A fundamental enabler in connecting people around the globe, DOCSIS technology has empowered millions to live, work, learn and play. Since the days of the first DOCSIS 1.0 cable modems (CMs) almost 30 years ago, DOCSIS technology has continued to evolve, benefitting from a robust ecosystem of operators and vendors working together with CableLabs to develop technologies that enable differentiated services.

Just in the last decade, operators have moved from DOCSIS 3.0 technology to deploying DOCSIS 3.1 technology at scale. Now, in 2024 and going into 2025, operators are evaluating, starting initial deployments and rolling out DOCSIS 4.0 networks.

Because DOCSIS networks always provide backward compatibility, older modems can coexist and provide service to customers even after the operator has moved ahead to newer technology. This is critical as modems often live in the network for many years.

Work at CableLabs is underway to define the future of DOCSIS networks and the technology’s role in our broader network strategy. For a better understanding of what’s ahead, let’s discuss some of the recent evolutionary steps in the DOCSIS technology ecosystem.

What Is DOCSIS 3.0?

DOCSIS 3.0 networks introduced channel bonding and allowed operators to bond multiple single carrier quadrature amplitude modulation (SC-QAM) channels together (in both the upstream and downstream directions) to increase the available speeds at the CM. A DOCSIS 3.0 CM with 32 SC-QAM channels in the downstream and four SC-QAM channels in the upstream could theoretically get a peak throughput of 1 Gbps/100 Mbps (downstream/upstream) on the network, though actual service tiers offered on individual networks may have differed.

What Is DOCSIS 3.1?

DOCSIS 3.1 technology introduced orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) technology. A DOCSIS 3.1 CM, typically with two OFDM channels and 32 SC-QAM channels in the downstream and two OFDMA channels and four SC-QAM channels in the upstream, theoretically would get to a throughput of 5 Gbps/1.7 Gbps on the network. Actual service tiers offered by operators would be dependent on their network configuration and channels and service tiers enabled.

DOCSIS 3.1 technology allowed operators to enable gigabit and multigigabit service offerings (downstream) in their markets. Depending on the operator upgrades to their outside plant, the upstream capacities could range from 100 to 250 Mbps on a low-split plant, to 250 to 575 Mbps on a mid-split plant, to 1.5 to 1.7 Gbps on a high-split plant.

What Is DOCSIS 3.1 Plus?

In the last year, vendors have built DOCSIS 3.1 cable modems with additional downstream channel capabilities, going up from two, to four or even five OFDM channels. This is a welcome product extension beyond the minimum device capabilities described in the DOCSIS 3.1 specifications.

CableLabs, along with our member operators in the industry and NCTA, are coalescing around the term DOCSIS 3.1 Plus (DOCSIS 3.1+) CM to identify this new class of modems. DOCSIS 3.1 Plus CMs will enable up to 8 or 9 Gbps on the downstream — again, depending on the spectrum available in the cable plant for an operator. Typically, a software upgrade is needed on the CMTS to enable the additional channels. Alternatively, an operator can also seed the network with DOCSIS 4.0 CMs, which have a minimum of five OFDM channels, on existing DOCSIS 3.1 CMTS to support similar increases in downstream speeds.

What Is DOCSIS 4.0?

DOCSIS 4.0 technology is the latest generation of high-speed broadband solutions over hybrid fiber coax (HFC) networks. DOCSIS 4.0 technology catapults the broadband network speeds up to 10 Gbps downstream and 6 Gbps upstream.

DOCSIS 4.0 specifications build on the OFDM and OFDMA technology. It increases the spectrum available for the upstream and downstream and then fills them with more OFDM and OFDMA channels. The technology allows different outside plant upgrade paths to operators, a frequency division duplex (FDD) mode or a full duplex (FDX) mode of operation. For FDD mode, there are different upstream/downstream splits an operator can choose for their outside plant, each providing an increase in upstream/downstream capacity. FDX mode also enables flexibility in how operators size and utilize the FDX portion of the spectrum to meet the needs of their customers.

In an FDD plant, for an FDD CM, the upstream capacities could range from 4.2 Gbps (on a UHS-396 MHz plant), to 6 Gbps on a (UHS-684 MHz plant) and the downstream capacities could range from 9-10 Gbps. In an FDX plant, an FDX CM also can reach up to 6 Gbps on the upstream and 9-10 Gbps or more on the downstream. This is assuming a DOCSIS 4.0 CM has the required minimum support for five OFDM downstream channels and seven OFDMA channels. A CM with more channels and on a plant where the additional spectrum is enabled could get downstream speeds beyond 10 Gbps.

Current product developments also enable devices that can operate on both types of networks — either FDD or FDX (albeit not at the same time, as the outside plant will be configured for either one mode of operation or the other). In addition, a DOCSIS 3.1 CM can also be software upgraded to participate in an FDX network, known as an FDX-Limited or an FDX-L CM, with limited capabilities for operating within the FDX band. Though this CM’s peak speeds remain the same, it allows operators to use the FDX spectrum flexibly, for both DOCSIS 3.1 CMs and DOCSIS 4.0 CMs.

The DOCSIS Technology Evolution

CableLabs has hosted nine DOCSIS 4.0 Interop·Labs events since July of 2023, and more are planned for 2025. Each event offers a new, up-close look into how DOCSIS 4.0 equipment is maturing. Operators are busy evaluating and testing the different components that will need to be upgraded for a DOCSIS 4.0 network — taps, amplifiers, RPDs, CCAP cores and modems.

The industry remains focused on implementing and deploying the DOCSIS 4.0 technology into the broadband networks. Large-scale deployment of DOCSIS 4.0 technology will bring customers into the 10G era in the near future.

So, what's next? What will the next generation of DOCSIS technology look like?

Continuing Industry Collaboration

As we shift from the speed era into the experience and adaptive eras — an evolution highlighted in CableLabs’ Technology Vision — DOCSIS technology will continue to evolve as well. The cable operator community, the vendor community and CableLabs have all been thinking and conducting research on how DOCSIS networks should move forward for the next big leap in broadband technology.

There is much work to be done to define new generations of DOCSIS technology and what it will truly look like. As always, CableLabs — which owns the DOCSIS trademark — will work closely with its members and working groups to oversee the development of future versions of the technology.

The impact to the outside plant and the physical characteristics of the coax are important considerations. The technology development work will include analysis and decisions on the spectrum range we ultimately target (for example, 3 GHz or 6 GHz or 7 GHz), where the upstream/downstream/full duplex regions will be, as well as what the underlying physical layer technology (fidelity requirements, channel sizes, FEC, etc.) and what the potential MAC layer technology improvements are going to be.

It’s an exciting time to be in the connectivity business! CableLabs looks forward to collaborating with the ecosystem on future developments for DOCSIS technology.

Follow the CableLabs blog to stay up to date on these developments and our Interop·Labs events.