The year-long project conducted by Northeastern University and University of Massachusetts Amherst found most throttling targets video streaming. However, while throttling does limit video resolution, the default settings in video streaming apps in some cases are the primary reason for low resolution.
Researchers discovered network providers to be deploying a series of differentiation policies that use different rate limits (eg, 1.5 Mbps and 4 Mbps) and targeting different apps.
However, of the 144 ISPs tested, throttling was only evident in 30 of them. There was no evidence of throttling on major ISPs such as Comcast and all broadband and cellular ISPs in France.
The study found Germany’s Deutsche Telekom to be scaling back YouTube and Amazon Prime to a rate of 1.5 Mbps, while on the UK’s Giffgaff and O2 networks YouTube and Netflix was scaled back to 1 and 1.5 Mbps.
In the United States, it was found T-Mobile was running delayed throttling to Netflix, whereby the first few seconds of transfer were at a rate of 20 Mbps, before the transfer was throttled back to 1.5 Mbps.
The majority of the restrictions are imposed over cellular networks, throttling over Wi-Fi is less likely to take place.