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77
Knowledge and Common Knowledge in a Distributed Environment
- Journal of the ACM
, 1984
"... : Reasoning about knowledge seems to play a fundamental role in distributed systems. Indeed, such reasoning is a central part of the informal intuitive arguments used in the design of distributed protocols. Communication in a distributed system can be viewed as the act of transforming the system&apo ..."
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Cited by 578 (55 self)
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: Reasoning about knowledge seems to play a fundamental role in distributed systems. Indeed, such reasoning is a central part of the informal intuitive arguments used in the design of distributed protocols. Communication in a distributed system can be viewed as the act of transforming the system's state of knowledge. This paper presents a general framework for formalizing and reasoning about knowledge in distributed systems. We argue that states of knowledge of groups of processors are useful concepts for the design and analysis of distributed protocols. In particular, distributed knowledge corresponds to knowledge that is "distributed" among the members of the group, while common knowledge corresponds to a fact being "publicly known". The relationship between common knowledge and a variety of desirable actions in a distributed system is illustrated. Furthermore, it is shown that, formally speaking, in practical systems common knowledge cannot be attained. A number of weaker variants...
Consistent global states of distributed systems: Fundamental concepts and mechanisms
- DISTRIBUTED SYSTEMS
, 1993
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Dynamic Fault-Tolerant Clock Synchronization
, 1996
"... This paper gives two simple efficient distributed algorithms: one for keeping clocks in a network synchronized and one for allowing new processors to join the network with their clocks synchronized. Assuming a fault tolerant authentication protocol, the algorithms tolerate both link and processor fa ..."
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Cited by 142 (9 self)
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This paper gives two simple efficient distributed algorithms: one for keeping clocks in a network synchronized and one for allowing new processors to join the network with their clocks synchronized. Assuming a fault tolerant authentication protocol, the algorithms tolerate both link and processor failures of any type. The algorithm for maintaining synchronization works for arbitrary networks (rather than just completely connected networks) and tolerates any number of processor or communication link faults as long as the correct processors remain connected by fault-free paths. It thus represents an improvement over other clock synchronization algorithms such as [LM,WL], although, unlike them, it does require an authentication protocol to handle Byzantine faults. Our algorithm for allowing new processors to join requires that more than half the processors be correct, a requirement that is provably necessary. 1 Introduction In a distributed system it is often necessary for processors to ...
Global clock synchronization in sensor networks
- IEEE TRANSACTIONS ON COMPUTERS
, 2006
"... Global synchronization is important for many sensor network applications that require precise mapping of collected sensor data with the time of the events, for example, in tracking and surveillance. It also plays an important role in energy conservation in MAC layer protocols. This paper describes ..."
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Cited by 137 (1 self)
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Global synchronization is important for many sensor network applications that require precise mapping of collected sensor data with the time of the events, for example, in tracking and surveillance. It also plays an important role in energy conservation in MAC layer protocols. This paper describes four methods to achieve global synchronization in a sensor network: a node-based approach, a hierarchical cluster-based method, a diffusion-based method, and a fault-tolerant diffusion-based method. The diffusion-based protocol is fully localized. We present two implementations of the diffusion-based protocol for synchronous and asynchronous systems and prove its convergence. Finally, we show that, by imposing some constraints on the sensor network, global clock synchronization can be achieved in the presence of malicious nodes that exhibit Byzantine failures.
A Comparison of Bus Architectures for Safety-Critical Embedded Systems
, 2001
"... Abstract. Embedded systems for safety-critical applications often integrate multiple “functions ” and must generally be fault-tolerant. These requirements lead to a need for mechanisms and services that provide protection against fault propagation and ease the construction of distributed fault-toler ..."
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Cited by 123 (5 self)
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Abstract. Embedded systems for safety-critical applications often integrate multiple “functions ” and must generally be fault-tolerant. These requirements lead to a need for mechanisms and services that provide protection against fault propagation and ease the construction of distributed fault-tolerant applications. A number of bus architectures have been developed to satisfy this need. This paper reviews the requirements on these architectures, the mechanisms employed, and the services provided. Four representative architectures (SAFEbus TM, SPIDER, TTA, and FlexRay) are briefly described. 1
A new fault-tolerant algorithm for clock synchronization
- INFORMATION AND COMPUTATION
, 1988
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Easy Impossibility Proofs for Distributed Consensus Problems
- DISTRIBUTED COMPUTING
, 1986
"... Easy proofs are given, of the impossibility of solving several consensus problems (Byzantine agreement, weak agreement, Byzantine firing squad, approximate agreement and clock synchronization) in certain communication graphs. It is shown that, in the presence of m faults, no solution to these proble ..."
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Cited by 98 (8 self)
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Easy proofs are given, of the impossibility of solving several consensus problems (Byzantine agreement, weak agreement, Byzantine firing squad, approximate agreement and clock synchronization) in certain communication graphs. It is shown that, in the presence of m faults, no solution to these problems exists for communication graphs with fewer than 3m+ 1 nodes or less than 2m+l connectivity. While some of these results had previously been proved, the new proofs are much simpler, provide considerably more insight, apply to more general models of computation, and (particularly in the case of clock synchronization) significantly strengthen the results.
A New Fault-Tolerant Algorithm for Clock Synchronization
, 1984
"... We describe a new fault-tolerant algorithm for solving a variant of Lamport's clock synchronization problem. The algorithm is designed for a system of distributed processes that communicate by sending messages. Each process has its own read-only physical clock whose drift rate from real time is ..."
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Cited by 78 (3 self)
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We describe a new fault-tolerant algorithm for solving a variant of Lamport's clock synchronization problem. The algorithm is designed for a system of distributed processes that communicate by sending messages. Each process has its own read-only physical clock whose drift rate from real time is very small. By adding a value to its physical clock time, the process obtains its local time. The algorithm solves the problem of .maintaining closely synchronized local times, assuming that processes' local times are clo. sely synchronized initially. The algorithm is able to tolerate the failure of just under a third of the participating processes. It maintains synchronization to within a small constant, whose magnitude depends upon the rate of clock drift, the message delivery time, and the initial closeness of synchronization. We also give a characterization of how far the clocks drift from real time. Reintegration of a repaired process can be accomplished using a slight modification of the 'basic algorithm. A similar style algorithm can also be used to achieve synchronization initially.
