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PCEP Extensions for LSP scheduling with stateful PCE
draft-ietf-pce-stateful-pce-lsp-scheduling-23

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8934.
Authors Huaimo Chen , Yan Zhuang , Qin Wu , Daniele Ceccarelli
Last updated 2020-08-07 (Latest revision 2020-07-13)
Replaces draft-zhuang-pce-stateful-pce-lsp-scheduling
RFC stream Internet Engineering Task Force (IETF)
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Stream WG state Submitted to IESG for Publication
Document shepherd Adrian Farrel
Shepherd write-up Show Last changed 2020-03-04
IESG IESG state Became RFC 8934 (Proposed Standard)
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Needs a YES. Needs 6 more YES or NO OBJECTION positions to pass.
Responsible AD Deborah Brungard
Send notices to Adrian Farrel <adrian@olddog.co.uk>
IANA IANA review state Version Changed - Review Needed
draft-ietf-pce-stateful-pce-lsp-scheduling-23
PCE Working Group                                           H. Chen, Ed.
Internet-Draft                                                 Futurewei
Intended status: Standards Track                          Y. Zhuang, Ed.
Expires: February 8, 2021                                          Q. Wu
                                                                  Huawei
                                                           D. Ceccarelli
                                                                Ericsson
                                                          August 7, 2020

          PCEP Extensions for LSP scheduling with stateful PCE
             draft-ietf-pce-stateful-pce-lsp-scheduling-23

Abstract

   This document defines a set of extensions needed to the stateful Path
   Computation Element (PCE) communication Protocol (PCEP), so as to
   enable Labeled Switched Path (LSP) path computation, activation,
   setup and deletion based on scheduled time intervals for the LSP and
   the actual network resource usage in a centralized network
   environment as stated in RFC 8413.

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 February 8, 2021.

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Motivation and Objectives . . . . . . . . . . . . . . . . . .   5
   4.  Procedures and Mechanisms . . . . . . . . . . . . . . . . . .   5
     4.1.  LSP Scheduling Overview . . . . . . . . . . . . . . . . .   5
     4.2.  Support of LSP Scheduling . . . . . . . . . . . . . . . .   7
       4.2.1.  LSP Scheduling  . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  Periodical LSP Scheduling . . . . . . . . . . . . . .   7
     4.3.  Scheduled LSP creation  . . . . . . . . . . . . . . . . .   9
     4.4.  Scheduled LSP Modifications . . . . . . . . . . . . . . .  10
     4.5.  Scheduled LSP activation and deletion . . . . . . . . . .  11
   5.  PCEP Objects and TLVs . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Stateful PCE Capability TLV . . . . . . . . . . . . . . .  11
     5.2.  LSP Object  . . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  SCHED-LSP-ATTRIBUTE TLV . . . . . . . . . . . . . . .  12
       5.2.2.  SCHED-PD-LSP-ATTRIBUTE TLV  . . . . . . . . . . . . .  15
   6.  The PCEP Messages . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  The PCRpt Message . . . . . . . . . . . . . . . . . . . .  16
     6.2.  The PCUpd Message . . . . . . . . . . . . . . . . . . . .  17
     6.3.  The PCInitiate Message  . . . . . . . . . . . . . . . . .  17
     6.4.  The PCReq message . . . . . . . . . . . . . . . . . . . .  17
     6.5.  The PCRep Message . . . . . . . . . . . . . . . . . . . .  17
     6.6.  The PCErr Message . . . . . . . . . . . . . . . . . . . .  18
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  18
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  Manageability Consideration . . . . . . . . . . . . . . . . .  19
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  19
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  20
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  20
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  20
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  20
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  20
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     10.1.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  20
       10.1.1.  Opt Field in SCHED-PD-LSP-ATTRIBUTE TLV  . . . . . .  21
       10.1.2.  Schedule TLVs Flag Field . . . . . . . . . . . . . .  21
     10.2.  STATEFUL-PCE-CAPABILITY TLV Flag field . . . . . . . . .  21
     10.3.  PCEP-Error Object  . . . . . . . . . . . . . . . . . . .  22
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22

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   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     12.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Contributors Addresses . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   The Path Computation Element Protocol (PCEP) defined in [RFC5440] is
   used between a Path Computation Element (PCE) and a Path Computation
   Client (PCC) (or other PCE) to enable path computation of Multi-
   protocol Label Switching (MPLS) Traffic Engineering Label Switched
   Paths (TE LSPs).

   [RFC8231] describes a set of extensions to PCEP to provide stateful
   control.  A stateful PCE has access to not only the information
   carried by the network's Interior Gateway Protocol (IGP) but also the
   set of active paths and their reserved resources for its
   computations.  The additional state allows the PCE to compute
   constrained paths while considering individual LSPs and their
   interactions.

   Traditionally, the usage and allocation of network resources,
   especially bandwidth, can be supported by a Network Management System
   (NMS) operation such as path pre-establishment.  However, this does
   not provide efficient usage of network resources.  The established
   paths reserve the resources forever, which can not be used by other
   services even when they are not used for transporting any service.
   [RFC8413] then provides a framework that describes and discusses the
   problem, and defines an appropriate architecture for the scheduled
   reservation of TE resources.

   The scheduled reservation of TE resources allows network operators to
   reserve resources in advance according to the agreements with their
   customers, and allows them to transmit data about scheduling such as
   a specified start time and duration, for example for a scheduled bulk
   data replication between data centers.  It enables the activation of
   bandwidth usage at the time the service is really being used while
   letting other services use it when this service is not using it.  The
   requirement of scheduled LSP provisioning is mentioned in [RFC8231]
   and [RFC7399].  Also, for deterministic networks
   [I-D.ietf-detnet-architecture], the scheduled LSP or temporal LSP can
   provide a better network resource usage for guaranteed links.  This
   idea can also be applied in segment routing [RFC8402] to schedule the
   network resources over the whole network in a centralized manner as
   well.

