



pce                                                             Q. Xiong
Internet-Draft                                                     H. Fu
Intended status: Standards Track                         ZTE Corporation
Expires: 7 June 2026                                     4 December 2025


  PCEP Extensions for Computing-Aware Traffic Steering (CATS) Service
                      draft-xf-pce-cats-service-00

Abstract

   The CATS (Computing-Aware Traffic Steering) can steer traffic between
   clients of a service and sites offering the service.  The C-PS may be
   deployed as a PCE and the ingress CATS-Router could be viewed as a
   PCC.  This document proposes the PCEP extensions for selecting and
   distributing the paths for CATS services.

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   This Internet-Draft will expire on 7 June 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
     2.1.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  C-PS as a PCE for CATS Service  . . . . . . . . . . . . . . .   3
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  LSP Object  . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  CS-ID TLV . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.2.  CSCI-ID Sub-TLV . . . . . . . . . . . . . . . . . . .   5
     4.2.  ERO Object  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [RFC5440] describes the Path Computation Element Protocol (PCEP)
   which is used between a Path Computation Element (PCE) and a Path
   Computation Client (PCC) (or other PCE) to enable computation of
   Multi-protocol Label Switching (MPLS) for Traffic Engineering Label
   Switched Path (TE LSP).  PCEP Extensions for the Stateful PCE Model
   [RFC8231] describes a set of extensions to PCEP to enable active
   control of MPLS-TE and Generalized MPLS (GMPLS) tunnels.

   The CATS (Computing-Aware Traffic Steering) as per
   [I-D.ietf-cats-framework] can steer traffic between clients of a
   service and sites offering the service.  The CATS service may be
   steered from an Ingress CATS-Router to an Egress CATS-Router while
   using an anycast IP address as the Computing-aware Service ID (CS-ID)
   associated with a service.  And the CATS Service Contact Instance ID
   (CSCI-ID) is representing a specific service contact instance which
   serves the service request.  The C-PS may be deployed as a PCE and
   the ingress CATS-Router could be viewed as a PCC.  This document
   proposes the PCEP extensions for selecting and distributing the paths
   for CATS services.

2.  Conventions Used in This Document

2.1.  Abbreviations






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2.2.  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.  C-PS as a PCE for CATS Service

   As per [I-D.ietf-cats-framework], a standalone C-PS can be a
   functional component of a centralized controller or PCE.  And C-PS
   will collect the metric information from C-SMA and C-NMA and also
   determine the best paths to forward traffic.  The metric information
   from C-NMA may include the topology information.  The C-PS may
   compute the path associated with the computing metric information.

   The Figure 1 shows an example of C-PS which is deployed as a PCE to
   select the best path for CATS service.  The compute information (e.g
   anycast IP addresses) will be distributed from the Service Sites to
   the C-PS through BGP extensions.  The PCE may select the egress
   router based on this information and compute the best path from
   ingress router to the egress node.  For example, the path is selected
   from CATS-Forwarder 1 as ingress node to CATS-Forwarder 2 as egress
   node for the CATS service refereed as CS-ID 1 which is also allocated
   by PCE.  Two service sites with service contact instances represented
   with CSCI-ID 1 and CSCI-ID 2 are connected to the CATS-Forwarder 2
   from the output interfaces.























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                             +------+
                     :<------| C-PS |
                     :       | (PCE)|<------+             Service Site 1
                     :       +------+       |               +---------+
                     :          ^           |           +---|CS-ID 1  |
                     :          |           |           |   |CSCI-ID 1|
                     :          |  +----------------+   |   +---------+
                     :          |  |    C-SMA       |---| Service Site 2
                     :          |  +----------------+   |   +---------+
                     :          |  |CATS-Forwarder 2|   +---|CS-ID 1  |
                     :          |  +----------------+       |CSCI-ID 2|
          +--------+ :          |            |              +---------+
          | Client | :  Network |  +----------------------+
          +--------+ :  metrics |  | +-------+            |
               |     :          +----| C-NMA |            |
               |     :             | +-------+            |
          +----------------+       |    |                 |
          |CATS-Forwarder 1|<-----------+                 |
          |(PCC)           |-------|                      |
          +----------------+       |       Underlay       |
                                   |     Infrastructure   |
                                   |                      |
                                   +----------------------+

                Figure 1: Example of PCE to Select Service Path for CATS

4.  PCEP Extensions

4.1.  LSP Object

   The LSP Object is defined in Section 7.3 of [RFC8231].  This document
   defines a new flag (C-flag) to present the CATS service path for the
   LSP-EXTENDED-FLAG TLV carried in LSP Object as defined in [RFC9357].

