I understand Facebook uses WebRtc to send voice data packet in network if any one end client is on the browser. Use of DTLS packets can be seen in captured (wireshark) file. But in case of mobile app to mobile app, we don't see any sign that it is encrypted. We can see some encrypted key running, but that cannot confirm that whether that key is used for RTP packet encryption or to keep the SIP (or other signal controlling packet) session alive. I dont want to believe that Facebook doesn't encrypt the calls, but can anybody please confirm if there is any way to confirm it?