HFC Network

A “101” on DOCSIS® Technology: The Heart of Cable Broadband

Oct 14, 2020

Welcome to the first installment of our CableLabs 101 series about a suite of breakthrough technologies that are instrumental in the path toward the cable industry’s 10G vision—a new era of connectivity that will revolutionize the way we live, work, learn and play. These technologies work together to further expand the capabilities of cable’s hybrid fiber coaxial (HFC) network by increasing connection speeds and capacity, lowering latency and enhancing network reliability and security to meet cable customers’ needs for many years to come.

Let’s begin with the DOCSIS specification that started it all. Without DOCSIS technology, cable broadband would look much different.


Initially released by CableLabs in 1997, DOCSIS—or Data Over Cable Service Interface Specification—is the technology that enables broadband internet service over an HFC network, now used by hundreds of millions of residential and business customers around the globe. It is essentially the set of specifications that allows different cable industry vendors to design interoperable cable modems (the piece of network equipment that sits in the home) and cable modem termination systems (CMTSs—the network equipment that sits in the cable operator’s hub site). The CMTS is a head-end traffic controller that routes data between the modem in the home and the internet.

DOCSIS technology helped usher in the era of broadband and “always on” internet connections, enabling a wave of innovation that continues to this day.  With DOCSIS technology, internet customers were no longer forced to use dial-up solutions that tied up home phone lines and probably caused a significant spike in family feuds. The DOCSIS solution changed everything. Not only did it allow for an “always-on” cable connection (no dial-up required!), it was also significantly faster than dial up.  We’ll talk about connection speed—along with capacity, latency and other network performance metrics—and how they affect you a little later in this article.

How Does It Work?

DOCSIS technology governs how data is transmitted over the HFC network. To understand how it works, we need to start with the HFC network—the physical infrastructure that most cable companies use to provide high-speed internet connectivity to their customers. As the name suggests, the HFC network is composed of two parts: the fiber optical network and the coaxial network. HFC networks are predominantly fiber, as illustrated in our recent blog post. The remaining portion of the HFC network is coaxial cable. The coaxial network is connected to the optical fiber network at a “fiber node,” where the (fiber) optical signals are converted to radio frequency electrical signals for transmission over the coaxial network to the subscriber’s home. The HFC network seamlessly transmits data from the CMTS to your cable modem (we call this “downstream” or “download” traffic) or from your modem back to the CMTS (“upstream” or “upload”). In turn, the CMTS is connected to the internet via a set of routers in the service provider’s network.

Think of the HFC network as a “highway” and the data as traffic moving in “lanes” in either direction. In the downstream direction, DOCSIS devices translate the data from the internet into signals carried on the fiber optic portion of the HFC network and then down the coaxial network to your modem. On the upstream, the data that you upload is sent back up the network on a separate upstream “lane.” Traditionally, this “highway” has had more lanes dedicated to the downstream traffic than upstream, which matches current customer traffic patterns. All of this is about to change with the 10G vision, which strives toward symmetrical upstream and downstream service speeds.

How Has This Technology Evolved?

DOCSIS technology has come a long way since 1997. Over the years, it has undergone a few iterations, through versions 1.0, 1.1, 2.0 and 3.0 to 3.1. As DOCSIS has evolved, it has gotten faster by adding more lanes in each direction and it has become more energy-efficient as well. Along the way, several additions to the base technology have been continuously added. These include enabling lower latencies, increased security of the traffic, and tools to make the network more reliable. Today’s cable networks leverage DOCSIS 3.1 technology, which has enabled the widespread availability of 1 Gbps cable broadband services, allowing us to easily enjoy services like 4K video, faster downloads, seamless online gaming and video calls.

DOCSIS 4.0, released in March 2020, is another stepping stone toward that 10G vision. It will quadruple the upstream capacity to 6 Gbps, to match changing data traffic patterns and open doors to even more gigabit services, such as innovative videoconferencing applications and more. DOCSIS 4.0 equipment is still in the process of being developed and is seeing great progress each day toward device certification. Once certification is complete, cable vendors will start mass-producing DOCSIS 4.0-compatible equipment. With the widespread deployment of DOCSIS 4.0 technology, cable operators will have the ability to offer symmetrical multigigabit broadband services over their HFC networks.

How Does This Technology Affect Me and My Future?

All this talk about connection speeds, low latency, reliability and other performance metrics matter to us technologists because it’s how we gauge progress. But it’s so much more than giga-this and giga-that. These metrics will directly impact your future in a real, tangible way.

Over the past two decades, high-speed internet connectivity went from an obscure tech geek novelty to an important part of modern life. We are now streaming in 4K, collaborating on video chat, playing online games with people around the world, driving connected cars and so on. Continuous advancements in DOCSIS technologies are helping make this reality possible by increasing download and upload speeds, lowering latency—or lag—for a more seamless experience, and improving reliability and security to protect our online information.

DOCSIS 4.0 technology will enable symmetrical multigigabit services, ushering in a new wave of innovation across industries and applications, including healthcare, education, entertainment, collaboration technologies, autonomous vehicles and many more. In the near future, we will see advanced health monitoring services, immersive learning and work applications, visually rich VR/AR, holodecks, omnipresent AI assistants and other game-changing innovations that we haven’t even thought of yet. In many ways, the reach and flexibility of cable’s HFC infrastructure is the backbone of our 10G future, and DOCSIS—in combination with other advanced network technologies—is key to helping us reach this Near Future.