Coterie join algorithm

Given a set of nodes in a distributed system, a coterie is a collection of subsets of the set of nodes such that any two subsets have a nonempty intersection and are not properly contained in one another. A subset of nodes in a coterie is called a quorum. An algorithm, called the join algorithm, which takes nonempty coteries as input, and returns a new, larger coterie called a composite coterie is introduced. It is proved that a composite coterie is nondominated if and only if the input coteries are nondominated. Using the algorithm, dominated or nondominated coteries may be easily constructed for a large number of nodes. An efficient method for determining whether a given set of nodes contains a quorum of a composite coterie is presented. As an example, tree coteries are generalized using the join algorithm, and it is proved that tree coteries are nondominated. It is shown that the join algorithm may be used to generate read and write quorums which may be used by a replica control protocol     

Minimizing the maximum delay for reaching consensus in quorum-basedmutual exclusion schemes

The use of quorums is a well-known approach to achieving mutual exclusion in distributed computing systems. This approach works based on a coterie, a special set of node groups where any pair of the node groups shares at least one common node. Each node group in a coterie is called a quorum. Mutual exclusion is ensured by imposing that a node gets consensus from all nodes in at least one of the quorums before it enters a critical section. In a quorum-based mutual exclusion scheme, the delay for reaching consensus depends critically on the coterie adopted and, thus, it is important to find a coterie with small delay. Fu (1997) introduced two related measures called max-delay and mean-delay. The former measure represents the largest delay among all nodes, while the latter is the arithmetic mean of the delays. She proposed polynomial-time algorithms for finding max-delay and mean-delay optimal coteries when the network topology is a tree or a ring. In this paper, we first propose a polynomial-time algorithm for finding max-delay optimal coteries and, then, modify the algorithm so as to reduce the mean-delay of generated coteries. Unlike the previous algorithms, the proposed algorithms can be applied to systems with arbitrary topology     

Recognizing nondominated coteries and wr-coteries by availability

Coterie is a widely accepted concept for solving the mutual exclusion problem. Nondominated coteries are an important class of coteries which have better performance than dominated coteries. The performance of a coterie is usually measured by availability. Higher availability of a coterie exhibits greater ability to tolerate node or communication link failures. In this paper, we demonstrate a way to recognize nondominated coteries using availability. By evaluating the availability of a coterie instead of using a formal proof, the coterie can be recognized as a nondominated coterie or not. Moreover, with regard to wr-coterie, a concept for solving the replica control problem, we also present a similar result for recognizing nondominated wr-coteries. Finally, we apply our results to some well-known coteries and wr-coteries     

Transversal merge operation: a nondominated coterie construction method for distributed mutual exclusion

A coterie is a set of subsets (called quorums) of the processes in a distributed system such that any two quorums intersect with each other and is mainly used to solve the mutual exclusion problem in a quorum-based algorithm. The choice of a coterie sensitively affects the performance of the algorithm and it is known that nondominated (ND) coteries achieve good performance in terms of criteria such as availability and load. On the other hand, grid coteries have some other attractive features: 1) a quorum size is small, which implies a low message complexity, and 2) a quorum is constructible on the fly, which benefits a low space complexity. However, they are not ND coteries unfortunately. To construct ND coteries having the favorite features of grid coteries, we introduce the transversal merge operation that transforms a dominated coterie into an ND coterie and apply it to grid coteries. We call the constructed ND coteries ND grid coteries. These ND grid coteries have availability higher than the original ones, inheriting the above desirable features from them. To demonstrate this fact, we then investigate their quorum size, load, and availability, and propose a dynamic quorum construction algorithm for an ND grid coterie.     

Nondominated coteries on graphs

Let C and D be two distinct coteries under the vertex set V of a graph G=(V,E) that models a distributed system. Coterie C is said to G-dominate D (with respect to G) if the following condition holds: For any connected subgraph H of G that contains a quorum in D (as a subset of its vertex set), there exists a connected subgraph H' of H that contains a quorum in C. A coterie C on a graph G is said to be G-nondominated (G-ND) (with respect to G) if no coterie D(≠C) on G G-dominates C. Intuitively, a G-ND coterie consists of irreducible quorums. This paper characterizes G-ND coteries in graph theoretical terms, and presents a procedure for deciding whether or not a given coterie C is G-ND with respect to a given graph G, based on this characterization. We then improve the time complexity of the decision procedure, provided that the given coterie C is nondominated in the sense of Garcia-Molina and Barbara (1985). Finally, we characterize the class of graphs G on which the majority coterie is G-ND     

