I am trying to call a contact via PJSIP but the INVITE request is not going through the server which is Kamailio. When I am in Mobile Data it works fine but when I am under WiFi which is NAT-ed it does not work. I am using PJSIP in my iOS application. I am able to REGISTER the client via NAT-ed wifi but RTP Communication is not happening. I saw client private IP(192.168.X.X) in many places in the RTP log when the call is being tried to make. I cam to know that you can override that by acc_cfg.rtp_cfg.public_addr = pj_str("103.78.19.8"); acc_cfg.rtp_cfg.port = 25314; The above code changes the private IP showing in the RTP log but still it is not able to do INVITE request. When I am in mobile data it's able to send the INVITE request. What can be the reason for this? Please help, stuck for many days into this.