Question: What triggers an attempted outgoing inter-eNB handover, and what is added to the relevant per handover cause measurement?
Option 1: Transmission of the S1AP message to MME, indicating the attempt of an outgoing inter-eNB handover.
Option 2: Transmission of the RRC ConnectionReconfiguration message to UE, triggering the handover from the source eNB to the target eNB.
Option 3: Receipt of the Handover Request message from the target eNB, indicating the attempt of an outgoing inter-eNB handover.
Option 4: Transmission of the Handover Command message to the UE, triggering the handover from the source eNB to the target eNB.
Explanation: According to the 3GPP specification, the transmission of the RRC ConnectionReconfiguration message to UE triggers the handover from the source eNB to the target eNB, indicating the attempt of an outgoing inter-eNB handover. Each RRCConnectionReconfiguration message transmitted is added to the relevant per handover cause measurement.