The industry is making significant progress with Full Duplex (FDX) DOCSIS, an extension to DOCSIS 3.1 that will position cable operators to deliver multi-gigabit symmetrical speeds on their HFC networks.
Though current consumer demand for an upstream path that’s so speedy isn’t hear-and-now need, FDX will get cable ahead of the curve before it truly is needed and give it a new option that will help MSOs compete with the “billboard” speeds that are being marketed today by telcos and other rivals that are delivering service on fiber-to-the-premises networks.
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“I think the biggest fear that the operators have is that their competition may one-up them and offering 1 Gbps service when they [the cable operators] are limited to 50 Mbps upstream or 100 Mbps upstream,” Tom Cloonan, chief technology officer of network solutions at Arris, said.
Cloonan said the upstream average today is somewhere in the neighborhood of 100 kbps, but acknowledged that being able to deliver billboard speed of 1-Gbps in the upstream will give cable operators a way to fire back in the marketing game as MSOs face off against FTTH competition that is already offering speeds of 500 Mbps or 1-Gig in the upstream direction.
Enabling FDX DOCSIS will help cable operators deliver on HFC the kind of symmetrical speeds that are delivered by fiber-to-the-home architectures. Early on, it’s more likely that FDX will help operators meet the upstream demands required by business service customers.
But starting to pivot in that direction today will also help cable operators future-proof their networks and get the best bang for the buck, according to John Chapman, a fellow at Cisco Systems and the CTO of the company’s cable access business.
“If you’re going to spend money on the plant…do you do a small upgrade, or do you do a big upgrade?” he asks. “Ideally you spend the money on the plant once and it lasts for a long time.”
Operators, he points out, could opt to do a mid-split, raising the available upstream spectrum to 85MHz – enough to open the door to about 400 Mbps.
“It’s not going to be a ten-year plan,” Chapman said. “It’s going to get tight at some point in time.”
Operators can also push the upstream to 204 MHz, sometimes called a “high-split,” which would put MSOs in a position to offer more than 1 Gbps in the upstream.
Chapman points out that it also requires a significant change to the plant, so if an operator is already committed to changing diplexers and amplifiers and return path amps, why not take the next step and implement a true next-gen frequency plan for the upstream and get ahead of the curve?
“What more bang for the buck could you get for that [work]?” he said. “We’ve Full Duplex lined up for that. It will have built-in future proofing…it negates the need to go to fiber [to-the-home].”
He also sees FDX being deeply coupled with other next-gen access network moves, such as fiber deep, which replaces one node with between 12 to 18, and new distributed architectures. “It’s like a package deal.”
Though there’s no immediate need for FDX, suppliers now have a technical path forward for products that will support it in the years to come.
Earlier this month, CableLabs released the physical layer specifications for FDX, arriving a little over a year after CableLabs started the specification writing process. CableLabs introduced the concept in February 2016.
CableLabs, which released the PHY layer specs on October 5, said this signals that FDX has reached the “advanced maturity stage,” enabling vendors to push ahead with their product development, Belal Hamzeh, vice president, research and development, wireless technologies at CableLabs, said.
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Cloonan said he expects operators to turn up spectrum in that FDX band in phases. “Maybe they’ll turn on 96 MHz or 192 MHz…and a few years later turn on another 96 MHz, or another 192 MHz chunk of spectrum,” said.
Some industry experts see FDX trials getting underway sometime next year and into 2019, with 2020 seen as the technology’s first significant deployment year.
Demos of FDX-facing technologies and products are expected to be on show at this week’s SCTE•ISBE Cable-Tec Expo in Denver.
Arris, Cloonan said, will offer an “early stage demo” of its FDX handiwork this week. “We’re not in the end zone yet, but we’re moving down the field quickly."
Cisco, Chapman said, will follow up on its earlier FDX-based demos, including a recent look at an echo-canceller technology that will be required. This week, it will also demo the concept of “sounding,” that involves the measuring of attenuation between the modems on a particular node. That will be used to put certain subscribers into separate transmission groups and on different frequency plans to ensure that they are not interfering with each other.
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That, in part, is “how we achieve the trick of Full Duplex” in a point-to-multipoint system, he said, noting that reusing spectrum for both upstream and downstream traffic seemed like a pipe dream just a couple short years ago. “A lot of this is pretty clever rocket science.”
“It’s a challenging design, one of the most challenging DOCSIS specs because of the complexities of managing bandwidth in the upstream and the downstream direction…and the echo-cancellation circuits that are needed to make this work,” Cloonan said.