一种优化的EPON动态带宽分配算法

EPON是基于以太网的无源光网络技术,目前以太网技术在局域网技术中应用最广泛。动态带宽分配算法作为EPON的关键技术之一,对提高系统服务质量,改进EPON系统时延等性能指标有着重要意义,为研究的热点。本文对已有DBA算法进行优化,算法思想为先将数据流进行分组,在两层动态带宽分配算法的基础上迭加根据各分组业务的权重优先级进行比例分配算法,并尝试引入预估计机制。仿真结果可以看出改进后的算法在系统带宽利用率、等待时延和服务质量上都能得到一定程度的优化。     

一种基于Agent的网络资源调整策略

当前服务质量是多媒体信息传输的关键,但是传统的Internet缺乏动态的服务质量控制机制。针对网络过载和闲置情况,以带宽为例提出了一种基于Agent的网络资源调整策略,通过用户Agent之间的协商来实现网络资源优化分配。并将这种调整策略进行了实验,实验结果表明了该方法的有效性。     

基于证据可信度的D-S理论协作频谱感知方法

D-S证据理论频谱感知算法中,针对当协作用户数增加时所引起的报告数据量迅速增大、带宽开销增加问题,将本地测量统计量中不确定度分配到确定信息中,减少了向融合中心发送的数据量,有效降低了带宽开销。其次,针对高冲突数据对D-S证据理论融合结果影响大的问题,通过评估每个证据的可信度,将可信度作为权重来计算加权平均证据,降低了高冲突证据对融合结果的影响。仿真结果表明,所提方法在有效降低了报告带宽开销的同时,能够减少高冲突证据对融合结果的影响。     

基于Credal网络的权重融合方法

针对多属性决策中属性权重的确定问题,利用Credal网络提出了一种新的融合方法。该方法假设属性权重有多方面的来源,包括以前决策时的经验信息,不同决策者的偏好产生的权重信息,不同方法计算的权重信息,等等。建立了一个Credal网络模型进行推理计算,得到了各属性的综合权重区间,使之既包含了以前的经验信息,又包含了多个决策者给出的偏好信息。用2个数值算例说明了方法的有效性。     

帧中继承载语音业务QoS策略仿真

帧中继(FR)作为一种快速分组交换技术,能够按需动态分配带宽,适于突发性,高速率和大流量的数据传输。在帧中继网络中实现语音和数据业务的融合,并保证语音业务的服务质量(QoS)问题得到人们的广泛关注。在网络仿真平台上设计了仿真实例,仿真结果表明,可以根据帧中继网络的传输特性,通过采用有效的带宽分配策略、流量控制策略、编码方案(如G.729或G.723.1)等QoS策略使得语音业务端到端的服务质量达到最优化。     

遗传投影寻踪确定权重的网络仿真评价方法

针对网络运行质量评价中多元指标权重难以确定的问题,为了提高网络传输速度等性能,采用投影寻踪方法对各指标分类特征进行发现以确定指标客观权重,并利用混合遗传算法解决难以合理求解的问题.采用NS2网络仿真获得确定指标客观权重所需要的网络运行样本数据.仿真实验表明,与主观赋权法相比方法确定的权重客观地反映了各指标之间的相对重要程度,能够为网络运行质量的计算提供重要依据,证明了方法的有效性和可行性.     

基于Pythagorean不确定语言的扩展VIKOR多属性群决策方法

针对属性值为Pythagorean不确定语言变量,属性权重和专家权重完全未知的群决策问题,提出一种扩展VIKOR多属性群决策方法.首先,给出Pythagorean不确定语言变量的概念,提出考虑语义变化的Pythagorean不确定语言变量运算规则、大小比较方法和Hamming距离测度;其次,提出基于Pythagorean 不确定语言模糊熵的属性权重确定方法和基于相似度的专家权重确定方法,进而提出一种新的扩展VIKOR方法;最后,通过国内航空公司服务质量评估实例验证所提出方法的有效性和可行性.     

基于AFDX的航空电子通信网络的设计

大型飞机复杂航空系统的增多,需要大量增加航空数据总线的带宽、提高通信的服务质量,为此设计了一种采用航空电子全双工通信制以太网交换(AFDX)的通信网络,并对该网络进行了分析和测试,测试结果表明该网络的带宽达100Mb/s,能够满足大型飞机复杂航空系统对带宽和通信服务质量的要求。     

客户端网络的服务质量解决方案--带宽管理

客户端带宽管理技术作为企业网络资源管理的一种手段,对于提高企业网络的效率和管理水平具有重要意义。文章从服务质量的角度对客户端带宽管理技术进行了介绍,包括带宽管理的基本原理、关键技术和带宽管理在企业网络中的应用方案。     

基于多项服务质量的组播路由算法

多点组播是指一个源点传送信息到多个目的节点,它是网络支持多媒体业务的关键技术之一。以服务质量（QoS）指标中的带宽和时延为优化进路准则,提出了一种受限的组播路由算法,仿真结果证明了该算法的有效性。     

Traffic Engineered Multicast Content Delivery Without MPLS Overlay

Multicast traffic engineering (TE) has recently attracted significant attention given the emergence of point-to-multipoint multimedia content delivery over the Internet. Existing multicast resource provisioning solutions tend to use explicit-routing based TE with multiprotocol label switching (MPLS) tunnels. In this paper, we shift away from this overlay approach and address native IP multicast traffic engineering based on link state routing protocols. The objective is that, through plain protocol independent multicast-sparse mode (PIM-SM) shortest path routing with optimized multitopology IGP (MT-IGP) link weights, the resulting multicast trees are geared towards minimal consumption of bandwidth resources. We apply genetic algorithms (GA) to the calculation of optimized MT-IGP link weights that specifically cater for engineered PIM-SM routing with statistical bandwidth guarantees in multimedia content delivery. Our evaluation results show that GA-based multicast traffic engineering consumes significantly less bandwidth in comparison to conventional IP approaches while also exhibiting higher service availability     

