Ajay D. Kshemkalyani

Clock synchronization for wireless sensor networks: a survey

Abstract Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity. The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensor-network application. Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols.

An efficient implementation of vector clocks

Abstract The system of vector clocks is an essential tool for designing distributed algorithms and reasoning about them. We present an efficient implementation of vector clocks that reduces the size of timestamp related information to be transferred in a message. The implementation assumes FIFO message delivery and is resilient to changes in the topology of the distributed system.

Efficient detection and resolution of generalized distributed deadlocks

We present an efficient one-phase algorithm that consists of two concurrent sweeps of messages to detect generalized distributed deadlocks. In the outward sweep, the algorithm records a snapshot of a distributed wait-for-graph (WFG). In the inward sweep, the algorithm performs reduction of the recorded distributed WFG to check for a deadlock. The two sweeps can overlap in time at a process. We prove the correctness of the algorithm. The algorithm has a worst-case message complexity of 4e/spl minus/2n+2l and a time complexity of 2d hops, where e is the number of edges, n is the number of nodes, l is the number of leaf nodes, and d is the diameter of the WFG. This is a notable improvement over the existing algorithms to detect generalized deadlocks. >

A fair distributed mutual exclusion algorithm

This paper presents a fair decentralized mutual exclusion algorithm for distributed systems in which processes communicate by asynchronous message passing. The algorithm requires between N-1 and 2(N-1) messages per critical section access, where N is the number of processes in the system. The exact message complexity can be expressed as a deterministic function of concurrency in the computation. The algorithm does not introduce any other overheads over Lamports and Ricart-Agrawalas algorithms, which require 3(N-1) and 2(N-1) messages, respectively, per critical section access and are the only other decentralized algorithms that allow mutual exclusion access in the order of the timestamps of requests.

Necessary and sufficient conditions on information for causal message ordering and their optimal implementation

Summary. This paper formulates necessary and sufficient conditions on the information required for enforcing causal ordering in a distributed system with asynchronous communication. The paper then presents an algorithm for enforcing causal message ordering. The algorithm allows a process to multicast to arbitrary and dynamically changing process groups. We show that the algorithm is optimal in the space complexity of the overhead of control information in both messages and message logs. The algorithm achieves optimality by transmitting the bare minimum causal dependency information specified by the necessity conditions, and using an encoding scheme to represent and transmit this information. We show that, in general, the space complexity of causal 0message ordering in an asynchronous system is

Temporal Interactions of Intervals in Distributed Systems

\Omega(n^{2})

An introduction to snapshot algorithms in distributed computing

, where

Objective-optimal algorithms for long-term Web prefetching

n

Decentralized network connection preemption algorithms

is the number of nodes in the system. Although the upper bound on space complexity of the overhead of control information in the algorithm is

Invariant-based verification of a distributed deadlock detection algorithm

O(n^{2})