SNMP协议在网络管理中的应用

论文首先分析了SNMP协议的概念,以及其重要的组成部分MIB,然后设计开发了基于SNMP的网络管理软件。给出了主要的程序框架,应用SNMP进行网络管理可以为我们综合应用、管理网络带来很大的方便,本文有着较强的实际应用价值。     

Bounds for the optimal decentralized access protocol in a local area network

Here, we consider a local area network under the set of decentralized access protocols. Lower and upper bounds are obtained for the optimal long-run average waiting cost. These bounds are shown to be quite tight for a typical network.     

Optimal routing policy of a stochastic-flow network

Under the assumption that each arc’s capacity of the network is deterministic, the quickest path problem is to find a path sending a given amount of data from the source to the sink such that the transmission time is minimized. However, in many real-life networks such as computer systems, telecommunication systems, etc., the capacity of each arc is stochastic due to failure, maintenance, etc. Such a network is named a stochastic-flow network. Hence, the minimum transmission time is not fixed. We try to evaluate the probability that d units of data can be sent through the stochastic-flow network within the time constraint according to a routing policy. Such a probability is named the system reliability, which is a performance index to measure the system quality. This paper mainly finds the optimal routing policy with highest system reliability. The solution procedure is presented to calculate the system reliability with respect to a routing policy. An efficient algorithm is subsequently proposed to derive the optimal routing policy.     

按空间网络中基于身份的TLS协议设计与仿真

传输层安全(TLS)协议存在着握手时延大,交互次数多,计算开销大等缺点,不能够适合空间网络的传输特点.在对基于身份的加密机制和TLS协议进行分析的基础上,设计了一种面向空间网络的基于身份的TLS协议,进行了安全性分析.基于OPNET建立了安全协议的模型,通过仿真对安全协议在空间网络中的性能进行了分析和比较.仿真结果表明,这种传输层安全协议是适合空间网络环境的有效安全机制.     

Zig Bee无线网络协议层在Linux系统中的构建

Zig Bee是基于IEEE 802.15.4的低速低耗电的无线网络技术,在目前广泛使用的开放式Linux操作系统上开发使用,首先,应解决ZigBee无线协议在Linux系统中的移植,而其移植的主要技术在于无线网络协议层在Linux系统中的构建。在深入研究IEEE80.15.4/ZigBee网络协议层工作机制和Linux网络子系统协议基础上,设计Linux-Zig Bee网络协议层,分析Zig Bee网络层实现的关键技术。最终,提出在Linux系统中实现Linux-Zig Bee无线网络结构的可靠框架,并进行分析。     

FPGA中网络通信协议栈的裁剪及其全硬件实现

针对基于FPGA的嵌入式系统中软件网络协议栈需要内置CPU的不足,阐述了采用全硬件方式实现网络协议栈的必要性,并提出了适合的网络通信协议栈裁剪方案.该协议栈包含精简的UDP、IP、以及MAC层驱动,可完成常规的网络通信.协议栈完全采用硬件描述语言编写,并在FPGA中实现.实验结果表明,该协议栈只占用2K逻辑资源,能以100Mbps的速率在FPGA与PC之间进行数据传输,为基于FPGA的系统调试及运行提供了一种简易的高速通信手段.     

Optimal placement of distributed generation units in distribution systems via an enhanced multi-objective particle swarm optimization algorithm

This paper deals with the optimal placement of distributed generation （DG） units in distribution systems via an enhanced multi-objective particle swarm optimization （EMOPSO） algorithm. To pursue a better simulation of the reality and provide the designer with diverse alternative options, a multi-objective optimization model with technical and operational con- straints is constructed to minimize the total power loss and the voltage fluctuation of the power system simultaneously. To enhance the convergence of MOPSO, special techniques including a dynamic inertia weight and acceleration coefficients have been inte- grated as well as a mutation operator. Besides, to promote the diversity of Pareto-optimal solutions, an improved non-dominated crowding distance sorting technique has been introduced and applied to the selection of particles for the next iteration. After verifying its effectiveness and competitiveness with a set of well-known benchmark functions, the EMOPSO algorithm is em- ployed to achieve the optimal placement of DG units in the IEEE 33-bus system. Simulation results indicate that the EMOPSO algorithm enables the identification of a set of Pareto-optimal solutions with good tradeoff between power loss and voltage sta- bility. Compared with other representative methods, the present results reveal the advantages of optimizing capacities and loca- tions of DG units simultaneously, and exemplify the validity of the EMOPSO algorithm applied for optimally placing DG units.     

