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Cable Tech

Charter tests DOCSIS 4.0 at 1.8GHz, hits multi-gigabit symmetrical speeds

Offering proof that the Frequency Division Duplexing (FDD) flavor of DOCSIS 4.0 has some legs, Charter Communications and Vecima Networks announced that recent lab trials of the technology generated speeds greater than 8.5Gbit/s downstream and 6Gbit/s upstream. That puts Charter within shouting distance of the cable industry's vision for "10G" networks.

Those lab tests demonstrated service delivery on hybrid fiber/coax (HFC) plant upgraded to 1.8GHz, the companies said.

"This provides proof that our network is capable of offering multi-gig speeds bi-directionally," Joe Godas, SVP of network engineering and technology at Charter, said in a statement. "Having this technology offers an option for future improvements and continuing to evolve our leading service for years to come."

The FDD flavor of DOCSIS 4.0, also known as Extended Spectrum DOCSIS (ESD), upgrades spectrum to 1.8GHz (up from today's plant built out to 860MHz, 1GHz or even 1.2GHz) and continues to operate downstream and upstream traffic in separate, dedicated spectrum. By contrast, Full Duplex DOCSIS (FDX), an option for DOCSIS 4.0 primarily being pursued by Comcast, keeps the spectrum ceiling at 1.2GHz but adds an FDX band (and the use of a technique called echo cancellation) that enables upstream and downstream traffic to run in the same block of spectrum.

Though Comcast has made progress with FDX, including recent lab trials that produced symmetrical speeds of more than 4 Gbit/s, most other operators are focused on the FDD version, arguing in part that FDD is less complex to pull off. Those in the FDD camp have also balked at the need to go with a fiber-deep, "node-plus zero" (N+0) architecture that eliminates all of the amplifiers between the home and the node. However, that N+0 requirement for FDX won't be necessary once a new breed of FDX Amplifiers, which bake the echo cancellation technology into the amp, start to hit the market.

A new pair of SoCs

Back to the Charter-Vecima trial, the companies said the demo was powered by new DOCSIS 4.0-based silicon for remote PHY devices (RMDs) on the network side of the equation as well as a new D4.0 modem chipset.

They didn't reveal the systems-on-a-chip (SoC) supplier used for the trial. But there's not exactly a huge number of options, given the limited group of chipmakers focused on DOCSIS 4.0 technology at this point.

Broadcom was involved in the aforementioned DOCSIS 4.0 FDX trial and, according to sources, Comcast, Cox Communications and Charter Communications are among the tier 1 operators that have signed joint development agreements with Broadcom for DOCSIS 4.0 technology. MaxLinear is also developing DOCSIS 4.0 products, and CommScope recently told Light Reading it is collaborating with a pair of silicon partners on the development of a DOCSIS 4.0-based architecture for network gear.

While it's not yet clear when DOCSIS 4.0 products will be ready for commercial deployment, the announcement of the Charter trial with Vecima indicates that things might be a little ahead of schedule. At last fall's SCTE Cable-Tec Expo, industry engineers said they expected to have DOCSIS 4.0-capable RMD devices ready for lab testing by the end of 2021, and access to FDD/DOCSIS 4.0 customer premises equipment (CPE) reference designs by early-to-mid-2022.

Meantime, CableLabs is already pushing ahead with interoperability testing for DOCSIS 4.0. It slated a pair of interops last fall, and, at last check, had ten weeks reserved for D4.0 interops in 2022.

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— Jeff Baumgartner, Senior Editor, Light Reading

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