Arobinda Gupta

Fault-containing self-stabilizing algorithms

Self-stabilization provides a non-masking approach to fault tolerance. Given this fact, one would hope that in a self-stabilizing system, the amount of disruption caused by a fault is proportional to the severity of the fault. However, this is not true for many self-stabilizing systems. Our paper addresses this weakness of distributed self-stabilizing systems by introducing the notion of fault containment. Informally, a fault-containing self-stabilizing algorithm is one that contains the effects of limited transient faults while retaining the property of self-st abilization. The paper begins with a formal framework for specifying and evaluating fault-containing self-stabilizing protocols. Then, it is shown that self-stabilization and fault containment are goals that can conflict. For example, it is shown that imposing a O(1) bound on the worst case recovery time from a l-faulty state necessitates added overhead for stabilization: for some tasks, the O(1) recovery time implies sfiabilization time cannot be within O(1) rounds from the optimum value. The paper then presents a transformer T that maps any non-reactive self-stabilizing algorithm P into an equivalent fault-containing self-stabilizing algorithm Pf that can repair any l-faulty state in O(1) time with O(1) space overhead. This transformation is baaed on a novel stabilizing timer paradigm that significantly simplifies the ti=k of fault containment. The paper concludes by generalizing the transformer ‘T into a parameterized transformer 7(k) such that for varying k we obtain varying performance measures for Pf.

Detecting misbehaviors in VANET with integrated root-cause analysis

Misbehavior detection schemes (MDSs) form an integral part of misbehaving node eviction in vehicular ad hoc networks (VANETs). A misbehaving node can send messages corresponding to an event that either has not occurred (possibly out of malicious intent), or incorrect information corresponding to an actual event (for example, faulty sensor reading), or both, causing applications to malfunction. While identifying the presence of misbehavior, it is also imperative to extract the root-cause of the observed misbehavior in order to properly assess the misbehaviors impact, which in turn determines the action to be taken. This paper uses the Post Crash Notification (PCN) application to illustrate the basic considerations and the key factors affecting the reliability performance of such schemes. The basic cause-tree approach is illustrated and used effectively to jointly achieve misbehavior detection as well as identification of its root-cause. The considerations regarding parameter tuning and impact of mobility on the performance of the MDS are studied. The performance of the proposed MDS is found to be not very sensitive to slight errors in parameter estimation.

An exercise in fault-containment: self-stabilizing leader election

Self-stabilizing algorithms are designed to guarantee convergence to some desired stable state from arbitrary initial states arising out of an arbitrarily large number of faults. However, in a well-designed system, the simultaneous occurrence of a large number of faults is rare. It is therefore desirable to design algorithms that are not only self-stabilizing, but also have the ability to recover very fast from a bounded number of faults. As an illustration, we present a simple self-stabilizing leader election protocol that recovers in O(1) time from a state with a single transient fault on oriented rings. Only the faulty node and its two neighbors change their state during convergence to a stable state. Thus, the effect of a single fault is tightly contained around the fault. The technique for transforming a self-stabilizing algorithm into its fault-contained version is simple and general, and can be applied to other problems as well that satisfy certain properties.

Distributed Misbehavior Detection in VANETs

In any vehicular adhoc network, there is always a possibility of incorrect messages being transmitted either due to faulty sensors and/or intentional malicious activities. Detecting and evicting sources of such misbehavior is an important problem. We observe that the performance of misbehavior detection schemes will depend on the application under consideration and the mobility dynamics of the detecting vehicle. Further, the underlying tradeoff in any such detection algorithm is the balance between False Positives and False Negatives; one would like to detect as many misbehaviors as possible, while at the same time ensuring that the genuine vehicles are not wrongly accused. In this work we propose and analyze (via simulations) the performance of a Misbehavior Detection Scheme (MDS) for Post Crash Notification (PCN) application. We observe that the performance of this proposed scheme is not very sensitive to the exact dynamics of the vehicle on small scales, so that slight error in estimating the dynamics of the detecting vehicle does not degrade the performance of the MDS.

A Review of Charge Scheduling of Electric Vehicles in Smart Grid

Electric vehicles (EVs) are being introduced by different manufacturers as an environment-friendly alternative to vehicles with internal combustion engines, with several benefits. The number of EVs is expected to grow rapidly in the coming years. However, uncoordinated charging of these vehicles can put a severe stress on the power grid. The problem of charge scheduling of EVs is an important and challenging problem and has seen significant research activity in the last few years. This review covers the recent works done in the area of scheduling algorithms for charging EVs in smart grid. The works are first classified into two broad classes of unidirectional versus bidirectional charging, and then, each class is further classified based on whether the scheduling is centralized or distributed and whether any mobility aspects are considered or not. It then reviews the key results in this field following the classification proposed. Some interesting research challenges that can be addressed are also identified.

