Progessively slower downloads?

Right now I'm dowloading a 600mb file from Oracle. When the download started, it reported a dowload speed of 230mbs. After downloading for a few minutes,  it slows down to about half that.  I'm at work right now, but I've also see seen this a lot at home on my cable modem. One theory I have is that the IE's download manager miscomputes the rate at first somehow, but I'm pretty sure I've seen similar behaviour from Firefox so that doesn't seem likely. Or it might be the remote server is intentionally limiting my throughput, but its seems like this happens on any site when downloading a large file.

Does anyone else see this? Why does it happen?

ronk!
Monday, August 23, 2004

I believe DSL (at least some types of DSL) traffic comes in 'bursts'.

You say you only notice it on large files so this makes even more sense. These are all numbers pulled from my arse btw....

Let's say a 'burst' lasts for 5 seconds. In those five seconds, 1 MB is transferred. In the following 2 seconds, only 1 KB is transferred.

If the sample rate for the 'downloadometer' were 3 seconds, the first read would be 200 KB/s, but the second read would lower it to ~167 KB/s. Each subsequent 'lull' lowers the figure from the astronomical burst rate.

I am not Jack anymore because I can't keep coming up with suitable facets of Jack to be
Monday, August 23, 2004

You must also consider that the presumed way to do this is to estimate the time remaining using the amount of data received, the time elapsed, and the amount remaining.

Naturally, the first estimates will be poor because you're doing things like dividing with less than 1 second, etc.  You're trying to predict averages with very few data points, which statisticians will cringe at.

You also have to wonder, how much data has arrived before the elapsed counter starts?  This can greatly affect the estimate.

Frank "Grimey" Grimes
Monday, August 23, 2004

Also, on Windows XP / IE, I *think* the download starts when the 'save as' box pops up, not when you click save. But the speed calculator doesn't take this into account. So, if you take your time choosing a file name & path, then you'll get an astronomical download speed straight away (as the 10mb that took 2 minutes to come down while you were saving, actually appears to have come in the first second after you clicked save) and it will slow down pretty quickly after that.

James U-S
Monday, August 23, 2004

Three possibilities:

1. Many binary files start out with lots of long streams of zeros that are easily compressed by the modem's compression routines. So you often see a burst for the first few k.

2. if you stopped downloading and later restarted, sometimes it will show a crazy rate based on how much is already downloaded untill the averaging algorithm smooths it out.

3. Some ISPs will prioritize traffic so that connections that are going a long time downloading a large file are given lower priority that new connections which are more likely to be user interaction and thus need to be delivered faster.

Tony Chang
Monday, August 23, 2004

"Also, on Windows XP / IE, I *think* the download starts when the 'save as' box pops up, not when you click save"

This is my observation too

gwyn
Monday, August 23, 2004

I think James and Gwyn are right.

Steven
Monday, August 23, 2004

I use a program called NetPerSec (used to be free form PC Magazine) that shows you how fast your connection is in real time.

I believe http://www.analogx.com/contents/download/network/nsl.htm does the same, plus some fancier things too. NetPerSec lives in the systray though.

www.MarkTAW.com
Monday, August 23, 2004

Also under WinXP, Ctrl-Alt-Del and the Networking tab under task manager will give you a nice realtime graph of bandwidth usage.

Matt
Tuesday, August 24, 2004

Is it an FTP download, ronk?

I think I saw some FTP servers having the option of progressively slowing downloads for I don't know what reason.

Egor
Tuesday, August 24, 2004

Good point matt. I always forget about that thing. Now why can't MS put that in the systray?

www.MarkTAW.com
Tuesday, August 24, 2004

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