There is not a single port that is used, but different ports for different functions. Plus, many of the ports used are dynamically allocated, so they change all the time. (These are ports out of the "well-known" port number range. The client application selects a source port number at random and uses it in its intial connection establishment message to the server. The server then uses it in all subsequent replies to the client -- ephemeral port numbers.)
The Symposium Web Client Server and the Symposium server must be able to communicate with each other on all TCP ports. The traditional Symposium "fat" classic client uses dynamically allocated TCP ports to communicate with the server and cannot be separated from the server by a packet filtering firewall.
If you are using the Symposium Web Client, it is possible to separate the supervisor PCs from the Web Client server with a firewall. It uses these ports:
80
3389
25 (SMTP)
8200
UDP Ports 6020,6030, 6040, 6050, 6060, 6070, 6080, 6090, 6100, 6110, 6120, 6130, 7020, 7030, 7040, 7050, 7060, 7070, 7080, 7090, 7100, 7110, 7120, 7130
More information can be found in the Symposium Web Client Planning, Installation, and Administration Guide.