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Versions: (draft-zhao-pce-pcep-extension-for-pce-controller) 00 01

PCE Working Group                                                Q. Zhao
Internet-Draft                                                     Z. Li
Intended status: Standards Track                                D. Dhody
Expires: May 8, 2019                                      S. Karunanithi
                                                     Huawei Technologies
                                                               A. Farrel
                                                   Juniper Networks, Inc
                                                                 C. Zhou
                                                           Cisco Systems
                                                        November 4, 2018


   PCEP Procedures and Protocol Extensions for Using PCE as a Central
                       Controller (PCECC) of LSPs
          draft-ietf-pce-pcep-extension-for-pce-controller-00

Abstract

   The Path Computation Element (PCE) is a core component of Software-
   Defined Networking (SDN) systems.  It can compute optimal paths for
   traffic across a network and can also update the paths to reflect
   changes in the network or traffic demands.

   PCE was developed to derive paths for MPLS Label Switched Paths
   (LSPs), which are supplied to the head end of the LSP using the Path
   Computation Element Communication Protocol (PCEP).  But SDN has a
   broader applicability than signaled (G)MPLS traffic-engineered (TE)
   networks, and the PCE may be used to determine paths in a range of
   use cases.  PCEP has been proposed as a control protocol for use in
   these environments to allow the PCE to be fully enabled as a central
   controller.

   A PCE-based central controller (PCECC) can simplify the processing of
   a distributed control plane by blending it with elements of SDN and
   without necessarily completely replacing it.  Thus, the LSP can be
   calculated/setup/initiated and the label forwarding entries can also
   be downloaded through a centralized PCE server to each network
   devices along the path while leveraging the existing PCE technologies
   as much as possible.

   This document specifies the procedures and PCEP protocol extensions
   for using the PCE as the central controller.

Status of This Memo

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




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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Basic PCECC Mode  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  PCEP Requirements . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Procedures for Using the PCE as the Central Controller
       (PCECC) . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Stateful PCE Model  . . . . . . . . . . . . . . . . . . .   6
     5.2.  New LSP Functions . . . . . . . . . . . . . . . . . . . .   6
     5.3.  PCECC Capability Advertisement  . . . . . . . . . . . . .   7
     5.4.  LSP Operations  . . . . . . . . . . . . . . . . . . . . .   8
       5.4.1.  Basic PCECC LSP Setup . . . . . . . . . . . . . . . .   8
       5.4.2.  Central Control Instructions  . . . . . . . . . . . .  10
         5.4.2.1.  Label Download  . . . . . . . . . . . . . . . . .  10
         5.4.2.2.  Label Cleanup . . . . . . . . . . . . . . . . . .  11
       5.4.3.  PCE Initiated PCECC LSP . . . . . . . . . . . . . . .  12
       5.4.4.  PCECC LSP Update  . . . . . . . . . . . . . . . . . .  14
       5.4.5.  Re Delegation and Cleanup . . . . . . . . . . . . . .  16
       5.4.6.  Synchronization of Central Controllers Instructions .  16



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       5.4.7.  PCECC LSP State Report  . . . . . . . . . . . . . . .  16
   6.  PCEP messages . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  The PCInitiate message  . . . . . . . . . . . . . . . . .  17
     6.2.  The PCRpt message . . . . . . . . . . . . . . . . . . . .  18
   7.  PCEP Objects  . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.1.  OPEN Object . . . . . . . . . . . . . . . . . . . . . . .  19
       7.1.1.  PCECC Capability sub-TLV  . . . . . . . . . . . . . .  19
     7.2.  PATH-SETUP-TYPE TLV . . . . . . . . . . . . . . . . . . .  20
     7.3.  CCI Object  . . . . . . . . . . . . . . . . . . . . . . .  20
       7.3.1.  Address TLVs  . . . . . . . . . . . . . . . . . . . .  21
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
     8.1.  Malicious PCE . . . . . . . . . . . . . . . . . . . . . .  23
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  23
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  23
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  23
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  23
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  23
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  23
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  24
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     10.1.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  24
     10.2.  New Path Setup Type Registry . . . . . . . . . . . . . .  24
     10.3.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . .  24
     10.4.  CCI Object Flag Field  . . . . . . . . . . . . . . . . .  24
     10.5.  PCEP-Error Object  . . . . . . . . . . . . . . . . . . .  25
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  25
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     12.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   The Path Computation Element (PCE) [RFC4655] was developed to offload
   path computation function from routers in an MPLS traffic-engineered
   network.  Since then, the role and function of the PCE has grown to
   cover a number of other uses (such as GMPLS [RFC7025]) and to allow
   delegated control [RFC8231] and PCE-initiated use of network
   resources [RFC8281].

   According to [RFC7399], Software-Defined Networking (SDN) refers to a
   separation between the control elements and the forwarding components
   so that software running in a centralized system, called a
   controller, can act to program the devices in the network to behave
   in specific ways.  A required element in an SDN architecture is a
   component that plans how the network resources will be used and how
   the devices will be programmed.  It is possible to view this



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   component as performing specific computations to place traffic flows
   within the network given knowledge of the availability of network
   resources, how other forwarding devices are programmed, and the way
   that other flows are routed.  This is the function and purpose of a
   PCE, and the way that a PCE integrates into a wider network control
   system (including an SDN system) is presented in [RFC7491].

