Youtube doesn't have neighbouring senders using Cubic, and doesn't try to fill the path's narrowest hop. It tries to send the video at exact playback speed and

Youtube doesn't have neighbouring senders using Cubic, and doesn't try to fill the path's narrowest hop. It tries to send the video at exact playback speed and if possible at high quality, and its notions of success will reflect that. IIRC (I read the paper too) the Youtube numbers assumed that the bandwidth available and needed are both largely stable, and that their success was in using that better. Ie. they assumed that if 4mbps appeared available most of the time, then it really was available all of the time. If the capacity of the narrowest point is 10Mbps and 4mbps youtube streaming briefly competes against a bulk download from a Cubic sender, then BPR would hold the Cubic-using download to 60%, which Youtube might count as success and you might or might not.