yes, Call setup on FACCH is also termed as Direct TCH Assignment. Basically this feature is optional.
The Direct TCH Assignment is used in order to decrease time needed for call set up in such a way that
authentication and ciphering are excluded.
Direct TCH assignment is used for emergency calls when usually authentication and ciphering are excluded and the call set up is provided up to 1 second instead of standardtime frame from 3 to 4 seconds.