HFC Network

Remote PHY 101: Why the Industry Is Working Together to Take Things Apart

CableLabs
CableLabs Admin

Mar 9, 2021

In our previous CableLabs 101 post about Distributed Access Architecture (DAA), we discussed the benefits of distributing key network functions throughout the cable access network to optimize its performance. Today, we delve deeper into Remote PHY—one of the earliest DAA solutions that cable operators are deploying to increase their network’s bandwidth and more.

What Is Remote PHY?

PHY stands for “physical radio frequency (RF) layer,” which delivers voice, video and data via the DOCSIS® protocol over the hybrid fiber-coax (HFC) network. Media Access Control (MAC) is an example of another CCAP layer that we’ll cover in our next CableLabs 101 post.

Prior to the introduction of the DAA concept, all CCAP functions, including PHY and MAC, were integrated at the Internet provider’s cable modem termination system (CMTS)—typically located at the headend or hub site—which sends and receives data to and from the modem in your home. This data exchange is the basis for how DOCSIS technology on HFC networks works. However, the integrated CCAP approach does not maximize the potential of the cable access network.

Once we figured out how to split the PHY and MAC functions, we were then able to distribute PHY closer to the end user, resulting in increased network capacity and greater speeds. You can refresh your memory about the benefits of DAA and Distributed CCAP Architecture (DCA) here.

Remote PHY was the first documented DCA specification that we officially released in 2015, followed by Flexible MAC Architecture (FMA), released in September 2020. These solutions are complementary and have similar benefits, giving cable operators the flexibility to architect their networks the way they see fit to support future high-bandwidth services. The specifications provide guidance to our industry vendors who are manufacturing Remote PHY–compatible equipment. Just like the other DOCSIS and Coherent Optics technologies, Remote PHY and the other DCA approaches are part of the 10G toolset.

How Does Remote PHY Work?

The Remote PHY specification defines ways to separate the physical RF layer from the MAC layer that remains at the headend and describes the interfaces between them. Let’s take a closer look at how it’s done.

The PHY layer of the CCAP system is placed in something called a Remote PHY Device (RPD). An RPD is a piece of equipment usually produced by a third-party cable vendor that contains all the PHY-related circuitry, as well as the pseudowire logic that connects back to the CCAP Core, which supports full DOCSIS functionality. In other words, all this rerouting on the back end is completely hidden from customers like you. Your network will function the same as before, only much faster because the PHY layer is now located much closer to where you live.

Speaking of location, the beauty of the Remote PHY architecture lies in its flexibility to place RPDs anywhere, including optical nodes closer to the network “edge”—a cable insider’s way of saying “closer to customers’ homes.” A single node can serve just a few blocks or even a single building; therefore, each customer modem connected to that node gets a bigger chunk of the bandwidth pie, so to speak. And, of course, more available bandwidth means better customer experience!

How Does This Technology Affect Me and My Future?

You might think that it makes no difference to you how your Internet provider’s CCAP is designed—and you would be right. What does matter, however, is the noticeable difference in your Internet quality, including how fast your apps work, how quickly you can download your movies or how much lag (or lack thereof) you experience when you play an online game with your friends. Looking forward to the near future, you may be using applications that utilize holographic displays, artificial intelligence, virtual rooms, 360° fully immersive entertainment experiences and other innovative technologies that require multi-gigabit bandwidth to function seamlessly.

This is why CableLabs and our partners in the cable industry are continuously inventing new ways to mine more bandwidth out of the available RF spectrum. Thanks to specifications like Remote PHY, FMA and others, we have all the pieces in place to deliver 10G symmetrical speeds—and more—to support future innovations. Now it’s just a matter of putting it all together.

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