Structures for fault-tolerant distributed protocols

Abstract

In distributed systems, many protocols have been formalized in terms of the data structures used by the protocols. These data structures, called quorum structures, include quorum sets, coteries, and bicoteries. However, quorum structures only have two states either a quorum is available or at is not. In order to obtain more information about the state of the system, d a t a structures that have multiple states must be used. In this paper, we formally define such structures, called multistate structures. Then, these structures are used to define new, fault-tolerant protocols. Such protocols represent a significant improvement over existing protocols because they are able to capture more information about the current state of the system. Consequently, they allow for graceful degradation. The cost of using these protocols is a small increase in message complexity. However, this small increase in message complexity can result in a significant increase in fault tole ran ce .