CableLabs sticks a fork into DOCSIS 4.0 specification

After years of fine-tuning, the cable industry now has its next-generation DOCSIS 4.0 specification in place to help drive faster gigabit speeds going forward. After first starting development four years ago, CableLabs announced the release of the DOCSIS 4.0 specification on Thursday.

DOCSIS 4.0 was designed to hit downstream speeds of up to 10 Gbps, which is twice the download speed of DOCSIS 3.1, and an upstream of up to 6 Gbps (quadruple the DOCSIS 3.1 upstream speed.) DOCSIS 4.0 is also a cornerstone of the cable industry's 10G platform.

DOCSIS 3.1, which is widely deployed, theoretically enables 10 Gbps downloads and 1 Gbps uploads, but cable operators have not come close to those numbers in either direction. Real-world implementations of DOCSIS 3.1 often max out at 940 Mbps down and 35 Mbps up. 

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"DOCSIS 4.0 is critical in setting the roadmap for all the technologies, and obviously for all of the components suppliers and system vendors to start developing to," said Jeff Heynen, senior research director at Dell’Oro Group. "We're really looking at a timeline from beginning in early 2022 as the early stages of deployment for infrastructure and upgrading the outside plant all the way through 2027 and potentially beyond. So that the theory is what DOCSIS 4.0 gets you.

"And of course, if full duplex is ultimately your end game for DOCSIS, then it could it could last longer than that."

The key factor for getting the DOCSIS 4.0 specification into the books was including both full duplex DOCSIS (FDX), which is backed by Comcast, and extended spectrum DOCSIS (ESD) into the specification, as well as low latency, according to Heynen.

Higher upstream speeds can be enabled through full-duplex functionality, which in turn requires a "node plus zero" (N+0), fiber deep architecture (no amplifiers after the cable node.) All of which, other than for Comcast, is a long way off for most cable networks. 

ESD enables operators to extend the usable downstream spectrum on their existing HFC networks up to 1.8GHz.

"Extended spectrum allows them to achieve those 10 gigabit speeds without having to go to node plus zero," Heynen said. "So that's a huge cost savings for them.  

"A lot of cable operators, like Cox and others, had looked at full duplex and then ended up realizing the construction costs and labor costs of redoing their nodes and amplifies was just going to be too costly. There was this groundswell over the last two years to expedite extended spectrum."

Heynen said Comcast has a few small full duplex deployments in some areas. While Comcast may be one of the few cable operators pursuing full duplex, Heynen said other North American operators in particular will probably end up using it as well as they convert their existing amplifiers to nodes as part of an upgrade cycle over the next few years.

"A lot of these North American operators know they are going to have to touch the amplifiers and taps over the coming years, which is why it's very important to get these different technologies into the 4.0 specification," he said.

Even with the 4.0 specification being released, DOCSIS 3.1 will have long shelf life on HFC networks going forward, according to Heynen.

"I think the other question before we even get to 4.0 is what is going to happen with 3.1 because there's still plenty of operators who are in the early stages of upgrading to 3.1," he said. "My analysis, from talking to the operators and the vendors, is that until 4.0 really becomes available through new line cards, nodes and amplifiers apps, they're still really focused on doing mid-splits, and some cases high-splits to improve the upstream bandwidth, and that's within the context of 3.1.

"So, just because 4.0 is being released, that certainly doesn't mean the end of 3.1."