PCEP Extension for Flexible Grid Networks
draft-ietf-pce-flexible-grid-21
| Document | Type | Active Internet-Draft (pce WG) | |
|---|---|---|---|
| Authors | Haomian Zheng , Young Lee , Ramon Casellas , Daniele Ceccarelli | ||
| Last updated | 2026-11-05 (Latest revision 2026-10-31) | ||
| Replaces | draft-lee-pce-flexible-grid | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Julien Meuric | ||
| Shepherd write-up | Show Last changed 2026-04-24 | ||
| IESG | IESG state | IESG Evaluation::Revised I-D Needed | |
| Action Holders | |||
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Has enough positions to pass. |
||
| Responsible AD | Ketan Talaulikar | ||
| Send notices to | julien.meuric@orange.com | ||
| IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-pce-flexible-grid-21
PCE Working Group H. Zheng, Ed.
Internet-Draft Huawei Technologies Co., Ltd.
Intended status: Standards Track Y. Lee
Expires: 4 May 2027 CRU
R. Casellas
CTTC
D. Ceccarelli
Cisco
31 October 2026
PCEP Extension for Flexible Grid Networks
draft-ietf-pce-flexible-grid-21
Abstract
This document provides the Path Computation Element Communication
Protocol (PCEP) extensions for the support of Routing and Spectrum
Assignment (RSA) in Flexible Grid networks.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 May 2027.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Spectrum Assignment (SA) Object . . . . . . . . . . . . . . . 5
4.1. Spectrum Assignment Object . . . . . . . . . . . . . . . 6
4.2. Frequency Slot Selection TLV . . . . . . . . . . . . . . 7
4.3. Frequency Slot Restriction TLV . . . . . . . . . . . . . 8
5. Encoding of an RSA . . . . . . . . . . . . . . . . . . . . . 10
5.1. Spectrum Allocation TLV . . . . . . . . . . . . . . . . . 11
5.2. Error Indicator . . . . . . . . . . . . . . . . . . . . . 13
5.3. NO-PATH Indicator . . . . . . . . . . . . . . . . . . . . 14
6. Operational Considerations . . . . . . . . . . . . . . . . . 14
6.1. Control of Function and Policy . . . . . . . . . . . . . 14
6.2. Information and Data Models . . . . . . . . . . . . . . . 15
6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 15
6.4. Verifying Correct Operation . . . . . . . . . . . . . . . 15
6.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . 15
6.6. Impact on Network Operation . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8.1. New PCEP Object . . . . . . . . . . . . . . . . . . . . . 16
8.2. SA Object Flag Field . . . . . . . . . . . . . . . . . . 16
8.3. New PCEP TLVs . . . . . . . . . . . . . . . . . . . . . . 17
8.4. Frequency Slot Selection TLV Flag Field . . . . . . . . . 17
8.5. Frequency Slot Assignment Method Values . . . . . . . . . 17
8.6. Frequency Slot Restriction TLV Action Values . . . . . . 18
8.7. Spectrum Allocation TLV Flag Field . . . . . . . . . . . 18
8.8. New No-Path Reasons . . . . . . . . . . . . . . . . . . . 19
8.9. New Error-Types and Error-Values . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
10. Contributors' Address . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
[RFC4655] defines a Path Computation Element (PCE)-based path
computation architecture and explains how a Path Computation Element
(PCE) can compute Label Switched Paths (LSPs) in Multiprotocol Label
Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
networks at the request of Path Computation Clients (PCCs). A PCC is
said to be any network component that makes such a request and can
be, for instance, an Optical Switching Element within a Wavelength
Division Multiplexing (WDM) network. The PCE, itself, can be located
anywhere within the network, and can be within an optical switching
element, a Network Management System (NMS), a Network Controller or
Operational Support System (OSS), or can be an independent network
server.
The Path Computation Element Communication Protocol (PCEP) [RFC5440]
is the communication protocol used between a PCC and a PCE, and can
also be used between cooperating PCEs. [RFC4657] sets out the common
protocol requirements for PCEP. Additional application-specific
requirements for PCEP are deferred to separate documents.
[RFC8780] provides the PCEP extensions for the support of Routing and
Wavelength Assignment (RWA) in Wavelength Switched Optical Networks
(WSON) based on the requirements specified in [RFC6163] and
[RFC7449].
