Client/Server communication via internet

Which is the best solution to communicate bidirectionally between a remote server and a client behind an internet box?

1. UPnP with Sockets.
2. HTTPS/Database Server and the client make 1 request every Xsec to know if there is new data.
3. Client opens 1 connection on the server and it maintains open to make a tunnel.
开发者_开发百科

It totally depends on the application (though you can immediately rule out UPnP, which is an ugly hack suitable for local networks only.) Start reading about the Internet foundation set of protocols - the TCP/IP, pick up the Stevens book - you will get a much better understanding of your options.