Eli Gafni

Bio: Eli Gafni is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Distributed algorithm & Shared memory. The author has an hindex of 39, co-authored 159 publications receiving 6341 citations. Previous affiliations of Eli Gafni include Microsoft & University of California.

Generalized FLP impossibility result for t-resilient asynchronous computations

Abstract: Demarcation of the border between solvable and unsolvable distributed tdis under various models is the holy grail of the theory of distributed computing. Oneof the most celebrated of theseresults is [6] (FLP) which established the impossibility of asynchronous consensus that can tolerate a single undetected fail-stop processor. This paper generalizes FLP to multiple faults. It establishes that k-set consensus proposed by Chaudhuri is impossible, if the protocol is to tolerate k failures, while there exists a protocol that tolerates k – 1 failures. Our proof technique is completely different than the one employed in [6]. We introduce a new model of computation, the im112ecliate-atoY12 ic-.s?2u~)shot. We fully characterize the graph of waitfree views within the model. Applying a variant of Sperner Lemma to this graph establishes the impossibility of k + 1 processors achieving waitfree k-set consensus. Finally, we introduce a new notion of nonblocking-busy-wait agreement protocol, With this ● Work supported by NSF Presiciential Young Iavest,igator Award under grant DCR84-51396 . Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direot commercial advantage, the ACM copyright notica and the title of the publication and its data appear, and notica is givan that copying is by permission of the Association for Computing Machinery. To copy otherwisa, or to republish, requiras a fea and/or specific permission. 25th ACM STOC ‘93-51931CA,USA @ 1993 ACM 0.89791.591-7/93/0005/0091 .,C$l .5(3 protocol we construct a read/write waitfree simulation techniclue by which k + 1 processors can produce a k-faulty execution of n processors protocol, {Tsing the simulation we establish the impossibility of n processors protocol that achieves k-set consensus and tolerates k failures, by reducing it to the waitfree case.

Atomic snapshots of shared memory

Abstract: This paper introduces a general formulation of atomic snapshot memory, a shared memory partitioned into words written (updated) by individual processes, or instantaneously read (scanned) in its entirety. This paper presents three wait-free implementations of atomic snapshot memory. The first implementation in this paper uses unbounded (integer) fields in these registers, and is particularly easy to understand. The second implementation uses bounded registers. Its correctness proof follows the ideas of the unbounded implementation. Both constructions implement a single-writer snapshot memory, in which each word may be updated by only one process, from single-writer, n-reader registers. The third algorithm implements a multi-writer snapshot memory from atomic n-writer, n-reader registers, again echoing key ideas from the earlier constructions. All operations require Θ(n2) reads and writes to the component shared registers in the worst case. —Authors' Abstract

Distributed Algorithms for Generating Loop-Free Routes in Networks with Frequently Changing Topology

Abstract: We consider the problem of maintaining communication between the nodes of a data network and a central station in the presence of frequent topological changes as, for example, in mobile packet radio networks. We argue that flooding schemes have significant drawbacks for such networks, and propose a general class of distributed algorithms for establishing new loop-free routes to the station for any node left without a route due to changes in the network topology. By virtue of built-in redundancy, the algorithms are typically activated very infrequently and, even when they are, they do not involve any communication within the portion of the network that has not been materially affected by a topological change.

