PCEP Extension for Segment Routing (SR) Bidirectional Associated Paths
draft-li-pce-sr-bidir-path-02

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PCE Working Group                                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                                D. Dhody
Expires: April 25, 2019                              Huawei Technologies
                                                                W. Cheng
                                                            China Mobile
                                                                   Z. Li
                                                                 J. Dong
                                                     Huawei Technologies
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                        October 22, 2018

 PCEP Extension for Segment Routing (SR) Bidirectional Associated Paths
                     draft-li-pce-sr-bidir-path-02

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.

   This document defines PCEP extensions for grouping two reverse
   unidirectional SR Paths into an Associated Bidirectional SR path when
   using a Stateful PCE for both PCE-Initiated and PCC-Initiated LSPs as
   well as when using a Stateless PCE.

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
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   This Internet-Draft will expire on April 25, 2019.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  PCEP Extension for Bidirectional SR Path  . . . . . . . . . .   4
     3.1.  Double-sided Bidirectional SR Path Association Group
           Object  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Bidirectional Flag  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Procedures of Bidirectional Path Computation  . . . . . . . .   6
     5.1.  PCE Initiated SR Paths  . . . . . . . . . . . . . . . . .   6
     5.2.  PCC Initiated SR Paths  . . . . . . . . . . . . . . . . .   7
     5.3.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Association Type  . . . . . . . . . . . . . . . . . . . .   9
     6.2.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Segment routing (SR) [RFC8402] leverages the source routing and
   tunneling paradigms.  SR supports to steer packets into an explicit
   forwarding path at the ingress node.

   [RFC5440] describes the Path Computation Element (PCE) Communication
   Protocol (PCEP).  PCEP enables the communication between a Path
   Computation Client (PCC) and a PCE, or between PCE and PCE, for the
   purpose of computation of Multiprotocol Label Switching (MPLS) as

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   well as Generalized MPLS (GMPLS) Traffic Engineering Label Switched
   Path (TE LSP) characteristics.

   [RFC8231] specifies a set of extensions to PCEP to enable stateful
   control of TE LSPs within and across PCEP sessions in compliance with
   [RFC4657].  It includes mechanisms to effect LSP State
   Synchronization between PCCs and PCEs, delegation of control over
   LSPs to PCEs, and PCE control of timing and sequence of path
   computations within and across PCEP sessions.  The model of operation
   where LSPs are initiated from the PCE is described in [RFC8281].

   [I-D.ietf-pce-segment-routing] specifies extensions to the Path
   Computation Element Protocol (PCEP) [RFC5440] for SR networks, that
   allow a stateful PCE to compute and initiate SR-TE paths, as well as
   a PCC to request, report or delegate SR paths.
   [I-D.negi-pce-segment-routing-ipv6] extend PCEP to support SR for
   IPv6 data plane.

   [I-D.ietf-pce-association-group] introduces a generic mechanism to
   create a grouping of LSPs which can then be used to define
   associations between a set of LSPs and/or a set of attributes, for
   example primary and secondary LSP associations, and is equally
   applicable to the active and passive modes of a Stateful PCE
   [RFC8231] or a stateless PCE [RFC5440].

   Currently, SR network only supports unidirectional path, but the
   bidirectional SR path is required in some scenarios, for example,
   mobile backhaul transport network.  The requirement of SR
   bidirectional path is specified in
   [I-D.cheng-spring-mpls-path-segment].

   [I-D.ietf-pce-association-bidir] defines PCEP extensions for grouping
   two reverse unidirectional MPLS TE LSPs into an Associated
   Bidirectional LSP when using a Stateful PCE for both PCE-Initiated
   and PCC-Initiated LSPs as well as when using a Stateless PCE.

   This document extends the bidirectional association to segment
   routing by specifying PCEP extensions for grouping two reverse
   unidirectional SR paths into a bidirectional SR path.

   [I-D.ietf-pce-association-bidir] specify the Double-sided
   Bidirectional procedure, where the PCE creates the association and
   provisions at the both ends, the RSVP-TE does the signaling to the
   egress the status of the forward LSP and the ingress about the
   reverse LSP.  Thus, the both ends learn both the LSPs forming the
   bidirectional association.  In case of SR, to support the
   bidirectional use-case, this is done via the PCEP protocol itself as
   described in Section 3.1.  This is done so that both ends are aware

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   of the Path Segment used by each of the unidirectional LSP, as well
   as the status, the ERO etc.