   In early PCE implementations, where the PCE was used to derive paths
   for MPLS Label Switched Paths (LSPs), paths were requested by network
   elements (known as Path Computation Clients (PCCs)), and the results
   of the path computations were supplied to network elements using the
   Path Computation Element Communication Protocol (PCEP) [RFC5440].
   This protocol was later extended to allow a PCE to send unsolicited
   requests to the network for LSP establishment [RFC8281].

   [RFC8283] introduces the architecture for PCE as a central controller
   as an extension of the architecture described in [RFC4655] and
   assumes the continued use of PCEP as the protocol used between PCE
   and PCC.  [RFC8283] further examines the motivations and
   applicability for PCEP as a Southbound Interface (SBI), and
   introduces the implications for the protocol.
   [I-D.ietf-teas-pcecc-use-cases] describes the use cases for the PCECC
   architecture.

   A PCE-based central controller (PCECC) can simplify the processing of
   a distributed control plane by blending it with elements of SDN and
   without necessarily completely replacing it.  Thus, the LSP can be
   calculated/setup/initiated and the label forwarding entries can also
   be downloaded through a centralized PCE server to each network
   devices along the path while leveraging the existing PCE technologies
   as much as possible.

   This draft specify the procedures and PCEP protocol extensions for
   using the PCE as the central controller for static LSPs, where LSPs
   can be provisioned as explicit label instructions at each hop on the
   end-to-end path.  Each router along the path must be told what label-
   forwarding instructions to program and what resources to reserve.
   The PCE-based controller keeps a view of the network and determines
   the paths of the end-to-end LSPs, and the controller uses PCEP to
   communicate with each router along the path of the end-to-end LSP.

   The extension for PCECC in Segment Routing (SR) is specified in a
   separate draft [I-D.zhao-pce-pcep-extension-pce-controller-sr].








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1.1.  Requirements Language

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

2.  Terminology

   Terminologies used in this document is same as described in the draft
   [RFC8283] and [I-D.ietf-teas-pcecc-use-cases].

3.  Basic PCECC Mode

   In this mode LSPs are provisioned as explicit label instructions at
   each hop on the end-to-end path.  Each router along the path must be
   told what label forwarding instructions to program and what resources
   to reserve.  The controller uses PCEP to communicate with each router
   along the path of the end-to-end LSP.

   Note that the PCE-based controller will take responsibility for
   managing some part of the MPLS label space for each of the routers
   that it controls, and may taker wider responsibility for partitioning
   the label space for each router and allocating different parts for
   different uses.  This is also described in section 3.1.2. of
   [RFC8283].  For the purpose of this document, it is assumed that
   label range to be used by a PCE is known and set on both PCEP peers.
   A future extension could add this capability to advertise the range
   via possible PCEP extensions as well.  The rest of processing is
   similar to the existing stateful PCE mechanism.

4.  PCEP Requirements

   Following key requirements associated PCECC should be considered when
   designing the PCECC based solution:

   1.  PCEP speaker supporting this draft MUST have the capability to
       advertise its PCECC capability to its peers.

   2.  PCEP speaker not supporting this draft MUST be able to reject
       PCECC related extensions with a error reason code that indicates
       that this feature is not supported.

   3.  PCEP speaker MUST provide a means to identify PCECC based LSP in
       the PCEP messages.





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   4.  PCEP procedures SHOULD provide a means to update (or cleanup) the
       label- download entry to the PCC.

   5.  PCEP procedures SHOULD provide a means to synchronize the labels
       between PCE to PCC in PCEP messages.

5.  Procedures for Using the PCE as the Central Controller (PCECC)

5.1.  Stateful PCE Model

   Active stateful PCE is described in [RFC8231].  PCE as a central
   controller (PCECC) reuses existing Active stateful PCE mechanism as
   much as possible to control the LSP.

5.2.  New LSP Functions

   This document defines the following new PCEP messages and extends the
   existing messages to support PCECC:

   (PCRpt):  a PCEP message described in [RFC8231].  PCRpt message is
      used to send PCECC LSP Reports.  It is also extended to report the
      set of Central Controller's Instructions (CCI) (label forwarding
      instructions in the context of this document) received from the
      PCE.  See Section 5.4.6 for more details.

   (PCInitiate):  a PCEP message described in [RFC8281].  PCInitiate
      message is used to setup PCE-Initiated LSP based on PCECC
      mechanism.  It is also extended for Central Controller's
      Instructions (CCI) (download or cleanup the Label forwarding
      instructions in the context of this document) on all nodes along
      the path.

   (PCUpd):  a PCEP message described in [RFC8231].  PCUpd message is
      used to send PCECC LSP Update.

   The new LSP functions defined in this document are mapped onto the
   messages as shown in the following table.














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   +----------------------------------------+--------------------------+
   | Function                               | Message                  |
   +----------------------------------------+--------------------------+
   | PCECC Capability advertisement         | Open                     |
   | Label entry Add                        | PCInitiate               |
   | Label entry Cleanup                    | PCInitiate               |
   | PCECC Initiated LSP                    | PCInitiate               |
   | PCECC LSP Update                       | PCUpd                    |
   | PCECC LSP State Report                 | PCRpt                    |
   | PCECC LSP Delegation                   | PCRpt                    |
   | PCECC Label Report                     | PCRpt                    |
   +----------------------------------------+--------------------------+


   This document specify a new object CCI (see Section 7.3) for the
   encoding of central controller's instructions.  In the scope of this
   document this is limited to Label forwarding instructions.  The CC-ID
   is the unique identifier for the central controller's instructions in
   PCEP.  The PCEP messages are extended in this document to handle the
   PCECC operations.

