CUCILync is simply a SIP softphone, so the call is no different from lets say IP Communicator. All signaling takes place between the device and CUCM server, voice and video stream is point to point between the sotphone and another endpoint. If you are using CUCILync to control a desk phone, then all it is doing is using CTI signaling to CUCM to instruct the controlled phone to go off hook, dial digits, etc.
HTH
Chris
