AT&T Wireless traffic shaping apparently making some websites unusable
> I already knew from previous experience that for some reason, AT&T traffic to fast.com is throttled. Why AT&T wants bandwidth to appear lower than reality is a mystery to me, but I digressThis I think is because they throttle ip addresses for known video streaming sites. That is one of (the only reliable) ways an ISP can get the streaming provider to drop the stream to a lower quality one by default. 
Since fast.com is a Netflix ip, and the isp can’t distinguish whether it’s video that is being transferred or a file to measure throughout, the speed test gets caught up in it. 
Said the other way around: fast.com is great to see actual throughput from Netflix as opposed to some fake throughout from a dedicated speed test site for the exact same reason.