5.3.  PCECC Capability Advertisement

   During PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
   advertise their support of PCECC extensions.

   This document defines a new Path Setup Type (PST)
   [I-D.ietf-pce-lsp-setup-type] for PCECC, as follows:

   o  PST = TBD: Path is setup via PCECC mode.

   A PCEP speaker MUST indicate its support of the function described in
   this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN
   object with this new PST included in the PST list.

   This document also defines the PCECC Capability sub-TLV
   Section 7.1.1.  PCEP speakers use this sub-TLV to exchange
   information about their PCECC capability.  If a PCEP speaker includes
   PST=TBD in the PST List of the PATH-SETUP-TYPE-CAPABILITY TLV then it
   MUST also include the PCECC Capability sub-TLV inside the PATH-SETUP-
   TYPE-CAPABILITY TLV.

   The presence of the PST and PCECC Capability sub-TLV in PCC's OPEN
   Object indicates that the PCC is willing to function as a PCECC
   client.






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   The presence of the PST and PCECC Capability sub-TLV in PCE's OPEN
   message indicates that the PCE is interested in function as a PCECC
   server.

   The PCEP protocol extensions for PCECC MUST NOT be used if one or
   both PCEP Speakers have not included the PST or the PCECC Capability
   sub-TLV in their respective OPEN message.  If the PCEP Speakers
   support the extensions of this draft but did not advertise this
   capability then a PCErr message with Error-Type=19(Invalid Operation)
   and Error-Value=TBD (Attempted PCECC operations when PCECC capability
   was not advertised) will be generated and the PCEP session will be
   terminated.

   A PCC or a PCE MUST include both PCECC-CAPABILITY sub-TLV and
   STATEFUL-PCE-CAPABILITY TLV ([RFC8231]) (with I flag set [RFC8281])
   in OPEN Object to support the extensions defined in this document.
   If PCECC-CAPABILITY sub-TLV is advertised and STATEFUL-PCE-CAPABILITY
   TLV is not advertised in OPEN Object, it SHOULD send a PCErr message
   with Error-Type=19 (Invalid Operation) and Error-value=TBD (stateful
   PCE capability was not advertised) and terminate the session.

5.4.  LSP Operations

   The PCEP messages pertaining to PCECC MUST include PATH-SETUP-TYPE
   TLV [I-D.ietf-pce-lsp-setup-type] in the SRP object to clearly
   identify the PCECC LSP is intended.

5.4.1.  Basic PCECC LSP Setup

   In order to setup a LSP based on PCECC mechanism, a PCC MUST delegate
   the LSP by sending a PCRpt message with PST set for PCECC (see
   Section 7.2) and D (Delegate) flag (see [RFC8231]) set in the LSP
   object.

   LSP-IDENTIFIER TLV MUST be included for PCECC LSP, the tuple uniquely
   identifies the LSP in the network.  The LSP object is included in
   central controller's instructions (label download) to identify the
   PCECC LSP for this instruction.  The PLSP-ID is the original
   identifier used by the ingress PCC, so the transit LSR could have
   multiple central controller instructions that have the same PLSP-ID.
   The PLSP-ID in combination with the source (in LSP-IDENTIFIER TLV)
   MUST be unique.  The PLSP-ID is included for maintainability reasons.
   As per [RFC8281], the LSP object could include SPEAKER-ENTITY-ID TLV
   to identify the PCE that initiated these instructions.  Also the CC-
   ID is unique on the PCEP session as described in Section 7.3.

   When a PCE receives PCRpt message with D flags and PST Type set, it
   calculates the path and assigns labels along the path; and set up the



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   path by sending PCInitiate message to each node along the path of the
   LSP.  The PCC generates a Path Computation State Report (PCRpt) and
   include the central controller's instruction (CCI) and the identified
   LSP.  The CC-ID is uniquely identify the central controller's
   instruction within PCEP.  The PCC further responds with the PCRpt
   messages including the CCI and LSP objects.

   Once the central controller's instructions (label operations) are
   completed, the PCE SHOULD send the PCUpd message to the Ingress PCC.
   The PCUpd message is as per [RFC8231] SHOULD include the path
   information as calculated by the PCE.

   Note that the PCECC LSPs MUST be delegated to a PCE at all times.

   LSP deletion operation for PCECC LSP is same as defined in [RFC8231].
   If the PCE receives PCRpt message for LSP deletion then it does Label
   cleanup operation as described in Section 5.4.2.2 for the
   corresponding LSP.

   The Basic PCECC LSP setup sequence is as shown below.































