Why 50G PON Looks Like a Clear Winner vs 25G

A guest post by LightCounting.

LightCounting looks back to predict the future

Deployments of FTTx accelerated in 2021 and LightCounting raised its forecast for this market segment in 2022-2027, driven by the strong uptake of 10G PON.

With 10G PON deployment well underway, the industry is looking at what will come next. What is the best option?

25G, 50G, and 100G/200G PONs are now being considered as successors to 10G PON by the IEEE, ITU, FSAN and other standards bodies, as summarized in Table 1. Symmetric 25G PON has no standard but instead an active MSA with 17 members including AOi, Ciena, Nokia, Chunghwa, and AT&T.

IEEE’s 802.3ca ‘50G-EPON task force’ began in January 2016 focused on developing N*25Gbps single/multiple wavelength symmetric service, with N up to 4 for a maximal 100G symmetric EPON based on channel bonding. By 2018, the scope was narrowed to 25G and 50G only, and 100G EPON was dropped and the objectives solidified on these targets:

• 25 Gb/s in downstream and 10 Gb/s or 25 Gb/s in upstream (25G-EPON)
• 50 Gb/s in downstream and 10 Gb/s, 25 Gb/s, or 50 Gb/s in upstream (50G-EPON)

The 50G-EPON standard, called “IEEE Std 802.3ca-2020”, was completed in June 2020.

Similarly, ITU-T with support from FSAN has a project designated as ‘G.hsp.50G’ whose goal is 50G-PON as a successor to XG(S)-PON. This work was consented to in April 2021 and received final approval in September 2021.

Huawei has gone all-in on 50G-PON, supported by the big three Chinese network operators. Huawei demonstrated an early prototype of 50G PON at Mobile World Congress 2019 based on mature 25G optical components. Huawei’s prototype delivered 50-Gbps transmission over a single wavelength through fiber dispersion compensation and transmitter/receiver bandwidth compensation technologies on the physical PON links. It had a reach of over 20 km, operated over existing fibers and filters, and was fully compatible with XG(S)-PON and 10G-EPON.

What does history tell us?

It is not the first time the industry is debating the next data rate. We have seen debates on 40GbE vs. 100GbE in the past and more recently on 200GbE vs. 400GbE. What we learned from these examples so far is summarized below:

• The highest data rate products will win; it will capture a larger market and have a longer lifecycle.
• Choices made by the largest customers will define a path for the market.
• Price reductions will continue to surprise us; the highest volume product will have the lowest cost.

Let us illustrate these observations with data collected from the market and by the most recent forecast. Figure 1 compares shipments of single mode fiber (SMF) 40GbE and 100GbE transceivers. It clearly illustrates the first point in the list above.

Prices of 100GbE and higher speed Ethernet SMF transceivers have declined to about US$1/Gbit/s – well ahead of anyone’s expectations. Competition among suppliers and high shipment volumes has enabled such a price reductions.

Will small businesses and consumers need 50G, or is 25G enough? 

The ongoing digital transformation of industries, enabled by AI and other cloud-based services, certainly benefits from higher bandwidth connectivity. Large companies can afford to lease private lines, but 25/50G PON will be more cost effective solutions for small and mid-size businesses.

Will this be too much bandwidth for consumers? Probably, but this will not stop network operators from offering such services.

In December 2012, Google Fiber project was announced with an objective to offer 1-Gbit/s connectivity to consumers. This was ridiculously high bandwidth at the time. The first users were only using this much bandwidth to run speed tests to see if it is really as fast as advertised.

Less than 10 years later, 1 Gbit/s is a standard FTTH offering in many countries and many of us would probably pay a bit extra for even higher speed connectivity. Apart from video games, none of the applications need such high bandwidth by itself, but all of them collectively could certainly use higher speeds. Having just two people on separate video calls at the same time can fill up current broadband offerings, even before one of the kids starts to upload a new TikTok video.

If service providers start offering 3-Gbit/s or 5-Gbit/s broadband, consumers (or their children) will find ways to use all of it. We do not know what these applications will be even in 3 years from now, not to mention by the end of this decade.

