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Versions: (draft-zhuang-pce-stateful-pce-lsp-scheduling) 00 01 02 03

PCE Working Group                                           H. Chen, Ed.
Internet-Draft                                            Y. Zhuang, Ed.
Intended status: Standards Track                                   Q. Wu
Expires: December 20, 2018                                 D. Dhody, Ed.
                                                                  Huawei
                                                           D. Ceccarelli
                                                                Ericsson
                                                           June 18, 2018


          PCEP Extensions for LSP scheduling with stateful PCE
             draft-ietf-pce-stateful-pce-lsp-scheduling-03

Abstract

   This document proposes a set of extensions needed to the stateful
   Path Computation Element (PCE) communication Protocol (PCEP), so as
   to enable Labeled Switched Path (LSP) scheduling for path computation
   and LSP setup/deletion based on the actual network resource usage
   duration of a traffic service in a centralized network environment as
   stated in [I-D.ietf-teas-scheduled-resources].

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 December 20, 2018.

Copyright Notice

   Copyright (c) 2018 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.  Architecture Overview . . . . . . . . . . . . . . . . . . . .   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 . . . . . . . . . .  10
   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  . . . . . . . . . . . . .  14
   6.  The PCEP Messages . . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  The PCRpt Message . . . . . . . . . . . . . . . . . . . .  15
     6.2.  The PCUpd Message . . . . . . . . . . . . . . . . . . . .  15
     6.3.  The PCInitiate Message  . . . . . . . . . . . . . . . . .  16
     6.4.  The PCReq message . . . . . . . . . . . . . . . . . . . .  16
     6.5.  The PCRep Message . . . . . . . . . . . . . . . . . . . .  16
     6.6.  The PCErr Message . . . . . . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  Manageability Consideration . . . . . . . . . . . . . . . . .  18
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .  18
     8.2.  Information and Data Models . . . . . . . . . . . . . . .  18
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  18
     8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  18
     8.5.  Requirements On Other Protocols . . . . . . . . . . . . .  18
     8.6.  Impact On Network Operations  . . . . . . . . . . . . . .  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  PCEP TLV Type Indicators  . . . . . . . . . . . . . . . .  18
     9.2.  STATEFUL-PCE-CAPABILITY TLV Flag field  . . . . . . . . .  19
     9.3.  Schedule TLVs Flag Field  . . . . . . . . . . . . . . . .  19
     9.4.  PCEP-Error Object . . . . . . . . . . . . . . . . . . . .  19
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  20



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     11.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  Scheduled LSP information synchronization  . . . . .  22
   Appendix B.  Contributor Addresses  . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

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
   Path (TE LSP).

   [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 network usage since the established paths
   exclude the possibility of being used by other services even when
   they are not used for undertaking any service.
   [I-D.ietf-teas-scheduled-resources] then provides a framework that
   describes and discusses the problem, and proposes an appropriate
   architecture for the scheduled reservation of TE resources.

   With the scheduled reservation of TE resources, it allows network
   operators to reserve resources in advance according to the agreements
   with their customers, and allow them to transmit data with scheduling
   such as specified starting 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 really being
   used while letting other services obtain it in spare time.  The
   requirement of scheduled LSP provision is mentioned in [RFC8231] and
   [RFC7399], so as to provide more efficient network resource usage for
   traffic engineering, which hasn't been solved yet.  Also, for
   deterministic networks, the scheduled LSP can provide a better
   network resource usage for guaranteed links.  This idea can also be
   applied in segment routing to schedule the network resources over the
   whole network in a centralized manner as well.

   With this in mind, this document proposes a set of extensions needed
   to the stateful PCE, so as to enable LSP scheduling for path



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   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
   LSP (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 terminologies are re-used from existing PCE documents.

   o  Active Stateful PCE [RFC8231];

   o  Passive Stateful PCE [RFC8231];

   o  Delegation [RFC8231];

   o  PCE-Initiated LSP [RFC8281];

   o  PCC [RFC5440], [RFC8231];

   o  PCE [RFC5440], [RFC8231];

   o  TE LSP [RFC5440], [RFC8231];

   o  TED [RFC5440], [RFC8231];

   o  LSP DB [RFC8231];

   In addition, this document defines the following terminologies.

   Scheduled TE LSP:  a LSP with the scheduling attributes,that carries
      traffic flow demand at a starting time and last for a certain
      duration.  The PCE operates path computation per LSP availability
      for the required time and duration.

   Scheduled LSP DB:  a database of scheduled LSPs

   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



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      knowing, at any time, the amount of available resources (does not
      include 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 time duration 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 teardown and
      removed from the data base.

