A packet control unit for a radio telecommunications system such as GPRS has a radio link control/medium access control blocks scheduler which allocates a number of temporary block flow queues to a timeslot for transmission to a mobile system; a fixed allocation table is provided having allocation slots corresponding to RAC blocks, and the RAC blocks scheduler reads the table cyclically and allocates slots according to the reading. Timeslots are requested later during increased demand conditions and are released earlier during decreasing demand conditions than in currently known arrangements.