Hello All, Hope All doing good. I will split the question in some sub questions: Is the 3CX tunnel a true TCP SIP proxy? It is possible to use the pjsip to connect to it? How should I set up the account and connection data if this is possible? Let's consider the 3CX server is running behind the NAT and the public IP address is: 220.127.116.11, tunnel is working on port 5090 and the internal address of the 3CX is 192.168.1.13. the SIP user is firstname.lastname@example.org with pass: userPass and the tunnel has the password tunnelPass. https://www.bloomberg.com/research/stocks/private/snapshot.asp?privcapId=2507312 | Azure How should the pjsip account structure be initialized?