With the world’s first live deployment of 25G PON by Proximus and the first demo of 100G PON technology with Vodafone both taking place earlier this year, broadband technology innovators continue to demonstrate the unlimited potential of fiber.
But at this point in 2021, most fiber broadband networks around the world (fiber-to-the-home or to-the-premises) still use 2.5G-capacity GPON, although next-generation PON technologies (predominantly 10G XGS-PON) are being deployed at an accelerating rate and will be the dominant PON technology within the next few years.
With GPON and XGS-PON largely capable of handling current demand, is there really any need for a next next-generation PON?
The short answer is yes, because the increased capacity creates new opportunities for broadband providers. Not many are thinking about delivering 10-Gbps or 20-Gbps home internet connectivity—at least not yet. But a 25G pipe solves some problems and opens some new doors for operators.
What’s the use?
The most obvious, and the most compelling from the point of view of costs, is convergence. Many operators today run separate networks for residential services, business services, and backhaul. The savings from having residential FTTH and mobile transport on the same network, for example, are significant, halving total costs of ownership for mobile transport over five years. 25G PON can easily support mobile transport and business services and still have capacity left for residential broadband.
With regards to residential services, 25G PON is primarily an opportunity to design a greenfield network with a high split ratio and connect more users on a single PON. But operators could also decide to differentiate with premium multi-gigabit offers in the near-future. With the pace of change in the entertainment sector with cloud gaming, virtual reality, and interactive video, multi-gigabit residential broadband may become a standard sooner than we think.
Another factor driving convergence is the arrival of 5G mobile. Mobile operators have realized that FTTH networks can provide 5G transport, letting them deploy more quickly and cheaply. The evolution of PON technologies will ensure that the transport requirements are met. 10G PON, 25G PON, and beyond ensure that PON has enough capacity for dense 5G deployments. In addition to speed, other innovations have enabled lower latency on a PON and can efficiently separate fixed and mobile traffic, so that mobile transport traffic has the quality of service it needs.
Then there are business services. Fiber is increasingly being used to connect business premises to the internet and as a local area network to connect all types of devices within the premise. Fiber is attractive because it supports very high symmetrical bit rates, it is the most energy efficient access technology, and it is the most cost-effective. Business services are lucrative, generating high revenues with good margins, and operators are considering how to differentiate their enterprise offerings to create more revenues. With increasing use of video and cloud computing applications, the gold standard for business broadband is becoming 10 Gbps. To connect multiple businesses with true 10-Gbps speeds, XGS-PON may not be enough, opening the door for 25G PON.
Greater capacity also creates new revenue opportunities through network sharing. It’s perhaps no surprise that many operators signing up to the 25GS-PON MSA group are wholesale providers. Wholesale needs big pipes to meet the demands of tenants and applications. 25G PON is ideally suited to software-defined network slicing, which can be used to maximize network utilization and differentiate quality of service for each tenant or service.
25G PON: the best next step
The evolution of PON has always depended on the existence of mature, high-volume technologies that would drive down the cost—a key condition for any new access technology to be massively adopted. In the past, PON relied on long-haul optical technologies. Today, there is a slightly different but highly efficient path that comes from the data center world. The increased demand for data center capacity has begun to drive large volumes and reduced costs on 25G components. This is the mature ecosystem that 25G PON leverages and that provides the baseline for further evolution to 50G and 100G PON.
25G PON makes the most sense as the next generation of PON for several reasons. Besides the high capacity, cost-efficiency, and compelling use cases described above, 25G PON is simple to introduce.
Co-existence is a major requirement for graceful migrations that avoid complicated (and costly) operations and disrupted services. One of the great attributes of 25G PON is that it can seamlessly co-exist with both GPON and XGS-PON, so there can be three generations of PON on the same fiber infrastructure. There are no forced migrations, no restrictions, and no overlay deployments.
Beyond 25G PON
Going beyond 25G PON is more of a quantum leap than an evolution because it will require a new generation of components. Running at such high speeds has technical challenges, and the options to address these challenges increase cost and complexity.
50G PON, which is also under standardization, will be able to use some 25-Gbps components, but not everything. For example, if a 25-Gbps transmitter is used to transmit at 50 Gbps, the signal will be distorted. There are two possible solutions: either use a 50-Gbps transmitter or a 25-Gbps transmitter in combination with amplifiers. In both cases the cost is higher. In receivers, 50G PON will be able to leverage 25-Gbps components but will need advanced digital signal processing (DSP) to achieve 50-Gbps bit rates with 25-Gbps optics. These DSPs will need to be integrated on a chip and reach high volumes to drive down the cost, and this could take 7-8 years. Co-existence is also proving a challenge. The current ITU standard for 50G PON enables co-existence with GPON or XGS-PON but not both at the same time. None of this is an issue for 25G PON.
As for 100G PON, trials may have taken place with Vodafone, but the actual commercial availability is still far away. 100G PON will need advanced DSPs, just like 50G PON, and these are not available yet. Once they become available for 50G PON, the step to 100G PON will be straightforward.
The beauty of PON evolution is not only in higher speeds. With every new generation of PON technology, new techniques become available to improve the overall performance: lower latency, software-defined automation, and so on. The 100G PON prototype tested with Vodafone also included flexible-rate transmission, which is an industry-first in a PON network. Flexible-rate transmission groups ONUs with similar physical characteristics (e.g., loss or dispersion), so these groups benefit from dedicated, optimized performance, e.g., more efficient data transmission, lower latency, lower power. But 100G PON comes with even higher power loss budgets than 50G, and this is an ongoing area of research.
New power of fiber
It is important to keep pushing the boundaries of PON technology and make sure today’s fiber networks will be usable for many years to come. After all, there will be no relenting in demand for faster, more responsive, and immersive internet services. 25G PON is ready to go, clearing a path for 50G and 100G in the next couple of decades. While they require much more research, development of a new generation of lasers, optical amplifiers and DSPs, and further optimization to reach maturity and an acceptable cost point, they will ensure fiber networks become a unified infrastructure to connect everything, everywhere.
Ana Pesovic is marketing director, Fixed Networks, at Nokia. She has more than 20 years of experience in fiber access technologies.