If you have any doubts, take another look at your smartphone. It includes a processor chip that would be fit for a supercomputer a decade ago. Do not underestimate the relentless progress of technology and inspiring creativity of the engineers.

What do network operators think?

China accounts for more than 70% of GPON ONUs deployed globally so far. The installation of fiber cables is the most expensive part of FTTH deployment. Once the fiber is available, upgrades to higher speeds are not as costly. China certainly benefited from the government policy of having all new apartment buildings equipped with fiber. The country reported 550 million FTTH subscribers in early 2022, and leads the world in the adoption of 10G PON. So there is every reason to expect China will be first and biggest in deployment of next-generation PON as well.

And the three large Chinese operators have made it clear that they are moving to 50G PON after 10G PON.

China Mobile spokesperson Li Junwei said in April 2021 and again in May 2022 that 50G PON is the preferred next-generation choice after XGS-PON. In April 2021, a trial was conducted that delivered 41 Gbit/s downstream and 16 Gbit/s upstream, with average upstream latency of about 80 μs. And at OFC 2022, a field trial was reported using 50G TDM-PON for 5G smallcell backhaul. China Mobile will begin 50G PON field trials in 2023 and expects that commercial use will begin around 2025. 

China Telecom spokesperson Zhang Dezhi said in 2021 that, “50G PON is the future of the PON, for three reaons: 50G TMD PON can unify of the next generation of different PON technologies, it can coexist with 10G EPON or XG(S)-PON, and it increases capacity by a factor of five versus 10G PON, which better supports new business requirements such as 4K, VR/AR.”

China Unicom has said little publicly about 25 vs 50G PON, but it is highly unlikely that it would select a different technology than China Mobile, China Telecom, and suppliers that Huawei are backing.

Among European countries, operators have been testing protoype next-gen PONs for some time already, and many of them also favor 50G PON as the successor to 10G PON:

• Orange head of fixed access networks Jesús Vallejo said in March 2022 that 50G PON has become the industry’s consensus choice of next-generation PON. Orange favors 50G PON because it allows easy reuse of existing network resources while evolving towards 50G PON, he said.
• Swisscom tested a 50G PON in October 2020, upgrading an existing OLT to 50G PON, and achieving 50-Gbit/s downstream speed and 25G upstream on a fixed network. A spokesperson said that 50G speeds would serve small businesses and 5G mobile traffic initially.
• Telefonica’s CTIO Enrique Blanco said in September 2021 that 50G PON was his company’s choice for fixed access beyond current 10G XGS PON deployments
• Turkcell said that it is planning to deploy 50G PON in 2024.
• Vodafone trialed a 100G PON in 2021, and seems likely to transition from 10G PON directly to 100G, some time in the distant future. A Vodafone technology manager said in 2020 that, “10G PON would probably be sufficient until 2030.”

The UK and Germany have the most catching up to do among the Western European countries in terms of fiber broadband deployment.

US operators have not been so quick to jump on the 50G bandwagon, but at 120 million or so fixed broadband users, the US has roughly 10% of the 1.2 billion global fixed broadband users.  And the fact is, technology choices made by AT&T, Comcast, and Verizon won’t determine the direction of the industry globally, just as they didn’t in the previous upgrade cycle. Verizon went down an evolutionary dead-end by adopting NG-PON2 several years ago, and AT&T recently joined the 25GS-PON MSA, and just announced it had completed a 25G symmetric PON demonstration, so they seem determined to go their own way again.

25G versus 50G PON adoption – LightCounting’s prediction

With these history lessons in mind, LightCounting offers its estimate for future shipments of 25G and 50G PON ONUs, illustrated in Figure 3.

With China’s backing we believe that 50G PON will emerge as a clear winner versus 25G in terms of total units shipped, starting with the very first deployments of both 25G and 50G PON. All the largest customers – China Mobile, China Telecom, China Unicom, and several European operators – have selected 50G PON for their deployments. Several service providers in North America and Europe may prefer 25G PON, but the scale of these deployment will be relatively small compared to 50G PON deployments.

Disclaimer: Any views and/or opinions expressed in this post by individual authors or contributors are their personal views and/or opinions and do not necessarily reflect the views and/or opinions of Huawei Technologies.