[SR-Users] Intermittent Audio/video call

Dear All, I am working on Kamailio server (V 4.1.2) with RTPproxy (1.2.1) integrated, in a standalone intranet infrastructure (no any connection with internet). I have a strange behavior with my set-up here is : --> Audio/Video calls are just go fine with only kamailio server (Without running RTPproxy instance). But with the same script and set-up sometimes i'm experiencing one-way audio/video !!. What could be the reason for this behavior ? Is it a NAT problem ? How can i solve this issue ? --> I was just suspecting it as NAT problem and installed RTPproxy server, with this all the audio/video calls are going fine. But i'm curious to know about this intermittent audio/video calls that too without any changes to Kamailio configuration and my set-up. Please below find the attachment for kamailio config file. Please anybody help me in resolving this issue. Any help will greatly appreciate. Regards, Ravi