Does Uploading affect Downloads? Print

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So here's the problem. Almost all Internet communication uses TCP (transport control protocol), where you request data from a server, and then acknowledge to that server when you receive the requested data. The data is split into units called "packets", and the packets are sequentially numbered, so if a packet somehow goes missing, your computer can request that the server to re-send it to you.

So what does this have to do with uploads affecting your download speed? If you're uploading at the very limit of what your connection can handle, then when you try to download something, all of the packet acknowledgement messages that you're sending back to the server that you're downloading from get stuck waiting in line behind the rest of the data that you're uploading. They get out eventually, but not quickly, so the download kind of stalls as it has to keep waiting for your computer to acknowledge that it received the previous packets.

If the program you're using to upload allows you to throttle the amount of bandwidth used, you should set the upload speed to something like 85% of your actual upload speed (as determined by a site like, and not based on what your ISP claims that you have). This will give you enough "wiggle room" to allow acknowledgement messages to get through while you're uploading.

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