Properties of variations in the periods of ring neural oscillators with noise

Effects of additive noise on a series of the periods of oscillations in unidirectionally coupled ring neural networks of ring oscillator type are studied. Kinematical models of the traveling waves of an inconsistency, i.e. the successive same signs in the states of adjacent neurons in the network, are derived. A series of the half periods in the network of N neuron is then expressed by the sum of N sequences of the N-first order autoregressive process, the process with the spectrum of exponential type and the first-order autoregressive process. Noise and the interaction of the inconsistency cause characteristic positive correlations in a series of the half periods of the oscillations. Further, an experiment on an analog circuit of the ring neural oscillator was done and it is shown that correlations in the obtained periods of the oscillations agree with the derived three expressions.     

The optimal location of replicas in a network using a READ-ONE-WRITE-ALL policy

We consider the problem of locating replicas in a network to minimize communications costs. Under the assumption that the read-one-write-all policy is used to ensure data consistency, an optimization problem is formulated in which the cost function estimates the total communications costs. The paper concentrates on the study of the optimal communications cost as a function of the ratio between the frequency of the read and write operations. The problem is reformulated as a zero-one linear programming problem, and its connection to the p-median problem is explained. The general problem is proved to be NP-complete. For path graphs a dynamic programming algorithm for the problem is presented. Received: May 1993 / Accepted: June 2001     

Optimal and efficient integration of heterogeneous summary tables in a distributed database

In any particular combination of domains, although a common understanding of the underlying low-level concepts concerning a domain attribute may exist, different concept hierarchies may have been built at different data-holding sites. A distributed database may therefore hold different views of the same data, or differently classified samples from the same population. Because of this, when statistical functions are applied to generate summary tables, the resulting summary-based partitions may be heterogeneous. In these situations, integration of such summary-based partitions can reveal latent information at a new, and finer, level of granularity. In this paper, the classification schemes are described using a matrix representation of the intersection hypergraph, and efficient numerical algorithms are proposed to determine the optimal granularity of the integrated summary data.     

基于稀疏树的战术通信网络路由协议研究

介绍了一种使用在战术无线通信网络环境的基于稀疏树的战术路由协议.STRP支持单向信道,它采用稀疏树路径生成算法来减少路由更新的数据量并减少网络链路的冗余,采用快速环路消除算法来消除网络拓扑动态变化过程中的环路与计数到无穷问题,采用增量更新来降低路由协议对传输带宽的需求.仿真结果表明,它较为适合战术无线通信网络环境.     

基于NS2的无线传感器网络LEACH协议的改进与仿真

针对LEACH协议中簇首分布不均匀、簇首与基站之间只能采用单跳路径的缺点,通过对经典分簇路由协议LEACH的分析,采取改变簇首产生方式和簇首与基站之间的通信方式的方法,缩短了簇首的建立时间和通信距离,均衡了节点的能耗.仿真结果表明,该算法能有效地降低无线传感器网络节点的能量消耗,延长网络存活时间,提高传统LEACH算法的性能.     

AdHoc网络功率控制协议应用与设计改进

对有关的网络功率控制协议进行了比较深入地分析,根据Ad Hoe网络的特点与需求,提出由单信道改为一个控制信道和一个数据信道双信道的协议,有效地解决了引入功率控制而产生的隐藏节点等问题,并在节省功率的同时提高了网络容量.     

一类具有数据包丢失的网络控制系统的最优控制

针对控制器和执行器均采用时钟驱动且最大丢包率和最大连续丢包长度被限定的短时延网络控制系统,提出一种数据包丢失的估值补偿方法.该方法可以根据历史状态向量和控制向量信息估算出当前的控制量.利用该方法和动态规划算法,导出了离散二次型性能指标下的网络控制系统的最优控制序列,进而给出最优控制律的实现算法.数值仿真算例验证了所得结果的有效性和正确性.     