3.  Motivation and Objectives

   A stateful PCE can support better efficiency by using LSP scheduling
   described in the use case of [RFC8231].  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 [I-D.ietf-teas-scheduled-resources], doing this as
   a part of PCEP in a centralized manner, has obvious advantages.

   The objective of this document is to provide a set of extensions to
   PCEP to enable LSP scheduling for LSPs creation/deletion under the
   stateful PCE control, according to traffic services from customers,
   so as to improve the usage of network resources.

4.  Architecture Overview

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 efficient utilization.

   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
   as a complementary to 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 document does not state any preference
   here.



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   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 should be maintained by all PCEs within the network environment.

   In case of implementing PCC-initiated scheduled LSPs, before a PCC
   delegates a scheduled LSP, it MAY use the PCReq/PCRep messages to
   learn the path for the scheduled LSP.  A PCC MUST delegate a
   scheduled LSP with information of its scheduling parameters,
   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 SHALL check the scheduled TED for the
   network resource availability on network nodes and computes 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 once receiving these messages since the
   path is not active yet (until its starting time).

   For a multiple PCE environment, in order to synchronize the scheduled
   LSP DB, the mechanism as described in [I-D.litkowski-pce-state-sync]
   are used to synchronize between PCEs.  The scheduled TED can be
   determined from the synchronized SLSP-DB.  The PCE with delegation
   for the scheduled LSP would report the scheduled LSP to other PCEs,
   any future update to the scheduled LSP is also updated to other PCEs.
   This way the state of all scheduled LSPs are synchronized among the
   PCEs.  [RFC7399] discusses some synchronization issues and
   considerations, that are also applicable to the scheduled databases.

   The scheduled LSP can also be initiated by PCE itself.  In case of
   implementing PCE-initiated scheduled LSP, the stateful PCE shall
   check the network resource availability for the traffic and computes
   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 case of former SCHED-
   LSP-ATTRIBUTE MUST be included in the message where as for the latter
   SCHED-LSP-ATTRIBUTE SHOULD NOT be included.

   In both modes, for activation of scheduled LSPs, the PCC could
   initiate the setup of scheduled LSP at the start time by itself or
   wait for the PCE to update the PCC to initiate the setup of LSP.
   Similarly on the scheduling usage expires, the PCC could initiate the
   removal by itself or wait for the PCE to request the removal of the
   LSP.  This is based on the Flag set in SCHED-LSP-ATTRIBUTE TLV.  The



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   state of the scheduled LSP is synchronized to other PCEs using the
   existing mechanism in [RFC8231] and [I-D.litkowski-pce-state-sync].

4.2.  Support of LSP Scheduling

4.2.1.  LSP Scheduling

   For a scheduled LSP, a user configures it with an arbitrary
   scheduling duration time from 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 represents Scheduling LSP 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 each of the scheduling intervals represented by the periodical
   scheduling interval is computed and the LSP along the path is set up
   to carry traffic in each of the scheduling intervals.

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




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   from (Ta+X) to (Tb+X), where -P <= X <= Q.  Note that both Ta and Tb
   may be 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+X) to (Tb+X)
   and |X| is the minimum value from 0 to max(P, Q).  That is, [Ta+X,
   Tb+X] is 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+X) to (Tb+X).

   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.  Graceful Periods

   Besides the stated time scheduling, a user may want to have some
   graceful periods for each or some of the time intervals for the LSP.
   Two graceful periods may be configured for a time interval.  One is
   the graceful 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 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 graceful 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 graceful periods from (Ta-GB) to Ta and from Tb to (Tb+GA),
   the LSP is up to carry traffic (maybe in best effort).






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4.3.  Scheduled LSP creation

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

   For PCC-Initiated scheduled LSPs, a PCC can 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
   computes the 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 PCE SHOULD add the scheduled LSP into
   its scheduled LSP DB and update its scheduled TED.  The PCE MUST also
   synchronize to other PCEs within the network if there is any, so as
   to keep their scheduling information synchronized as per
   [I-D.litkowski-pce-state-sync].

   For PCE-Initiated Scheduled LSP, the stateful PCE can compute a path
   for the scheduled LSP per requests from network management systems
   automatically based on the network resource availability in the
   scheduled TED, 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 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]).

