Re: CPS rate patch for apt
On Sun, 10 Oct 1999, Chris Frey wrote:
> Attached is a patch that makes the progress and ETA for apt sessions
> a bit more accurate. I use a modem which is not the most steady of
> connections. With this patch, the time estimate gets more stable as
> the download progresses, which makes it easier to determine how much
> longer the download will be.
More accurate in this case is highly subjective. Your patch converts the
instantenous CPS into a running CPS which gives very poor results when you
have parallel downloads going or get large inter-file delays when using
ftp.
The only reason the value is not more stable when using a modem is because
there is a sampling effect going on in the gathering of CPS data. The
timestamping of the exact moment a new packet comes in is quantized to the
update rate of the display so it can get a timestamp +0.7s from what it
really is which throws the calculations because a 1k packet off by .7s
over 5s (say 7.5k of data) is -200b/s on the transfer rate. Apply the same
calculation to the PPP mtu and line speed and you add another 200b/s
varience. The same problem comes in with PPP and the IP stack but to a
lesser degree.
Two fixes are longer term averaging which makes the variance from this
effect very small (but makes short term rate changes very bad) or more
acurate timestamping.
Jason
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