Performance of quorum consensus protocols for mutual exclusion from the user´s point of view

Quorum consensus protocols are used for achieving mutual exclusion in distributed systems. With these protocols, an operation must obtain permission from a group of coordinators before it can proceed to completion. The authors consider a store-and-forward network with coordinators resident in some of the switching nodes. The main motivations for having multiple coordinators is to enhance system availability. The authors consider the user point-of-view availability, defined as the probability that a mutual exclusion operation originating at a given site can proceed to completion. Scenarios where the network links, as well as the network nodes, may fail are considered. The objective is to analyze the user experienced availability and to determine how best to design a system so as to obtain high availability