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                  +-------+                             +-------+
                  |PCC    |                             |  PCE  |
                  |Ingress|                             +-------+
           +------|       |                                 |
           | PCC  +-------+                                 |
           | Transit| |                                     |
    +------|        | |-- PCRpt,PLSP-ID=1, PST=TBD, D=1---->| PCECC LSP
    |PCC   +--------+ |                                     |
    |Egress  |  |     |                                     |
    +--------+  |     |                                     |
        |       |     |                                     |
        |<------ PCInitiate,CC-ID=X,PLSP-ID=1  ------------ | Label
        |       |     |                                     | download
        |------- PCRpt,CC-ID=X,PLSP-ID=1  ----------------->|
        |       |     |                                     |
        |       |<----- PCInitiate,CC-ID=Y,PLSP-ID=1  ----- | Label
        |       |     |                                     | download
        |       |-----  PCRpt,CC-ID=Y,PLSP-ID=1  ---------->|
        |       |     |                                     |
        |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=1  - | Label
        |       |     |                                     | download
        |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=1  ------>|
        |       |     |                                     |
        |       |     |<-- PCUpd,PLSP-ID=1,PST=TBD, D=1-----| PCECC LSP
        |       |     |                                     | Update
        |       |     |                                     |


                      Figure 2: Basic PCECC LSP setup

   The PCECC LSP are considered to be 'up' by default (on receipt of
   PCUpd message from PCE).  The Ingress MAY further choose to deploy a
   data plane check mechanism and report the status back to the PCE via
   PCRpt message.

5.4.2.  Central Control Instructions

   The new central controller's instructions (CCI) for the label
   operations in PCEP is done via the PCInitiate message, by defining a
   new PCEP Objects for CCI operations.  Local label range of each PCC
   is assumed to be known at both the PCC and the PCE.

5.4.2.1.  Label Download

   In order to setup an LSP based on PCECC, the PCE sends a PCInitiate
   message to each node along the path to download the Label instruction
   as described in Section 5.4.1.




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   The CCI object MUST be included, along with the LSP object in the
   PCInitiate message.  The LSP-IDENTIFIER TLV MUST be included in LSP
   object.  The SPEAKER-ENTITY-ID TLV SHOULD be included in LSP object.

   If a node (PCC) receives a PCInitiate message which includes a Label
   to download as part of CCI, that is out of the range set aside for
   the PCE, it MUST send a PCErr message with Error-type=TBD (PCECC
   failure) and Error-value=TBD (Label out of range) and MUST include
   the SRP object to specify the error is for the corresponding label
   update via PCInitiate message.  If a PCC receives a PCInitiate
   message but failed to download the Label entry, it MUST send a PCErr
   message with Error-type=TBD (PCECC failure) and Error-value=TBD
   (instruction failed) and MUST include the SRP object to specify the
   error is for the corresponding label update via PCInitiate message.

   New PCEP object for central control instructions (CCI) is defined in
   Section 7.3.

5.4.2.2.  Label Cleanup

   In order to delete an LSP based on PCECC, the PCE sends a central
   controller instructions via a PCInitiate message to each node along
   the path of the LSP to cleanup the Label forwarding instruction.

   If the PCC receives a PCInitiate message but does not recognize the
   label in the CCI, the PCC MUST generate a PCErr message with Error-
   Type 19(Invalid operation) and Error-Value=TBD, "Unknown Label" and
   MUST include the SRP object to specify the error is for the
   corresponding label cleanup (via PCInitiate message).

   The R flag in the SRP object defined in [RFC8281] specifies the
   deletion of Label Entry in the PCInitiate message.



















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                  +-------+                              +-------+
                  |PCC    |                              |  PCE  |
                  |Ingress|                              +-------+
           +------|       |                                  |
           | PCC  +-------+                                  |
           | Transit| |                                      |
    +------|        | |-- PCRpt,PLSP-ID=1,PST=TBD,D=1,R=1--->| PCECC LSP
    |PCC   +--------+ |                                      | remove
    |Egress  |  |     |                                      |
    +--------+  |     |                                      |
        |       |     |                                      |
        |<------ PCInitiate,CC-ID=X,PLSP-ID=1  ------------  | Label
        |       |     |                   R=1                | cleanup
        |------- PCRpt,CC-ID=X,PLSP-ID=1  ------------------>|
        |       |     |                                      |
        |       |<----- PCInitiate,CC-ID=Y,PLSP-ID=1  ------ | Label
        |       |     |                          R=1         | cleanup
        |       |-----  PCRpt,CC-ID=Y,PLSP-ID=1  ----------->|
        |       |     |                                      |
        |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=1  -- | Label
        |       |     |                              R=1     | cleanup
        |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=1  ------->|
        |       |     |                                      |


   As per [RFC8281], following the removal of the Label forwarding
   instruction, the PCC MUST send a PCRpt message.  The SRP object in
   the PCRpt MUST include the SRP-ID-number from the PCInitiate message
   that triggered the removal.  The R flag in the SRP object MUST be
   set.

5.4.3.  PCE Initiated PCECC LSP

   The LSP Instantiation operation is same as defined in [RFC8281].

   In order to setup a PCE Initiated LSP based on the PCECC mechanism, a
   PCE sends PCInitiate message with Path Setup Type set for PCECC (see
   Section 7.2) to the Ingress PCC.

   The Ingress PCC MUST also set D (Delegate) flag (see [RFC8231]) and C
   (Create) flag (see [RFC8281]) in LSP object of PCRpt message.  The
   PCC responds with first PCRpt message with the status as "GOING-UP"
   and assigned PLSP-ID.

   Note that the label forwarding instructions from PCECC are send after
   the initial PCInitiate and PCRpt exchange.  This is done so that the
   PLSP-ID and other LSP identifiers can be obtained from the ingress
   and can be included in the label forwarding instruction in the next



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   PCInitiate message.  The rest of the PCECC LSP setup operations are
   same as those described in Section 5.4.1.

