PCE Controlled ID Space
draft-li-pce-controlled-id-space-03

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Network Working Group                                              C. Li
Internet-Draft                                                   M. Chen
Intended status: Experimental                                    J. Dong
Expires: December 29, 2019                                         Z. Li
                                                     Huawei Technologies
                                                                 A. Wang
                                                           China Telecom
                                                                W. Cheng
                                                            China Mobile
                                                                 C. Zhou
                                                            Cisco System
                                                           June 27, 2019

                        PCE Controlled ID Space
                  draft-li-pce-controlled-id-space-03

Abstract

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   The Stateful PCE extensions allow stateful control of Multiprotocol
   Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths
   (LSPs) using PCEP.  Furthermore, PCEP can be used for computing paths
   in SR networks.

   Stateful PCE provide active control of MPLS-TE LSPs via PCEP, for a
   model where the PCC delegates control over one or more locally
   configured LSPs to the PCE.  Further, stateful PCE could also create
   and delete PCE-initiated LSPs itself.  A PCE-based central controller
   (PCECC) simplify the processing of a distributed control plane by
   integrating with elements of Software-Defined Networking (SDN).

   In some use cases, such as PCECC or Binding Segment Identifier (SID)
   for Segment Routing (SR), there are requirements for a stateful PCE
   to make allocation of labels, SIDs, etc.  These use cases require PCE
   aware of various identifier spaces where to make allocations on
   behalf of PCC.  This document describes a mechanism for PCC to inform
   the PCE of the identifier space under its control via PCEP.  The
   identifier could be MPLS label, SID or any other to-be-defined
   identifier to be allocated by a PCE.

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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Use cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  PCE-based Central Control . . . . . . . . . . . . . . . .   4
       3.1.1.  PCECC for MPLS/SR-MPLS  . . . . . . . . . . . . . . .   4
       3.1.2.  PCECC for SRv6  . . . . . . . . . . . . . . . . . . .   5
     3.2.  Binding SID Allocation  . . . . . . . . . . . . . . . . .   5
   4.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Objects . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Open Object . . . . . . . . . . . . . . . . . . . . . . .   7
       5.1.1.  LABEL-CONTROL-SPACE TLV . . . . . . . . . . . . . . .   7
       5.1.2.  FUNCT-ID-CONTROL-SPACE TLV  . . . . . . . . . . . . .   8
   6.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11

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     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   [RFC5440] defines the stateless Path Computation Element
   communication Protocol (PCEP) for Path Computation Elements (PCEs) to
   perform path computations in response to Path Computation Clients
   (PCCs) requests.  For supporting stateful operations, [RFC8231]
   specifies a set of extensions to PCEP to enable stateful control of
   LSPs within and across PCEP sessions in compliance with [RFC4657].
   Furthermore, [RFC8281] describes the setup, maintenance, and teardown
   of PCE-initiated LSPs under the stateful PCE model, without the need
   for local configuration on the PCC, thus allowing for a dynamic
   network that is centrally controlled and deployed.

   [RFC8283] introduces the architecture for PCE as a central
   controller, it examines the motivations and applicability for PCEP as
   a control protocol in this environment, and introduces the
   implications for the protocol.  Also,
   [I-D.ietf-pce-pcep-extension-for-pce-controller] specifies the
   procedures and PCEP protocol extensions for using the PCE as the
   central controller, where LSPs are calculated/setup/initiated and
   label forwarding entries are downloaded through extending PCEP.
   However, the document assumes that label range to be used by a PCE is
   known and set on both PCEP peers.  This extension adds the capability
   to advertise the range via a PCEP extension.

   Similarly, [I-D.zhao-pce-pcep-extension-pce-controller-sr] specifies
   the procedures and PCEP protocol extensions when a PCE-based
   controller is also responsible for configuring the forwarding actions
   on the routers (SR SID distribution in this case), in addition to
   computing the paths for packet flows in a segment routing network and
   telling the edge routers what instructions to attach to packets as
   they enter the network.  However, the document assumes that label
   range to be used by a PCE is known and set on both PCEP peers.  This
   extension adds the capability to advertise the range (from SRGB or
   SRLB of the node) via a PCEP extension.

   In addition, [I-D.dhody-pce-pcep-extension-pce-controller-srv6]
   specifies the procedures and PCEP protocol extensions of PCECC for
   SRv6.  An SRv6 SID is represented as LOC:FUNCT where LOC is the L
   most significant bits and FUNCT is the 128-L least significant bits.
   The FUNCT part of the SID is an opaque identification of a local
   function bound to the SID.  This extension adds the capability to
   advertise the range of Function ID (FUNCT part) via a PCEP extension.

