QWebSocketServer cannot listen to external IP address (or Public IP address)

My Qt Application uses QWebSocket for communication between two remote machines through network. I am able to start QWebSocketServer, listen to local IP address and connection is establishing between QWebSocketServer (let say USER1) and QWebSocket client (let say USER2) with-in the same local network(i.e with-in the same organization). But if I want to establish connection between QWebSocketServer and QWebSocket client which are in different networks (i.e between different organizations), then cannot establish a connection. How to establish a connection between QWebSocketServer and client which are in different network(i.e between different organizations)? I think definitely we need external IP address (i.e Public IP address and port), but QWebSocketServer::listen(public_IP, port) returns false. How to fix this? or How to establish a connection between QWebSocketServer and client which are in different network(i.e between different organizations)?