   In both modes:

   o  The stateful PCE is required to update its local scheduled LSP DB
      and scheduled TED with the scheduled LSP.  Besides, it shall send
      a PCRpt message with the scheduled LSP to other PCEs within the
      network, so as to achieve the scheduling traffic engineering
      information synchronization as per [I-D.litkowski-pce-state-sync].

   o  Upon receiving the PCUpd message or PCInitiate message for the
      scheduled LSP from PCEs with a found path, the PCC knows that it




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      is a scheduled path for the LSP and does not trigger signaling for
      the LSP setup on LSRs immediately.

   o  The stateful PCE can update the Scheduled LSP parameters on any
      network events using the PCUpd message to PCC.  These changes are
      also synchronized to other PCEs as per
      [I-D.litkowski-pce-state-sync].

   o  Based on the configuration (and the C flag in scheduled TLVs),
      when it is time (i.e., at the start time) for the LSP to be set
      up, either the PCC triggers the LSP to be signaled or the
      delegated PCE sends 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.

   In PCC-Initiated case, the PCC can send 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 would 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
   same should be conveyed by the use of empty ERO in the PCEP messages.

   In 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.

   In any case, the scheduled databases SHALL be updated and the PCE
   MUST synchronize this information to other PCEs as per
   [I-D.litkowski-pce-state-sync].

4.5.  Scheduled LSP activation and deletion

   In PCC-Initiated case, based on the configuration (and the C flag in
   scheduled TLVs), when it is time (i.e., at the start time) for the
   LSP to be set up, either the PCC triggers the LSP to be signaled or
   the delegated PCE sends 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 would report the status of the active LSP as



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   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 TLVs to indicate that the LSP is active now.  After the
   scheduled duration expires, based on the C flag, the PCC triggers the
   LSP deletion on it self or the delegated PCE sends a PCUpd message to
   the PCC to delete the LSP as per the procedures in [RFC8231].

   In 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.  In other case, the
   PCE would send the PCInitiate message at the start time to the PCC to
   create a normal LSP without the scheduled TLVs and remove the LSP
   after the duration expires as per [RFC8281].

   Additionally, the scheduled databases SHALL be updated and
   synchronization to other PCEs MUST be done as per
   [I-D.litkowski-pce-state-sync].

5.  PCEP Objects and TLVs

5.1.  Stateful PCE Capability TLV

   After a TCP connection for a PCEP session has been established, a PCC
   and a PCE indicates its ability to support LSP scheduling during the
   PCEP session establishment phase.  For a multiple-PCE environment,
   the PCEs should also establish 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 defined in
   [RFC8231].  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) flag for 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.

   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.  The PD bit MUST be




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      set by both PCEP peers in order to support periodical LSP
      scheduling for path computation.

5.2.  LSP Object

   The LSP object is defined in [RFC8231].  This document add 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 SCHED-LSP-ATTRIBUTE TLV in the LSP object indicates
   that this LSP is requesting scheduled parameters while the SCHED-PD-
   LSP-ATTRIBUTE TLV indicates that this scheduled LSP is periodical.
   The scheduled 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 can be used in LSP Object for
   each periodic scheduled LSP carried in the PCEP messages.

   Only one of these TLV SHOULD be present in the LSP object.  In case
   more than one scheduling TLV is found, the first instance is
   processed and others ignored.

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 SHOULD be included only if both PCEP peers have set the B
   (LSP-SCHEDULING-CAPABILITY bit) in STATEFUL-PCE-CAPABILITY TLV
   carried in open message.

   The format of the SCHED-LSP-ATTRIBUTE TLV is shown in the following
   figure:

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



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   The type of the TLV is [TBD1] and the TLV has a fixed length of 20
   octets.

   The fields in the format are:

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

      R (1 bit):  Set to 1 to indicate the Start-Time is a relative
         time, which is relative to the current time; set to 0 to
         indicate the the Start-Time is an absolute 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.


      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).


   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.


   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 is tear down and deleted.


   The Start-Time indicates a calendar time (e.g.,2018/12/13 8:29:58),
   at or before which the scheduled LSP must be set up.  The value of
   the Start-Time represents the number of seconds since 00:00 hours,Jan
   1, 1970 UTC when R bit is set to 0.  When R bit is set to 1, it
   represents the number of seconds from the current time.

   In addition, it contains an non zero grace-before and grace-after if
   graceful periods are configured.  It includes an non zero elastic
   range lower bound and upper bound if there is an elastic range
   configured.




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

   o  GrA (Grace-After -16 bits): The graceful 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 SHOULD be included only if 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.

   The format of the SCHED-PD-LSP-ATTRIBUTE TLV is shown in the
   following figure:

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

   The type of the TLV is [TBD2] and the TLV has a fixed length of 24
   octets.  The description, format and meaning of the Flags (R, C and A




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

   The following fields are new :

   Opt: (4 bits)  Indicates options to repeat.

