Ethernet-based fieldbus protocols, are rapidly becoming the preferred choice for networked control systems (NCS) in Factory Automation. Identification of real-time Ethernet (RTE) traffic flows (TFs) is needed for networks that support parameterized QoS services. In this paper, we present a method based on cross-layer packet inspection to identify TFs of RTEs. The method is tested on hardware that uses some of the most popular RTEs used in industrial automation: PROFINET RT, EtherNet/IP and Modbus TCP/IP. The set of parameters chosen to generate the TF signature lead to a correct identification of all cyclic flows in all tested scenarios.