The GPIB port on the GSS6700 is intended for internal use only. Spirent has not qualified the GSS6700 for use over this interface.
The user may find that the GSS6700 behaves like a replacement for the GSS6300 for single channel automation purposes if you were to connect to this port, but the GSS6700 has not been qualified for use in this manner nor is it a supported mode of operation.