To allow efficient allocation of optical spectral bandwidth for
systems that have high bit-rates, the International Telecommunication
Union Telecommunication Standardization Sector (ITU-T) has extended
its Recommendations [ITU-T_G.694.1] to include an enhanced Dense
Wavelength Division Multiplexing (DWDM) grid by defining a set of
nominal central frequencies, channel spacings, and the concept of the
"frequency slot". In such an environment, a data-plane connection is
switched based on allocated, variable-sized frequency ranges within
the optical spectrum, creating what is known as a flexible grid
(flexi-grid). [RFC7698] provides Framework and Requirements for
GMPLS-Based Control of Flexi-Grid Dense Wavelength Division
Multiplexing (DWDM) Networks. [RFC7792] and [RFC8363] define the
extensions to the Resource Reservation Protocol - Traffic Engineering
(RSVP-TE) signaling protocol and Open Shortest Path First - Traffic
Engineering (OSPF-TE) to support Label Switched Paths (LSPs) in a
GMPLS-controlled network that includes devices using the flexible
optical grid.
The term "Routing and Spectrum Assignment" (RSA) is introduced in
[RFC7698] to refer to the process that determines a route and
frequency slot for an LSP. Hence, when a path is computed, the
spectrum assignment process determines the central frequency and slot
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width. The term "Spectrum Switched Optical Networks" is also
introduced in [RFC7698] to refer to a flexi-grid enabled DWDM
network, which can be controlled by a GMPLS or PCE control plane.
This document provides PCEP extensions to support RSA in Flexi-grid
networks. The extensions in this document apply to point-to-point
LSPs; support for point-to-multipoint (P2MP) LSPs is out of scope for
this document.
Figure 1 shows one typical PCE-based implementation, which is
referred to as the Combined Routing and Spectrum Assignment (RSA)
[RFC7698]. With this architecture, the two processes of routing and
spectrum assignment are accessed via a single PCE. This architecture
is the base architecture from which the PCEP extensions are specified
in this document.
+----------------------------+
+-----+ | +-------+ +--+ |
| | | |Routing| |SA| |
| PCC |<----->| +-------+ +--+ |
| | | |
+-----+ | PCE |
+----------------------------+
Figure 1: Combined Routing and Spectrum Assignment Architecture
This document aligns with GMPLS extensions for PCEP [RFC8779] for
generic properties such as label, label-set and label assignment,
noting that flexi-grid frequency slot is a type of label per
[RFC7699]. Frequency slots are encoded as Flexi-Grid Labels
[RFC7699], and frequency slot restrictions reuse the field encodings
of [RFC8363].
2. Terminology
This document uses the terminology defined in [RFC4655], [RFC5440],
and [RFC7698].
3. 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.
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4. Spectrum Assignment (SA) Object
The SA Object enables a PCC to request spectrum assignment from the
PCE and to express preferences such as assignment mode and frequency-
slot restrictions. It thus allows a PCE to perform the combined RSA
according to the PCC's policies.
Spectrum allocation can be performed by the PCE by different means:
a. By means of Explicit Label Control (ELC) [RFC3471], where the PCE
allocates the frequency slot to use on each link along the path.
The PCC requests this by setting the M bit of the SA Object to 1
(Section 4.1).
b. By means of a set of candidate frequency slots, where the PCE
provides for each link the frequency slots from which the slot is
selected during signaling. The PCC requests this by setting the
M bit of the SA Object to 0 (Section 4.1).
Option b. allows distributed spectrum allocation (performed during
signaling) to complete spectrum assignment. When the PCE performs
the assignment (option a.), a PCReq can convey the method the PCE is
to use to select among the feasible frequency slots in the Frequency
Slot Selection TLV (Section 4.2); in option b., the selection is made
by the nodes during signaling.
The format Routing Backus-Naur Form (RBNF) [RFC5511] of a PCReq
message per [RFC5440] after incorporating the Spectrum Assignment
(SA) Object is as follows:
<PCReq Message> ::= <Common Header>
[<svec-list>]
<request-list>
Where:
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<SA>]
[other optional objects...]
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If the SA Object is present in the PCReq message, it MUST be encoded
after the END-POINTS Object. The slot width requested for the LSP is
conveyed in the GENERALIZED-BANDWIDTH object (Section 2.3 of
[RFC8779]), using Bandwidth Spec Type 8 (SSON), which carries the
slot width parameter m defined in Section 4.1 of [RFC7792]. The
Frequency Slot Restriction TLV (Section 4.3) constrains which
frequency slots and slot widths can be used; it does not convey the
requested slot width.
4.1. Spectrum Assignment Object
This document specifies the use of the SA Object in the PCReq
message. The use of the SA Object in other PCEP messages, such as
the LSP Initiate Request (PCInitiate) message defined in [RFC8281],
is out of scope for this document.
The SA Object-Class is TBD1 (to be assigned by IANA). The SA Object-
Type is 1.
