Comcast completes DOCSIS 4.0 puzzle with amplifier test

SCTE CABLE-TEC EXPO - Comcast reached what one operator executive called a “critical milestone” on its road to rolling out DOCSIS 4.0 next year, touting the successful test of a 10G capable full duplex (FDX) amplifier. With network and modem trials already under its belt, the amplifier news this week fills in the final puzzle piece Comcast needed to make DOCSIS 4.0 a reality.

The test used an amplifier based on a Broadcom reference design and delivered speeds of 6 Gbps downstream and 4 Gbps upstream in a node-plus-6 amplifier cascade. Elad Nafshi, EVP and Chief Network Officer at Comcast Cable, told Fierce the latter detail is important because it means the technology can easily slot into the “vast majority” of Comcast’s existing network.

Those who have been closely tracking the industry’s DOCSIS 4.0 progress might remember Charter Communications in April delivered speeds of more than 8 Gbps downstream in a node+4 amplifier trial. However, Nafshi noted that demonstration focused on the extended spectrum (ESD) version of DOCSIS 4.0, which requires less complicated amplifiers than FDX does. That’s because FDX involves the simultaneous transmission of data upstream and downstream using the same spectrum whereas ESD uses separate chunks of spectrum for the upstream and downstream flows.

So, Nafshi said, the amplifier Comcast used incorporated complicated noise cancellation technology not included in the ESD amplifiers.

“This is a major technical achievement, to be able to do that and certainly over a six amplifier cascade and still deliver those speeds,” Nafshi told Fierce. “We’re just getting started. We fully expect those speeds to get faster as we get more time and better automation across the configuration of these amplifiers.”

Nafshi said it used a preproduction amplifier for its test and will spend the rest of this year and early next year hardening the technology for field deployments. That process includes ensuring the amplifier can perform in a wide range of different physical environments, such as sub-zero weather in the Midwest and 100-plus-degree temperatures in Arizona. It also includes software refinements to ensure the amplifier can effectively self-configure.

The FDX amplifier is the last piece of the DOCSIS 4.0 puzzle for Comcast. In October 2021, the operator demonstrated an end-to-end DOCSIS 4.0 link which handed traffic from its virtual cable modem termination system (vCMTS) over a node and to a modified DOCSIS 3.1 modem operating in the FDX band. It followed up with a trial of a prototype DOCSIS 4.0 modem for customer CPE in January. Comcast previously said it planned to begin testing FDX amplifiers in July 2022 and was targeting a node+6 architecture.

When it finally comes time to roll out DOCSIS 4.0, Nafshi said that will be done via a software upgrade to its vCMTS, module swaps on its digital nodes (more than 50,000 of which have already been deployed), electronic swaps of its amplifiers and a CPE upgrade on the consumer side.

Comcast EVP and Deputy CFO and Treasurer Jason Armstrong recently said Comcast is aiming to be in the market with DOCSIS 4.0 by the second half of 2023.