Researchers from Northeastern University and University of Massachusetts Amherst published research that shows online video traffic throttling happens everywhere all the time and not only to avoid congestion and bottlenecks in Internet service provider (ISPs) networks. David Choffnes, associate professor at Northeastern University and one of the study's authors, told Bloomberg that 'they (ISPs) are doing it all the time, 24/7, and it's not based on networks being overloaded'. The year-long project found that AT&T throttled Netflix 70% and YouTube 74% of the time, but did not slow down Amazon Prime at all. Additionally, T-Mobile US throttled Amazon Prime in about 51% of the tests, but did not throttle Skype and Vimeo. The study also found Germany's Deutsche Telekom throttled YouTube and Amazon Prime, while the UK's Giffgaff and O2 networks did the same with YouTube and Netflix. Another important finding is the majority of the restrictions are imposed over cellular networks, while throttling over wi-fi is less likely to take place.