Unfortunately, I still have no answer to my question: Techniques of remote access to non IP IoT devices.
Even though, I made some researches and I found two remote access techniques that do not require a port forwarding on the home Internet gateway.
1) Cloud Broker: (from the answer of @ChrisStratton to the question: Contacting Arduino through internet without port forward) (figure).
2) Cloud Broker with direct URL: (from Domotz) This is similar to cloud broker method, except that that URL method provides the remote user with a direct access link, rather than trusting the broker to dispatch his messages to the IoT device (figure).
My question is about the second method (Direct URL): When the remote user type the URL on his remote web/mobile App, how does the traffic bypass through the NAT of the home gateway? I am not sure, but this method does not suppose to use port forwarding.