Cable Tech

Comcast 'making a lot of good progress' with DOCSIS 4.0

SCTE CABLE-TEC EXPO 2021 – The cable industry's DOCSIS 4.0 era is in its early stages, but Comcast is "making a lot of good progress" with the technology in the lab as the operator also plows ahead with deployments of a distributed access architecture (DAA), a top engineering exec at the cable operator said.

Comcast isn't ready to say when DOCSIS 4.0 equipment might reach production levels, "but we're making a lot of progress on the integration front," Rob Howald, a top network architecture engineering exec at Comcast, said Monday at a pre-show session held online that focused on "10G," an industry initiative focused on bringing 10 Gbit/s symmetrical speeds, low latencies and enhanced security to the access network.

"This is a big integration year for us. Next year will be an integration year as well," Howald said of Comcast's DOCSIS 4.0-facing activities. Most of that work is happening in the lab, but plans are underway to pivot some of that work into the field to see how it works in "real environments," he added.

Howald noted that Comcast's virtual cable modem termination system (vCMTS), which has ties to Harmonic's CableOS platform, "speaks" DOCSIS 4.0 now, and work is underway to bring D4.0 features to that platform.

Meanwhile, Comcast is making progress with respect to getting its plant ready for DOCSIS 4.0, primarily through the deployment of DAA.

"We have done a lot of DAA already," Howald said, noting that the operator has thousands of remote PHY devices (RPDs) already deployed. "That's a really large step. That was a big, transformational thing to do."

With respect to DOCSIS 4.0, Comcast is largely focused on the Full Duplex DOCSIS (FDX) flavor of the spec, which supports a buildout to 1.2GHz and enables upstream and downstream traffic to operate in the same block of spectrum. The other flavor of DOCSIS 4.0, Extended Spectrum DOCSIS (ESD), keeps the upstream and downstream traffic separate and envisions a spectrum upgrade to 1.8GHz.

Howald said Comcast and its partners are making progress on an FDX Amplifier that builds in key echo-cancellation technology required by FDX that would typically be housed at the node. That development will enable Comcast to deploy FDX to more of its network and not limit it to portions that are upgraded to a "node+0" architecture that eliminates all of the amplifiers between the node and the home. An FDX Amplifier could, for example, allow an operator to deploy FDX in networks that use a node+1 or node+2 architecture.

That development has "accelerated our thinking" about FDX, Howald explained. "It obviously simplifies, architecturally, where we can put FDX."

Comcast expects to have FDX Amplifier prototypes in hand by sometime in 2022.

All of that DOCSIS 4.0-related work is coming together a few months after Comcast announced results of an FDX lab trial using Broadcom silicon that produced symmetrical speeds of more than 4 Gbit/s.

Comcast isn't alone in preparing for DOCSIS 4.0, which requires operators to touch the plant and migrate to DAA.

Such work is underway at Cox Communications. About 30% of its network is outfitted with DAA and remote PHY devices, Guy McCormick, SVP of engineering at Cox, said.

"We won't necessary jump into [DOCSIS] 4.0; we'll step into 4.0," McCormick said of that transition. "We're just now getting hands on some of the prototype SOCs [systems on chip] and starting to kick those things around in the lab."

Cox, he added, is largely focused on a "high split" that would expand the amount of spectrum dedicated to the upstream to 204MHz and pair that with an expansion of the HFC plant to 1.2GHz. That should put Cox in position to deliver symmetrical gigabit speeds on HFC and prepare it for the multi-Gig world of DOCSIS 4.0.

Ecosystem developing

Though DOCSIS 4.0 technology is well into the development phase, don't expect the full ecosystem to be ready for prime time right away. Silicon and software are still being developed, and vendors and operators will need to run batteries of tests on products that are powered by those new technologies.

"I think there's a general feeling that to really kind of nail it with a full 4.0 solution, it's probably two or three years away," John Chapman, Cisco's chief technology officer of broadband technologies, predicted. "There's more work than people realize behind the scenes to really get these out."

But the good news is that the complexity of going from DOCSIS 3.1 to DOCSIS 4.0 is expected to be less of a jump than it was to go from DOCSIS 3.0 to DOCSIS 3.1, according to Zoran Maricevic, engineering fellow, access technologies at CommScope. He pointed out that the move from DOCSIS 3.0 to DOCSIS 3.1 required a major change to the channel modulation – going from the bonding of single-channel QAM signals to blocks of OFDM subcarriers – and that this change will carry over to future DOCSIS 4.0 networks.

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— Jeff Baumgartner, Senior Editor, Light Reading

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