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The popularity of network-based control systems (NBCS) is continuously growing. One of the most intriguing aspects is the transportation of control network data over IP-based networks using accepted standards such as EIA-852. To a large extent the actual quality of control (QoC) in such systems depends on the network timing such as delay and delay jitter. This paper presents a classification of relevant quality of service parameters and identifies application classes. Subsequently, the paper focuses on the effect of delay jitter at a fixed mean delay on the QoC. Two sources of delay jitter are identified in IP-based control systems: 1) network traffic induced and 2) protocol induced. As an example of a simple control loop implemented over an EIA-852-based system we investigate how the induced jitter affects the QoC using a time-discrete simulation model. Conclusions are drawn as to how the findings in the EIA-852 system can be interpreted and extended to a generalized NBCS.
Date of Publication: Dec. 2004