Broadcast networks that are characterised by havingdifferent physical layers (PhL) demand some kind oftraffic adaptation between segments, in order toavoid traffic congestion in linking devices. In manyLANs, this problem is solved by the actual linkingdevices, which use some kind of flow controlmechanism that either tell transmitting stations topause (the transmission) or just discard frames. Inthis paper, we address the case of token-passingfieldbus networks operating in a broadcast fashionand involving message transactions overheterogeneous (wired or wireless) physical layers.For the addressed case, real-time and reliabilityrequirements demand a different solution to thetraffic adaptation problem. Our approach relies onthe insertion of an appropriate idle time before astation issuing a request frame. In this way, weguarantee that the linking devices’ queues do notincrease in a way that the timeliness properties of theoverall system turn out to be unsuitable for thetargeted applications.
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