移动自组网的访问控制技术研究

网络资源的共享与保护是移动自组网需要解决的关键问题之一。运用Voronoi图模型和quorum系统的思想,提出了一种移动自组网的动态路径quorum系统,设计了动态路径quorum的生成算法。基于移动自组网的动态路径quorum系统,提出了基于quorum系统的移动自组网的分布式访问控制机制,详细描述了节点的身份认证、网络资源的访问控制和权限管理协议。与传统的基于单个节点自身的访问控制机制相比,该访问控制机制具有较强的抗攻击能力和较高的可靠性,能够有效地提高移动自组网的资源共享与保护水平。     

A Token-Based Distributed Group Mutual Exclusion Algorithm with Quorums

The group mutual exclusion problem is a generalization of mutual exclusion problem such that a set of processes in the same group can enter critical section simultaneously. In this paper, we propose a distributed algorithm for the group mutual exclusion problem in asynchronous message passing distributed systems. Our algorithm is based on tokens, and a process that obtains a token can enter critical section. For reducing message complexity, it uses coterie as a communication structure when a process sends a request messages. Informally, coterie is a set of quorums, each of which is a subset of the process set, and any two quorums share at least one process. The message complexity of our algorithm is $O(|Q|)$ in the worst case, where $|Q|$ is a quorum size that the algorithm adopts. Performance of the proposed algorithm is presented by analysis and discrete event simulation. Especially, the proposed algorithm achieves high concurrency, which is a performance measure for the number of processes that can be in critical section simultaneously.     

A delay optimal coterie on the k-dimensional folded Petersen graph

Coteries are an effective tool for enforcing mutual exclusion in distributed systems. Communication delay is an important metric to measure the performance of a coterie. The topology of the interconnection network in a distributed system also has an impact on its performance. The k-dimensional folded Petersen graph, a graph with 10^k nodes and diameter 2k, qualifies as a good network topology for large distributed systems. In this paper, we present a delay optimal coterie on the k-dimensional folded Petersen graph, FP_k. For any positive integer k, the coterie has message complexity 4^k and delay k. Moreover, this coterie is not vote-assignable.     

Diamond Quorum Consensus for High Capacity and Efficiency in a Replicated Database System

Many quorum consensus protocols have been proposed for the management of replicated data in a distributed environment. The advantages of a replicated database system over a non-replicated one include high availability and low response time. We note further that the multiple sites can act as multiple agents so that at any time, multiple requests can be handled in parallel. This feature leads to the desirable consequence of high workload capacity. In this paper, we define a new metric of read-capacity for this feature. We propose a new protocol called diamond quorum consensus which has two major properties that are superior to the previous protocols of majority, tree, grid, and hierarchical quorum consensus: (1) it has the highest read-capacity, (2) it has the smallest optimal read quorum size of 2. We show that these two features are achievable without jeopardizing the availability. The small quorum size is a significant feature because it relates to the messaging cost. Few previous work on quorum consensus has discussed the handling of partition failure, which in many cases will depend on the quorum consensus protocol, we show how we can use the generalized virtual partition protocol to handle partition failure in the case of diamond quorum consensus.     

On multilevel voting

Summary In a distributed system mutual exclusion is often used to maintain consistency when restricted operations are performed. Mechanisms guaranteeing mutual exclusions should be both resilient and efficient. Resiliency implies high resource availability in the face of failures, while efficiency implies low overhead incurred by performing restricted operations. In this paper, we propose and study a general paradigm, called multilevel voting, which provides a general framework to assist in the design of resilient and efficient mutual exclusion mechanisms. The proposed method uses multiple level quorum consensus. Unlike another method based on the use of multiple quorum consensus, the proposed model only contains one type of integrity constraints. This has the benefit of being conceptually simple and easy to reason about. The strong resemblance with the traditional quorum consensus makes it easy for the proposed paradigm to embed any technique based on traditional quorum schemes. We show that the proposed model represents the exact class of coteries. This means that not only does it have all the power of coteries, but also all schemes under the model are correct. Thus, should the need arise, we can interchange two schemes freely without using any extra mechanisms to ensure correctness. We study a number of issues that have impact on performance such as the degree of a multilevel scheme and the order of a coterie. We explain how the model can be extended also to model the schemes for the synchronization of read and write of replicated data. We provide algorithms for the design of multilevel schemes in the context of mutual exclusion and that of read and write of replicated data. J. Tang received the M.S. degree in computer science from the University of Iowa in 1983 and the Ph.D degree in computer science from the Pennsylvania State University in 1988. Since 1988, he has been an assistant professor with the Department of Computer Science, Memorial University of Newfoundland, St. John's, Newfoundland, Canada. His current research interests include distributed computing, fault tolerance in distributed systems, database modeling and multidatabase systems.This work was supported in part by the Natural Sciences and Engineering Research Council of Canada, individual operating grant OGP0041916     

