Message from the cloud to a machine behind NAT / Firewall

I want a cloud machine to send a message to a machine behind a corporate NAT / Firewall.

My idea is to install on the corporate machine a client which sends a long HTTP request to the cloud machine and when the cloud has a message it returns the response.

I thought I invented the wheel until I read about "http tunneling" (is this what I am doing?). I also read that some firewalls block non html traffic even if it is on http. So what is my chance to make it work?

I have also read that skype uses a more sophisticated machanism. Is it because my idea does not work or because their idea is faster?

I can compromise on speed now - which approach works and easy to implement?

Solution

I know you'd like to do it with TCP/HTTP, but the way I'd do it is use UDP to NAT 'hole punch', thus establishing a UDP channel, and then use UDP packets sent over that channel as the signaling mechanism...

These may (or may not) be useful or relevant:

http://en.wikipedia.org/wiki/STUN
http://en.wikipedia.org/wiki/Hole_punching
http://en.wikipedia.org/wiki/UDP_hole_punching
http://en.wikipedia.org/wiki/TCP_hole_punching

Also -- if you really have to use HTTP, you could simply issue a new HTTP request every X seconds...

HTTP Polling, if you will...