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Cable upstream growth went 'bonkers' during early stages of pandemic – CommScope

The demands placed on residential cable networks during the COVID-19 pandemic could be a wake-up call for cable operators to beef up their upstream capacity.

Although peak data usage on hybrid fiber/coax (HFC) networks has plateaued in recent weeks, the demand placed on residential networks as millions hunkered down to work and school from home has caused MSOs to accelerate discussions about longer-term moves that will add critically needed capacity to the upstream, a top CommScope exec says.

"It has changed the conversation," Tom Cloonan, chief technology officer, broadband networks, at CommScope, said, noting that one of the company's MSO customers plans to deploy a year's worth of node splits in the next three months to ensure it can handle today's demands and stay ahead of the curve. "Medium-term plans are becoming near-term plans."

And those plans are being pushed up a bit amid the recent surge in usage of videoconferencing and online collaboration tools and other apps and services that put more pressure on cable's upstream.

According to data generated from some of CommScope's cable operator customers around the globe, upstream usage surged in March when stay-at-home orders became more prevalent. Specifically, upstream usage during midday hours grew between 30% for some operators and an astounding 150% for one European-based operator. Plus, during normal busy primetime hours, upstream demand climbed 20% to 50%.

But rather than peaking at night as in pre-COVID-19 times, the upstream peak now resembles a long, flat curve, starting at 7 a.m. and running till midnight, according to CommScope's data. "The upstream was sorta going bonkers through the whole day like that," Cloonan observed.

Downstream usage also climbed during this period, but the overall rise in peak demands put much more pressure on the available upstream overhead. That's mostly due to the asymmetric nature of the HFC network, as much more spectrum is currently dedicated to downstream traffic than the upstream.

CommScope has posted some additional details on its findings, data usage trends and suggestions on how MSOs can get on top of it all using a range of near-term and longer-term solutions in this blog post.

Nearing the upstream ceiling
Although HFC networks have been up to the task so far, with upstream peaks rising close to the limit on some networks, the concern is that the "new normal" won't simply revert back to the peak usage patterns seen prior to the pandemic. The expectation is that demand for upstream capacity will remain heavier than normal, and possibly grow even heavier, requiring cable operators to push forward on upstream bandwidth expansions.

"There's been generally an awakening that we banged our heads on the ceiling here and we're closer to the ceiling than we realized," Cloonan said.

Possible moves could include a "mid-split" that raises the upstream to 85MHz (up from today's 42MHz on most North American DOCSIS networks) or a "high-split" that lifts the ceiling to 204MHz. In tandem, cable operators could also beef up the spectrum available for the downstream by upgrading the network to 1.2GHz using today's DOCSIS 3.1 technologies, and use that as a stepping stone toward an expansion to 1.8GHz and DOCSIS 4.0.

Cloonan said some cable operators will be increasingly active with upstream augmentation activities this year, expecting some trials to get underway this year and expand into 2021. He noted that an 85MHz mid-split appears to be the current "sweet spot" for several cable operators.

Near-term tools
But expanding the upstream is a time-consuming and complicated task that requires operators to touch the network. Even if those plans do speed up, they won't be accomplished overnight.

In the meantime, cable operators have access to several tools that can help them reduce upstream congestion on the HFC network today, Cloonan said. He noted that a recently assembled task force put together a list of things MSOs could implement to relieve some of the pressure.

An option that has proved popular early on is raising the "Tmax" value on cable broadband customers that are on low-level tiers that might be the first to feel the pain. Customers on tiers with small upstream data allowances could be bumped up a smidge to provide some relief when upstream congestion occurs. Tweaking those Tmax values can be done by adjusting the "mapper" of the cable modem termination system (CMTS) and making a small change at the modem level.

"That's been the most popular of the proposals," Cloonan said. "It's a simple change to a CM [cable modem] config file and – boom – they suddenly have a little more bandwidth given to them during crunch times."

Some cable operators are also looking to switch on TCP ACK suppression in modems. That move can excise some data out of the upstream mix by tossing aside unnecessary TCP ACK packets that are typically sent upstream to tell servers it's okay to send the next batch of downstream packets to the modem.

Cloonan said yet another tool that cable ops have is ensuring that buffer control TLVs (time length values) are turned on in the modems to ensure that the devices aren't retaining a bunch of packets during congestion periods that lead to "buffer bloat" and cause latency-sensitive apps to suffer.

"Upstream traffic is the main bottleneck right now and [cable] modems have a lot to say about how things pass through the network," Cloonan said. He adds that upgrades of Wi-Fi routers or the introduction of extenders are among other short-term, quick fixes available to cable ops.

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— Jeff Baumgartner, Senior Editor, Light Reading

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