   The LSP deletion operation for PCE Initiated PCECC LSP is same as
   defined in [RFC8281].  The PCE should further perform Label entry
   cleanup operation as described in Section 5.4.2.2 for the
   corresponding LSP.

   The PCE Initiated PCECC LSP setup sequence is shown below -


                 +-------+                              +-------+
                 |PCC    |                              |  PCE  |
                 |Ingress|                              +-------+
          +------|       |                                  |
          | PCC  +-------+                                  |
          | Transit| |                                      |
   +------|        | |<--PCInitiate,PLSP-ID=0,PST=TBD,D=1---| PCECC LSP
   |PCC   +--------+ |                                      | Initiate
   |Egress  |  |     |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1--->   | PCECC LSP
   +--------+  |     |       (GOING-UP)                     |
       |       |     |                                      |
       |<------ PCInitiate,CC-ID=X,PLSP-ID=2 -------------- | Label
       |       |     |                                      | download
       |------- PCRpt,CC-ID=X,PLSP-ID=2  ------------------>|
       |       |     |                                      |
       |       |<----- PCInitiate,CC-ID=Y,PLSP-ID=2 ------- | Label
       |       |     |                                      | download
       |       |-----  PCRpt,CC-ID=Y,PLSP-ID=2  ----------->|
       |       |     |                                      |
       |       |     |<--- PCInitiate,CC-ID=Z,PLSP-ID=2 --- | Label
       |       |     |                                      | download
       |       |     |---- PCRpt,CC-ID=Z,PLSP-ID=2  ------->|
       |       |     |                                      |
       |       |     |<-- PCUpd, PLSP-ID=2, PST=TBD, D=1--- | PCECC LSP
       |       |     |      (UP)                            | Update
       |       |     |--- PCRpt,PLSP-ID=2,P=1,D=1,C=1--->   |
       |       |     |      (UP)                            |


   Once the label operations are completed, the PCE SHOULD send the
   PCUpd message to the Ingress PCC.  The PCUpd message is as per
   [RFC8231].








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5.4.4.  PCECC LSP Update

   In case of a modification of PCECC LSP with a new path, a PCE sends a
   PCUpd message to the Ingress PCC.  But to follow the make-before-
   break procedures, the PCECC first update new instructions based on
   the updated LSP and then update to ingress to switch traffic, before
   cleaning up the old instructions.  A new CC-ID is used to identify
   the updated instruction, the existing identifiers in the LSP object
   identify the existing LSP.  Once new instructions are downloaded, the
   PCE further updates the new path at the ingress which triggers the
   traffic switch on the updated path.  The Ingress PCC acknowledges
   with a PCRpt message, on receipt of PCRpt message, the PCE does
   cleanup operation for the old LSP as described in Section 5.4.2.2.

   The PCECC LSP Update sequence is shown below -




































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                +-------+                             +-------+
                |PCC    |                             |  PCE  |
                |Ingress|                             +-------+
         +------|       |                                 |
         | PCC  +-------+                                 |
         | Transit| |                                     |
  +------|        | |                                     |
  |PCC   +--------+ |                                     |
  |Egress  |  |     |                                     |
  +--------+  |     |                                     |
      |       |     |                                     | New Path for
      |<------ PCInitiate,CC-ID=XX,PLSP-ID=1 -----------  | LSP trigger
      |       |     |                                     | new instruct
      |------- PCRpt,CC-ID=XX,PLSP-ID=1  ---------------->|
      |       |     |                                     |
      |       |<----- PCInitiate,CC-ID=YY,PLSP-ID=1------ | Label
      |       |     |                                     | download
      |       |-----  PCRpt,CC-ID=YY,PLSP-ID=1  --------->|
      |       |     |                                     |
      |       |     |<--- PCInitiate,CC-ID=ZZ,PLSP-ID=1 - | Label
      |       |     |                                     | download
      |       |     |---- PCRpt,CC-ID=ZZ,PLSP-ID=1  ----->|
      |       |     |                                     |
      |       |     |<-- PCUpd, PLSP-ID=1, PST=TBD, D=1-- | PCECC
      |       |     |    SRP=S                            | LSP Update
      |       |     |                                     |
      |       |     |-- PCRpt,PLSP-ID=1,PST=TBD,D=1    -->| Trigger
      |       |     |       (SRP=S)                       | Delete old
      |       |     |                                     | instruct
      |       |     |                                     |
      |<------ PCInitiate,CC-ID=X, PLSP-ID=1 -----------  | Label
      |       |     |                    R=1              | cleanup
      |------- PCRpt,CC-ID=X, PLSP-ID=1  ---------------->|
      |       |     |                                     |
      |       |<----- PCInitiate,CC-ID=Y, PLSP-ID=1 ----- | Label
      |       |     |                           R=1       | cleanup
      |       |-----  PCRpt,CC-ID=Y, PLSP-ID=1  --------->|
      |       |     |                                     |
      |       |     |<--- PCInitiate,CC-ID=Z, PLSP-ID=1 - | Label
      |       |     |                               R=1   | cleanup
      |       |     |---- PCRpt,CC-ID=Z, PLSP-ID=1  ----->|
      |       |     |                                     |


   The modified PCECC LSP are considered to be 'up' by default.  The
   Ingress MAY further choose to deploy a data plane check mechanism and
   report the status back to the PCE via PCRpt message.