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   With this in mind, this document defines a set of extensions needed
   to PCEP used for stateful PCEs so as to enable LSP scheduling for
   path computation and LSP setup/deletion based on the actual network
   resource usage duration of a traffic service.  A scheduled LSP is
   characterized by a starting time and a duration.  When the end of the
   LSP life is reached, it is deleted to free up the resources for other
   LSPs (scheduled or not).

2.  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.

2.1.  Terminology

   The following terminology is re-used from existing PCE documents.

   o  Active Stateful PCE [RFC8051]

   o  Delegation [RFC8051]

   o  PCE-Initiated LSP [RFC8281]

   o  PCC [RFC5440]

   o  PCE [RFC5440]

   o  TE LSP [RFC5440]

   o  TED [RFC5440]

   o  LSP-DB [RFC8051]

   In addition, this document defines the following terminologies.

   Scheduled TE LSP (or Scheduled LSP for short):  an LSP with the
      scheduling attributes, that carries traffic flow demand at a
      starting time and lasts for a certain duration (or from a starting
      time to an ending time, where the ending time is the starting time
      plus the duration).  A scheduled LSP is also called a temporal
      LSP.  The PCE operates path computation per LSP availability for
      the required time and duration.

   Scheduled LSP-DB:  a database of scheduled LSPs.

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   Scheduled TED:  Traffic engineering database with the awareness of
      scheduled resources for TE.  This database is generated by the PCE
      from the information in TED and scheduled LSP-DB and allows
      knowing, at any time, the expected amount of available resources
      (discounting the possibility of failures in the future).

   Starting time (start-time):  This value indicates when the scheduled
      LSP is used and the corresponding LSP must be setup and active.
      In other time (i.e., before the starting time or after the
      starting time plus Duration), the LSP can be inactive to include
      the possibility of the resources being used by other services.

   Duration:  This value indicates the length of time that the LSP is
      undertaken by a traffic flow and the corresponding LSP must be
      setup and active.  At the end of which, the LSP is torn down and
      removed from the database.

3.  Motivation and Objectives

   A stateful PCE [RFC8231] can support better efficiency by using LSP
   scheduling described in the use case of [RFC8051].  This requires the
   PCE to maintain the scheduled LSPs and their associated resource
   usage, e.g.  bandwidth for Packet-switched network, as well as have
   the ability to trigger signaling for the LSP setup/tear-down at the
   correct time.

   Note that existing configuration tools can be used for LSP
   scheduling, but as highlighted in section 3.1.3 of [RFC8231] as well
   as discussions in [RFC8413], doing this as a part of PCEP in a
   centralized manner, has obvious advantages.

   This document provides a set of extensions to PCEP to enable LSP
   scheduling for LSP creation/deletion under the stateful control of a
   PCE and according to traffic service requests from customers, so as
   to improve the usage of network resources.

4.  Procedures and Mechanisms

4.1.  LSP Scheduling Overview

   The LSP scheduling allows PCEs and PCCs to provide scheduled LSP for
   customers' traffic services at its actual usage time, so as to
   improve the network resource utilization efficiency.

   For stateful PCE supporting LSP scheduling, there are two types of
   LSP databases used in this document.  One is the LSP-DB defined in
   PCEP [RFC8231], while the other is the scheduled LSP database (SLSP-
   DB, see section 6).  The SLSP-DB records scheduled LSPs and is used

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   in conjunction with the TED and LSP-DB.  Note that the two types of
   LSP databases can be implemented in one physical database or two
   different databases.  This is an implementation matter and this
   document does not state any preference.

   Furthermore, a scheduled TED can be generated from the scheduled LSP-
   DB, LSP-DB and TED to indicate the network links and nodes with
   resource availability information for now and future.  The scheduled
   TED MUST be maintained by all PCEs within the network environment.

   In case of implementing PCC-initiated scheduled LSPs, when delegating
   a scheduled LSP, a PCC MUST include its scheduling parameters (see
   Section 5.2.1), including the starting time and the duration using
   PCRpt message.  Since the LSP is not yet signaled, at the time of
   delegation the LSP would be in down state.  Upon receiving the
   delegation of the scheduled LSP, a stateful PCE MUST check whether
   the parameters are valid.  If they are valid, it SHALL check the
   scheduled TED for the network resource availability on network nodes
   and compute a path for the LSP with the scheduling information and
   update to the PCC as per the active stateful PCE techniques
   [RFC8231].

   Note that the active stateful PCE can update to the PCC with the path
   for the scheduled LSP at any time.  However, the PCC should not
   signal the LSP over the path on receiving these messages since the
   path is not active yet; PCC signals the LSP at the starting time.

   In case of multiple PCEs within a single domain, the PCE would need
   to synchronize their scheduling information with other PCEs within
   the domain.  This could be achieved by proprietary database
   synchronization techniques or via a possible PCEP extension [I-
   D.litkowski-pce-state-sync].  The technique used to synchronize SLSP-
   DB is out of scope for this document.  When the scheduling
   information is out of synchronization among some PCEs, some of
   scheduled LSPs may not be set up successfully.

   The scheduled LSP can also be initiated by a PCE itself.  In case of
   implementing PCE-initiated scheduled LSP, the stateful PCE SHALL
   check the network resource availability for the traffic and compute a
   path for the scheduled LSP and initiate a scheduled LSP at the PCC
   and synchronize the scheduled LSP to other PCEs.  Note that, the PCC
   could be notified immediately or at the starting time of the
   scheduled LSP based on the local policy.  In the former case, the
   SCHED-LSP-ATTRIBUTE TLV (see Section 5.2.1) MUST be included in the
   message whereas, for the latter the SCHED-LSP-ATTRIBUTE TLV SHOULD
   NOT be included.  Either way the synchronization to other PCEs MUST
   be done when the scheduled LSP is created.