Assigning labels in an unknown anonymous network with a leader

We consider the task of assigning distinct labels to nodes of an unknown anonymous network in a distributed manner. A priori, nodes do not have any identities, except for one distinguished node, called the source, and do not know the topology or the size of the network. They execute identical algorithms, apart from the source which plays the role of a leader and starts the labeling process. Our goal is to assign short labels, as fast as possible. The quality of a labeling algorithm is measured by the range from which the algorithm picks the labels, or alternatively, the length of the assigned labels. Natural efficiency measures are the time, i.e., the number of rounds required for the label assignment, and the message and bit complexities of the label assignment protocol, i.e., the total number of messages (resp., bits) circulating in the network. We present label assignment algorithms whose time and message complexity are asymptotically optimal and which assign short labels. On the other hand, we establish inherent trade-offs between quality and efficiency for labeling algorithms. Received: July 2000 / Accepted: February 2001     

基于GSM网络的数据处理主机软硬件设计与实现

城市的水网、气网和环保领域都需要连续对现场的物理参数进行监测,并通过网络将监测数据传送到管理中心进行数据处理、分析和管理.针对各种监测领域数据处理的工作特点及要求,提出了系统主要实现的功能.详细地叙述了基于GSM网络的进行数据传输时采用的主要AT命令的作用和使用方法,根据主机和监测站点硬件性能的特点自定制的通信协议,以保证通信的可靠性与有效性.论述了基于数据库的触发器技术完成对实际测量数据的维护与管理的实现方法.本系统已应用于污水流量监测等环保领域,经过长期的运行,可靠性高,使用灵活,安装方便,应用前景广阔.     

Real-time detection of changes in network with OpenFlow based on NetFPGA implementation

Sketch-based algorithms are extensively applied in a wide range of networking applications. This work develops the compact implementation of a system for detecting changes in traffic in real time with OpenFlow on a NetFPGA 1G (4 × 1G) platform. The system can monitor network traffic at a line rate of up to 4 Gbps with the required detection accuracy needed with limited memory on-board. The system utilizes a one-pass method to determine when the flow exceeds a predefined threshold. Based on the flow IDs identified, actions are issued immediately to switches to respond properly according to the OpenFlow protocol.     

Optimal and robust control of a class of nonlinear systems using dynamically re-optimised single network adaptive critic design

Following the philosophy of adaptive optimal control, a neural network-based state feedback optimal control synthesis approach is presented in this paper. First, accounting for a nominal system model, a single network adaptive critic (SNAC) based multi-layered neural network (called as NN₁) is synthesised offline. However, another linear-in-weight neural network (called as NN₂) is trained online and augmented to NN₁ in such a manner that their combined output represent the desired optimal costate for the actual plant. To do this, the nominal model needs to be updated online to adapt to the actual plant, which is done by synthesising yet another linear-in-weight neural network (called as NN₃) online. Training of NN₃ is done by utilising the error information between the nominal and actual states and carrying out the necessary Lyapunov stability analysis using a Sobolev norm based Lyapunov function. This helps in training NN₂ successfully to capture the required optimal relationship. The overall architecture is named as ‘Dynamically Re-optimised single network adaptive critic (DR-SNAC)’. Numerical results for two motivating illustrative problems are presented, including comparison studies with closed form solution for one problem, which clearly demonstrate the effectiveness and benefit of the proposed approach.     

Global exponential periodicity of three-unit neural networks in a ring with time-varying delays

This paper formulates and studies a model of three-unit neural networks in a ring. The model can well describe many practical architectures of delayed neural networks, which is generalization of some existing neural networks under a time-varying environment. Without assuming the boundedness, monotonicity, and differentiability of activation functions and any symmetry of interconnections, we establish some sufficient conditions for checking the existence of periodic solution and global exponential stability for the neural networks. A continuation theorem of the coincidence degree and inequality analysis are employed. Our results are all independent of the delays and maybe more convenient to design a circuit network.     

Optimal placement of active bars in active vibration control for piezoelectric intelligent truss structures with random parameters

Considering the randomness of physical parameters of structural material, geometric dimensions of active bars and passive bars, applied loads and control forces simultaneously, the optimization of active bar’s placement and feedback gains for the vibration control of intelligent truss structures are studied in this paper. Firstly, the performance function is developed based on the maximization of dissipation energy due to control action. Then, the optimal mathematical model with the reliability constraints on dynamic stress and displacement response is built. The numerical feature of dynamic response based on probability of intelligent structure is developed. Finally, a planar intelligent truss structure is used as an example to demonstrate the rationality and validity of the presented model and approach in structural active vibration control.