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5.4.5.  Re Delegation and Cleanup

   As described in [RFC8281], a new PCE can gain control over the
   orphaned LSP.  In case of PCECC LSP, the new PCE MUST also gain
   control over the central controllers instructions in the same way by
   sending a PCInitiate message that includes the SRP, LSP and CCI
   objects and carries the CC-ID and PLSP-ID identifying the
   instruction, it wants to take control of.

   Further, as described in [RFC8281], the State Timeout Interval timer
   ensures that a PCE crash does not result in automatic and immediate
   disruption for the services using PCE-initiated LSPs.  Similarly the
   central controller instructions are not removed immediately upon PCE
   failure.  Instead, they are cleaned up on the expiration of this
   timer.  This allows for network cleanup without manual intervention.
   The PCC MUST support removal of CCI as one of the behaviors applied
   on expiration of the State Timeout Interval timer.

5.4.6.  Synchronization of Central Controllers Instructions

   The purpose of Central Controllers Instructions synchronization
   (labels in the context of this document) is to make sure that the
   PCE's view of CCI (Labels) matches with the PCC's Label allocation.
   This synchronization is performed as part of the LSP state
   synchronization as described in [RFC8231] and [RFC8233].

   As per LSP State Synchronization [RFC8231], a PCC reports the state
   of its LSPs to the PCE using PCRpt messages and as per [RFC8281], PCE
   would initiate any missing LSPs and/or remove any LSPs that are not
   wanted.  The same PCEP messages and procedure is also used for the
   Central Controllers Instructions synchronization.  The PCRpt message
   includes the CCI and the LSP object to report the label forwarding
   instructions.  The PCE would further remove any unwanted instructions
   or initiate any missing instructions.

5.4.7.  PCECC LSP State Report

   As mentioned before, an Ingress PCC MAY choose to apply any OAM
   mechanism to check the status of LSP in the Data plane and MAY
   further send its status in PCRpt message to the PCE.

6.  PCEP messages

   As defined in [RFC5440], a PCEP message consists of a common header
   followed by a variable-length body made of a set of objects that can
   be either mandatory or optional.  An object is said to be mandatory
   in a PCEP message when the object must be included for the message to
   be considered valid.  For each PCEP message type, a set of rules is



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   defined that specify the set of objects that the message can carry.
   An implementation MUST form the PCEP messages using the object
   ordering specified in this document.

   LSP-IDENTIFIERS TLV MUST be included in the LSP object for PCECC LSP.

6.1.  The PCInitiate message

   The PCInitiate message [RFC8281] can be used to download or remove
   the labels, the message has been extended as shown below -


        <PCInitiate Message> ::= <Common Header>
                                 <PCE-initiated-lsp-list>
     Where:
        <Common Header> is defined in [RFC5440]

        <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                     [<PCE-initiated-lsp-list>]

        <PCE-initiated-lsp-request> ::=
                               (<PCE-initiated-lsp-instantiation>|
                                <PCE-initiated-lsp-deletion>|
                                <PCE-initiated-lsp-central-control>)

        <PCE-initiated-lsp-central-control> ::= <SRP>
                                                <LSP>
                                                <cci-list>

        <cci-list> ::=  <CCI>
                        [<cci-list>]

     Where:
        <PCE-initiated-lsp-instantiation> and
        <PCE-initiated-lsp-deletion> are as per
         [RFC8281].

        The LSP and SRP object is defined in [RFC8231].


   When PCInitiate message is used for central controller's instructions
   (labels), the SRP, LSP and CCI objects MUST be present.  The SRP
   object is defined in [RFC8231] and if the SRP object is missing, the
   receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory
   Object missing) and Error-value=10 (SRP object missing).  The LSP
   object is defined in [RFC8231] and if the LSP object is missing, the
   receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory
   Object missing) and Error-value=8 (LSP object missing).  The CCI



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   object is defined in Section 7.3 and if the CCI object is missing,
   the receiving PCC MUST send a PCErr message with Error-type=6
   (Mandatory Object missing) and Error-value=TBD (CCI object missing).
   More than one CCI object MAY be included in the PCInitiate message
   for the transit LSR.

   To cleanup the SRP object must set the R (remove) bit.

   At max two instances of CCI object would be included in case of
   transit LSR to encode both in-coming and out-going label forwarding
   instructions.  Other instances MUST be ignored.

6.2.  The PCRpt message

   The PCRpt message can be used to report the labels that were
   allocated by the PCE, to be used during the state synchronization
   phase.


         <PCRpt Message> ::= <Common Header>
                             <state-report-list>
      Where:

         <state-report-list> ::= <state-report>[<state-report-list>]

         <state-report> ::= (<lsp-state-report>|
                             <central-control-report>)

         <lsp-state-report> ::= [<SRP>]
                                <LSP>
                                <path>

         <central-control-report> ::= [<SRP>]
                                      <LSP>
                                      <cci-list>

         <cci-list> ::=  <CCI>
                         [<cci-list>]

       Where:
         <path> is as per [RFC8231] and the LSP and SRP object are
         also defined in [RFC8231].

   When PCRpt message is used to report the central controller's
   instructions (labels), the LSP and CCI objects MUST be present.  The
   LSP object is defined in [RFC8231] and if the LSP object is missing,
   the receiving PCE MUST send a PCErr message with Error-type=6
   (Mandatory Object missing) and Error-value=8 (LSP object missing).



