During my career I met with this issue several times and of course, the most recent case the misconfiguration of the firewall was the root cause. You have to carefully configure the media ports! Not only for the audio ports of course, but in this post I’d like to highlight the client audio port ranges, what you can easily check with the following command:


The client ports has been correctly configured on the firewalls, but let me share my last experience with Checkpoint R77.30 where we also had half-way audio, however the UDP ports has been allowed for both directions. The the following error message was found: 

“message_info: Violated unidirectional connection”

Believe or not, the reply for the UDP packets also required in case of this CISCO device, so the following configuration was the solution to our problem: