there are several things to be considered here.
20Mb is 20 Megabits a second.
a typical web cam usually delivers around a res of 640*480. this is really FAR less then 5 megapixels, in fact it's a third of a megapixel- but it'll do for the comparision.
640 * 480 resolution, multiply by 32 bits (4 bytes) and you get a total storage space of 1,228,800 bytes.
This is a single frame. a conservative frames per second would be 24. so, in a single second, your webcam, at a LOW resolution of 640x480, must push 29,491,200 bytes of data to the PC every second. the PC, in turn, must push thos amount through your 20 M-bit connection.
a 20 megabit connection is 20 million bits. this is equal to 2,500,000 bytes.
Now, doing the math, we see that 20 megabits of speed is not quite fast enough- 2,500,000 versus over 29,491,200 bytes- and I was being conservative,- if your web-cam is actually set using the 5 megapixel resolution, then you'll end up with 5 million, times 4, or 20 million bytes for a single frame. multiply this by another conservative 24 frames per second to come up with the collosal 480 million bytes that your webcam, if you were to have "lag free" viewing, must push through your 2.5 million byte connection. As patio said- you need an industrial strength web connection- nothing a consumer can get. and even if you had that- that 480 million bytes is over 8 times higher then the maximum bandwidth limit for USB, which is 480 megabits.
And so you see, not only is 20 megabits not "plenty", but really it's impossible with modern technology to get "lag free" viewing of webcam images.
