Path Computation and Control Extention Requirements for Fine-Granularity Transport Network
draft-han-pce-path-computation-fg-transport-02
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Liuyan Han , Haomian Zheng , Minxue Wang , Yang Zhao , Haibin Huang , Li Zhang | ||
| Last updated | 2026-03-01 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-han-pce-path-computation-fg-transport-02
PCE Working Group L. Han
Internet-Draft CMCC
Intended status: Standards Track H. Zheng
Expires: 2 September 2026 Huawei
M. Wang
Y. Zhao
H. Huang
CMCC
L. Zhang
Huawei
1 March 2026
Path Computation and Control Extention Requirements for Fine-Granularity
Transport Network
draft-han-pce-path-computation-fg-transport-02
Abstract
This document focuses on the requirements for path computation and
control of the fine-granularity transport network. It provides the
general context of the use cases of path computation and the
considerations on the requirements of PCE extension in such fine-
granularity transport network.
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 2 September 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
Han, et al. Expires 2 September 2026 [Page 1]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. fgMTNP network layer . . . . . . . . . . . . . . . . . . . . 4
5. Path Computation Requirements in Fine-grain Transport
Network . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Use Cases of Fine-grain Path Computation . . . . . . . . . . 6
7. Requirements of PCE Extension for Fine-grain Transport
Network . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Manageability Consideration . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
11. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
With the proposal of new service demand, the technology of the
transport network is constantly developing. TDM based Optical
Transport Network (OTN) and Metro Transport Network (MTN)
technologies are both moving towards fine-grain hard slices. The
vertical industries and dedicated line services have higher
requirements on isolation, security and reliability but with smaller
bandwidth. Fine-grain TDM technology can provide the flexible
N*10Mbps bandwidth for these connections.
ITU-T has a series of recommendations for fgOTN (fine grain OTN ) and
fgMTN (fine grain MTN). The fgOTN overview is defined in
[ITU-T_G.709.20], fgOTN layer architecture is defined in
[ITU-T_G.872], fgOTN Interface and server adaptation is defined in
[ITU-T_G.709], fgOTN equipment is defined in [ITU-T_G.798], fgOTN
synchronization is defined in [ITU-T_G.8251], fgOTN management
requirementsis defined in [ITU-T_G.874] and protocol-neutral
information model is defined in [ITU-T_G.875]. The fgMTN overview is
defined in[ITU-T_G.8312.20], fgMTN layer architecture is defined in
[ITU-T_G.8310], fgMTN interface is defined in [ITU-T_G.8312], fgMTN
equipment is defined in [ITU-T_G.8321], fgMTN synchronization is
Han, et al. Expires 2 September 2026 [Page 2]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
defined in [ITU-T_G.mtn-sync], and management requirement and
information model is defined in [ITU-T_G.8350]. Both the fgOTN and
fgMTN protection are defined in [ITU-T_G.808.4].
The new fine-grain transport technology will significantly increase
the number of path connections in the network compared to the
traditional connections based on optical wavelength or ODUk with
larger bandwidth. For the future massive fine-grain channel
connections, how to effectively perform end-to-end path computation
and control will be an important technical topic.
The architecture of a Path Computation Element (PCE)-based model has
been presented in [RFC4655]. It discusses PCE-based implementations
including composite, external, and multiple PCE path computation.
[RFC8779]addresses the extensions required for GMPLS applications and
routing requests, for example, for Optical Transport Networks (OTNs)
and Wavelength Switched Optical Networks (WSONs). Due to the new
features of fine-grain technology, PCE may need to be extended.
This document focuses on the requirements for path computation and
control of the fine-grain transport network. Section 6 provides the
general context of the use cases of path computation. Section 7
provides the considerations on the requirements of PCE extension in
such fine-grain transport network.
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
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
Domain:
A domain, as defined in [RFC4655], is "any collection of network
elements within a common sphere of address management or path
computation responsibility". Specifically, within this document,
we mean a part of an operator's network under common management
(i.e., under shared operational management using the same
instances of a tool and the same policies). Network elements are
often grouped into domains based on technologies, vendor profiles,
or geographic proximity.
FG:
Han, et al. Expires 2 September 2026 [Page 3]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
Fine Grain
MTN:
Metro Transport Network
OTN:
Optical Transport Network
4. fgMTNP network layer
MTN(Metro Transport Network) [ITU-T_G.8310] is a new generation of
transport network technology system defined by ITU-T. MTN integrates
packet and TDM technologies, enabling compatibility with Ethernet
protocol stacks while meeting differentiated requirements of the 6G
era, such as hard isolation, low latency, and high reliability, thus
further enhancing the bearer capability of 5G networks.
