The in-sequence delivery function of the NR RLC device may refer to a function of sequentially transmitting RLC SDUs received from a lower layer to a higher layer. The in-sequence delivery function may include a function of reassembling and transmitting multiple RLC SDUs if one RLC SDU has been originally segmented into the multiple RLC SDUs and received. The in-sequence delivery function may include a function of reordering received RLC PDUs based on an RLC SN or a PDCP SN, a function of reordering orders and recording lost RLC PDUs, a function of transmitting a status report on lost RLC PDUs to the transmission side, a function of requesting the retransmission of lost RLC PDUs, a function of sequentially transmitting only RLC SDUs prior to a lost RLC SDU to a higher layer when the lost RLC SDU occurs, a function of sequentially transmitting all of RLC SDUs received until a given timer expires to a higher layer when the timer expires although there is a lost RLC SDU, and a function of sequentially transmitting all of RLC SDUs received so far to a higher layer when a given timer expires although there is a lost RLC SDU. The in-sequence delivery function may include a function of processing RLC PDUs in an order that the RLC PDUs are received (in an order of arrival regardless of the order of SNs) and transmitting the RLC PDUs to a PDCP device regardless of their order (e.g., out-of-sequence delivery). The in-sequence delivery function may include a function of receiving segments stored in a buffer or segments to be received subsequently, reconfiguring the segments in one complete RLC PDU, processing the RLC PDU, and transmitting the RLC PDU to the PDCP device. The NR RLC layer may not include a concatenation function. The concatenation function may be performed by the NR MAC layer or may be substituted with the multiplexing function of the NR MAC layer.