1. A VCON-only multicast session with 3rd party viewer support disabled

In this case, the multicast transmission does not actually begin until the first remote VCON participant is joined. Joining a multicast is accomplished either by dialing the Chair or by the Chair dialing the remote participants.

2. A multicast session with 3rd party viewer support enabled

If 3rd party viewer support is enabled, the multicast transmission actually begins as soon as the Chair starts the multicast. This is due to the fact that the 3rd party viewers are "passive" and not visible by the multicast chair.