated LSPs under the
   active stateful PCE model, without the need for local configuration
   on the PCC. However, both the documents left out the specification
   for technology-specific objects/TLVs, and do not cover the GMPLS-
   controlled networks (e.g., Wavelength Switched Optical Network
   (WSON), Optical Transport Network (OTN), Synchronous Optical Network
   (SONET)/Synchronous Digital Hierarchy (SDH), etc. technologies).

   This document focuses on the extensions that are necessary in order
   for the deployment of stateful PCEs and the requirements for PCE-
   initiated LSPs in GMPLS-controlled networks. Section 3 provides a
   general context of the usage of Stateful PCE and PCEP for GMPLS.
   The various requirements for stateful GMPLS, including PCE-
   initiation for GMPLS LSPs, are provided in Section 4. An overview of
   the PCEP extensions are specified in Section 5, as a solution to
   address such requirements with PCEP object extensions in Section 6.

1.1. Conventions used in this document

   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.

2. Terminology

   Terminology used in this document is the same as terminology used in
   [RFC5440], [RFC8231], [RFC8281], and [RFC8779]



3. General Context of Stateful PCE and PCEP for GMPLS

   This section is built on the basis of Stateful PCE specified in
   [RFC8231] and PCEP for GMPLS specified in [RFC8779].




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   The operation for Stateful PCE on LSPs can be divided into two types,
   active stateful PCE and passive stateful PCE as described in
   [RFC8051].

   For active stateful PCE, a Path Computation Update Request (PCUpd)
   message is sent from PCE to PCC to update the LSP state for the LSPs
   delegated to the PCE. Any changes to the delegated LSPs generate a
   Path Computation State Report (PCRpt) message from the PCC to PCE to
   convey the changes of the LSPs. Any modifications to the
   Objects/TLVs that are identified in this document to support GMPLS
   technology-specific attributes will be carried in the PCRpt and
   PCUpd messages.

   For passive stateful PCEs, PCReq/PCRep messages are used to request
   for path computation.  GMPLS-technology specific Objects and TLVs
   are defined in [RFC8779], this document builds on it and adds the
   stateful PCE aspects where applicable. Passive Stateful PCE makes
   use of PCRpt messages when reporting LSP State changes sent by PCCs
   to PCEs.  Any modifications to the Objects/TLVs that are identified
   in this document to support GMPLS technology-specific attributes
   will be carried in the PCRpt message.

   Furthermore, the LSP Initiation function of PCEP is defined in
   [RFC8281] to allow the PCE to initiate LSP establishment after the
   path is computed. An LSP Initiate Request (PCInitiate) message is
   used to trigger the end node to set up the LSP. Any modifications to
   the Objects/TLVs that are identified in this document to support
   GMPLS technology-specific attributes will be carried in the
   PCInitiate messages.

   [RFC8779] defines GMPLS-technology specific Objects/TLVs in
   stateless PCEP, and this document makes use of these Objects/TLVs
   without modifications where applicable. Where these Objects/TLVs
   require modifications to incorporate stateful PCE, they are
   described in this document. PCE-Initiated LSPs follow the principle
   specified in [RFC8281], and the GMPLS-specific extensions are also
   included in this document.

4. Main Requirements

   This section notes the main functional requirements for PCEP
   extensions to support stateful PCE for use in GMPLS-controlled
   networks, based on the description in [RFC8051].  Many
   requirements are common across a variety of network types (e.g.,
   MPLS-TE networks and GMPLS networks) and the protocol extensions to
   meet the requirements are already described in [RFC8231], such as
   LSP update, delegation and state synchronization/report.  Protection
   context information that describes the GMPLS requirement can also


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   follow the description in [RFC8745].  This document does not repeat
   the description of those protocol extensions.  This document
   presents protocol extensions for a set of requirements which are
   specific to the use of a stateful PCE in a GMPLS-controlled network.

   The requirements for GMPLS-specific stateful PCE are as follows:

      o Advertisement of the stateful PCE capability.  This generic
        requirement is covered in Section 5.4 of [RFC8231]. The GMPLS-
        CAPABILITY TLV specified in section 2.1 of [RFC8779] and its
        extension in this document needs to be advertised as well.

      o All the PCEP messages need to be capable of indicating GMPLS-
        specific switching capabilities.  GMPLS LSP
        creation/modification/deletion requires knowledge of LSP
        switching capability (e.g., Time-Division Multiplex Capable
        (TDM), Layer 2 Switch Capable (L2SC), OTN-TDM, Lambda Switch
        Capable (LSC), etc.) and the generalized payload (G-PID) to be
        used according to [RFC3471], [RFC3473]. It also requires the
        specification of data flow specific traffic parameters (also
        known as Traffic Specification (Tspec)), which are technology
        specific. Such information would need to be included in various
        PCEP messages.

      o In some technologies, path calculation is tightly coupled with
        label selection along the route.  For example, path calculation
        in a Wavelength Division Multiplexing (WDM) network may include
        lambda continuity and/or lambda feasibility constraints and
        hence a path computed by the PCE is associated with a specific
        lambda (label).  Hence, in such networks, the label information
        needs to be provided to a PCC in order for a PCE to initiate
        GMPLS LSPs under the active stateful PCE model, i.e., explicit
        label control may be required.

      o Stateful PCEP messages also need to indicate the protection
        context information for the LSP specified by GMPLS, as defined
        in [RFC4872], [RFC4873].

