How Broadcom and MaxLinear will push the limits of DOCSIS 3.1

DOCSIS 4.0 is cable's Next Big Thing in broadband, poised to enable symmetrical multi-gigabit speeds alongside lower latencies and enhanced security on widely deployed hybrid fiber/coax (HFC) networks.

Comcast intends to go big on DOCSIS 4.0, having lit up the technology in a pair of markets in preparation for a broad rollout. Other large and midsized operators, including Charter Communications, Cox Communications, Cable One and Mediacom Communications, intend to deploy D4.0 in some shape or form.

But, as Light Reading recently reported, there's a groundswell of interest among operators to push the limits of their DOCSIS 3.1 networks by taking advantage of new/upgraded D3.1 modems that can utilize additional blocks of OFDM (orthogonal frequency-division multiplexing) spectrum in tandem with some tweaks to existing, chassis-based cable modem termination systems (CMTSs). There's also interest in delivering more speed by operating new DOCSIS 4.0 modems on DOCSIS 3.1 networks.

Some initial estimates indicate that this approach could enable operators to deliver DOCSIS 4.0-like speeds on today's D3.1 networks – something in the order of up to 8 Gbit/s downstream and more than 1 Gbit/s upstream. Full DOCSIS 4.0 technologies will be capable of delivering a bit more downstream speed along with multiple gigabits per second in the upstream direction.

Related:All roads won't lead to DOCSIS 4.0

And when paired with a node split or two, this extended/boosted approach could extend the life of DOCSIS 3.1 networks for years, effectively delaying the need for some operators – in the US and abroad – to push ahead full-blown DOCSIS 4.0 network upgrades.

What's next for DOCSIS 3.1

The ability to add two or more OFDM channels in DOCSIS 3.1 modems (up from the two OFDM channels supported in today's equipment) is covered in the CableLabs DOCSIS 3.1 specs. However, suppliers and operators have been referring to this emerging option as "enhanced" or "extended" DOCSIS 3.1 (or DOCSIS 3.1e), "ultra DOCSIS" or even DOCSIS 3.1+. Harmonic called it "boosted" DOCSIS 3.1 at demos shown at the recent SCTE Cable-Tec Expo in Denver that paired modems from Vantiva and Sagemcom with its current lineup of network gear and software.

But whatever label is being applied, two cable modem chip-makers – Broadcom and MaxLinear – are already laser-focused on this development.

Broadcom's BCM3392

Broadcom, Light Reading has learned, is developing the BCM3392, a new DOCSIS 3.1 chip that can support four 192MHz-wide OFDM channels for downstream traffic (up from the two OFDM channels supported by the current-gen BCM3390 chip).

Related:Comcast unleashes DOCSIS 4.0 service under 'X-Class Internet' brand

Broadcom declined to comment about the BCM3392, but multiple industry sources said the new chip is already sampling and is expected to be ready for commercial deployment in early 2024.

Perhaps the bigger implication for operators and modem makers is that the BCM3392 is not subject to a restrictive (and expensive) joint development agreement (JDA) that temporarily limits access to Broadcom's new DOCSIS 4.0 chipsets to those that sign the JDA – a group that includes Comcast, Charter Communications, Rogers Communications and Liberty Global.

Jeff Heynen, VP at Dell'Oro Group, believes Broadcom's new D3.1 chip and its lack of a JDA requirement will have some legs. The BCM3392 is poised to supply operators with access to a new line of interim "boosted" DOCSIS 3.1 modems that can quickly improve the performance out of their D3.1 networks and put them in better position against fiber competition, he said.

"It will allow them to take an incremental approach and stay competitive on the billboard speed side," Heynen explained

"It's got some interesting potential," a cable industry source familiar with Broadcom's new D3.1 chip said.

It's a "big deal" that the operators and suppliers will be able to source products based on the BCM3392 without signing a JDA with Broadcom, the source added. "It's completely unencumbered. Every vendor and operator worldwide can use that chip."

Related:Comcast, Broadcom chip in to unify DOCSIS 4.0

Broadcom hasn't released any formal details about the BCM3392, but industry sources said pricing on it is expected to be only incrementally higher than the current-generation BCM3390 D3.1 chip. There's some expectation that Broadcom will make the BCM3392 its primary D3.1 chip and eventually end-of-life the BCM3390.

