Widescale deployments of DOCSIS 4.0 are still years out on the horizon, but CableLabs and its Kyrio subsidiary are already preparing to conduct an initial wave of interoperability tests with suppliers later this year and into 2022.

That activity will start to ramp up soon after this year's SCTE Cable-Tec Expo, as the first interop is scheduled to take place in October, followed by one in December. Another ten weeks have already been reserved for D4.0 interops in 2022. All will take place at CableLabs' facilities in Louisville, Colorado.

Those dates have been announced to suppliers. "When will somebody first show up? I don't know that yet," Doug Jones, principal architect at CableLabs, said.

But he said it made sense for CableLabs to set dates for interoperability testing based on feedback from cable operators and their suppliers. "Operators are now formulating their plans for DOCSIS 4.0 and what that includes with what they're going to do with their network," Jones said.

DOCSIS 4.0 is designed to support up to 10 Gbit/s downstream and 6 Gbit/s upstream, complemented by new low-latency and advanced security capabilities. To help cut through some of the engineering details and technical jargon, CableLabs just this week published a new video primer on DOCSIS 4.0.

New nuances for DOCSIS 4.0

As it's been for earlier generations of DOCSIS, the interoperability testing (as well as future product certification and qualification testing) will largely focus on customer premises equipment (CPE) and the network-facing cable modem termination system (CMTS). CableLabs expects some of the early interop activity to focus on the basic functionality of new DOCSIS silicon.

What's a bit different this time is the fact that D4.0 will utilize a distributed access architecture (DAA) that extends the PHY layer of the CMTS (with remote PHY) and possibly the MAC as well (remote MACPHY), resulting in an advanced class of nodes and shelves.

CableLabs will also be faced with testing new virtualized forms of the CMTS, whereby some elements that traditionally function as hardware will instead function as software.

To iron out that new testing wrinkle, CableLabs has built a data center – not a more traditional cable headend – to host the virtualized pieces of these new CMTSs. "We've prepped for it," Jones said.

Jones also points out that DOCSIS 4.0 is the first version that requires operators to upgrade the return split of the hybrid fiber/coax (HFC) plant. The Extended Spectrum DOCSIS (ESD) flavor of DOCSIS 4.0 envisions a plant built out to 1.8GHz along with a "mid-split" or "high-split" that dedicates more capacity to the HFC network upstream, while keeping downstream traffic separate. Full Duplex DOCSIS (FDX) envisions HFC built to 1.2GHz with an FDX band that can run both upstream and downstream traffic.

"DOCSIS 4.0 is all about more return capacity," Jones said. "It does not just drop in … It's that whole HFC ecosystem."

That means it's not just about swapping in a new modem or CMTS, but extends to other elements of the HFC plant requiring new, upgraded passive devices and amplifiers.

The CableLabs DOCSIS 4.0 interops will focus on getting the modems and CMTSs from multiple vendors to talk to each other. But some of the work will also extend to these new, more advanced components of the HFC network.

The good news is that the coax that's already built out won't need to be replaced, Jones said, noting that a field test on some coax built in the late 1980s worked as expected in a 1.8GHz environment.

"The coax supports what we're doing with DOCSIS 4.0," he said. "The coax that's hanging out there that's really expensive to replace, that stuff works."

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— Jeff Baumgartner, Senior Editor, Light Reading