An access control function (ZF) which checks a requested use (NU) of a service (DI) by considering an available capacity Cv which is detected by considering the entire transmission capacity (G) and is available to an access node (ZK) for transmitting traffic flows (VS) to the communications network. The service is carried out in at least one communications network (KN) that is provided with an entire transmission capacity (G). The access node (ZK) is allocated to the access control function (ZF) which checks the requested use (NU) of the service (DI).