I had the same question, I have an Agilent GPIB to network bridge and wondered what it would take to make the GPIB devices appear as serial ports.
The way to try a connection is:
1) Write a device definition file in the device directory, with this contents:
#idString xxx,xxx,
#name xxx
#handle xxx
#port 5025
The port must match the connected device!
2) Restart test controller and select device, enter IP address in the red field:
3) Press "Reconnect" and look on the first screen. It hopefully shows something like:
;; 10.0.0.79 Device do not match: KEITHLEY INSTRUMENTS,MODEL DMM6500,04395798,1.0.02a
4) Modify the new device file with the above name:
#idString KEITHLEY INSTRUMENTS,MODEL DMM6500,
#name Keithley DMM6500
#handle DMM6500
#port 5025
5) Restart TestController, remove the xxx device and select the above device on the "Load devices" page and enter the IP address again. Then press "Reconnect"
6) It hopefully gives you this message on the first screen (With the device name you are working with):
;; Found Keithley DMM6500 on 10.0.0.79 sn: 4395798
You are online with the device and can write SCPI commands on the TestController command line and start making a fully featured definition file.
See other files in the devices directory for examples, the manual is here:
https://lygte-info.dk/project/TestControllerConfigDevice%20UK.html