For optimal usage, the firewall needs to be configured to allow all outgoing ports on both UDP and TCP. That will permit the direct peer-to-peer connection for the different streams.

This is needed by WebRTC, that choses random ports (in a big range of something like 10000-65535) when establishing the connection.

If this is not possible, a workaround is possible by allowing outgoing both TCP & UDP on ports 80 and 443. This will force your devices use our relay servers. This can add a little latency to the call and is not the ideal solution.