Comcast wields low latency as broadband differentiatorComcast wields low latency as broadband differentiator

Comcast introduced a standards-based low-latency feature that's estimated to reduce 'working' latency by about 75%. Apple, Meta, Valve and Nvidia have partnered with Comcast to extend support to latency-sensitive apps and services.

Jeff Baumgartner, Senior Editor

January 29, 2025

6 Min Read
Back view of a man playing online multiplayer shooter game
(Source: ronstik/Alamy Stock Photo)

Speeds and feeds remain important attributes of home broadband services. But Comcast is looking to improve the overall performance of its home broadband service with the launch of a new low-latency technology that will eventually become available to all of its high-speed Internet customers.

Following trials that got underway back in 2023, Comcast is now starting to deploy a new low-latency capability in a handful of upgraded markets and its latest family of DOCSIS gateways. Early on, Comcast's new low-latency tech will be compatible with a range of apps and services from several partners, including Apple, Meta, Nvidia and Valve.

Initially focused on its widely deployed DOCSIS network with support for fiber-to-the-premises (FTTP) networks on deck, Comcast's new, standards-based feature will reduce "working latency" by about 75%, according to Jason Livingood, Comcast's VP of technology policy, product and standards.

A primary goal is to reduce latency variability. That means more predictable levels of latency and the elimination of spikes that can send latencies into the hundreds of milliseconds, even under normal network load conditions. Livingood estimates that Comcast now has the ability to cut down latency on its DOCSIS network to the neighborhood of 45 milliseconds when active queue management (AQM) is turned on, and reduced further – to 21ms or 22ms – when Low Latency DOCSIS NQB (non-queue building) capabilities are added to the mix.

Related:Comcast sparks field trials of low-latency DOCSIS

Livingood said bringing this improved level of consistency to latency will benefit not only broadband customers but application developers as well. App developers, he said, can adapt to certain levels of latency, but can struggle when there's high and unpredictable variability that, for example, can cause buffering.

In the broadband world, this approach also aims to give latency equal footing with bandwidth, and to have low-latency play a significant role in improving the performance of video conferencing apps, video streaming, online gaming and other types of latency-sensitive apps.

"In this era when people have 1-Gig connections, [some] still have poor gaming and video conferencing … the reason's not bandwidth; it's latency," he explained. "There's not a big difference from the user experience of going from 1-Gig to 2-Gig, but going from a few hundred milliseconds of working latency down to 30 milliseconds … that's a really big deal."

Livingood said Comcast's low-latency trials confirmed that most every user experience problem could be traced to a latency problem and not a lack of bandwidth. "We saw a real benefit in terms of application experience," he explained.

Related:Comcast unveils first DOCSIS 4.0 gateway, tests 'high fidelity video'

Using low latency as a differentiator

Though Comcast's new low-latency tech is sure to grab the attention of avid online gamers, the operator is not selling it as a premium add-on. Instead, Comcast will weave the feature into its core home broadband products and use it as a differentiator against fixed wireless access (FWA) competition.

"The more broadly we make it available to our customers, the more that is a magnet for developers to implement the standard," Livingood said.

That wide-scale, built-in approach also makes sense given that past uses of low-latency premium offerings geared toward gamers have not performed well. Cox Communications, for example, began testing a premium low-latency service called "Elite Gamer" in 2019 for $14.99 per month and later deployed it on a commercial basis for $7 per month. Though there was hope that Elite Gamer, a white-labeled version of the WTFast low-lag service, would drive up broadband average revenues per user (ARPU) for the gaming crowd, Cox shut it down at the end of 2023 due to lower than expected consumer demand.

Comcast is initially deploying the new low-latency feature to a handful of markets, including Atlanta; Chicago; Colorado Springs; Philadelphia; San Francisco; and Rockville, Maryland, with more to be added in the coming months.

Related:Comcast ready to hit the accelerator on DOCSIS 4.0

Early on, Comcast said it will support low-latency for FaceTime on Apple's iPhone, iPad, Macs, Apple TV devices and the Apple Vision Pro, select apps that run on Meta's mixed reality headsets, Nvidia's GeoForce Now cloud gaming service and "many games" from Valve's Steam platform. Other yet-to-be-named partners are also running tests with Comcast, Livingood said.

