Method for operating a communication system for transmitting time-critical data, in which - datagrams are sent from a first communication device in a first subnetwork and to a second communication device in a second subnetwork via a third subnetwork, the first and third subnetworks being connected by means of a first switch and the second and third subnetworks being connected by means of a second switch, - the first communication device inserts an identifier of a first virtual local area network and a priority specification into the datagrams, - the datagrams are forwarded from the first communication device to the first switch using the identifier of the first virtual local area network and the priority specification, - the first switch encapsulates each of the datagrams sent by the first communication device in data frames assigned to a data stream by way of the third subnetwork and inserts an identifier of a second virtual local area network into the data frames, the data frames in which each of the datagrams are encapsulated being VXLAN frames or frames for layer 2 tunnelling of the datagrams, and the first switch encapsulating each of the datagrams by inserting them into a payload data area of the data frames that comprises the identifier of the first virtual local area network and the priority specification, - the data stream is transmitted in the third subnetwork by using the identifier of the second virtual local area network to reserve resources along a selected path between the first switch and the second switch, - the second switch extracts the datagrams encapsulated in the data frames assigned to the data stream from received data frames and forwards the extracted datagrams to the second communication device using the identifier of the first virtual local area network and the priority specification. - datagrams are sent from a first communication device in a first subnetwork and to a second communication device in a second subnetwork via a third subnetwork, the first and third subnetworks being connected by means of a first switch and the second and third subnetworks being connected by means of a second switch, - the first communication device inserts an identifier of a first virtual local area network and a priority specification into the datagrams, - the datagrams are forwarded from the first communication device to the first switch using the identifier of the first virtual local area network and the priority specification, - the first switch encapsulates each of the datagrams sent by the first communication device in data frames assigned to a data stream by way of the third subnetwork and inserts an identifier of a second virtual local area network into the data frames, the data frames in which each of the datagrams are encapsulated being VXLAN frames or frames for layer 2 tunnelling of the datagrams, and the first switch encapsulating each of the datagrams by inserting them into a payload data area of the data frames that comprises the identifier of the first virtual local area network and the priority specification, - the data stream is transmitted in the third subnetwork by using the identifier of the second virtual local area network to reserve resources along a selected path between the first switch and the second switch, - the second switch extracts the datagrams encapsulated in the data frames assigned to the data stream from received data frames and forwards the extracted datagrams to the second communication device using the identifier of the first virtual local area network and the priority specification.