A method for detecting a connection failure by a first base station in a wireless communication system, the method comprising: receiving a message including an radio link failure, RLF, indication including an RLF report from a second base station which receives the RLF report from user equipment, UE, if the connection failure occurs at the UE, the first base station being a base station that served the UE before the connection failure; determining that a cause for the connection failure is a too early inter-radio access technology, RAT, handover, if the UE has been handed over between different RATs before the connection failure and a cell in which the UE attempted to re-establish a radio resource control, RRC, connection after the connection failure is a cell of the first base station or a cell of the RAT to which the first base station belongs, based on the received message; and determining that the cause for the connection failure is a too late inter-RAT handover, if the UE has not been handed over before the connection failure, and the cell in which the UE attempted to re-establish the RRC connection after the connection failure is a cell of a different RAT than the RAT to which the first base station belongs, based on the received message, wherein a timer reported to the first base station is smaller than a configured threshold if the cause for the connection failure is the too early inter-RAT handover, and the timer reported to the first base station is larger than the configured threshold if the cause for the connection failure is the too late inter-RAT handover, and wherein the timer reported to the first base station is included in the received message. receiving a message including an radio link failure, RLF, indication including an RLF report from a second base station which receives the RLF report from user equipment, UE, if the connection failure occurs at the UE, the first base station being a base station that served the UE before the connection failure; determining that a cause for the connection failure is a too early inter-radio access technology, RAT, handover, if the UE has been handed over between different RATs before the connection failure and a cell in which the UE attempted to re-establish a radio resource control, RRC, connection after the connection failure is a cell of the first base station or a cell of the RAT to which the first base station belongs, based on the received message; and determining that the cause for the connection failure is a too late inter-RAT handover, if the UE has not been handed over before the connection failure, and the cell in which the UE attempted to re-establish the RRC connection after the connection failure is a cell of a different RAT than the RAT to which the first base station belongs, based on the received message, wherein a timer reported to the first base station is smaller than a configured threshold if the cause for the connection failure is the too early inter-RAT handover, and the timer reported to the first base station is larger than the configured threshold if the cause for the connection failure is the too late inter-RAT handover, and wherein the timer reported to the first base station is included in the received message. <EOS>