According to the present invention, a receiving node of a telecommunications network (20) (e.g. a radio base station (22) in uplink, or a mobile terminal (24) in downlink) transmits a single acknowledgement message to a transmitting node (e.g. a mobile terminal (24) in uplink, or a radio base station (22) in downlink) in respect of signals received over a plurality of frequency-aggregated carriers (component carriers) (10) between the transmitting and receiving nodes. If all signals are decoded correctly in the receiving node, a positive acknowledgement message (ACK) is sent to the transmitting node; if not all signals are decoded correctly, a negative acknowledgement message (NACK) is sent, or no acknowledgement message is sent. In this way, a single acknowledgement message can be sent for signals received over multiple carriers. The acknowledgement message can have the same format as legacy standards (for example, as specified in Release 8 of the 3GPP specifications), providing compatibility with existing equipment. The number of messages is also reduced compared with the straightforward approach of transmitting individual acknowledgement messages per component carrier.