A communication system which has a PROFINET IRT system with first communication devices for isochronous transmission. A special IRT bridge device is created, so that a traditional standard Ethernet communication device can also transmit real time-critical data over the PROFINET IRT system. The bridge device has a timer, which is synchronized in time with the timers of the first communication devices. In addition, a device for analysis of the transmission point in time of a real time-critical data telegram received by the communication device and a control unit are provided, such that the control unit controls the forwarding of the respective real time-critical data telegram to at least one second communication device as a function of the analyzed transmission point in time.