[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05

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
                                                                 J. Dong
                                                                   Z. Li
                                                     Huawei Technologies
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                        October 22, 2018


  Path Computation Element Communication Protocol (PCEP) Extension for
                  Path Segment in Segment Routing (SR)
                    draft-li-pce-sr-path-segment-03

Abstract

   The Path Computation Element (PCE) provides path computation
   functions in support of traffic engineering in Multiprotocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks.

   The Source Packet Routing in Networking (SPRING) architecture
   describes how Segment Routing (SR) can be used to steer packets
   through an IPv6 or MPLS network using the source routing paradigm.  A
   Segment Routed Path can be derived from a variety of mechanisms,
   including an IGP Shortest Path Tree (SPT), explicit configuration, or
   a Path Computation Element (PCE).

   Path identification is needed for several use cases such as
   performance measurement in Segment Routing (SR) network.  This
   document specifies extensions to the Path Computation Element
   Protocol (PCEP) to support requesting, replying, reporting and
   updating the Path Segment ID (Path SID) between PCEP speakers.

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/.





Li, et al.               Expires April 25, 2019                 [Page 1]


Internet-Draft          PCEP for SR Path Segment            October 2018


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

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

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   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.  Overview of Path Segment Extensions in PCEP . . . . . . . . .   4
   4.  Objects and TLVs  . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   5
       4.1.1.  The SR PCE Capability sub-TLV . . . . . . . . . . . .   5
       4.1.2.  The SRv6 PCE Capability sub-TLV . . . . . . . . . . .   6
       4.1.3.  PCECC-CAPABILITY sub-TLV  . . . . . . . . . . . . . .   6
     4.2.  LSP Object  . . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Path Segment TLV  . . . . . . . . . . . . . . . . . .   7
     4.3.  FEC Object  . . . . . . . . . . . . . . . . . . . . . . .   9
     4.4.  CCI Object  . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  PCC Allocated Path Segment  . . . . . . . . . . . . . . .  11
       5.1.1.  Egress PCC Allocated Path Segment . . . . . . . . . .  11
     5.2.  PCE Allocated Path Segment  . . . . . . . . . . . . . . .  15
       5.2.1.  PCE Controlled Label Spaces Advertisement . . . . . .  15
       5.2.2.  Ingress PCC request Path Segment to PCE . . . . . . .  15
       5.2.3.  PCE allocated Path Segment on its own . . . . . . . .  16
   6.  Dataplane Considerations  . . . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  SR PCE Capability Flags . . . . . . . . . . . . . . . . .  17
     7.2.  SRv6 PCE Capability Flags . . . . . . . . . . . . . . . .  18



Li, et al.               Expires April 25, 2019                 [Page 2]


Internet-Draft          PCEP for SR Path Segment            October 2018


     7.3.  New LSP Flag Registry . . . . . . . . . . . . . . . . . .  18
     7.4.  New PCEP TLV  . . . . . . . . . . . . . . . . . . . . . .  18
       7.4.1.  Path Segment TLV  . . . . . . . . . . . . . . . . . .  18
     7.5.  New CCI Flag Registry . . . . . . . . . . . . . . . . . .  19
     7.6.  New FEC Type Registry . . . . . . . . . . . . . . . . . .  19
     7.7.  PCEP Error Type and Value . . . . . . . . . . . . . . . .  20
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  20
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     11.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   [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 Generalzied 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.zhao-pce-pcep-extension-for-pce-controller] 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.

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

   An SR path needs to be identified in some use cases such as
   performance measurement.  For identifying an SR path,
   [I-D.cheng-spring-mpls-path-segment] introduces a new segment that is
   referred to as Path Segment.

   [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



Li, et al.               Expires April 25, 2019                 [Page 3]


Internet-Draft          PCEP for SR Path Segment            October 2018


   a PCC to request, report or delegate SR paths.
   [I-D.negi-pce-segment-routing-ipv6] extend PCEP to support SR paths
   for IPv6 data plane.

   [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.

   This document specifies a mechanism to carry the SR path
   identification information in PCEP messages [RFC5440] [RFC8231]
   [RFC8281].  The SR path identifier 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.  This document also extends the PCECC-SR mechanism to inform
   the Path Segment to the egress PCC.

2.  Terminology

   This memo makes use of the terms defined in [RFC4655],
   [I-D.ietf-pce-segment-routing], 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.  Overview of Path Segment Extensions in PCEP

   This document specifies a mechanism of encoding (and allocating) Path
   Segment in PCEP extensions.  For supporting Path Segment in PCEP,
   several TLVs and flags are defined.  The formats of the objects and
   TLVs are described in Section 4.  The procedures of Path Segment
   allocation are described in Section 5.

