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Wireless carriers slow streaming video content even in off-peak hours

  • Researchers say that wireless carriers "throttle" streaming video content around the clock -- not just during times of peak congestion.
  • AT&T throttled YouTube and Netflix content, but not Amazon Prime video, they found in a recent study.
  • Experts say that the FCC's 2017 repeal of net neutrality rules enables broadband companies to play favorites with content providers.

The four largest U.S. wireless carriers are deliberately slowing the speed at which some video content is streamed on the internet, researchers contend. The findings could fuel concerns about the Federal Communications Commission's move in 2017 to strike down "net neutrality" rules, a move critics warned could allow broadband providers to offer faster transmission speeds for preferred content providers.

The practice, known as "throttling," refers to internet service providers' intentional slowing of internet speeds to reduce bandwidth congestion during peak hours. Yet a number of carriers — including AT&T, Sprint, T-Mobile and Verizon — are throttling content even at off-peak times, according to a study from Northeastern University and the University of Massachusetts Amherst.

The analysis found that, over a 12-month period ending in early 2019, AT&T slowed the speed of Netflix programming 70% of time and YouTube content 74% of the time, while never throttling Amazon's Prime video-streaming service. T-Mobile throttled Amazon Prime video in 51% of the tests, Netflix in 61% and YouTube in 67% of the tests. 

"What we found empirically is that when it comes to throttling, and when it comes to which apps are targeted, they tend to be video-streaming apps," said David Choffnes, assistant professor of computer science at Northeastern University and one of the study's authors.

Around-the-clock throttling

Researchers used an app called Wehe to determine if an internet provider is affecting the speed of different services, including Amazon Prime Video, YouTube and Netflix. Users voluntarily downloaded the app, which measures how much bandwidth is consumed by video from a given app. Researchers then conducted a control test using scrambled data that couldn't be identified as video, and recorded any differences in bandwidth usage. 

"We repeated these tests with data that looks like YouTube data and data that doesn't look like anything multiple times, back-to-back," Choffnes told CBS MoneyWatch. 

The results suggest that wireless providers are throttling video content around the clock, not simply when usage by customers is high. 

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"There is no evidence that any of the throttling was based on time, which makes us think this is happening 24/7, and it does not seem to be in response to when the network is busy," he added.

While internet providers conduct regular tests to regulate network congestion, the study raises concern that that major content provider are getting special treatment, some experts said.

"Bandwidth isn't free, and I think most of the time these companies are trying to provide customers with an experience they would be reasonably happy with, and occasionally they have to make trade offs," said Kentaro Toyama, a professor of community information at the University of Michigan.

But what he called the "discrepancy" in speeds between content from certain companies is hard to explain, he said. "That is the kind of back-end deal companies are cutting now because of the lifting of net neutrality. It could be that Amazon is paying for that privilege," Toyama told CBS MoneyWatch. 

AT&T: "We don't throttle"

AT&T disputed the study's methodology, attributing the differences in streaming speeds to consumers' individual network plans and settings and denying that the carrier is deliberately slowing select internet content.

"We are committed to an open internet. We don't block websites. We don't censor online content. And we don't throttle, discriminate or degrade network performance based on content," AT&T spokesman Jim Greer told CBS MoneyWatch. 

CTIA, the trade association representing wireless communications companies, said in a blog post last year that the Wehe app, which runs speed tests between mobile devices and its own servers using simulated data traffic, doesn't "account for basic wireless network engineering, consumer preference and how mobile content is distributed over the internet." 

Post-net neutrality world?

Other experts said they're not surprised by the study's findings that carriers are throttling content.

"It's pretty clear from the carriers that they are singling out video as a category and throttling it when there is no need to throttle it on the network," said Ryan Singel, a media and strategy fellow at Stanford Law School's Center for Internet Society. 

It's easy to throttle video content -- which consumes a lot of bandwidth -- without cutting consumers off entirely by streaming it at lower resolutions. Throttling also allows the companies to charge higher rates to consumers who are willing to pay for better-quality service. 

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"They are degrading the experience for users as a way to upgrade them to more expensive plans," Singel said. He also raised concerns that internet providers are capitalizing on the repeal two years ago of the net-neutrality regulations.

"We are seeing carriers use a mix of technical measures and non-technical measures — like a pricing regime — to violate net neutrality," Singel said. 

Florian Schaub, assistant professor of computer science at the University of Michigan, also found the results credible. 

"This study clearly shows that [internet service providers] are actively prioritizing traffic and are thus violating net neutrality — there might be just some variations that the researchers could not measure. The only entities who could provide a more accurate picture are ISPs or service providers," he said. 

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