CableLabs develops DOCSIS 4.0 annex targeting 25 Gbps via 3GHz spectrum

The push toward 3GHz is a strategic defensive play to keep hybrid fiber-coaxial (HFC) competitive with 10G and 25G PON fiber technologies. By aiming for 25 Gbps, cable operators hope to extend the lifespan of existing copper infrastructure without the capital expense of full fiber overbuilds. However, the requirement for new amplifiers and high power consumption at multi-GHz frequencies adds operational complexity. The industry is currently in a transition phase where 'interoperability' milestones for DOCSIS 3.1 networks are serving as a bridge while full DOCSIS 4.0 certification remains pending. Watch for the August CableLabs interop event to signal whether vendor hardware is stabilizing around the 1.8GHz standard before the 3GHz pivot begins.

CableLabs has moved quickly from announcement to published specification on the 3GHz front. The organization published the DOCSIS 4.0 optional annex physical layer specifications in September 2026, roughly one year after CEO Phil McKinney announced the initiative at SCTE TechExpo 2025. The completed spec defines downstream requirements to 3GHz for both Node/Remote PHY Device equipment and cable modems, marking an industry first. The annex continues to rely on 192MHz-wide OFDM downstream channels and addresses performance areas including Total Composite Power and Carrier-to-Composite Noise. CableLabs convened a DOCSIS 4.0 PHY Working Group open to all interested participants, which developed cable plant models to determine technical feasibility at frequencies up to 3GHz.

On the vendor and deployment side, hardware readiness remains the primary bottleneck. Applied Optoelectronics demonstrated a prototype 3GHz amplifier at SCTE TechExpo 2026 in Atlanta, showing that generating and amplifying signals at those frequencies is possible but acknowledging that power consumption and attenuation challenges remain unresolved. The company indicated that cable deployment of 3GHz-based technology likely will not happen for several years. CableLabs' Karthik Sundaresan, a distinguished technologist and director of HFC solutions, noted that interoperability across remote PHY devices, modems, amplifiers, and taps must be ensured before vendors can build compatible components at scale.

The competitive backdrop centers on fiber-to-the-home pressure. CableLabs CEO Phil McKinney announced at SCTE TechExpo 2025 that the organization would pursue both 3GHz for 25 Gbps and a longer-term 6GHz path for approximately 50 Gbps over HFC. The 6GHz work has not yet been assigned a formal DOCSIS specification number. Current DOCSIS 4.0 technology at 1.8GHz has demonstrated downstream speeds of approximately 14 to 16 Gbps in CableLabs interop events, with the 3GHz annex targeting a significant capacity jump to keep HFC competitive against symmetric multi-gigabit PON offerings from fiber competitors.