Deadlock-free dynamic reconfiguration schemes for increased network dependability

Network-based parallel computing systems often require the ability to reconfigure the routing algorithm to reflect changes in network topology if and when voluntary or involuntary changes occur. The process of reconfiguring a network's routing capabilities may be very inefficient and/or deadlock-prone if not handled properly. We propose efficient and deadlock-free dynamic reconfiguration schemes that are applicable to routing algorithms and networks which use wormhole, virtual cut-through, or store-and-forward switching, combined with hard link-level flow control. One requirement is that the network architecture use virtual channels or duplicate physical channels for deadlock-handling as well as performance purposes. The proposed schemes do not impede the injection, transmission, or delivery of user packets during the reconfiguration process. Instead, they provide uninterrupted service, increased availability/reliability, and improved overall quality-of-service support as compared to traditional techniques based on static reconfiguration.     

基于网络协议和转信的综合网络通信系统设计

通过无线或有线网络、卫星进行通信传输,是当前主流的数据通信手段,但在许多环境下,使用电台、有线电话进行通信联络也是必要的.多种通信手段和方式的并存,必然要实现它们之间的互连互通,才能实现统一的、对用户透明的通信网络.重点介绍一种基于TCP/IP网络协议和转信控制的综合通信网络系统的设计,可以实现不同制式通信终端、有线通信等多种通信手段的互连互通.     

An adaptive zero-variance importance sampling approximation for static network dependability evaluation

We propose an adaptive parameterized method to approximate the zero-variance change of measure for the evaluation of static network reliability models, with links subject to failures. The method uses two rough approximations of the unreliability function, conditional on the states of any subset of links being fixed. One of these approximations, based on mincuts, under-estimates the true unknown unreliability, whereas the other one, based on minpaths, over-estimates it. Our proposed change of measure takes a convex linear combination of the two, estimates the optimal (graph-dependent) coefficient in this combination from pilot runs, and uses the resulting conditional unreliability approximation at each step of a dynamic importance sampling algorithm. This new scheme is more general and more flexible than a previously proposed zero-variance approximation scheme, based on mincuts only, and which was shown to be robust asymptotically when unreliabilities of individual links decrease toward zero. Our numerical examples show that the new scheme is often more efficient when low unreliability comes from a large number of possible paths connecting the considered nodes rather than from small failure probabilities of the links.     

A unified model of dependability: capturing dependability in context

In contemporary societies, individuals and organizations increasingly depend on services delivered by sophisticated software-intensive systems to achieve personal and business goals. So, a system must have engineered and guaranteed dependability, regardless of continuous, rapid, and unpredictable technological and context changes. The International Federation for Information Processing Working Group defines dependability as "the trustworthiness" of a computing system, which allows reliance to be justifiably placed on the services it deliver.     

Interprocess communication dependency on network load

Results of an analysis of the communication performance as perceived by the application layer in the presence of background load are presented. The analysis was carried out on two distinct protocol suites, TCP/IP and XNS, on a single Ethernet LAN with personal computer workstations. Service times for a reliable transfer and an unreliable transmission as perceived by the application layer were measured. An appropriate model of the reliable transfer process was used to derive service time analytical estimates. Owing to the close relation between measured and estimated values, the model was used to identify the major sources of delay and to evaluate the effects of possible improvements. The most important causes affecting the transport layer performance as background load increases are identified, and different strategies are examined in order to reduce their impact. The improvement margin offered by the implementation of a lightweight transport protocol specifically tailored to the requirements of a bulk data transfer over an Ethernet is addressed     

一种基于双变异算子的免疫网络算法

针对遗传算法难以解决多峰函数优化的问题,提出一种基于双变异算子的免疫网络算法.该算法借鉴免疫系统的克隆选择和免疫网络理论,采用双变异算子提高算法的全局和局部搜索能力.利用动态网络抑制策略保持神群的多样性,自适应地调节抗体群的规模.仿真结果表明,该算法能有效地改善种群的多样性,较好地实现全局优化与局部优化的有机结合,具有更强的多峰函数优化能力.     

Impact of physical handicaps on operators of agricultural equipment

Physically handicapped farm operators and agricultural workers face barriers which make the completion of many essential farm-related tasks difficult or even impossible. These barriers are especially burdensome with respect to the operation and maintenance of agricultural equipment. This paper reports on work being done at Purdue University to assist handicapped farmers and agricultural workers who wish to continue working in spite of their disabilities. The nature of physical handicaps and proportion of farmers affected by these handicaps is discussed. Potential health and safety risks that these operators are exposed to when operating agricultural equipment are addressed. In addition, a brief overview of the Purdue project and recent activities is provided.     