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   Once the PCC/node has given control over an ID space (for example
   labels), the PCC/node MUST NOT allocate the ID from this ID space.
   For example, a PCC/node MUST NOT use this labels from the PCE
   controlled label space to make allocation for VPN Prefix distributed
   via BGP or labels used for LDP/RSVP-TE signalling.  This is done to
   make sure that the PCE control over ID space does not conflict with
   the existing node allocation.

   The use case are described in Section 3.  The ID space range
   information can be advertised via the TLVs in the Open message.  The
   detailed procedures are described in Section 4, and the objects'
   format is specified in Section 5.

2.  Terminology

   This memo makes use of the terms defined in [RFC5440], [RFC8231],
   [RFC8283] and [RFC8402].

2.1.  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.

3.  Use cases

3.1.  PCE-based Central Control

   A PCE-based central controller (PCECC) can simplify the processing of
   a distributed control plane by integrating with elements of SDN.
   Thus, the LSP/SR path can be calculated/setup/initiated and the
   label/SID 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.

3.1.1.  PCECC for MPLS/SR-MPLS

   [I-D.ietf-pce-pcep-extension-for-pce-controller] describes a mode
   where 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.  For this to work, the PCE-
   based controller will take responsibility for managing some part of
   the MPLS label space for each router that it controls as described in

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   section 3.1.2. of [RFC8283].  A mechanism for a PCC to inform the PCE
   of such a label space to control is needed within PCEP.

   [I-D.ietf-pce-segment-routing] specifies extensions to PCEP that
   allow a stateful PCE to compute, update or initiate SR-TE paths.
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] describes the
   mechanism for PCECC to allocate and provision the node/prefix/
   adjacency label (SID) via PCEP.  To make such allocation, PCE needs
   to be aware of the label space from Segment Routing Global Block
   (SRGB) or Segment Routing Local Block (SRLB) [RFC8402] of the node
   that it controls.  A mechanism for a PCC to inform the PCE of such
   label space to control is needed within PCEP.  The full SRGB/SRLB of
   a node could be learned via existing IGP or BGP-LS mechanism.

3.1.2.  PCECC for SRv6

   [I-D.dhody-pce-pcep-extension-pce-controller-srv6] describes the
   mechanism for PCECC to allocate and provision the SRv6 SID via PCEP.
   An SRv6 SID is represented as LOC:FUNCT
   ([I-D.ietf-spring-srv6-network-programming]) where LOC is the L most
   significant bits and FUNCT is the 128-L least significant bits.  The
   FUNCT part of the SID is an opaque identification of a local function
   bound to the SID.  To make such allocation, PCE needs to be aware of
   the Function ID space (FUNCT part) of the node that it controls.  A
   mechanism for a PCC to inform the PCE of such a Function ID space to
   control is needed within PCEP.

3.2.  Binding SID Allocation

   The headend of an SR Policy binds a Binding SID to its policy
   [I-D.ietf-spring-segment-routing-policy].  The instantiation of which
   may involve a list of SIDs.  Currently Binding SID are allocated by
   the node, but there is an inherent advantage in the Binding SID to be
   allocated by a PCE to allow SR policies to be dynamically created,
   updated according to the network status and operations.  This is
   described in [I-D.ietf-pce-pcep-extension-for-pce-controller].
   Therefore, a PCE needs to obtain the authority and control to
   allocate Binding SID actively from the PCC's label space as described
   in above use case.

4.  Overview

   During PCEP Initialization Phase, Open messages are exchanged between
   PCCs and PCEs.  The OPEN object may also contain a set of TLVs used
   to convey capabilities in the Open message.  The term 'ID' in this
   document, could be a MPLS label, SRv6 Function ID or any other future
   ID space for PCE to control and allocate from.  A PCC can include a
   corresponding ID-CONTROL-SPACE TLVs in the OPEN Object to inform the

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   corresponding ID space information that it wants the PCE to control.
   This TLV MUST NOT be included by the PCE and MUST be ignored on
   receipt by a PCC.  This is an optional TLV, the PCE could be aware of
   the ID space from some other means outside of PCEP.