5. Overview of Stateful PCEP Extensions for GMPLS Networks

5.1. Capability Advertisement for Stateful PCEP in GMPLS

   Capability Advertisement has been specified in [RFC8231], and can be
   achieved by using the "STATEFUL-PCE-CAPABILITY TLV" in the Open
   message. Another GMPLS-CAPABILITY TLV has been defined in [RFC8779].
   A subregistry to manage the Flag field of the GMPLS-CAPABILITY TLV
   is created by the IANA as requested by [RFC8779].  The following
   bits are introduced by this document in the GMPLS-CAPABILITY TLV as


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   flags to indicate the capability for LSP report, update and
   initiation in GMPLS networks: LSP-REPORT-CAPABILITY(TBDa), LSP-
   UPDATE-CAPABILITY (TBD1), and LSP-INSTANTIATION-CAPABILITY (TBD2).

5.2. LSP Synchronization

   After the session between the PCC and a stateful PCE is initialized,
   the PCE must learn the state of a PCC's LSPs (including its
   attributes) before it can perform path computations or update LSP
   attributes in a PCC. This process is known as LSP state
   synchronization.  The LSP attributes including bandwidth, associated
   route, and protection information etc., are stored by the PCE in the
   LSP database (LSP-DB).  Note that, as described in [RFC8231], the
   LSP state synchronization covers both the bulk reporting of LSPs at
   initialization as well the reporting of new or modified LSPs during
   normal operation. Incremental LSP-DB synchronization may be desired
   in a GMPLS-controlled network and it is specified in [RFC8232].

   The format of the PCRpt message is specified in [RFC8231] and
   extended in [RFC8623] to include the END-POINTS object. The END-
   POINTS object is extended for GMPLS in [RFC8779]. The END-POINTS
   object can be carried in the PCRpt message as specified in [RFC8623].
   The END-POINTS object type for GMPLS is included in the PCRpt
   message as per the same.

   The BANDWIDTH, LSP Attributes (LSPA), Include Route Object (IRO) and
   Exclude Route Object (XRO) objects are extended for GMPLS in
   [RFC8779] and are also used in the PCRpt in the same manner. These
   objects are carried in the PCRpt message as specified in [RFC8231]
   (as the attribute-list defined in Section 6.5 of [RFC5440] and
   extended by many other documents that define PCEP extensions for
   specific scenarios).

   The SWITCH-LAYER object is defined in [RFC8282]. This object is
   carried in PCRpt message as specified in section 3.2 of [RFC8282].

5.3. LSP Delegation and Cleanup

   LSP delegation and cleanup procedure specified in [RFC8231] are
   equally applicable to GMPLS LSPs and this document does not modify
   the associated usage.

5.4. LSP Operations

   Both passive and active stateful PCE mechanisms in [RFC8231] are
   applicable in GMPLS-controlled networks. Remote LSP Initiation in
   [RFC8281] is also applicable in GMPLS-controlled networks.



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6. PCEP Object Extensions

6.1. Existing Extensions used for Stateful GMPLS

   Existing extensions defined in [RFC8779] can be used in the Stateful
   PCEP with no changes or slightly changes for GMPLS network control,
   including the following:

   o END-POINTS: Generalized END-POINTS was specified in [RFC8779] to
   include GMPLS capabilities. All Stateful PCEP messages MUST include
   the END-POINTS with Generalized Endpoint object type, containing the
   LABEL-REQUEST TLV.  Further note that

    *  As per [RFC8779] for stateless GMPLS path computation, the
      Generalized END-POINTS object may contain a LABEL-REQUEST TLV
      and/or LABEL-SET. In this document, only the LABEL-REQUEST TLV is
      used to specify the switching type, encoding type and G-PID of the
      LSP.

    *  If unnumbered endpoint addresses are used for the LSP, the
      UNNUMBERED-ENDPOINT TLV [RFC8779] MUST be used to specify the
      unnumbered endpoint addresses.

