Does anyone understand how the DM calculates its forecasts? I frequently
see numbers that don't make sense (see attached screenshot).
In this example, it says I've downloaded 589 MB of 1.0 GB (rounded from
1010 MB), or 58%, and this much makes good sense.
It also says I've spent 3 hours, 21 minutes so far, which I accept, and
that I have 11 minutes remaining for the other 421 MB. That forecast
makes no sense at all.
The quoted rate is 684 KB/sec, which works out to 41,040 KB/min, or
40.08 MB/min. Then the remaining 421 MB should take 10.50 minutes, about
as predicted. But the overall rate for the transmission is 589 MB in 201
minutes, or 2.93 MB/min = 50.00 KB/sec; this is the website's stated
speed limit. At that rate, the remaining 421 MB will take 143.67
minutes, or 2 hours and 24 minutes. I would say that's a much more
plausible forecast. In fact, the complete transmission took 5 hours and
45 minutes, a perfect match with my forecast of 3:21 + 2:24 = 5:45.
I've noticed that the transmission rate varies over time, and the
forecast adjusts, but I don't know how it's calculated. If it were an
average over the entire transmission, it should be asymptotic or nearly
so, because recent conditions will make up a smaller and smaller
proportion of the average. If it's an average over some recent period,
such as the last five minutes, it can vary much more widely.
How is the forecast calculated? What recent period is it based on?
Clearly it's not based on the overall rate for the whole transmission.
--
War doesn't determine who's right, just who's left.
--
Paul B. Gallagher
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