Messages are transmitted to a target device over a wireless network comprising a primary channel in which first messages are transmitted in a random access procedure, and a secondary channel in which second messages are transmitted using a dedicated access procedure, wherein each of the first messages comprises a pointer to the secondary channel, each first message comprising information about the transmitting device and the target device. For each of the first and second message, a transmission opportunity comprising a time slot for transmitting the corresponding message is selected and the primary channel is scanned to determine, based on the received first messages, whether a second message will be transmitted in the time slots selected for the first or second message in which the transmitting device or the target device is involved. The selected transmission opportunities are confirmed or amended based on a result of the scanning.