I found a workaround solutionand I would like to share it with you. In our environment with mediaproxy we had the problem that mediaproxy had to bind to th lokal IP behind nat. So he also announced the local nat to the UAs. We modified rtphandler.py at the very end: def endpointAddresses(self): '''Return the IP address and the RTP data port(s) that will be used by this session''' ports = [str(stream.rtpStream.addr[1]) for stream in self.mediaStreams] return " ".join(["PublicIP"] + ports) We simply added our public IP (last line) to the script (replace "PublicIP" with your public IP e.g. "123.123.234.234"). Now The mediaproxy is bound to the local IP thus announcing the public IP to the other parties. We traced SIP and RTP traffic and so far it worked fine in the following scenario. UA <=> NAT <=> Internet <=> NAT <=> OpenSER + Mediaproxy <=> NAT <=> UA. It may not work under all circumstances. We will continue to test in other scenarios. Anybody else has tried this and has experience in this? Best regards Peter Peter P GMX schrieb: