By default, the Macromedia Flash Player communicates with the Adobe Flash Communication Server using
RTMP protocol over port 1935. If that fails, it will try again over ports 443 and 80 in an attempt to workaround firewall settings within a company, which prevents TCP/IP connections over non-standard ports. The above approach allows approximately 96% of all users to access publicly accessible Flash Communication servers.
To support closer to 100% of the users we need the Macromedia Flash Player to negotiate connection to the external Flash Communication server though a proxy server (if there is one), or use HTTP protocol to transmit RTMP packets (HTTP tunneling) if there is a firewall (which allows only HTTP content to be sent out to public servers).
The current player supports connection requests using 1 of 3 protocols:
RTMP (default port 1935)
RTMPT (tunnel via http - default port of 80)
RTMPS (tunnel via https - default port of 443)