A notation for deterministic cooperating processes

This paper proposes extensions of sequential programming languages for parallel programming that have the following features: 1) Dynamic Structures: The process structure is dynamic. Processes and variables can be created and deleted. 2) Paradigm Integration: The programming notation supports shared memory and message passing models. 3) Determinism: Demonstrating that a program is deterministic-all executions with the same input produce the same output-is straightforward, Programs can be written so that compilers can verify that the programs are deterministic. Nondeterministic constructs can be introduced in a sequence of refinement steps to obtain greater efficiency if required. The ideas have been incorporated in an extension of Fortran, but the underlying sequential imperative language is not central to the ideas described here. A compiler for the Fortran extension, called Fortran M, is available by anonymous ftp From Argonne National Laboratory. Fortran M has been used for a variety of parallel applications     

JMF技术和实时语音通信的实现

文章介绍了流媒体的基本概念，描述了由JMF RTP APIs所提供的对实时媒体流的支持，阐述了怎样通过网络发送和接收流媒体数据。     

基于最短路径的多子网链路层拓扑发现算法

针对当前基于地址转发表实现链路层拓扑发现的典型算法在复杂多子网环境下应用存在的问题,提出利用下行链路完整地址转发表构建并优化同一子网交换设备间的最短路径,实现链路层拓扑自动发现的算法。经理论和实际环境验证,证明该算法可以较好地发现复杂多子网链路层拓扑结构,具有较强的实践意义和推广价值。     

Autonomic communication services: a new challenge for software agents

The continuous growth in ubiquitous and mobile network connectivity, together with the increasing number of networked devices populating our everyday environments, call for a deep rethinking of traditional communication and service architectures. The emerging area of autonomic communication addresses such challenging issues by trying to identify novel flexible network architectures, and by conceiving novel conceptual and practical tools for the design, development, and execution of “autonomic” (i.e., self-organizing, self-adaptive and context-aware) communication services. In this paper, after having introduced the general concepts behind autonomic communication and autonomic communication services, we analyze the key issue of defining suitable “component” models for autonomic communication services, and discuss the strict relation between such models and agent models. On this basis, we survey and compare different approaches, and eventually try to synthesize the key desirable characteristics that one should expect from a general-purpose component model for autonomic communication services. The key message we will try to deliver is that current research in software agents and multi-agent systems have the potential for playing a major role in inspiring and driving the identification of such a model, and more in general for influencing and advancing the whole area of autonomic communication.     

基于卫星通信网络的链路监测方法

依据卫星星地链路误码率的统计特性,提出一种采用变序列长直接监测链路误码率的新方法。该方法利用误码率分段分析的策略,采用统计学统计置信度原理,并通过对训练序列长度、误差精度和监测可信度进行仿真验证与统计分析,确定了链路监测中序列序列长度的选取准则。实验数据表明,变序列长链路直接监测方法在保证一定信道资源的前提下,有效扩大了链路监测的范围,降低了运算复杂度,在星地链路监测方面具有一定的优越性。     

基于通信网抗毁性的链路重要性比较

为了比较通信链路在通信网抗毁性中的重要性,提出了一种基于链路收缩的算法。该算法通过比较每条链路收缩后的通信网生成树数目,判断每条链路对通信网抗毁性影响的重要程度,生成树数目越多,表明该链路越重要,对通信网抗毁性的影响越大。实验结果表明,该算法计算简单,可以精确地反映不同链路对通信网抗毁性的重要程度。     

部分子块通讯的分布式PCA厂级工业过程监测方法

针对现代工业过程具有检测、控制变量多,且变量关系复杂、耦合严重等特点,厂级工业过程监测通常采用分块的方式建立模型.然而,实际过程中每个子块间存在物流、能流的交换和信息的传递,这种建模方式通常只利用子块本身的信息建立模型,恰恰忽略了子块之间内在的联系,可能导致子块监测模型一定程度上丢失其他子块所提供的过程信息.针对现有方法的局限性,提出一种部分子块通讯的分布式主元分析(PCA)过程监测方法.首先利用先验知识对厂级过程进行分块,增加用于描述子块间连接方式的拓扑矩阵;以迭代更新的思路,利用其他节点提供的压缩信息,按照拓扑矩阵不断更新系数矩阵,进而得到最终的监测模型;代入待监测数据后,综合考虑其余子块携带的异常信息得出监测结果.在tennessee eastman过程和加氢裂化过程中,将所提出的方法与传统分块PCA、全部子块交互的分布式PCA方法进行对比,所得结果表明了所提出方法的合理性和有效性.     

