Global Standardization Activities

Trends in the Second Plenary Meeting of ITU-T SG15 (Networks, Technologies and Infrastructures for Transport, Access and Home)

Ryo Koma, Ryo Igarashi, Takashi Matsui, Yoshifumi Wakisaka, Chihiro Kito, and Kazuhide Nakajima

Abstract

The second plenary meeting of ITU-T (International Telecommunication Union - Telecommunication Standardization Sector) Study Group 15 for the 2025–2028 study period was held in Geneva, Switzerland, from 13 to 24 October 2025. This article reports on the outcomes of this meeting, with a particular focus on optical access network standards and optical physical-layer standards.

Keywords: ITU-T SG15, optical access network, optical physical layer

1. Overview of ITU-T SG15

The International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) Study Group 15 (SG15) [1] discusses international standards for optical communication networks, including home and access networks. This article introduces the major topics addressed in Working Party 1 (WP1), which covers home and access network standards, and WP2, which handles physical-layer standards for terrestrial and submarine optical communication systems. For trends in WP3, which focuses on the characteristics of optical transport networks, please refer to the article “Optical Network Technology for Future Ultra-high-capacity Communications in the Beyond 5G and Big Data Era” [2].

2. Trends in WP1/SG15

In Question 2, discussions focus on passive optical network (PON) systems connecting central offices and customer premises via optical fiber. Current discussions include future high-speed PON systems as well as technology and requirement considerations for diverse use cases not only for conventional residential services but also industrial networks, mobile fronthaul, and ultra-low-latency networks, and so on.

At the second plenary meeting, Supplement G.Suppl.88 [3] summarizing use cases, requirements, and candidate technologies for next-generation high-speed PON exceeding 100 Gbit/s per wavelength was agreed. As signal waveform degradation is a key challenge for higher speeds, G.Suppl.88 includes various candidate technologies such as coherent schemes, which enable waveform-degradation compensation at the receiver, cost-effective intensity-modulation direct-detection (IMDD) schemes based on single-sideband modulation or transmitter-side dispersion-compensation technologies, and hybrid IMDD–coherent schemes. It was also agreed to begin work on Revision 1 to further discuss items not included in this edition.

Regarding the physical-layer specification Recommendation G.9804.4 for 50G-TWDM (time and wavelength division multiplexing)-PON, which achieves further speed increases by wavelength-multiplexing 50-Gbit/s-class signals, the applicability of technologies discussed in G.Suppl.88 is also being considered.

For accommodating diverse use cases, discussions continue on the new Supplement G.Suppl. LLSoT(W)DM, which summarizes the requirements and candidate technologies for applying PON systems in mobile fronthaul for wireless communication systems (LLSoT(W)DM: Low Layer Split Mobile Fronthaul over T(W)DM PON).

In association with the Technical Report GSTR.ION-2030—prepared mainly by SG15 Question 12 and summarizing network architectures, component technologies, and use cases beyond 2030—work on the new Supplement G.Suppl.ION-aiBB (Use cases and requirements of AI enhanced ION-2030 for broadband) has been initiated to study artificial intelligence (AI)-enhanced broadband-access use cases and requirements.

In Question 3, discussions focus on transmission technologies mainly for in-building and in-premises networks, as well as communication for smart-grid applications. At the second plenary meeting, five recommendations—Recommendation G.9930 Amendment 2, Recommendation G.9943, Recommendation G.9949, Recommendation G.9949 Amendment 1, and Recommendation G.9975 [4–7]—were approved, and three supplements related to in-home optical fiber communication technologies—Supplement G.Suppl.89, Supplement G.Suppl.90, and Supplement G.Suppl.91 [8–10]—were agreed and published.

3. Topics in WP2/SG15

In Question 5, which is responsible for optical fiber and cable characteristics, discussions are progressing on new recommendations for multi-core optical fibers, which contain multiple optical paths within a single cladding, on the basis of contributions from Japan. It has been agreed to consider multi-core fibers with the same cladding diameter as existing single-mode fibers (SMFs) (i.e., standard-cladding diameter). At the second plenary meeting, work on new recommendations on two types of standard-cladding diameter multi-core fibers, Recommendation G.smmcf and Recommendation G.csmcf, featuring optical compatibility with conventional SMF and low-loss cutoff-shifted fiber was approved. It was also agreed that these new recommendations will target 2-core and 4-core structures.

Proposals on information and technical properties for hollow-core fibers, in which light is guided through air, have been active. Questions 2, 5, and 6 (the latter covering terrestrial optical transmission system interfaces) will jointly discuss future study directions of hollow-core fiber.

Optical fiber sensing technology using optical networks is being discussed in Questions 2, 6, and 8 (which handles submarine optical transmission system standards). In Question 6, ITU-T approved and established Recommendation G.681 [11], the first recommendation specifying optical-interface requirements for distributed fiber-optic sensing (DFOS) in terrestrial optical transmission networks. Future discussions will explore practical application scenarios for DFOS.

Question 8 is considering sensing systems using submarine optical cable. Recommendation G.9730.1 (for sensing-dedicated submarine systems) and Recommendation G.9730.2 (for combined communication-and-sensing systems) have already been approved. Work continues on developing Recommendation G.9730, a new recommendation summarizing general considerations for submarine-cable-based sensing.

