Broadcast protocols for distributed systems

An innovative approach is presented to the design of fault-tolerant distributed systems that avoids the several rounds of message exchange required by current protocols for consensus agreement. The approach is based on broadcast communication over a local area network, such as an Ethernet or a token ring, and on two novel protocols, the Trans protocol, which provides efficient reliable broadcast communication, and the Total protocol, which with high probability promptly places a total order on messages and achieves distributed agreement even in the presence of fail-stop, omission, timing, and communication faults. Reliable distributed operations, such as locking, update, and commitment, typically require only a single broadcast message rather than the several tens of messages required by current algorithms     

一种利用云环境实现Web服务组合容错的方法

随着Web服务迅猛发展,基于SOA的服务组合容错性研究成为了业界关注的焦点.服务组合中组件的失效,会导致整个组合执行失败,而资源不足、服务器负载过重是引发组件失效的主要原因之一.云计算作为一种新的计算泛型,其资源整合、动态分配的特点为解决传统SOA下因资源受限而引发的失效提供了新的容错思路.FTEL层将中间件技术应用到服务组合容错上,借助云环境完成服务替换,对传统SOA下较难解决的由于资源问题引起的组件失效进行了容错.     

一种分布式计算中的容错选举算法

选举算法被广泛应用于分布式计算中,而且它已经被证明比合意问题更难.在分析了选举问题和合意问题的关系之后,提出了一种新的容错选举算法.该算法是稳定的、通信有效的,并且该算法可以容忍进程和链路的暂时性错误.所提出的算法不仅解决了选举问题,并且也提供了解决合意问题的一条新的途径.     

融合门限公钥加密和纠删码的安全云存储模型

针对当前云存储系统中的机密性和容错性问题,展开分析和研究.指出目前的主流解决方案往往仅能解决机密性问题或容错性问题中的一个,而不能将二者兼顾起来进行考虑.为此,将门限公钥加密技术与指数纠删码（Erasure Codes over Exponents,EC-E）相融合,设计并提出了一个同时能满足机密性与容错性要求的安全云存储模型（A Secure Cloud Storage Model with Data Confidentiality and Fault-Tolerant,SCSM-DCF）.给出了模型的形式化定义、安全性定义以及实体间通信协议;对模型的性能进行分析,指出其在能够保证安全性的同时,具有较好的代价优势.     

Verification of consensus algorithms using satisfiability solving

Consensus is at the heart of fault-tolerant distributed computing systems. Much research has been devoted to developing algorithms for this particular problem. This paper presents a semi-automatic verification approach for asynchronous consensus algorithms, aiming at facilitating their development. Our approach uses model checking, a widely practiced verification method based on state traversal. The challenge here is that the state space of these algorithms is huge, often infinite, thus making model checking infeasible. The proposed approach addresses this difficulty by reducing the verification problem to small model checking problems that involve only single phases of algorithm execution. Because a phase consists of a small, finite number of rounds, bounded model checking, a technique using satisfiability solving, can be effectively used to solve these problems. The proposed approach allows us to model check several consensus algorithms up to around 10 processes.     

A new efficient optimistic fair exchange protocol without random oracles

Optimistic fair exchange (OFE) is a kind of protocols to solve the problem of fair exchange between two parties. Most of the previous work on this topic are provably secure in the random oracle model. In this work, we propose a new construction of OFE from another cryptographic primitive, called time capsule signature. The construction is efficient and brings almost no overhead other than the primitive itself. The security of our new construction is based on that of the underlying primitive without relying on the random oracle heuristic. Applying our generic construction to the time capsule signature scheme recently proposed by Libert and Quisquater, we obtain a new concrete and efficient OFE construction secure based on Computational Diffie–Hellman assumption in the standard model.     

Group key agreement for secure group communication in dynamic peer systems

Self-organizing group key agreement protocols without a centralized administrator are essential to secure group communication in dynamic peer systems. In this paper, we propose a generic construction of a one-round self-organizing group key agreement protocol based on the Chinese Remainder Theorem. In the proposed construction, all group members contribute their own public keys to negotiate a shared encryption public key, which corresponds to all different decryption keys. Using his/her own secret key, each group member is able to decrypt any ciphertext encrypted by the shared encryption key. Following the generic construction, we instantiate a one-round self-organizing group key agreement protocol using the efficient and computationally inexpensive public key cryptosystem NTRU. Both the public key and the message in this protocol are secure against the known lattice attacks. Furthermore, we also briefly describe another concrete scheme with our generic idea, based on the ElGamal public key cryptosystem.     

Leader-follower consensus for a class of nonlinear multi-agent systems

This paper deals with the leader-follower consensus problem for a class of nonlinear multiagent systems. All agents have identical nonlinear dynamics in the strict feedback form with Lipschitz growth condition. Both full state consensus protocol and dynamic output consensus protocol are provided. It is shown that under a connected undirected information communication topology, the proposed protocols can solve the leader-follower consensus problem. Two consensus protocol design procedures are presented and a numerical example is given to illustrate the proposed protocols.     

