A bus coupler comprising: an external interface for connecting to an external network on which network-specific telegrams can be transferred; an internal interface (34, 35) for connecting a plurality of bus subscribers (40 - 70) in series to a ring-shaped transfer path of an underlying bus system; and a converter device which is adapted so as to be able to convert a network-specific telegram received via the external interface into an internal data telegram for transmission via the ring-shaped transfer path and that contains no control data of the network-specific telegram, wherein the internal data telegram is relayed to the internal interface and is output to the ring-shaped transfer path, wherein the internal data telegram contains at least one state information field for internal control information, wherein when the internal data telegram passes on the ring-shaped transfer path through a bus subscriber connected to the internal interface (34, 35) each respective bus subscriber (40 - 70) exchanges the payload data intended for the respective bus subscriber with the internal data telegram circulating on the transfer path, wherein the bus subscriber is adapted so as to be able to extract payload data from a data block associated with the bus subscriber in the data field of the internal data telegram and to extract internal control information from the at least one state information field of the internal data telegram, and in turn to insert payload data into the data block associated with the bus subscriber of the data field of the internal data telegram, and to insert its internal control information into the at least one state information field of the internal data telegram. an external interface for connecting to an external network on which network-specific telegrams can be transferred; an internal interface (34, 35) for connecting a plurality of bus subscribers (40 - 70) in series to a ring-shaped transfer path of an underlying bus system; and a converter device which is adapted so as to be able to convert a network-specific telegram received via the external interface into an internal data telegram for transmission via the ring-shaped transfer path and that contains no control data of the network-specific telegram, wherein the internal data telegram is relayed to the internal interface and is output to the ring-shaped transfer path, wherein the internal data telegram contains at least one state information field for internal control information, wherein when the internal data telegram passes on the ring-shaped transfer path through a bus subscriber connected to the internal interface (34, 35) each respective bus subscriber (40 - 70) exchanges the payload data intended for the respective bus subscriber with the internal data telegram circulating on the transfer path, wherein the bus subscriber is adapted so as to be able to extract payload data from a data block associated with the bus subscriber in the data field of the internal data telegram and to extract internal control information from the at least one state information field of the internal data telegram, and in turn to insert payload data into the data block associated with the bus subscriber of the data field of the internal data telegram, and to insert its internal control information into the at least one state information field of the internal data telegram.