From the bottom up, MTN network is composed of three network layers:
MTN section layer, MTN path layer and fgMTN path layer.
Client Signal (Ethernet MAC frame or Constant Bitrate)
|
+------------------------+
| fgMTN path layer |
| | |
| MTN path layer |
| | |
| MTN section layer |
+------------------------+
Figure 1: MTN Network Layers
As shown in Figure 1, the fgMTN technology
[ITU-T_G.8312.20]incorporates fine-grained slicing into the MTN
architecture, providing a low-cost, refined, hard-isolated, and fine-
grained bearer channels. The fgMTN technology further refines the
granularity of hard slicing from 5 Gbit/s to 10 Mbit/s, meeting the
differentiated service bearer requirements of vertical industry
applications and private line services, such as small bandwidth, high
isolation, and high security.
Han, et al. Expires 2 September 2026 [Page 4]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
5. Path Computation Requirements in Fine-grain Transport Network
Compared to traditional optical networks, fine-grain transport
networks require more quantity, faster, and more flexible path set-up
and removing capabilities. The path computation architecture should
be reliable, scalable and efficient to facilitate the configuration
of a large amount of fine-granularity channel connections.
+-----------------------+ +------------------------+
| Domain A | | Domain B |
+-+-+ +--+ +--+ ++-+ +-++ +--+ +--+ +-+-+
--->|PE1+---+P1+----+P2+---->+P4|------>|P5+----+P6+----+P7+---->+PE2|--->
+-+-+ +--+ +--+ ++-+ +-++ +--+ +--+ +-+-+
| | | |
+-----------------------+ +------------------------+
^ ^
| |
+-----------------E2E fine-grain LSP-------------------------+
Figure 2: Scenario of E2E fine-grain connection
o The number of fine-grain TDM channels will significantly increase:
FgOTN and fgMTN support 10Mbit/s level tributary slots
granularity. One ODU2 channel can support up to 952 fgOTN
connections. One 5Gbps MTN channel can support up to 480 fgMTN
connections. For transport devices with a switching capacity of
several Tbps, they can support fine-grain channel connections of
tens of thousands or even tens of thousands. Therefore, for the
network, the number of connections throughout the entire network
will significantly increase.
o According to service requirements, fine-grain paths may change
frequently and dynamically:
One fine-grain channel can carry and correspond to a certain CBR
or Ethernet service, rather than serving as a large optical
channel. When the services appear or end, or its bandwidth
changes, or the destination address changes, they will cause
changes in fine-grain channels. Therefore, compared to serving as
an optical bandwidth channel for the routers, the fine-granularity
channels serve directly as service channels, which are more likely
to change.
Han, et al. Expires 2 September 2026 [Page 5]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
6. Use Cases of Fine-grain Path Computation
To address the massive fine-grain path computation issues, it is
necessary to combine centralized control systems and distributed
control protocols. On the one hand, a centralized control system is
used to calculate the global optimal routing and develop resource
scheduling strategies. On the other hand, distributed control
protocols between devices are used to perform operations such as
cross connection configuration and time slot occupation assignment.
The applications of fine-grain path computation and related
capabilities at least include:
Fine-grain path set-up:
The control system calculates service routing in a centralized way
and sends messages to the source node. Then, the connection is
established between devices through connection control signaling.
The end-to-end fine-grain connections may cross one or more
domains.
Fine-grain resource management:
The topology and resource information of fine-grain devices and
slots need to be collected and reported, so that the centralized
system can calculate new routes based on this information and
allocate slot resources for the new connections.
Fine-grain path update:
During the connection, fine-grain channels can undergo hitless
bandwidth adjustment. When channel bandwidth increases or
decreases, time slots need to be added or removed. It is needed
to control and update the existing path parameter.
Fine-grain path removal:
When the service no longer needs this connection, it is necessary
to remove this fine-grain channel and release the corresponding
resources.
Han, et al. Expires 2 September 2026 [Page 6]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
7. Requirements of PCE Extension for Fine-grain Transport Network
FgMTN uses the management and control system to perform centralized
path computation. The functions of topology and resource collection
can use PCEP-LS [I-D.ietf-pce-pcep-ls] to enable the collection of
link-state and TE information from MTN networks and sharing with PCE
by extending a new LS Report message. Therefore, the PCEP-LS can be
extended to support the reporting of fgMTN topology resources.
