Dual mode of operation multiple access system for data link communication

In a data link communications system there is provided a dual mode of operation multiple access system for communication between a plurality of spoke stations and a central hub station which generates a spoke epoch time comprising a plurality of time division slots in which a spoke station can communicate a priority interrupt request to the central hub station. The spoke epoch time comprises one or more dedicated spoke time slots in which only one hub station may transmit to the hub station to the exclusion of all other spoke stations. The spoke epoch time further comprising one or more priority interrupt request time slots in which all spoke stations can transmit priority interrupt requests to the hub station. Controller means in the hub station provides for evaluating priority interrupt requests from the spoke stations and for granting transmission access to one of said spoke stations during predetermined time slots in the next spoke epoch time.