By default, when launched, the TN3270 mainframe display connects automatically to the enterprise server associated with your project.
If you are using the embedded 
                  		  Rumba+ Desktop display and it is not configured to connect automatically, when you launch the display you need to connect it to the server
                  manually by clicking the 
                  		  Connect button 
                  		   .
. 
                  		
               
This is the behavior when you are trying to connect to a server and the display is already in use and is connected to a different server:
Closing Rumba+ Desktop disconnects all active sessions.