Local area networks have long been establi … Local area networks have long been established as the basis for distributed systems. Continuity of service and bounded and known message delivery latency are requirements of a number of applications, which are imperfectly fulfilled by standard LANs. Most previous studies have assumed only a normal LAN operation in the derivation of worst-case access/transmission delays.
However, LANs are subject to failures, namely partitions. Since most applications can live with temporary glitches, reliable real-time operation is possible on non?replicated LANs, provided that these temporary partitions are time-bounded. We call these periods of inaccessibility, to differentiate from classical partitions.
This work investigates the inaccessibility characteristics of a given set of standardised token-based local area networks, namely ISO 8802/4 Token-Bus, ISO 8802/5 Token-Ring and ISO 9314 FDDI. This study allows, for each one of the mentioned LANs, the derivation of a worst-case inaccessibility figure, to be added to the worst-case transmission delay in the absence of faults. The study is interesting on the grounds that it provides a basis to predict LAN performance in the presence of failures, and provides guidance on how to improve the inaccessibility time figures. improve the inaccessibility time figures.