Comcast claims first with end-to-end full duplex DOCSIS 4.0 link

Comcast staked a claim as the first in the world to deliver an end-to-end full duplex (FDX) DOCSIS 4.0 connection from its network to a customer gateway, building on earlier trials of individual network components.

Earlier this year, the operator hit 4 Gbps in a test of a full duplex system-on-chip from Broadcom. Prior to that, it achieved symmetrical speeds of 1.26 Gbps in a DOCSIS 4.0 test conducted in October 2020.

Elad Nafshi, SVP of next generation access networks at Comcast Cable, told Fierce its trial in April marked the first time it had DOCSIS 4.0 silicon for the node section of the network and was able to pass traffic through that equipment. But “what we’re talking about today is starting to fill in the rest of the building blocks of the ecosystem.”

Specifically, it connected a virtual cable modem termination system (vCMTS) which now speaks DOCSIS 4.0 to a node and passed traffic on to a specialized DOCSIS 3.1 modem which was configured to operate in the FDX band. Comcast did not disclose the speeds it achieved in the latest trial.

Nafshi said the fact that its vCMTS is now DOCSIS 4.0 capable is a huge step forward. “The significance of the CMTS is really showcasing and proving out that the protocol works and we’re obviously able to run it on our existing virtualized platform,” he explained. “The really cool thing about it is that it doesn’t require any hardware upgrade…this is a software download to the existing virtualized platform. And so now we’re able to innovate at the speed of software.”

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Of course, there’s still more work to be done. Nafshi said the next items on Comcast’s list are development of a DOCSIS 4.0 cable modem and an FDX amplifier.

While amplifiers will continue to serve the same purpose – extending the reach of a signal from a node – in next generation networks, Nafshi noted “you can’t just deploy your grandfather’s amp.” The amps of the future will require special echo cancellation technology to enable full duplex operation.

“At the end of the day, that ability to be able to overlay the upstream and downstream frequencies right on top of each other is the secret sauce behind DOCSIS 4.0 FDX,” he concluded.

During SCTE’s Cable-Tec Expo earlier this week, Robert Howald, a fellow in Comcast’s Next Gen Access Network organization, said the operator expects to begin testing prototype FDX amplifiers in its lab next year.