In Question 7, which covers maintenance, operation, and connectivity of optical physical infrastructures, interest is growing in applying DFOS to outdoor optical-facilities maintenance and inspection. For example, considering the use of DFOS for remote monitoring after disasters, the revised Recommendation L.391 (Monitoring systems for outside plant facilities) [12] was consented. To incorporate DFOS into Recommendation L.302 (Optical fibre outside plant maintenance support, monitoring and testing system), a new revision effort has begun.

4. Summary

As described above, active discussions are ongoing in ITU-T SG15 WP1 and WP2 regarding technologies for higher-speed and higher-performance optical access networks as well as new optical fiber technologies and optical sensing applications. Further progress is expected. The third plenary meeting of ITU-T SG15 is scheduled to be held in Montreal, Canada, from 29 June to 11 July 2026, together with a joint workshop with IEEE (Institute of Electrical and Electronics Engineers) 802.3 Ethernet.

References

[1]	ITU-T SG15, https://www.itu.int/en/ITU-T/studygroups/2025-2028/15/Pages/default.aspx
[2]	M. Murakami, “Optical Network Technology for Future Ultra-high-capacity Communications in the Beyond 5G and Big Data Era,” NTT Technical Review, Vol. 20, No. 6, pp. 43–51, June 2022. https://doi.org/10.53829/ntr202206gls
[3]	Supplement G.Suppl.88, https://www.itu.int/rec/T-REC-G.Sup88-202510-P
[4]	Recommendation G.9930 Amendment 2, https://www.itu.int/rec/T-REC-G.9930-202511-I!Amd2
[5]	Recommendation G.9943, https://www.itu.int/rec/T-REC-G.9943-202510-P
[6]	Recommendation G.9949, https://www.itu.int/rec/T-REC-G.9949-202510-P
[7]	Recommendation G.9975, https://www.itu.int/rec/T-REC-G.9975-202510-P
[8]	Supplement G.Suppl.89, https://www.itu.int/rec/T-REC-G.Sup89-202510-P
[9]	Supplement G.Suppl.90, https://www.itu.int/rec/T-REC-G.Sup90-202510-P
[10]	Supplement G.Suppl.91, https://www.itu.int/rec/T-REC-G.Sup91-202510-P
[11]	Recommendation G.681, https://www.itu.int/rec/T-REC-G.681-202511-P
[12]	Recommendation L.391, https://www.itu.int/rec/T-REC-L.391-202511-I

	Ryo Koma Distinguished Researcher, Optical Access Systems Project, Access Network Service Systems Laboratories, NTT, Inc. He received a B.E. from the Tokyo University of Science in 2010, M.E. from the University of Tokyo in 2012, and Ph.D. from Hokkaido University in 2018. In 2012, he joined NTT, where he has been engaged in research on digital-signal-processing-based PON systems.
	Ryo Igarashi Research Engineer, Access Network Service Systems Laboratories, NTT, Inc. He received a B.E. from Niigata University in 2015, M.S. from Tohoku University, Miyagi, in 2017, and Ph.D. from Hokkaido University in 2024. In 2017, he joined NTT Access Network Service Systems Laboratories, where he has been engaged in research and development of advanced optical access transmission systems.
	Takashi Matsui Distinguished Researcher/Group Leader, Access Network Service Systems Laboratories, NTT, Inc. He received a B.E., M.E., and Ph.D. in electronic engineering from Hokkaido University in 2001, 2003, and 2008. He also attained the status of Professional Engineer (P.E.Jp) in Electrical and Electronic Engineering in 2009. In 2003, he joined NTT, where he has been engaged in research on optical fiber design and measurement. He is currently a senior member of IEEE, and a member of Optica and the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan.
	Yoshifumi Wakisaka Associate Distinguished Researcher, Access Network Management Project, Access Network Service Systems Laboratories, NTT, Inc. He received a B.S. and M.S. from the University of Tokyo in 2014 and 2016. He joined NTT Access Network Service Systems Laboratories in 2017, where he has been engaged in research on optical fiber sensing technology. He is a member of IEICE of Japan and the Japan Society of Applied Physics (JSAP).
	Chihiro Kito Senior Research Engineer, Access Network Management Project, Access Network Service Systems Laboratories, NTT, Inc. He received a B.E. and M.E. from Toyota Technological Institute, Aichi, in 2009 and 2011 and Ph.D. from Shimane University in 2017. He joined NTT Access Network Service Systems Laboratories in 2011, where he has been engaged in research on optical fiber measurement technology for efficient maintenance of optical access networks. He also has been acting as a rapporteur of Q7/SG15 of ITU-T since 2021. He is a member of IEICE of Japan.
	Kazuhide Nakajima NTT Fellow, Access Network Service Systems Laboratories, NTT, Inc. He received an M.S. and Ph.D. in electrical engineering from Nihon University, Chiba, in 1994 and 2005. In 1994, he joined NTT Access Network Service Systems Laboratories, where he has been engaged in research on optical fiber design and related measurement techniques. He has been acting as a rapporteur of Question 5 of ITU-T SG15 since 2009. He is a member of IEEE, Optica, IEICE, and JSAP.

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