A method performed by a terminal in a wireless communication system where the terminal communicates with a master base station and a secondary base station, the method comprising: receiving configuration information for a split bearer from the master base station; identifying whether a bearer for indicating an amount of data available for transmission is the split bearer; in case that the bearer for indicating the amount of the data available for transmission is the split bearer, identifying at least one medium access control, MAC, entity of the terminal for indicating the amount of the data available for transmission based on the configuration information; indicating the amount of the data available for transmission from a packet data convergence protocol, PDCP, layer of the terminal to the at least one identified MAC entity of the terminal; and triggering a buffer status reporting, BSR, based on the amount of the data available for transmission by the at least one MAC entity of the terminal, wherein in case that a threshold value associated with the split bearer is configured in the configuration information for the split bearer and the amount of the data available for transmission is larger than the threshold value, the amount of the data available for transmission is indicated to both a MAC entity, of the terminal, for secondary cell group, SCG, associated with the secondary base station and a MAC entity, of the terminal, for master cell group, MCG, associated with the master base station, wherein in case that the threshold value is not configured in the configuration information, the amount of the data available for transmission is indicated to a MAC entity, of the terminal, of an exclusive cell group configured in the configuration information. receiving configuration information for a split bearer from the master base station; identifying whether a bearer for indicating an amount of data available for transmission is the split bearer; in case that the bearer for indicating the amount of the data available for transmission is the split bearer, identifying at least one medium access control, MAC, entity of the terminal for indicating the amount of the data available for transmission based on the configuration information; indicating the amount of the data available for transmission from a packet data convergence protocol, PDCP, layer of the terminal to the at least one identified MAC entity of the terminal; and triggering a buffer status reporting, BSR, based on the amount of the data available for transmission by the at least one MAC entity of the terminal, wherein in case that a threshold value associated with the split bearer is configured in the configuration information for the split bearer and the amount of the data available for transmission is larger than the threshold value, the amount of the data available for transmission is indicated to both a MAC entity, of the terminal, for secondary cell group, SCG, associated with the secondary base station and a MAC entity, of the terminal, for master cell group, MCG, associated with the master base station, wherein in case that the threshold value is not configured in the configuration information, the amount of the data available for transmission is indicated to a MAC entity, of the terminal, of an exclusive cell group configured in the configuration information.