   There are various modes of operations, such as -

   o  The Path Segment can be allocated by Egress PCC.  The PCE should
      request the Path Segment from Egress PCC.

   o  The PCE can allocate a Path Segment on its own accord and inform
      the ingress/egress PCC, useful for PCE-initiated LSPs.



Li, et al.               Expires April 25, 2019                 [Page 4]


Internet-Draft          PCEP for SR Path Segment            October 2018


   o  Ingress PCC can also request PCE to allocate the Path Segment, in
      this case, the PCE would either allocate and inform the assigned
      Path Segment to the ingress/egress PCC using PCEP messages, or
      first request egress PCC for Path Segment and then inform it to
      the ingress PCC.

   The path information to the ingress PCC and PCE is exchanged via an
   extension to [I-D.ietf-pce-segment-routing] and
   [I-D.negi-pce-segment-routing-ipv6].  The Path Segment information to
   the egress PCC can be informed via an extension to the PCECC-SR
   procedures [I-D.zhao-pce-pcep-extension-pce-controller-sr].

   For the PCE to allocate a Path Segment, the PCE SHOULD be aware of
   the MPLS label space from the PCCs.  This is done via mechanism as
   described in [I-D.li-pce-controlled-id-space].  Otherwise, the PCE
   should request the egress PCC for Path Segment allocation.

4.  Objects and TLVs

4.1.  The OPEN Object

4.1.1.  The SR PCE Capability sub-TLV

   [I-D.ietf-pce-segment-routing] defined a new Path Setup Type (PST)
   and SR-PCE-CAPABILITY sub-TLV for SR.  PCEP speakers use this sub-TLV
   to exchange information about their SR capability.  The TLV defines a
   Flags field that includes one bit (L-flag) to indicate Local
   Significance [I-D.ietf-pce-segment-routing].

   This document adds an additional flag for Path Segment allocation, as
   follows -

      P (Path Segment Identification bit): A PCEP speaker sets this flag
      to 1 to indicate that it has the capability to encode SR path
      identification (Path Segment, as per
      [I-D.cheng-spring-mpls-path-segment]).

    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=26            |            Length=4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reserved              |   Flags |P|N|L|      MSD      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: P-flag in SR-PCE-CAPABILITY TLV





Li, et al.               Expires April 25, 2019                 [Page 5]


Internet-Draft          PCEP for SR Path Segment            October 2018


   The figure is included for the ease of the reader and can be removed
   at the time of publication.

4.1.2.  The SRv6 PCE Capability sub-TLV

   [I-D.negi-pce-segment-routing-ipv6] defined a new Path Setup Type
   (PST) and SRv6-PCE-CAPABILITY sub-TLV for SRv6.  PCEP speakers use
   this sub-TLV to exchange information about their SRv6 capability.
   The TLV includes a Flags field and one bit (L-flag) was allocated in
   [I-D.negi-pce-segment-routing-ipv6].

   This document adds an additional flag for Path Segment allocation, as
   follows -

      P (Path Segment Identification bit): A PCEP speaker sets this flag
      to 1 to indicate that it has the capability to encode SRv6 path
      identification.(Path Segment, as per
      [I-D.li-spring-srv6-path-segment]).

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Type=TBD1          |            Length=4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      max-SL   |  Reserved     |             Flags         |P|L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: P-flag in SRv6-PCE-CAPABILITY TLV

   The figure is included for the ease of the reader and can be removed
   at the time of publication.

4.1.3.  PCECC-CAPABILITY sub-TLV

   Along with the SR sub-TLVs, the PCECC Capability as per
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] should be advertised
   if the PCE allocates the Path Segment and acts as a Central
   Controller that manages the Label space.

   The PCECC Capability should also be advertised on the egress PCEP
   session, along with the SR sub-TLVs.  This is needed to ensure that
   the PCE can use the PCECC objects/mechanism to request/inform the
   egress PCC of the Path Segment as described in this document.








Li, et al.               Expires April 25, 2019                 [Page 6]


Internet-Draft          PCEP for SR Path Segment            October 2018


4.2.  LSP Object

   The LSP Object is defined in Section 7.3 of [RFC8231].  This document
   adds the following flags to the LSP Object:

      P (Path Segment Allocation bit): If the bit is set to 1, it
      indicates that the Path Segment needs to be allocated by the PCE
      for this LSP.  A PCC would set this bit to 1 to request for
      allocation of Path Segment by the PCE in the PCReq or PCRpt
      message.  A PCE would also set this bit to 1 to indicate that the
      Path Segment is allocated by PCE and encoded in the PCRep, PCUpd
      or PCInitiate message (the PATH-SEGMENT TLV MUST be present in LSP
      object).  Further, a PCE would set this bit to 0 to indicate that
      the Path Segment should be allocated by the PCC as described in
      Section 5.1.1.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                PLSP-ID                | Flag|P|C|  O  |A|R|S|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                        TLVs                                 //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 3: P-flag in LSP Object

   The figure is included for the ease of the reader and can be removed
   at the time of publication.

