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**1 - 3**of**3**### Statement of Research, Teaching and Service Contributions

, 2005

"... As computing systems become an increasingly integral part of our lives, the need for fault-tolerance and security in these systems is constantly growing. These computing systems include telecommunication, power systems, collaborative group-oriented systems, sensor networks and electronic commerce. A ..."

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As computing systems become an increasingly integral part of our lives, the need for fault-tolerance and security in these systems is constantly growing. These computing systems include telecommunication, power systems, collaborative group-oriented systems, sensor networks and electronic commerce. Also, the faulttolerance requirement of a system tends to evolve with new technology. Hence, one needs to add reliability requirements to them while preserving existing ones. Moreover, these systems need to be adaptive so that the approach used for fault-tolerance and security can be modified based on environmental conditions. With this motivation, our work has focused on design of fault-tolerant and secure systems. In this document, we identify our research, teaching and service activities in the context of fault-tolerant and secure systems. 1 Research Accomplishments The initial work on fault-tolerance began during undergraduate studies where we designed a fault-tolerant mutual exclusion algorithm [1]. Subsequently, as a graduate student at Ohio State University, we focused on identifying foundations of fault-tolerant systems. This work (cf. Section 1.1) has resulted in development of general-purpose methods for designing fault-tolerance that have been extensively used in design of multitolerant systems â€“that tolerate multiple classes of faults while providing a different level of fault-tolerance. Subsequently, in last 6 years, as an assistant professor at Michigan State University, our work has focused

### doi:10.1093/comjnl/bxl085 State-Optimal Alternator for Uniform Synchronous Rings 1

"... An alternator is a network of concurrent nodes, which satisfies the following conditions: (i) if one node enters its critical section, no neighboring nodes could enter their critical sections at the same computing phase; (ii) along any infinite computing phases, each node enters its critical section ..."

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An alternator is a network of concurrent nodes, which satisfies the following conditions: (i) if one node enters its critical section, no neighboring nodes could enter their critical sections at the same computing phase; (ii) along any infinite computing phases, each node enters its critical section infinitely often. An alternator is said to exhibit strong fairness if condition (ii) is changed to: between any two consecutive critical steps of a node, all neighbors enter their critical sections exactly once. In this paper, we propose a state-optimal alternator algorithm for uniform rings with n nodes, where n is any positive integer greater than one. The proposed algorithm operates correctly for synchronous mode. Every node maintains only a two-state variable. The proposed algorithm has the snap property that the system always satisfies condition (i) of the alternator even if some transient fault occurs. The stabilization time of the proposed alternator algorithm is O(n) phases. After stabilization, the system satisfies the strong fairness property and achieves the maximal performance. We say that an alternator achieves the maximal performance if a node is allowed to enter its critical section when both its neighbors do not enter their critical sections. In the worst case, the proposed algorithm allows each node to enter its critical section every three phases.

### Advance Access publication on January 26, 2007 doi:10.1093/comjnl/bxl085 State-Optimal Alternator for Uniform Synchronous Rings 1

"... An alternator is a network of concurrent nodes, which satisfies the following conditions: (i) if one node enters its critical section, no neighboring nodes could enter their critical sections at the same computing phase; (ii) along any infinite computing phases, each node enters its critical section ..."

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An alternator is a network of concurrent nodes, which satisfies the following conditions: (i) if one node enters its critical section, no neighboring nodes could enter their critical sections at the same computing phase; (ii) along any infinite computing phases, each node enters its critical section infinitely often. An alternator is said to exhibit strong fairness if condition (ii) is changed to: between any two consecutive critical steps of a node, all neighbors enter their critical sections exactly once. In this paper, we propose a state-optimal alternator algorithm for uniform rings with n nodes, where n is any positive integer greater than one. The proposed algorithm operates correctly for synchronous mode. Every node maintains only a two-state variable. The proposed algorithm has the snap property that the system always satisfies condition (i) of the alternator even if some transient fault occurs. The stabilization time of the proposed alternator algorithm is O(n) phases. After stabilization, the system satisfies the strong fairness property and achieves the maximal performance. We say that an alternator achieves the maximal performance if a node is allowed to enter its critical section when both its neighbors do not enter their critical sections. In the worst case, the proposed algorithm allows each node to enter its critical section every three phases.