Synchronous Byzantine quorum systems

Summary. Quorum systems have been used to implement many coordination problems in distributed systems such as mutual exclusion, data replication, distributed consensus, and commit protocols. Malkhi and Reiter recently proposed quorum systems that can tolerate Byzantine failures; they called these systems Byzantine quorum systems and gave some examples of such quorum systems. In this paper, we propose a new definition of Byzantine quorums that is appropriate for synchronous systems. We show how these quorums can be used for data replication and propose a general construction of synchronous Byzantine quorums using standard quorum systems. We prove tight lower bounds on the load of synchronous Byzantine quorums for various patterns of failures and we present synchronous Byzantine quorums that have optimal loads that match the lower bounds for two failure patterns. Received: June 1998 / Accepted: August 1999     

Obtaining coteries that optimize the availability of replicateddatabases

Techniques for implementing the coterie scheme and for obtaining optimal coteries for a system are presented. Central to the techniques is the notion of an acceptance set, which is an alternative representation of the information contained in a coterie. Using this concept, the coterie scheme can be implemented efficiently, and an optimal coterie for a system can be obtained more directly. The problem of determining an optimal acceptance set is formulated as a sparse zero-one linear programming problem. Hence, the optimization problem can be handled using the very rich class of existing techniques for solving such problems. Experimental results indicate that the optimization approach is feasible for up to eight nodes at least. The ways in which the scheme and the optimization approach can be used for systems that distinguish between read and write operations are indicated     

A quorum-based protocol for searching objects in peer-to-peer networks

Peer-to-peer (P2P) system is an overlay network of peer computers without centralized servers, and many applications have been developed for such networks such as file sharing systems. Because a set of peers dynamically changes, design and verification of efficient protocols is a challenging task. In this paper, we consider an object searching problem under a resource model such that there are some replicas in a system and the lower bound of the ratio /spl rho/=n'/n is known in advance, where n' is a lower bound of the number of peers that hold original or replica for any object type and n is the total number of peers. In addition, we consider object searching with probabilistic success, i.e., for each object search, object must be found with at least probability 0相似文献   

基于影响力网络模型的多智能体一致性协议

如何增强系统一致性是多智能体系统研究中的一个重要问题。传统一致性协议通常未考虑拓扑中的关键节点,并且拓扑权重单一,从而导致系统更容易分裂。基于人际关系网络中的关键人物可以促进不同社区信息交流的思想,提出了一种影响力网络模型（influence network model,INM）。首先,提出了分布式的Hub Node识别算法（distributed hub node identify algorithm,DHNI）,用于区分关键节点和非关键节点,可以应用在分布式多智能体系统中。其次,提出了基于分布式hub node的拓扑权重设计算法（distributed hub node-based topology reweighting algorithm,DHNTR）,量化不同节点对其邻居的影响力。最后提出了基于影响力网络的一致性协议。设计了公共Lyapunov函数,分析了系统的全局稳定性,证明了系统具有Lyapunov意义下的稳定性。仿真实验表明该协议可以增强系统一致性。     

共识协议的形式化验证研究现状与展望

分布式系统在计算环境中发挥重要的作用,其中的共识协议算法用于保证节点间行为的一致性.共识协议的设计错误可能导致系统运行故障,严重时可能对人员和环境造成灾难性的后果,因此保证共识协议设计的正确性非常重要.形式化验证能够严格证明设计模型中目标性质的正确性,适合用于验证共识协议.然而,随着分布式系统的规模增大,问题复杂度提升,使得分布式共识协议的形式化验证更为困难.采用什么方法对共识协议的设计进行形式化验证、如何提升验证规模,是共识协议形式化验证的重要研究问题.对目前采用形式化方法验证共识协议的研究工作进行调研,总结其中提出的重要建模方法和关键验证技术,并展望该领域未来有潜力的研究方向.     

