How to establish a connection between a client and server on the internet with dynamic external ip-address ? c#

UPnPNAT upnpnat = new UPnPNAT();
            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); 
            IPAddress ipAddress = null; 
            IPEndPoint Addr = null; 
            NATUPNPLib.IStaticPortMappingCollection mappings = upnpnat.StaticPortMappingCollection;
            mappings.Add(20131, "TCP", 20131, "46.175.163.14", true, "Test Open Port");
            Addr = new IPEndPoint(IPAddress.Parse("192.168.0.111"), 20131); //"localhost" = 127.0.0.1

            s.Bind(Addr);

            s.Listen(10);