Question: What triggers the increment of the successful outgoing handovers per handover cause measurement in an E-UTRAN network?
Option 1: Receipt of a RRC message RRCConnectionReconfigurationComplete sent from the UE to the source eNB.
Option 2: Receipt at the target eNB of UE CONTEXT RELEASE over the X2 from the source eNB following a successful inter-eNB handover.
Option 3: Receipt of UE CONTEXT RELEASE COMMAND at the target eNB following a successful inter-eNB handover via S1.
Option 4: All of the above options are correct triggers for incrementing the measurement.
Explanation: According to the text, all three options (RRCConnectionReconfigurationComplete, X2AP UE CONTEXT RELEASE message, and S1AP UE CONTEXT RELEASE COMMAND message) trigger the increment of the successful outgoing handovers per handover cause measurement in an E-UTRAN network.