in a cellular communications system in which a plurality of mobile subscriber units attempt to access at least one bts , which is controlled by a controller , a method of controlling system congestion is provided . the subscriber units record a number of failed access attempt transmissions . the failed attempt data is transmitted to the bts in subsequent access messages . from the failed attempt data , the controller generates an array of access restriction values , which are transmitted to the subscriber units within the access parameters message . the access restriction values are used by the subscriber units to perform one or more persistence tests . the access restriction values control the probability of the persistence tests passing for any given access slot . the present method provides dynamic control of system load , allowing for a higher percentage of successful call attempts when the system is experiencing a heavy load .