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   In both modes, for activation of scheduled LSPs, the PCC MUST
   initiate the setup of scheduled LSP at the start time.  Similarly on
   scheduled usage expiry, the PCC MUST initiate the removal of the LSP
   based on the Flag set in SCHED-LSP-ATTRIBUTE TLV.

4.2.  Support of LSP Scheduling

4.2.1.  LSP Scheduling

   For a scheduled LSP, a user configures it with an arbitrary
   scheduling duration from time Ta to time Tb, which may be represented
   as [Ta, Tb].

   When an LSP is configured with arbitrary scheduling duration [Ta,
   Tb], a path satisfying the constraints for the LSP in the scheduling
   duration is computed and the LSP along the path is set up to carry
   traffic from time Ta to time Tb.

4.2.2.  Periodical LSP Scheduling

   In addition to LSP Scheduling at an arbitrary time period, there are
   also periodical LSP Scheduling.

   A periodical LSP Scheduling means an LSP has multiple time intervals
   and the LSP is set up to carry traffic in every time interval.  It
   has a scheduling duration such as [Ta, Tb], a number of repeats such
   as 10 (repeats 10 times), and a repeat cycle/time interval such as a
   week (repeats every week).  The scheduling interval: "[Ta, Tb]
   repeats n times with repeat cycle C" represents n+1 scheduling
   intervals as follows:

   [Ta, Tb], [Ta+C, Tb+C], [Ta+2C, Tb+2C], ..., [Ta+nC, Tb+nC]

   When an LSP is configured with a scheduling interval such as "[Ta,
   Tb] repeats 10 times with a repeat cycle a week" (representing 11
   scheduling intervals), a path satisfying the constraints for the LSP
   in every interval represented by the periodical scheduling interval
   is computed once.  Note that the path computed for one recurrence may
   be different from the path for another recurrence.  And then the LSP
   along the path is set up to carry traffic in each of the scheduling
   intervals.  If there is no path satisfying the constraints for some
   of the intervals, the LSP MUST NOT be set up at all.  It MUST
   generate a PCEP Error (PCErr) with Error-type = 29 (Path computation
   failure) and Error-value = TBD7 (Path could not be found for some
   intervals).

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4.2.2.1.  Elastic Time LSP Scheduling

   In addition to the basic LSP scheduling at an arbitrary time period,
   another option is elastic time intervals, which is represented as
   within -P and Q, where P and Q is an amount of time such as 300
   seconds.  P is called elastic range lower bound and Q is called
   elastic range upper bound.

   For a simple time interval such as [Ta, Tb] with an elastic range,
   elastic time interval: "[Ta, Tb] within -P and Q" means a time period
   from (Ta+X) to (Tb+X), where -P <= X <= Q.  Note that both Ta and Tb
   are shifted by the same 'X'.

   When an LSP is configured with elastic time interval "[Ta, Tb] within
   -P and Q", a path is computed such that the path satisfies the
   constraints for the LSP in the time period from (Ta+Xv) to (Tb+Xv)
   and an optimization is performed on Xv from -P to Q.  The
   optimization makes [Ta+Xv, Tb+Xv] to be the time interval closest to
   time interval [Ta, Tb] within the elastic range.  The LSP along the
   path is set up to carry traffic in the time period from (Ta+Xv) to
   (Tb+Xv).

   Similarly, for a recurrent time interval with an elastic range,
   elastic time interval: "[Ta, Tb] repeats n times with repeat cycle C
   within -P and Q" represents n+1 simple elastic time intervals as
   follows:

   [Ta+X0, Tb+X0], [Ta+C+X1, Tb+C+X1], ..., [Ta+nC+Xn, Tb+nC+Xn]
         where -P <= Xi <= Q, i = 0, 1, 2, ..., n.

   If a user wants to keep the same repeat cycle between any two
   adjacent time intervals, elastic time interval: "[Ta, Tb] repeats n
   times with repeat cycle C within -P and Q SYNC" may be used, which
   represents n+1 simple elastic time intervals as follows:

   [Ta+X, Tb+X], [Ta+C+X, Tb+C+X], ..., [Ta+nC+X, Tb+nC+X]
        where -P <= X <= Q.

4.2.2.2.  Grace Periods

   Besides the stated time scheduling, a user may want to have some
   grace periods (short for graceful time periods) for each or some of
   the time intervals for the LSP.  Two grace periods may be configured
   for a time interval.  One is the grace period before the time
   interval, called grace-before, which extends the lifetime of the LSP
   for grace-before (such as 30 seconds) before the time interval.  The
   other is the one after the time interval, called grace-after, which

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   extends the lifetime of the LSP for grace-after (such as 60 seconds)
   after the time interval.

   When an LSP is configured with a simple time interval such as [Ta,
   Tb] with grace periods such as grace-before GB and grace-after GA, a
   path is computed such that the path satisfies the constraints for the
   LSP in the time period from Ta to Tb.  The LSP along the path is set
   up to carry traffic in the time period from (Ta-GB) to (Tb+GA).
   During grace periods from (Ta-GB) to Ta and from Tb to (Tb+GA), the
   LSP is up to carry traffic in best effort.

4.3.  Scheduled LSP creation

   In order to realize PCC-Initiated scheduled LSPs in a centralized
   network environment, a PCC MUST separate the setup of an LSP into two
   steps.  The first step is to request/delegate and get an LSP but not
   signal it over the network.  The second step is to signal the
   scheduled LSP over the LSRs (Label Switching Router) at its starting
   time.

