Verizon Wireless customers this week noticed that Netflix's speed test tool appears to be capped at 10Mbps, raising fears that the carrier is throttling video streaming on its mobile network.

When contacted by Ars this morning, Verizon acknowledged using a new video optimization system but said it is part of a temporary test and that it did not affect the actual quality of video. The video optimization appears to apply both to unlimited and limited mobile plans.

But some YouTube users are reporting degraded video, saying that using a VPN service can bypass the Verizon throttling. The Federal Communications Commission generally allows mobile carriers to limit video quality as long as the limitations are imposed equally across different video services despite net neutrality rules that outlaw throttling. The net neutrality rules have exceptions for network management.

"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. "The testing should be completed shortly. The customer video experience was not affected."

Netflix speed test reveals limit

Our testing appears to back this up in the case of Netflix, though there might be some instances in which users get lower-quality Netflix video, such as when they tether their phone to other devices. On a Verizon Wireless iPhone, we got a 10Mbps download speed on fast.com, which is Netflix's speed test tool. On Ookla's Speedtest app, we got nearly 82Mbps download speeds on the same Verizon LTE network.





But will that actually harm your Netflix video? Probably not, as long as you're watching on your mobile device and not tethering. Netflix says its Ultra HD quality video can require 25Mbps but that's apparently just for non-mobile devices. For mobile devices, Netflix offers a few quality settings, including "Unlimited," which it says "may use 1GB per 20 minutes or more depending on your device and network speeds."

That number appears to be an average. But if the bitrate is relatively constant and doesn't vary much, a connection of less than 7Mbps would be sufficient for Netflix's highest mobile quality, and 10Mbps would thus be enough to stream without any noticeable limits. In our testing on the Verizon phone, we were able to play a Netflix video in the "unlimited" mobile quality with no buffering.

But what if you're tethering your Verizon phone to a device that can stream in Netflix's 25Mbps Ultra HD? That's probably an unusual scenario, but in that case, you might not get the full quality. Verizon told us that the video optimization limits are applied "the same whether you are tethered or not."

Netflix used to throttle its own video streams on Verizon and AT&T to just 600kbps in order to help users stay under their data caps. But Netflix changed that policy last year when it began letting users pick from several different quality settings on mobile devices.

When contacted by Ars, Netflix did not provide any statement specifically on Verizon throttling. “We don’t cap data and don't cap for any mobile network. We offer settings inside the Netflix app to empower our members to control their own quality preferences and data usage," Netflix told Ars.

We also contacted YouTube today and will update this story if we get a response.

YouTube problems reported

The Verizon video limits were reported by The Verge last night, following Reddit threads on the topic. There's also a Howard Forums thread in which users who checked the YouTube app's "stats for nerds" section say that high-quality videos are being hurt.

"YouTube is being throttled to 10Mbps as well," one person wrote yesterday. "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 60fps though."

"Confirmed here too," another person wrote in response. "1440p videos are throttled at a constant 9.59Mbps. It wasn't even able to keep up and buffered at a few points."

Verizon once said it doesn't ”manipulate“ video

Verizon appears to have changed course from an earlier statement that it passes along video in the same quality provided by the video service. "We deliver whatever the content provider gives us. We don’t manipulate the data," Verizon said when it introduced its new unlimited plan in February.

This was in contrast to T-Mobile USA, whose $70-per-month unlimited data plan limited streaming video quality to 480p or about 1.5Mbps. T-Mobile added HD video to the plan in order to combat Verizon's new offer. More recently, T-Mobile CEO John Legere claimed that the Verizon and AT&T networks "seem to be choking after we forced them to go unlimited."

We asked Verizon if the new video optimization is a change in policy from when it said, "We deliver whatever the content provider gives us."

"We're always looking for ways to optimize our network without impacting our customers' experience," the company replied. Verizon provided no further details.

Verizon's video optimization apparently also applies to Verizon's own video services, such as Go90. "It is across the board," Verizon said when asked if Go90 and other Verizon properties are affected.

A Verizon webpage about its video optimization says, "This network management technology is designed to transmit data more efficiently, ease capacity burdens on the network, primarily from video files, and improve the user experience with faster downloads and decreased Internet latency."