For applications which require high reliability of communications the backup systems are used. That means the main communication system is backed up by a second communication system. In the case of failure communication with the main communication system the backup system replaces this communication. In a number of similar applications mobile communications are used as backup lines for the fixed lines. More often mobile communication is used as the main communication line even for important applications requiring a high degree of reliability. In these cases the mobile communication is also used as a backup line. In a standard fashion the backup line solves the failure of the mobile communication infrastructure by using the mobile communication infrastructure of another provider.