Another way cable ops are squeezing more out of their DOCSIS networks

It's becoming increasingly clear that DOCSIS still has plenty of gas left in the tank as cable operators explore options that allow them to defer fiber-to-the-premises (FTTP) upgrades well into the future.

In addition to the ongoing use of traditional node splits, operators are looking to "stretch" the life of DOCSIS 3.1 networks with new modems and cable modem termination system (CMTS) software updates that support additional OFDM (orthogonal frequency division multiplexing) channels, putting them in position to deliver about 8 Gbit/s in the downstream. Others are moving toward DOCSIS 4.0 – an upgrade of the hybrid fiber/coax (HFC) network that delivers symmetrical multi-gigabit broadband speeds.

Another option at cable's disposal that doesn't get quite the same billing is the Profile Management Application (PMA), a technique that helps DOCSIS 3.1 modems take advantage of the highest available modulations, even in the presence of speed-reducing noise. Instead of having all of the nearby modems run at a relatively low modulation level that's supported by the worst-performing modem in the lot, PMA enables DOCSIS 3.1 modems to dynamically and automatically operate at the highest modulation level they can support as network conditions change.

Related:CableLabs unit and OpenVault connect on tech that squeezes more out of DOCSIS 3.1

PMA developers claim that the technology can boost the efficiency of an operator's OFDM (downstream) or OFDMA (upstream) channels by up to 40%.

If one D3.1 modem is generating a lot of noise, it can force other nearby modems to connect to lower modulations or refuse to connect to OFDM channels and instead shift their connections down to DOCSIS 3.0-style 6MHz-wide QAM channels. In that scenario, those D3.1 modems are not getting the optimum speed while also tapping into network capacity that's typically set aside for DOCSIS 3.0-only modems. That situation exists in part because DOCSIS 3.1 modems are backwards-compatible – they support blocks of the newer, more efficient OFDM channels, which comprises tiny subcarriers, or the less-efficient 6MHz QAM channels that are being bonded together for DOCSIS 3.0.

But issues can arise if there are impairments on OFDM channels, which can cause D3.1 modems to refuse to connect to the OFDM channels set aside for DOCSIS 3.1.

PMA jams more bits down the pipe

To help remedy that, PMA is designed to help cable operators pump more bits down the pipe in the same amount of bandwidth. Without PMA, operators stand to waste their existing bandwidth.

PMA was spawned out of CableLabs, which has also developed network-deployable software that operators can use on their DOCSIS 3.1 access networks. Kyrio, a subsidiary of CableLabs known for things like DOCSIS certification testing, recently launched a PMA Partner Program to help vendors accelerate their respective PMA strategies. In turn, cable tech suppliers have developed PMA products and have since moved ahead with operator trials and deployments.

Related:OpenVault adds network troubleshooting tech as cable preps for DOCSIS 4.0

OpenVault and ZCorum have partnered on PMA products. OpenVault primarily focuses on selling PMA to large operators while ZCorum focuses on Tier 2/3 operators. Comcast is taking a similar approach with "Octave," an AI-assisted technology that it fast-tracked during the earlier phases of the pandemic as broadband usage surged as millions of customers worked and schooled from home. It's not clear if or when Comcast will syndicate Octave as it has other technologies and products, such as X1.

A critical component of PMA is automation, explained Rick Yuzzi, VP of marketing at ZCorum, a company that counts customers such as Crossroad Fiber (a Massachusetts municipality), Southern Kansas Telephony Company and Benton Communications. By running PMA as a closed-loop running in the background, modem modulation profiles can be changed dynamically as plant conditions change.

"It takes a lot of work" to manage those modem modulation profiles manually, Yuzzi said.

"The key idea is to use clustering algorithms to group modems that have similar signal-to-noise signatures across the channel and then design a profile for each group," Karthik Sundaresan, a distinguished technologist at CableLabs, explained in this 2019 blog post about PMA. "The PMA algorithm searches for the best set of profile definitions to maximize the overall capacity and at the same time keeps the individual profiles robust to observable interference patterns."

Sundaresan estimated at the time that operators can use PMA to boost bandwidth efficiency by 15% to 40%, translating to 200 Mbit/s to 400 Mbit/s of extra capacity on each OFDM channel while also deferring the need for node splits.

Trial and deployment activity

Operators are starting to explore the benefits of PMA.

PMA "is a huge part of our pipeline," OpenVault CEO Mark Trudeau said, noting that PMA has a synergistic relationship with another product area – proactive network maintenance (PNM), which is focused on finding and fixing plant impairments.

PMA, he says, helps operators work around those impairments and boosts the capacity of customers with DOCSIS 3.1 modems that are at risk of dropping off the OFDM spectrum.

A recent test with an unnamed cable operator highlighted the benefits of PMA. In that scenario, 134 DOCSIS 3.1 modems in a location had dropped off of the OFDM spectrum to DOCSIS 3.0 channels because of an impairment. However, optimizations with PMA enabled 124 of them – about 92% – to shift back to the DOCSIS 3.1 part of the network, he said.

"It not only is helping the DOCSIS 3.1 customers get what they are paying for and the operators optimizing the investments they've made in DOCSIS 3.1, but it's helping DOCSIS 3.0 customers as well," Trudeau said. "The capacity on that [DOCSIS 3.0] side of the network more than doubles the available capacity through the use of PMA. It really does help everybody."

Trudeau said OpenVault has nearly three dozen trials underway or planned with operators, with several on tap to convert to commercial deployments.  

Given that some data sets for PMA and PNM use the same tools, OpenVault is looking into ways to integrate those products into a single platform, he said.

Yuzzi said ZCorum, which sells other services focused on areas such as cybersecurity and provisioning, also has trials underway and has some operators who have committed to deployments.

OpenVault and ZCorum have yet to reveal those operator partners.