Abstract: The present disclosure relates to converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT), and may be applied to intelligent services, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method according to disclosed aspects includes receiving a first control message including a first random access response window for a first cell group, receiving a second control message for adding a second cell group, including information on a second random access response window size for the second cell group, transmitting, on a cell of the second cell group, a random access preamble, and monitoring, on the cell of the second cell group, a random access response based on the second random access response window size for the second cell group.