Putting together what you said, plus what David W. Hodgins said, plus what Jasen Betts said, is this how it works?
(1) If I turn off UPnP on the router (and in Transmission?) then nobody can connect to "me" for me to "upload" to them with them using my public IP address through a port forwarded through my router via UPnP.
(2) This means that I can only upload to other clients that have a public socket, but if the other clients don't have a public socket, I can't upload to them (or, said more directly, they can't get files from me).
(3) Since bittorrent maintains two download queues, the first priority going to those who are uploading data and the second going to those who are not uploading data, if I'm not uploading data, then I will only download data when the first queue is empty.
(4) That means two different things. - For those people with public sockets, I will be in the first queue because they can get data from me even though I don't have a public socket myself. - For those people without public sockets, I will be in the second queue because, to them, I'm not uploading any data because I don't have a public upload socket open.
(5) Overall, this will probably increase my download times (depending on a combination of how many other people have public sockets open and on how full that first queue is).
(6) If I want to upload data to everyone, in order to ensure I'm in the first queue, I will need to "open" a port for uploading data.
(7) The "easiest" way to open that outgoing (upload) port is to enable UPnP in my router (and in the Transmission GUI?).
(8) HERE IS WHERE I'M STILL CONFUSED! The "safest" way to open that outgoing upload port is to set up something called "port forwarding" in the router.
MY QUESTION: If all this is correct, then all I really need to learn next is how to set up port forwarding in the router.
The router has a menu for "port forwarding" & "port triggering." The first dropdown menu has a "Service Name" for me to select: (The choices are ftp, http, icuii, ip phone, netmeeting h.323, news, quake II & III, real audio, telnet, & vpn/pptp). Notice "bittorrent" is conspicuously missing from the dropdown menu.
Once I select a service name, the rest of the choices are: - External Start Port = ? - External End Port = ? - Internal Start Port = ? - Internal End Port = ? - Internal IP address = (this would be the IP address of my computer)
So, I have to figure out what is an External and Internal port, and then what is the difference between a Start and End port.
One bit of confusion is that Transmission is picking random ports.
So, how do I set up port forwarding in the router when Transmission doesn't know what port it will be using at any given time?
Do I tell Transmission to pick a STATIC port?