   For PCC-Initiated scheduled LSPs, a PCC MUST delegate the scheduled
   LSP by sending a path computation report (PCRpt) message by including
   its demanded resources with the scheduling information to a stateful
   PCE.  Note the PCC MAY use the PCReq/PCRep with scheduling
   information before delegating.

   Upon receiving the delegation via PCRpt message, the stateful PCE
   MUST compute a path for the scheduled LSP per its starting time and
   duration based on the network resource availability stored in
   scheduled TED (see Section 4.1).

   The stateful PCE will send a PCUpd message with the scheduled path
   information as well as the scheduled resource information for the
   scheduled LSP to the PCC.  The stateful PCE MUST update its local
   scheduled LSP-DB and scheduled TED with the scheduled LSP and would
   need to synchronize the scheduling information with other PCEs in the
   domain.

   For PCE-Initiated Scheduled LSP, the stateful PCE MUST compute a path
   for the scheduled LSP per requests from network management systems
   automatically based on the network resource availability in the
   scheduled TED and send a PCInitiate message with the path information
   back to the PCC.  Based on the local policy, the PCInitiate message
   could be sent immediately to ask the PCC to create a scheduled LSP
   (as per this document) or the PCInitiate message could be sent at the
   start time to the PCC to create a normal LSP (as per [RFC8281]).

   For both PCC-Initiated and PCE-Initiated Scheduled LSPs:

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   o  The stateful PCE MUST update its local scheduled LSP-DB and
      scheduled TED with the scheduled LSP.  Besides, it MUST send a
      PCRpt message with the scheduled LSP to its next hop PCE along the
      path of the LSP, so as to achieve the scheduling traffic
      engineering information synchronization.

   o  Upon receiving the PCUpd message or PCInitiate message for the
      scheduled LSP from PCEs with a found path, the PCC determines that
      it is a scheduled path for the LSP by the SCHED-LSP-ATTRIBUTE TLV
      (see Section 5.2.1) or SCHED-PD-LSP-ATTRIBUTE TLV (see
      Section 5.2.2) in the message, and does not trigger signaling for
      the LSP setup on LSRs immediately.

   o  The stateful PCE MUST update the Scheduled LSP parameters on any
      network events using the PCUpd message to PCC.  These changes are
      also synchronized to other PCEs.

   o  When it is time for the LSP to be set up (i.e., at the start
      time), based on the value of the C flag for the scheduled TLV,
      either the PCC MUST trigger the LSP to be signaled or the
      delegated PCE MUST send a PCUpd message to the head end LSR
      providing the updated path to be signaled (with A flag set to
      indicate LSP activation).

4.4.  Scheduled LSP Modifications

   After a scheduled LSP is configured, a user may change its parameters
   including the requested time as well as the bandwidth.  For a
   periodic scheduled LSP, its unused recurrences can be modified or
   cancelled.  For a scheduled LSP that is currently active, its
   duration (the lifetime) can be reduced.

   In the PCC-Initiated case, the PCC MUST send the PCE a PCRpt message
   for the scheduled LSP with updated parameters as well as scheduled
   information included in the SCHED-LSP-ATTRIBUTE TLV (see
   Section 5.2.1) or SCHED-PD-LSP-ATTRIBUTE TLV (see Section 5.2.2)
   carried in the LSP Object.  The PCE SHOULD take the updated resources
   and schedule into considerations and update the new path for the
   scheduled LSP to the PCC as well as synchronize to other PCEs in the
   network.  In case path cannot be set based on new requirements, the
   previous LSP will not be impacted and the same MUST be conveyed by
   the use of empty ERO in the PCEP messages.

   In the PCE-Initiated case, the Stateful PCE would recompute the path
   based on updated parameters as well as scheduled information.  In
   case it has already conveyed to the PCC this information by sending a
   PCInitiate message, it SHOULD update the path and other scheduling
   and resource information by sending a PCUpd message.

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4.5.  Scheduled LSP activation and deletion

   In the PCC-Initiated case, when it is time for the LSP to be set up
   (i.e., at the start time), based on the value of the C flag for the
   scheduled TLV, either the PCC MUST trigger the LSP to be signaled or
   the delegated PCE MUST send a PCUpd message to the head end LSR
   providing the updated path to be signaled (with A flag set to
   indicate LSP activation).  The PCC MUST report the status of the
   active LSP as per the procedures in [RFC8231] and at this time the
   LSP MUST be considered as part of the LSP-DB.  The A flag MUST be set
   in the scheduled TLV to indicate that the LSP is active now.  After
   the scheduled duration expires, based on the C flag, the PCC MUST
   trigger the LSP deletion on itself or the delegated PCE MUST send a
   PCUpd message to the PCC to delete the LSP as per the procedures in
   [RFC8231].

   In the PCE-Initiated case, based on the local policy, if the
   scheduled LSP is already conveyed to the PCC at the time of creation,
   the handling of LSP activation and deletion is handled in the same
   way as PCC-Initiated case as per the setting of C flag.  Otherwise,
   the PCE MUST send the PCInitiate message at the start time to the PCC
   to create a normal LSP without the scheduled TLV and remove the LSP
   after the duration expires as per [RFC8281].

5.  PCEP Objects and TLVs

5.1.  Stateful PCE Capability TLV

   A PCC and a PCE indicates its ability to support LSP scheduling
   during their PCEP session establishment phase.  For a multiple-PCE
   environment, the PCEs SHOULD also establish a PCEP session and
   indicate its ability to support LSP scheduling among PCEP peers.  The
   Open Object in the Open message contains the STATEFUL-PCE-CAPABILITY
   TLV.  Note that the STATEFUL-PCE-CAPABILITY TLV is defined in
   [RFC8231] and updated in [RFC8281] and [RFC8232]".  In this document,
   we define a new flag bit B (SCHED-LSP-CAPABLITY) in the Flags field
   of the STATEFUL-PCE-CAPABILITY TLV to indicate the support of LSP
   scheduling and another flag bit PD (PD-LSP-CAPABLITY) to indicate the
   support of LSP periodical scheduling.

