Comcast, Charter push DOCSIS 4.0 limits in CableLabs showcase

CableLabs held its inaugural 10G Showcase this week, highlighting operator efforts to push the industry toward faster speeds, lower latency, greater reliability and increased security. While CableLabs stressed its broader 10G initiative includes passive optical networking and wireless technologies, the event homed in on the latest advances in DOCSIS 4.0 technology.

Heavy hitters Comcast and Charter Communications demonstrated their progress to date, with the former focusing on the full duplex (FDX) version of DOCSIS 4.0 and the latter on extended spectrum DOCSIS (ESD). Speeds were a notable part of each exhibit, with Comcast showing up to 8.5 Gbps in the downstream and 5 Gbps in the upstream. Charter, meanwhile, hit as much as 8.9 Gbps in the downstream and 6.2 Gbps in the upstream. But there was plenty more to be gleaned from the event.

Here are Fierce’s top five takeaways.

Comcast is aiming to begin trials of prototype FDX amplifiers in July

Amplifiers have been a key sticking point for both FDX and ESD. For FDX in particular, though, operators must develop and integrate new noise cancellation technology that will allow the amplifiers to work in a simultaneous transmission environment. Until now, there have been plenty of questions about when the new technology might be ready.

During the CableLabs event, Comcast VP of Network Architecture Rob Howald said it will begin testing prototype amplifiers in the lab in July. He didn’t offer further detail, but Comcast Cable EVP and Chief Network Operator Elad Nafshi said it expects to share more news on this front in the second half of this year.

Comcast is targeting a node+6 architecture

While Comcast has hyped up its FDX progress to date, there was one key issue with its most recent trial in January and the demo it conducted at the CableLabs event: both used a node+0 setup. In simple terms, that means there are no amplifiers between the node and the user. That means that as it stands, the technology can’t be used in many parts of the network today. As Howald put it, “we have more N+X than we have N+0.”

But Comcast is working to change that by developing new amplifiers with the noise cancellation technology mentioned above. Specifically, Nafshi said it’s targeting a node+6 arrangement.

Howald explained that while performance does degrade with each amplifier in the network today and Comcast doesn’t expect that to change in an FDX world, it has already quantified the expected impact in the modeling it has done with vendors. It’ll know more about actual performance following the aforementioned trials coming later this year, he added.

Dell’Oro Group VP Jeff Heynen said it will be a big deal if Comcast is able to make FDX work in a node+6 setup.

“That’s going to turn the heads of some operators who were not previously even considering full duplex because it required them to pull fiber so much deeper” to achieve a node+0 or even node+2 architecture in their outside plant, he explained.

Charter proves ESD performance in a node+4 setup

Unlike FDX, the ESD flavor of DOCSIS 4.0 that Charter is pursuing was designed to work with amplifiers. The question, though, has been whether sufficient performance could be achieved given the degradation that occurs over longer cascades. In its CableLabs demo, Charter delivered the aforementioned 8 Gbps speed using a node+4 arrangement.

John Williams, Charter’s VP of Engineering, said the setup was designed to showcase “the art of the possible.” He added an N+4 architecture is “pretty typical of what’s out in the network,” given Charter has been able to reduce the size of its cascades in recent years. That said, he noted the technology could likely support longer amplifier cascades.

“We believe that it’s not going to be that much of a challenge,” Williams said. “We’re doing it with prototype chips right now. Once we get the GA [general availability] chips, we will be able to see what is the optimal stepdown…As we get to more production-like stuff, we can optimize the tilts and the levels for the operator for longer cascades.”

Williams also noted the amplifiers it plans to use will be “drop in modules” that will work with its existing node spacing.

According to Heynen, that could help operators like Charter speed their deployment time and reduce the operational costs of their DOCSIS 4.0 upgrades.

Comcast can use the same node housing for fiber and HFC

One of the other things Comcast highlighted was a new node housing which incorporates both optical line terminals for fiber and Remote PHY for its coaxial plant. Nafshi said this will provide Comcast with more flexibility in how it chooses to serve new locations.

Some operators could end up using both FDX and ESD

Executives at the event pointed out FDX and ESD are meant to be complementary, not competing technologies. This means that some operators might end up deploying both.

Expanding on this, a CableLabs representative told Fierce “we have heard that there are likely strategic reasons for some operators to use both modes of operation.”

While each operator will make its own technology choices based on the capabilities of their specific plant, “the important thing is that operators can choose to deploy different options across their footprint. The modes of operation in the DOCSIS 4.0 solution share many commonalities, for example, both provide approximately 1 GHz of spectrum for downstream transmission and up to 684 MHz of spectrum for upstream transmission,” the representative said.

Beyond plant conditions, factors which might influence such decisions include targeted amplifier cascades, long-term fiber plans, available spectrum, competition and deployment timelines, the representative concluded.