By default the browser or application checks if there are any UDP ports above 10000 open through the firewall. 

If not, both signalling and media traffic will use a single TCP port 443.

However, if the firewall has the below UDP ports open, then the browser will use:

  • TCP port 443 for call signalling.
  • UDP ports 1024-65535 for media traffic (audio, video and content)