Asynchronous RFC

In our Scenario from an Asynchronous RFC we are sending a message to XI and then a Synchronous call to webservice, the response from the Webservice will be sent to another Asynchronous RFC (Let us say RFC2).

Question 1 : Whether Asynchronous RFC is possible? if so what are all the steps to be done as Sender and Receiver RFC side.

Question 2 : When we import an RFC whether it will behave like an Message Interface or should we need to create a Message interface Explicitly?

Any blogs or links or suggestions will be appreciated.

Karen