My main question is the communcation through a firewall. How does servent A communicate with servent B (behind a firewall)?

How does a discovery query work?
How does a search query work?
How does a file request work?
(From servent A to servent B)

Is a TCP/IP connection made through an open firewall port? I have a feeling it's quite simple, but I just keep missing the point. Please, if someone could just point it out to me... I'd REALLY appreciate it! Thanks.

stan