Question: What type of message should be returned in response to a SETUP message containing invalid mandatory information?
Option 1: RELEASE COMPLETE message with cause # 96 "invalid mandatory information"
Option 2: RELEASE message with cause value # 96 "invalid mandatory information"
Option 3: STATUS message with cause value # 96 "invalid mandatory information"
Option 4: DISCONNECT message with cause value # 96 "invalid mandatory information"
Explanation: According to the call control procedures, when a SETUP message contains invalid mandatory information, a RELEASE COMPLETE message with cause # 96 "invalid mandatory information" should be returned. This ensures that the call setup process is terminated and the network resources are released.