David Choffnes, a mobile systems expert at Northeastern University, and his research colleagues have released a novel Android app for detecting traffic differentiation in mobile networks.

The Differentiation Detector, which identifies changes to the performance of network traffic, can be downloaded for free from the research team’s website.

Traffic differentiation, Choffnes explained, is the practice of offering better (or worse) performance to certain classes of Internet traffic, and could be used to protect ISPs from bandwidth-hungry applications or limit services that compete with those offered by the network provider.

The release of his one-of-a-kind app comes on the heels of the Federal Communications Commission’s vote to pass new net neutrality rules, which happened Thursday. The new regulations ban Internet service providers from blocking or throttling broadband access, ensuring that all Internet content will move at the same speed.

“Reasonable network management practices are an important part of the Internet,” said Choffnes, an assistant professor in the College of Computer and Information Science. “But innovation could be stifled if ISPs don’t give every application fair access to their network resources.”

The Differentiation Detector represents the first approach to reliably detecting differentiation from mobile devices without special privileges, and is part of Choffnes’ larger research project aimed at improving the transparency of mobile systems. Over the next several months, he and his research partners—Alan Mislove, an assistant professor in the College of Computer and Information Science, and computer science doctoral candidate Arash Molavi Kakhki, as well as his colleagues from Stony Brook University—plan to collect differentiation data from tens of thousands of users and develop a website to make their results public.

“Many of our Internet policies today are not informed by science and data, and that’s what we’re trying to bring to bear,” Choffnes said. “Giving users the chance to participate in revealing ISP practices will help us influence policy and help users make informed choices when selecting mobile providers.”

The app itself utilizes a virtual private network proxy to record traffic generated by arbitrary applications—YouTube, say, or Netflix—and then replays that traffic both with and without the VPN in order to identify differentiation.

Because the FCC voted for net neutrality, the practice of traffic differentiation will become illegal when the regulations go into effect. And without the app, there would be no way for the typical Internet user to test whether his network is violating the law.

“We’ve validated our techniques with commercial shaping devices that have been used in the operational setting,” Choffnes said. “There are other tools that look for differentiation, but our tests of these tools showed that they didn’t work.”

What’s more, the app could be used to help consumers choose the best service provider. “People will be able to look at the differentiation data on our website and then make more informed choices about their carriers,” Choffnes said. “If carrier X is slowing the network connection for YouTube but carrier Y is not, maybe they’ll want to switch.”