   B (LSP-SCHEDULING-CAPABILITY) - 1 bit [Bit Position - TBD3]:  If set
      to 1 by a PCC, the B Flag indicates that the PCC allows LSP
      scheduling; if set to 1 by a PCE, the B Flag indicates that the
      PCE is capable of LSP scheduling.  The B bit MUST be set by both
      PCEP peers in order to support LSP scheduling for path
      computation.

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   PD (PD-LSP-CAPABLITY) - 1 bit: [Bit Position - TBD4]  If set to 1 by
      a PCC, the PD Flag indicates that the PCC allows LSP scheduling
      periodically; if set to 1 by a PCE, the PD Flag indicates that the
      PCE is capable of periodical LSP scheduling.  Both the PD bit and
      the B bit MUST be set to 1 by both PCEP peers in order to support
      periodical LSP scheduling for path computation.  If the PD bit or
      B bit is 0, then the periodical LSP scheduling capability MUST be
      ignored.

5.2.  LSP Object

   The LSP object is defined in [RFC8231].  This document adds an
   optional SCHED-LSP-ATTRIBUTE TLV for normal LSP scheduling and an
   optional SCHED-PD-LSP-ATTRIBUTE TLV for periodical LSP scheduling.

   The presence of the SCHED-LSP-ATTRIBUTE TLV in the LSP object
   indicates that this LSP has scheduled parameters while the SCHED-PD-
   LSP-ATTRIBUTE TLV indicates that this scheduled LSP is periodical.
   The SCHED-LSP-ATTRIBUTE TLV MUST be present in LSP Object for each
   scheduled LSP carried in the PCEP messages.  For periodical LSPs, the
   SCHED-PD-LSP-ATTRIBUTE TLV MUST be used in the LSP Object for each
   periodic scheduled LSP carried in the PCEP messages.

   Only one SCHED-LSP-ATTRIBUTE TLV SHOULD be present in the LSP object.
   In case more than one SCHED-LSP-ATTRIBUTE TLV is found, the first
   instance is processed and others ignored.  The SCHED-PD-LSP-ATTRIBUTE
   TLV is the same as the SCHED-LSP-ATTRIBUTE TLV regarding to its
   presence in the LSP object.

5.2.1.  SCHED-LSP-ATTRIBUTE TLV

   The SCHED-LSP-ATTRIBUTE TLV MAY be included as an optional TLV within
   the LSP object for LSP scheduling for the requesting traffic service.

   This TLV MUST NOT be included unless both PCEP peers have set the B
   (LSP-SCHEDULING-CAPABILITY) bit in STATEFUL-PCE-CAPABILITY TLV
   carried in the Open message.  If the TLV is received by a peer when
   both peers didn't set the B bit to one, the peer MUST generate a PCEP
   Error (PCErr) with a PCEP-ERROR object having Error-type = 19
   (Invalid Operation) and Error-value = TBD6 (Attempted LSP Scheduling
   if the scheduling capability was not advertised).

   The format of the SCHED-LSP-ATTRIBUTE TLV is shown in Figure 1.

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type (TBD1)       |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Flags |R|C|A|G|               Reserved (0)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Start-Time                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Duration                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   GrB / Elastic-Lower-Bound   |   GrA / Elastic-Upper-Bound   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: SCHED-LSP-ATTRIBUTE TLV

   The type of the TLV is [TBD1] and the TLV has a fixed length of 16
   octets.

   The fields in the format are:

   Flags (8 bits):  The following flags are defined in this document

      R (1 bit):  Set to 1 to indicate the Start-Time is a relative
         time, which is the number of seconds from the current time.
         The PCEs and PCCs MUST synchronized their clocks when relative
         time is used.  It is RECOMMENDED that the Network Time Protocol
         [RFC5905] be used to synchronize clocks among them.  When the
         transmission delay from a PCE or PCC to another PCE or PCC is
         too big such as greater than 1 second, the scheduling interval
         represented is not accurate if the delay is not considered.
         Set to 0 to indicate that the 32-bit Start-Time is an absolute
         time, which is the number of seconds since the epoch.  The
         epoch is 1 January 1970 at 00:00 UTC.  It wraps around every
         2^32 seconds, which is roughly 136 years.  The next wraparound
         will occur in the year 2106.  The received Start-Time is
         considered after the wraparound if the resulting value is less
         than the current time.  In which case, the value of the 32-bit
         Start-Time is considered as the number of seconds from the time
         of wraparound (because the Start-Time is always a future time).

      C (1 bit):  Set to 1 to indicate the PCC is responsible to setup
         and remove the scheduled LSP based on the Start-Time and
         duration.  The PCE holds these responsibilities when the bit is
         set to zero.

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      A (1 bit):  Set to 1 to indicate the scheduled LSP has been
         activated and should be considered as part of LSP-DB (instead
         of Scheduled LSP-DB).

      G (1 bit):  Set to 1 to indicate the Grace period is included in
         the fields GrB/Elastic-Lower-Bound and GrA/Elastic-Upper-Bound;
         set to 0 indicate the elastic range is included in the fields.

   Reserved (24 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Start-Time (32 bits):  This value in seconds, indicates when the
      scheduled LSP is used to carry traffic and the corresponding LSP
      MUST be setup and activated.  Note that the transmission delay
      SHOULD be considered when R=1 and the value of Start-Time is
      small.

