The aim of the present invention is that of establishing a fault-tolerant global time in a fault-tolerant communication system of a distributed real-time system. For this purpose, a fault-tolerant message switching unit is provided, which is composed of four independent switching units. These four independent switching units jointly establish a fault-tolerant time. The terminal systems are connected to a fault-tolerant message switching unit via two independent fail-silent communication channels, so that the clock synchronization and network connections are preserved, even if a part of the fault-tolerant switching unit or of a communication channel fails.