    *  The Generalized END-POINTS MAY contain other TLVs defined in
      [RFC8779].

   o RP: RP object extension, together with the Routing Granularity
   (RG) flag defined in [RFC8779], are applicable in the Stateful PCEP
   for GMPLS networks.

   o BANDWIDTH: Generalized BANDWIDTH was specified in [RFC8779] to
   represent GMPLS features, including asymmetric bandwidth and G-PID
   information.

   o LSPA: LSPA Extensions in Section 2.8 of [RFC8779] is applicable
   in Stateful PCEP for GMPLS networks.

   o IRO: IRO Extensions in Section 2.6 of [RFC8779] is applicable in
   Stateful PCEP for GMPLS networks.

   o XRO: XRO Extensions in Section 2.7 of [RFC8779] is applicable in
   Stateful PCEP for GMPLS networks. A new flag is defined in section
   7.2.2 of this document.

   o ERO: The Explicit Route Object (ERO) was not extended in
   [RFC8779], and nor in this document.




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   o SWITCH-LAYER: SWITCHING-LAYER definition in Section 3.2 of
   [RFC8282] is applicable in Stateful PCEP messages for GMPLS networks.

6.2. New Extensions

 6.2.1. GMPLS-CAPABILITY TLV in OPEN Object

   In [RFC8779], IANA has allocated value 45 (GMPLS-CAPABILITY) from
   the "PCEP TLV Type Indicators" sub-registry.  The TLV is extended
   with three flags to indicate the Report, Update, and Initiation
   capabilities.

   R (LSP-REPORT-CAPABILITY(TBDa) -- 1 bit): if set to 1 by a PCC, the
   R flag indicates that the PCC is capable of reporting the current
   state of an GMPLS LSP, whenever there's a change to the parameters
   or operational status of the GMPLS LSP; if set to 1 by a PCE, the R
   Flag indicates that the PCE is interested in receiving GMPLS LSP
   State Reports whenever there is a parameter or operational status
   change to the LSP.  The LSP-REPORT-CAPABILITY flag must be
   advertised by both a PCC and a PCE for PCRpt messages to be allowed
   on a PCEP session for GMPLS LSP.

   U (LSP-UPDATE-CAPABILITY(TBD1) -- 1 bit): if set to 1 by a PCC, the
   U flag indicates that the PCC allows modification of GMPLS LSP
   parameters; if set to 1 by a PCE, the U flag indicates that the PCE
   is capable of updating GMPLS LSP parameters.  The LSP-UPDATE-
   CAPABILITY flag must be advertised by both a PCC and a PCE for PCUpd
   messages to be allowed on a PCEP session for GMPLS LSP.

   I (LSP-INSTANTIATION-CAPABILITY(TBD2) -- 1 bit): If set to 1 by a
   PCC, the I flag indicates that the PCC allows instantiation of a
   GMPLS LSP by a PCE.  If set to 1 by a PCE, the I flag indicates that
   the PCE supports instantiating GMPLS LSPs.  The LSP-INSTANTIATION-
   CAPABILITY flag must be set by both the PCC and PCE in order to
   enable PCE-initiated LSP instantiation.

 6.2.2. New LSP Exclusion Sub-object in the XRO

   [RFC5521] defines a mechanism for a PCC to request or demand that
   specific nodes, links, or other network resources are excluded from
   paths computed by a PCE.  A PCC may wish to request the computation
   of a path that avoids all link and nodes traversed by some other LSP.

   To this end this document defines a new sub-object for use with
   route exclusion defined in [RFC5521].  The LSP exclusion sub-object
   is as follows:




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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |X|Type (TBD3)  |     Length    |   Reserved    |    Flags      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //                    Symbolic Path Name                       //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: New LSP Exclusion Sub-object Format

     X bit: Same as the X bit defined in XRO sub-objects by [RFC5521]
     (i.e., mandatory vs. desired).

     Type: Sub-object Type for an LSP exclusion sub-object. Value of
     TBD3. To be assigned by IANA.

     Length: The Length contains the total length of the sub-object in
     bytes, including the Type and Length fields.

     Reserved: MUST be set to zero on transmission and ignored on
     receipt.

     Flags: This field may be used to further specify the exclusion
     constraint with regard to the LSP. Currently, no flags are defined.

     Symbolic Path Name: This is the identifier given to an LSP and is
     unique in the context of the PCC address as defined in [RFC8231].
     It is worth noting that given that the Symbolic Path Name is
     unique in the context of the headnode, only LSPs that share the
     same headnode/PCC could be excluded.

   This sub-object MAY be present multiple times in the exclude route
   object (XRO) to exclude resources from multiple LSPs.  When a
   stateful PCE receives a PCReq message carrying this sub-object, it
   MUST search for the identified LSP in its LSP-DB and then exclude
   from the new path computation all resources used by the identified
   LSP.

   Note that this XRO Sub-object could also be used by non-GMPLS LSPs.
   The description of usage of non-GMPLS LSPs is not in the scope of
   this document.