   Duration (32 bits):  The value in seconds, indicates the duration
      that the LSP is undertaken by a traffic flow and the corresponding
      LSP MUST be up to carry traffic.  At the expiry of this duration,
      the LSP MUST be torn down and deleted.  Value of 0 MUST NOT be
      used in Duration since it does not make any sense.  The value of
      Duration SHOULD be greater than a constant MINIMUM-DURATION
      seconds, where MINIMUM-DURATION is 5.

   The Start-Time indicates a time at or before which the scheduled LSP
   MUST be set up.  The value of the Start-Time represents the number of
   seconds since the epoch when R bit is set to 0.  When R bit is set to
   1, the value of the Start-Time represents the number of seconds from
   the current time.

   In addition, it contains G flag set to 1 and an non zero grace-before
   and grace-after in the fields GrB/Elastic-Lower-Bound and GrA/
   Elastic-Upper-Bound if grace periods are configured.  It includes G
   flag set to 0 and an non zero elastic range lower bound and upper
   bound in the fields if there is an elastic range configured.  A TLV
   can configure a non-zero grace period or elastic range, but it MUST
   NOT provide both for an LSP.

   o  GrB (Grace-Before -16 bits): The grace period time length in
      seconds before the starting time.

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   o  GrA (Grace-After -16 bits): The grace period time length in
      seconds after time interval [starting time, starting time +
      duration].

   o  Elastic-Lower-Bound (16 bits): The maximum amount of time in
      seconds that time interval can shift to lower/left.

   o  Elastic-Upper-Bound (16 bits): The maximum amount of time in
      seconds that time interval can shift to upper/right.

5.2.2.  SCHED-PD-LSP-ATTRIBUTE TLV

   The periodical LSP is a special case of LSP scheduling.  The traffic
   service happens in a series of repeated time intervals.  The SCHED-
   PD-LSP-ATTRIBUTE TLV can be included as an optional TLV within the
   LSP object for this periodical LSP scheduling.

   This TLV MUST NOT be included unless both PCEP peers have set the B
   (LSP-SCHEDULING-CAPABILITY) bit and PD (PD-LSP-CAPABLITY) bit in
   STATEFUL-PCE-CAPABILITY TLV carried in open message to one.  If the
   TLV is received by a peer when either the B bit or PD bit is zero,
   the peer MUST generate a PCEP Error (PCErr) with a PCEP-ERROR object
   having Error-type = 19 (Invalid Operation) and Error-value = TBD6 (
   Attempted LSP Scheduling if the scheduling capability was not
   advertised).

   The format of the SCHED-PD-LSP-ATTRIBUTE TLV is shown in Figure 2.

    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 (TBD2)        |         Length                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Flags|R|C|A|G| Opt   |           NR          |  Reserved (0) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Start-Time                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Duration                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Repeat-time-length                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   GrB / Elastic-Lower-Bound   |   GrA / Elastic-Upper-Bound   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: SCHED-PD-LSP-ATTRIBUTE TLV

   The type of the TLV is [TBD2] and the TLV has a fixed length of 20
   octets.  The description, format and meaning of the Flags (R, C, A

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   and G bit), Start-Time, Duration, GrB, GrA, Elastic-Lower-Bound and
   Elastic-Upper-Bound fields remain the same as in the SCHED-LSP-
   ATTRIBUTE TLV.

   The following fields are new :

   Opt: (4 bits)  Indicates options to repeat.  When a PCE receives a
      TLV with a unknown Opt value, it does not compute any path for the
      LSP.  It MUST generate a PCEP Error (PCErr) with a PCEP-ERROR
      object having Error-type = 4 (Not supported object) and Error-
      value = 4 (Unsupported parameter).

         Opt = 1: repeat every day;

         Opt = 2: repeat every week;

         Opt = 3: repeat every month;

         Opt = 4: repeat every year;

         Opt = 5: repeat every Repeat-time-length.

   NR: (12 bits)  The number of repeats.  During each repetition, LSP
      carries traffic.

   Reserved (8 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.

   Repeat-time-length: (32 bits)  The time in seconds between the start-
      time of one repetition and the start-time of the next repetition.

6.  The PCEP Messages

6.1.  The PCRpt Message

   Path Computation State Report (PCRpt) is a PCEP message sent by a PCC
   to a PCE to report the status of one or more LSPs as per [RFC8231].
   Each LSP State Report in a PCRpt message contains the actual LSP's
   path, bandwidth, operational and administrative status, etc.  An LSP
   Status Report carried on a PCRpt message is also used in delegation
   or revocation of control of an LSP to/from a PCE.  In case of
   scheduled LSP, a scheduled TLV MUST be carried in the LSP object and
   the ERO conveys the intended path for the scheduled LSP.  The
   scheduled LSP MUST be delegated to a PCE.

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6.2.  The PCUpd Message

   Path Computation Update Request (PCUpd) is a PCEP message sent by a
   PCE to a PCC to update LSP parameters, on one or more LSPs as per
   [RFC8231].  Each LSP Update Request on a PCUpd message contains all
   LSP parameters that a PCE wishes to be set for a given LSP.  In case
   of scheduled LSP, a scheduled TLV MUST be carried in the LSP object
   and the ERO conveys the intended path for the scheduled LSP.  In case
   no path can be found, an empty ERO is used.  The A bit is used in
   PCUpd message to indicate the activation of the scheduled LSP in case
   the PCE is responsible for the activation (as per the C bit).

6.3.  The PCInitiate Message

   An LSP Initiate Request (PCInitiate) message is a PCEP message sent
   by a PCE to a PCC to trigger LSP instantiation or deletion as per
   [RFC8281].  In case of scheduled LSP, based on the local policy, PCE
   MAY convey the scheduled LSP to the PCC by including a scheduled TLV
   in the LSP object.  Or the PCE would initiate the LSP only at the
   start time of the scheduled LSP as per the [RFC8281] without the use
   of scheduled TLVs.

