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PCE Working Group                                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: February 20, 2020                                      W. Cheng
                                                            China Mobile
                                                                   Z. Li
                                                                 J. Dong
                                                     Huawei Technologies
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                                Q. Xiong
                                                         ZTE Corporation
                                                         August 19, 2019


PCEP Extensions for Associated Bidirectional Segment Routing (SR) Paths
                     draft-li-pce-sr-bidir-path-06

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 Segment Routing (SR) TE 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on February 20, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  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  . . . . . . . . . . . . . . . . . . . . .   6
   5.  Procedures for Associated Bidirectional SR Path Computation .   6
     5.1.  PCE Initiated Associated Bidirectional SR Paths . . . . .   7
     5.2.  PCC Initiated Associated Bidirectional SR Paths . . . . .   8
     5.3.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   9
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Huawei's Commercial Delivery  . . . . . . . . . . . . . .  10
     6.2.  ZTE's Commercial Delivery . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  11
     7.2.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  12
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  12
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  12
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  12
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  12
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  12
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  12
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  13
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13



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     12.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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
   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.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 networks only support unidirectional paths.  However,
   bidirectional SR Paths are required in some networks, for example, in
   mobile backhaul transport networks.  The requirement of bidirectional
   SR Path is specified in [I-D.ietf-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.






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   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] specifies the Double-sided
   Bidirectional LSP Association procedure, where the PCE creates the
   association and provisions at both endpoints, 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 endpoints learn the reverse
   LSPs forming the bidirectional LSP association.  In case of SR, to
   support the bidirectional path use-case, this is done using the PCEP
   protocol.  This is done so that both endpoints are aware of the the
   unidirectional SR Path, as well as the status and other SR path
   related information.

   [I-D.li-pce-sr-path-segment] defines a procedure for Path Segment
   Identifier (PSID) in PCEP for SR using PATH-SEGMENT TLV.  The PSID
   can be a Path Segment Identifier in SR-MPLS
   [I-D.ietf-spring-mpls-path-segment].  The PSID can be used for an
   associated bidirectional SR Path for identifying the SR Path.

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 associated bidirectional SR
   Paths by defining a new bidirectional association group (Double-sided



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   Bidirectional SR Path Association Group).  The document further
   describes the mechanism for associating two unidirectional SR Paths
   into a bidirectional SR Path.  [I-D.li-pce-sr-path-segment] defines a
   procedure for communicating Path Segment in PCEP for SR using PATH-
   SEGMENT TLV.  The bidirectional SR Path can also use the PATH-SEGMENT
   TLV.

   Note that an association group is defined in this document to define
   procedures specific to SR Paths (and the procedures are different
   than the RSVP-TE bidirectional association groups defined in
   [I-D.ietf-pce-association-bidir]).

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 follow
   the similar 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



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   [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.

5.  Procedures for Associated Bidirectional SR 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 document
   extends these association mechanisms for bidirectional SR Paths.  Two
   SR Paths can be associated together by using the Bidirectional SR
   Path Association Group defined in this document for 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.

   For bidirectional SR Paths, there is a need to know the reverse
   direction SR paths.  The PCE SHOULD inform the reverse SR Paths to
   the ingress PCCs 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 reverse direction SR Path can be
   used for several use-cases, such as directed BFD
   [I-D.ietf-mpls-bfd-directed].

   For a bidirectional LSP computation when using both direction LSPs on
   a node, the same LSP would need to be identified using 2 different
   PLSP-IDs based on the PCEP session to the ingress or the egress.  In
   other words, the LSP will have a PLSP-ID A at the ingress node while
   it will have the PLSP-ID B at the egress node.  The PCE will maintain
   the two PLSP-IDs for the same LSP.  For instance, an ingress PCC
   requests a bidirectional SR Path computation, and the PCE computes a
   forward LSP1 with PLSP-ID say 100.  The reverse LSP2 from the egress
   to the ingress with PLSP-ID say 200 is allocated by the egress PCC.
   Since the PLSP-ID space is independent at each PCC, the PLSP-ID
   allocated by the egress PCC can not be used for the LSP at the
   ingress PCC (PLSP-ID conflict may occur).  Hence, the PCE needs to



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   allocate a PLSP-ID for LSP2 from the ingress PCC's PLSP-ID space ,
   say 101.  Similarly for LSP1, it has PLSP-ID 100 at the ingress, and
   may have say PLSP-ID 201 at the egress node.

5.1.  PCE Initiated Associated Bidirectional SR Paths

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

   o  Stateful PCE can create and update the forward and reverse SR
      Paths independently for a 'Double-sided Bidirectional SR Path
      Association Group'.

   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 reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
      D) SHOULD be informed by PCE via PCInitiate message with the
      matching association group.

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

         Figure 1: PCE-Initiated Double-sided Bidirectional SR Path
                   with Forward and Reverse Direction SR Paths







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5.2.  PCC Initiated Associated Bidirectional SR Paths

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

   o  PCC can create and update the forward and reverse SR Paths
      independently for a 'Double-sided Bidirectional SR Path
      Association Group'.

   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].

   o  The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
      D) SHOULD be informed by PCE via PCInitiate message with the
      matching association group.




