 6.2.3. New flags in the LSP-EXTENDED-FLAG TLV in LSP Object

   The LSP Object is defined in Section 7.3 of [RFC8231], and the new
   extended flags TLV is defined in [I-D.ietf-pce-lsp-extended-flags].


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   This TLV is used in PCUpd, PCRpt and PCInitiate messages for GMPLS,
   with the following flags defined in this document.

   o G (GMPLS LSP(TBDb) -- 1 bit) :  If set to 1, it indicates the LSP
   is a GMPLS LSP.

   o B (Bidirectional LSP(TBD4) -- 1 bit):  If set to 0, it indicates
   a request to create a uni-directional LSP.  If set to 1, it
   indicates a request to create a bidirectional co-routed LSP.

   o RG (Routing Granularity(TBDc) -- 2 bits) :  RG flag for GMPLS is
   also defined in the LSP-EXTENDED-FLAG TLV  The value are defined as
   per [RFC8779]:

    00: reserved
    01: node
    10: link
    11: label

7. Update to Error Handling

   A PCEP-ERROR object is used to report a PCEP error and is
   characterized by an Error-Type that specifies the type of error and
   an Error-value that provides additional information about the error.
   In this document the following error handling procedures are
   introduced.  All the error handling specified in section 3 of
   [RFC8779] is applicable and MUST be supported for stateful PCE in
   GMPLS networks.

7.1. Error Handling in PCEP Capabilities Advertisement

   The PCEP extensions described in this document for stateful PCEs
   with GMPLS capability MUST NOT be used if the PCE has not advertised
   its stateful capability with GMPLS as per Section 5.2.  If the PCC
   understands the U flag that indicates the stateful LSP-UPDATE-
   CAPABILITY but did not advertise this capability, then upon receipt
   of a PCUpd message for GMPLS LSP from the PCE, it SHOULD generate a
   PCErr with error-type 19 ("Invalid Operation"), error-value TBDx
   ("Attempted LSP Update Request for GMPLS if stateful PCE capability
   for GMPLS was not advertised"), and terminate the PCEP session.

   If the PCE understands the R flag that indicates the stateful LSP-
   REPORT-CAPABILITY but did not advertise this capability, then upon
   receipt of a PCRpt message for GMPLS LSP from the PCC, it SHOULD
   generate a PCErr with error-type 19 ("Invalid Operation"), error-
   value TBDy ("Attempted LSP Report Request for GMPLS if stateful PCE
   capability for GMPLS was not advertised"), and terminate the PCEP
   session.


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   The PCEP extensions described in this document for PCC or PCE with
   the PCE-Initiation capability for GMPLS LSPs MUST NOT be used if the
   PCC or PCE has not advertised its stateful capability with
   Instantiation and GMPLS-CAPABILITY as per [RFC8779].  If the PCC
   understands the I flag that indicates LSP-INSTANTIATION-CAPABILITY
   but did not advertise this capability, then upon receipt of a
   PCInitiate message for GMPLS LSP from the PCE, it SHOULD generate a
   PCErr with error-type 19 ("Invalid Operation"), error-value TBDz
   ("Attempted LSP Instantiation Request for GMPLS if stateful PCE
   instantiation capability for GMPLS was not advertised"), and
   terminate the PCEP session.

7.2. Error Handling in LSP Re-optimization

   A stateful PCE is expected to perform an LSP re-optimization when
   receiving a message with the R bit set in the RP object. If no LSP
   state information is available to carry out re-optimization, the
   stateful PCE SHOULD report the error "LSP state information
   unavailable for the LSP re-optimization" (Error Type = 19, Error
   value= TBD6).  Note that this error message could also be used by
   non-GMPLS LSPs.  The PCE MAY suppress this error message by a
   configurable threshold.

7.3. Error Handling in Route Exclusion

   The LSP exclusion sub-object in XRO is defined in section 6.2.2 of
   this document MAY be present multiple times.  When a stateful PCE
   receives a PCEP message carrying this sub-object, it searches for
   the identified LSP in its LSP-DB and then excludes from the new path
   computation all the resources used by the identified LSP.  If the
   stateful PCE cannot recognize symbolic path name of the identified
   LSP, it SHOULD send an error message PCErr reporting Error-type = 19
   ("Invalid Operation"), Error-value = TBD7 ("The LSP state
   information for route exclusion purpose cannot be found").
   Optionally, it may also provide with the unrecognized symbolic path
   name information to the requesting PCC using the error reporting
   techniques described in [RFC5440].  However, the PCE MAY suppress
   this error message by a configurable threshold.