6.4.  The PCReq message

   The Path Computation Request (PCReq) message is a PCEP message sent
   by a PCC to a PCE to request a path computation [RFC5440] and it may
   contain the LSP object [RFC8231] to identify the LSP for which the
   path computation is requested.  In case of scheduled LSP, a scheduled
   TLV MUST be carried in the LSP object in PCReq message to request the
   path computation based on scheduled TED and LSP-DB.  A PCC MAY use
   PCReq message to obtain the scheduled path before delegating the LSP.
   The parameters of the LSP may be changed (refer to Section 4.4).

6.5.  The PCRep Message

   The Path Computation Reply (PCRep) message is a PCEP message sent by
   a PCE to a PCC in reply to a path computation request [RFC5440] and
   it may contain the LSP object [RFC8231] to identify the LSP for which
   the path is computed.  A PCRep message can contain either a set of
   computed paths if the request can be satisfied, or a negative reply
   if not.  The negative reply may indicate the reason why no path could
   be found.  In case of scheduled LSP, a scheduled TLV MUST be carried
   in the LSP object in PCRep message to indicate the path computation
   based on scheduled TED and LSP-DB.  A PCC and PCE MAY use PCReq and
   PCRep message to obtain the scheduled path before delegating the LSP.

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6.6.  The PCErr Message

   The Path Computation Error (PCErr) message is a PCEP message as
   described in [RFC5440] for error reporting.  The current document
   defines new error values for several error types to cover failures
   specific to scheduling and reuse the applicable error types and error
   values of [RFC5440] and [RFC8231] wherever appropriate.

   The PCEP extensions for scheduling MUST NOT be used if one or both
   PCEP speakers have not set the corresponding bits in the STATEFUL-
   PCE-CAPABILITY TLV in their respective OPEN message to ones.  If the
   PCEP speaker supports the extensions of this specification but did
   not advertise this capability, then upon receipt of LSP object with
   the scheduled TLV, it MUST generate a PCEP Error (PCErr) with Error-
   type=19 (Invalid Operation) and error-value TBD6 (Attempted LSP
   Scheduling if the scheduling capability was not advertised), and it
   SHOULD ignore the TLV.  As per Section 7.1 of [RFC5440], a legacy
   PCEP implementation that does not understand this specification,
   would consider a scheduled TLV as unknown and ignore them.

   If the PCC decides that the scheduling parameters proposed in the
   PCUpd/PCInitiate message are unacceptable, it MUST report this error
   by including the LSP-ERROR-CODE TLV (Section 7.3.3 of [RFC8231]) with
   LSP error-value = 4 "Unacceptable parameters" in the LSP object (with
   the scheduled TLV) in the PCRpt message to the PCE.

   The scheduled TLV MUST be included in the LSP object for the
   scheduled LSPs, if the TLV is missing, the receiving PCEP speaker
   MUST send a PCErr message with Error-type=6 (Mandatory Object
   missing) and Error-value TBD5 (Scheduled TLV missing).

7.  Implementation Status

   [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.

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   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".

   At the time of posting the -09 version of this document, there are no
   known implementations of this mechanism.  It is believed that two
   vendors/organizations are considering prototype implementations, but
   these plans are too vague to make any further assertions.

8.  Security Considerations

   This document defines LSP-SCHEDULING-CAPABILITY TLV and SCHED-LSP-
   ATTRIBUTE TLV, the security considerations discussed in [RFC5440],
   [RFC8231], and [RFC8281] continue to apply.  In some deployments the
   scheduling information could provide details about the network
   operations that could be deemed as extra sensitive.  Additionally,
   snooping of PCEP messages with such data or using PCEP messages for
   network reconnaissance may give an attacker sensitive information
   about the operations of the network.  A single PCEP message can now
   instruct a PCC to set up and tear down an LSP every second for a
   number of times.  That single message could have a significant effect
   on the network.  Thus, such deployments should employ suitable PCEP
   security mechanisms like TCP Authentication Option (TCP-AO) [RFC5925]
   or [RFC8253], which [RFC8253] is considered a security enhancement
   and thus is much better suited for the sensitive information.  PCCs
   may also need to apply some form of rate limit to the processing of
   scheduled LSPs.

9.  Manageability Consideration

9.1.  Control of Function and Policy

   The LSP-Scheduling feature MUST be controlled per tunnel by the
   active stateful PCE, the values for parameters like starting time,
   duration SHOULD be configurable by customer applications and based on
   the local policy at PCE.  The suggested default values for starting
   time and duration are one day in seconds from the current time and
   one year in seconds respectively.  One day has 86,400 seconds.  One
   year has 31,536,000 seconds.

   When configuring the parameters about time, a user SHOULD consider
   leap-years and leap-seconds.  If a scheduled LSP has a time interval
   containing a leap-year, the duration of the LSP is 366 days plus the
   rest of the interval.

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9.2.  Information and Data Models

   An implementation SHOULD allow the operator to view the information
   about each scheduled LSP defined in this document.  To serve this
   purpose, the PCEP YANG module [I-D.ietf-pce-pcep-yang] could be
   extended.

9.3.  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 [RFC5440].

9.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440].  An implementation SHOULD allow a user to view the
   information including status about a scheduled LSP through CLI.  In
   addition, it SHOULD check and handle the cases where there is a
   significant time correction or a clock skew between PCC and PCE.

9.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.

9.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on network
   operations in addition to those already listed in [RFC5440].

