bittorrent, azureus, ports and routers

[Thufir]

I'm presently downloading a torrent with the bittorrent-gui, which seems
to be progressing fine.  However, I've previously run into problems with
azureus.

Azureus is a bittorrent client.  What's happening that bittorrent, itself,
works fine, yet azureus doesn't work due to blocked ports?  What is a port?

Apparently bittorrent works regardless of blocked ports.  What is it about
azureus that's different?


thanks,

Thufir