In recent years, the cable industry has chewed on a plethora of technologies, architectures, and abbreviations. An example of this last “morsel” is DAA – Distributed Access Architecture. As operators attempt to create and implement their DAA strategies, it’s worthwhile to consider how the industry is today talking about Remote PHY and MACPHY architectures as options for the future cable access networks.
Networks are evolving rapidly on many fronts. The back office is transforming from purpose-built hardware and “big iron” implementations to cloud-native virtual applications (Figure 1). The DOCSIS standard itself has continued to evolve. DOCSIS 3.1 is pretty much mainstream today and, to push networks to 10G speeds, plans for DOCSIS 4.0 migration and extending the spectrum from 1.2 GHz to 1.8 GHz are already being drafted. DAA technologies such as Remote PHY and MACPHY can accelerate the major transformation from analog optics to Ethernet and IP-based transmission and converged interconnect networks (CINs) that underpin these evolutions.
As many of the developments are interconnected, operators need a package of roadmap plans to move simultaneously forward on the many parallel frontiers:
- Back office: from hardware-based CMTS and CCAP core deployments to a fully virtualized back office
- DOCSIS: from DOCSIS 3.0 to DOCSIS 4.0
- Cable access: from classical analog optics and 1-GHz HFC to CIN and 1.8-GHz HFC.
As part of these transformations, it is essential to understand the evolution of DAA from pre-standard MACPHY to Remote PHY and standardized Remote MACPHY.
Why Remote PHY is a popular first step
The first DAA step for most cable system operators has been Remote PHY. A main reason for this has been the presence of the existing CCAP core assets. DOCSIS 3.1 capable CCAP core systems were deployed widely in 2014-2015 and still had plenty of life in them as operators subsequently pondered their initial DAA strategies. Their CCAP investments would have been wasted by moving to networks based on Remote MACPHY devices (RMDs), as working capacity would have been thrown away.
There are also big architectural changes within the systems as networks migrate to DAA. The cable industry has traditionally opted for predictable, step-by-step development, avoiding major technology risks. Remote PHY enables operators to take the big step of replacing analog optics with CINs without carrying out complex reintegration of the back office simultaneously.
In addition, there were also concerns related to moving MAC functionality to the field, including questions about power consumption, as well as deploying and maintaining tens of thousands of RMDs. The common desire within the industry was to ensure a committed multivendor ecosystem to back up technology transformation, and this was achieved with Remote PHY. When Remote PHY was selected as the way forward, a solid set of specifications was published by CableLabs to guide its development and deployment.
If Remote PHY works, why move to MACPHY?
The big iron CCAP core installed base is now aging in many cases, and it needs to be gradually replaced when moving towards DOCSIS 4.0. This gives operators more freedom for strategic decisions. Today, a strong consensus has emerged that moving the back office from purpose-built hardware solutions to virtualized cloud environments can achieve a more dynamic way to manage back-office assets. The same development is taking place also in the mobile industry, and there is no reason why fixed DOCSIS networks could not follow or even lead such a transformation.
Within this context, pushing the real-time MAC processing to the field devices gives more freedom in virtualization of the back office. Distance limits are gone thanks to lower latency, more flexible centralizations can be accomplished, and there is more freedom for implementations once the real-time processes are running on the RMD itself. With the most recent systems-on-a-chip alternatives, it also looks very feasible to implement RMDs within the existing power constraints. Several vendors have achieved robust MACPHY implementations and the advanced network management tools are there to support the maintenance of the devices in the field through, e.g., automation.
DAA is a mandatory step for all coax-based network evolution strategies. It leads to 10G broadband speeds with the existing coaxial assets and enables automation through virtualization and next-generation telemetry tools. With CIN enabling converged fixed-mobile networks, operators can also lower the capex and opex per subscriber of their versatile infrastructures. All this can be achieved in a predictable manner in two steps: begin the work now with the mature DOCSIS 3.1 technology, CIN networks, and Remote PHY-based distributed access; and then start preparing for MACPHY and virtualization as the next step on the network evolution path towards 10G.