The format of the Spectrum Assignment (SA) Object body is as shown in
Figure 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SA Object
Reserved (16 bits): the Reserved field MUST be set to zero by the
sender and ignored by the receiver.
Flags (16 bits): bits 0-14 are currently unassigned. They MUST be
set to zero by the sender and ignored by the receiver.
One flag bit is allocated as follows:
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M (Mode - bit 15): M bit is used to indicate the mode of spectrum
assignment. When the M bit is set to 1, this indicates that the
spectrum assigned by the PCE MUST be explicit. That is, the selected
way to convey the allocated spectrum is by means of Explicit Label
Control (ELC) [RFC3471]. Otherwise, when the M bit is set to 0, the
spectrum assigned by the PCE does not need to be explicit, but it can
be suggested in the Allocated Spectrum field of the Spectrum
Allocation TLV, defined in Section 5 of this document.
IANA maintains the "SA Object Flag Field" registry requested in
Section 8.2.
4.2. Frequency Slot Selection TLV
The Frequency Slot Selection TLV in the SA Object is used to indicate
the frequency slot selection constraint in regard to the order of
frequency slot assignment to be returned by the PCE. This TLV is
only applied when the M bit is set to 1 in the SA Object specified in
Section 4.1. The Frequency Slot Selection TLV SHOULD NOT be present
and MUST be ignored when the M bit is set to 0.
The Frequency Slot Selection TLV type is TBD2 (to be assigned by
IANA). The TLVs carried in the SA Object use the PCEP TLV format
defined in Section 7.1 of [RFC5440]; the Length of the Frequency Slot
Selection TLV is 4.
The Frequency Slot Selection TLV value field format is defined as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Flag | FSA Method | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags (8 bits): bits 1-7 are currently unassigned. They MUST be set
to zero by the sender and ignored by the receiver.
S (Symmetry - 1 bit): This flag is only meaningful when the request
is for a bidirectional LSP, i.e., when the B (Bi-directional) flag is
set in the RP Object (see Section 7.4.1 of [RFC5440]) or B
(Bidirectional LSP) flag is set in the LSP-EXTENDED-FLAG TLV in LSP
Object (see Section 6.2.3 of [RFC9504]); otherwise it is ignored.
The value 0 for S flag denotes requiring the same frequency slot in
both directions; 1 denotes that different spectrum in the two
directions is allowed.
Frequency Slot Assignment (FSA) Method (8 bits):
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* 0: unspecified (any); This does not constrain the SA method used
by a PCE. This value is implied when the Frequency Slot Selection
TLV is absent.
* 1: First-Fit. All the feasible frequency slots are numbered
(based on 'n' parameter), and this SA method chooses the available
frequency slot with the lowest index, where 'n' is the parameter
in f = 193.1 THz + n x 0.00625 THz where 193.1THz is the ITU-T
'anchor frequency' and 'n' is a positive or negative integer
including 0 [RFC7698].
* 2: Random. This SA method chooses a feasible frequency slot value
of 'n' randomly.
* 3-255: Unassigned.
IANA maintains the "Frequency Slot Assignment Method Values" registry
requested in Section 8.5.
Reserved (16 bits): the Reserved field MUST be set to zero by the
sender and ignored by the receiver.
At most one instance of the Frequency Slot Selection TLV MAY be
present in the SA Object. If more than one Frequency Slot Selection
TLV is present, only the first instance is processed and subsequent
instances MUST be ignored.
4.3. Frequency Slot Restriction TLV
For any request that contains a frequency slot assignment, the
requester (PCC) needs to be able to specify a restriction on the
frequency slots to be used. This restriction is to be interpreted by
the PCE as a constraint on the tuning ability of the origination
laser transmitter or on any other maintenance related constraints.
The Frequency Slot Restriction TLV type is TBD5 (to be assigned by
IANA). This TLV MAY appear more than once in the SA Object to be
able to specify multiple restrictions. When more than one Frequency
Slot Restriction TLV applies to a link, the PCE MUST select a
frequency slot that satisfies all of them. If no frequency slot
does, the PCE responds with a NO-PATH object as described in
Section 5.3. The TLV data is defined as shown in Figure 3.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Action | Count | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifiers |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frequency Slot Restriction |
// . . . . //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Frequency Slot Restriction TLV value field Encoding
The fields in the value field of Frequency Slot Restriction TLV are
as follows:
* Action (8 bits) The following values are defined:
- 0 - Inclusive List indicates that one or more link identifiers
are included in the Link Identifiers field. Each identifies a
separate link that is part of the list.