基于有效容量链路模型的无线局域网帧聚合算法研究

为了在链路质量波动的情况下提供统计的延迟保证,提出一种 可应用于高速IEEE802.11无线局域网的新型帧聚合算法。首先,通过目标延迟界限和超时概率的形式来表示QoS保证,并将其视作一个优化问题来构建有效容量模型。然后,应用适当的近似值推导出一个简单的公式,并通过使用比例-积分-微分(PID)控制器来求解。提出的PID控制器聚合算法能够独立地适应每个链接的时间限度,而这只需要在发射机端(如接入AP)就可以实现,无需对介质访问控制(MAC)做出任何改变。NS-3模拟结果显示,相比于最早到期优先算法,所提算法更胜一筹,表现出更加良好的性能。     

一种信任增强的Web服务综合评估模型

基于信任的网络交易业务日益增多,然而Web服务环境下的信任评估模型还不健全,存在Web服务请求方身份不明、信任度量因素考虑不周全及信任评估主观性强等问题。针对上述问题,提出了一种Web服务环境下信任增强的综合评估模型——WS-TECEM（Trust Enhanced Comprehensive Evaluation Model for Web Services）。WS-TECEM在传统模型的基础上,引入信任关系强度、第一手、第二手、第三手信誉看法及第三方信誉推荐者的可信度等思想,提出一种信任粒度更细、信任指数更强的评估模型,仿真实验表明,WS-TECEM能更全面、更准确地度量Web服务环境下交互双方的可信度。     

轻松组建局域网——一个经济型多功能局域网的实现

很多单位在多年前就已经使用计算机实现了办公自动化和日常事务处理。近年来由于计算机技术的飞速发展，尤其是硬件设备的频繁升级，现在这些单位的计算机基本是由３８６、４８６和ＰＥＮＴＩＵＭ组成的大家庭。怎样充分有效地利用这些计算机资源，大家都在寻求一种最佳的...     

VI architecture communication features and performance on the Giganet cluster LAN

The virtual interface (VI) architecture standard was developed to satisfy the need for a high throughput, low latency communication system required for cluster computing. VI architecture aims to close the performance gap between the bandwidths and latencies provided by the communication hardware and visible to the application, respectively, by minimizing the software overhead on the critical path of the communication. This paper presents the results of a performance study of one VI architecture hardware implementation, the Giganet cLAN (cluster LAN). The focus of the study is to assess and compare the performance of different VI architecture data transfer modes and specific features that are available to higher-level communication software like MPI in order to aid the implementor to decide which VI architecture options to employ for various communication scenarios. Examples of such options include the use of send/receive vs. RDMA data transfers, polling vs. blocking to check completion of communication operations, multiple VIs, completion queues and scatter capabilities of VI architecture.     

Physical layer network security: What your LAN can do for you

The basic simplicity and ease of use of Local Area Networks (LANs) has produced an explosive growth in connectivity over the past few years so that today they have become an integral part of most business organizations. This growth has been in spite of some fundamental problems that the technology highlights in the area of security. However, these issues have almost been totally ignored in the past mainly because of a lack of understanding of the issues rather than complacency.     

Multicriteria decision making for enhanced perception-based multimedia communication

This paper proposes an approach that integrates technical concerns with user perceptual considerations for intelligent decision making in the construction of tailor-made multimedia communication protocols. Thus, the proposed approach, based on multicriteria decision making (MDM), incorporates not only classical networking considerations, but, indeed, user preferences as well. Furthermore, in keeping with the task-dependent nature consistently identified in multimedia scenarios, the suggested communication protocols also take into account the type of multimedia application that they are transporting. Lastly, this approach also opens the possibility for such protocols to dynamically adapt based on a changing operating environment and user's preferences.     