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   The CCI object is defined in Section 7.3 and if the CCI object is
   missing, the receiving PCC MUST send a PCErr message with Error-
   type=6 (Mandatory Object missing) and Error-value=TBD (CCI object
   missing).  Two CCI object can be included in the PCRpt message for
   the transit LSR.

7.  PCEP Objects

   The PCEP objects defined in this document are compliant with the PCEP
   object format defined in [RFC5440].

7.1.  OPEN Object

   This document defines a new optional TLVs for use in the OPEN Object.

7.1.1.  PCECC Capability sub-TLV

   The PCECC-CAPABILITY sub-TLV is an optional TLV for use in the OPEN
   Object for PCECC capability advertisement in PATH-SETUP-TYPE-
   CAPABILITY TLV.  Advertisement of the PCECC capability implies
   support of LSPs that are setup through PCECC as per PCEP extensions
   defined in this document.

   Its format 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=TBD      |            Length=4             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Flags                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The type of the TLV is TBD and it has a fixed length of 4 octets.

   The value comprises a single field - Flags (32 bits).

   No flags are assigned right now.

   Unassigned bits are considered reserved.  They MUST be set to 0 on
   transmission and MUST be ignored on receipt.








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7.2.  PATH-SETUP-TYPE TLV

   The PATH-SETUP-TYPE TLV is defined in [I-D.ietf-pce-lsp-setup-type];
   this document defines a new PST value:

   o  PST = TBD: Path is setup via PCECC mode.

   On a PCRpt/PCUpd/PCInitiate message, the PST=TBD in PATH-SETUP-TYPE
   TLV in SRP object indicates that this LSP was setup via a PCECC based
   mechanism.

7.3.  CCI Object

   The Central Control Instructions (CCI) Object is used by the PCE to
   specify the forwarding instructions (Label information in the context
   of this document) to the PCC, and MAY be carried within PCInitiate or
   PCRpt message for label download.

   CCI Object-Class is TBD.

   CCI Object-Type is 1 for the MPLS Label.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            CC-ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved            |              Flags           |O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Label                 |     Reserved          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        Optional TLV                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The fields in the CCI object are as follows:

   CC-ID:  A PCEP-specific identifier for the CCI information.  A PCE
      creates an CC-ID for each instruction, the value is unique within
      the scope of the PCE and is constant for the lifetime of a PCEP
      session.  The values 0 and 0xFFFFFFFF are reserved and MUST NOT be
      used.

   Flags:  is used to carry any additional information pertaining to the
      CCI.  Currently, the following flag bit is defined:



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      *  O bit(Out-label) : If the bit is set, it specifies the label is
         the OUT label and it is mandatory to encode the next-hop
         information (via IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or
         UNNUMBERED-IPV4-ID-ADDRESS TLV in the CCI object).  If the bit
         is not set, it specifies the label is the IN label and it is
         optional to encode the local interface information (via
         IPV4-ADDRESS TLV or IPV6-ADDRESS TLV or UNNUMBERED-IPV4-ID-
         ADDRESS TLV in the CCI object).

   Label (20-bit):  The Label information.

   Reserved (12 bit):  Set to zero while sending, ignored on receive.

7.3.1.  Address TLVs

   This document defines the following TLVs for the CCI object to
   associate the next-hop information in case of an outgoing label and
   local interface information in case of an incoming label.

































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   IPV4-ADDRESS TLV:

    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=TBD          |  Length = 4                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IPv4 address                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IPV6-ADDRESS TLV:

    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=TBD          |   Length = 16                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                IPv6 address (16 bytes)                      //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   UNNUMBERED-IPV4-ID-ADDRESS TLV:

    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=TBD          |   Length = 8                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Node-ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Interface ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The address TLVs are as follows:

   IPV4-ADDRESS TLV:  an IPv4 address.

   IPV6-ADDRESS TLV:  an IPv6 address.

   UNNUMBERED-IPV4-ID-ADDRESS TLV:  a pair of Node ID / Interface ID
      tuples.








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8.  Security Considerations

   The security considerations described in [RFC8231] and [RFC8281]
   apply to the extensions described in this document.  Additional
   considerations related to a malicious PCE are introduced.

8.1.  Malicious PCE

   PCE has complete control over PCC to update the labels and can cause
   the LSP's to behave inappropriate and cause cause major impact to the
   network.  As a general precaution, it is RECOMMENDED that these PCEP
   extensions only be activated on authenticated and encrypted sessions
   across PCEs and PCCs belonging to the same administrative authority,
   using Transport Layer Security (TLS) [RFC8253], as per the
   recommendations and best current practices in [RFC7525].

9.  Manageability Considerations

9.1.  Control of Function and Policy

   A PCE or PCC implementation SHOULD allow to configure to enable/
   disable PCECC capability as a global configuration.

9.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, this MIB can be extended to get the
   PCECC capability status.

   The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
   enable/disable PCECC capability.

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] and [RFC8231].

9.5.  Requirements On Other Protocols

   PCEP extensions defined in this document do not put new requirements
   on other protocols.




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9.6.  Impact On Network Operations

   PCEP extensions defined in this document do not put new requirements
   on network operations.

