DOCSIS 4.0 is the next-generation, high-bandwidth standard that is enabling cable companies, like Comcast and Charter, to enhance their networks and modems to better compete with the end-to-end fiber optic connectivity being delivered by fiber to the home (FTTH) network providers. The shift to DOCSIS 4.0 is being driven by consumer demand for higher data rates, coupled with a desire from the cable companies to preserve and grow their 75+ million broadband subscribers across the United States.
DOCSIS 4.0 is a hybrid fiber-coaxial (HFC) network evolution, which has the ability to deliver multi-gigabit, symmetrical speeds. The DOCSIS 4.0 specification is designed to enable up to 10 gigabit per second (Gbps) downstream capacity and 6 Gbps upstream capacity.
Dgtl Infra provides an in-depth overview of DOCSIS 4.0, including its release date, modem, and architectures – namely Full Duplex (FDX) and Extended Spectrum DOCSIS (ESD). Additionally, we review the latest DOCSIS 4.0-related developments from the largest cable companies like Comcast (Xfinity), Charter (Spectrum), Cox, and Cable One. Finally, Dgtl Infra breaks down important comparisons between DOCSIS 3.1 vs 4.0 and DOCSIS 4.0 vs Fiber to the Home (FTTH).
DOCSIS 4.0
DOCSIS (Data Over Cable Service Interface Specification) 4.0 is a hybrid fiber-coaxial (HFC) network evolution, which has the ability to deliver multi-gigabit, symmetrical (download and upload) speeds. Specifically, the DOCSIS 4.0 specification is designed to enable up to 10 gigabit per second (Gbps) downstream capacity and 6 Gbps upstream capacity.
By reaching downstream rates of 10 Gbps, DOCSIS 4.0 forms a piece of the broader “10G” branding, which is the cable industry’s upgrade approach for the future of cable networks. In addition to speeds, DOCSIS 4.0 supports high reliability and security, as well as low latency connections.
DOCSIS technology “splits” the downstream and upstream spectrum that it uses for high-bandwidth data transmission over cable networks. This means that the standard’s capacity is defined by the amount of available spectrum.
To improve on prior releases, the DOCSIS 4.0 specification achieves higher capacity by enabling greater availability of spectrum, while significantly improving the efficiency of spectrum utilization. In turn, DOCSIS 4.0 can deliver multi-gigabit, symmetrical speeds.
DOCSIS 4.0 Release Date
The DOCSIS 4.0 technology standard has not set a specific release date, however, it will likely become available in networks that consumers use in late 2024 or 2025. This future timeline is dependent on cable operators working with equipment suppliers and system-on-chip (SoC) manufacturers to develop the necessary network components, as well as testing the technology in a lab environment.
To-date, the DOCSIS 4.0 technology specifications have been written, by a company called CableLabs, and the technology is now in the lab testing phase, with tests being conducted by cable companies like Comcast and Charter.
DOCSIS 4.0 Architectures
DOCSIS 4.0 is the first DOCSIS standard to incorporate both Full Duplex (FDX) and Extended Spectrum DOCSIS (ESD), which are the two primary architectures employed to improve existing hybrid fiber-coaxial (HFC) networks.
Broadly, FDX prioritizes downstream bandwidth, while ESD borrows from downstream bandwidth to allocate more spectrum to upstream bandwidth. Both of these architectures are elaborated upon below:
Full Duplex (FDX) in DOCSIS 4.0
DOCSIS 4.0 with the enablement of Full Duplex (FDX) improves capacity by transmitting both downstream spectrum and upstream spectrum on top of one another – between the 108 MHz and 684 MHz frequency range. In other words, FDX shares the same spectrum, simultaneously, which effectively doubles the spectral efficiency.
As illustrated below, the red “FDX” boxes represent downstream spectrum and the dark blue “D4.0 FDX” boxes represent upstream spectrum.
Notably, Full Duplex (FDX) in DOCSIS 4.0 maintains the same downstream spectrum “upper limit” of 1.2 GHz, as in DOCSIS 3.1 (signified by the bright blue box).
N+0 (Node+0) Architecture
Full Duplex (FDX) requires an N+0 (Node+0) upgrade, meaning pushing fiber and the optical node (i.e., the optical-to-electrical conversion point) deeper into the hybrid fiber-coaxial (HFC) network and closer to the end customer.
The cost and speed of this N+0 upgrade is dependent on the mix of infrastructure types and agreements. Nevertheless, FDX requires extensive fiber builds further downstream and closer to customers.
READ MORE: Fiber Optic Cable Installation Process – Connecting Homes
Extended Spectrum DOCSIS (ESD) in DOCSIS 4.0
DOCSIS 4.0 with the enablement of Extended Spectrum DOCSIS (ESD), also known as Frequency Division Duplex (FDD), increases capacity by shifting the downstream spectrum “upper limit” beyond 1.2 GHz, to 1.8 GHz, allowing the upstream spectrum to extend as high as 684 MHz. Said differently, the downstream spectrum is run above the upstream spectrum.
