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PCE WG                                                        Quan Xiong
Internet-Draft                                                Fangwei Hu
Intended status: Standards Track                         Shuangping Zhan
Expires: September 6, 2018                               ZTE Corporation
                                                           March 5, 2018


                       PCEP extensions for SR-TP
              draft-xiong-pce-pcep-extension-sr-tp-00.txt

Abstract

   This document proposes a set of extensions to PCEP for Segment
   Routing in MPLS Transport Profile (SR-TP) networks and defines a
   mechanism to create the bi-directional SR tunnel in SR-TP networks
   with PCE.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 6, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The SR-TP Architecture with PCE . . . . . . . . . . . . . . .   3
   3.  PCEP extensions for SR-TP . . . . . . . . . . . . . . . . . .   4
     3.1.  Bi-directional LSP extension  . . . . . . . . . . . . . .   4
       3.1.1.  The B flag in SRP Object  . . . . . . . . . . . . . .   4
     3.2.  SR-TP ERO extension . . . . . . . . . . . . . . . . . . .   4
     3.3.  Processing Rules  . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Informative References  . . . . . . . . . . . . . . . . .   6
     7.2.  Normative References  . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Path Computation Element Communication Protocol (PCEP) defined in
   [RFC5440] provides mechanisms for Path Computation Elements (PCEs) to
   perform path computations in response to Path Computation Clients
   (PCCs) requests.

   [I-D.ietf-pce-segment-routing] proposes extensions to PCEP that allow
   a stateful PCE to compute Traffic Engineering (TE) paths in segment
   routing (SR) networks.  But it is applicable to Multi-protocol Label
   Switching (MPLS) networks.  [I-D.hu-spring-sr-tp-use-case] describes
   the use case of SR tunnel to be deployed in MPLS Transport Profile
   (SR-TP) network.  It is required to extend the PCEP protocol to meet
   the new requirement for SR-TP.

   This document proposes a set of extensions to PCEP for Segment
   Routing in MPLS Transport Profile (SR-TP) networks and defines a
   mechanism to create the bi-directional SR tunnel in SR-TP networks
   with PCE.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].







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1.2.  Terminology

   The terminology is defined as [RFC5440],
   [I-D.ietf-pce-segment-routing] and [I-D.hu-spring-sr-tp-use-case].

2.  The SR-TP Architecture with PCE

   As described in [I-D.hu-spring-sr-tp-use-case], in SR-TP networks,
   the centralized controller may calculate the end to end SR paths, and
   creates the ordered segment list.  The centralized controller may be
   replaced to PCE as the Figure 1 shown.  The PCE can calculate the SR
   paths and initiate a SR path on a PCC.

                                          |
                                          |
                                          V
                                      +---+--+
                       +--------------+ PCE  +---------------+
                       |              +---+--+               |
               +-------|-------------------------------------|--------+
               |       |          SR-TP network              |        |
               |       |                                     |        |
               |   +---+--+           +---+--+           +---+--+     |
               |   |  A   +-----------+   B  +-----------+   C  +     |
               |   +------+           +------+           +------+     |
               |                                                      |
               +------------------------------------------------------+

              +------------+                              +------------+
              |  Label A   |                              |  Label C   |
              +------------+                              +------------+
              |     ...    |                              |     ...    |
              +------------+                              +------------+
              |  Label C   |                              |  Label A   |
              +------------+                              +------------+
              | Path Label |                              | Path Label |
              +------------+                              +------------+

                           Figure 1 The SR-TP Architecture with PCE


   It is required to support bi-direction tunnel to meet the requirement
   of SP-TP networks.  A label named Path segment at both ends of the
   paths was defined to identify the direction of the SR paths as
   described in [I-D.cheng-spring-mpls-path-segment].  It mainly aims to
   bind two unidirectional SR paths to a single bi-directional tunnel.





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3.  PCEP extensions for SR-TP

3.1.  Bi-directional LSP extension

3.1.1.  The B flag in SRP Object

   The format of the SRP object is defined in [RFC8231] and included
   here for easy reference with the addition of the new B flag.