   [I-D.li-pce-sr-path-segment] defines a procedure for Path Segment in
   PCEP for SR by defining the PATH-SEGMENT TLV.  The Path Segment can
   be a Path Segment in SR-MPLS [I-D.cheng-spring-mpls-path-segment], or
   a Path Segment in SRv6 [I-D.li-spring-srv6-path-segment], or other
   IDs that can identify an SR path.  The PATH-SEGMENT TLV SHOULD be
   included for associated bidirectional SR paths.

2.  Terminology

   This document makes use of the terms defined in
   [I-D.ietf-pce-segment-routing].  The reader is assumed to be familiar
   with the terminology defined in [RFC5440], [RFC8231], [RFC8281],
   [I-D.ietf-pce-association-group] and
   [I-D.ietf-pce-association-bidir].

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.  PCEP Extension for Bidirectional SR Path

   As per [I-D.ietf-pce-association-group], LSPs are associated by
   adding them to a common association group.
   [I-D.ietf-pce-association-bidir] specifies PCEP extensions for
   grouping two reverse unidirectional MPLS-TE LSPs into an Associated
   Bidirectional LSP for both single-sided and double-sided initiation
   cases by defining two new Bidirectional LSP Association Groups.

   This document extends the procedure for SR bidirectional associated
   paths by defining a new bidirectional association type (i.e.  Double-
   sided Bidirectional SR Path Association Group).  The document further
   describes the mechanism of associating two unidirectional SR path
   into a bidirectional SR path.  [I-D.li-pce-sr-path-segment] defines a
   procedure for Path Segment in PCEP for SR by defining the PATH-
   SEGMENT TLV.  The bidirectional SR path can also use the PATH-SEGMENT
   TLV.

   Note that a new association type is created by this document to
   create new procedures applicable to SR-path (and are quite different
   than the RSVP-TE bidirectional association groups).

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3.1.  Double-sided Bidirectional SR Path Association Group Object

   As defined in [I-D.ietf-pce-association-bidir], two LSPs are
   associated as a bidirectional MPLS-TE LSP by a common bidirectional
   LSP association group.  For associating two SR paths, this document
   defines a new association group called 'Double-sided Bidirectional SR
   Path Association Group' as follows:

   o  Association Type (TBD1 to be assigned by IANA) = Double-sided
      Bidirectional SR Path Association Group

   Similar to other bidirectional associations, this Association Type is
   operator-configured in nature and statically created by the operator
   on the PCEP peers.  The paths belonging to this association is
   conveyed via PCEP messages to the PCEP peer.  Operator-configured
   Association Range TLV [I-D.ietf-pce-association-group] MUST NOT be
   sent for these Association Types, and MUST be ignored, so that the
   entire range of association ID can be used for them.  The handling of
   the Association ID, Association Source, optional Global Association
   Source and optional Extended Association ID in this association are
   set in the same way as [I-D.ietf-pce-association-bidir].

   A member of the Double-sided Bidirectional SR Path Association Group
   can take the role of a forward or reverse SR path and follows the
   rules similar to the rules defined in
   [I-D.ietf-pce-association-bidir] for LSPs.

   o  An SR path (forward or reverse) can not be part of more than one
      Double-sided Bidirectional SR Path Association Group.

   o  The endpoints of the SR paths in this associations cannot be
      different.

   For describing the SR paths in this association group, such as
   direction and co-routed information, this association group reuses
   the Bidirectional LSP Association Group TLV defined in
   [I-D.ietf-pce-association-bidir].  All fields and processing rules
   are as per [I-D.ietf-pce-association-bidir].

4.  Bidirectional Flag

   As defined in [RFC5440], the B-flag in RP object MUST be set when the
   PCC specifies that the path computation request relates to a
   bidirectional TE LSP.  In this document, the B-flag also MUST be set
   when the PCC specifies that the path computation request relates to a
   bidirectional SR path.  When a stateful PCE initiates or updates a
   bidirectional SR paths including LSPs and SR paths, the B-flag in SRP
   object [I-D.ietf-pce-pcep-stateful-pce-gmpls] may be set as well.

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5.  Procedures of Bidirectional Path Computation

   Two unidirectional SR paths can be associated by the association
   group object as specified in [I-D.ietf-pce-association-group].  A
   bidirectional LSP association group object is defined in
   [I-D.ietf-pce-association-bidir] (for MPLS-TE).  This documents
   extends the mechanism for bidirectional SR paths.  Two SR paths can
   be associated together by including the Bidirectional SR Path
   Association Group in the PCEP messages.  The PATH-SEGMENT TLV
   [I-D.li-pce-sr-path-segment] SHOULD also be included in the LSP
   object for these SR paths to support required use-cases.

