EXFO FTB-500 (Window XP) - Manual (Page 155)

Managing Data
FTB-500 145
Using the USB to RS-232 Adapter
Using the USB to RS-232 Adapter
If you want to transfer data between your unit and a device that is only
equipped with RS-232 (serial) ports, you have to use a USB/RS-232 adapter.
You can use any USB/RS-232 adapter that you like.
Once the adapter has been detected, the unit assigns it a COM port
number. This COM port number is kept in memory even when you turn the
unit off. This means that next time you connect the same adapter to any of
the USB ports, the unit will recognize the adapter and identify it with the
saved COM port number.
Note: For some adapters, the port values do not begin at COM 1. You may want to
verify the actual port number.
The communication between your unit and the device is established using
the PuTTY application.