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Do simultaneous uploads slow down my downloads?

I am currently in Greece and have a 128 Kbps full-duplex link. Do simultaneous uploads slow down my downloads?
The slow down you will experience when simultaneously downloading and uploading will depend on your type of connection and ISP. Since you've mentioned you are in Greece I think can safely assume you are talking about a 128 Kbps ISDN connection.

A 128 Kbps ISDN connection translates to two 64 Kbps channels which can be used in as separate channels, one 64K upload and one 64K download, or you can combine them to achieve one a 128kb channel.

In the first scenario, both directions are limited to 64 Kbps, so if you happen to be downloading while someone else is uploading, speeds will remain the same for both since each user is using a different channel.

However, in the case of a combined 128 Kbps channel, both users are sending and receiving over the same channel. This means that speeds will be affected and this will depend on a number of parameters. If for example you're connected to a server with a fast connection and downloading at 15 Kbps and the remote user downloading from your PC is on a 64 Kbps ISDN, then you will most probably experience a 4-5 kbps decrease in your download speed.

While this might be a problem for you, keep in mind that you can find programs that will automatically limit the speed of which users can download from your connection, thus, you can set this limit to 30-40 Kbps so the impact on your download speed is minimum.

This was last published in February 2004

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