- 1 - Inclusive Range indicates that the Link Identifiers field
defines a range of links. It contains two link identifiers.
The first identifier indicates the start of the range
(inclusive). The second identifier indicates the end of the
range (inclusive). All links with numeric values between the
bounds are considered to be part of the range. A value of zero
in either position indicates that there is no bound on the
corresponding portion of the range. The Action field MUST be
set to 0 (Inclusive List) when unnumbered link identifiers are
used, since a range of unnumbered link identifiers is not
meaningful.
* Count(8 bits): The number of the link identifiers .
* Reserved: Reserved for future use (16 bits). It MUST be set to
zero by the sender and ignored by the receiver.
* Link Identifiers: Contains one or more Link Identifier Records.
The interpretation of each record depends on the Action field.
When Action=0 (Inclusive List), each record consists of a single
link identifier. When Action=1 (Inclusive Range), there are
exactly two records, indicating the start and end of the range
(inclusive). All link identifiers in the same list MUST be of the
same type. See Section 4.3.1 in [RFC8780] for Link Identifier
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encoding. If the Action value is unknown, if Action=1 and Count
is not 2, or if the link identifiers in the same list are not of
the same type, the PCE MUST reject the request rather than ignore
the TLV.
* Frequency Slot Restriction: this field is encoded as shown in
Figure 4; its fields are described 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C.S. | Starting n | No. of Effective Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bitmap ... ~
~ ... | padding bits ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | C.F.G | S.W.G | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min Slot Width | Max Slot Width |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Frequency Slot Restriction Encoding
The fields "C.S", "Starting n", "No. of Effective Bits", "Bitmap" and
"padding bits" are as per Section 4.1.1. of [RFC8363]. Whereas the
fields "C.F.G", "S.W.G", "Reserved", and "Min Slot Width" are as per
Section 4.2. of [RFC8363]. The field "Max Slot Width" (16 bits) is a
positive integer, whose value indicates the multiple of 2*C.S. (in
GHz), in terms of the supported max slot width. The field MBZ
(4-bits) MUST be set to zero and ignored on receipt.
A PCC MAY add a frequency slot restriction that applies to all links
by setting the Count field to zero and specifying just a set of
frequency slots.
IANA maintains the "Frequency Slot Restriction TLV Action Values"
registry requested in Section 8.6.
5. Encoding of an RSA
This section provides the encoding of an RSA, in the PCRep message
or, for an LSP delegated to a stateful PCE, in the PCUpd message
[RFC8231], for frequency slot allocation as discussed in Section 4.
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5.1. Spectrum Allocation TLV
The Spectrum Allocation TLV type is TBD6 (to be assigned by IANA).
The value portion of the TLV is defined as shown in Figure 5. The
Spectrum Allocation TLV uses the Attribute TLV format of Section 3 of
[RFC5420]: its Length field gives the total length of the TLV in
octets, including the Type and Length fields. The size of the ERO
Hop Attributes subobject limits a Hop Attributes TLV to 250 bytes
(Section 2.1 of [RFC7570]); this bounds the number of Flexi-Grid
Labels that a Spectrum Allocation TLV can carry.
The Spectrum Allocation TLV is carried as an Attribute TLV [RFC5420]
in the ERO Hop Attribute subobjects [RFC7570] in the Explicit Route
Object (ERO) [RFC5440] to indicate the spectrum to be assigned on the
identified link.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Allocated Spectrum |
// . . . . //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Spectrum Allocation TLV value field Encoding
* Reserved (16 bits): The Reserved field MUST be set to zero by the
sender and ignored by the receiver.
* Flags (16 bits): bits 0-14 are unassigned. They MUST be set to
zero by the sender and ignored by the receiver.
* M (Mode - bit 15): 1 bit
- 1 indicates the allocation is under Explicit Label Control: the
Allocated Spectrum field carries exactly one Flexi-Grid Labels
sub-field, which is the frequency slot (a single or a compound
label) to be used on the link.
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- 0 indicates that the Allocated Spectrum field carries a set of
candidates: the Allocated Spectrum field carries one or more
Flexi-Grid Labels sub-fields, each of which is one candidate
frequency slot (a single or a compound label) for the link,
from which the slot is selected during signaling.
* Link Identifier: Identifies the link ID for which the spectrum
allocation is applied. See Section 4.3.1 in [RFC8780] for Link
Identifier encoding.
