You might have faced the problem of dead air while making VoIP calls. It is a condition in which call is made but you can neither hear the voice nor see the video. People used to traditional phones might find this a bit problematic, as in the case of VoIP the route of media is totally independent from the signaling route and if due to some reasons the path of the media breaks you would be experiencing a condition called dead air as described above. Let's figure out what could be the reason behind this and what should be done in this situation. First of all check the connectivity, in case there is silence on both the ends i.e. dead air is symmetrical, then check the connectivity with the remote media endpoint. Using Ethereal you could check the SIP response for capturing the network trace and determine endpoint's remote address and then Ping it.

Check the firewalls. The VoIP providers might be having specific range of RTP ports which could be used for sending and receiving media to and from. In case the softphone has not been configured correctly for using this range the media streams might get blocked. Another reason for dead air could be codec mismatch. Just look at the network trace captured using Ethereal in order to figure out the mismatch.

In case you face dead air check the points stated above in order to find a solution.

Thnx Kapanga