Optical Networking, Redefined.
March 13, 2024

Trends in DAA Expansions and the Potential of 25G DOCSIS – an Optical (and Tunable) Transceiver Perspective

The more things change, the more they stay the same. Anywhere you look, subscriber demand for increased bandwidth, speed and reliability is constantly growing. And that means continued pressure on MSOs and other cable operators. For them, the mission is always to do more with what they have while making smart investments in the right infrastructure for the future. It’s a delicate balancing act.

For many cable network operators, Distributed Access Architecture (DAA) continues to be a preferred mechanism by which they can achieve the greater bandwidth, reliability and scalability they seek. DAA deployments and expansions help MSOs and other cable operators keep up with growing adoption of videoconferencing, telehealth, IP-based smart home platforms and other data-intensive applications. In this blog, we delve into the intricacies of DAA evolution from an optical transceiver perspective, exploring its benefits, key considerations, and the forward-looking shift to DOCSIS 4.0 and 25G technology, which DAA will play a vital role in supporting.

A Quick DAA Refresher

In traditional centralized access architecture (CAA), all network functions and equipment existed in the headend facility. DAA represents a paradigm shift by decentralizing and virtualizing headend and network functions to create software-defined networks (SDNs) that enhance performance and scalability.

In more practical terms, DAA distributes select network functions closer to end-users, to digital fiber nodes in the field. With Remote PHY (R-PHY), the DOCSIS physical (PHY) layer of the Cable Modem Termination System (CMTS) is relocated out of the headend to the fiber node, converting the previous analog connections between the headend and the nodes into digital ones. This enables a far more efficient use of existing cable infrastructure, supporting augmented capacity via higher orders of modulation. Additionally, because RF signals now begin at the node versus at the headend, DAA improves quality of service for end-users by lowering signal-to-noise ratio (SNR).

Remote MAC-PHY (RMACPHY) goes even further, moving both the DOCSIS PHY and the DOCSIS media access control (MAC) functions out of the headend. Importantly, R-PHY and RMACPHY support full duplex DOCSIS, which enables symmetric multi-Gigabit upstream and downstream services over existing HFC networks. That’s going to be key for MSOs and other cable network operators as they look to ensure their competitiveness in the wider service provider industry. In fact, in the summer of 2023, Comcast reached a milestone of 100,000 R-PHY nodes installed across its HFC/DOCSIS network. According to the company, these nodes will be instrumental in supporting its implementation of full duplex DOCSIS 4.0 and 10G. Overall, by moving certain network functions out of the headend, DAA enhances performance, scalability, and flexibility as node counts increase and more traffic is placed onto the network.

As MSOs and network operators embrace DAA, especially to build out 10G networks, the choice of optical transceivers becomes increasingly critical, with tunable transceivers emerging as a pivotal component. As Keith Habberfield, our SVP of Sales and Marketing said recently in a press release announcing a partnership between us and Charter Communications for their DAA network expansion, “Optics and their components are the integration point that enables networks to communicate.”

Tunable Transceivers Improve Flexibility, Reduce TCO for Cable Operators Using DAA

As cable operators look to deploy 10G networks utilizing DAA, tunable transceivers offer unparalleled wavelength agility, enabling operators to dynamically adjust wavelengths to suit varying network requirements. Fixed-channel transceivers significantly constrain scalability and cost savings for MSOs and other network operators as multiple backups are needed to minimize network downtime in a DWDM environment, given the range of wavelengths present. By contrast, tunable transceivers allow on-site wavelength adjustment, transcending the limitations of traditional fixed-channel transceivers. Even though tunable transceivers tend to cost more than their fixed-channel counterparts, in the longer run, they minimize cost and maximize a network operator’s ability to scale in response to the needs of a growing network. By simplifying inventory management, future-proofing network infrastructure, and optimizing optical network flexibility, tunable transceivers will serve as a cornerstone in the successful implementation of DAA.

It’s not just theory that we base this conclusion on, but a real-world example. At Precision OT, we offer 10G DWDM tunable optics, which Charter recently partnered with us to deploy in their DAA network expansion (alongside other products of ours, which include our Bluetooth® DWDM tuning modules). Our products will play a crucial role in Charter’s plans to leverage R-PHY to deliver download speeds of 5 Gbps across most of its footprint (with top tier speeds of 10 Gbps using extended spectrum (ESD) DOCSIS 4.0) by 2025. With our tunable optics and tuning modules, we give our customers the agility and flexibility they need right now to carry out complex, multi-phase upgrades to their networks leveraging DAA.

DAA Supports Cable Operators in the Shift to 25G DOCSIS, But There’s a Challenge

As LightReading notes, there’s a growing consensus in the cable operator industry that “a baseline move to DAA will put cable operators in a position to upgrade to DOCSIS 4.0 as well as FTTP.” While no one is suggesting cable operators must choose between DOCSIS 4.0 or FTTP, evolving HFC networks to DAA will be critical to meet the demands of tomorrow.

For cable operators, one of those needs will be in ensuring competitiveness with advancements in the FTTH PON sector that are enabling it to offer 25 or even 50 Gbps services. Already, HFC network operators have a pathway to 10 Gbps with DOCSIS 3.1, so network operators adopting DOCSIS 4.0 are already thinking ahead to 25 Gbps DOCSIS. In fact, some are already examining solutions for achieving 3 GHz, 25G ESD DOCSIS 4.0. To date, however, this discussion has been more theoretical than practical. The current distance limitations of existing 25G DWDM solutions have posed technical challenges that have delayed the viability of 25G networks in real world scenarios that often require links of 40km and beyond.

While current 10G DWDM transceivers enable transmission distances of 40 km and beyond (hence their popularity in current DAA network expansions), existing 25G DWDM options limit network operators to 10-15km unless specialized equipment is used. This constraint has hamstrung real-world efforts to bring 25G into their networks given that most access networks feature links of 40km or further. As the bandwidth needs of end-users only continue to escalate, it’s important to give network operators the capability and the freedom of choice to leverage 25G DWDM optics within their DAA networks as needed.

That’s why, in October 2023, we announced a break-through solution for overcoming the gap between link distance and performance. It’s our proprietary GeneseeTM Dispersion Compensation ASIC-enabled (application-specified integrated circuit) technology, which has enabled a cutting-edge, 25G tunable module that enables users to reach distances of 40km and beyond without leveraging specialized equipment.

At Precision OT, our business is to forecast the needs of the customers we work with, delivering solutions that not only benefit them today, but also set them up for success tomorrow. The world of DAA evolution is exciting with significant advancements just around the corner. With our engineering and systems integration expertise, we listen to our customers’ goals and work with them to deliver the rigorously tested solutions that will empower them on their journey.

In closing, here’s what Greg Mott, SVP Field Operations Engineering at Charter Communications had to say about our partnership: “The team at Precision OT has a clear understanding of Charter’s broadband network evolution — cost, scale, and speed — and their mix of solutions will help us deliver on our commitments across our 41-state service area.”

If you’d like to find out more about how we can help you on your network evolution journey, contact us today.