10.  IANA Considerations

10.1.  PCEP TLV Type Indicators

   IANA is requested to confirm the early allocation of the following
   TLV Type Indicator values within the "PCEP TLV Type Indicators" sub-
   registry of the PCEP Numbers registry, and to update the reference in
   the registry to point to this document, when it is an RFC:

        Value          Meaning                        Reference
        TBD            PCECC-CAPABILITY               This document
        TBD            IPV4-ADDRESS TLV               This document
        TBD            IPV6-ADDRESS TLV               This document
        TBD            UNNUMBERED-IPV4-ID-ADDRESS TLV This document

10.2.  New Path Setup Type Registry

   IANA is requested to allocate new PST Field in PATH- SETUP-TYPE TLV.
   The allocation policy for this new registry should be by IETF
   Consensus.  The new registry should contain the following value:

         Value          Description                 Reference
         TBD            Traffic engineering path is This document
                        setup using PCECC mode

10.3.  PCEP Object

   IANA is requested to allocate new registry for CCI PCEP object.

          Object-Class Value Name                  Reference
          TBD                CCI Object-Type       This document
                             1                     MPLS Label

10.4.  CCI Object Flag Field

   IANA is requested to create a registry to manage the Flag field of
   the CCI object.

   One bit to be defined for the CCI Object flag field in this document:

   Codespace of the Flag field (CCI Object)





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            Bit            Description           Reference
            7              Specifies label       This document
                           is out label

10.5.  PCEP-Error Object

   IANA is requested to allocate new error types and error values within
   the "PCEP-ERROR Object Error Types and Values" sub-registry of the
   PCEP Numbers registry for the following errors:


   Error-Type   Meaning
   ----------   -------
   19           Invalid operation.

                 Error-value = TBD :                 Attempted PCECC
                                                     operations when
                                                     PCECC capability
                                                     was not advertised
                 Error-value = TBD :                 Stateful PCE
                                                     capability was not
                                                     advertised
                 Error-value = TBD :                 Unknown Label
   6            Mandatory Object missing.

                 Error-value = TBD :                 CCI object missing
   TBD          PCECC failure.

                 Error-value = TBD :                 Label out of range.
                 Error-value = TBD :                 Instruction failed.

11.  Acknowledgments

   We would like to thank Robert Tao, Changjing Yan, Tieying Huang and
   Avantika for their useful comments and suggestions.

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>.







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   [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>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [RFC8233]  Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
              "Extensions to the Path Computation Element Communication
              Protocol (PCEP) to Compute Service-Aware Label Switched
              Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
              2017, <https://www.rfc-editor.org/info/rfc8233>.

   [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>.

12.2.  Informative References

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






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   [RFC7025]  Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
              Margaria, "Requirements for GMPLS Applications of PCE",
              RFC 7025, DOI 10.17487/RFC7025, September 2013,
              <https://www.rfc-editor.org/info/rfc7025>.

   [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>.

   [RFC7491]  King, D. and A. Farrel, "A PCE-Based Architecture for
              Application-Based Network Operations", RFC 7491,
              DOI 10.17487/RFC7491, March 2015,
              <https://www.rfc-editor.org/info/rfc7491>.

   [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>.

   [RFC8283]  Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and the PCE Communication
              Protocol (PCEP) in a Network with Central Control",
              RFC 8283, DOI 10.17487/RFC8283, December 2017,
              <https://www.rfc-editor.org/info/rfc8283>.

   [I-D.ietf-teas-pcecc-use-cases]
              Zhao, Q., Li, Z., Khasanov, B., Dhody, D., Ke, Z., Fang,
              L., Zhou, C., Communications, T., Rachitskiy, A., and A.
              Gulida, "The Use Cases for Path Computation Element (PCE)
              as a Central Controller (PCECC).", draft-ietf-teas-pcecc-
              use-cases-02 (work in progress), October 2018.

   [I-D.ietf-pce-lsp-setup-type]
              Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
              Hardwick, "Conveying path setup type in PCEP messages",
              draft-ietf-pce-lsp-setup-type-10 (work in progress), May
              2018.

   [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-09 (work in progress), October 2018.






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   [I-D.zhao-pce-pcep-extension-pce-controller-sr]
              Zhao, Q., Li, Z., Dhody, D., Karunanithi, S., Farrel, A.,
              and C. Zhou, "PCEP Procedures and Protocol Extensions for
              Using PCE as a Central Controller (PCECC) of SR-LSPs",
              draft-zhao-pce-pcep-extension-pce-controller-sr-03 (work
              in progress), June 2018.













































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Appendix A.  Contributor Addresses

   Udayasree Palle
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: udayasreereddy@gmail.com

   Mahendra Singh Negi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: mahendrasingh@huawei.com

   Katherine Zhao
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   EMail: katherine.zhao@huawei.com

   Boris Zhang
   Telus Ltd.
   Toronto
   Canada

   EMail: boris.zhang@telus.com


Authors' Addresses

   Quintin Zhao
   Huawei Technologies
   125 Nagog Technology Park
   Acton, MA  01719
   USA

   EMail: quintin.zhao@huawei.com








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   Zhenbin Li
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing    100095
   China

   EMail: lizhenbin@huawei.com


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

   EMail: dhruv.ietf@gmail.com


   Satish Karunanithi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: satishk@huawei.com


   Adrian Farrel
   Juniper Networks, Inc
   UK

   EMail: adrian@olddog.co.uk


   Chao Zhou
   Cisco Systems

   EMail: chao.zhou@cisco.com













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