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Flags                              |B|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        SRP-ID-number                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       //                      Optional TLVs                          //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 2 The SRP Object Format

   A new flag is defined to indicate a bi-directional LSP operation
   initiated by the PCE:

   B(Bi-directional -- 1 bit):when set, the PCE specifies that the
   request relates to a bi-directional TE LSP that has the same traffic
   engineering requirements including fate sharing, protection and
   restoration, LSRs, TE links, and resource requirements (e.g., latency
   and jitter) in each direction.  When cleared, the TE LSP is
   unidirectional.

3.2.  SR-TP ERO extension

   As described in [I-D.hu-spring-sr-tp-use-case], it is required to
   support bi-directional tunnel to meet the requirement of SP-TP
   networks.  But it is the uni-directional tunnel for SR and
   engineering traffic network as discussed in
   [I-D.ietf-pce-segment-routing].  The SR path is carried in the
   Segment Routing Explicit Route Object (SR-ERO), which consists of a
   sequence of SR subobjects.  This document proposes the extension of
   the SR-ERO Subobject to carry the bi-directional tunnel information
   as the Figure 3 shown.






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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |L|    Type     |     Length    |  ST   |     Flags   |R|F|S|C|M|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              SID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //            Path Label information (variable)                //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3 Extension of SR-ERO Subobject format

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Path Label               | TC  |S|       TTL     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 4  Path Label information



   ST (SID Type -- 4 bit):TBD, indicates the type of information
   associated with the Path Label contained in the object body. when the
   ST indicates the Path Label type, the NAI is filled with the Path
   Label information as the Figure 4 shown.

   R (Reverse Flag -- 1 bit): indicates the SR path direction, when it
   is clear, it indicates the forward direction and when it is set, it
   indicates the reverse direction.

   The definition of other fields is the same with
   [I-D.ietf-pce-segment-routing].

3.3.  Processing Rules

   As discussed in [I-D.cheng-spring-mpls-path-segment], the bi-
   directional SR tunnel is created from two binding unidirectional SR
   paths.  As defined in [RFC8281], the stateful PCE calculates the SR
   paths and initiates the bi-directional LSP with Initiate Request
   message (PCInitiate).

   The B bit in SRP Object MUST be set and the two unidirectional SR
   paths may be computed from the forward and reverse direction and sent
   to the source and destination PCC respectively in SR-ERO object.  The
   path labels which binding the paths may be generated in PCE and sent
   to the related PCC carried in the bottom of the SR-ERO.  When the
   PCCs at both ends receiving the PCInitiate message with the labels in




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   SR-ERO subobjects, they may forward the packets from bi-directional
   tunnel in SR-TP networks.

4.  Security Considerations

   TBD.

5.  IANA Considerations

   TBD.

6.  Acknowledgements

   TBD.

7.  References

7.1.  Informative References

   [I-D.hu-spring-sr-tp-use-case]
              hu, f., Xiong, Q., Mirsky, G., and W. Cheng, "Segment
              Routing Transport Profile Use Case", draft-hu-spring-sr-
              tp-use-case-01 (work in progress), March 2018.

7.2.  Normative References

   [I-D.cheng-spring-mpls-path-segment]
              Cheng, W., Wang, L., Li, H., Chen, M., Zigler, R., and S.
              Zhan, "Path Segment in MPLS Based Sement Routing Network",
              draft-cheng-spring-mpls-path-segment-01 (work in
              progress), March 2018.

   [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-11 (work in progress),
              November 2017.

   [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>.




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   [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>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Wuhan, Hubei  430223
   China

   Phone: +86 27 83531060
   Email: xiong.quan@zte.com.cn


   Fangwei Hu
   ZTE Corporation
   No.889 Bibo Rd
   Shanghai  201203
   China

   Phone: +86 21 68896273
   Email: hu.fangwei@zte.com.cn


   Shuangping Zhan
   ZTE Corporation
   Liuxian Rd
   Shenzhen  518057
   China

   Phone: +86 755 26773770
   Email: zhan.shuangping@zte.com.cn









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