PCEP Extensions for Computing-Aware Traffic Steering (CATS) Service
draft-xf-pce-cats-service-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Quan Xiong , Huakai.Fu | ||
| Last updated | 2026-06-15 | ||
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| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
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draft-xf-pce-cats-service-01
pce Q. Xiong
Internet-Draft H. Fu
Intended status: Standards Track ZTE Corporation
Expires: 17 December 2026 15 June 2026
PCEP Extensions for Computing-Aware Traffic Steering (CATS) Service
draft-xf-pce-cats-service-01
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 17 December 2026.
Copyright Notice
Copyright (c) 2026 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/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
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
5.1. CATS Service Path Computation . . . . . . . . . . . . . . 6
5.2. Stateful PCE Operations . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 7
7.2. LSP-EXTENDED-FLAG TLV Flag Field . . . . . . . . . . . . 7
7.3. ERO Subobject Flags . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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.
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2. Conventions Used in This Document
2.1. Abbreviations
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
5.1. CATS Service Path Computation
When a PCC (e.g., an ingress CATS-Router) requires path computation
for a CATS service, it sends a PCReq message to the PCE (C-PS). The
LSP Object MUST include the C-flag set to 1 in the LSP-EXTENDED-FLAG
TLV, indicating a request for CATS service path computation. The CS-
ID TLV MAY be included to specify a particular CATS service
identifier.
Upon receiving a CATS service path computation request, the PCE
evaluates both network metrics (e.g., bandwidth, latency) and
computing metrics (e.g., server load, computational capacity)
collected from C-NMA and C-SMA. The PCE selects the optimal egress
CATS-Router that connects to the appropriate service contact instance
(CSCI-ID). The PCE computes the path from the ingress CATS-Router to
the selected egress CATS-Router.
In the PCRep message, the LSP Object MUST have the C-flag set to 1 in
the LSP-EXTENDED-FLAG TLV. The CS-ID TLV MUST be included,
containing the assigned or confirmed CATS service identifier. The
CSCI-ID Sub-TLV MUST be included within the CS-ID TLV, identifying
the selected service contact instance. The ERO Object MUST include
the computed path, with the C-flag set to 1 in the sub-object
representing the egress CATS-Router.
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5.2. Stateful PCE Operations
During LSP initialization (PCInitiate), the PCE MAY include CATS
service parameters in the LSP Object to establish CATS service paths
proactively. For LSP update (PCUpd), the PCE MAY modify existing
CATS service paths based on changes in computing resource status or
network conditions. The PCC SHOULD report LSP state (PCRpt)
including CATS service parameters to enable the PCE to maintain
synchronized state information.
6. Security Considerations
The existing PCEP security considerations as described in [RFC5440],
[RFC8231], and other relevant stateful PCEP specifications are also
applicable to the PCEP extensions defined in this document.
7. IANA Considerations
This document requests IANA to make the following allocations in the
PCEP parameters registries.
7.1. PCEP TLV Type Indicators
IANA is requested to allocate the following TLV Type values from the
"PCEP TLV Type Indicators" registry:
+===========+=======================+===============+
| TLV Type | TLV Name | Reference |
+===========+=======================+===============+
| TBD1 | CS-ID TLV | This document |
+-----------+-----------------------+---------------+
| TBD2 | CSCI-ID Sub-TLV | This document |
+-----------+-----------------------+---------------+
7.2. LSP-EXTENDED-FLAG TLV Flag Field
IANA is requested to allocate a new bit from the "LSP-EXTENDED-FLAG
Object LSP-EXTENDED-FLAG Field" sub-registry of the "Path Computation
Element Protocol (PCEP) Numbers" registry:
+===========+===============================+===============+
| Bit | Description | Reference |
+===========+===============================+===============+
| TBD3 | Request for CATS Service Path | This document |
| | (C-flag) | |
+-----------+-------------------------------+---------------+
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7.3. ERO Subobject Flags
IANA is requested to allocate a new flag from the "ERO Subobject
Flags" registry:
+===========+=====================================+==============+
| Bit | Description | Reference |
+===========+=====================================+==============+
| TBD4 | Indicate egress router for CATS | This document|
| | service (C-flag) | |
+-----------+-------------------------------------+--------------+
8. 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-24, 2 April 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-cats-
framework-24>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
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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