Comcast has taken DOCSIS 4.0 another step forward with word that it has lab-tested a prototype modem based on the new CableLabs specs that pumped out symmetrical speeds of 4 Gbit/s – effectively matching the performance it saw in earlier network-side trials announced last April. Comcast said the D4.0-based modem was based on new silicon from Broadcom, which, according to sources, has DOCSIS 4.0 joint development agreements in place with several Tier 1 cable operators, including Comcast, Charter Communications and Cox Communications. This diagram illustrates a sample allocation of HFC network spectrum, including an FDX band that allows for upstream and downstream traffic to be overlapped in a block of spectrum occupying 108MHz-684MHz.Click here for a larger version of this image. (Source: Comcast/SCTE Cable-Tec Expo 2021) Comcast said the lab test represented a connection comprised of all DOCSIS 4.0-based components. It adds up to another milestone for an emerging platform for hybrid fiber/coax (HFC) networks that target speeds of 10 Gbit/s down and 6 Gbit/s up, along with enhanced security and low-latency capabilities. Comcast has largely championed the Full Duplex DOCSIS (FDX) flavor of DOCSIS 4.0, which envisions an HFC plant built to 1.2GHz and support of an FDX band (108MHz to 684MHz) that uses echo cancellation techniques that allow for upstream and downstream traffic to run in the same block of spectrum. The operator also billed the lab test as another step toward 10G, an industry initiate focused on bringing symmetrical 10-gig capabilities to HFC, fiber-to-the-premises (FTTP) and wireless networks. This latest trial followed a network-to-modem test conducted by Comcast late last year based on the operator's virtual cable modem termination system (vCMTS) speaking to a DOCSIS 3.1 modem configured to operate in the FDX band. Faster speeds on the horizon DOCSIS 4.0 will put cable operators in position to deliver multi-gig services on HFC. Comcast's top-end DOCSIS service currently offers up to 1.25 Gbit/s downstream and 35 Mbit/s upstream. Gigabit Pro, Comcast's targeted fiber-to-the-premises residential service, offers symmetrical 3-Gig speeds. Comcast is not making a public prediction on when it expects DOCSIS 4.0 technology to be ready for commercial deployment. But it's clear that the initial wave of network and CPE has reached the testing phase, setting things up for initial deployments by the end of 2022 and into 2023. Word of the modem test caps off a recent string of other DOCSIS 4.0 activity. Last week, Charter Communications and Vecima Networks said recent lab trials of D4.0 tech produced speeds of more than 8.5 Gbit/s down and 6 Gbit/s up. That test was based on the Frequency Division Duplexing (FDD) flavor of DOCSIS 4.0 that utilizes plant built to 1.8GHz but continues to keep downstream and upstream traffic running in dedicated spectrum.