In a UMTS, the AICH is arranged to send, in addition to a signal acknowledging that a preamble from a mobile is at an acceptable strength, an additional signal indicating that the mobile is not currently permitted to send its message; this may apply when the BTS does not have hardware resources available. If the BTS can predict when the hardware will become available, the additional signal can include a time out (T) after which the mobile system can send its message signal.