4.2.1.  Path Segment TLV

   The PATH-SEGMENT TLV is an optional TLV for use in the LSP Object for
   Path Segment allocation.  The type of this TLV is to be allocated by
   IANA (TBA4).  The format is shown below.

    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              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       ST      |  Flag       |L|            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~              (Variable length) Path Segment                   ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 4: The PATH-SEGMENT TLV Format



Li, et al.               Expires April 25, 2019                 [Page 7]


Internet-Draft          PCEP for SR Path Segment            October 2018


   The type (16-bit) of the TLV is TBA4 (to be allocated by IANA).  The
   length (16-bit) has a fixed value of 8 octets.  The value contains
   the following fields:

      ST (The Segment type - 8 bits): The ST field specifies the type of
      the Path Segment field, which carries a Path Segment corresponding
      to the SR path.

      *  0: MPLS Path Segment, which is an MPLS label as defined in
         [I-D.cheng-spring-mpls-path-segment].  The PST type MUST be set
         to SR (MPLS).

      *  1: SRv6 Path Segment, which is a 128 bit IPv6 address as
         defined in [I-D.li-spring-srv6-path-segment].  The PST type
         MUST be set to SRv6.

      Flags (8 bits): Two flags are currently defined:

      *  L-Bit (Local/Global - 1 bit): If set, then the Path Segment
         carried by the PATH-SEGMENT TLV has local significance.  If not
         set, then the Path Segment carried by this TLV has global
         significance (i.e.  Path Segment is global within an SR
         domain).

      *  The unassigned bits MUST be set to 0 and MUST be ignored at
         receipt.

      Reserved (16 bits): MUST be set to 0 and MUST be ignored at
      receipt.

      Path Segment: The Path Segment of an SR path.  The Path Segment
      type is indicated by the ST field.  When the ST is 0, it is a MPLS
      Path Segment [I-D.cheng-spring-mpls-path-segment] in the MPLS
      label format.  When the ST field is 1, it is a 128-bit SRv6 Path
      Segment as defined in [I-D.li-spring-srv6-path-segment].

   In general, only one instance of PATH-SEGMENT TLV will be included in
   LSP object.  If more than one PATH-SEGMENT TLV is included, the first
   one is processed and others MUST be ignored.  Multiple Path Segment
   allocation for use cases like alternate-making will be considered in
   future version of this draft.

   When the Path Segment allocation is enable, a PATH-SEGMENT TLV should
   be included in the LSP object.

   If the label space is maintained by PCC itself, and the Path Segment
   is allocated by Egress PCC, then the PCE should request the Path
   Segment from Egress PCC as described in Section 5.1.1.  In this case,



Li, et al.               Expires April 25, 2019                 [Page 8]


Internet-Draft          PCEP for SR Path Segment            October 2018


   the PCE should send a PCUpdate or PCInitiate message to the egress
   PCC to request the Path Segment.  The P-flag in LSP should be unset
   in this case.

   If the PCC requests the Path Segment to be allocated by the PCE, P
   flag in LSP object is set to 1 and PATH-SEGMENT TLV MAY be skipped.
   After the PCE has allocated a Path Segment, it MUST include the PATH-
   SEGMENT TLV in a LSP object.

   If the PCE allocated the Path Segment on its own accord, a PATH-
   SEGMENT TLV MUST be included in a LSP object.

   If a PCEP node does not recognize the PATH-SEGMENT TLV, it would
   behave in accordance with [RFC5440] and ignore the TLV.  If a PCEP
   node recognizes the TLV but does not support the TLV, it MUST send
   PCErr with Error-Type = 2 (Capability not supported).

4.3.  FEC Object

   The FEC Object [I-D.zhao-pce-pcep-extension-pce-controller-sr] is
   used to specify the FEC information and MAY be carried within
   PCInitiate or PCRpt message for the PCECC-SR operations.  The PCE
   MUST inform the Path Identification information to the Egress PCC.
   To do this, this document extends the procedures of
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] by defining a new FEC
   object type for Path.