7.4. Error Handling for generalized END-POINTS

   Note that the ENDPOINT object in the Stateful PCEP messages was
   introduced for P2MP [RFC8623]. Similarly, the END-POINTS object MUST
   be carried for the GMPLS LSP.  If the END-POINTS object is missing


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   and the GMPLS flag in LSP-EXTENDED-FLAG is set, the receiving PCE or
   PCC MUST send a PCErr message with Error-type=6 ("Mandatory Object
   missing") and Error-value=3 ("END-POINTS object missing") (defined
   in [RFC5440]). Similarly, if the END-POINTS object with the
   Generalized Endpoint object type is received but if the LSP-
   EXTENDED-FLAG TLV is missing in the LSP object or if the G flag in
   the LSP-EXTENDED-FLAG TLV is not set, the receiving PCE or PCC MUST
   send a PCErr message with Error-type = 19 ("Invalid Operation"),
   Error-value = TBD9 ("Use of Generalized Endpoint object type for
   non-GMPLS LSP").

   If the ENDPOINT object with Generalized Endpoint Object Type is
   missing the LABEL-REQUEST TLV, the receiving PCE or PCC MUST send a
   PCErr message with Error-type=6 ("Mandatory Object missing") and
   Error-value=TBD8 ("LABEL-REQUEST TLV missing").

8. Implementation

   [NOTE TO RFC EDITOR : This whole section and the reference to RFC
   7942 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".

8.1. Huawei Technologies

      o  Organization: Huawei Technologies, Co. LTD
      o  Implementation: Huawei NCE-T



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      o  Description: PCRpt, PCUpd and PCInitiate messages for GMPLS
   Network
      o  Maturity Level: Production
      o  Coverage: Full
      o  Contact: zhenghaomian@huawei.com

9. IANA Considerations

9.1. New Flags in GMPLS-CAPABILITY TLV

   [RFC8779] defines the GMPLS-CAPABILITY TLV; per that RFC, IANA
   created a registry to manage the value of the GMPLS-CAPABILITY TLV's
   Flag field.  This document requests IANA to allocate new bits in the
   GMPLS-CAPABILITY TLV Flag Field registry, as follows:

       Bit  Description                      Reference
       ---  -------------------------------- -------------
       TBDa   LSP-REPORT-CAPABILITY (R)         [This.I-D]
       TBD1   LSP-UPDATE-CAPABILITY (U)         [This.I-D]
       TBD2   LSP-INSTANTIATION-CAPABILITY (I)  [This.I-D]

9.2. New Sub-object for the Exclude Route Object

   IANA maintains the various XRO Subobjects types within the "XRO
   Subobjects" subregistry of the PCEP Numbers registry.  IANA is
   requested to allocate a codepoint for another XRO subobject as
   follows:

   Value       Description                    Reference
  ----------+------------------------------+-------------
    TBD3        LSP                            [This.I-D]

9.3. Flags Field for LSP exclusion Sub-object

   IANA is requested to create a registry to manage the Flag field of
   the LSP Exclusion sub-object in the XRO.  No Flag is currently
   defined for this flag field in this document.

      Codespace of the Flag field (LSP Exclusion sub-object)
        Bit      Description             Reference
        0-7      Unassigned             [This.I-D]

   New values are to be assigned by Standards Action [RFC8126].
   Each bit should be tracked with the following qualities:

      o  Bit number (counting from bit 0 as the most significant bit)
      o  Capability description
      o  Defining RFC


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9.4. New  Flags in the LSP-EXTENDED-FLAGS TLV

   [I-D.ietf-pce-lsp-extended-flags] requested IANA to create a
   subregistry, named the "LSP-EXTENDED-FLAG TLV Flag Field", within
   the "Path Computation Element Protocol (PCEP) Numbers" registry, to
   manage the Flag field of the LSP-EXTENDED-FLAG TLV.

   IANA is requested to make following assignment from this registry as
   follows:

       Bit      Description                        Reference
       ---      ----------------------------       ----------
       TBDb     GMPLS LSP (G)                      [This.I-D]
       TBD4     Bi-directional co-routed LSP (B)   [This.I-D]
       TBDc*    Routing Granularity Flag (RG)      [This.I-D]

   * - 2 bits needs to be allocated

9.5. New PCEP Error Codes

   IANA is requested to make the following allocation in the "PCEP-
   ERROR Object Error Types and Values" registry.

