Currently, hard real-time communication over multi-hop switched Ethernet is still an open problem for researchers. In this paper, a novel hard real-time communication approach over multi-hop switched Ethernet is introduced without any modifications to existing Ethernet hardware. Firstly, the upper delay bounds are analyzed using the network calculus theories. Then the dual-level traffic smoothing technique is proposed, which combines the node-level traffic smoothing with the global-level traffic controlling techniques. Thorough measurements are made to demonstrate the hard real-time communication performance of this approach over multi-hop switched Ethernet.