* Allocated Spectrum (variable): Indicates the spectrum allocated to
the link associated with the link identifier. The field carries
one or more Flexi-Grid Labels sub-fields, which encodes either a
single label (see Section 4.1 of [RFC7699]), or a Composite label
(see Section 4.3 of [RFC7699]). The encoding of the Flexi-Grid
Labels sub-fields is as shown in Figure 6 below which matches the
fields and description in Section 4.3 of [RFC7699]. Each 64-bit
Flexi-Grid Label follows the encoding defined in Figure 1 of
[RFC7699].
The Spectrum Allocation TLV is valid only in an ERO Hop Attributes
subobject associated with an ERO subobject that identifies a link.
The ERO Hop Attributes subobject containing the Spectrum Allocation
TLV MUST be placed immediately after the link-identifying ERO
subobject or after any Label subobjects associated with that link,
otherwise, it is ignored.
The ordering of the ERO Hop Attributes subobject relative to the
Label subobjects associated with the same link is not significant for
the interpretation of the Spectrum Allocation TLV. In either case,
the Spectrum Allocation TLV specifies the spectrum allocation for the
identified link.
The Spectrum Allocation TLV specifies the spectrum allocation the PCE
computed for the identified link. A node processing the ERO need not
modify, add, or remove the Spectrum Allocation TLV. A PCE MAY
provide a different spectrum allocation by generating a new or
updated ERO using the applicable PCEP procedures.
Processing of unrecognized Spectrum Allocation TLVs follows the
procedures specified in Section 2.3 of [RFC7570], including the
required and optional attribute processing rules of [RFC5420]
according to the R bit of the enclosing ERO Hop Attributes subobject.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (4 + 8r) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Grid | C.S. | Identifier | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Grid | C.S. | Identifier | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Flexi-Grid Labels sub-field Encoding
The Length (16 bits) encodes the length of the Flexi-Grid Labels sub-
field which is 4 plus 8 bytes for each 64-bit Flexi-Grid Label. The
Reserved field (16-bits) MUST be set to zero by the sender and
ignored by the receiver. The other fields are as per [RFC7699].
IANA maintains the "Spectrum Allocation TLV Flag Field" registry
requested in Section 8.7.
The Spectrum Allocation TLV is specific to PCEP. Its type is
assigned from the "PCEP TLV Type Indicators" registry (Section 9.3),
as for the Wavelength Allocation TLV of [RFC8780], and not from the
RSVP-TE "Attributes TLV Space" registry. A PCC that uses the
computed ERO for RSVP-TE signaling MUST NOT include the Spectrum
Allocation TLV in the ERO that it signals; the allocated spectrum is
signaled using the Label subobjects of Explicit Label Control or the
flexi-grid signaling procedures of [RFC7792].
5.2. Error Indicator
To indicate errors associated with the RSA request, a new Error-Type
(TBD7, Flexi-Grid RSA Error) and subsequent error-value are defined
for inclusion in the PCEP-ERROR Object:
* Error-Type=TBD7 (Flexi-Grid RSA Error); Error-value=1: if a PCE
receives an RSA request and the PCE is not capable of RSA
computation, the PCE MUST send a PCErr message with a PCEP-ERROR
Object (Error-Type=TBD7) and an Error-value (Error-value=1). The
PCE stops processing the request. The corresponding RSA
computation MUST be cancelled at the PCC.
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Note that generic resource exhaustion at the PCE (e.g., insufficient
memory) is not signaled via this Error-Type; the PCEP overload
mechanism (see Section 7.14 of [RFC5440]) applies.
5.3. NO-PATH Indicator
To communicate the reasons for not being able to find RSA for the
path request, the NO-PATH Object can be used in the corresponding
response. The format of the NO-PATH Object body is defined in
[RFC5440]. The object MAY contain a NO-PATH-VECTOR TLV to provide
additional information about why a path computation has failed.
One new bit flag is defined to be carried in the Flags field in the
NO-PATH-VECTOR TLV carried in the NO-PATH Object.
* Bit TBD8: When set to 1, the PCE indicates no feasible path was
found that meets all the optical spectrum constraints associated
with the path computation request.
This flag is specific to spectrum-related path computation failures;
other path-computation failure reasons continue to use the existing
PCEP NO-PATH mechanisms.
6. Operational Considerations
Manageability of flexi-grid Routing and Spectrum Assignment (RSA)
with PCE includes the following considerations:
6.1. Control of Function and Policy
In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuring the
following PCEP session parameters on a PCC:
* The ability to send a Flexi-Grid RSA request.
In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuring the
following PCEP session parameters on a PCE:
* The support for Flexi-Grid RSA.
* A set of Flexi-Grid RSA specific policies (authorized sender,
request rate limiter, etc).