As shown below, the yellow “FDD-Enabled Bandwidth OFDM Downstream” box extends beyond 1.2 GHz frequencies and up to 1.8 GHz frequencies.
Moreover, Charter Communications’ CEO, Tom Rutledge, has previously stated that, through lab tests, the company has pushed the downstream spectrum “upper limit” to 3.2 GHz.
DOCSIS 4.0 Network and Modem
DOCSIS 4.0 leverages the modulation schemes of DOCSIS 3.1, namely OFDM (orthogonal frequency-division multiplexing) and OFDMA (orthogonal frequency-division multiple access). Additionally, DOCSIS 4.0 offers additional spectrum to increase capacity.
DOCSIS 4.0 Network
In order to achieve DOCSIS 4.0’s increase in capacity, changes are required to the active and passive components in the hybrid fiber-coaxial (HFC) network, to support the new downstream and upstream frequencies. Particularly, these components include:
- Active: amplifiers, nodes, remote PHY devices (RPDs)
- Passive: taps, splitters
Overall, DOCSIS 4.0 is a completely new electronic drop-in and a whole new modulation scheme and thus requires new customer premises equipment (CPE). Specifically, this CPE is telecommunications hardware, such as a modem or gateway, that is located at the home or business of a customer.
DOCSIS 4.0 Modem
A DOCSIS 4.0 modem will be able to support maximum speeds of up to 10 gigabit per second (Gbps) downstream and 6 Gbps upstream. For DOCSIS 4.0-based modems, the number of downstream SC-QAM (Single-Carrier Quadrature Amplitude) channels will vary from 8 to 44.
DOCSIS – Modem Types and Bandwidth
Below is a summary of the different modem types and bandwidth of each major DOCSIS standard:
| Modem Type | Max Speed | SC-QAM Bonding | OFDM/A Capable? |
| DOCSIS 2.0 | 40 Mbps DS 30 Mbps US | 1 DS 1 US | No |
| DOCSIS 3.0 | 1 Gbps DS 120 Mbps US | 8 DS 4 US | No |
| DOCSIS 3.1 | 10 Gbps DS 1 Gbps US | 32 DS 8 US | Yes |
| DOCSIS 4.0 | 10 Gbps DS 6 Gbps US | 44 DS 8 US | Yes |
The DOCSIS 4.0 modem will be a point of entry (PoE) device when used in DOCSIS 4.0 mode, making it the sole hybrid fiber-coaxial (HFC)-terminating device in the unit. Additionally, there will be no need for a splitter network to feed other boxes, such as set-top boxes, and in many instances also the cabling inside the unit.
As an example, in January 2022, Comcast announced its xFi Advanced Gateway that incorporates WiFi 6E, which became the first DOCSIS 4.0 device with the capability of delivering multi-gigabit, symmetrical speeds.
DOCSIS 4.0 and Cable Operators
In the United States, the largest cable multiple system operators (MSOs), including Comcast, Charter, Cox, and Cable One, are all pursuing the development of the DOCSIS 4.0 specification. These cable companies are upgrading their equipment and changing their hybrid fiber-coaxial (HFC) network layouts to support consumer demand for higher data rates.
Comcast (Xfinity) DOCSIS 4.0
In January 2022, Comcast, which operates under the Xfinity brand, lab-tested a prototype Full Duplex (FDX) DOCSIS 4.0 system-on-chip (SoC) cable modem built by Broadcom. These were connected over a lab-based hybrid fiber-coaxial (HFC) network to a virtualized cable modem termination system (vCMTS) operating in DOCSIS 4.0 mode.
Using the vCMTS, Comcast demonstrated a complete 10G connection – from network to modem. Overall, the delivered download and upload speeds were faster than 4 gigabits per second (Gbps).
Additionally, this test proves Comcast’s ability to upgrade its existing vCMTS platform, via a software upgrade, to Full Duplex (FDX) DOCSIS 4.0.
Charter (Spectrum) DOCSIS 4.0
In July 2022, Charter Communications, which operates under the Spectrum brand, stated that its recent testing using DOCSIS 4.0 technology simultaneously delivered over 8 gigabits per second (Gbps) in downstream speeds and over 6 Gbps in upstream speeds, using a 4 amplifier cascade to a single modem. An amplifier cascade allows for coverage of a large portion of a cable company’s network without having to move nodes closer to customers.
Overall, this test demonstrated that Charter can successfully drive bi-directional, multi-gigabit speed offerings across its entire cable network.
