Problem: In the setup sketch below, which uses the 3CX PBX Express V15, the phones on the PAP-2T ATA work perfectly. All three Counterpath Bria softphones drop outbound calls only after 30 seconds. I finally found the problem today. All three Brias' "auto" mode had defaulted to TCP signaling. The PAP-2T uses UDP. Forcing the Brias to use UDP solved the problems. They now can call outbound as well as receive calls. Note that this affected the PC Bria on a public IP (an experiment)! Not easy to find as I chased many "common problems with one-way audio and 30 second calls" with net tracing at the 3CX end and on the PC with the Bria PC. Not to mention the learning curve with the Microsoft Message Analyzer (which I now really appreciate). Question: Why would TCP not work while UDP does? Looking at the INVITE's they look good in both cases, but the 200s don't get back and thus the ACKs don't appear. My eyes have glazed over with net traces ha ha especially after following through to look for the "common" problems as well as some answers for really exotic topologies. Thanks: Moving my old on-premises 3CX V10 to the "PBX Express" was surprisingly easy and smooth. I know very little about Linux (except there are so many flavors and I feel like I am transported back to PDP-11/RSX-11 days ha ha). It went great. Kudos to the developers of that process. Also the Capture button on Activity Logs is so easy to use and so great a tool. The .cap files load right into Message Analyzer for deep insight and analysis. It's not easy (impossible) to capture some of this traffic at the client end with ethernet switches and WiFi. The view from the switch it where you see the real deal anyway. Thank you.