Showing papers on "Distributed algorithm published in 1981"

The Architectural Organization of a Mobile Radio Network via a Distributed Algorithm

Abstract: In this paper we consider the problem of organizing a set of mobile, radio-equipped nodes into a connected network. We require that a reliable structure be acquired and maintained in the face of arbitrary topological changes due to node motion and/or failure. We also require that such a structure be achieved without the use of a central controller. We propose and develop a self-starting, distributed algorithm that establishes and maintains such a connected architecture. This algorithm is especially suited to the needs of the HF Intra-Task Force (ITF) communication network, which is discussed in the paper.

An optimal algorithm for mutual exclusion in computer networks

Abstract: An algorithm is proposed that creates mutual exclusion in a computer network whose nodes communicate only by messages and do not share memory. The algorithm sends only 2*(N - 1) messages, where N is the number of nodes in the network per critical section invocation. This number of messages is at a minimum if parallel, distributed, symmetric control is used; hence, the algorithm is optimal in this respect. The time needed to achieve mutual exclusion is also minimal under some general assumptions. As in Lamport's "bakery algorithm," unbounded sequence numbers are used to provide first-come firstserved priority into the critical section. It is shown that the number can be contained in a fixed amount of memory by storing it as the residue of a modulus. The number of messages required to implement the exclusion can be reduced by using sequential node-by-node processing, by using broadcast message techniques, or by sending information through timing channels. The "readers and writers" problem is solved by a simple modification of the algorithm and the modifications necessary to make the algorithm robust are described.

Asynchronous distributed simulation via a sequence of parallel computations

Abstract: An approach to carrying out asynchronous, distributed simulation on multiprocessor messagepassing architectures is presented. This scheme differs from other distributed simulation schemes because (1) the amount of memory required by all processors together is bounded and is no more than the amount required in sequential simulation and (2) the multiprocessor network is allowed to deadlock, the deadlock is detected, and then the deadlock is broken. Proofs for the correctness of this approach are outlined.

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.

Crash Recovery in a Distributed Data Storage System

Abstract: An algorithm is described which guarantees reliable storage of data in a distributed system, even when different portions of the data base, stored on separate machines, are updated as part of a single transaction. The algorithm is implemented by a hierarchy of rather simple abstractions, and it works properly regardless of crashes of the client or servers. Some care is taken to state precisely the assumptions about the physical components of the system (storage, processors and communication).

Analysis of Chordal Ring Network

Abstract: A family of regular graphs of degree 3, called Chordal Rings, is presented as a possible candidate for the implementation of a local network of message-connected (micro) computers. For a properly constructed graph in this family having n nodes the diameter, or maximum length message path, is shown to be of 0(n 1/2). The symmetry of the graphs makes it possible to determine message routing by using a simple distributed algorithm. The given algorithm is also potentially useful for the determination of alternate paths in the event of node or link failure.

Distributed dynamic programming

Abstract: We consider distributed algorithms for solving dynamic programming problems whereby several processors participate simultaneously in the computation while maintaining coordination by information exchange via communication links. A model of asynchronous distributed computation is developed which requires very weak assumptions on the ordering of computations, the timing of information exchange, the amount of local information needed at each computation node, and the initial conditions for the algorithm. The class of problems considered is very broad and includes shortest path problems, and finite and infinite horizon stochastic optimal control problems. When specialized to a shortest path problem the algorithm reduces to the algorithm originally implemented for routing of messages in the ARPANET.

Natural and Social System Metaphors for Distributed Problem Solving: Introduction to the Issue

Abstract: Naturally occurring information systems provide a number of useful metaphors for distributed problem solving. An introduction to some aspects of these metaphors is given which simultaneously serves as a guest editorial for a special issue devoted to the topic. The ubiquity of a distributed mode of computation in information processing in natural phenomena in general and in human societies in particular is observed and related to the evolutionary and complexity-reducing advantages of this mode. The forms of communication media available to coordinate the problem solving activities of the individual processors are examined. Some general remarks are made on how problem solving is distributed and coordinated in some human organizations, and the potential usefulness of the " society of specialists" notion in explicating cognitive activity is pointed out. Along the way, the contents of the papers in the special issue are considered in relation to various points raised in the discussion.