MaxLinear: 'Puma 8' chip can do extended DOCSIS 3.1 or D4.0

MaxLinear is also focused on this developing part of the DOCSIS tech sector.

MaxLinear recently introduced the Puma 8, a cable modem chipset that uses the extended spectrum DOCSIS (ESD)/frequency division duplex (FDD) flavor of DOCSIS 4.0.

However, the Puma 8 can also be adapted – with a "minor board change" – to work as an extended DOCSIS 3.1 modem that supports up to five OFDM downstream channels, according to Will Torgerson, VP and GM of MaxLinear's Broadband Business Unit.

That D3.1-focused version of the Puma 8 – something MaxLinear likes to call "Ultra DOCSIS" – would feature the same baseline silicon and software as the D4.0 version, but would not include a programmable gain amplifier (PGA) that delivers the higher upstream splits (up to 684MHz) in the full-blown D4.0 version. The elimination of that PGA would also ensure that the D3.1 version of the Puma 8 costs only "incrementally" more than MaxLinear's legacy DOCSIS 3.1 Puma 7 chip, Torgerson said.

Effectively, cable modem suppliers could create multiple models based on the Puma 8 – a version with DOCSIS 3.1e/Ultra DOCSIS, and another that implements the full DOCSIS 4.0 specifications.

"Operators that don't want to deploy DOCSIS 4.0 still have an upgrade path," Torgerson said. "We've always viewed the cable market as needing evolutionary steps that don't break the bank."

He said options with the Puma 8 could open up a wide range of deployment scenarios.

While some operators might deploy the DOCSIS 3.1 version knowing they won't ever upgrade the network to DOCSIS 4.0, others could opt to deploy the DOCSIS 4.0 iteration and run it on their DOCSIS 3.1 networks while they upgrade to DOCSIS 4.0. Still others might use the DOCSIS 3.1 version of the Puma 8 initially while network upgrades are underway and then later swap out those modems with the modems running the full DOCSIS 4.0 Puma 8 chipset.

"We see a lot of interest in the market just for offering that incremental speed step" in North America and Europe, Torgerson said.

Can legacy CMTSs handle the load?

Alongside these cable modem developments, there is a debate underway about whether legacy, integrated CMTSs outfitted with updated software can handle this upgraded form of DOCSIS 3.1 and the additional capacity it brings with it. That limitation might instead lead operators to instead pursue distributed access architecture (DAA) paired and virtual CMTS upgrades.

Dell'Oro's Heynen reckons that some operator decisions will be driven by the age of their legacy CMTSs.

But D3.1e might prolong the life of newer CMTSs, Heynen said. Using that legacy gear might also be particularly attractive to cable operators seeking a way to quickly deploy gigabit or multi-gigabit broadband service to fend off a competitive fiber overbuilder, he added.

But Heynen also believes that many cable operators will ultimately choose to move to DAA to take advantage of the network performance and reliability, space and power benefits they'll get by moving to a distributed network. Those performance and operational issues were present well before DOCSIS 3.1+ started to emerge, he points out.

Harmonic, the market's leading vCMTS provider and a major supplier of DAA nodes, naturally believes that cable operators face a better future if they pair a "boosted" DOCSIS 3.1 rollout with a distributed network and a virtualized access platform.

"We think it's a great step ... and it's our experience that having a vCMTS is crucial there," Asaf Matatyaou, senior vice president, product, for Harmonic's broadband business, said.

Some legacy integrated CMTSs could have trouble scaling to support the additional capacities enabled by extended DOCSIS 3.1, he said, echoing skepticism that some cable operator engineers have expressed to Light Reading.

"Supporting more OFDMs comes at the expense of port density on that aging equipment ... that's the tradeoff," he said.

Harmonic's current lineup of software and remote PHY devices "have no problems supporting these boosted DOCSIS 3.1 speeds," Matatyaou said.

Harmonic, he added, is already working with "multiple [cable modem] silicon vendors" that intend to roll out updated cable modem chipsets capable of delivering higher counts of OFDM channels in early 2024.