         Options = 1: repeat every day;

         Options = 2: repeat every week;

         Options = 3: repeat every month;

         Options = 4: repeat every year;

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

   NR:(4 bits)  The number of repeats.  In each of repeats, LSP carries
      traffic.  If value is set to 0xFFFF, it indicates forever.

   Reserved (16 bits):  This field MUST be set to zero on transmission
      and MUST be ignored on receipt.


   Repeat-time-length:(32 bits)  The time length in seconds after which
      LSP starts to carry traffic again for the Duration.

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, the scheduled TLVs 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.  This message is also used
   to synchronize the scheduled LSPs to other PCE as described in
   [RFC8231] and [I-D.litkowski-pce-state-sync].

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



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   LSP parameters that a PCE wishes to be set for a given LSP.  In case
   of scheduled LSP, the scheduled TLVs 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).
   This message is also used to synchronize the scheduled LSPs to other
   PCE as described in [I-D.litkowski-pce-state-sync].

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 the scheduled
   TLVs 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, the
   scheduled TLVs 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.

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, the scheduled TLVs 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.  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 terminate the PCEP session.  As per Section 7.1 of [RFC5440],
   a legacy PCEP implementation that does not understand this
   specification, would consider the scheduled TLVs 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) with LSP error-
   value="Unacceptable parameters" in the LSP object (with scheduled
   TLVs) in the PCRpt message to the PCE.

   The scheduled TLVs 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.  Security Considerations

   This document defines LSP-SCHEDULING-CAPABILITY TLV and SCHED- LSP-
   ATTRIBUTE TLV which does not add any new security concerns beyond
   those discussed in [RFC5440] and [RFC8231].  But 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.  Thus, such deployment should
   employ suitable PCEP security mechanisms like TCP Authentication
   Option (TCP-AO) [RFC5925] or [RFC8253].  The procedure based on
   Transport Layer Security (TLS) in [RFC8253] is considered a security
   enhancement and thus is much better suited for the sensitive service-
   aware information.




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8.  Manageability Consideration

8.1.  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.

8.2.  Information and Data Models

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

8.3.  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].

8.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440].

8.5.  Requirements On Other Protocols

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

8.6.  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].

9.  IANA Considerations

9.1.  PCEP TLV Type Indicators

   This document defines the following new PCEP TLV.  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.






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

9.2.  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.

   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

9.3.  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 to manage the Flag field in the SCHED-LSP-ATTRIBUTE
   and SCHED-PD-LSP-ATTRIBUTE TLVs.  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      R-bit                                          This document
   1      C-bit                                          This document
   2      A-bit                                          This document

9.4.  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:





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      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

10.  Acknowledgments

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

11.  References

11.1.  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>.

   [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>.






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   [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>.

11.2.  Informative References

   [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-07 (work in progress), March 2018.

   [I-D.ietf-teas-scheduled-resources]
              Zhuangyan, Z., Wu, Q., Chen, H., and A. Farrel, "Framework
              for Scheduled Use of Resources", draft-ietf-teas-
              scheduled-resources-07 (work in progress), April 2018.

   [I-D.litkowski-pce-state-sync]
              Litkowski, S., Sivabalan, S., and D. Dhody, "Inter
              Stateful Path Computation Element communication
              procedures", draft-litkowski-pce-state-sync-03 (work in
              progress), April 2018.

   [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>.

   [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>.






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Appendix A.  Scheduled LSP information synchronization

   As for a stateful PCE, it maintains a database of LSPs (LSP-DB) that
   are active in the network, so as to reveal the available network
   resources and place new LSPs more cleverly.

   With the scheduled LSPs, they are not activated while creation, but
   should be considered when operating future path computation.  Hence,
   a scheduled LSP Database (SLSP-DB) is suggested to maintain all
   scheduled LSP information.

   The information of SLSP-DB MUST be shared and synchronized among all
   PCEs within the centralized network by using PCRpt and PCUpd message
   with scheduled LSP information as per the mechanism described in
   [I-D.litkowski-pce-state-sync].

   The PCE should generate and maintain a scheduled TED based on LSP DB,
   scheduled LSP DB and TED, which is used to indicate the network
   resource availability on network nodes for LSP path computation.

Appendix B.  Contributor Addresses






























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      Xufeng Liu
      Ericsson
      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







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   Huaimo Chen  (editor)
   Huawei
   Boston, MA
   USA

   Email: huaimo.chen@huawei.com


   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


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

   Email: dhruv.ietf@gmail.com


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

   Email: daniele.ceccarelli@ericsson.com









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