Additionally red5 uses some ports internally. However those ports are not in use by OpenMeetings by default.
You need to change two files:
|Config-Name||Default-value||Name in red5.properties||Name in public/config.xml|
A common way of bypassing the firewall is to change HTTP port to 80
A short description about the connection mechanism: The application first tries connecting to rtmp 3 times, because rtmp is the protocol that is less performance hungry. If that fails the application will fallback to rtmpT.
You can run OpenMeetings completely over SSL. See RTMPSAndHTTPS.