   +===========+================+=========================+===========+
   | Error-Type| Meaning        | Error-value             | Reference |
   +===========+================+=========================+===========+
   | 6         | Mandatory      | TBD8: LABEL-REQUEST TLV | This I-D  |
   |           | Object missing | missing                 |           |
   |-----------|----------------+-------------------------+-----------+
   |19         | Invalid        | TBD6: LSP state info    | This I-D  |
   |           | Operation      | unavailable for the     |           |
   |           |                | Re-optimization         |           |
   |           |                +-------------------------+-----------+
   |           |                |TBD7: LSP state info for | This I-D  |
   |           |                |route exclusion not found|           |
   |           |                +-------------------------+-----------+
   |           |                | TBDx: Attempted LSP     | This I-D  |
   |           |                | Update Request for GMPLS|           |
   |           |                | if stateful PCE         |           |
   |           |                |capability not advertised|           |
   |           |                +-------------------------+-----------+
   |           |                |TBDy: Attempted LSP State| This I-D  |
   |           |                |Report for GMPLS if      |           |
   |           |                |stateful PCE capability  |           |
   |           |                |not advertised           |           |
   |           |                +-------------------------+-----------+
   |           |                |TBDz: Attempted LSP      | This I-D  |
   |           |                |Instantiation Request for|           |


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   |           |                |GMPLS if stateful PCE    |           |
   |           |                |instantiation capability |           |
   |           |                |not advertised           |           |
   |           |                +-------------------------+-----------+
   |           |                | TBD9: use of Generalized| This I-D  |
   |           |                | Endpoint object type for|           |
   |           |                | non-GMPLS LSP           |           |
   +-----------+----------------+-------------------------+-----------+

10. Manageability Considerations

   General PCE management considerations are discussed in [RFC4655] and
   [RFC5440], and GMPLS specific PCEP management considerations are
   described in [RFC8779].  In this document the management
   considerations for stateful PCEP extension in GMPLS are described.

   This section follows the guidance of [RFC6123].

10.1. Control of Function through Configuration and Policy

   In addition to the parameters already listed in Section 8.1 of
   [RFC5440], a PCEP implementation SHOULD allow configuration of the
   following PCEP session parameters on a PCC:

   o  The ability to send stateful PCEP messages for GMPLS LSPs.

   o  The ability to use path computation constraints (e.g, XRO).

   In addition to the parameters already listed in Section 8.1 of
   [RFC5440], a PCEP implementation SHOULD allow configuration of the
   following PCEP session parameters on a PCE:

   o  The ability to compute path in a stateful manner in GMPLS
   networks.

   o  A set of GMPLS-specific constraint.

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

10.2. Information and Data Models

   The YANG model in [I-D.ietf-pce-pcep-yang] can be used to configure
   and monitor PCEP states and messages. To make sure that the YANG
   model is useful for the extensions as described in this document, it



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   would need to include advertised GMPLS stateful capabilities etc. A
   future version of [I-D.ietf-pce-pcep-yang] will include this.

   As described in [I-D.ietf-teas-yang-path-computation], a YANG-based
   interface can be used in some cases to request GMPLS path
   computations, instead of PCEP. Refer [I-D.ietf-teas-yang-path-
   computation] for details.

10.3. Liveness Detection and Monitoring

   This document makes no change to the basic operation of PCEP, so
   there are no changes to the requirements for liveness detection and
   monitoring in [RFC4657] and [RFC5440], Section 8.3.

10.4. Verifying Correct Operation

   This document makes no change to the basic operations of PCEP and
   the considerations described in [RFC5440], Section 8.4.  New errors
   defined by this document should satisfy the requirement to log error
   events.

10.5. Requirements on Other Protocols and Functional Components

   When the detailed route information is included for LSP state
   synchronization (either at the initial stage or during LSP state
   report process), this requires the ingress node of an LSP carry the
   RRO object in order to enable the collection of such information.

10.6. Impact on Network Operation

   This document makes no change to the basic operations of PCEP and
   the considerations described in [RFC5440], Section 8.6.  In addition
   to the limit on the rate of messages sent by a PCEP speaker, a limit
   MAY be placed on the size of the PCEP messages.

11. Security Considerations

   The security considerations elaborated in [RFC5440] apply to this
   document.  The PCEP extensions to support GMPLS-controlled networks
   should be considered under the same security as for MPLS networks,
   as noted in [RFC7025].  So the PCEP extension to support GMPLS
   specified in [RFC8779] is used as the foundation of this document
   and the security considerations in [RFC8779] should also be
   applicable to this document.  The secure transport of PCEP specified
   in [RFC8253] allows the usage of Transport Layer Security (TLS).
   The same can also be used by the PCEP extension defined in this
   document.



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   This draft provides additional extensions to PCEP so as to
   facilitate stateful PCE usage in GMPLS-controlled networks, on top
   of [RFC8231] and [RFC8281].  Security issues caused by the extension
   in [RFC8231] and RFC8281] are not altered by the additions in this
   draft.  The security considerations in [RFC8231] and [RFC8281],
   including both issues and solutions, apply to this document as well.

12. Acknowledgement

   We would like to thank Adrian Farrel, Cyril Margaria, George Swallow
   and Jan Medved for the useful comments and discussions.

   Thanks to Dhruv Dhody for Shepherding this document and providing
   useful comments.

