The ITECH products have a non-isolated TTL level (UART) interface on the back, and use an optoisolated comms cable to communicate with other equipment. A USB cable is normally included with a purchase (or RS232 on request), but if you need spares - here they are.

Models available are:
IT-E131 - optoisolated RS232 interface, DB9
IT-E132 - optoisolated USB interface (a serial bridge), USB-A plug
IT-E133 - optoisolated GPIB interface

Note: I have had trouble with the GBIP interface, probably a configuration issue, but keep in mind that you may experience difficulties. The test word has pretty exclusively moved to USB these days anyway.