Subscribe to Netflix and stream movies over Verizon? Chances are you were throttled. On Friday, the internet provider acknowledged that it capped customers’ speeds to 10Mbps this week as part of a “video optimization test.”

“We’ve been doing network testing over the past few days to optimize the performance of video applications on our network,” a Verizon spokesperson told Ars Technica. “The testing should be completed shortly. The customer video experience was not affected.”

Verizon said that the experiment, which used a new “video optimization system” designed to slow down streams from specific video sources, was temporary, and that the quality of video shouldn’t have been affected. But some YouTube users on Reddit and Howard Forums reported excessive buffering, longer-than-average loading times, and other visual issues brought on by Verizon’s throttling.

At least two Verizon subscribers observed reduced speeds in the YouTube app’s “stats for nerds” section.

“YouTube is being throttled to 10Mbps as well,” one person wrote on Thursday. “In the ‘stats for nerds’ it would load at roughly 1,250KBps which translates to 10Mbps. Put the VPN on and that number tripled easily. Didn’t have an issue playing 1080p in 60fps, though.”

“Confirmed here too,” another person wrote. “1440p videos are throttled at a constant 9.95Mbps. I wasn’t even able to keep up and buffered at a few points.”

Verizon’s traffic-shaping would appear to skirt the FCC’s net neutrality rules, which generally outlaw throttling. But Verizon says that the test fell within the bound’s of the FCC’s exceptions, which allow carriers to impose limitations as long as they’re (1) metered out equally across services, and (2) imposed for the purposes of network management.

“We deliver whatever the content provider gives us,” a Verizon spokesperson said. “We’re always looking for ways to optimize our network without impacting our customers’ experience.”

As Ars Technica notes, Verizon’s throttling wasn’t severe enough to impact most subscribers’ experiences. Netflix says that its highest mobile quality setting, Unlimited, “may use up to 1GB per 20 minutes or more depending on your device and network speeds.” Assuming the download rate is relatively consistent, a connection of less than 7Mbps — much slower than the 10Mbps limit to which Verizon subjected subscribers — would be sufficient.

Until last year, Netflix throttled its own video streams on AT&T and Verizon in order to help users stay under their data caps. But it changed when it began letting users choose from several different quality settings.

It’s not the first time an internet provider has been caught imposing caps on services. In 2008, Comcast began throttling — and in some cases blocking altogether — peer-to-peer (P2P) BitTorrent traffic on its network. The cable provider initially denied responsibility for the reduced speeds, but later acknowledged in a memo to the FCC that it had “engaged in traffic management techniques” in order to “ensure a high-quality, reliable Internet experience.”

In 2009, it agreed to settle a class-action lawsuit brought on by angry customers for $16 million.

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