On the Adaptation of Broadcast Transactions in Token-passing Fieldbus Networks with Heterogeneous Transmission Media

* This work was partially supported by the European Commission, under the project IST -1999-11316 (RFieldbus). Abstract: Broadcast networks that are characterised by having different physical layers (PhL) demand some kind of traffic adaptation between segments, in order to avoid traffic congestion in linking devices. In many LANs, this problem is solved by the actual linking devices, either behaving like gateways or “intelligent bridges” that use some kind of congestion control/avoidance mechanism. In this paper, we address the case of token-passing fieldbus networks operating in a broadcast fashion and involving message transactions over heterogeneous (wired or wireless) physical layers. For the addressed case, real-time (bounded message response times) and reliability (loss of frames not allowed) requirements demand a new solution to the traffic adaptation problem. Our approach relies on the insertion of an appropriate idle time before a station issuing a request frame. In this way, we guarantee that the linking devices’ queues do not increase in a way that the timeliness properties of the overall system turn out to be unsuitable for the targeted applications.