   FEC Object-Type is TBA6 'Path'.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                           TLV(s)                            //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: The path FEC object Format

   One or more following TLV(s) are allowed in the 'path' FEC object -

   o  SYMBOLIC-PATH-NAME TLV: As defined in [RFC8231], it is a human-
      readable string that identifies an LSP in the network.

   o  LSP-IDENTIFIERS TLVs: As defined in [RFC8231], it is optional for
      SR, but could be used to encode the source, destination and other
      identification information for the path.




Li, et al.               Expires April 25, 2019                 [Page 9]


Internet-Draft          PCEP for SR Path Segment            October 2018


   o  SPEAKER-ENTITY-ID TLV: As defined in [RFC8232], a unique
      identifier for the PCEP speaker, it is used to identify the
      Ingress PCC.

   Either SYMBOLIC-PATH-NAME TLV or LSP-IDENTIFIERS TLV MUST be
   included.  SPEAKER-ENTITY-ID TLV is optional.  Only one instance of
   each TLV is processed, if more than one TLV of each type is included,
   the first one is processed and others MUST be ignored.

4.4.  CCI Object

   The Central Control Instructions (CCI) Object is used by the PCE to
   specify the forwarding instructions is defined in
   [I-D.zhao-pce-pcep-extension-for-pce-controller].  Further
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] defined a CCI object
   type for SR.

   The Path Segment information is encoded directly in the CCI SR
   object.  The Path Segment TLV as described in the Section 4.2.1, MUST
   also be included in the CCI SR object as the TLV (as it includes
   additional information regarding the Path Segment identifier).

   This document adds the following flags to the CCI Object:

   o  C (PCC Allocation bit): If the bit is set to 1, it indicates that
      the allocation needs to be done by the PCC for this central
      controller instruction.  A PCE set this bit to request the PCC to
      make an allocation from its SR label space.  A PCC would set this
      bit to indicate that it has allocated the CC-ID and report it to
      the PCE.

    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                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      MT-ID    |    Algorithm  |        Flags      |C|N|E|V|L|O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                  SID/Label/Index (variable)                 //
   +---------------------------------------------------------------+
   |                                                               |
   //                        Optional TLV                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 6: The CCI object for SR





Li, et al.               Expires April 25, 2019                [Page 10]


Internet-Draft          PCEP for SR Path Segment            October 2018


   (Editor's Note - An update is planned for
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] in the next revision
   detailing this procedure, and the above text might move there.)

5.  Operations

   The Path Segment allocation and encoding is as per the stateful PCE
   operations for segment routing.  The procedures are as per the
   corresponding extensions defined in [I-D.ietf-pce-segment-routing]
   and [I-D.negi-pce-segment-routing-ipv6] (which are further based on
   [RFC8231] and [RFC8281]).  The additional operations for Path Segment
   are defined in this section.

   To notify (or request) the Path Segment to the Egress PCC, the
   procedures are as per the PCECC-SR
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] (which is based on
   [I-D.zhao-pce-pcep-extension-for-pce-controller]).  The additional
   operations are defined in this section.

5.1.  PCC Allocated Path Segment

5.1.1.  Egress PCC Allocated Path Segment

   As defined in [I-D.cheng-spring-mpls-path-segment], a Path Segment
   can be allocated by the egress PCC.  In this case, the label space
   may be maintained on the PCC itself.

   On receiving a stateful path computation request with Path Segment
   allocation request from an ingress PCC, or by initiating or updating
   an LSP with Path Segment actively, a PCE can request the egress PCC
   to allocate a Path Segment.  This is needed if the PCE does not
   control the Path Segment allocation for the egress PCC or the label
   space is maintained by the egress PCC itself.

   The mechanism of Path Segment request and reply may be achieved by
   using PCInitiate and PCUpd message as described in this section.

5.1.1.1.  Using CCI and FEC objects (PCECC)

   The PCE can request the egress to allocate the Path Segment using the
   PCInitiate message as described in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  The C flag in the
   CCI object is set to 1 and the CC-ID is set to a special value of
   0x0000 to indicate that the allocation needs to be done by the PCC.
   The PATH-SEGMENT TLV is also be included in CCI object along with the
   FEC object identifying the SR-Path.  The egress PCC would allocate
   the Path Segment and would report to the PCE using the PCRpt message
   as described in [I-D.zhao-pce-pcep-extension-pce-controller-sr] with



Li, et al.               Expires April 25, 2019                [Page 11]


Internet-Draft          PCEP for SR Path Segment            October 2018


   the allocated Path Segment in the CC-ID field as well as in the PATH-
   SEGMENT TLV.