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These parameters can be configured as default parameters for any PCEP
session the PCEP speaker participates in, or can apply to a specific
session with a given PCEP peer or a specific group of sessions with a
specific group of PCEP peers.
6.2. Information and Data Models
This document does not define YANG extensions. The PCEP YANG module
[RFC9826] could be augmented to cover the Flexi-Grid RSA information
introduced in this document, such as the S flag, the FSA method and
the assignment mode; such extensions are outside the scope of this
document.
6.3. Liveness Detection and Monitoring
Liveness Detection and Monitoring Mechanisms defined in this document
do not imply any new liveness detection and monitoring requirements
in addition to those already listed in Section 8.3 of [RFC5440].
6.4. Verifying Correct Operation
Mechanisms defined in this document do not imply any new verification
requirements in addition to those already listed in section 8.4 of
[RFC5440].
6.5. Requirements on Other Protocols and Functional Components
The PCE Discovery mechanisms ([RFC5088] and [RFC5089]) can be used to
advertise Flexi-Grid RSA path computation capabilities to PCCs.
6.6. Impact on Network Operation
Mechanisms defined in this document do not imply any new network
operation requirements in addition to those already listed in
Section 8.6 of [RFC5440].
7. Security Considerations
The extensions defined in this document convey the frequency slots
computed for an LSP on each link and the frequency slot restrictions
of a PCC's transceivers. This information reveals spectrum usage and
equipment capabilities that an operator might wish to keep private.
An attacker able to modify PCEP messages could cause a frequency slot
to be signaled that overlaps one already in use, disrupting existing
optical connections on the affected links, or could cause requests to
be rejected or mis-computed.
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These extensions are intended for use between PCEs and PCCs within a
single administrative domain. To protect them against eavesdropping,
modification, insertion and replay, PCEP sessions carrying them
SHOULD be secured usingTransport Layer Security (TLS) [RFC8253]
[RFC9916], as per the recommendations and the best current practices
are in [RFC9325].
8. IANA Considerations
This document requests the following IANA actions.
8.1. New PCEP Object
IANA is requested to allocate a new object class from the "PCEP
Objects" registry (http://www.iana.org/assignments/pcep/
pcep.xhtml#pcep-objects) under the “Path Computation Element Protocol
(PCEP) Numbers” registry group :
+====================+======+========================+===========+
| Object-Class Value | Name | Object-Type | Reference |
+====================+======+========================+===========+
| TBD1 | SA | 0: Reserved | |
| | +------------------------| |
| | | 1: Spectrum Assignment | [This.I-D]|
| | +------------------------| |
| | | 2-15: Unassigned | |
+--------------------+------+------------------------+-----------+
8.2. SA Object Flag Field
IANA is requested to create the "SA Object Flag Field" registry
within the "Path Computation Element Protocol (PCEP) Numbers"
registry. New values are to be assigned by IETF Review [RFC8126].
Bits are numbered from bit 0 as the most significant bit.
+=======+==========================+===========+
| Bit | Description | Reference |
+=======+==========================+===========+
| 0-14 | Unassigned | |
+-------+--------------------------|[This.I-D] |
| 15 | Spectrum Assignment Mode | |
+-------+--------------------------+-----------+
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8.3. New PCEP TLVs
IANA is requested to allocate three new TLV types, the Frequency Slot
Selection TLV, the Frequency Slot Restriction TLV, the Spectrum
Allocation TLV. All these TLVs are from the "PCEP TLV Type
Indicators" registry (http://www.iana.org/assignments/pcep/
pcep.xhtml#pcep-tlv-type-indicators) under the “Path Computation
Element Protocol (PCEP) Numbers” registry group.
+=======+============================+===========+
| Value | Description | Reference |
+=======+============================+===========+
| TBD2 | Frequency Slot Selection | [This.I-D]|
+=======+============================+===========+
| TBD5 | Frequency Slot Restriction | [This.I-D]|
+=======+============================+===========+
| TBD6 | Spectrum Allocation | [This.I-D]|
+-------+----------------------------+-----------+
8.4. Frequency Slot Selection TLV Flag Field
IANA is requested to create the "Frequency Slot Selection TLV Flag
Field" registry within the "Path Computation Element Protocol (PCEP)
Numbers" registry. New values are to be assigned by IETF Review
[RFC8126]. Bits are numbered from bit 0 as the most significant bit.
+=======+==========================+===========+
| Bit | Description | Reference |
+=======+==========================+===========+
| 0 | Symmetry | |
+-------+--------------------------| [This.I-D]|
| 1-7 | Unassigned | |
+-------+--------------------------+-----------+
8.5. Frequency Slot Assignment Method Values
IANA is requested to create the "Frequency Slot Assignment Method
Values" registry within the "Path Computation Element Protocol (PCEP)
Numbers" registry. New values are to be assigned by IETF Review
[RFC8126].
