A controller controls the admit rate of messages passed to a node in a communications system according to a control value that controls the maximum average admit rate. The controller periodically updates the control value in which the updated control value is the lesser of an increasing function of the previous control value; and an increasing function of the previous admit rate. The updated control value is the lesser of an increasing function of the previous control value and the time period since the previous update; and an increasing function of the previous admit rate.