Arris CTO: What's Next for DOCSIS?
As an extension to DOCSIS 3.1, Full Duplex DOCSIS (FDX) will put cable operators in position to deliver symmetrical gigabit speeds over their widely deployed HFC networks, in part by letting upstream and downstream traffic live and breathe in the the same block of spectrum.
While FDX is generally viewed as the next step in cable's HFC evolution, one of its constraints is the requirement of an "N+0" architecture whereby fiber is pulled deeper into the network and all the amplifiers are eliminated between the node and the home. That is the road companies like Comcast Corp. (Nasdaq: CMCSA, CMCSK) are taking as they push ahead with N+0, Remote PHY, and distributed access architectures (DAA), setting up the path to Full Duplex DOCSIS. (See Comcast Eyes 'Scale Deployments' of Remote PHY in 2018.)
But what about the operators out there that have N+3, N+6 or even N+10 environments and those that will not, at least for the foreseeable future, get to N+0? Based on the current requirements of FDX, they're on the outside looking in.
Arris Group Inc. (Nasdaq: ARRS), one of the cable industry's key network infrastructure vendors, says it is making progress with research in two areas -– extended spectrum DOCSIS and a new class of what it refers to as "FDX Amplifiers" -- that would provide MSOs with some of the key benefits of Full Duplex DOCSIS (namely multi-gigabit symmetrical gigabit capacities) without N+0. Looking further ahead, Arris estimates that access networks will need to be ready to deliver about 20 Gbit/s to the home within the next ten to 15 years.
Among the options being explored, expanded spectrum DOCSIS centers on pushing capacity well beyond frequencies such as 1.2GHz or 1.7GHz (1.7GHz is the current, optional spectrum ceiling specified by DOCSIS 3.1), into the nether regions of 3GHz, 6GHz and even 25GHz. Arris execs at a CableLabs conference in the fall of 2015, postulating that capacities of 50 Gbit/s -– or even 200 Gbit/s -- or more are possible by raising the ceiling into those lofty frequencies and, therefore, tacking on capacity before today's DOCSIS and HFC technologies run out of gas by the mid-2020s. (See Here Comes DOCSIS 4.0 and Why DOCSIS May Never Die.)
Fast-forwarding to today, Arris believes that it's possible for Full Duplex DOCSIS and extended spectrum DOCSIS to co-habit and interoperate. Taking it a step further, Arris reckons that it's also possible to tweak expanded spectrum DOCSIS in a way that would keep the downstream and upstream traffic separate -– possibly with a guard band –- using Frequency Division Duplex (how cable separates the upstream and downstream today), rather than having them live together on the same block of spectrum.
In that scenario, the upstream ceiling would be lifted to 300MHz, 492MHz or perhaps 684MHz (something Arris refers to as an "Ultra-High Split"), while the downstream would live above that -- up to 1.8GHz, and potentially even higher up in the spectrum.
That work continues to be ongoing and "semi-promising," Tom Cloonan, CTO of Network Solutions, at Arris, said. Heading to 3GHz and beyond "is a 2035 kind of thing, but, nevertheless, it's doable."
Coincidentally, Arris started to noodle on that when the idea of Full Duplex DOCSIS started to spring up.
"It's an area of research right now" that could be attractive to operators that haven't gone to N+0, or have no near-term plans to do so, Cloonan said. "We view it as a twist or tweak on the extended spectrum DOCSIS proposal."
The idea requires new development as well, but Cloonan notes that this was also the case for FDX three years ago, and that Full Duplex DOCSIS is now on the cusp of becoming a deployment reality as products start to emerge next year and into 2020.
Arris's other, somewhat competitive, research program is focused on the FDX Amplifier, a new-age PHY layer device that would allow Full Duplex (upstream and downstream traffic running on top of each other in the same block of spectrum) to operate in an N+1 or maybe even N+3 environment.
Cloonan said cable operators are starting to study these emerging options, but stressed that it's not clear yet if one or both will pan out and have enough buy-in to turn them into a full-fledged commercial endeavor.
"They all have their ears open to the options," he said. "There's no obvious, clear 100% bet you can place and know it's the winner. We have to look at all of them."
It's also possible that they could both be used, as a phased deployment or a deployment that employs both at the same time.
Next page: Potential product paths and staving off the need to go to FTTP
Extending the life of DOCSIS and HFC, of course, would be good news for vendors in the sector that bank on those technologies and the revenues that future upgrades bring through the door. Although the ideal path, at least from a PHY layer perspective, would be to enable these new capabilities with modules that can snap into existing gear, such upgrades are likely to also require new network equipment (including CMTSs, nodes and active devices), as well as modems that can support the new, proposed upstream split and extended spectrum for the downstream.
If one or both of the ideas have legs, it could eventually make it up to the CableLabs level. The organization has made no announcement about a formal initiative. However, at a panel in June, CableLabs principal architect Doug Jones hinted that the organization was working on a plan to get cable operators to symmetrical 1-Gig based on an N+5 environment.
And the crystal ball says...
Cloonan said it's too hard to predict when either option under study might reach commercial status. But he guesses that the mid-2020s is a possibility, though that target will likely move based on operator requirements and how network traffic patterns fluctuate in the coming years.
For now, Arris is running tests (mostly as lab simulations, as it originally did with FDX and DOCSIS 3.1) and has done some early product design work. Cloonan said Arris will have some of that handiwork on display at this week's Society of Cable Telecommunications Engineers (SCTE) Cable-Tec Expo in Atlanta.
And if there's anyone qualified to opine on the future of DOCSIS and the HFC network, it's Cloonan. After all, he's been front and center and a major engineering force in driving the direction of DOCSIS's past, present and future, and ensuring that cable stays a few steps ahead of the capacity curve.
Cloonan, who was with Bell Labs for 17 years working on technologies like ATM switching and high-speed routing before pivoting to cable, was involved in the early, 1.0 days of DOCSIS at Cadant, a cable modem termination system (CMTS) startup that Arris acquired in 2002. Since then, he's been shepherding the spec to 1.1, 2.0, 3.0, 3.1, and FDX… and likely will help influence where it goes next.
HFC or FTTP? The debate that never dies
Arris is also pursuing what could be next in HFC's evolution amid the ongoing debate on when -- rather than if -- MSOs will just make the leap to fiber-to-the-premises. Though Altice USA is an outlier among domestic operators, most US cable operators continue to upgrade HFC networks incrementally as they push fiber closer to the home. (See Altice USA Lights Up FTTH Service in Long Island.)
Cloonan says the debate centers on the economics and the business case, noting that the company's own studies continue to show that switching to PON on a per-subscriber basis still costs a lot more than it does to enhance and upgrade capacity on existing HFC networks.
Greenfield scenarios are a different story. "If you're putting something new in the ground, you should probably put fiber," he said.
— Jeff Baumgartner, Senior Editor, Light Reading