If your host software communicates on TCP socket, the socket is only opened by standalone application only if the cabin is connected. So if it can connect it is good
if your software communicates in serial RS232 method 3.1 does not work.
in both cases you send the S character to see if the cabin responds or not (certainly with the drawback of launching a cycle for nothing)
there is no other method for querying the standalone on the condition of the cabin.