Abstract: A method for operating a bus system of an automation system, wherein the bus system has an Ethernet-based network and a coupler and a local bus and a local bus user. An Ethernet telegram is received via the Ethernet-based network at the coupler, wherein the Ethernet telegram has an identifier associated with a fieldbus protocol wherein the Ethernet telegram has process data, conforming to the fieldbus protocol, for the local bus user. The process data is acquired and the identifier from the Ethernet telegram by the coupler. A local bus telegram is generated by the coupler, wherein the local bus telegram has a local-bus-specific local bus header and a local bus payload section. The process data is inserted, together with the identifier, into the local bus telegram by the coupler. The local bus telegram is transmitted from the coupler to the local bus user.