I'm very new to the Gnutella network of sharing, so I'm trying to understand how the system works. Can someone break it down for me? Is it a web-like structure, or a pyramid? I'm trying understand why some days I'm a "Peer" and DL at about 20kb/s, others (like tonight) an "Ultrapeer", and my download speeds are surpassing 100kb/s.

TIA,