How audio online system sends voice data

Hi guys, I’m trying to figure out how the Audio Online System sends the voice data from client to server and vice-versa. So I have read the sources of the Voice Interface implementation of the OnlineSubsystemNull and as far as I have understood it just replicates the data all over the connected client, so there is no special communication channel, isn’t there?
The port used by the system should be the default one (7777), right?