13. References

13.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

   [RFC5440] Vasseur, J.-P., and Le Roux, JL., "Path Computation
             Element (PCE) Communication Protocol (PCEP)", RFC 5440,
             March 2009.

   [RFC5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the
             Path Computation Element Communication Protocol (PCEP) for
             Route Exclusions", RFC 5521, April 2009.

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

   [RFC8231] Crabbe, E., Medved, J., Varga, R., Minei, I., "Path
             Computation Element Communication Protocol (PCEP)
             Extensions for Stateful PCE", RFC 8231, September 2017.

   [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., Dhody, D., "PCEPS:
             Usage of TLS to Provide a Secure Transport for the Path
             Computation Element Communication Protocol (PCEP)", RFC
             8253, October 2017.

   [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
             Computation Element Communication Protocol (PCEP)
             Extensions for PCE-Initiated LSP Setup in a Stateful PCE
             Model", RFC 8281, December 2017.




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   [RFC8779] Margaria, C., Gonzalez de Dios, O., Zhang, F., "Path
             Computation Element Communication Protocol (PCEP)
             extensions for GMPLS", RFC 8779, July 2020.

   [I-D.ietf-pce-lsp-extended-flags] Xiong, Q., "LSP Object Flag
             Extension of Stateful PCE", Work in progress.

13.2. Informative References

   [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>.

   [RFC8051] Zhang, X., Minei, I., et al, "Applicability of Stateful
             Path Computation Element (PCE) ", RFC 8051, January 2017.

   [RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
             and D. Dhody, "Optimizations of Label Switched Path State
             Synchronization Procedures for a Stateful PCE", RFC 8232,
             September 2017.

   [RFC8282] Oki, E., Takeda, T., Farrel, A., and F. Zhang, "Extensions
             to the Path Computation Element communication Protocol
             (PCEP) for Inter-Layer MPLS and GMPLS Traffic Engineering",
             RFC 8282, December 2017.

   [RFC3471]  Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Functional Description", RFC
             3471, January 2003.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
             Switching (GMPLS) Signaling Resource ReserVation Protocol
             Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
             January 2003.

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

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

   [RFC4872]  Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
             Ed., "RSVP-TE Extensions in Support of End-to-End
             Generalized Multi-Protocol Label Switching (GMPLS)
             Recovery", RFC 4872, May 2007.


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   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
             "GMPLS Segment Recovery", RFC 4873, May 2007.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
             Used to Form Encoding Rules in Various Routing Protocol
             Specifications", RFC5511, April 2005.

   [RFC6123]  Farrel, A., "Inclusion of Manageability Sections in Path
             Computation Element (PCE) Working Group Drafts", RFC 6123,
             February 2011,

   [RFC7025]  Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
             Margaria, "Requirements for GMPLS Applications of PCE",
             RFC 7025, September 2013,

   [RFC7399]  Farrel, A., King, D., "Unanswered Questions in the Path
             Computation Element Architecture", RFC 7399, October 2014.

   [RFC8126]  Cotton M., Leiba, B., Narten, T., "Guidelines for Writing
             an IANA Considerations Section in RFCs ", June, 2017.

   [RFC8623]  Palle, U., Dhody, D., Tanaka, Y., Beeram, V., "Stateful
             Path Computation Element (PCE) Protocol Extensions for
             Usage with Point-to-Multipoint TE Label Switched Paths
             (LSPs)" June 2019.

   [RFC8745]  Ananthakrishnan, H., Sivabalan, S., Barth, C., Minei, I.,
             Negi, M., "Path Computation Element Communication Protocol
             (PCEP) Extensions for Associating Working and Protection
             Label Switched Paths (LSPs) with Stateful PCE", March 2020.

   [I-D.ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V.,
             Tantsura, J., "A YANG Data Model for Path Computation
             Element Communications Protocol (PCEP)", Work in progress.

   [I-D.ietf-teas-yang-path-computation] Busi, I., Belotti, S.,
             Gonzalez de Dios, O., Sharma. A., Ceccarelli, D., "A YANG
             Data Model for requesting path computation", Work in
             progress.










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14. Contributors' Address

   Xian Zhang
   Huawei Technologies
   Email: zhang.xian@huawei.com


   Dhruv Dhody
   Huawei Technology
   India
   Email: dhruv.ietf@gmail.com


   Yi Lin
   Huawei Technologies
   Email: yi.lin@huawei.com

   Fatai Zhang
   Huawei Technologies
   Email: zhangfatai@huawei.com

   Ramon Casellas
   CTTC
   Av. Carl Friedrich Gauss n7
   Castelldefels, Barcelona 08860
   Spain
   Email: ramon.casellas@cttc.es

   Siva Sivabalan
   Cisco Systems
   Email: msiva@cisco.com


   Clarence Filsfils
   Cisco Systems
   Email: cfilsfil@cisco.com

   Robert Varga
   Pantheon Technologies
   Email: nite@hq.sk

Appendix A: PCEP Messages

   This section uses the Routing Backus-Naur Form (RBNF) [RFC5511] to
   illustrate the PCEP messages. The RBNF in this section is reproduced
   for informative purposes. It is also expanded to show the GMPLS
   specific objects.