Optimization of the Number of Copies in a Distributed Data Base

Abstract: We consider the effect on system performance of the distribution of a data base in the form of multiple copies at distinct sites. The purpose of our analysis is to determine the gain in READ throughput that can be obtained in the presence of consistency preserving algorithms that have to be implemented when UPDATE operations are carried out on each copy. We show that READ throughput diminishes if the number of copies exceeds an optimal value. The theoretical model we develop is applied to a system in which consistency is preserved through the use of Ellis' ring algorithm.

Design and strategy for distributed data processing

Abstract: We may not be able to make you love reading, but design and strategy for distributed data processing will lead you to love reading starting from now. Book is the window to open the new world. The world that you want is in the better stage and level. World will always guide you to even the prestige stage of the life. You know, this is some of how reading will give you the kindness. In this case, more books you read more knowledge you know, but it can mean also the bore is full.

The Poisson Multiple-Access Conflict Resolution Problem

Abstract: The major thrust of system theory research in recent years has been directed at multiterminal, or decentralized, problems. These are characterized by the fact that system functions — such as coding, routing, control, decision, and estimation — are effected simultaneously at several physically distinct sites within the system. The information available differs, in general, from site to site. This necessitates the development of distributed algorithms aimed at cooperatively achieving optimum, or near-optimum, performance in the face of topologically complex information patterns. In previous lectures at CISM, several investigators including myself have treated multiterminal information theory problems involving distributed algorithms for encoding and decoding. In these lectures I concentrated instead on an intriguing problem in multiterminal communication theory, the conflict resolution problem in packet-switched communication networks. After stating the problem, we recast it as one of “fishing in a Poisson stream with a weak net”. The slotted ALOHA protocol is described ana analyzed. Gallager’s improvement on Capetanakis’s algorithm is then treated in considerable detail; a closed-form expression for its efficiency is derived. Recursive equations developed by the Russian and French schools are presented as an alternative means of analyzing this algorithm and others. Then we present Pippenger’s and Molle’s upper bounds to the maximum efficiency attainable. We conclude with what we feel to be a convincing case for our belief that Molle’s method can be improved upon to yield an upper bound of 0.5254 which is only 0.0377 above the efficiency of 0.4877 achieved by the optimized version of Gallager’s algorithm.

A Distributed System for Real-Time Transaction Processing

Abstract: An experimental system designed as part of INRIA's Project Sirius, Delta implements a distributed executive for real-time transactional systems.

The complexity of distributed concurrency control

Abstract: We present a formal framework for distributed databases, and we study the complexity of the concurrency control problem in this framework. Our transactions are partially ordered sets, of actions, as opposed to the straight-line programs of the centralized case. The concurrency control algorithm, or scheduler, is itself a distributed program. Three notions of performance of the scheduler are studied and interrelated: (i) its parallelism, (ii) the computational complexity of the problems it needs to solve, and (iii) the cost of communication between the various parts of the scheduler. We show that the number of messages necessary and sufficient to support a given level of parallelism is equal to the minmax value of a combinatorial game. We show that this game is PSPACE-complete. It follows that, unless NP=PSPACE, a scheduler cannot simultaneously minimize communication and be computationally efficient. This result, we argue, captures the quantum jump in complexity of the transition from centralized to distributed concurrency control problems.

Distributed algorithms for synchronizing interprocess communication within real time

Abstract: This paper considers a fixed (possibly infinite) set π of distributed asynchronous processes which at various times are willing to communicate with each other. We describe probabilistic algorithms for synchronizing this communication with boolean “flag” variables, each of which can be written by only one process and read by at most one other process. With very few assumptions (the speeds of processes may vary in time within fixed arbitrary bounds, and the processes may be willing to communicate with a time varying set of processes (but bounded in number), and no probability assumptions about system behavior) we show our synchronization algorithms have real time response: If a pair of processes are mutually willing to communicate within a constant time interval, they establish communication in that interval, with high likelihood (for the worst case behavior of the system). Our communication model and synchronization algorithms are quite robust. They are applied to solve a large class of real time resource synchronization problems, as well as real time implementation of the synchronization primitives of Hoare's multiprocessing language CSP.

