What can go wrong?

There are two completely separate flows in telecommunication: Signaling and media. They often take completely unrelated paths from caller to callee that is, their IP packets traverse different gateways and routers. Also, the two flows are managed by separate software (or by different parts of the same application) using different protocols. Signaling and media have nothing to do with each other; each one can work or fail independently from the other flow. But you need both to work correctly for your user to have a complete communication session.

Signaling is a flow of information that defines who is calling whom, taking which paths, and which technology is used to transmit which content. The most used signaling protocol in telecommunication is SIP. It defines the caller's IP address and port, the callee's IP address and port, and the IP addresses and ports of all intermediate servers that the signaling is sent through, and it also announces the various phases...