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takyon [soylentnews.org] writes:

+mobile +software

Researchers at Northeastern University and the University of Southern California have published a paper [choffnes.com] confirming findings [eff.org] by the Electronic Frontier Foundation that T-Mobile's "Binge On" scheme is simply throttling. The researchers also showed how the throttling lowered video quality while hurting the battery life of tested devices, due to the increased download times needed. But wait, there's more [eff.org]:

And they didn't stop there. They actually reverse-engineered the classifier T-Mobile uses to decide whether or not data should be zero-rated. In other words, they figured out exactly what parts of a data stream T-Mobile looks at to decide if a flow of packets should count against a customer's data cap or not, and which values triggered zero-rating. With that knowledge in hand, they also figured how to subvert the classifier into zero-rating any data—not just video streams.

There was one technical discrepancy between the researchers' findings and our findings from back in January. The researchers found that changing the "Content-Type" HTTP header from "video/mp4" to something else prevents T-Mobile from recognizing that a file is actually video, and thus causes Binge On not to throttle or zero-rate the file. Our test, on the other hand, showed that changing the file extension (and thus the Content-Type header) wasn't sufficient—T-Mobile still recognized the file as video and throttled it.

To figure out the source of the discrepancy, we ran our test again, and also provided a packet log of our test to the researchers. They confirmed our results, and also ran some different tests to explore further what was going on. Together, we realized that both of our results were correct. That's because in addition to matching against the "Content-Type" header, T-Mobile also scans the first response packet for the string "mp4." (This string was present in the video file we used for EFF's tests, since it's part of the headers of the file itself [tripod.com].) If either match is found, Binge On throttles the stream. Thus, our test with different headers did show throttling, since our file had the string "mp4" in it. And the researchers' test with different headers didn't show throttling, because the content payload in their test didn't include the magic string.

Previously: Why Free Services from Telecoms Can Be a Problem on the Internet [soylentnews.org]
T-Mobile Throttles All Video Streams and Downloads to 1.5Mbps, EFF Says [soylentnews.org]

Original Submission