Communicating data in a wireless telecommunications system, the system comprising a base station and one or more terminals operable to communicate via a wireless interface and in accordance with a mobile communication protocol, the wireless interface being provided by at least a first component carrier within a first frequency band and a second component carrier within a second frequency band. The method comprising transmitting a link control layer Packet Data Unit “PDU” from a link control module to an access control layer module for transmission; transmitting first access control layer data using resources allocated within the first component carrier; identifying that transmission of data for the PDU has been unsuccessful; and upon identification that transmission of data for the PDU has been unsuccessful, re-transmitting the POU and causing the re-transmitted POU to be transmitted via second access control layer data using resources allocated within the second component carrier.