It could be that, the person who is uploading from you has ended their internet connection. Or, that they have decided to download from another user who has a faster connection speed, and therefore cancelled the download from you.
Well, even using high speed dsl, the speed at which you can download from people varies greatly. Someone may have 12 people hanging on their connection trying to download stuff. Others may have none.
I know if I want a track (I use Soulseek), I will click several users who have the file. Whichever one is downloading the quickest I keep with, and abort the others.
Upload speeds is determined by your upload bandwith. For home users this is normally between 128 - 256 kbps (For high speed broadband). Although people using work connections will often be able to upload a lot faster.
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