Eventual Clusterer: A Modular Approach to Designing Hierarchical Consensus Protocols in MANETs

This paper proposes a modular approach to the design of hierarchical consensus protocols for the mobile ad hoc network with a static and known set of hosts. A two-layer hierarchy is imposed on the network by grouping mobile hosts into clusters, each with a clusterhead. The messages from and to the hosts in the same cluster are merged/unmerged by the clusterhead so as to reduce the message cost and improve the scalability. The proposed modular approach separates the concerns of clustering hosts from achieving consensus. A clustering function, called eventual clusterer (denoted as diamC), is designed for constructing and maintaining the two-layer hierarchy. Similar to unreliable failure detectors, diamC greatly facilitates the design of hierarchical protocols by providing the fault-tolerant clustering function transparently. We propose an implementation of diamC based on the failure detector diamS. Using diamC, we design a new hierarchical consensus protocol. As shown by the performance evaluation results, the proposed consensus protocol can save both message cost and time cost. Our proposed modular design is therefore effective and can lead to efficient solutions to achieving consensus in mobile ad hoc networks.     

Consensus of linear multi-agent systems subject to actuator saturation

This paper is aimed at studying the consensus of linear multi-agent systems subject to actuator saturation. In order to solve the consensus problem, a new family of scheduled low-and-high-gain decentralized control laws are designed, provided that the dynamics of each agent is asymptotically null controllable with bounded controls, and such control laws rely on the asymptotic property of a class of parametric algebraic Ricatti equations. It is shown that the consensus of the systems with connected and fixed topology can be achieved semi-globally asymptotically via the local error low-and-high-gain feedback. An illustrative example with simulations shows that our method as well as control protocols is effective for the consensus of the linear multi-agent systems subject to actuator saturation.     

带有完全分布式观测器的多智能体系统自适应容错一致性

针对一类同时带有执行器故障, 未知非线性动态和非匹配干扰的多智能体系统, 本文提出一种新的自适应 容错控制方案. 首先, 设计一种适用于有向切换拓扑的完全分布式观测器估计领导者的信息, 将一致性问题转化为 局部的信号跟踪问题. 其次, 拆解转化后的误差系统为两个耦合的子系统, 实现非匹配干扰与匹配因子分离. 然后, 利用径向基神经网络近似非线性动态, 并结合反步法设计3种自适应故障补偿器, 使系统能够在线补偿故障和未知 动态的影响. 最后, 数值仿真验证了所提方案的有效性.     

Distributed event-triggered consensus for multi-agent systems with quantisation

This paper studies the consensus problem for multi-agent systems with quantised information communication via event-triggered control. First, the asynchronous event-triggered control for multi-agent systems is considered based on distributed uniform-quantised protocols. It is shown that practical consensus among agents is guaranteed and occurrence of Zeno behaviour is prevented under the designed event-triggering mechanisms. Second, under the proposed protocols using logarithmic quantised information, both synchronous and asynchronous event-triggered control algorithms are given to solve the practical consensus problem. Meanwhile, Zeno behaviour of the closed-loop systems can be excluded under the proposed event-triggered algorithms. Finally, numerical simulations are given to illustrate the effectiveness of the derived results.     

A new framework of consensus protocol design for complex multi-agent systems

This paper aims to find a simple but efficient method for consensus protocol design. This paper presents two consensus protocols to solve the consensus problem of complex multi-agent systems that consist of inhomogeneous subsystems. The limitations of current studies are analyzed, and a novel model based on transfer functions is presented. This model can be used to describe both homogeneous and inhomogeneous multi-agent systems in a unified framework. Based on this model, two sufficient and necessary conditions for the consensus of complex multi-agent systems have been obtained. One is for the systems without any external input, and the other is for the systems with the same external input. Then, two corresponding distributed consensus protocols are presented. Considering that the complex multi-agent systems may require different outputs sometimes, the relationship between inputs and outputs is analyzed. Finally, some simulations are given to demonstrate the performance and effectiveness of the proposed approaches.     

Reaching agreement on processor-group membrship in synchronous distributed systems

Reaching agreement on the identity of correctly functioning processors of a distributed system in the presence of random communication delays, failures and processor joins is a fundamental problem in fault-tolerant distributed systems. Assuming a synchronous communication network that is not subject to partition occurrences, we specify the processor-group membership problem and we propose three simple protocols for solving it. The protocols provide all correct processors with consistent views of the processor-group membership and guarantee bounded processor failure detection and join delays. Flaviu Cristian is a computer scientist at the IBM Almaden Research Center in San Jose, California. He received his PhD from the University of Grenoble, France, in 1979. After carrying out research in operating systems and programming methodology in France and working on the specification, design, and verification of fault-tolerant software in England, he joined IBM in 1982. Since then he has worked in the area of fault-tolerant distributed systems and protocols. He has participated in the design and implementation of a highly available distributed system prototype at the Almaden Research Center, has reviewed and consulted for several fault-tolerant distributed system designs, both in Europe and the American divisions of IBM, and is now a technical leader in the design of a new Air Traffic Control System for the US which must satisfy very stringent availability requirements.     