Temporally enhanced erasure codes for reliable communication protocols

In forward error correction (FEC), redundant encoded packets are transmitted to and decoded by receiver(s) so that up to a certain number of lost packets can be recovered by using those redundant packets. The data stream is divided into blocks, and encoded packets are generated within each block. Hence, the encoding and decoding are performed on block-by-block basis.In this paper, a new mechanism named as temporally enhanced FEC (TEFEC) is proposed as an enhancement to the existing block-based FEC codes such as erasure codes. In TEFEC, the scopes of encoding and decoding are expanded beyond block boundaries, and they may overlap with scopes of neighboring blocks. To show its feasibility, TEFEC is applied to erasure codes to enhance their error correction capability, and new codes named as temporally enhanced erasure codes (TEEC) are developed and presented in this paper. In addition, to show its advantages, a reliable protocol was designed and simulated by combining both automatic repeat request and TEEC techniques. In terms of average packet retransmission rates and end-to-end delays for packet delivery, it is shown that the protocol employing TEEC outperforms block-by-block based protocols in most of the cases.     

New efficient communication services for ISO 11898 networks

Fieldbus networks should be able to support several kinds of data exchanges, which are characterised by very different requirements. The most popular solutions available today have been designed with some sets of specific needs in mind and usually, they are not always able to satisfy, equally well, the different kinds of communications which can be found in the industrial and process control environments. Often, system integrators and designers are forced to trade responsiveness (needed in event-driven systems) for efficiency (mostly required in systems which are based on the periodic polling of the controlled devices), or vice-versa. In this paper, a modification of the basic ISO 11898 protocol is described which supports some new transmission services that significantly increase the communication efficiency for periodic exchanges of process data and for messages devoted to high level functions. These services maintain a good degree of compatibility with the original protocol and do not affect its very good responsiveness and flexibility.     

Formal models of communication services: a case study

Formal methods can play an important role in exploring new communication systems services. The telecommunications and data communications communities have long accepted the need for formally describing protocols, but only recently have they considered formally describing a service by abstracting specifications from a particular protocol that provides that service. Specifying a service at an abstract level meets two important needs: standardization and customization. The author presents a simplified atomic multicast as an example service and input/output automata for the formal model. He shows how to represent the service specification, a protocol, and implementations of that protocol. He also sketches how to prove the correctness of the protocol and implementation, that is, how to show that the specified service is actually provided     

一种基于数据链路层的局域网时间同步新机制

常用的网络时间协议在应用层实现时精度较低,而在物理层实现时虽精度高但有一定的硬件要求。借鉴著名的网络抓包软件——WinPcap时间戳管理机制,在数据链路层以纯软件方式实现了一种高精度的局域网(LAN)相对时间同步算法。在Windows XP 环境下的小型局域网内的测试结果表明,该算法可达100μs以内的同步精度。     

用改进的OBDD方法计算通信网可靠度*

提出一种改进的OBDD（ordered binary decision diagram）方法来计算通信网可靠度。该方法考虑了网络共因失效带来的部件故障,使得计算更加准确。在创建原始网络的OBDD结构后,根据共因变量集来计算网络可靠度。由于只创建并保存一个OBDD结构,可节省大量的计算时间和存储空间。实验证明,该方法能有效计算网络可靠度,其计算时间和存储空间要低于一般的OBDD方法。     

基于GPU与CPU协作的实时波束形成实现方法*

波束形成的实时性一直是声纳和雷达等领域信号处理过程中的重点和难点。本文采用基于CUDA(Compute Unified Device Architecture,统一计算设备架构)的GPU(Graphic Processing Unit,图形处理器)与CPU协作处理方法,实现了宽带波束形成的实时处理。本方法的处理速度相较于matlab和CPU平台可以提高一至两个数量级,相较于同等处理速度的多DSP平台则体现了开发周期短、费用低、工作量小和可靠性高等众多优势。