RS232通信网络与CAN总线通信网络互联设计

基于CAN总线原理,结合CAN控制器SJA1000、CAN收发器CTM和ATmega128的特性,针对CAN总线和RS232互联问题,提出了RS232-CAN接口模块的设计方案,详细介绍了硬软件设计模块以及本设计的具体应用。     

一种通信网络抗毁性评价的改进模型

分析了现代战场通信网抗毁性评价的需求,针对现有通信网抗毁性测度评价模型无法准确评价网络抗毁性测度和节点重要性,以及不同节点数的网络间抗毁性的问题,利用基于最短路径数和跳面节点法节点重要性多指标评价方法对该模型进行改进。在此基础上,提出一种基于节点的全网平均等效抗毁性测度的网络抗毁性评价模型,并验证了模型的有效性。     

分布式虚拟环境的网络通信机制研究与应用

分布式虚拟环境(Distributed Virtual Environments,简称DVEs),其网络通信模块的开发,技术复杂,工作量大.而WTK支持分布式虚拟环境,可实现高效系统开发.介绍了WTK的网络体系结构,重点分析了分布式虚拟环境的网络结构、通信模型,深入研究了状态更新消息传递机制.在此基础上,给出了一个基于WTK实现分布式虚拟环境的设计方案,并介绍了应用程序仿真循环.实验结果表明:基于该设计方案的DVEs应用可较好满足交互的动态性和一致性要求,具有可行性.     

基于时间触发通信的机载网络可靠性

根据分布式综合模块化航空电子(DIMA)系统的组网需求,对比事件触发(ET)机制和时间触发(TT)机制,分析时间触发以太网(TTE)的网络特性,说明TTE应用到DIMA的可行性和必要性。针对航空电子系统的高可靠性需求,采用贝叶斯网络分析TTE在环形拓扑、网状拓扑和星型拓扑等结构下的系统可靠性,分析结果表明,在多余度的情况下,星型拓扑具有最高的可靠性。总结了TTE应用到DIMA的拓扑结构选择和余度设计原则,即根据不同的应用场景和通信节点的重要程度,选择合适的拓扑结构和余度。     

Warning: to err is human [human-friendly robot dependability]

In this article we describe current and future technologies for ensuring the safety of the operators maneuvering a Skill-Assist working in an automobile final assembly process. It proposes a method that allows a Skill-Assist to detect operation slip from a sequence of an operator's hand motion trajectory data represented using hidden Markov models (HMM). The method can also determine either safety- or productivity-oriented control policy throughout two-way interpretation of the belief structure. A workability improvement process that comprises a fault-warning (FW) safety-preservation (SP) space policy and teaching data renewal subprocesses allows for optimal reconstruction of the policy determinant observation space and HMMs. Some experimental results are shown to demonstrate the effectiveness of both the control policy determination and the workability improvement process.     

Impact of workload on cognitive performance of control room operators

Cognition, Technology & Work - Workload has long been considered as one of the important factors for personal functions and malfunctions, particularly in complex systems. Undertaking operations...     

基于AADL的软件可靠性验证

针对软件可靠性面临的安全等级和流延迟两类问题,提出了一种基于结构分析与设计语言(AADL)的软件可靠性验证方法。首先建立两类问题的需求模型,并将需求模型转化为设计模型;其次是调用分析插件对设计模型进行分析,查找模型中存在的问题;最后根据存在的问题对设计模型进行修改和完善。仿真结果表明,所提出的方法有效验证了安全等级和流延迟两类问题,为AADL在航电系统软件验证方面的应用奠定了基础。     

基于两级传播理论的舆论超网络传播分析

社交网络挖掘可以使人们更好地认识信息在网络中的传播规律,分析信息在事件中的传播特点。现有的文献研究主要集中于舆论事件社交网络的静态建模,以及针对一些共性特点的仿真验证,而对舆论事件模型结构变化的讨论较少。本文尝试从两级传播理论出发,采用三层超网络结构对舆论事件不同时段构建传播分析模型,给出舆论演化分析度量指标,挖掘超网络结构变化的特点,探索舆论酝酿期积蓄力量的潜在因素。以长生疫苗事件进行分析,发现需要在酝酿期有多样化的意见领袖不断在各个话题中进行牵引,在积累了潜在的舆论人群之后才能促成舆论爆发。     

Model-driven assessment of system dependability

Designers of complex real-time systems need to address dependability requirements early on in the development process. This paper presents a model-based approach that allows developers to analyse the dependability of use cases and to discover more reliable and safe ways of designing the interactions of the system with the environment. The hardware design and the dependability of the hardware to be used also needs to be considered. We use a probabilistic extension of statecharts to formally model the interaction requirements defined in the use cases. The model is then evaluated analytically based on the success and failure probabilities of events. The analysis may lead to further refinement of the use cases by introducing detection and recovery measures to ensure dependable system interaction. A visual modelling environment for our extended statecharts formalism supporting automatic probability analysis has been implemented in AToM³, A Tool for Multi-formalism and Meta-Modelling. Our approach is illustrated with an elevator control system case study.

基于改进网络编码的匿名通信机制研究

针对现有基于网络编码的匿名系统,由于转发节点的不稳定性以及匿名消息的多路径转发,使得数据发送的成功率较低的问题,提出了一种基于网络编码与数据冗余方法的新匿名通信机制ACSNC（anonymous communication system based on network coding）。首先采用数据冗余机制对要发送的数据进行冗余分片,并沿多条路径发送;然后中间转发节点对信息进行随机编码后转发,使信息通过节点前后的统计特性发生变化;最后,目的节点根据收到的数据片与编码系数恢复匿名信息。仿真结果表明,该机制在显著提高数据发送成功率的基础上,能够有效地保障通信的匿名性与安全性。