You're not going to be able to use IP control unless RTI has a driver written for it.

Also, if your RTI driver has both an IP and RS232 option, make sure you have RS232 selected.  You can have IP selected and also show an RS232 port selected.  i.e. you can have "Connection Type" set to "Networks (TCP/IP)" and you will still show a serial port used for the driver ("Serial Port   [RS-232] Port 1") even though it's not in use.  

I'd say that's borderline on being a "bug".... really wish they would grey out the Serial drop-down when IP is selected...