Do you have a diagram to understand better?
I'm assuming the call is between a Cisco IP Phone (registered with CUCM) and another endpoint (resisted with Asterisk).
No matter what, CUCM is the middle man between the Cisco IP Phone and Asterisk, so it will communicate/forward all the different SIP states the call is in, so I'm not sure if the transparency you are looking is possible but Asterisk should be able to understand and do the call setup correctly on its end.
I do not understand the "when the PBX make a call the operator is listening the ringing".
What PBX? Who/what made the call? The called phone should not ring?
Regards.
Rolando A. Valenzuela.