A method by a terminal in a wireless communication system, comprising: receiving, from a first base station associated with a first cell group, a control message for configuring a second cell group associated with a second base station; identifying that a packet data convergence protocol, PDCP, protocol data unit, PDU, is to be delivered to both of a first radio link control, RLC, entity and a second RLC entity, in case that the control message includes first information indicating that a duplication transmission using two RLC entities is activated, wherein the first RLC entity of the two RLC entities is associated with the first cell group and the second RLC entity of the two RLC entities is associated with the second cell group; delivering the PDCP PDU, from a PDCP entity, to both of the first RLC entity and the second RLC entity based on a result of the identification; and delivering the PDCP PDU from the first RLC entity to a first medium access control, MAC, entity associated with the first cell group and from the second RLC entity to a second MAC entity associated with the second cell group, wherein the PDCP PDU is transmitted to the first base station associated with the first cell group from the first MAC entity, and to the second base station associated with the second cell group from the second MAC entity