Expect Comcast to shine the light on FWA's struggles with latency as the operator rolls out this new capability. One notable source of those struggles is Cloudflare Radar, a web-based tool that provides info about Internet traffic trends. For example, this Cloudflare Radar page illustrates that T-Mobile's 5G Home Internet service sees decent latencies of about 36.6ms when the network is idle, but shoots up to 386ms when the network is loaded.

Time will tell if low-latency will fuel Comcast's ability to gain and retain customers. The new feature is emerging as Comcast strives to return to broadband subscriber growth. Comcast, which lost broadband subs in recent quarters, is scheduled to report Q4 2024 results on Thursday (January 30).

Comcast is starting to get the word out about its new low-latency capabilities, with an early emphasis on its role in live sports streaming. Among recent examples is this promotional spot featuring former NBA star and current NBC/Peacock analyst Jalen Rose leading a meeting at the "Xfinity Engineering Dept." and posing the question: "How do we stream all of these games?"

Comcast's approach

Comcast is leaning on open standards for its low-latency feature, believing it will allow for more scale across the technology ecosystem.

Notable is Comcast's use of the Internet Engineering Task Force's Low Latency Low Loss Scalable Throughput (L4S) standards, which are used to process and support latency-sensitive traffic. LLD, which is part of the Low Latency DOCSIS specs, works by separating small, delay-sensitive, non-queue-building traffic (such as key clicks for an online game) from the primary (and much heavier) queue-building traffic that, for example, might carry a video stream or a large file upload or download.

Livingood said having big names such as Apple, Nvidia, Valve and Meta put their weight behind L4S is a good signal to developers.

"It's a pretty big deal that Apple built L4S into iOS, because that means that once they do it and show the benefit on FaceTime – an app they control – there's a whole ecosystem of iOS developers that now know what the pathway is to go do the same thing," Livingood said.

Staying with the network, Comcast is initially targeting its new low-latency capability to upgraded DOCSIS networks. That includes networks that run Comcast's new virtual cable modem termination system (vCMTS), have implemented "mid-split" upgrades that beef up the amount of spectrum dedicated to the upstream, and have introduced Full Duplex (FDX) DOCSIS, a technique that lets Comcast run upstream and downstream traffic in the same block of spectrum.

Underneath that, the low-latency-enabled vCMTSs are equipped with upstream active queue management, downstream active queue management and L4S/Low Latency DOCSIS for both the upstream and downstream paths.

Comcast also plans to bring its new low-latency technology to its EPON-based fiber networks. Notably, Comcast's vCMTS has been adapted to support both hybrid fiber/coax (HFC) and FTTP access networks.   

In the home, Comcast has begun to extend low-latency support to its latest line of DOCSIS gateways that run the Reference Design Kit (RDK) software stack. Those initial models include DOCSIS 3.1 gateways such as the XB6, XB7 and XB8 as well as the new XB10, a DOCSIS 4.0 gateway outfitted with Wi-Fi 7.

Livingood said Comcast also plans to extend support to customer-owned retail modems that are qualified to operate on Comcast's next-generation network areas. A number of retail DOCSIS gateway suppliers are in the lab now iterating their code to work with FDX, he said.

Livingood said having control of the vCMTS and RDK software has enabled Comcast to iterate quickly and put the cable operator in position to be the first to deploy its new low-latency tech.

"That, for us, was a foundational enabler to do all of this in software," he said.

About the Author

Jeff Baumgartner

Senior Editor, Light Reading

Jeff Baumgartner is a Senior Editor for Light Reading and is responsible for the day-to-day news coverage and analysis of the cable and video sectors. Follow him on X and LinkedIn.

Baumgartner also served as Site Editor for Light Reading Cable from 2007-2013. In between his two stints at Light Reading, he led tech coverage for Multichannel News and was a regular contributor to Broadcasting + Cable. Baumgartner was named to the 2018 class of the Cable TV Pioneers.

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