All roads won't lead to DOCSIS 4.0

DOCSIS 4.0 is making progress in terms of technology, products and some initial deployments. But some operators may put DOCSIS 4.0, virtual cable modem termination systems (vCMTSs) and distributed access architecture (DAA) network upgrades on the backburner as they look to squeeze all they can out of their existing DOCSIS 3.1 platforms.

Deploying DOCSIS 4.0 modems on DOCSIS 3.1 networks outfitted with CMTSs running updated software can put cable operators in position to beef up overall capacity and provide symmetrical 1-Gig broadband services. There's no official cable industry term for this approach, but suppliers are starting to apply labels to it.

CommScope execs have recently called it "extended" or "enhanced" DOCSIS 3.1, and some cable operator engineering execs have referred to the idea unofficially as "DOCSIS 3.1E." Meanwhile, Kishore Seendripu, CEO of MaxLinear, a chipmaker that recently introduced its first chipset for D4.0 modems, dubbed the idea "ultra DOCSIS 3.1" during the company's recent Q3 earnings call.

Update: Going back further in time, cable industry vet, former Charter Communications CTO and current Broadband Success Partners CTO Jay Rolls has described this (tongue-in-cheek) as DOCSIS 3.5 – viewing it as an important, interim step between traditional DOCSIS 3.1 and DOCSIS 4.0.

Related:DOCSIS 4.0 modems might first run rampant on DOCSIS 3.1 networks

The general idea behind this enhanced form of DOCSIS 3.1 is to run new D4.0 modems or updated DOCSIS 3.1 modems on D3.1 networks that have been upgraded with a "mid-split" or "high-split" that dedicates more network capacity to the upstream. The CMTSs and modems in question would effectively override the DOCSIS 3.1 specs by bonding up to five OFDM (orthogonal frequency-division multiplexing) blocks in the downstream (instead of the two supported in current D3.1 modems), and two OFDMA channels in the upstream.

Update: There's been some pushback on the notion that the approach being outlined here "overrides" the DOCSIS 3.1 specs, because those capabilities, in reality, are included in the D3.1 specs. While initial DOCSIS 3.1 cable modems support only two OFDM channels, the D3.1 specs have always supported more than 2 OFDM channels, an industry engineering exec and DOCSIS expert points out. The idea from the start, the person notes, is that new generations of D3.1 silicon would enable support of more OFDM channels just as prior DOCSIS 3.0 silicon generations were made to bond an increasing number of single-channel QAM channels. However, the industry is now starting to move forward with new modems powered by DOCSIS 4.0-based silicon rather than new generations of D3.1 chipsets.

Related:MaxLinear joins Broadcom in DOCSIS 4.0 chip race with 'Puma 8'

Still, such an enhancement to current-generation D3.1 technology effectively "widens the pipe," explained Guy Sucharczuk, SVP and president of CommScope's Access Network Solutions unit.

What's not required? DAA or a virtual CMTS.

Assuming a hybrid fiber/coax (HFC) network built to 1.2GHz with a high-split and the elimination of spectrum towards QAM-based video services, operators could generate about 8 Gbit/s downstream and 1.7 Gbit/s upstream by switching out the modem, Sucharczuk said.

He acknowledged that eliminating QAM-based video is still out on the horizon for most cable operators. But even if the capacity dedicated to DOCSIS is cut in half, operators could still deliver as much as 4 Gbit/s downstream and 1-Gig upstream in this enhanced DOCSIS 3.1 scenario, Sucharczuk added.

Such an approach could provide some cable operators with a "fast and easy" upgrade that would rapidly enable near-DOCSIS 4.0 speeds. It would also buy operators time by temporarily pushing out the need to pursue DAA upgrades or install a vCMTS.

Sucharczuk said the idea gained some interest and traction at last month's SCTE Cable-Tec Expo in Denver. "Even the bigger operators are thinking about it," he said.

Related:Comcast, Broadcom chip in to unify DOCSIS 4.0

CommScope CEO Chuck Treadway echoed that on the company's recent Q3 earnings call.  

"At the show, we introduced DOCSIS 3.1 extended," which includes a CMTS software update that can enable symmetrical 1Gbit/s-plus speeds while avoiding a "major investment" in network upgrades, Treadway said. "We're seeing a lot of interest in that," he added.

MaxLinear's Seendripu said he expects cable operators to be "very selective about DOCSIS 4.0," predicting that "ultra" DOCSIS 3.1 could absorb an astounding 80% of the market.

"DOCSIS 4.0 is not the same for everybody," Seendripu said. "It's a very, very costly network rollout… Ultra DOCSIS 3.1 is what I put my bet on."

CMTS limitations, competition concerns

But there's also skepticism about whether the idea of DOCSIS 3.1E will pan out. Some engineers note that processing limitations of legacy CMTS line cards need to be considered.

"The reality [of DOCSIS 3.1E] is more complex than the theory," a cable industry engineering exec familiar with those discussions told Light Reading. "There are some inherent limitations to the processing power of existing [CMTS] chassis."

