Question: What triggers the measurement of successful outgoing inter-frequency handovers with gap-assisted measurement in E-UTRAN?
Option 1: Receipt of a RRC message RRCConnectionReconfigurationComplete sent from the UE to the target eNB/RN, indicating a successful incoming intra-eNB/RN inter-frequency handover.
Option 2: Receipt of a RRC message RRCConnectionReconfigurationComplete sent from the UE to the target (=source) eNB/RN, indicating a successful outgoing intra-eNB/RN inter-frequency handover when measurement gaps are used.
Option 3: Receipt at the source eNB/RN of UE CONTEXT RELEASE over the X2 from the target eNB or DeNB following an unsuccessful inter-frequency handover when measurement gaps are not used.
Option 4: Receipt of UE CONTEXT RELEASE COMMAND at the source eNB following a successful intra-eNB/RN inter-frequency handover without measurement gaps.
Explanation: The correct answer is Option 2 because it accurately describes one of the triggers for measuring successful outgoing inter-frequency handovers with gap-assisted measurement in E-UTRAN, as specified in the provided text. This trigger involves the receipt of a specific RRC message indicating a successful outgoing intra-eNB/RN inter-frequency handover when measurement gaps are used.