Comcast’s L4S low-latency tech promises up to a 78% latency reduction, testing begins in select cities

According to comments made to The Verge this morning, Comcast is now rolling out a new latency reduction technology, L4S, to its Xfinity Internet service customers in select cities. The company plans to eventually roll out the feature to all its Xfinity Internet customers.

According to Comcast spokesperson Joel Shadle, L4S trials have shown that “we were able to reduce working latency—the latency under normal conditions in the home when people are using the Internet—by 78 percent.”

L4S, which stands for “Low Latency, Low Loss, Scalable Throughput,” is a technology that assigns indicators to packets of Internet traffic. These indicators show when traffic gets congested from point A to point B, allowing the devices on either end to adjust to this issue. In theory, this should reduce or even eliminate congestion.

Of course, this doesn’t magically increase bandwidth, especially throughput in raw download/upload speed. However, more intelligent traffic routing and management on the client and host sides can make a big difference. Comcast has been developing and testing this with help from Valve, Nvidia, and Apple. This should mean improved performance with game streaming, online gaming in general, and real-time video calling (mainly through FaceTime).

For those familiar with Internet traffic, you may already know the concept of “QoS,” or Quality of Service. Quality of Service typically happens within a router or a data center, where packets are sorted by type and latency sensitivity to ensure real-time gaming and video streaming function as intended. Not all QoS implementations are created equally, though, and it’s usually understood as an optional router setting.

Comcast is now doing L4S similarly, but it is a bit more advanced to allow for more dynamic traffic adjustments even within specific types of traffic, not just how that traffic is allocated within given bandwidth constraints. While hands-on testing of L4S has yet to be seen, lowering latency for online calls or gaming, especially game-streaming, is imperative for a consistent and reliable experience. And trust me: playing competitively in today’s market of high-refresh rate monitors and high-end PCs owned by your opponents, you want every bit of latency reduction you can get.

Don’t be a weird monster who insists on running games at uncapped framerates. If you’re too lazy to find the right in-engine FPS cap, please set a framerate cap, even Nvidia Reflex or AMD Anti-Lag 2. Variable framerate means variable input lag, and maximizing GPU resources contributes to higher input lag in general and worsens performance dips where they occur since you have no overhead to compensate.