   (Editor's Note - An update is planned for
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] in the next revision
   detailing this procedure)

   If the value of CC-ID/Path Segment is 0 and the C flag is set, it
   indicates that the PCE is requesting a Path Segment for this LSP.  If
   the CC-ID/Path Segment is set to a value 'n' and the C flag is set in
   the CCI object, it indicates that the PCE requests a specific value
   'n' of Path Segment.  If the Path Segment is allocated successfully,
   the egress PCC should report the Path Segment via PCRpt message with
   the CCI object along with the PATH-SEGMENT TLV.  Else, it MUST send a
   PCErr message with Error-Type = TBA7 ("Path SID failure") and Error
   Value = 1 ("Invalid SID").  If the value of Path Segment in CCI
   object is valid, but the PCC is unable to allocate the Path Segment,
   it MUST send a PCErr message with Error-Type = TBA7 ("Path label/SID
   failure") and Error Value = 2 ("Unable to allocate the specified
   label/SID").

   Once the PCE receives the PCRpt message with the CCI object, it can
   obtain the Path Segment information from the egress PCC and then
   update the path with Path Segment or reply to the ingress PCC, the
   path information with Path Segment.

   If the SR-Path is setup the ingress PCC will acknowledge with a PCRpt
   message to the PCE.  In case of error, as described in
   [I-D.ietf-pce-segment-routing], an PCErr message will be sent back to
   the PCE.  The PCE MUST request the withdraw of the Path Segment
   allocation by sending a PCInitiate message to remove the central
   controller instruction as per
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  When the LSP is
   deleted or the Path Segment is removed, the PCE should synchronize
   with the egress PCC.

   If the egress PCC wishes to withdraw or modify a previously reported
   Path Segment value, it MUST send a PCRpt message without any PATH-
   SEGMENT TLV or with the PATH-SEGMENT TLV containing the new Path
   Segment respectively in the CCI object.  The PCE would further
   trigger the removal of the central controller instruction as per
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].

   If a PCE wishes to modify a previously requested Path Segment value,
   it MUST send a new PCInitiate message with an allocation request CC-
   ID/PATH-SEGMENT TLV containing the new Path Segment value and C flag
   is set.  The PCE should trigger the removal of the older Path Segment
   next as per [I-D.zhao-pce-pcep-extension-pce-controller-sr].



Li, et al.               Expires April 25, 2019                [Page 12]


Internet-Draft          PCEP for SR Path Segment            October 2018


               Ingress                                    Egress
               +-+-+                +-+-+                 +-+-+
               |PCC|                |PCE|                 |PCC|
               +-+-+                +-+-+                 +-+-+
   1) LSP State  | ----  PCRpt ---->  |                     |
      Delegate   |     Delegate=1     |                     |
                 |     P=1            |2) PCE update        |
                 |                    |   the LSP-DB and    |
                 |                    |   request Path SID  |
                 |                    |                     |
                 |                    | --- PCInitiate ---> | Egress
                 |                    |      CC-ID=0        | allocates
                 |                    |      FEC=Path       | a Path-SID
                 |                    |                     | from its
                 |                    | <----- PCRpt ------ | space
                 |                    |       CC-ID=        |
                 |                    |       Path SID      |
                 |                    |                     |
                 |<----  PCUpd ----   |3)Paths update with  |
                 |  PATH-SEGMENT TLV  |  Path SID            |
                 |                    |                     |
   4) LSP State  | -----  PCRpt --->  |                     |
      Report     |                    |                     |
                 |                    |                     |

                Figure 7: Egress PCC Allocated Path Segment

5.1.1.2.  Using LSP objects (PCEP-SR)

   The PATH-SEGMENT TLV MUST be included in an LSP object in the
   PCInitiate message sent from the PCE to the egress to request path
   identification allocation by the egress PCC.  The P flag in LSP
   object MUST be set to 0.  This PCInitiate message to egress PCC would
   be the similar to the one sent to ingress PCC as per
   [I-D.ietf-pce-segment-routing], but the egress PCC would only
   allocate the Path Segment and would not trigger the initiation/update
   operation.

   If the value of Path Segment is 0x0 it indicates that the PCE is
   requesting a Path Segment for this LSP.  If the Path Segment is set
   to a value 'n' and the P flag is unset in the LSP object, it
   indicates that the PCE requests a specific value 'n' of Path Segment.
   If the Path Segment is allocated successfully, the egress PCC should
   report the Path Segment via PCRpt message with PATH-SEGMENT TLV in
   LSP object.  Else, it MUST send a PCErr message with Error-Type =
   TBA7 ("Path SID failure") and Error Value = 1 ("Invalid SID").  If
   the value of Path Segment is valid, but the PCC is unable to allocate
   the Path Segment, it MUST send a PCErr message with Error-Type = TBA7



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


Internet-Draft          PCEP for SR Path Segment            October 2018


   ("Path label/SID failure") and Error Value = 2 ("Unable to allocate
   the specified label/SID").