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                              +-----+
                              | PCE |
                              +-----+
   Report/Delegate:           ^     ^          Report/Delegate:
   Tunnel 1 (F)              /       \         Tunnel 2 (F)
   (LSP1 (F))               /         \        (LSP2 (F))
   Association #2          /           \       Association #2
                          /             \
                         /               \
                    +-----+    LSP1     +-----+
                    |  S  |------------>|  D  |
                    |     |<------------|     |
                    +-----+    LSP2     +-----+
                          <no signaling>

     Figure 2a: Step 1: PCC-Initiated Double-sided Bidirectional SR Path
                with Forward Direction SR Paths


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

   Figure 2b: Step 2: PCE-Upd/Initiated Double-sided Bidirectional Path
              Along with Reverse Direction SR Paths


5.3.  Error Handling

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

   The PCEP Path Setup Type (PST) MUST be set to 'TE Path is Setup using
   Segment Routing' [I-D.ietf-pce-segment-routing] for the LSP belonging
   to the 'Double-sided Bidirectional SR Path Association Group'.  In
   case a PCEP speaker receives a different PST value for this
   association group, it MUST send a PCErr message with Error-Type = 29



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   (Early allocation by IANA) (Association Error) and Error-Value = TBD2
   (Bidirectional LSP Association - Path Setup Type Mismatch).

6.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

6.1.  Huawei's Commercial Delivery

   The feature is developing based on Huawei VRP8.

   o  Organization: Huawei

   o  Implementation: Huawei's Commercial Delivery implementation based
      on VRP8.

   o  Description: The implementation is under development.

   o  Maturity Level: Product

   o  Contact: tanren@huawei.com

6.2.  ZTE's Commercial Delivery

   o  Organization: ZTE





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   o  Implementation: ZTE's Commercial Delivery implementation based on
      Rosng v8.

   o  Description: The implementation is under development.

   o  Maturity Level: Product

   o  Contact: zhan.shuangping@zte.com.cn

7.  IANA Considerations

7.1.  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


7.2.  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 -
               Path Setup Type Mismatch

8.  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



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   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.

9.  Manageability Considerations

   All manageability requirements and considerations listed in
   [RFC5440], [RFC8231], and [RFC8281] apply to PCEP protocol extensions
   defined in this document.  In addition, requirements and
   considerations listed in this section apply.

9.1.  Control of Function and Policy

   The mechanisms defined in this document do not imply any control or
   policy requirements in addition to those already listed in [RFC5440],
   [RFC8231], and [RFC8281].

9.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, there are no new MIB Objects
   defined for Bidirectional SR Path associations.  The PCEP YANG module
   [I-D.ietf-pce-pcep-yang] defines data model for Bidirectional SR Path
   associations.

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], [RFC8231], and [RFC8281].

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], [RFC8231], and [I-D.ietf-pce-segment-routing] .

9.5.  Requirements On Other Protocols

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

9.6.  Impact On Network Operations

   Mechanisms defined in [RFC5440], [RFC8231], and
   [I-D.ietf-pce-segment-routing] also apply to PCEP extensions defined
   in this document.



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10.  Contributors

   The following people have substantially contributed to this document:

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

       Email: dhruv.ietf@gmail.com

11.  Acknowledgments

   Many thanks to Marina Fizgeer for detailed review and comments.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [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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Internet-Draft    SR Bidirectional Association in PCEP       August 2019


   [I-D.ietf-pce-association-group]
              Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships Between Sets of Label Switched Paths
              (LSPs)", draft-ietf-pce-association-group-10 (work in
              progress), August 2019.

   [I-D.ietf-pce-association-bidir]
              Gandhi, R., Barth, C., and B. Wen, "PCEP Extensions for
              Associated Bidirectional Label Switched Paths (LSPs)",
              draft-ietf-pce-association-bidir-03 (work in progress),
              March 2019.

   [I-D.ietf-pce-pcep-stateful-pce-gmpls]
              Lee, Y., Zheng, H., Dios, O., Lopezalvarez, V., and Z.
              Ali, "Path Computation Element (PCE) Protocol Extensions
              for Stateful PCE Usage in GMPLS-controlled Networks",
              draft-ietf-pce-pcep-stateful-pce-gmpls-11 (work in
              progress), March 2019.

   [I-D.li-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Dong, J., Li, Z., Gandhi, R.,
              and Q. Xiong, "Path Computation Element Communication
              Protocol (PCEP) Extension for Path Segment in Segment
              Routing (SR)", draft-li-pce-sr-path-segment-07 (work in
              progress), July 2019.

12.2.  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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   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [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>.

   [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-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path", draft-ietf-mpls-bfd-directed-11 (work in progress),
              April 2019.

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment-00 (work in progress),
              March 2019.

   [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-12 (work in progress), July 2019.

Authors' Addresses

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

   Email: chengli13@huawei.com







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Internet-Draft    SR Bidirectional Association in PCEP       August 2019


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

   Email: Mach.chen@huawei.com


   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


   Quan Xiong
   ZTE Corporation
   China

   Email: xiong.quan@zte.com.cn





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