A method for small data transmission performed by a user equipment, UE, the method comprising: receiving a Radio Resource Control, RRC, release message from a base station, BS, while in an RRC_CONNECTED state, the RRC release message including a small data transmission configuration, the small data transmission configuration indicating at least one radio bearer to be retained for supporting the small data transmission; suspending all established signaling radio bearers, SRBs, and data radio bearers, DRBs, except SRB0 and the indicated at least one radio bearer; transitioning from the RRC_CONNECTED state to one of an RRC_INACTIVE state and an RRC_IDLE state according to the RRC release message; performing an access barring check based on an access category associated with the small data transmission and an access identity associated with the small data transmission to determine whether the small data transmission is allowed by the BS; performing the small data transmission via a random access, RA, procedure while the UE is in one of the RRC_INACTIVE state and the RRC_IDLE state by applying the small data transmission configuration; receiving, from the BS, a downlink, DL, response message including a specific uplink, UL, resource indication in response to the small data transmission, the specific UL resource indication indicating a Physical Uplink Shared Channel, PUSCH, associated with a configured grant; and determining whether to perform subsequent data transmission after receiving a random access response, RAR, for the RA procedure according to the specific UL resource indication, the subsequent data transmission performed while remaining in the one of the RRC_INACTIVE state and the RRC_IDLE state. receiving a Radio Resource Control, RRC, release message from a base station, BS, while in an RRC_CONNECTED state, the RRC release message including a small data transmission configuration, the small data transmission configuration indicating at least one radio bearer to be retained for supporting the small data transmission; suspending all established signaling radio bearers, SRBs, and data radio bearers, DRBs, except SRB0 and the indicated at least one radio bearer; transitioning from the RRC_CONNECTED state to one of an RRC_INACTIVE state and an RRC_IDLE state according to the RRC release message; performing an access barring check based on an access category associated with the small data transmission and an access identity associated with the small data transmission to determine whether the small data transmission is allowed by the BS; performing the small data transmission via a random access, RA, procedure while the UE is in one of the RRC_INACTIVE state and the RRC_IDLE state by applying the small data transmission configuration; receiving, from the BS, a downlink, DL, response message including a specific uplink, UL, resource indication in response to the small data transmission, the specific UL resource indication indicating a Physical Uplink Shared Channel, PUSCH, associated with a configured grant; and determining whether to perform subsequent data transmission after receiving a random access response, RAR, for the RA procedure according to the specific UL resource indication, the subsequent data transmission performed while remaining in the one of the RRC_INACTIVE state and the RRC_IDLE state.