The silent calls initiated by automatic calling equipment at the call center and terminated by the same equipment immediately after the called individual answers the phone.That happens because no live operator is available to take the set up call. Properly run call centres will strive to ensure that they do not generate more calls than their operators can handle.
Silent calls are generated by Mobile itself automatically when call originated by user is faild due to any reasons(RFloss,access fail etc.)This is also known as silent Re-Origination. In the RAN report, it can be seen as silent seizers.
silent call may occur when CIC in ISUP-trunk not coincide at both nodes of one direction.
ZB: 1-st timeslot in 1-st E1 at one side have CIC=1, at another – CIC=0.
and physically voice (tx/rx) is switched at 2 different timeslots.