10.  IANA Considerations

10.1.  PCEP TLV Type Indicators

   This document defines the following new PCEP TLVs.  IANA maintains a
   sub-registry "PCEP TLV Type Indicators" in the "Path Computation
   Element Protocol (PCEP) Numbers" registry.  IANA is requested to make
   the following allocations from this sub-registry.

   Value     Meaning                         Reference
    TBD1 SCHED-LSP-ATTRIBUTE                 This document
    TBD2 SCHED-PD-LSP-ATTRIBUTE              This document

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10.1.1.  Opt Field in SCHED-PD-LSP-ATTRIBUTE TLV

   IANA is requested to create and maintain a new sub-registry named
   "SCHED-PD-LSP-ATTRIBUTE TLV Opt field" within the "Path Computation
   Element Protocol (PCEP) Numbers" registry.  Initial values for the
   sub-registry are given below.  New values are assigned by Standards
   Action [RFC8126].

     Value    Name                              Reference
     -----    ----                              ----------
      0       Reserved
      1       REPEAT-EVERY-DAY                  This document
      2       REPEAT-EVERY-WEEK                 This document
      3       REPEAT-EVERY-MONTH                This document
      4       REPEAT-EVERY-YEAR                 This document
      5       REPEAT-EVERY-REPEAT-TIME-LENGTH   This document
      6-14    Unassigned
      15      Reserved

10.1.2.  Schedule TLVs Flag Field

   IANA is requested to create a new sub-registry, named "Schedule TLVs
   Flag Field", within the "Path Computation Element Protocol (PCEP)
   Numbers" registry.  New values are 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

   The following values are defined in this document:

   Bit    Description                                    Reference
   0-3    Unassigned
   4      Relative Time (R-bit)                          This document
   5      PCC Responsible (C-bit)                        This document
   6      LSP Activated (A-bit)                          This document
   7      Grace Period Included (G-bit)                  This document

10.2.  STATEFUL-PCE-CAPABILITY TLV Flag field

   This document defines new bits in the Flags field in the STATEFUL-
   PCE-CAPABILITY TLV in the OPEN object.  IANA maintains a sub-registry
   "STATEFUL-PCE-CAPABILITY TLV Flag Field" in the "Path Computation
   Element Protocol (PCEP) Numbers" registry.  IANA is requested to make
   the following allocations from this sub-registry.

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   The following values are defined in this document:

   Bit    Description                                 Reference
    TBD3   LSP-SCHEDULING-CAPABILITY (B-bit)          This document
    TBD4   PD-LSP-CAPABLITY (PD-bit)                  This document

10.3.  PCEP-Error Object

   IANA is requested to allocate the following new error types to the
   existing error values within the "PCEP-ERROR Object Error Types and
   Values" subregistry of the "Path Computation Element Protocol (PCEP)
   Numbers" registry:

      Error-Type  Meaning
         6        Mandatory Object missing

                   Error-value
                   TBD5:  Scheduled TLV missing

         19       Invalid Operation

                   Error-value
                   TBD6: Attempted LSP Scheduling if the scheduling
                         capability was not advertised

         29       Path computation failure

                   Error-value
                   TBD7: Constraints could not be met for some intervals

11.  Acknowledgments

   The authors of this document would also like to thank Rafal Szarecki,
   Adrian Farrel, Cyril Margaria for the review and comments.

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>.

   [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>.

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   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [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,
              DOI 10.17487/RFC8232, September 2017,
              <https://www.rfc-editor.org/info/rfc8232>.

   [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, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8413]  Zhuang, Y., Wu, Q., Chen, H., and A. Farrel, "Framework
              for Scheduled Use of Resources", RFC 8413,
              DOI 10.17487/RFC8413, July 2018,
              <https://www.rfc-editor.org/info/rfc8413>.

12.2.  Informative References

   [I-D.ietf-detnet-architecture]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-13 (work in progress), May 2019.

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   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", draft-ietf-pce-pcep-
              yang-14 (work in progress), July 2020.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC7399]  Farrel, A. and D. King, "Unanswered Questions in the Path
              Computation Element Architecture", RFC 7399,
              DOI 10.17487/RFC7399, October 2014,
              <https://www.rfc-editor.org/info/rfc7399>.

   [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., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/info/rfc8051>.

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,
              <https://www.rfc-editor.org/info/rfc8253>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Appendix A.  Contributors Addresses

      Dhruv Dhody
      Huawei
      Divyashree Techno Park, Whitefield
      Bangalore, Karnataka  560066
      India

      Email: dhruv.ietf@gmail.com

      Xufeng Liu
      Ericsson

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      USA
      Email: xliu@kuatrotech.com

      Mehmet Toy
      Verizon
      USA
      Email: mehmet.toy@verizon.com

      Vic Liu
      China Mobile
      No.32 Xuanwumen West Street, Xicheng District
      Beijing,   100053
      China
      Email: liu.cmri@gmail.com

      Lei Liu
      Fujitsu
      USA
      Email: lliu@us.fujitsu.com

      Khuzema Pithewan
      Infinera
      Email: kpithewan@infinera.com

      Zitao Wang
      Huawei
      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China

      Email: wangzitao@huawei.com

      Xian Zhang
      Huawei Technologies
      Research Area F3-1B,
      Huawei Industrial Base,
      Shenzhen, 518129, China

      Email: zhang.xian@huawei.com

Authors' Addresses

   Huaimo Chen  (editor)
   Futurewei
   Boston, MA
   USA

   Email: huaimo.chen@futurewei.com

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   Yan Zhuang (editor)
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: zhuangyan.zhuang@huawei.com

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: bill.wu@huawei.com

   Daniele Ceccarelli
   Ericsson
   Via A. Negrone 1/A
   Genova - Sestri Ponente
   Italy

   Email: daniele.ceccarelli@ericsson.com

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