基于区块链技术的分布式可信网络接入认证

针对网络接人终端自身安全性较差,易被攻击等问题,提出基于区块链技术的分布式可信网络接入认证方法.根据区块链技术,采用数据层、网络层、共识层以及合约层架构分布式网络框架,整合全部树结构特征的树形数据结构、P2P拓扑结构、有向无环图共识结构以及设定自动执行脚本的智能合约,构建物联网分布式网络框架;将网络运营商设定分布式网络...     

一种高效能的分布式请求集生成算法

分布式互斥请求集的长度、对称性和生成的难易程度以及生成算法占用的空间及耗费的时间直接影响着基于该请求集的分布式互斥算法的消息复杂度、对称性和算法的应用规模。本文在折半循环编码算法的基础上,提出了一种增加算法初始化节点数量和引入松弛差集的对称分布式互斥请求集生成算法,使算法的时间复杂度和消息复杂度大幅度降低。     

Rendezvous Facilities in a Distributed Computer System

The distributed computer system described in this paper is a set of computer nodes interconnected in an interconnection network via packet-switching interfaces.The nodes communicate with each other by means of message-passing protocols.This paper presents the implementation of rendezvous facilities as high-level primitives provided by a parallel programming language to support interprocess communication and synchronization.     

Quorum and connected dominating sets based location service in wireless ad hoc, sensor and actuator networks

Location service provides position of mobile destination to source node to enable geo-routing. In existing quorum-based location service protocols, destination node registers its location along a ‘column’ while source node makes a query along a ‘row’. Grid and quorum-based location service is based on division of network into square grids, and selecting ‘leader’ location server node in each grid. Location updates, leader reelection and information transfer are performed whenever destination and leader nodes are moving to a different grid. We propose here to apply connected dominating sets (DS) as an alternative to grids. We also improved basic quorum, and applied on DS-quorum (DS based quorum) better criterion for triggering local information exchanges and global location updates, by meeting two criteria: certain distance movement and certain number of observed link changes with (DS) nodes. Backbones created by DS nodes (using 1-hop neighborhood information) are small size, do not have a parameter like grid size, and preserve network connectivity without the help of other nodes. Location updates and destination searches are restricted to backbone nodes. Both methods use ‘hello’ messages to learn neighbors. While this suffices to construct DS, grid leader (re)election requires additional messages. Simulation results show that using DS as backbone for quorum construction is superior to using grid as backbone or no backbone at all. The proposed DS-quorum location service can achieve higher (or similar) success rate with much less communication overhead than grid-based approaches.     

On the asymptotical optimality of multilayered decentralized consensus protocol

A decentralized consensus protocol refers to a process for all nodes in a distributed system to collect the information/status from every other node and reach a consensus among them. Two classes of decentralized consensus protocols have been studied before: the one without an initiator and the one with an initiator. While the one without an initiator has been well studied in the literature, it is noted that the prior protocols with an initiator mainly relied upon the one without an initiator and thus did not fully exploit the intrinsic properties of having an initiator. By exploiting the concept of multilayered execution, we develop in this paper an efficient multilayered decentralized consensus protocol for a distributed system with an initiator. By adapting itself to the number of nodes in the system, the proposed protocol can determine a proper layer for execution and reach the consensus in the minimal numbers of message steps while incurring a much smaller number of messages than required by prior works. Several illustrative examples are given and performance analysis of the proposed algorithm is conducted to provide many insights into the problem studied. It is shown that the decentralized consensus protocols developed in this paper for the case of having an initiator significantly outperform prior schemes. Specifically, it is proven that (1) the ratio of the average number of messages incurred by the proposed algorithm to that by the prior method approaches zero as the number of nodes increases and (2) the proposed algorithm is asymptotically optimal in the sense that the message number required by the proposed algorithm and that of the optimal one are asymptotically of the same complexity with respect to the number of nodes in the system, showing the very important advantage of the proposed algorithm.