Remote Media Streaming over internet

I followed the tutorial (and the windows help) to set up allow internet access to home media (remote media streaming) on 2 win 7 machines.

As long as they are on the same network, both machines can see the other one under "other libraries" and streaming video works.

However, when I tether my laptop to my cell phone and try to connect the desktop over internet, both machines disappear from "other libraries." The desktop has port forwarded and it's in Home network.

What am I doing wrong?

I don't know what I did, but it's now working from my office. Perhaps just a patience?