A method of transmitting an acknowledgment message in a random access procedure in a mobile telecommunications system, the method includes transmitting an uplink random access request; responsive to the random access request, transmitting a downlink allocation message indicating downlink resources for sending a downlink message; transmitting the downlink message using the resources indicated in the downlink allocation message; responsive to receiving the downlink message, transmitting an uplink message; and transmitting an acknowledgement message in respect of the uplink message and using one or more acknowledgment resources. The one or more acknowledgment resources are identified based on at least one of the downlink allocation message, and the downlink message and the uplink random access request.