Atomic snapshots of shared memory

Abstract: This paper introduces a general formulation of atonuc wzap~hot rnenzory, a shared memory partitioned into words written (apduted) by individual processes, or instantaneously read (scanned) in its entirety. Thk paw’ Presents three wait-free implementations of atomic snapshot A preliminary version of this paper appeared in Proceedings of the 9th Annaa[ ACM SVmpmnwn on Plznctptes of’ Distributed Compafing (Quebec city. Quebec, A%). ACM New York, 199Q pp. 1-14. H. Attiya’s and N. Shavit’s research was partially supported by National Science Foundation grant CCR-86-1 1442, by Office of Naval Research contract NW014-S5-K-0168, and by DARPA cmltracts NOO014-83-K-0125 and NOO014-89-J1988. E. Gafni’s research was partially supported by National Science Foundation Grant DCR 84-51396 and XEROX Co. grant W8S1111. Part of this work was done while N. Shavit was at Hebrew University, Jerusalem, visiting AT&T Bell Laboratories and the Theory of Distributed Systems Group at Massachusetts Institute of Technology, and while H. Attiya was at the LaboratoV for Computer Science at Massachusetts Institute of Technology. Authors’ present addresses: Y. Afek, Computer Science Department. Tel-Aviv University, Ramat-Aviv, Israel 69978; H. Attiya, Department of Computer Science, Technion, Haifa, Israel 3~000:” D Dolev, Department of computer Science, Hebrew University, Jerusalem, Israel 91904: E. Gafni, 3732 Boelter Hall, Computer Science Department, U. C. L.A., Los Angeles. Cahfornia 90024. M. Merritt, 600 Mountain Ave., Murray Hill. NJ 07974; N. Shavit, Laborato~ for Computer Scienee, MIT NE43, 367 Technology Square, Cambridge MA 02139. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice N gwen that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. (!2 1993 ACM 0004-541 1/93/0900-0873 $01.50 Joumd of ihe Amocl.]tmn for Computmg Mdchmerv, Vd 40. No 4. Scptemhcr 1993. pp 873-89[1

Projection methods for variational inequalities with application to the traffic assignment problem

Abstract: It is well known [2, 3, 16] that if \(\bar T:R^n \to R^n\) is a Lipschitz continuous, strongly monotone operator and X is a closed convex set, then a solution x *∈X of the variational inequality \((x - x^ * )'\bar T(x^ * ) \geqslant 0\), ∨x∈X can be found iteratively by means of the projection method \(x_{k - 1} = Px[x_k - \alpha \bar T(x_k )]\), x 0∈X, provided the stepsize α is sufficiently small. We show that the same is true if \(\bar T\) is of the form \(\bar T = A'TA\), where A:R n→R m is a linear mapping, provided T:R m→R m is Lipschitz continuous and strongly monotone, and the set X is polyhedral. This fact is used to construct an effective algorithm for finding a network flow which satisfies given demand constraints and is positive only on paths of minimum marginal delay or travel time.

Probabilistic Reasoning in Intelligent Systems: Networks of Plausible Inference

Abstract: From the Publisher: Probabilistic Reasoning in Intelligent Systems is a complete andaccessible account of the theoretical foundations and computational methods that underlie plausible reasoning under uncertainty. The author provides a coherent explication of probability as a language for reasoning with partial belief and offers a unifying perspective on other AI approaches to uncertainty, such as the Dempster-Shafer formalism, truth maintenance systems, and nonmonotonic logic. The author distinguishes syntactic and semantic approaches to uncertainty—and offers techniques, based on belief networks, that provide a mechanism for making semantics-based systems operational. Specifically, network-propagation techniques serve as a mechanism for combining the theoretical coherence of probability theory with modern demands of reasoning-systems technology: modular declarative inputs, conceptually meaningful inferences, and parallel distributed computation. Application areas include diagnosis, forecasting, image interpretation, multi-sensor fusion, decision support systems, plan recognition, planning, speech recognition—in short, almost every task requiring that conclusions be drawn from uncertain clues and incomplete information. Probabilistic Reasoning in Intelligent Systems will be of special interest to scholars and researchers in AI, decision theory, statistics, logic, philosophy, cognitive psychology, and the management sciences. Professionals in the areas of knowledge-based systems, operations research, engineering, and statistics will find theoretical and computational tools of immediate practical use. The book can also be used as an excellent text for graduate-level courses in AI, operations research, or applied probability.

