A bus system for connecting a number of data processing units via a bus consisting of two signal lines, wherein - the bus is acted upon by analogue signals lying within several non-overlapping frequency bands; - each data processing unit is coupled to the bus via a modem unit, characterised in that each data processing unit has a frequency band with a centre frequency assigned to it, and the modem unit comprises the following components: - an interface unit to which the data processing unit can be connected and communicate with the same by means of a digital communication protocol (e.g. IEEE 802.3); - a narrow-band modulation unit, which converts the user data stream into a signal, which is transferable via the frequency bands; - a filter-bank synthesis unit, which as a polyphase filter bank converts the data of the interface unit to the centre frequency assigned to the data processing unit and suppresses interferences between adjacent frequency bands; - a digital/analogue converter, which converts the signal of the filter-bank synthesis unit into an analogue signal; - a bus coupling unit, in order to couple the signal of the digital/analogue converter to be transferred, into the bus in a galvanically isolated manner and to decouple signals received from the bus; - an analogue/digital converter, which digitises the bus signals received from the bus coupling unit; - a filter bank analysis unit (38, 40), which as a polyphase filter-bank divides the digitised bus signals into individual filter bands and supplies the data assigned to the individual frequency bands to the interface unit; - a narrow-band demodulation unit, which demodulates the data stream of the filter-bank analysis unit (38, 40) and the supplies the user data to the interface unit. - the bus is acted upon by analogue signals lying within several non-overlapping frequency bands; - each data processing unit is coupled to the bus via a modem unit, - an interface unit to which the data processing unit can be connected and communicate with the same by means of a digital communication protocol (e.g. IEEE 802.3); - a narrow-band modulation unit, which converts the user data stream into a signal, which is transferable via the frequency bands; - a filter-bank synthesis unit, which as a polyphase filter bank converts the data of the interface unit to the centre frequency assigned to the data processing unit and suppresses interferences between adjacent frequency bands; - a digital/analogue converter, which converts the signal of the filter-bank synthesis unit into an analogue signal; - a bus coupling unit, in order to couple the signal of the digital/analogue converter to be transferred, into the bus in a galvanically isolated manner and to decouple signals received from the bus; - an analogue/digital converter, which digitises the bus signals received from the bus coupling unit; - a filter bank analysis unit (38, 40), which as a polyphase filter-bank divides the digitised bus signals into individual filter bands and supplies the data assigned to the individual frequency bands to the interface unit; - a narrow-band demodulation unit, which demodulates the data stream of the filter-bank analysis unit (38, 40) and the supplies the user data to the interface unit.