Query processing in distributed data bases

Abstract: : This paper describes two new distributed query processing algorithms. The MST Algorithm minimizes the total communication costs associated with a query while the MDT Algorithm minimizes the response time. These two algorithms are easy to analyze and to implement, since they are based on the minimum spanning tree and the shortest path problems, for which numerous algorithms exist. In addition, these two algorithms can be implemented using distributed computation, i.e., each node using only information available from adjacent nodes. We also develop the 'artificial file node' technique to extend existing query processing algorithms which are designed for non-redundant databases to that for general, redundant databases. The two algorithms are illustrated by simple examples. (Author)

Real-Time Distributed Computer Systems

Abstract: Publisher Summary This chapter describes real-time distributed computer systems in regard to their design and implementation. It discusses the motivation for distributed computer systems in terms of possible system characteristics attained by distributing the computational resources. The chapter also characterizes the real-time control application environment. Further, the chapter reviews the options and issues related to hardware and software designs for distributed systems, and examines the details of the design and implementation of the Honeywell Experimental Distributed Computing System (HXDP). Distributed computer systems essentially contain several computers and provide increased system availability and reliability. Their design is complex, involving the design of communications mechanisms in hardware and software, and the selection of policies and mechanisms for distributed system control. However, the complex design issues can have simple solutions in a well-understood application environment. Distributed systems are considered attractive as they provide efficiency, modularity, robustness to failure, and extensibility. Moreover, for real-time environments, these systems allow physical distribution of functionality, placing computing power at places where required.

The Soma: A Programming Construct for Distributed Processing

Abstract: A construct is proposed for parallel programming, called soma (software machine). A soma is a sequential process that can communicate with other somas by exchanging messages via mailboxes. The soma construct is well suited for implementation on conventional as well as on distributed computer architectures, the main characteristic of the latter being the absence of a common store.

Two approaches to deadlock in distributed systems

Abstract: A novel reflective light-polarizing lamination comprising a light polarizer laminated to the matte surface of aluminum foil and useful in display cells for field-effect transition liquid crystal displays.

Performance analysis of update synchronization algorithms for distributed databases

Abstract: One of the most critical problem in the implementation of distributed databases is that of concurrency control. The problem is to preserve the consistency of data (that may otherwise be destroyed by concurrent accesses). One of the major goals in the research of distributed databases is to develop design methodology and guidelines for designing good concurrency control methods for a given system environment. In this thesis, we have set out to approach the goal by analyzing some of the concurrency control schemes in an effort to understand their relative merits, investigate the sensitivity of the performance to different parameters, and to provide some guidelines for designing resilient concurrency algorithms for distributed databases. Several update synchronization algorithms are modelled and analyzed in this dissertation. Algorithms investigated in this dissertation include a resilient centralized locking algorithm, some distributed algorithms using timestamps, and some algorithms using clock messages in addition to timestamps. Results from the analysis allowed us to pinpoint inefficiency and suggest some new algorithms.

A distributed minimum hop routing algorithm

Abstract: A two-part distributed algorithm for minimum hop routing in message-switched networks subject to end-to-end average message delay constraints is developed. The first part of the algorithm provides for unconstrained minimum hop routing, while the second corrects this routing to satisfy the delay constraints. Both parts are implemented nodewise via low-order linear programs wherein the information exchange required for each node to carry out its computations involves only adjacent neighbor nodes. The algorithm is illustrated via an example of an 8- node, 14-link network with 7 commodities, and directions for future research to enhance present results are indicated.

A note on the distributed program component cell

Abstract: This paper presents a new language construct for distributed computing. This construct, called cell, allows one to simulate a variety of language constructs. Its salient features provide the programmer with an effective synchronization scheme, and a mechanism to control the order in which various activities within a cell should be executed.