   Once the PCE receives the PCRpt message, it can obtain the Path
   Segment information from the egress PCC and then update the path with
   Path Segment or reply to the ingress PCC, the path information with
   Path Segment.

   If the SR-Path is setup the ingress PCC will acknowledge with a PCRpt
   message to the PCE.  In case of error, as described in
   [I-D.ietf-pce-segment-routing], an PCErr message will be sent back to
   the PCE.  The PCE MUST request the withdraw of the Path Segment
   allocation by sending a PCUpd message to remove the LSP and
   associated Path Segment by setting the R flag in the SRP object.
   When the LSP is deleted or the Path Segment is removed, the PCE
   should send a PCUpd message to synchronize with the egress PCC.

   If the egress PCC wishes to withdraw or modify a previously reported
   Path Segment value, it MUST send a PCRpt message without any PATH-
   SEGMENT TLV or with the PATH-SEGMENT TLV containing the new Path
   Segment respectively.

   If a PCE wishes to modify a previously requested Path Segment value,
   it MUST send a PCUpd message with PATH-SEGMENT TLV containing the new
   Path Segment value and P flag is LSP object would be unset.  Absence
   of the PATH-SEGMENT TLV in PCUpd message means that the PCE wishes to
   withdraw the Path Segment.

   If a PCC receives a valid Path Segment value from a PCE which is
   different than the current Path Segment, it MUST try to allocate the
   new value.  If the new Path Segment is successfully allocated, the
   PCC MUST report the new value to the PCE.  Otherwise, it MUST send a
   PCErr message with Error-Type = TBA7 ("Path label/SID failure") and
   Error Value = 2 ("Unable to allocate the specified label/SID").

















Li, et al.               Expires April 25, 2019                [Page 14]


Internet-Draft          PCEP for SR Path Segment            October 2018


               Ingress                                    Egress
               +-+-+                +-+-+                 +-+-+
               |PCC|                |PCE|                 |PCC|
               +-+-+                +-+-+                 +-+-+
   1) LSP State  | ----  PCRpt ---->  |                     |
      Delegate   |     Delegate=1     |                     |
                 |     P=1            |2) PCE update        |
                 |                    |   the LSP-DB and    |
                 |                    |   request Path SID  |
                 |                    |                     |
                 |                    | --- PCInitiate ---> | Egress
                 |                    |      PATH-SEGMENT   | allocates
                 |                    |      TLV in LSP     | a Path-SID
                 |                    |                     | from its
                 |                    | <----- PCRpt ------ | space
                 |                    |       Path SID      |
                 |                    |                     |
                 |<----  PCUpd ----   |3)Paths update with  |
                 |  PATH-SEGMENT TLV  |  Path SID           |
                 |                    |                     |
   4) LSP State  | -----  PCRpt --->  |                     |
      Report     |                    |                     |
                 |                    |                     |


                Figure 8: Egress PCC Allocated Path Segment

5.2.  PCE Allocated Path Segment

5.2.1.  PCE Controlled Label Spaces Advertisement

   For allocating the Path Segments to SR paths by the PCEs, the PCE
   controlled label space MUST be known at PCEs via configurations or
   any other mechanism.  The PCE controlled label spaces MAY be
   advertised as described in [I-D.li-pce-controlled-id-space].

5.2.2.  Ingress PCC request Path Segment to PCE

   The ingress PCC could request the Path Segment to be allocated by the
   PCE via PCRpt message as per [RFC8231].  The delegate flag (D-flag)
   MUST also be set for this LSP.  Also, the P-flag in the LSP object
   MUST be set.

   If the ingress requests for an expected value of path segment, then a
   PATH-SEGMENT TLV MUST be included with the expected value.  Else,
   there is no need to include a PATH-SEGMENT TLV in the LSP object.





Li, et al.               Expires April 25, 2019                [Page 15]


Internet-Draft          PCEP for SR Path Segment            October 2018


   If the Path Segment is allocated successfully, the PCE would further
   respond to Ingress PCC with PCUpd message as per [RFC8231] and MUST
   include the PATH-SEGMENT TLV in a LSP object.  Else, it MUST send a
   PCErr message with Error-Type = TBA7 ("Path SID failure") and Error
   Value = 1 ("Invalid SID").  If the value of Path Segment is valid,
   but the PCC is unable to allocate the Path Segment, it MUST send a
   PCErr message with Error-Type = TBA7 ("Path label/SID failure") and
   Error Value = 2 ("Unable to allocate the specified label/SID").