The path calculation request/reply message from the PCC or the PCE
must contain the information specifying appropriate fine-grain
channel attributes, including the fine-grain switching capability/
type, the fine-grain server layer type, the fine-grain time slots,
the fine-grain client ID, end-to-End fine-granularity path protection
type, etc.
Based on the above analysis, the specific PCEP and its link status
extensions are provided by [I-D.ietf-pce-pcep-ls] and
[I-D.ietf-pce-pcep-ls].
8. Manageability Consideration
TBD
9. Security Considerations
TBD
10. IANA Considerations
TBD
11. Normative References
[I-D.ietf-pce-pcep-ls]
Dhody, D., Peng, S., Lee, Y., Ceccarelli, D., Wang, A.,
and G. S. Mishra, "PCEP extensions for Distribution of
Link-State and TE Information", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-ls-04, 14 October
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-ls-04>.
[ITU-T_G.709]
ITU-T, "ITU-T G.709: Interfaces for the optical transport
network;", https://www.itu.int/rec/T-REC-G.709.
Han, et al. Expires 2 September 2026 [Page 7]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
[ITU-T_G.709.20]
ITU-T, "ITU-T G.709.20: Overview of fine grain
OTN;", Work in progress.
[ITU-T_G.798]
ITU-T, "ITU-T G.798: Characteristics of optical transport
network hierarchy equipment functional
blocks;", https://www.itu.int/rec/T-REC-G.798.
[ITU-T_G.808.4]
ITU-T, "ITU-T G.808.4: Linear protection for fgMTN and
fgOTN;", Work in progress.
[ITU-T_G.8251]
ITU-T, "ITU-T G.8251: The control of jitter and wander
within the optical transport network
(OTN);", https://www.itu.int/rec/T-REC-G.8251.
[ITU-T_G.8310]
ITU-T, "ITU-T G.8310: Architecture of the metro transport
network; 01/2024", Work in progress, January 2024.
[ITU-T_G.8312]
ITU-T, "ITU-T G.8312:Interfaces for metro transport
networks; 01/2024", https://www.itu.int/rec/T-REC-G.8312,
January 2024.
[ITU-T_G.8312.20]
ITU-T, "ITU-T G.8312.20:Overview of fine grain MTN;
01/2024", https://www.itu.int/rec/T-REC-G.8312.20,
January 2024.
[ITU-T_G.8321]
ITU-T, "ITU-T G.8321:Characteristics of metro transport
network equipment functional
blocks;", https://www.itu.int/rec/T-REC-G.8321.
[ITU-T_G.8350]
ITU-T, "ITU-T G.8350: Management and Control of metro
transport networks;", https://www.itu.int/rec/T-REC-
G.8350.
[ITU-T_G.872]
ITU-T, "ITU-T G.872: Architecture of the optical transport
network;", https://www.itu.int/rec/T-REC-G.872.
Han, et al. Expires 2 September 2026 [Page 8]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
[ITU-T_G.874]
ITU-T, "ITU-T G.874: Management aspects of optical
transport network elements;", https://www.itu.int/rec/T-
REC-G.874.
[ITU-T_G.875]
ITU-T, "ITU-T G.875: Optical transport network: Protocol-
neutral management information model for the network
element view;", https://www.itu.int/rec/T-REC-G.875.
[ITU-T_G.mtn-sync]
ITU-T, "ITU-T G.mtn-sync:Synchronization aspects of metro
transport network", Work in progress.
[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>.
[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>.
[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>.
[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>.
Authors' Addresses
Liuyan Han
China Mobile
No.32 Xuanwumen west street
Beijing
100053
China
Email: hanliuyan@chinamobile.com
Haomian Zheng
Huawei
H1, Huawei Xiliu Beipo Village, Songshan Lake.
Han, et al. Expires 2 September 2026 [Page 9]
Internet-Draft draft-han-pce-path-computation-fg-transp March 2026
Dongguan
Guangdong, 523808
China
Email: Zhenghaomian@huawei.com
Minxue Wang
China Mobile
No.32 Xuanwumen west street
Beijing
100053
China
Email: wangminxue@chinamobile.com
Yang Zhao
China Mobile
No.32 Xuanwumen west street
Beijing
100053
China
Email: zhaoyangyj@chinamobile.com
Haibin Huang
China Mobile
No.32 Xuanwumen west street
Beijing
100053
China
Email: huanghaibin@chinamobile.com
Li Zhang
Huawei
Beiqing Road
Beijing
China
Email: zhangli344@huawei.com
Han, et al. Expires 2 September 2026 [Page 10]