Leader election for anonymous asynchronous agents in arbitrary networks

We consider the problem of leader election among mobile agents operating in an arbitrary network modeled as an undirected graph. Nodes of the network are unlabeled and all agents are identical. Hence the only way to elect a leader among agents is by exploiting asymmetries in their initial positions in the graph. Agents do not know the graph or their positions in it, hence they must gain this knowledge by navigating in the graph and share it with other agents to accomplish leader election. This can be done using meetings of agents, which is difficult because of their asynchronous nature: an adversary has total control over the speed of agents. When can a leader be elected in this adversarial scenario and how to do it? We give a complete answer to this question by characterizing all initial configurations for which leader election is possible and by constructing an algorithm that accomplishes leader election for all configurations for which this can be done.     

Leader election in hierarchical star network

We propose a new leader election algorithm for the oriented hierarchical star networks that has linear message complexity.     

Leader election in the presence of link failures

We study the problem of leader election in the presence of intermittent link failures. We assume that up to N/2-1 links incident on each node may fail during the execution of the protocol. We present a message optimal algorithm with message complexity O(N²)     

Reliable election in broadcast networks

Election in a computer network is an operation in which one process is selected from among a group of processes to perform a particular task. An election is characterized by (1) the capacities of the candidates, and (2) the agreement reached by all processes to elect the master. In this paper, we show that election is in fact a very general style of computation. Many problems in computer networks can be solved by means of election. We then examine the election problem in computer networks with broadcast support. Basic design issues of election algorithms are addressed, and a number of election algorithms are presented based on various environments. These algorithms allow all nonfaulty processes to elect one and only one process as the master, and, by changing the definition of the capacities, they can be applied to a variety of problems.     

Distributed election in complete networks

An improved version of Afek and Gafni's synchronous algorithm for distributed election in complete networks is given and anO(n) expected message complexity is shown. M.Y. Chan received her Ph.D. in 1988 from the University of Hong Kong, and her M.S. and B.A. degrees in computer science from the University of California, San Diego in 1980 and 1981, respectively. She is currently an Assistant Professor at the University of Texas at Dallas. Francis Y.L. Chin (S71-M76-SM85) received the B.Sc. degree in engineering science from the University of Toronto, Toronto, Canada, in 1972, and the M.S., M.A., and Ph.D. degrees in electrical engineering and computer science from Princeton University, New Jersey, in 1974, 1975, and 1976, respectively. Since 1975, he has taught at the University of Maryland, Baltimore Country, University of California, San Diego, University of Alberta, and Chinese University of Hong Kong. He is currently Head of the Department of Computer Science, University of Hong Kong. He has served as a program co-chairman of the 1988 International Conference on Computer Processing of Chinese and Oriental Languages (Toronto) and the International Computer Science Conference '88 (Hong Kong). His current research interests include algorithm design and analysis, parallel and distributed computing.     

无线传感器网络汇聚节点自组织选举协议

无线传感器网络是由能够感知环境信息和能够进行无线通信的传感器节点构成的网络,广泛应用在环境监测、目标跟踪等方面.无线传感器网络中,汇聚节点(Sink)的位置选取关系到整个网络的性能和生命期,并与节点的部署情况、网络的拓扑结构紧密关联.本文对汇聚节点位置对于无线传感器网络性能和生命期的影响进行了分析之后,以全网能耗、平均-最大端到端延迟为权衡指标,设计了汇聚节点选举协议.仿真表明,运行该协议的网络能够以较小的代价,迅速地选举出具备最优权衡指标的Sink,同时网络还体现出优秀的自组织组网能力.     

New model and algorithms for leader election in synchronousfiber-optic networks

We improve on I. Cidon, I. Gopal and S. Kutten's leader election algorithm (Proc. 7th ACM Symp. Principles Distrib. Computing, Toronto, Ont., Canada. Aug. 1988) by presenting an algorithm that uses only O(√n log D + f) time units to run on synchronous networks of degree f and diameter D, where f⩾3. When f is 2, the algorithm uses only O(log D) time units     

Design and analysis of dynamic leader election protocols in broadcast networks

Summary.  The well-known problem of leader election in distributed systems is considered in a dynamic context where processes may participate and crash spontaneously. Processes communicate by means of buffered broadcasting as opposed to usual point-to-point communication. In this paper we design a leader election protocol in such a dynamic context. As the problem at hand is considerably complex we develop the protocol in three steps. In the initial design processes are considered to be perfect and a leader is assumed to be present initially. In the second protocol, the assumption of an initial leader is dropped. This leads to a symmetric protocol which uses an (abstract) timeout mechanism to detect the absence of a leader. Finally, in the last step of the design processes may crash without giving any notification of other processes. The worst case message complexity of all protocols is addressed. A formal approach to the specification and verification of the leader election protocols is adopted. The requirements are specified in a property-oriented way and the protocols are denoted by means of extended finite state machines. It is proven using linear-time temporal logic that the fault-tolerant protocol satisfies its requirements. Received: September 1993 / Revised: September 1995     

