DOCSIS 4.0 Overview: FDX, FDD, and Spectrum Updates

Do you know your FDD from your FDX?

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Key Takeaways: What You’ll Learn About DOCSIS 4.0

► DOCSIS 4.0 uses OFDM/OFDMA for better data efficiency.

► It supports higher modulation (up to 4k-QAM) for faster speeds.

► DOCSIS 4.0 supports higher modulation (up to 4k-QAM) for faster speeds.

► Enables flexible spectrum sharing for modern internet use.

What is DOCSIS 4.0?

Data Over Cable Service Interface Specifications, much better known as  DOCSIS is the technology that is used to communicate and transfer data across RF or coaxial cable. This technology has been around since 1997 and continues to evolve today.

Since then, the demand and requirements of DOCSIS have completely transformed, which is clear in every revision. In 2025, MSOs must boost the speed and capacity of upstream by increasing its bandwidth and this is being solved with DOCSIS 4.0. The next revision of DOCSIS has a broader frequency range for upstream at 684MHz which has the potential to deliver speeds of 10Gbps for downstream and up to 7Gbps upstream.

Key differences between DOCSIS 4.0 and 3.1

Upon the release of 3.1, DOCSIS began leveraging OFDM (Orthogonal Frequency Division Multiplexing) and OFDMA (orthogonal frequency-division multiple access). OFDM transmits each piece of data across multiple narrowband subchannel frequencies as opposed to only one wideband channel.

What happens with OFDM is that instead of only 1 carrier for specific bandwidth, you have multiple carriers, and they are orthogonal, so they cannot interfere with each other. Each carrier is then independently modulated, and you can efficiently use the bandwidth instead of using specific bandwidth transmit only. OFDMA, as multiple access implies, takes a channel and subdivides it, which can be distributed to many devices more efficiently. By employing higher and more efficient modulation orders as 1k-QAM to 4k-QAM instead of the 256-QAM, cable providers can pack in more bits per hertz.

DOCSIS 3.1 has a set limit for upstream and the market is showing that it is not high enough. With the normalization of constant streaming and video calls, the usage is growing by 50% every year. At this rate the maximum capacity for upstream will be surpassed very soon. Additionally, the demand is for not only for symmetric multi-gigabit speed over HFC networks, but it is for low latency, constant jitter and reliability. This was the catalyst to move into DOCSIS 4.0 and 10G, which is the next step. 10G offers higher speed, more reliability, better security and lower latency.

How it enables symmetric multi-gigabit internet

DOCSIS 4.0 is a major upgrade in the technology, and this is partially because upload and download speeds are both extremely fast and balanced. This can be credited to a few things:

The introduction of Full Duplex DOCSIS (FDX), the ability to transmit data upstream and downstream simultaneously over the same spectrum.
Expanded Spectrum Usage of up to 1.8 GHz.
Like 3.1, DOCSIS 4.0 uses OFDM and other modulation techniques to include more data into each transmission.
DOCSIS 4.0 works well with Distributed Access Architecture (DAA), which decentralizes network functions. This helps maintain high speeds when there are many users.
DOCSIS 4.0 is backwards compatible with older versions so cable operators can upgrade without disrupting service.

Why cable providers are upgrading to DOCSIS 4.0

4.0 is a big upgrade from DOCSIS 3.1 and especially DOCSIS 3.0 where there are still some cable operators who have not upgraded yet. The switch comes with many benefits including easy adaptation to severe channel conditions and flexible modulation schemes. Additionally, it promotes efficient use of the spectrum by sharing the spectrum between several users with multiple access technology. This results in a major reduction in interference. Their users benefit from faster uploads, lower latency, and more reliable performance, even during peak usage.

DOCSIS 4.0 FDD vs. FDX: What are the Differences?

DOCSIS 4.0 comes in 2 different flavors to meet the demands of its users. These are FDD (Frequency Division Duplex) and FDX as mentioned above. MSOs have the flexibility to pick the technology they will be moving forward with, whether that is FDD or FDX, but cannot choose to do both, as it is too expensive. It is undecided which is preferred but CableLabs has developed 4.0 specifications for both technologies.

FDD mode is essentially an extension of DOCSIS 3.1, leveraging the same technology. FDX is a new technology that hasn’t been used before.

FDD is also known as Extended Spectrum DOCSIS (ESD). This implies that it extends the upstream-only spectrum and the downstream-only spectrum independent of one another. With FDD, 5-85MHz is used for legacy (as before) while the upstream spectrum can be extended as high as 684MHz. This leaves 108-684MHz for upstream-only while the downstream-only spectrum is extended to 1.8GHz. MSOs can offer more bandwidth and higher data rates for both upstream and downstream, and it is symmetrical.

FDX technology improves capacity by enabling network devices to simultaneously transmit both downstream and upstream channels in the same 108-684MHz spectrum. Additionally, the downstream-only spectrum further extends up to 1.2GHz. The increased upstream capacity with FDX is within the shared spectrum and it is more flexible and efficient. Different users can use the 108-684 band for different purposes and there is no issue. With people using both upstream and downstream in the same channel, it should cause interference. It is the CM (cable modem) that needs to stop that interference. This is not an issue for the 3.1 architecture and, of course, FDD.

DOCSIS 4.0 Frequency Range

What spectrum does DOCSIS 4.0 use?

The frequency range for FDD mode is up to 1.8 GHz downstream and Up to 684 MHz upstream.

The frequency range for FDX mode is 108 MHz to 1218 MHz downstream and 5–85 MHz and 108–684 MHz upstream.

When is DOCSIS 4.0 Coming Out? Release Date

While DOCSIS 4.0 was announced by CableLabs in 2017, it has taken time to release due to infrastructure upgrades and compatibility testing. Now, in 2025, DOCSIS 4.0 is moving towards live networks.

Field trials and early rollouts in North America

In North America, several major players have begun field trials and limited rollouts. Comcast completed a successful DOCSIS 4.0 field trial in 2022 and began partial market rollouts in 2023. Broader deployment is expected throughout 2025 as MSOs upgrade their hybrid fiber-coax (HFC) networks with DOCSIS 4.0-ready nodes and amplifiers.

Vecima Networks has also launched DOCSIS 4.0-ready hardware, including their “Forever Nodes,” which support 1.8 GHz spectrum and offer a future-proof path to 10G.

Availability in Europe and other regions

In Europe and other global markets, DOCSIS 4.0 adoption is expected but with a minor delay in the timeline. European operators are currently evaluating both the infrastructure and regulatory requirements before committing to full-scale rollouts. However, DOCSIS 4.0 is still positioned to become key to global broadband strategies.

Ready to Prepare Your Network for DOCSIS 4.0?

The key is the right telecommunications testing equipment. The Jupiter 310 CPE design verification system has been developed by Averna to automatically run the PHY ATPs for DOCSIS 3.0, 3.1 and 4.0. Chipset manufacturers all over the world leverage this instrument to assure certification. It is hugely important for all the tests to pass, because it can become a very expensive and time-consuming endeavor the more often a CM is sent in to be certified. To avoid any test failures, companies keep their own Jupiter 310 onsite to pre-qualify and resolve any discrepancy against the ATP. It also quickly generates the required documentation companies require for traceability.

For information on RF testing, please have a look at our DOCSIS test equipment or contact Averna.