Method for operating a communication system for transmitting time-critical data, in which - selected datagrams are assigned to data streams and transmitted between first communication devices at first network nodes and second communication devices at second network nodes via paths comprising at least the first and second network nodes, wherein a local cycle duration that is a multiple of a general cycle duration can be set on selected communication devices in each case, - reservation requests, which comprise in each case at least details pertaining to a first and a second network node and quality of service parameters, are transmitted, to reserve resources to be provided by communication devices for a transfer of data streams, to a superordinate communication control device in each case by a reservation function component (201, 311, 411) that is assigned to a first or second communication terminal or to a communication device (200, 301-302, 401-403) that is connected thereto and forwards datagrams, - in the event of reservation requests the superordinate communication control device in each case ascertains a path and checks whether sufficient resources for the transfer of the data streams while observing the specified quality of service parameters are available in the communication devices along the respective path, and ascertains a proposed local cycle duration for the selected communication devices, - if there are sufficient resources then the superordinate communication control device transmits configuration information comprising proposed local cycle durations to configuration control units (202, 312, 412, 421, 431) that are assigned to the communication devices at the network nodes that the respective path comprises, - the configuration control units (202, 312, 412, 421, 431) set up the assigned communication devices for resource provision for the transfer of the data streams in accordance with the transmitted configuration information, - the superordinate communication control device continually monitors at least one predefined communication network domain for topology changes, - the superordinate communication control device ascertains updated configuration information for changed paths resulting from topology changes and transmits said information for the purpose of updated device setup to the configuration control units (202, 312, 412, 421, 431) that are assigned to the communication devices at network nodes that changed paths comprise. - selected datagrams are assigned to data streams and transmitted between first communication devices at first network nodes and second communication devices at second network nodes via paths comprising at least the first and second network nodes, wherein a local cycle duration that is a multiple of a general cycle duration can be set on selected communication devices in each case, - reservation requests, which comprise in each case at least details pertaining to a first and a second network node and quality of service parameters, are transmitted, to reserve resources to be provided by communication devices for a transfer of data streams, to a superordinate communication control device in each case by a reservation function component (201, 311, 411) that is assigned to a first or second communication terminal or to a communication device (200, 301-302, 401-403) that is connected thereto and forwards datagrams, - in the event of reservation requests the superordinate communication control device in each case ascertains a path and checks whether sufficient resources for the transfer of the data streams while observing the specified quality of service parameters are available in the communication devices along the respective path, and ascertains a proposed local cycle duration for the selected communication devices, - if there are sufficient resources then the superordinate communication control device transmits configuration information comprising proposed local cycle durations to configuration control units (202, 312, 412, 421, 431) that are assigned to the communication devices at the network nodes that the respective path comprises, - the configuration control units (202, 312, 412, 421, 431) set up the assigned communication devices for resource provision for the transfer of the data streams in accordance with the transmitted configuration information, - the superordinate communication control device continually monitors at least one predefined communication network domain for topology changes, - the superordinate communication control device ascertains updated configuration information for changed paths resulting from topology changes and transmits said information for the purpose of updated device setup to the configuration control units (202, 312, 412, 421, 431) that are assigned to the communication devices at network nodes that changed paths comprise.