   There is also a need to include the reverse direction path in the
   PCEP messages, to do this the PCE SHOULD inform the reverse SR path
   to the ingress PCC and vice versa.  To achieve this a PCInitiate
   message for the reverse SR path is sent to the ingress PCC and a
   PCInitiate message for the forward SR path is sent to the egress PCC
   (with the same association group).  These PCInitiate message MUST NOT
   trigger initiation of SR paths.  The information of reverse direction
   path can be used for several scenarios, such as directed BFD
   [I-D.ietf-mpls-bfd-directed].

5.1.  PCE Initiated SR Paths

   As specified in [I-D.ietf-pce-association-group] Bidirectional SR
   Association Group can be created by a Stateful PCE.

   o  Stateful PCE can create and update the forward and reverse SR path
      independently for Double-sided Bidirectional SR Path Association
      Groups.

   o  Stateful PCE can establish and remove the association relationship
      on a per SR path basis.

   o  Stateful PCE can create and update the SR path and the association
      on a PCC via PCInitiate and PCUpd messages, respectively, using
      the procedures described in [I-D.ietf-pce-association-group].

   o  The PATH-SEGMENT TLV SHOULD be included for each SR path in the
      LSP object.

   o  The opposite direction SR path (LSP2(R) at S, LSP1(F) at D )
      SHOULD be informed via PCInitiate message with the matching
      association group.

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                               +-----+
                               | PCE |
                               +-----+
   PCUpd/PCInitiate            /    \         PCUpd/PCInitiate
   Tunnel 1 (F)               /      \        Tunnel 2 (R)
   (LSP1 (F), LSP2 (R))      /        \       (LSP2 (R), LSP1 (F))
   Assoc#1                  /          \      Assoc#1
                           /            \
                          v              v
                     +-----+    LSP1     +-----+
                     |  S  |------------>|  D  |
                     |     |<------------|     |
                     +-----+    LSP2     +-----+
                           <no signaling>

    Figure 1: PCE-Initiated Double-sided Bidirectional SR Path

5.2.  PCC Initiated SR Paths

   As specified in [I-D.ietf-pce-association-group] Bidirectional SR
   Association Group can also be created by a PCC.

   o  PCC can create and update the forward and reverse SR paths
      independently for Double-sided Bidirectional SR Path Association
      Groups.

   o  PCC can establish and remove the association relationship on a per
      SR path basis.

   o  PCC MUST report the change in the association group of an SR path
      to PCE(s) via PCRpt message.

   o  PCC can report the forward and reverse SR paths independently to
      PCE(s) via PCRpt message.

   o  PCC can delegate the forward and reverse SR paths independently to
      a Stateful PCE, where PCE would control the SR paths.

   o  Stateful PCE can update the SR paths in the Double-sided
      Bidirectional SR Path Association Group via PCUpd message, using
      the procedures described in [I-D.ietf-pce-association-group].

   o  The PATH-SEGMENT TLV MUST be handled as defined in
      [I-D.li-pce-sr-path-segment].

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   o  The opposite direction SR path (LSP2(R) at S, LSP1(F) at D )
      SHOULD be informed via PCInitiate message with the matching
      association group.

                               +-----+
                               | PCE |
                               +-----+
   Reports/Delegates:          ^    ^       Reports/Delegates
   Tunnel 1 (F)               /      \        Tunnel 2 (R)
   (LSP1 (F))                /        \       (LSP2 (R))
                            /          \
                           /            \
                          /              \
                      +-----+    LSP1     +-----+
                      |  S  |------------>|  D  |
                      |     |<------------|     |
                      +-----+    LSP2     +-----+

     Figure 2a: PCC-Initiated Double-sided Bidirectional SR Path

                               +-----+
                               | PCE |
                               +-----+
   PCUpd/PCInitiate            /    \         PCUpd/PCInitiate
   Tunnel 1 (F)               /      \        Tunnel 2 (R)
   (LSP1 (F), LSP2 (R))      /        \       (LSP2 (R), LSP1 (F))
   Assoc#1                  /          \      Assoc#1
                           /            \
                          v              v
                     +-----+    LSP1     +-----+
                     |  S  |------------>|  D  |
                     |     |<------------|     |
                     +-----+    LSP2     +-----+

     Figure 2b: PCC-Initiated Double-sided Bidirectional SR Path
                along with opposite direction SR path

5.3.  Error Handling

   The error handling as described in section 5.5 of
   [I-D.ietf-pce-association-bidir] continue to apply.

   The Path Setup Type (PST) MUST be set to SR for the LSP belonging to
   the 'Double-sided Bidirectional SR Path Association Group', in case a
   PCEP speaker receives a different PST value, it MUST send an PCErr
   message with Error-Type = 29 (Early allocation by IANA) (Association

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   Error) and Error-Value = TBD2 (Bidirectional LSP Association - PST
   Mismatch).