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+=========+=============+===========+
| Value | Description | Reference |
+=========+=============+===========+
| 0 | Unspecified | [This.I-D]|
+---------+-------------+-----------+
| 1 | First-Fit | [This.I-D]|
+---------+-------------+-----------+
| 2 | Random | [This.I-D]|
+---------+-------------+-----------+
| 3-255 | Unassigned | |
+---------+-------------+-----------+
8.6. Frequency Slot Restriction TLV Action Values
IANA is requested to create the "Frequency Slot Restriction TLV
Action Values" registry within the "Path Computation Element Protocol
(PCEP) Numbers" registry. New values are to be assigned by IETF
Review [RFC8126].
+=======+=================+===========+
| Value | Description | Reference |
+=======+=================+===========+
| 0 | Inclusive List | [This.I-D]|
+-------+-----------------+-----------+
| 1 | Inclusive Range | [This.I-D]|
+-------+-----------------+-----------+
| 2-255 | Unassigned | |
+-------+-----------------+-----------+
8.7. Spectrum Allocation TLV Flag Field
IANA is requested to create the "Spectrum Allocation TLV Flag Field"
registry within the "Path Computation Element Protocol (PCEP)
Numbers" registry. New values are to be assigned by IETF Review
[RFC8126]. Bits are numbered from bit 0 as the most significant bit.
+=======+==========================+===========+
| Bit | Description | Reference |
+=======+==========================+===========+
| 0-14 | Unassigned | |
+-------+--------------------------| [This.I-D]|
| 15 | Spectrum Allocation Mode | |
+-------+--------------------------+-----------+
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8.8. New No-Path Reasons
IANA is requested to allocate a new bit flag from the PCEP "NO-PATH-
VECTOR TLV Flag Field" registry
(http://www.iana.org/assignments/pcep/pcep.xhtml#no-path-vector-tlv)
under the “Path Computation Element Protocol (PCEP) Numbers” registry
group.
+=======+=============================+===========+
| Bit | Description | Reference |
+=======+=============================+===========+
| TBD8 | No spectrum constraints met | [This.I-D]|
+-------+-----------------------------+-----------+
8.9. New Error-Types and Error-Values
IANA is requested to allocate a new Error-Type and Error-value from
the "PCEP-ERROR Object Error Types and Values" registry
(http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-error-object)
under the “Path Computation Element Protocol (PCEP) Numbers” registry
group.
+============+================+====================+===========+
| Error-Type | Meaning | Error-value | Reference |
+============+================+====================+===========+
| TBD7 | Flexi-Grid RSA | 0: Unassigned | [This.I-D]|
| | Error | 1: RSA computation | |
| | | not supported | |
| | | 2: Unassgiend range| |
+------------+----------------+--------------------+-----------+
9. Acknowledgements
Thanks to Francesco Lazzeri for the technical contribution, and Quan
Xiong, Dhruv Dhody and Adrian Farrel for useful comments. Thanks to
Ketan Talaulikar for his detailed AD review and helpful suggestions.
10. Contributors' Address
Ricard Vilalta
CTTC
Spain
Email: ricard.vilalta@cttc.es
11. References
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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>.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, DOI 10.17487/RFC3471, February 2003,
<https://www.rfc-editor.org/info/rfc3471>.
[RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
Ayyangar, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
Engineering (RSVP-TE)", RFC 5420, DOI 10.17487/RFC5420,
February 2009, <https://www.rfc-editor.org/info/rfc5420>.
[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>.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511, April
2009, <https://www.rfc-editor.org/info/rfc5511>.
[RFC7570] Margaria, C., Ed., Martinelli, G., Balls, S., and B.
Wright, "Label Switched Path (LSP) Attribute in the
Explicit Route Object (ERO)", RFC 7570,
DOI 10.17487/RFC7570, July 2015,
<https://www.rfc-editor.org/info/rfc7570>.
[RFC7699] Farrel, A., King, D., Li, Y., and F. Zhang, "Generalized
Labels for the Flexi-Grid in Lambda Switch Capable (LSC)
Label Switching Routers", RFC 7699, DOI 10.17487/RFC7699,
November 2015, <https://www.rfc-editor.org/info/rfc7699>.
[RFC7792] Zhang, F., Zhang, X., Farrel, A., Gonzalez de Dios, O.,
and D. Ceccarelli, "RSVP-TE Signaling Extensions in
Support of Flexi-Grid Dense Wavelength Division
Multiplexing (DWDM) Networks", RFC 7792,
DOI 10.17487/RFC7792, March 2016,
<https://www.rfc-editor.org/info/rfc7792>.
