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We take a signiicant step toward unifying the synchronous, semi-synchronous, and asynchronous message-passing models of distributed computation. The key idea is the concept of a pseudosphere, a n e w combinatorial structure in which each process from a set of processes is independently assigned a value from a set of values. Pseudospheres have a number of(More)
This paper introduces and explores a new <italic>condition based</italic> approach to solve the consensus problem in asynchronous systems. The approach consists of identifying sets of input vectors, called <italic>conditions</italic>, for which it is possible to design a protocol solving consensus despite the occurrence of up to <italic>f</italic> process(More)
We present a shared memory algorithm that allows a set of f+1 processes to wait-free “simulate” a larger system of n processes, that may also exhibit up to f stopping failures. Applying this simulation algorithm to the k-set-agreement problem enables conversion of an arbitrary k-fault-tolerant{\it n}-process solution for the k-set-agreement problem into a(More)
This paper introduces a simple notion of layering as a tool for analyzing well-behaved runs of a given model of distributed computation. Using layering, a model-independent analysis of the consensus problem is performed and then applied to proving lower bounds and impossibility results for consensus in a number of familiar and less familiar models. The(More)
The problem of achieving optimal clock synchronization in a communication network with arbitrary topology and perfect clocks (that do not drift) is studied. Clock synchronization algorithms are presented for a large family of delay assumptions. Our algorithms are modular and consist of three major components. The first component holds for any type of delay(More)
This paper introdu es the notion of stability for a longlived onsensus system. This notion re e ts how sensitive to hanges the de isions of the system are, from one invoation of the onsensus algorithm to the next, with respe t to input hanges. Stable long-lived onsensus systems are proposed, and tight lower bounds on the a hievable stability are proved, for(More)
We introduce a simple notion of layering that provides a tool for defining submodels of a given model of distributed computation. We describe two layerings, the synchronic and the permutation layering, and show that they induce appropriate submodels of several asynchronous models of computation. The synchronic layering applies to the synchronous model too.(More)
Solving agreement problems (such as consensus and <i>k</i>-set agreement) in asynchronous distributed systems prone to process failures has been shown to be impossible. To circumvent this impossibility, distributed oracles (also called unreliable failure detectors) have been introduced. A failure detector provides information on failures, and a failure(More)