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Cable Tech

DOCSIS 3.1 has lots of gas left in the tank

CABLE NEXT-GEN TECHNOLOGIES & STRATEGIES 2022 – DOCSIS 4.0 represents the future of the hybrid fiber/coax (HFC) network, but industry experts believe that squeezing everything out of DOCSIS 3.1 sets up cable operators to cost-effectively keep pace with fiber competition for several years.

Getting more out of DOCSIS 3.1 means upgrading HFC network spectrum to 1.2GHz (versus 750MHz, 860MHz or even 1GHz today) paired with a "high-split" that significantly beefs up the amount of capacity dedicated to the upstream.

That combo effectively puts cable in position to offer 4.5 Gbit/s to 5.5 Gbit/s downstream and in the range of 1.3 Gbit/s to 1.6 Gbit/s in the upstream, Jay Rolls, senior advisor at Broadband Success Partners, explained. That will enable cable to pivot from a somewhat uncomfortable 10:1 downstream/upstream ratio to a more comfortable ratio of about 4:1, he said.

"We still have a lot of headroom with DOCSIS 3.1," agreed Robin Lavoie, fellow, network architecture and strategy at Canada's Cogeco Communications.

"It's definitely enough [capacity] for the next few years," said Rolls, a cable industry vet who formerly was the CTO of Charter Communication. "I think that should be a major strategy from operators when they look at DOCSIS 3.1."

That's partly because the technology is ready today, as it can be supported on widely deployed DOCSIS 3.1 modems. "There's nothing revolutionary about this. It's about taking DOCSIS 3.1 out to its capabilities," Rolls explained.

Rob Flask, head of product line management, cable instrument solutions, at Viavi, also points out that cable operators still have the opportunity to mine more spectrum that can be applied toward DOCSIS 3.1 as they shift to IPTV and start to turn down legacy video services that use QAM transmission. That sort of move would enable operators to fill up most of their spectrum with DOCSIS 3.1 carriers and to use dynamic bonding groups to support more services.

Rolls noted that D3.1 enhancement costs are also attractive. Deployment models he's seen for the 1.2GHz/high-split option suggests a cost of about $100 per home passed, and about $50 per home passed in deferred node split capex. Meanwhile, the deployment of new 1.8GHz network elements are heading to market, and operators can take advantage of those to seed the network for future DOCSIS 4.0 upgrades.

"It's a very compelling, interesting case that I think people should be really looking hard at," Rolls said.

Midco, a mid-sized US operator, is among the MSOs that are exploring this option in the labs, according to Pao Lo, Midco's VP of network engineering. "We're testing it; we're then looking to operationalize it to see how we might roll this thing out while we're waiting on DOCSIS 4.0," he said.

Multi-gig symmetrical speeds on the rise

Panelists acknowledged that AT&T's widespread launch of symmetrical 2-Gig and 5-Gig services over fiber has grabbed the cable industry's attention. Whether consumers or today's range of apps actually need those speeds is an entirely different question.

"I think it's more of a marketing ploy," James Brannan, senior manager of product management, cable and mobility technical marketing at Cisco, said.

Lo said he's "not worried at all" about AT&T's recent multi-gig moves, noting that Midco offers 10-Gig EPON in its fiber-to-the-premises (FTTP) markets. "We don't need to offer 5-Gig to 10-Gig today unless competition introduces it. But we have the levers to do that," he said.

But Lo acknowledged that the bigger concern from a competition standpoint is the emergence of new PON technologies that will support 25-Gig and 50-Gig. "That's really going to accelerate this technology push and technology upgrade cycle."

The role of DOCSIS 4.0

So, where does this leave DOCSIS 4.0? Rolls believes that the need to have D4.0 in cable's arsenal is important, even if the need to deploy it is not imminently pressing. "I think some DOCSIS 4.0 deployments could be quite a few years out to really hit broad, mass market – as many as five years out from now," he said.

James Brannan, senior manager of product management, cable and mobility technical marketing at Cisco, believes that enhanced D3.1 and D4.0 will have a critical role to play as multi-gigabit offerings continue to seep into the market, and particularly in competitive markets where cable operators might not yet have a PON offering to put forth.

But it's also clear that D4.0 won't be the only path forward, as operators go with FTTP in greenfields and possibly in some brownfield areas as well, when necessary.

Lavoie said Cogeco will use a mix of access network technologies. "I know DOCSIS 4.0 will apply...DOCSIS 4.0 will be a tool that's usable, just not everywhere." DOCSIS 4.0 will add capacity on top of DOCSIS 3.1, "but not that much," and will require new customer premises equipment (CPE), he added.

The bigger question, Lo said, is when operators eventually "cap" the HFC network. They'll need to weigh whether to go with DOCSIS 4.0 and a new virtual cable modem termination system (vCMTS) or to spend that money on OLTs (optical line terminals).

Lo noted in a follow-up keynote presentation that the cost of an OLT is lower than a vCMTS, and that fiber-to-the-premises is the true "end game."

"I'm not ruling out [DOCSIS 4.0], but I'm going to say that the timing of it is going to suffer because 25-Gig is upon us and C-PON [coherent PON] is slowly getting there. When that really hits, I think it might be a limited play at best," he explained.

Midco, Lo added, will vet DOCSIS 4.0. In the meantime, Midco's HFC network strategy is focused on 1.2GHz plant with a "mid-split" (moving the upstream path up to 85MHz) and an N+0 architecture that pushes fiber deeper and eliminates all amplifiers between the home and the node. Midco is also pursuing a distributed access architecture (DAA) with remote PHY and is starting to evaluate 1.8GHz technology.

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— Jeff Baumgartner, Senior Editor, Light Reading

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