   For delegating multiple types of ID space, multiple TLVs
   corresponding to each ID type MUST be included in an Open message.
   The ID type can be MPLS label or other type of ID.  The following ID-
   CONTROL-SPACE TLV is defined in this document -

   o  LABEL-CONTROL-SPACE TLV - for MPLS Labels (including for SR-MPLS)

   o  FUNCTION-ID-CONTROL-SPACE TLV - for SRv6 SID Function ID

   The procedure of ID space control to PCE is shown below:

              +-+-+                                     +-+-+
              |PCC|                                     |PCE|
              +-+-+                                     +-+-+
                |                                         |
                |   Open msg (LABEL-CONTROL-SPACE,etc)    |
                |                                         |
                |--------                                 |
                |        \                     Open msg   |
                |         \  -----------------------------|
                |          \/                             |
                |          /\                             |
                |         /  ---------------------------->|
                |        /                                |
                |<------                       Keepalive  |
                |             ----------------------------|
                |Keepalive   /                            |
                |--------   /                             |
                |        \/                               |
                |        /\                               |
                |<------   ------------------------------>|
                |                                         |

                     Figure 1: ID space control to PCE

   If the ID space control procedure is successful, the PCE will return
   a KeepAlive message to the PCC.  If there is any error in processing
   the corresponding TLV, an Error (PCErr) message will be sent to the
   PCC with Error-Type=1 (PCEP session establishment failure) and Error-
   value=TBD (ID space control failure).

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   After this process, a stateful PCE can learn the PCE controlled ID
   spaces of a node (PCC) under its control.  A PCE can then allocate
   IDs within the control ID space.  For example, a PCE can actively
   allocate labels and download forwarding instructions for the PCECC
   LSP as described in [I-D.ietf-pce-pcep-extension-for-pce-controller].
   A PCE can also allocate labels from the PCE controlled portion of the
   SRGB/SRLB for PCECC-SR
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  The full SRGB/SRLB
   of a node could be learned via existing IGP or BGP-LS mechanism.

5.  Objects

5.1.  Open Object

   For advertising the PCE controlled ID space to a PCE, this document
   defines several TLVs within the OPEN object.

5.1.1.  LABEL-CONTROL-SPACE TLV

   For a PCC to inform the label space under the PCE control, this
   document defines a new LABEL-CONTROL-SPACE TLV.

   The LABEL-CONTROL-SPACE TLV is an optional TLV in the OPEN object,
   and 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=TBA           |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Block        |                   Flags                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Start (1)                  |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Range (1)                  |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Start (n)                  |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Range (n)                  |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 2: LABEL-CONTROL-SPACE TLV

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   The type (16 bits) of the TLV is TBA.  The length field (16 bits) and
   has a variable value.

   Block(8 bits): the number of ID blocks.  The range of a block is
   described by a start field and a range field.

   Flags (24 bits): No flag is currently defined.  The unassigned bits
   of Flags field MUST be set to 0 on transmission and MUST be ignored
   on receipt.

   Start(i) (24 bits): indicates the beginning of the label block i.

   Range(i) (24 bits): indicates the range of the label block i.

   Reserved: SHOULD be set to 0 on transmission and MUST be ignored on
   reception.

   LABEL-CONTROL-SPACE TLV SHOULD be included only once in a Open
   Message.  On receipt, only the first instance is processed and others
   MUST be ignored.

   A stateful PCE can actively allocate labels and download forwarding
   instructions for the PCECC LSP as described in
   [I-D.ietf-pce-pcep-extension-for-pce-controller].  A PCE can also
   allocate labels from SRGB/SRLB for PCECC-SR
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  The Binding
   Segments can also be selected for the PCE controlled space
   [I-D.ietf-pce-pcep-extension-for-pce-controller].

5.1.2.  FUNCT-ID-CONTROL-SPACE TLV

   For a PCC to inform the SRv6 SID Function ID space under the PCE
   control, this document defines a new FUNCT-ID-CONTROL-SPACE TLV.

   The FUNCT-ID-CONTROL-SPACE TLV is an optional TLV for use in the OPEN
   object, and its format is shown in the following figure:

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Type=TBA           |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Block      |             Flags                           |L|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Start (1)                          |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Range (1)                          |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             ......                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Start (n)                          |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                            Range (n)                          |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Loc Size     | Locator (variable)...                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: FUNCT-ID-CONTROL-SPACE TLV

   The type (16 bits) of the TLV is TBA.  The length field (16 bits) and
   has a variable value.

   Block(8 bits): the number of ID blocks.  The range of a block is
   described by a start field and a range field.