   The active PCE would allocate the Path Segment as per the PATH-
   SEGMENT flags and in case PATH-SEGMENT is not included, the PCE MUST
   act based on the local policy.

   The PCE would further inform the egress PCC about the Path Segment
   allocated by the PCE using the PCInitiate message as described in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].

                     Ingress                                    Egress
                     +-+-+                +-+-+                 +-+-+
                     |PCC|                |PCE|                 |PCC|
                     +-+-+                +-+-+                 +-+-+
   1) LSP State        | ----  PCRpt ---->  |                     |
      Delegate         |     Delegate=1     |                     |
                       |     P=1            |2) PCE update        |
                       |                    |   the LSP-DB and    |
                       |                    |   allocate Path SID |
                       |<----  PCUpd ----   |3)Paths update with  |
                       |  PATH-SEGMENT TLV  |  Path SID           |
                       |                    |                     |
   4) LSP State Report | -----  PCRpt --->  |                     |
                       |                    |                     |
                       |5) PCE informs the  | --- PCInitiate ---> |
                       |  Path SID to Egress|     FEC=Path        |
                       |                    |                     |
                       |                    | <-------- PCRpt --- |
                       |                    |                     |


             Figure 9: Ingress PCC request Path Segment to PCE

5.2.3.  PCE allocated Path Segment on its own

   The PCE could allocate the Path Segment on its own for a PCE-
   Initiated (or delegated LSP).  The allocated Path Segment needs to be
   informed to the Ingress and Egress PCC.  The PCE would use the
   PCInitiate message [RFC8281] or PCUpd message [RFC8231] towards the
   Ingress PCC and MUST include the PATH-SEGMENT TLV in the LSP object.
   The PCE would further inform the egress PCC about the Path Segment



Li, et al.               Expires April 25, 2019                [Page 16]


Internet-Draft          PCEP for SR Path Segment            October 2018


   allocated by the PCE using the PCInitiate message as described in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].

                     Ingress                                    Egress
                     +-+-+                +-+-+                 +-+-+
                     |PCC|                |PCE|                 |PCC|
                     +-+-+                +-+-+                 +-+-+
                       |                    |                     |
                       | <--PCInitiate---   |1)Initiate LSP with  |
                       | PATH-SEGMENT TLV   |  Path SID           |
                       |                    |                     |
    2)LSP delegation   |---PCRpt, D=1--->   | (Confirm)           |
                       |                    |                     |
                       |3) PCE informs the  | --- PCInitiate ---> |
                       |  Path SID to Egress|     FEC=Path        |
                       |                    |                     |
                       |                    | <-------- PCRpt --- |
                       |                    |                     |


             Figure 10: PCE allocated Path Segment on its own

6.  Dataplane Considerations

   As described in [I-D.cheng-spring-mpls-path-segment], in an SR-MPLS
   network, when a packet is transmitted along an SR path, the labels in
   the MPLS label stack will be swapped or popped.  So that no label or
   only the last label may be left in the MPLS label stack when the
   packet reaches the egress node.  Thus, the egress node cannot
   determine from which SR path the packet comes.  For this reason, it
   introduces the Path Segment.

   Apart from allocation and encoding of the Path Segment (described in
   this document) for the LSP, it would also be included in the SID/
   Label stack of the LSP (usually for processing by the egress).  To
   support this, the Path Segment MAY also be a part of SR-ERO as
   prepared by the PCE as per [I-D.ietf-pce-segment-routing].  The PCC
   MAY also include the Path Segment while preparing the label stack
   based on the local policy and use-case.

7.  IANA Considerations

7.1.  SR PCE Capability Flags

   SR PCE Capability TLV is defined in [I-D.ietf-pce-segment-routing],
   and the registry to manage the Flag field of the SR PCE Capability
   TLV is requested in [I-D.ietf-pce-segment-routing].  IANA is




Li, et al.               Expires April 25, 2019                [Page 17]


Internet-Draft          PCEP for SR Path Segment            October 2018


   requested to make the following allocation in the aforementioned
   registry.

    Bit     Description                                    Reference

   TBA1     Path Segment Allocation is supported(P)        This document


7.2.  SRv6 PCE Capability Flags

   SRv6 PCE Capability TLV is defined in defined in
   [I-D.negi-pce-segment-routing-ipv6], and the registry to manage the
   Flag field of the SRv6 PCE Capability Flags is requested in
   [I-D.negi-pce-segment-routing-ipv6].  IANA is requested to make the
   following allocation in the aforementioned registry.