6.  IANA Considerations

6.1.  Association Type

   This document defines a new Association Type for the Association
   Object defined [I-D.ietf-pce-association-group].  IANA is requested
   to make the assignment of a value for the sub-registry "ASSOCIATION
   Type Field" (to be created in [I-D.ietf-pce-association-group]), as
   follows:

   Value  Name                                            Reference
   -------------------------------------------------------------------
   TBD1   Double-sided Bidirectional                    This document
          SR Path Association Group

6.2.  PCEP Errors

   This document defines new Error value for Error Type 29 (Association
   Error).  IANA is requested to allocate new Error value within the
   "PCEP-ERROR Object Error Types and Values" sub-registry of the PCEP
   Numbers registry, as follows:

   Error Type  Description                               Reference
   -------------------------------------------------------------------
    29         Association Error

               Error value: TBD2                        This document
               Bidirectional LSP Association - PST Mismatch

7.  Security Considerations

   The security considerations described in [RFC5440], [RFC8231],
   [RFC8281], and [I-D.ietf-pce-segment-routing] apply to the extensions
   defined in this document as well.

   A new Association Type for the Association Object, Double-sided
   Associated Bidirectional SR Path Association Group is introduced in
   this document.  Additional security considerations related to LSP
   associations due to a malicious PCEP speaker is described in
   [I-D.ietf-pce-association-group] and apply to this Association Type.
   Hence, securing the PCEP session using Transport Layer Security (TLS)
   [RFC8253] is recommended.

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8.  Acknowledgments

9.  References

9.1.  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>.

   [I-D.ietf-pce-association-group]
              Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "PCEP Extensions for
              Establishing Relationships Between Sets of LSPs", draft-
              ietf-pce-association-group-06 (work in progress), June
              2018.

   [I-D.ietf-pce-association-bidir]
              Barth, C., Gandhi, R., and B. Wen, "PCEP Extensions for
              Associated Bidirectional Label Switched Paths (LSPs)",
              draft-ietf-pce-association-bidir-01 (work in progress),
              May 2018.

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   [I-D.ietf-pce-pcep-stateful-pce-gmpls]
              Zhang, X., Lee, Y., Zhang, F., Casellas, R., Dios, O., and
              Z. Ali, "Path Computation Element (PCE) Protocol
              Extensions for Stateful PCE Usage in GMPLS-controlled
              Networks", draft-ietf-pce-pcep-stateful-pce-gmpls-08 (work
              in progress), February 2018.

   [I-D.negi-pce-segment-routing-ipv6]
              Negi, M., Dhody, D., Sivabalan, S., and P. Kaladharan,
              "PCEP Extensions for Segment Routing leveraging the IPv6
              data plane", draft-negi-pce-segment-routing-ipv6-03 (work
              in progress), October 2018.

   [I-D.li-pce-sr-path-segment]
              Li, C., Chen, M., Dhody, D., Cheng, W., Dong, J., Li, Z.,
              and R. Gandhi, "Path Computation Element Communication
              Protocol (PCEP) Extension for Path Identification in
              Segment Routing (SR)", draft-li-pce-sr-path-segment-02
              (work in progress), September 2018.

   [I-D.li-spring-srv6-path-segment]
              Li, C., Chen, M., Dhody, D., Li, Z., Dong, J., and R.
              Gandhi, "Path Segment for SRv6 (Segment Routing in IPv6)",
              draft-li-spring-srv6-path-segment-00 (work in progress),
              October 2018.

9.2.  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>.

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

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

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   [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-14 (work in progress),
              October 2018.

   [I-D.ietf-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path", draft-ietf-mpls-bfd-directed-10 (work in progress),
              September 2018.

   [I-D.cheng-spring-mpls-path-segment]
              Cheng, W., Wang, L., Li, H., Chen, M., Gandhi, R., Zigler,
              R., and S. Zhan, "Path Segment in MPLS Based Segment
              Routing Network", draft-cheng-spring-mpls-path-segment-03
              (work in progress), October 2018.

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

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

   Email: dhruv.ietf@gmail.com

Li, et al.               Expires April 25, 2019                [Page 12]
Internet-Draft    SR Bidirectional Association in PCEP      October 2018

   Weiqiang Cheng
   China Mobile
   China

   Email: chengweiqiang@chinamobile.com

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

   Email: lizhenbin@huawei.com

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

   Email: jie.dong@huawei.com

   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com

Li, et al.               Expires April 25, 2019                [Page 13]