Performance evaluation of switched Ethernet for networked control systems

The real-time industrial network, often referred to as fieldbus, is an important element for building automated manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices such as sensors, actuators, and controllers, numerous standard organizations and vendors have developed various fieldbus protocols. As a result, IEC 61158 standard including Profibus, WorldFIP, and Foundation Fieldbus was announced as an international standard. These fieldbus protocols have an important advantage over the widely used Ethernet (IEEE 802.3) in terms of the deterministic characteristics. However, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multi-vendor products. In order to solve these problems, the computer network technology, especially Ethernet (IEEE 802.3), is being adopted by the industrial automation field. The key technical obstacle for Ethernet for industrial applications is that its nondeterministic behavior makes it inadequate for real-time applications where the frames containing real-time information such as control command and alarm signal have to be delivered within a certain time limit. The development of switched Ethernet shows a very promising prospect for industrial applications due to the elimination of uncertainties in the network operation that leads to the dramatically improved performance. This paper focuses on the application of the switched Ethernet for networked control systems. More specifically, this paper presents an implementation method for using the switched Ethernet for industrial automation along with the performance evaluation on an experimental network testbed.