Cox DOCSIS 4.0
In February 2022, Cox Communications announced that it would make a “multibillion-dollar” annual infrastructure investment over the next several years to build a 10 Gbps capable network. In particular, Cox highlighted the use of DOCSIS 4.0 technology to enable it to deliver multi-gigabit symmetrical speeds to both residential and business customers.
Cable One DOCSIS 4.0
Cable One expects to begin DOCSIS 4.0 upgrades in late 2022, which will enable the company to offer symmetrical gigabit speeds. To this end, Cable One states that these upgrades will allow it to further improve plant capacity in support of ongoing increases in consumer demand.
At the company’s Investor Day in March 2022, Senior Vice President of Technology Services, Ken Johnson, highlighted Cable One’s preference to pursue “the DOCSIS 4.0 path for upgrades because it’s significantly less expensive”.
When analyzing hybrid fiber-coaxial (HFC) upgrades for DOCSIS 4.0, versus fiber upgrades, Cable One found that overbuilding its network with fiber is “3x to 6x as expensive, as simply going to a DOCSIS 4.0 upgrade”. More specifically, of this difference in cost, “labor is the biggest driver”. Furthermore, Johnson stated that both technologies provide Cable One with “the same relative performance”.
DOCSIS 4.0 vs 3.1 and Fiber to the Home (FTTH)
What is the Latest DOCSIS Version?
The DOCSIS 3.1 standard is the latest DOCSIS version currently available, with the specification having been first issued in 2013. At the time of its release, DOCSIS 3.1 brought forward capacity and efficiency progression, OFDM, and wideband channel to the standard.
DOCSIS 3.1 vs 4.0
DOCSIS 4.0 maintains the 10 Gbps downstream capacity enabled in DOCSIS 3.1, while increasing the upstream capacity to 6 Gbps, from 1 to 2 Gbps. In turn, DOCSIS 4.0 delivers a more symmetrical connection than DOCSIS 3.1.
| Category | DOCSIS 3.1 | DOCSIS 4.0 |
| Downstream Capacity | 10 Gbps | 10 Gbps |
| Upstream Capacity | 1 to 2 Gbps | 6 Gbps |
| Downstream Spectrum | 750 MHz to 1 GHz | 1.2 GHz to 1.8 GHz |
| Upstream Spectrum | 42 to 65 MHz | 204 to 684 MHz |
| Modulation | OFDM + SC-QAM | OFDM + SC-QAM |
Another key difference between DOCSIS 3.1 vs 4.0 is that DOCSIS 4.0 enlarges the total amount of spectrum available for both downstream and upstream transmissions.
DOCSIS 4.0 increases the downstream spectrum to 1.2 GHz, and even up to 1.8 GHz with Extended Spectrum DOCSIS (ESD), also known as Frequency Division Duplex (FDD).
In comparison, DOCSIS 3.1 only offers up to 1 GHz of downstream spectrum. Also, in terms of upstream spectrum, the gains between DOCSIS 3.1 vs 4.0 are even more drastic, with an improvement of 5x to 16x.
DOCSIS 4.0 vs Fiber
The DOCSIS 4.0 standard uses hybrid fiber-coaxial (HFC) infrastructure which combines the use of optical fiber and coaxial cable to form a network.
HFC networks send television signals from a cable headend (i.e., distribution facility) to local neighborhoods through optical fiber. The fiber terminates at an optical node, where the light/optical signals are then converted to electrical signals and distributed to homes through coaxial cable lines.
DOCSIS 4.0 vs Fiber to the Home (FTTH)
Fiber to the home (FTTH) or fiber to the premises (FTTP) is often viewed as the “very” long-term end goal of every broadband operator, including cable companies and telecommunications providers. Still, DOCSIS 4.0 represents an attractive medium-term step given that it is a cost-effective upgrade to achieve multi-gigabit, symmetrical speeds.
READ MORE: Fiber to the Home (FTTH) vs FTTP, FTTN, FTTC, and FTTB
In Australia, nbn (National Broadband Network) is a state-owned national wholesale open-access broadband network which utilizes a combination of copper, coaxial, and fiber to service its population. As shown below, nbn is currently assessing its next major investment cycle, expected to be in 2025 and 2026. Specifically, nbn is evaluating between:
- HFC: make DOCSIS investments using Distributed Access Architectures (DAA) and DOCSIS 4.0
- FTTP: overbuild fiber to the premises (FTTP) to every residential home
The nbn example illustrates how during the 2030s, HFC and FTTP will yield similar speed tiers and performance from a residential service perspective. However, in the “very” long-term, meaning 2040+, FTTP will ultimately be the prevailing technology. Therefore, cable companies must decide whether to initially upgrade to HFC, as interim step, before ultimately overbuilding with FTTP networks.
READ MORE: Fiber Optic Network Construction – Process and Build Costs