Another limiting factor is mining additional spectrum that can be applied toward DOCSIS. Eliminating QAM video traffic could free up about 200MHz of spectrum, but going all-IP is a "big, honking change" that's still many years out on the horizon for most cable operators, the exec said.

Competition is another determining factor. Offering between 1 Gbit/s to 2 Gbit/s might be good enough in certain instances, but operators will need more – and a possible upgrade to 1.8GHz of capacity on the HFC network – to deliver speeds that can compete with fiber-to-the-premises (FTTP) competition.

Enhanced DOCSIS 3.1 paired with the ongoing use of node splits can help operators manage congestion and offer a 1-Gig or 2-Gig speed tier and could provide a few years of runway where competitive FTTP doesn't exist. But it won't do as much as D4.0 can with respect to keeping competition in check, the exec added.

"If you're trying to compete with fiber, you need DOCSIS 4.0 in all its glory," the engineer said. Additionally, incremental investments for DAA and DOCSIS 4.0 will also get operators closer to an eventual "end goal" of FTTP – if and when it's needed.

Dell'Oro Group VP and analyst Jeff Heynen agreed that some operators could generate speed benefits with enhanced DOCSIS 3.1, but he believes that operators stand to derive more benefits from DAA alongside the deployment of upstream-enhancing mid-split and high-split upgrades.

Discussions about enhanced DOCSIS 3.1 could slow the pace of some HFC network upgrades and put near-term pressure on suppliers. Several cable tech vendors, including Harmonic, CommScope, Vecima Networks and Casa Systems, have warned that operators have dialed back spending in the near term but are hopeful that spending will rebound in the second half of 2024.

Some cable operators are "tapping the brakes" as they weigh the best path forward for their respective HFC networks, the cable operator exec admitted.

DOCSIS 4.0 plows ahead

Despite the ongoing debate about enhanced DOCSIS 3.1 and the various components of HFC network upgrades, DOCSIS 4.0 is making progress.

On the technology and product side, Broadcom and Comcast have teamed up on a "unified" family of silicon for DOCSIS 4.0-powered modems, nodes and amplifiers that supports both flavors of the specs: Full Duplex (FDX), an option championed by Comcast, and Extended Spectrum DOCSIS (ESD), an option that many other cable operators are pursuing.

Those new, unified chipsets will also bake in some key artificial intelligence and machine learning technology designed to help operators closely monitor the network and rapidly pinpoint issues that might crop up.

Those chipsets are expected to play a big role in Comcast's DOCSIS 4.0 deployment, which is already underway in parts of Colorado Springs, Colorado and in Atlanta, with a rollout in the operator's hometown of Philadelphia on deck for later this year.

Meanwhile, MaxLinear has introduced the Puma 8, a modem chipset that supports the ESD option of DOCSIS 4.0. Askey, CommScope and Hitron are among the "early access partners" for the Puma 8. MaxLinear has not announced plans to develop DOCSIS 4.0 silicon for nodes.

Dell'Oro's Heynen noted in a blog post that Broadcom's unified approach makes great sense at the CPE level, but he wondered if the premium for unified chips for other parts of the network, including the amps and the node, will draw much interest from cable operators that are already fixated on the ESD option for DOCSIS 4.0.

"It is hard to imagine an operator who has committed to one DOCSIS 4.0 technology being willing to spend additional money on optionality it likely will never use in significant volumes," he wrote.

Heynen, along with other industry sources, said the additional telemetry, artificial intelligence (AI) and machine learning (ML) components associated with those unified D4.0 node and amplifier chips provide some solid benefits, but operators will need to determine whether those benefits are worth the premium.

Broadcom JDA concerns

Meanwhile, initial access to those new unified chips is limited to operators that have signed a joint development agreement (JDA) with Broadcom. Those JDAs, sources said, can cost up to $20 million, covering technology development and certain volume commitments.

One industry source said the costs of the Broadcom JDA are based on a per-subscriber basis and spread over multiple years.

"It's all about Broadcom making sure operators are serious about them developing this next-generation chip," the source said.

Broadcom has committed to opening up access to its new unified D4.0 chipsets to the general market but has not pinpointed when operators outside the JDA can gain access.

Industry sources said Comcast, Charter Communications, Rogers Communications, Cox Communications and Liberty Global are among the operators that signed Broadcom's original D4.0 JDA. But it's unclear if Charter is onboard with the JDA for the new unified silicon. Charter is currently leaning towards MaxLinear's D4.0 chip, which is not encumbered by a JDA, the sources said.

MaxLinear has not announced plans to develop DOCSIS 4.0 node silicon for the ESD option of the specs. Notably, such a product would drive much lower volumes than the D4.0 modem chips. However, operator interest in MaxLinear's JDA-free approach is giving the chipmaker more reason to pursue such a project, another industry source familiar with DOCSIS developments said.