A framework for robust active super tier systems

The scenario in which services are obtained by combining sub services is of a great importance. Reliability and fault tolerance are important concerns in the design of such distributed systems. This paper proposes a framework for designing robust client-server tier systems. First, we suggest implementing robust tier automata for each tier τ_i used by the processors that the tier contains. The robust tier automata are useful abstractions that allow distribution of the tier's tasks (and its stubs) in a way that ensures availability, consistency, and recovery in the presence of faults. Then we suggest an active tier framework in which the computation of a user request progresses on several paths in the tier system; those paths may intersect, leaving footprints for each other. And last, we propose the super tier architecture, which correlates equivalent tiers in order to gain more robustness and load balancing. We present and analyze optimistic, pessimistic, and semi-optimistic approaches for computing over the active tier system with super tiers.