Distributed algorithms

Abstract: In Distributed Algorithms, Nancy Lynch provides a blueprint for designing, implementing, and analyzing distributed algorithms. She directs her book at a wide audience, including students, programmers, system designers, and researchers. Distributed Algorithms contains the most significant algorithms and impossibility results in the area, all in a simple automata-theoretic setting. The algorithms are proved correct, and their complexity is analyzed according to precisely defined complexity measures. The problems covered include resource allocation, communication, consensus among distributed processes, data consistency, deadlock detection, leader election, global snapshots, and many others. The material is organized according to the system model-first by the timing model and then by the interprocess communication mechanism. The material on system models is isolated in separate chapters for easy reference. The presentation is completely rigorous, yet is intuitive enough for immediate comprehension. This book familiarizes readers with important problems, algorithms, and impossibility results in the area: readers can then recognize the problems when they arise in practice, apply the algorithms to solve them, and use the impossibility results to determine whether problems are unsolvable. The book also provides readers with the basic mathematical tools for designing new algorithms and proving new impossibility results. In addition, it teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures. Table of Contents 1 Introduction 2 Modelling I; Synchronous Network Model 3 Leader Election in a Synchronous Ring 4 Algorithms in General Synchronous Networks 5 Distributed Consensus with Link Failures 6 Distributed Consensus with Process Failures 7 More Consensus Problems 8 Modelling II: Asynchronous System Model 9 Modelling III: Asynchronous Shared Memory Model 10 Mutual Exclusion 11 Resource Allocation 12 Consensus 13 Atomic Objects 14 Modelling IV: Asynchronous Network Model 15 Basic Asynchronous Network Algorithms 16 Synchronizers 17 Shared Memory versus Networks 18 Logical Time 19 Global Snapshots and Stable Properties 20 Network Resource Allocation 21 Asynchronous Networks with Process Failures 22 Data Link Protocols 23 Partially Synchronous System Models 24 Mutual Exclusion with Partial Synchrony 25 Consensus with Partial Synchrony

Cognitive Radio An Integrated Agent Architecture for Software Defined Radio

Abstract: An Integrated Agent Architecture for Software Defined Radio. Rapid-prototype cognitive radio, CR1, was developed to apply these.The modern software defined radio has been called the heart of a cognitive radio. Cognitive radio: an integrated agent architecture for software defined radio. Http:bwrc.eecs.berkeley.eduResearchMCMACR White paper final1.pdf. The cognitive radio, built on a software-defined radio, assumes. Radio: An Integrated Agent Architecture for Software Defined Radio, Ph.D. The need for software-defined radios is underlined and the most important notions used for such. Mitola III, Cognitive radio: an integrated agent architecture for software defined radio, Ph.D. This results in the set-theoretic ontology of radio knowledge defined in the. Cognitive Radio An Integrated Agent Architecture for Software.This article first briefly reviews the basic concepts about cognitive radio CR. Cognitive Radio-An Integrated Agent Architecture for Software Defined Radio. Cognitive Radio RHMZ 2007. Software-defined radio SDR idea 1. Cognitive radio: An integrated agent architecture for software.Cognitive Radio SOFTWARE DEFINED RADIO, AND ADAPTIVE WIRELESS SYSTEMS2 Cognitive Networks. 3 Joseph Mitola III, Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio Stockholm.

Analysis and simulation of a fair queueing algorithm

Abstract: We discuss gateway queueing algorithms and their role in controlling congestion in datagram networks. A fair queueing algorithm, based on an earlier suggestion by Nagle, is proposed. Analysis and s...

Analysis and simulation of a fair queueing algorithm

Abstract: We discuss gateway queueing algorithms and their role in controlling congestion in datagram networks. A fair queueing algorithm, based on an earlier suggestion by Nagle, is proposed. Analysis and simulations are used to compare this algorithm to other congestion control schemes. We find that fair queueing provides several important advantages over the usual first-come-first-serve queueing algorithm: fair allocation of bandwidth, lower delay for sources using less than their full share of bandwidth, and protection from ill-behaved sources.