Dell'Oro: 50G PON moves closer to deployment

Communications World Wide Web News (CWW) In 2022, global broadband spending will hit a record high as service providers push forward with major network upgrades and expansions. Most of these investments have focused on expanding fiber optic coverage for business and home services to eventually replace older coaxial Cable and Digital Subscriber Line (DSL) networks.

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The network upgrade mainly includes investment in PON technology, which can provide 10Gbps bandwidth through a single OLT port, and the bandwidth is shared by dozens of users. The short-term goal is to be able to provide consistent symmetric 1-5Gbps bandwidth for each family user. The focus on network speed has driven a substantial increase in investment in 10Gbps technologies, including 10G EPON, XG-PON and XGS-PON. Spending on OLT platforms and ONTs supporting 10Gbps technology will increase by 308% from 2020 to 2022 (Figure 1).

While these technologies will serve most operators well over the next 5 years, operators in a growing number of markets still want to ensure that the substantial investments they make today in expanding fiber optic networks and Optical Distribution Networks (ODN) will pay off, And hope to have a technology roadmap that will enable them not only to be ahead of competitors in terms of network speed and latency, but also to achieve multiple architectural goals, including using the same technology and ODN to provide home and enterprise services, merging access and Converge networks to reduce the total number of network platforms, simplify the upgrade path through the coexistence of multiple PON technologies, and provide wholesale mobile backhaul services, etc.

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At present, the demand for bandwidth is still growing. According to the International Telecommunication Union (ITU), global bandwidth consumption will grow at a compound annual growth rate (CAGR) of 50% from 2015 to 2021, rising from 719 Tbps in 2020 to 932 Tbps . Bandwidth consumption will undoubtedly continue to accelerate over the next few years as governments and operators focus on expanding networks to connect more homes and businesses, and applications such as virtual reality (VR) and online gaming develop.

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For some operators facing fierce competition, 25G PON may be an option, because the demand for bandwidth above 10Gbps in the short term and satisfying the needs of home and business customers through a single ODN force them to take action in the next 1-2 years , but will face long-term evolution challenges.

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At the same time, operators and equipment suppliers want to accelerate the availability of products so that they can undergo the rigorous testing and certification required by any new technology, which drives the ITU-T's 50G PON standard and corresponding prototype platforms and components to continue rapidly develop. ITU-T has made great contributions in defining physical layer parameters, delay requirements and forward error correction (FEC).

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Major operators, including China Mobile, China Telecom, China Unicom, Globe, Orange, STC, Swisscom, Telefónica, Telekom Malaysia, and Turkcell, have conducted early laboratory tests of 50G PON prototype equipment, or put the technology as their next choice. Other operators are still focused on launching XGS-PON, but are also watching the 50G PON standardization process to make formal commitments.

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In addition, operators want to determine the power budget requirements and dispersion compensation and the use of digital signal processors (DSP) will not change the existing ODN, so system suppliers want products to market quickly, which also promotes the rapid development of the component ecosystem.

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latest progress

In September 2022, at the plenary meeting of ITU-T Study Group 15, some major steps in the evolution of 50G PON were announced. The most important point is to reach a consensus on the details of the coexistence of all three PON technologies defined by the ITU (50G PON, XGS-PON and GPON) on a single ODN network. Previously, the coexistence of GPON and XGS-PON has not been defined, which means that operators must upgrade the GPON network to XGS-PON before starting to deploy 50G PON.

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As the G.9804.1 standard adds a third uplink wavelength band (1284-1288nm) between the existing 1260-1280 and 1290-1310 frequency bands, 50G PON, XGS-PON and GPON can now coexist on the same ODN network. In addition, 50G PON+XGS-PON, 50G PON+GPON, and even 50G PON+XGS-PON+GPON can now be used to implement Combo PON deployment.

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Supporting tri-mode coexistence and Combo PON deployment as a complement is critical, as operators have repeatedly stated that they do not want to disrupt ODN networks as they evolve to new technologies. In addition, operators are expected to transition to 50G PON by using Combo PON, which not only utilizes the existing space at the central office, does not need to modify the ODN network, but also does not need to use wavelength division multiplexing equipment to avoid optical power loss.

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The challenge remains

Compared with today's 10Gbps technology, 50G PON has achieved significant improvements in bandwidth availability and latency. However, while it brings benefits, it also faces some challenges, the biggest technical challenge being at the physical layer. Specifically, there are potential risks in the optical power budget, dispersion penalty and intersymbol interference (ISI) required by the 50G PON system. As the bandwidth increases, the overall performance usually degrades, especially when the existing ODN needs to support a defined 32dB power budget, the risk is greater. The use of digital signal processing (DSP) technology can reduce or completely solve these physical layer problems. However, previous PON technology did not use DSP technology, so operators want to carefully test this technology and ensure that the point-to-multipoint communication between the OLT port and the ONT works as expected. DSP in particular helps reduce dispersion and bandwidth limitation penalties and ensures more efficient support for low-bandwidth GPON and XGS-PON ONTs.

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At present, the bandwidth of the 50G prototype is asymmetrical. The downlink provides 50G bandwidth, and the uplink provides 25G or 12.5G bandwidth. Although system vendors are investigating the best options for delivering consistent, symmetric rate bandwidth and have delivered some prototypes using semiconductor optical amplifiers (SOAs) and FPGA-based DSPs, in practice ITU-T Study Group 15 will In September 2009, it was agreed to further study the possibility of providing symmetric rate bandwidth. Obviously, operators prefer to use symmetric bandwidth as early as possible. However, the dramatically increased downstream bandwidth and advertised network speeds should be more than enough for users until upstream technologies and components are standardized and applied to OLTs and ONTs.

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Opportunities continue

Despite its early days, Dell'Oro Group believes total 50G PON equipment revenue will grow from less than $3 million to $1.5 billion between 2023 and 2027. This revenue growth will become more pronounced from 2027 onwards as operators begin to evolve their 10G PON networks to next-generation technologies (Figure 2).

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In addition to being able to predict the future bandwidth growth requirements of consumer applications such as VR, AR, online games, video conferencing and 8k video, 50G PON can also help operators solve business service problems. Specifically, 50G PON allows operators to provide four 10G Ethernet connections, which can support multiple services separately. In addition, 50G PON is ideal for deploying passive optical local area networks (POL), which can support fiber extension to the desktop. At the same time, compared with the traditional point-to-point Ethernet architecture, the POL based on 50G PON has lower power consumption, saves rack space and does not require special heat dissipation.

Similarly, 50G PON is also used in public Wi-Fi hotspots and wireless LAN private network backhaul. With the availability and deployment of Wi-Fi 6E and Wi-Fi 7, the bandwidth of these two backhaul scenarios will increase significantly. Wi-Fi 6E allows a single user burst rate of 9.6Gbps, while Wi-Fi 7 quadruples the throughput to nearly 40Gbps. In addition, the Wi-Fi 7 standard defines extremely low latency and jitter, which is also incorporated into the evolving 50G PON standard.

Ultimately, 50G PON is expected to become a common technology for delivering cross-network services as operators continue to converge their home, business and wholesale fiber networks onto a single ODN network. Mobile midhaul and fronthaul applications, extended IoT devices and services, wholesale fiber access to macro cellular networks, fixed wireless access (FWA) node backhaul – all of the above scenarios can theoretically be implemented using 50G PON. As operators continue to integrate different networks into a shared ODN, provide throughput and services through 50G PON, and benefit from it, more and more applications and use cases will follow.

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