Service drop outs

I've had Comcast cable broadband for about a week and my LinkSys is
connected through USB. Every couple days my connection drops out once or
several times. I know when it happens because of the audible USB disconnect
sounds. I know that it happens because I try clicking up Google and get a
disconnect page on the browser instead.

How can I tell if this loss of connection is Comcast based or USB based?
Or, for that matter, LinkSys based?

Incidentally, the LinkSys will do ethernet, but I don't have a short
ethernet cable yet.

Also incidental is that twice when I got such dropouts I was actually on
Comcast CHAT - and, of course, lost them.

Thanks

--
JimL