Fedora firewall with UPnP?

I'm using Fedora 15 and Transmission BT client. Transmission can't open ports unless the firewall is disabled. I searched some posts that said add 1900 to the trusted ports, or via a iptable rule: -A INPUT -m state --state NEW -m udp -p udp --sport 1900 -j ACCEPT". However, Transmission can't open ports anyway. I also tested with upnp-inspector, which is better than Transmission, it could detect my upnp router after add 1900 to the trusted ports, but the detection is slower than if the firewall is disabled. Any ideas on how to let Transmission UPnP works with the Firewall?