50G PON: Evolution Direction Beyond 10G PON

After the release of the XGS-PON standard in 2016, ITU-T embarked on research into next-generation PON technology. In 2018, ITU-T determined that 50G PON would be the technology development direction after 10G PON. In the second half of 2021, the first version of the 50G PON standard was officially released. 50G PON, with a bandwidth five times higher than 10G PON, provides a better service experience to meet future requirements, covers more scenarios, and supports a smooth migration from 10G PON to 50G PON.

50G PON Technology and Industry Chain are Maturing

According to ITU-T G.9804, 50G PON provides a bandwidth five times higher than 10G PON, and supports a downlink single-wavelength rate of 50 Gbps and flexible uplink rate options of 12.5 Gbps,

25 Gbps, and 50 Gbps. 50G PON maintains the P2MP topology, and provides a coverage distance of up to 20 km with a splitting ratio of up to 1: 256, catering to bandwidth access from 10 Gbps to 50 Gbps. In the 50G PON rate verification test carried out by German operator DNS:NET, 50G PON reached a downlink rate of 45.62 Gbps and an uplink rate of 21.87 Gbps.

50G PON uses single-fiber bidirectional transmission, employing broadcast mode in the downstream and TDMA in the upstream for point-to-multipoint communication between OLTs and ONUs. Key technologies encompasses wavelength selection, line coding, line rate, FEC, common TC, and PHY layer components. ZTE is committed to improving 50G PON standards and industry chain maturity and has made significant breakthroughs in some key component technologies. The company has submitted over 75 50G PON standard proposals, with those on technologies including the physical layer parameters, low latency, and FEC already adopted by standard organizations.

With the rapid growth of video services and the digital transformation of enterprises/campuses, there are increasing requirements for network determinacy that covers deterministic bandwidth, latency, and jitter control to support multiple business scenarios. Deterministic 50G PON technology provides broadband scalability and is compatible with multiple access rates, enabling precise bandwidth  control. Furthermore, it ensures high reliability by providing technical support for high-reliability service applications, including Ethernet uplink protection, Type B/C and hand-in-hand protection at the PON port level. By using the end-to-end low-latency rigid hard pipe technology, deterministic 50G PON can implement high-level service isolation, and construct rigid pipes with low latency and low jitter. Deterministic 50G PON also provides precise latency and jitter control capabilities to meet the requirements of industrial control scenarios that are sensitive to latency and jitter.

To meet the requirements of deterministic campus networks, ZTE has introduced industry’s first precise 50G PON technology at MWC 2022.

Currently, the 50G PON standards are almost complete and in the final preparation stage for commercial use. The focus of 50G PON has been shifted from standard formulation to commercial deployment. ZTE has carried out 50G PON demonstrations, tests, and pilots with more than 30 operators, continuously promoting cooperation and maturity of the industry chain in this field.

50G PON Covers Diverse Application Scenarios

As the next-generation optical fiber access technology, 50G PON is expected to be commercially available by 2025, starting with ToB scenarios and expanding to ToH scenarios.

50G PON offers uplink and downlink symmetric 50 Gbps bandwidth, meeting the high-bandwidth service requirements of enterprises and enabling symmetric 10G LAN applications. On the one hand, 50G PON+FTTR-B can meet the application requirements of small and medium-sized enterprises (SMEs), such as hotels, street stores, and cafes, ensuring a good user experience. On the other hand, 50G PON can implement 10G all-optical access for campuses and enterprises, meeting the deterministic requirements for latency and jitter in scenarios such as development zones, industrial parks, and factories.

In September 2022, China Mobile and ZTE successfully completed the 50G PON backhaul field trial with 5G small cells in its existing network, confirming that the 50G PON equipment, integrated with the latest optoelectronic devices, can precisely carry and guarantee high bandwidth and low latency services of 5G small cells. In September 2023, China Telecom Guangdong and ZTE jointly launched China's first 10G-to-the-enterprise application with 50G PON technology at the Nanshan Science and Technology Park in Shenzhen.

For home networks, 50G PON+FTTR can provide ultra-high bandwidth, accommodating various services such as smart home, online education, online games, VR, and online live streaming. The high bandwidth, low latency, and low jitter features of 50G PON also support mobile backhaul and indoor coverage requirements.

ZTE will continue to work with operators to verify the technical feasibility and equipment maturity of 50G PON in different application scenarios while exploring more application scenarios.

Smooth 50G PON Upgrade Protects Investment

In terms of network evolution, ZTE recommends the Combo PON concept for a smooth migration from existing PON to 50G PON. This concept enables GPON, XG(S)-PON, and 50G PON to coexist on a single platform and line card, tripling the equipment life cycle and saving network construction investments.

With the addition of a third uplink wavelength band (1284–1288 nm) to the 50G PON standard at the beginning of 2023, 50G PON does not need to reuse the existing GPON and XGS-PON wavelengths, laying the foundation for the coexistence of 50G PON, 10G PON, and GPON ONUs on the same network.

ZTE took the industry lead by releasing the 50G PON & 10G PON & GPON three-mode Combo PON solution (Fig. 1) at MWC 2023, and ZTE is also the first vendor to apply the Combo concept to the upgrade from 10G PON to 50G PON. This solution, featuring an independent wavelength stacking mechanism, supports GPON, 10G PON and 50G PON, shares the same ODN and platform, and solves the problems of high construction costs, large footprint, complex optical fiber cabling, and difficult operation and maintenance during the evolution from GPON to 10G PON and then to 50G PON. This solution helps operators quickly and flexibly provision high-bandwidth services, simplifies network construction, and saves deployment costs.

In the network upgrade process, the three-mode Combo PON solution does not need to adjust the ODN or change the existing OLT configurations and user service data during network upgrade, facilitating flexible deployment and smooth network evolution. Meanwhile, the solution integrates the 50G PON, 10G PON, GPON, and optical multiplexer functions into the same optical module without requiring extra equipment or additional equipment room space, which greatly saves the types of line cards and simplifies maintenance and management.

In addition, the solution uses the wavelength division mode, automatically matches the 50G PON channel, 10G PON channel, and GPON channel with different types of ONUs, and inherits the existing OSS provisioning process. The service provisioning flow remains unchanged while both the service provisioning and the cutover get easy. The solution is applicable to a variety of scenarios, such as the broadband network upgrade and reconstruction, greenfield, and MSOs’ optical fiber transformation. It is a highly applicable cost-effective solution that allows for continuous bandwidth upgrade and evolution of FTTx network.

Conclusion

As a technology leader in the optical access field, ZTE has achieved several significant milestones in the development of 50G PON technology. In 2022, ZTE launched the world's first precise 50G PON prototype at MWC 2022 and the world's first 50G PON+Wi-Fi 7 ONU prototype at the FTTH Conference. In 2023, ZTE introduced its three-mode Combo PON solution at MWC 2023 and its Tbit-level all-optical access platform, ZXA10 C600E designed for the large-scale deployment of 50G PON networks at the Network X exhibition.

Leveraging its extensive experience in the development of FTTx and profound understanding of the future development direction of PON technologies, ZTE will continue to drive innovation in 50G PON technology, expand the 50G PON all-optical foundation, and accelerate the advancement of the 50G PON industry chain.