A user equipment (UE) may have data in a buffer for uplink (UL) transmission. The UE may transmit a buffer status report (BSR) indicating the amount of data. The BSR may fail or a base station may not grant sufficient resources for transmission of the data. A BSR failure condition may be based on a radio link control (RLC) operating mode of the data. For example, the data may be an acknowledgement (ACK) for an acknowledged mode (AM) DL transmission. In this case, the UE may initiate a BSR retransmission (Retx-BSR) timer and determine whether any duplicate transmissions have been received. The data may also be associated with an unacknowledged mode (UM), and the BSR failure condition may include waiting for a time interval that is less than the Retx-BSR time interval. When the BSR failure condition is satisfied, the UE may transmit a scheduling request to the base station.