Internet-Draft draft-han-pce-path-computation-fg-transp March 2024
Han, et al. Expires 5 September 2024 [Page]
PCE Working Group
Intended Status:
Standards Track
L. Han
China Mobile
H. Zheng
Huawei Technologies
M. Wang
China Mobile
Y. Zhao
China Mobile

Path Computation and Control Extention Requirements for Fine-Granularity Transport Network


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

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 5 September 2024.

Table of Contents

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 defined in [] , 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 3 provides the general context of the use cases of path computation. Section 4 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Terminology





4. 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        |
    +-+-+   +--+    +--+     ++-+       +-++    +--+    +--+     +-+-+
    +-+-+   +--+    +--+     ++-+       +-++    +--+    +--+     +-+-+
      |                       |           |                        |
      +-----------------------+           +------------------------+
      ^                                                            ^
      |                                                            |
      +-----------------E2E fine-grain connection----------------+
Figure 1: Scenario of E2E fine-grain connection

o The number of fine-grain TDM channels will significantly increase:

o According to service requirements, fine-grain paths may change frequently and dynamically:

5. 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:

o Fine-grain path set-up:

o Fine-grain resource management:

o Fine-grain path update:

o Fine-grain path removal:

o Service awareness and mapping:

6. Requirements of PCE Extension for Fine-grain Transport Network

The centralized computation model of PCE architecture seems to be suitable for the fine-grain transport network, while the PCEP (PCE communication protocol) needs to be extended to meet the fine-grain transport requirements.

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.

The protocol and signaling should support the application of fine-grain path set-up/update/removal and resource management.

7. PCEP Extension for Fine-grain Transport Network

Fine-grain path set-up/adjustment,service awareness and mapping and fine- grain resource management may be invovled in PCEP extensions. The specific extentions will continue to apply in the future.

8. Manageability Consideration


9. Security Considerations


10. IANA Considerations


11. Normative References

Liu, S., Zheng, H., Guo, A., Zhao, Y., and D. King, "Problem Statement and Gap Analysis for Connecting to Cloud DCs via Optical Networks", Work in Progress, Internet-Draft, draft-liu-ccamp-optical2cloud-problem-statement-05, , <>.
ITU-T, "ITU-T G.709: Interfaces for the optical transport network;",
ITU-T, "ITU-T G.709.20: Overview of fine grain OTN;", Work in progress.
ITU-T, "ITU-T G.798: Characteristics of optical transport network hierarchy equipment functional blocks;",
ITU-T, "ITU-T G.808.4: Linear protection for fgMTN and fgOTN;", Work in progress.
ITU-T, "ITU-T G.8251: The control of jitter and wander within the optical transport network (OTN);",
ITU-T, "ITU-T G.8310: Architecture of the metro transport network; 01/2024", Work in progress, .
ITU-T, "ITU-T G.8312:Interfaces for metro transport networks; 01/2024",, .
ITU-T, "ITU-T G.8312.20:Overview of fine grain MTN; 01/2024",, .
ITU-T, "ITU-T G.8321:Characteristics of metro transport network equipment functional blocks;",
ITU-T, "ITU-T G.8350: Management and Control of metro transport networks;",
ITU-T, "ITU-T G.872: Architecture of the optical transport network;",
ITU-T, "ITU-T G.874: Management aspects of optical transport network elements;",
ITU-T, "ITU-T G.875: Optical transport network: Protocol-neutral management information model for the network element view;",
ITU-T, "ITU-T aspects of metro transport network", Work in progress.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <>.
Farrel, A., Vasseur, J.-P., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
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, , <>.

Authors' Addresses

Liuyan Han
China Mobile
No.32 Xuanwumen west street
Beijing, 100053
Haomian Zheng
Huawei Technologies
H1, Huawei Xiliu Beipo Village, Songshan Lake.
Guangdong, 523808
Minxue Wang
China Mobile
No.32 Xuanwumen west street
Beijing, 100053
Yang Zhao
China Mobile
No.32 Xuanwumen west street
Beijing, 100053