All too often, people equate the word “cable” with “coax” (aka coaxial cable), the insulated copper cable that cable companies have historically used to connect devices around the world and deliver information and entertainment. “Cable,” however, isn’t just made of metal but also of glass: fiber-optic cable (aka fiber).
The use of fiber in cable networks is nothing new. In fact, it’s been a dominant part of the industry for decades — hence, the F in HFC, which is short for hybrid fiber coax, the network architecture used in modern cable networks. That fiber is taking on increasing importance as cable operators develop new ways to leverage its capabilities. Leveraging the capabilities of that fiber is an essential part of evolving cable networks.
Cable operators are transitioning the fiber portions of their networks from analog to digital, increasing capacity and reliability. At the same time, they are pushing fiber deeper into the network and closer to the customer — and, in some cases, all the way to the customer. When that happens, it is referred to as fiber to the premises (FTTP), typically using passive optical network (PON) technology. But in all cases, fiber’s ability to scale to higher and higher capacities to support the applications of today and tomorrow is and will be a critical component for success across the cable industry.
In case you missed it, fiber’s increasing importance was on display at SCTE TechExpo 2024 this year in Atlanta. Multiple sessions covered a variety of topics ranging from the challenges of deploying FTTP, improving PON operations and management, and the history and evolution of PON technology.
Three of those sessions are now available to watch on demand:
- Practical Strategies for Deploying FTTH
- Boosting Performance: PNM for Optical Networks
- Operationalizing and Automating PON
An additional session went a step further to examine an emerging new technology that holds the promise of revolutionizing how we use the fiber in cable networks: coherent PON (CPON).
What Is CPON?
In May 2023, CableLabs announced the release of a new specification: the Coherent PON Architecture Specification. That specification provided an overview of how coherent technology could be applied to a PON to dramatically increase its potential: leveraging the improved sensitivity of coherent detection to improve spectral efficiency (which increases network capacity) while simultaneously extending the reach of the network across greater distances and higher split ratios.
The objective of CPON as laid out in that specification is to support 100 Gbps of capacity on a single wavelength that can be shared by up to 512 end users at today’s typical PON distances. Alternatively, CPON can be used to extend the reach of the network to 80 kilometers with fewer end users (in other words, a lower split ratio). Both of these features make the technology uniquely suited to existing cable operator networks without impacting its usefulness for non-cable operators, which promotes interoperability, scale and competition. Further, the CPON Architecture Specification envisions potential use cases for those enhanced capabilities, ranging from running fiber directly to business and residential customers to the aggregation of other networks’ devices, such as Remote PHY devices for DOCSIS 4.0 deployments or mobile xHaul equipment.
Of course, that was just the first step in bringing this new technology to life: CableLabs has continued to work with our members and the manufacturer community to develop the suite of specifications that will enable the development and deployment of interoperable devices. Extensive progress has been made to:
- refine operator requirements
- review contributions and proposals from the manufacturer community, cable operators and CableLabs engineers
- develop consensus around how the technology will work
And although that work isn’t yet finished, we’re starting to get a sense of what it might look like.
A CPON Vision
One of the TechExpo presentations was based on a paper titled “What Could You Do With 100 GBPS Coherent PON?” by Edward W. Boyd (Ciena), John Bender (GCI), Kevin Noll (CableLabs) and James Harley (Ciena). In this paper, the authors explore a possible CPON network that:
- has a full 100 Gbps of capacity (unlike other PON technologies, which operate at less than their advertised rate).
- supports tuning and multiple wavelengths in the C-band to enable CPON devices to operate over existing dense wave division multiplexing (DWDM) networks.
- adapts to different network deployment scenarios.
- supports the expansion of total network capacity in the future.
The paper also looks at how CPON could be applied to a variety of use cases, and how it can do so cost-effectively.
Enabling the CPON Vision
Although that presentation provided a vision of what CPON might look like when completed, another presentation looked at some other essential elements of CPON, including methods for keeping costs down and enabling burst operation (something new to coherent technology but a key part of the operation of a PON). That presentation was based on a paper titled “Unleashing the Power of Coherent Optical Technology,” authored by several CableLabs engineers: Haipeng Zhang, Zhensheng (Steve) Jia and L. Alberto Campos.
This paper examines several key topics:
- how to keep optical network unit (ONU) costs low using various technologies
- how to handle upstream burst transmissions efficiently and effectively
- how to adapt to different user requirements
- how to ensure CPON resilience and reliability to support a broader range of use cases than today’s PON systems
Getting Involved
Although these papers may or may not represent the technologies that will be a part of the final CPON solution, they do provide examples of the types of requirements and technology proposals that the CableLabs CPON Working Group is reviewing even now.
Many decisions have already been made, with the group moving at an impressively fast clip to wrap up key specification work in the coming year, but there’s still an opportunity to influence this emerging new technology. If you have the time and the expertise, we’re always looking to add more contributors with new perspectives and ideas to the group.
If that describes you and you’d like to get involved, please contact us using this form. Otherwise, keep an eye on this space as we continue to define this next-generation technology.