Frame Conversion Schemes for Cascaded Wired / Wireless Communication Networks of Factory Automation

Typical communication networks for closed-loop control application in factory automation are designed to grant short cycle times, precise synchronicity in the microseconds range and high reliability with low packet error rates. However, new requirements for greater flexibility and scalability can only be fulfilled in combination with wireless networks. Therefore, cascaded communication networks with combinations of wired and wireless subnetworks will arise. However, combining heterogeneous communication protocols will lead to additional latencies. In order to reduce their influence on the real-time behavior of the overall network as far as possible, this latency must be completely known to the application and minimized as far as possible. In this paper, we analyze one additional source of latencies resulting from frame conversion for different subnetworks. With an abstract network model we introduce, we are able to analyze the timing independent of a specific protocol implementation. Using this, we are able to show different existing frame conversion concepts with their properties regarding latency and jitter. By simulating a typical network for automation technology and a currently developed wireless real-time communication network, we were able to verify our investigations.