Isomorphic coupled-task scheduling problem with compatibility constraints on a single processor

The problem presented in this paper is a generalization of the usual coupled-tasks scheduling problem in presence of compatibility constraints. The reason behind this study is the data acquisition problem for a submarine torpedo. We investigate a particular configuration for coupled tasks (any task is divided into two sub-tasks separated by an idle time), in which the idle time of a coupled task is equal to the sum of durations of its two sub-tasks. We prove \(\mathcal{NP}\)-completeness of the minimization of the schedule length, we show that finding a solution to our problem amounts to solving a graph problem, which in itself is close to the minimum-disjoint-path cover (min-DCP) problem. We design a \((\frac{3a+2b}{2a+2b})\)-approximation, where a and b (the processing time of the two sub-tasks) are two input data such as a>b>0, and that leads to a ratio between \(\frac {3}{2}\) and \(\frac{5}{4}\). Using a polynomial-time algorithm developed for some class of graph of min-DCP, we show that the ratio decreases to \(\frac{1+\sqrt{3}}{2}\approx 1.37\).     

The election problem in asynchronous distributed systems with bounded faulty processes

Determining the “weakest” failure detectors is a central topic in solving many agreement problems such as Consensus, Non-Blocking Atomic Commit and Election in asynchronous distributed systems. So far, this has been studied extensively for several such fundamental problems. It is stated that Perfect Failure Detector P is the weakest failure detector to solve the Election problem with any number of faulty processes. In this paper, we introduce Modal failure detector M and show that to solve Election, M is the weakest failure detector to solve election when the number of faulty processes is less than ⌈n/2⌉. We also show that it is strictly weaker than P.

Solving the generalized eigenvalue problem on a synchronous linear processor array

We present a parallel method to solve the generalized eigenvalue problem on a linear array of processors, each connected to their nearest neighbors and operating synchronously. We also include a wrap-around connection from end to end. Our method is based on the well-known QZ algorithm of Moler and Stewart, which simultaneously reduces two n × n matrices to upper triangular form by orthogonal or unitary transformations. We show how this algorithm may be partitioned and distributed of n + 1 processors, achieving a speed-up over the serial algorithm of O(n). We use the concept of windows to describe the action of each processor at each step. We show how to incorporate singles shifts, and how to apply orthogonal plane rotations on either side of a matrix without the need to transpose the matrix itself.     

传感器网络中基于平均剩余能量的数据汇聚节点选择算法

针对如何根据变动的网关节点在网络内部选择合适的数据汇聚节点以传输采集的数据这一问题,综合考虑节点剩余能量和距离因素,提出了一种基于平均剩余能量的数据汇聚节点选择算法,以均衡节点能耗、延长网络生命周期。与基于最大剩余能量的数据汇聚节点选择算法比较,证明该算法能够在保持相近生命周期的情况下大大减少计算量,更适用于资源有限的传感器网络。     

Optimal control of linear systems with quadratic costs which are not necessarily positive definite

The calculus of variations is applied to the problem of finding the optimal control for linear systems with quadratic costs which are not necessarily positive definite. The conjugate point condition is transformed to an explicit condition upon the parameters of the problem, in the one-dimensional case for arbitrary costs and in then-dimensional case for final costs only. The expressions for the optimal controls are given. A numerical example of a second-order system is solved.     

Entity-relationship diagrams which are in BCNF

In Ref. 8, we introduced a simplifying assumption about entity-relationship diagrams (ERDs), called regularity, and showed that regular ERDs have several desirable properties. One such property is that every relation schema in the ERD's canonical relational scheme can be put into Third Normal Form. We left open there the more basic question: under what conditions would the original relation schemas actually be in Boyce-Codd Normal Form (BCNF)? Since the visible semantics of ERDs determine naturally their associated functional dependencies (fd's), it is important to know when an ERD, as designed, already has this strongest normal form given purely in terms of fd's. We show here a sufficient diagrammatic condition (loop-free) under which a regular ERD will have databases enjoying the benefits of BCNF.     

计算机网络中的多播路由问题

在计算机网络中,多播是目前研究最多、应用最广的连接方式。就目前存在的多播路由算法及路由协议进行了分析与总结,给出了解决多播问题的一般方法,提出了在光网络中推行多播的必要性。