   Flags (24 bits): Following flags are currently defined

   o  L-flag: Locator flag, set when the locator information is included
      in this TLV.  If L-flag is unset, Loc Size and variable Locator
      field MUST NOT be included in this TLV, and the ID spaces are
      applicable to all Locators.

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   The unassigned bits of Flags field MUST be set to 0 on transmission
   and MUST be ignored on receipt.

   Start(i) (128 bits): indicates the beginning of the Function ID block
   i.

   Range(i) (128 bits): indicates the range of the Function ID block i.

   Loc size(8 bits): indicates the bit length of a Locator.  Appears
   only when the L-flag is set.

   Locator (variable length): the value of a Locator.  The Function ID
   spaces specified in this TLV are associated with this locator.

   As per [RFC5440], the value portion of the PCEP TLV needs to be
   4-bytes aligned, so a FUNCT-ID-CONTROL-SPACE TLV is padded with
   trailing zeros to a 4-byte boundary.

   Multiple FUNCT-ID-CONTROL-SPACE TLVs MAY be included in a OPEN object
   to specify Function ID space specefic to each locator.

   A stateful PCE can actively allocate SRv6 SID and download forwarding
   instructions for the PCECC SRv6 path as described in
   [I-D.dhody-pce-pcep-extension-pce-controller-srv6].

   Note that SRv6 SID allocation involves LOC:FUNCT; the LOC is assumed
   to be known at PCE and FUNCT is allocated from the PCE controlled
   Function ID block.

6.  Other Considerations

   In case of multiple PCEs, a PCC MAY decide to give control over
   different ID space to each instance of the PCE.  In case a PCC
   includes the same ID space to multiple PCEs, the PCE SHOULD use
   synchronization mechanism (such as [I-D.litkowski-pce-state-sync]) to
   avoid allocating the same ID.

   The PCE would allocate ID from the PCE controlled ID space.  The PCC
   would not allocate ID by itself from this space as long as it has an
   active PCEP session to a PCE to which it has given control over the
   ID space.

   Note that if there is any change in the ID space, the PCC MUST bring
   the session down and re-establish the session with new TLVs.  During
   state synchronization the PCE would need to consider the new ID space
   into consideration and SHOULD re-establish the LSP/SR-paths if
   needed.

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   The PCC can regain control of the ID space by closing the PCEP
   session and require new session without ID space TLVs specified in
   this document.

7.  IANA Considerations

   TBA.

8.  Security Considerations

   TBA.

9.  Acknowledgements

   TBD.

10.  References

10.1.  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>.

   [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>.

   [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>.

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   [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>.

10.2.  Informative References

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

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

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-16 (work in progress),
              March 2019.

   [I-D.ietf-pce-pcep-extension-for-pce-controller]
              Zhao, Q., Li, Z., Negi, M., and C. Zhou, "PCEP Procedures
              and Protocol Extensions for Using PCE as a Central
              Controller (PCECC) of LSPs", draft-ietf-pce-pcep-
              extension-for-pce-controller-01 (work in progress),
              February 2019.

   [I-D.zhao-pce-pcep-extension-pce-controller-sr]
              Zhao, Q., Li, Z., Negi, M., 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-04 (work in progress),
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   [I-D.litkowski-pce-state-sync]
              Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter
              Stateful Path Computation Element (PCE) Communication
              Procedures.", draft-litkowski-pce-state-sync-05 (work in
              progress), March 2019.

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   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
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              Negi, M., Li, Z., and X. Geng, "PCEP Procedures and
              Protocol Extensions for Using PCE as a Central Controller
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              controller-srv6-01 (work in progress), February 2019.

   [I-D.ietf-spring-srv6-network-programming]
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              programming-00 (work in progress), April 2019.

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Appendix A.  Contributors

   Dhruv Dhody

   Huawei Technologies

   Divyashree Techno Park, Whitefield

   Bangalore, Karnataka 560066

   India

   EMail: dhruv.ietf@gmail.com

Authors' Addresses

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   EMail: chengli13@huawei.com

   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   EMail: Mach.chen@huawei.com

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   EMail: jie.dong@huawei.com

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

   EMail: lizhenbin@huawei.com

   Aijun Wang
   China Telecom
   Beiqijia Town,
   Beijing, Changping District  102209
   China

   EMail: wangaj.bri@chinatelecom.cn

   Weiqiang Cheng
   China Mobile

   EMail: chengweiqiang@chinamobile.com

   Chao Zhou
   Cisco System
   San Jose
   USA

   EMail: chao.zhou@cisco.com

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