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A.1  The PCRpt Message

   According to [RFC8231], the PCRpt Message is used to report the
   current state of an LSP. This document extends the message in
   reporting the status of LSPs with GMPLS characteristics.

   The format of the PCRpt message is as follows:
         <PCRpt Message> ::= <Common Header>
                             <state-report-list>
   Where:

         <state-report-list> ::= <state-report>[<state-report-list>]
         <state-report> ::= [<SRP>]
                            <LSP>
                    [<END-POINTS>]
                            <path>
   Where:
         <path>::= <intended-path>
                   [<actual-attribute-list><actual-path>]
                   <intended-attribute-list>
         <actual-attribute-list>::=[<BANDWIDTH>]
                                   [<metric-list>]

   Where:

     The END-POINTS object MUST be carried in a PCRpt message when the
   G flag is set in the LSP-EXTENDED-FLAG TLV in the LSP object for a
   GMPLS LSP.

     <intended-path> is represented by the ERO object defined in
   Section&nbsp;7.9 of [RFC5440], augmented in [RFC8779] with explicit label
   control (ELC) and Path Keys.

     <actual-attribute-list> consists of the actual computed and
   signaled values of the <BANDWIDTH> and <metric-lists> objects
   defined in [RFC5440].

     <actual-path> is represented by the RRO object defined in
   Section&nbsp;7.10 of [RFC5440].

     <intended-attribute-list> is the attribute-list defined in
   Section&nbsp;6.5 of [RFC5440] and extended by many other documents that
   define PCEP extensions for specific scenarios as shown below:

       <attribute-list>::=[<of-list>]
                               [<LSPA>]


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                               [<BANDWIDTH>]
                               [<metric-list>]
                               [<IRO>][<XRO>]
                               [<INTER-LAYER>]
                               [<SWITCH-LAYER>]
                               [<REQ-ADAP-CAP>]
                               [<SERVER-INDICATION>]

   A.2 The PCUpd Message

   The format of a PCUpd message is as follows:

         <PCUpd Message> ::= <Common Header>
                             <update-request-list>
   Where:
         <update-request-list> ::= <update-request>[<update-request-
   list>]
         <update-request> ::= <SRP>
                              <LSP>
                              [<END-POINTS>]
                              <path>
   Where:
         <path>::= <intended-path><intended-attribute-list>

   Where:

      The END-POINTS object MUST be carried in a PCUpd message for the
   GMPLS LSP.

      <intended-path> is represented by the ERO object defined in
   Section&nbsp;7.9 of [RFC5440], augmented in [RFC8779] with explicit label
   control (ELC) and Path Keys.

      <intended-attribute-list> is the attribute-list defined in
   [RFC5440] and extended by many other documents that define PCEP
   extensions for specific scenarios and as shown for PCRpt above.

A.3 The PCInitiate Message

     According to [RFC8281], the PCInitiate Message is used allow LSP
   Initiation. This document extends the message in initiating LSPs
   with GMPLS characteristics.  The format of a PCInitiate message is
   as follows:

        <PCInitiate Message> ::= <Common Header>
                                 <PCE-initiated-lsp-list>
   Where:



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        <Common Header> is defined in [RFC5440].

        <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                     [<PCE-initiated-lsp-list>]
        <PCE-initiated-lsp-request> ::= (<PCE-initiated-lsp-
   instantiation>|
                                         <PCE-initiated-lsp-deletion>)
        <PCE-initiated-lsp-instantiation> ::= <SRP>
                                              <LSP>
                                              [<END-POINTS>]
                                              <ERO>
                                              [<attribute-list>]
        <PCE-initiated-lsp-deletion> ::= <SRP>
                                         <LSP>

   The format of the PCInitiate message is unchanged from Section&nbsp;5.1
   of [RFC8281]. All fields are similar to the PCRpt and the PCUpd
   message.































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Authors' Addresses


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

   Haomian Zheng
   Huawei Technologies
   H1, Huawei Xiliu Beipo Village, Songshan Lake
   Dongguan, Guangdong  523808
   China
   Email: zhenghaomian@huawei.com

   Oscar Gonzalez de Dios
   Telefonica
   Phone: +34 913374013
   Email: oscar.gonzalezdedios@telefonica.com


   Victor Lopez
   Nokia
   Email: victor.lopez@nokia.com

   Zafar Ali
   Cisco Systems
   Email: zali@cisco.com






















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