CableLabs, which develops standards for U.S. cable network operators that are often adopted by cable operators internationally, says it has published the latest version of its Data Over Cable Service Interface Specification (DOCSIS). DOCSIS 4.0 leverages full-duplex and extended spectrum capabilities to enable 10-Gbps downstream and 6-Gbps upstream transmission rates over hybrid fiber/coax (HFC) architectures. The organization hails the specifications as an important step toward the goal of symmetrical 10G capabilities for HFC networks.
Full-duplex technology, specifications for which were completed in 2017, supports the delivery of multi-gigabit symmetrical services by enabling concurrent transmissions in different directions within the same spectrum. Self-interference cancellation technology and intelligent scheduling are keystones of this capability. The extended spectrum approach, as the name implies, expands the previous 1.2 GHz of usable spectrum to 1.6 GHz. Specifications for extended spectrum were completed last fall.
The downstream and upstream capabilities are significant improvements over the previous version of DOCSIS, DOCSIS 3.1. While that specification was initially described as enabling “up to” 10 Gbps downstream (and is still described that way in places on the CableLabs website as of today), CableLabs now classifies it as supporting only 5 Gbps downstream and (still) 1-2 Gbps upstream. A member of CableLabs’ media relations team explains that the initial DOCSIS 3.1 specifications began at 5 Gbps with an intention of evolving to 10-Gbps support in the future. The full-duplex efforts initially began under the DOCSIS 3.1 umbrella as a step toward achieving this goal. However, both the full-duplex and extended spectrum efforts were moved to DOCSIS 4.0 in June 2019, leaving DOCSIS 3.1 at 5 Gbps downstream.
The specification publication is the first of three steps necessary before certified DOCSIS 4.0 technology is ready for fielding. The next step includes interoperability events; information on the first such event has not been released. A program by which products can be certified as standards compliant would follow. In addition to the higher transmission rates, the DOCSIS 4.0 specifications cover means by which security and reliability can be improved.
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