[SR-Users] Audio on Calls Stopping After 15 Minutes

All, hi: I'm a Kamailio newbie! I've managed to set up a proxy server with the minimal configuration file found here: https://github.com/kamailio/kamailio/blob/master/misc/examples/mixed/kamail…. The issue that I'm having is that the audio on calls simply stop precisely after 15 minutes. It's always precisely at 15 minutes. The calls continue connected but without any audio. A summary about my set up: 1. This is an Amazon AWS EC2 server so it doesn't have a public IP directly attached to the interface. This makes me believe that the issue might be related to NAT. 2. I use Flowroute as the SIP trunk for these tests. 3. My phone system, for testing purposes, works on UDP port 6060 an the RTP ports are 20,000 to 30,000. 4. I am not using, for the time being, TLS nor SRTP. 5. My phone system is inside the same subnet as the Kamailio server. Questions: 1) Am I missing the NATHELPER module and if so how could we combine it to the minimal proxy configuration described above? Assuming that my Kamailio server uses local IP 10.80.10.5 and the PBX 10.80.10.6, both on UDP port 6060 for SIP. 2) May I simply combine the example file for nathelper.cfg as per this URL: https://github.com/kamailio/kamailio/blob/master/misc/examples/mixed/nathel… to the proxy example files, change IP addresses, ports, etc.? If not, how would one go about adding the NATHELPER module to the minimal proxy configuration? 3) Could it be some other issue that is causing the 15-minute interruption on audio? Thank you so much for your help!