基于推荐信任模型改进拜占庭容错共识算法

针对拜占庭容错算法存在通信开销大、节点选取简单、对恶意节点缺乏惩罚机制的问题,提出了一种基于推荐信任模型的改进拜占庭容错共识算法。引入P2P网络下的推荐信任模型,根据节点在共识阶段的行为,计算各节点的全局信任值,使用节点选取机制,解决节点选取简单的问题。全局信任值高的节点进入共识组,恶意节点被踢出共识组不再参与共识,解决恶意节点缺乏惩罚机制的问题。实验表明,R-PBFT较PBFT具有更低的网络开销和更高的容错性。     

Fault-tolerant control systems design via subdivision of parameter region

This paper presents a linear matrix inequality （LMI） approach to solve the fault-tolerant control （FTC） problem of actuator faults. The range of actuator faults is considered as a parameter region and subdivided into several subregions to achieve a certain desired performance specification. Based on the integral quadratic constraint （IQC） approach, a passive fault-tolerant controller for the whole fault region and multiple fault-tolerant controllers for each fault subregion are designed for guaranteeing stability and improving performance of the FTC system, respectively. According to the estimation of parameters by FDI process, the corresponding subregion controller is chosen for the stability and optimal performance of closed-loop systems when the fault occurs. The case of incorrect estimation is also considered by comparing the performance index between the switched controller and the passive fault-tolerant controller. The proposed design technique is finally evaluated in the light of a simulation example.     

Conditions for Set Agreement with an Application to Synchronous Systems

The k-set agreement problem is a generalization of the consensus problem:considering a system made up of n processes where each process proposes a value,each non-faulty process has to decide a value such that a decided value is a proposed value,and no more than k different values are decided.While this problem cannot be solved in an asynchronous system prone to t process crashes when t≥k,it can always be solved in a synchronous system;(?)+1 is then a lower bound on the number of rounds(consecutive commun...     

物联网智能物流系统容错服务组合建模与分析

针对物流领域的服务组合存在容错性差和服务不可靠等问题，提出一种基于π网的物联网智能物流系统物流服务容错组合模型。首先，在简单介绍物联网智能物流系统后，给出了物联网智能物流系统的容错服务组合框架；然后，基于π网建立了物联网智能物流系统物流服务容错组合模型，并对模型进行了容错正确性和拟合性分析；最后，对提出的模型进行了服务可靠性、服务故障容错可靠性实验，并与Petri网、QoS动态预测算法、模糊卡诺模型和改进粒子群优化的服务组合方法针对服务组合的执行时间、用户满意度、可靠性和最优度进行对比实验。实验结果表明，所提模型具有更高的服务可靠性和服务故障容错可靠性，同时在服务组合的执行时间、用户满意度、可靠性和最优度等方面也具有一定的优越性。     

Allowable sampling period for consensus control of multiple general linear dynamical agents in random networks

This article studies the consensus problem for a group of sampled-data general linear dynamical agents over random communication networks. Dynamic output feedback protocols are applied to solve the consensus problem. When the sampling period is sufficiently small, it is shown that as long as the mean topology has globally reachable nodes, the mean square consensus can be achieved by selecting protocol parameters so that n???1 specified subsystems are simultaneously stabilised. However, when the sampling period is comparatively large, it is revealed that differing from low-order integrator multi-agent systems the consensus problem may be unsolvable. By using the hybrid dynamical system theory, an allowable upper bound of sampling period is further proposed. Two approaches to designing protocols are also provided. Simulations are given to illustrate the validity of the proposed approaches.     

Distributed Fault-Tolerant Consensus Tracking of Multi-Agent Systems Under Cyber-Attacks

This paper investigates the distributed fault-tolerant consensus tracking problem of nonlinear multi-agent systems with general incipient and abrupt time-varying actuator faults under cyber-attacks. First, a decentralized unknown input observer is established to estimate relative states and actuator faults. Second, the estimated and output neighboring information is combined with distributed fault-tolerant consensus tracking controllers. Criteria of reaching leader-following exponential consensus tracking of multi-agent systems under both connectivity-maintained and connectivity-mixed attacks are derived with average dwelling time, attack frequency, and attack activation rate technique, respectively. Simulation example verifies the effectiveness of the fault-tolerant consensus tracking algorithm.