Fault-containing network protocols

Self-stabilization is a simple and elegant approach towards designing fault-tolerant network protocols. While self-stabilization provides automatic recovery from arbitrary transient faults, self-stabilizing systems do not incorporate any optimization for more efficient recovery from limited transient faults, even though such limited faults are more likely to occur in practice than arbitrary faults. Fault-containing self-stabilizing protocols are proposed to efficiently contain the effects of more frequent, limited transient faults while retaining the desirable property of self-stabilization. In this paper, we propose a methodology for designing fault-containing selfstabilizing network protocols. The methodology views the properties of self-stabilization and fault-containment in separation. Since self-stabilizing protocols already exist for many important network problems, the design starts with an existing self-stabilizing protocol, and adds to it the fault-containment property. The feasibilitv of this technique is illustrated bv the design of a fault-containing self-stabilizing protocol for the breadthfirst-search (BFS) spanning tree problem. The applicability of the technique used in deriving the BFS protocol to other problems is also discussed.

Fault-containing self-stabilizing distributed protocols

Self-stabilization is an elegant approach for designing a class of fault-tolerant distributed protocols. A self-stabilizing protocol is guaranteed to eventually converge to a legitimate state after a transient fault. However, even a minor transient fault can cause vast disruption in the system before legitimacy is reached. This paper introduces the notion of fault-containment to address this particular weakness of self-stabilizing systems. Informally, a fault-containing self-stabilizing protocol, in addition to providing self- stabilization, contains the effects of faults. This ensures that disruption during recovery from faults, is proportional to the extent of the faults. The paper begins with a formal framework for specifying and evaluating fault-containing self-stabilizing protocols. The main result of the paper is a transformer that converts any non-reactive self-stabilizing protocol into an equivalent fault-containing self-stabilizing protocol that can repair any single fault in the system in O(1) time. For a large class of input protocols, the corresponding output protocols produced by the transformer have O(1) space overhead. The small time and space overhead make the fault-containing self-stabilizing protocol a practical alternative to the original self-stabilizing protocol. The transformer is based on a novel stabilizing timer paradigm that significantly simplifies the task of fault-containment.

A self-stabilizing algorithm for the maximum flow problem

Summary. The maximum flow problem is a fundamental problem in graph theory and combinatorial optimization with a variety of important applications. Known distributed algorithms for this problem do not tolerate faults or adjust to dynamic changes in network topology. This paper presents a distributed self-stabilizing algorithm for the maximum flow problem. Starting from an arbitrary state, the algorithm computes the maximum flow in an acyclic network in finitely many steps. Since the algorithm is self-stabilizing, it is inherently tolerant to transient faults. It can automatically adjust to topology changes and to changes in other parameters of the problem. The paper presents results obtained by extensively experimenting with the algorithm. Two main observations based on these results are (1) the algorithm requires fewer than n2 moves for almost all test cases and (2) the algorithm consistently performs at least as well as a distributed implementation of the well-known Goldberg-Tarjan algorithm for almost all test cases. The paper ends with the conjecture that the algorithm correctly computes a maximum flow even in networks that contain cycles.

PMM: a parallel architecture for production systems

The authors investigate methods to speed up the match phase of the execution of production systems. The Rete match algorithm is taken as the basis of the implementation. A partially shared Rete network is proposed for parallel implementation and a hierarchical two-level parallel architecture based on this network is outlined. The proposed architecture achieves significant speedup by reducing the dynamic scheduling overheads of fine-grained jobs in a multiprocessor implementation of the Rete network, while still taking advantage of the sharing of common computations in the network.<<ETX>>

A Distributed Self-Stabilizing Algorithm for Finding a Connected Dominating Set in a Graph

A connected dominating set of a graph G is a set of nodes of G such that every node in G is either in the set or is adjacent to some node in the set, and the graph induced by the elements of the set is connected. Connected dominating sets have major applications in routing in wireless ad-hoc networks. In this paper, we present a distributed self-stabilizing algorithm for finding a connected dominating set of a graph. Starting from an arbitrary initial state, the algorithm finds a connected dominating set in O(N^2) time, where N is the number of nodes. We also show detailed simulation results to indicate that in practice, the algorithm finds small-sized connected dominating sets in a short time.