For the PROFIBUS, a standardized and well-knownfieldbus system, it is attractive to use wireless media. A naturalapproach in creating such a system is to re-use as much existingtechnology as possible. In the area of wireless local area networks(WLANs) clearly the IEEE 802.11 standard is the leadingtechnology. Hence, the question comes up, how this technologycan be used in the creation of a wireless PROFIBUS. In thispaper we consider the solution of running the existing PROFIBUSMAC and link-layer protocol directly on top of an IEEE 802.11DSSS PHY, without the 802.11 MAC functionality. We show thatthe PROFIBUS MAC protocol (a token-passing scheme on topof a broadcast medium, stations organized in a logical ring) isvulnerable against bit errors and packet losses. Specifically, themembership of a station in the logical ring is harmed by lossof token frames. Ring membership is important, since only ringmembers are allowed to transmit data. Lost stations can’t do so,no matter how time-critical and important their data is. Their reinclusioninto the ring takes some time. The problems are seriousand we conclude that for creation of a wireless PROFIBUSalternative solutions for MAC- and link-layer protocols shouldbe investigated.
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