It depends on the type of stream and the quality of that stream. It takes into account a lot of things:
Is the stream progressive scan or interlaced?
Is the stream 480p, 720p, 1080i, 1080p?
What kind of audio is being streamed? 2 channel? 5.1 channels? What bitrate?
What's the framerate of the stream?
What type of stream? AVI, MP4, WMV, MKV?
All of these things need to be answered before anyone can make an educated guess as to what upload capabilities you will need.