    Bit    Description                                    Reference

   TBA2    Path Segment Allocation is supported(P)        This document


7.3.  New LSP Flag Registry

   [RFC8231] defines the LSP object; per that RFC, IANA created a
   registry to manage the value of the LSP object's Flag field.  IANA
   has allocated a new bit in the "LSP Object Flag Field" subregistry,
   as follows:

    Bit    Description                                Reference

   TBA3    Request for Path Segment Allocation(P)     This document


7.4.  New PCEP TLV

   IANA is requested to add the assignment of a new allocation in the
   existing "PCEP TLV Type Indicators" subregistry as follows:

   Value    Description                   Reference

   TBA4     PATH-SEGMENT TLV                   This document

7.4.1.  Path Segment TLV

   This document requests that a new subregistry named "PATH-SEGMENT TLV
   Segment Type (ST) Field" to be created to manage the value of the ST
   field in the PATH-SEGMENT TLV.




Li, et al.               Expires April 25, 2019                [Page 18]


Internet-Draft          PCEP for SR Path Segment            October 2018


   Value    Description                      Reference

     0      MPLS Path Segment(MPLS label)    This document
     1      SRv6 Path Segment(IPv6 address)  This document


   Further, this document also requests that a new subregistry named
   "PATH-SEGMENT TLV Flag Field" to be created to manage the Flag field
   in the PATH-SEGMENT TLV.  New values are assigned by Standards Action
   [RFC8126].  Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Capability description

   o  Defining RFC

   Bit   Description                               Reference

    7    Local Signification(L)                    This document


7.5.  New CCI Flag Registry

   CCI object is defined in defined in
   [I-D.zhao-pce-pcep-extension-for-pce-controller], further
   [I-D.zhao-pce-pcep-extension-pce-controller-sr] defined a CCI object
   type for SR. and the subregistry to manage the Flag field of the CCI
   object for SR is requested in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  IANA is requested
   to make the following allocation in the aforementioned subregistry.

    Bit    Description                              Reference

   TBA5    PCC is requested to                      This document
           allocate resource(C)


7.6.  New FEC Type Registry

   A new PCEP object called FEC is defined in
   [I-D.zhao-pce-pcep-extension-pce-controller-sr].  IANA is requested
   to allocate a new Object-Type for FEC object in the "PCEP Objects"
   subregistry.







Li, et al.               Expires April 25, 2019                [Page 19]


Internet-Draft          PCEP for SR Path Segment            October 2018


   Value    Description                   Reference

    TBA6    SR path                       This document


7.7.  PCEP Error Type and Value

   IANA is requested to allocate code-points in the "PCEP-ERROR Object
   Error Types and Values" subregistry for the following new error-types
   and error-values:

   Error-Type   Meaning                     Reference

   TBA7         Path SID failure:           This document
                Error-value = 1
                Invalid SID

                Error-value = 2
                Unable to allocate
                Path SID

8.  Security Considerations

   TBA

9.  Acknowledgments

10.  Contributors

   The following people have substantially contributed to this document:

   Zafar Ali
   Cisco Systems, Inc.
   Email: zali@cisco.com


11.  References

11.1.  Normative References

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







Li, et al.               Expires April 25, 2019                [Page 20]


Internet-Draft          PCEP for SR Path Segment            October 2018


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

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE", RFC 8232,
              DOI 10.17487/RFC8232, September 2017,
              <https://www.rfc-editor.org/info/rfc8232>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [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.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.








Li, et al.               Expires April 25, 2019                [Page 21]


Internet-Draft          PCEP for SR Path Segment            October 2018


   [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.

   [I-D.zhao-pce-pcep-extension-for-pce-controller]
              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 LSPs", draft-
              zhao-pce-pcep-extension-for-pce-controller-08 (work in
              progress), June 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.

11.2.  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>.

   [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.li-pce-controlled-id-space]
              Li, C., Chen, M., Dong, J., Li, Z., and D. Dhody, "PCE
              Controlled ID Space", draft-li-pce-controlled-id-space-00
              (work in progress), June 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.




Li, et al.               Expires April 25, 2019                [Page 22]


Internet-Draft          PCEP for SR Path Segment            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


   Weiqiang Cheng
   China Mobile
   China

   Email: chengweiqiang@chinamobile.com


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

   Email: jie.dong@huawei.com








Li, et al.               Expires April 25, 2019                [Page 23]


Internet-Draft          PCEP for SR Path Segment            October 2018


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

   Email: lizhenbin@huawei.com


   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com





































Li, et al.               Expires April 25, 2019                [Page 24]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/