Jungle Monkey channels are built upon multicast. Multicast lets you send one thing to many computers at once. The alternative is to use unicast, which lets you send one thing to one computer. However, if you needed to send something to multiple computers you would need to send it multiple times. A channel in Jungle Monkey is a multicast group.
People send announcements for their files to the group.
Announcements are sent periodly, so it may take a while before you see announcements for a channel you just joined. When you download a file, you first connect to rendezvous server. The rendezvous server has a list of mirrors of that file. JM then figures out which mirror is closest and downloads the file from that mirror. End-host multicast organizes a bunch of computers together in a tree so that they can share data efficiently.