   C (Request for CATS Service Path) : If the bit is set to 1, it
   indicates that the PCC requests PCE to compute the CATS service path.
   A PCE would also set this bit to 1 to indicate that the CATS service
   path is included by PCE and encoded in the PCRep, PCUpd or PCInitiate
   message.

4.1.1.  CS-ID TLV

   The CS-ID TLV is an optional TLV for use in the LSP Object for the
   allocation of CATS service identification.  The format is as shown
   below.






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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Type              |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           CS-ID                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           sub-TLVs                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        Figure 2: CS-ID TLV

   where:

   *  Type: TBD.

   *  Length: variable.

   *  CS-ID: indicates the identifier associated with the CATS service.
      It is 4 octets which carry a 32-bit unsigned non-zero number in
      IPv4 networks and 16 octets which carry a 128-bit unsigned non-
      zero number in IPv6 networks.

4.1.2.  CSCI-ID Sub-TLV

   The format of CSCI-ID Sub-TLV is shown in Figure 3 as follows:

       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      |     Flags     |   RESERVED    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           CSCI-ID                             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 3: CSCI-ID Sub-TLV

   where:

   *  Type: TBD.

   *  Length: variable.

   *  Flags: 1 octet of flags.  None are defined at this stage.  Flags
      SHOULD be set to zero on transmission and MUST be ignored on
      receipt.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be set to zero on
      transmission and MUST be ignored on receipt.



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   *  CSCI-ID: indicates the identifier for a specific service contact
      instance.  It is 4 octets which carry a 32-bit unsigned non-zero
      number in IPv4 networks and 16 octets which carry a 128-bit
      unsigned non-zero number in IPv6 networks.

4.2.  ERO Object

   The ERO (Explicit Route Object) specified in [RFC3209] and [RFC5440]
   can be used to carry a set of computed paths.  The SR-TE and SRv6-TE
   paths can be specified by means of SR-ERO subobject as per [RFC8664]
   and SRv6-ERO subobject as per [RFC9603].  This document defines a new
   flag (C-flag) to present the CATS service path for the PCC to
   identify the egress router associated with the service instances.

   C (Indicate the egress router for CATS service) : If the bit is set
   to 1, it indicates that this node is the egress router associated
   with the service instances.
   For example, in SR networks, it indicates the service SID for the
   egress router in CATS when the C is set to 1 which is carried in SR-
   ERO subobject.

5.  Operations

   To be discussed in future versions of this document.

6.  Security Considerations

   To be discussed in future versions of this document.

7.  IANA Considerations

   TBD.

8.  References

8.1.  Normative References

   [I-D.ietf-cats-framework]
              Li, C., Du, Z., Boucadair, M., Contreras, L. M., and J.
              Drake, "A Framework for Computing-Aware Traffic Steering
              (CATS)", Work in Progress, Internet-Draft, draft-ietf-
              cats-framework-19, 20 November 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-cats-
              framework-19>.







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   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/rfc/rfc3209>.

   [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/rfc/rfc5440>.

   [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/rfc/rfc8231>.

   [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/rfc/rfc8402>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/rfc/rfc8664>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/rfc/rfc9256>.

   [RFC9357]  Xiong, Q., "Label Switched Path (LSP) Object Flag
              Extension for Stateful PCE", RFC 9357,
              DOI 10.17487/RFC9357, February 2023,
              <https://www.rfc-editor.org/rfc/rfc9357>.

   [RFC9603]  Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
              and Y. Zhu, "Path Computation Element Communication
              Protocol (PCEP) Extensions for IPv6 Segment Routing",
              RFC 9603, DOI 10.17487/RFC9603, July 2024,
              <https://www.rfc-editor.org/rfc/rfc9603>.

   [RFC9830]  Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
              P., and D. Jain, "Advertising Segment Routing Policies in
              BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
              <https://www.rfc-editor.org/rfc/rfc9830>.




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8.2.  Informative 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/rfc/rfc2119>.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/rfc/rfc768>.

   [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/rfc/rfc8174>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   Email: xiong.quan@zte.com.cn


   Huakai Fu
   ZTE Corporation
   Email: fu.huakai@zte.com.cn


























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