said by scubascythan:Shaw doesn't throttle downloads at all. It's just bad congestion in your area during peak hours.
This explains neither why every download during these times download would begin at full speed (~12 Megabytes / sec) then taper to almost nothing within 20 seconds, nor why the Shaw Speed Test is able to report full speed all the time. If my nodes were saturated, neither would be possible.
It looks a lot like Shaw's main pipe to the rest of the internet is saturated during peak hours, which is triggering auto traffic shaping based on length of a connection (longer connection = shaping engaged). Just a theory, but hard to explain this behaviour any other way.