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[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/rfc8253>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8363] Zhang, X., Zheng, H., Casellas, R., Gonzalez de Dios, O.,
and D. Ceccarelli, "GMPLS OSPF-TE Extensions in Support of
Flexi-Grid Dense Wavelength Division Multiplexing (DWDM)
Networks", RFC 8363, DOI 10.17487/RFC8363, May 2018,
<https://www.rfc-editor.org/info/rfc8363>.
[RFC8779] Margaria, C., Ed., Gonzalez de Dios, O., Ed., and F.
Zhang, Ed., "Path Computation Element Communication
Protocol (PCEP) Extensions for GMPLS", RFC 8779,
DOI 10.17487/RFC8779, July 2020,
<https://www.rfc-editor.org/info/rfc8779>.
[RFC8780] Lee, Y., Ed. and R. Casellas, Ed., "The Path Computation
Element Communication Protocol (PCEP) Extension for
Wavelength Switched Optical Network (WSON) Routing and
Wavelength Assignment (RWA)", RFC 8780,
DOI 10.17487/RFC8780, July 2020,
<https://www.rfc-editor.org/info/rfc8780>.
[RFC9325] Sheffer, Y., Ed., Saint-Andre, P., Ed., and T. T. Fossati,
Ed., "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/info/rfc9325>.
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[RFC9504] Lee, Y., Zheng, H., Gonzalez de Dios, O., Lopez, V., and
Z. Ali, "Path Computation Element Communication Protocol
(PCEP) Extensions for Stateful PCE Usage in GMPLS-
Controlled Networks", RFC 9504, DOI 10.17487/RFC9504,
December 2023, <https://www.rfc-editor.org/info/rfc9504>.
[RFC9916] Dhody, D., Turner, S., and R. Housley, "Updates to the
Usage of TLS to Provide a Secure Transport for the Path
Computation Element Communication Protocol (PCEP)",
RFC 9916, DOI 10.17487/RFC9916, July 2026,
<https://www.rfc-editor.org/info/rfc9916>.
11.2. Informative References
[ITU-T_G.694.1]
ITU-, T., "SERIES G: TRANSMISSION SYSTEMS AND MEDIA,
DIGITAL SYSTEMS AND NETWORKS; Digital networks; Spectral
grids for WDM applications: DWDM frequency grid", ITU-T
Rec. G.694.1 , October 2020,
<https://www.itu.int/rec/T-REC-G.694.1>.
[RFC4655] Farrel, A., Vasseur, J.-P., 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.L. 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>.
[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
January 2008, <https://www.rfc-editor.org/info/rfc5088>.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
January 2008, <https://www.rfc-editor.org/info/rfc5089>.
[RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
"Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, DOI 10.17487/RFC6163, April 2011,
<https://www.rfc-editor.org/info/rfc6163>.
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[RFC7449] Lee, Y., Ed., Bernstein, G., Ed., Martensson, J., Takeda,
T., Tsuritani, T., and O. Gonzalez de Dios, "Path
Computation Element Communication Protocol (PCEP)
Requirements for Wavelength Switched Optical Network
(WSON) Routing and Wavelength Assignment", RFC 7449,
DOI 10.17487/RFC7449, February 2015,
<https://www.rfc-editor.org/info/rfc7449>.
[RFC7698] Gonzalez de Dios, O., Ed., Casellas, R., Ed., Zhang, F.,
Fu, X., Ceccarelli, D., and I. Hussain, "Framework and
Requirements for GMPLS-Based Control of Flexi-Grid Dense
Wavelength Division Multiplexing (DWDM) Networks",
RFC 7698, DOI 10.17487/RFC7698, November 2015,
<https://www.rfc-editor.org/info/rfc7698>.
[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>.
[RFC9826] Dhody, D., Beeram, V., Hardwick, J., and J. Tantsura, "A
YANG Data Model for the Path Computation Element
Communication Protocol (PCEP)", BCP 205, RFC 9826,
DOI 10.17487/RFC9826, September 2025,
<https://www.rfc-editor.org/info/rfc9826>.
Authors' Addresses
Haomian Zheng (editor)
Huawei Technologies Co., Ltd.
Email: zhenghaomian@huawei.com
Young Lee
CRU
Email: younglee.tx@gmail.com
Ramon Casellas
CTTC
Email: ramon.casellas@cttc.es
Daniele Ceccarelli
Cisco
Email: dceccare@cisco.com
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