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Upload slows down Download


Upload slows down Download

In the investigation of why my connection can be sluggish sometimes, I have discovered that if something is being uploaded from my PC, the download speed is severly restricted.
To prove this, I checked my download speed using the F-O tester and got 314.6kbps (seems very slow for 3.50pm Tues anyway)
Then I started uploading a file to my F-O webspace, which went at around 24000 bytes/sec.
I re-ran the speed checker and only got 166.2kbps.
I understood that with ADSL the download and upload do not affect each other?
Is there anyone else out there who can try this test and see if they get similar results?

Thanks in advance

Upload slows down Download

There was a question along these lines over on the Force9 forum a while back (see Simultaneous Upload/Download [you may have to sign on with the guest account to view the topic]).

You will find that if you're uploading at your maximum rate that your download speed will drop to about half the potential maximum.

Unfortunately, he didn't give a reason why the download speed should be so dramatically affected by uploading. For uploads using the TCP protocol (as distinct from the "message-in-a-bottle" style UDP) you'd expect download speeds to be affected, because TCP will require acknowledgements from the connection partner, which, obviously, requires some of the download capacity.