A method of transmitting data is performed by detecting a triggering of a first event, further detecting a triggering of a second event until a third event occurs, and performing a first action if the triggering of the second event is not detected, wherein the first action is based on the detected first event. The first event may be the expiry of a poll retransmit timer, the second event may be a detecting whether a ACK or NACK is not received, the third event may be a next transmission opportunity, and the first action may be setting a polling bit of a data PDU to be transmitted.