Fairness performance of dynamic weights in the ATM ABR service

Traditional schemes fail to achieve fair distribution of bandwidth among available bit rate connections. In this paper, a new scheme called Active Fairness is proposed which substantially improves fairness in bandwidth allocation. Contrary to one set of weights used in traditional schemes, Active Fairness maintains two sets of weights at each link. The first set is the same as that used in traditional schemes, which represents the relative bandwidth allocation desired out of the available bandwidth at the link. If these weights are used directly in bandwidth allocation, the actual proportion of the bandwidth utilized by an individual connection can deviate substantially due to factors such as the number of links traversed by the connection, its round-trip propagation delay, etc. In order to take into account these factors, another set of weights (dynamic in nature) is derived at each link, which is used in bandwidth allocation. Active Fairness achieves significant fairness improvement which is demonstrated through simulations involving bursty background traffic, network bottlenecks, dynamic VC mixes and different fairness definitions.     

概率多值中智集的关联系数及其应用

为了研究不同概率多值中智集的相关关系,提出了概率多值中智集的关联系数。提出了概率多值中智集的期望关联系数、精确度关联系数和信息完全度关联系数,以便测量不同概率多值中智集在平均程度、精确程度和信息完全度之间的相关关系。为了测量不同概率多值中智集的整体相关关系,基于三种关联系数和加权平均算子的思想定义了包含参数的概率多值中智集的综合关联系数,并且给出了关联系数的性质。考虑到权重的重要性,提出了概率多值中智集的一系列加权关联系数。基于概率多值中智集的加权关联系数构建一种可以有效地确定参数且适用于属性权重已知的多属性决策模型,并通过具体案例和对比分析验证该模型的有效性和合理性。     

MADM based on distance and correlation coefficient measures with decision-maker preferences under a hesitant fuzzy environment

In multiple attribute decision making (MADM), hesitant fuzzy sets (HFSs) are powerful tools for expressing uncertain and vague information. Recently, MADM problems with hesitant fuzzy information have attracted increasing attention, and many MADM methods have been developed. However, only a limited amount of research has considered MADM problems that simultaneously determine attribute weights and decision-maker (DM) preferences. Therefore, we propose an MADM approach for such problems under a hesitant fuzzy environment. First, we derive extended distance and correlation coefficient measures for HFSs that are more reasonable and effective when the DM preferences are considered. We then apply the extended distance measure to subjective and objective preference information to determine attribute weights, and use these to calculate the weighted correlation coefficient between the ideal choice and each alternative. Further, we determine the ranking order of all alternatives, from which it is easy to identify the best choice. Finally, we present an example that demonstrates the practicality of the proposed approach.     

Mutual-information based weighted fusion for target tracking in underwater wireless sensor networks

Underwater wireless sensor networks (UWSNs) can provide a promising solution to underwater target tracking. Due to limited energy and bandwidth resources, only a small number of nodes are selected to track a target at each interval. Because all measurements are fused together to provide information in a fusion center, fusion weights of all selected nodes may affect the performance of target tracking. As far as we know, almost all existing tracking schemes neglect this problem. We study a weighted fusion scheme for target tracking in UWSNs. First, because the mutual information (MI) between a node’s measurement and the target state can quantify target information provided by the node, it is calculated to determine proper fusion weights. Second, we design a novel multi-sensor weighted particle filter (MSWPF) using fusion weights determined by MI. Third, we present a local node selection scheme based on posterior Cramer-Rao lower bound (PCRLB) to improve tracking efficiency. Finally, simulation results are presented to verify the performance improvement of our scheme with proper fusion weights.     

Harmonic proportional bandwidth allocation and scheduling for service differentiation on streaming servers

To provide ubiquitous access to the proliferating rich media on the Internet, scalable streaming servers must be able to provide differentiated services to various client requests. Recent advances of transcoding technology make network-I/O bandwidth usages at the server communication ports controllable by request schedulers on the fly. In this article, we propose a transcoding-enabled bandwidth allocation scheme for service differentiation on streaming servers. It aims to deliver high bit rate streams to high priority request classes without overcompromising low priority request classes. We investigate the problem of providing differentiated streaming services at application level in two aspects: stream bandwidth allocation and request scheduling. We formulate the bandwidth allocation problem as an optimization of a harmonic utility function of the stream quality factors and derive the optimal streaming bit rates for requests of different classes under various server load conditions. We prove that the optimal allocation, referred to as harmonic proportional allocation, not only maximizes the system utility function, but also guarantees proportional fair sharing between classes with different prespecified differentiation weights. We evaluate the allocation scheme, in combination with two popular request scheduling approaches, via extensive simulations and compare it with an absolute differentiation strategy and a proportional-share strategy tailored from relative differentiation in networking. Simulation results show that the harmonic proportional allocation scheme can meet the objective of relative differentiation in both short and long timescales and greatly enhance the service availability and maintain low queueing delay when the streaming system is highly loaded.     

Dynamic multiple-frame bandwidth provisioning with fairness and revenue considerations for Broadband Wireless Access Systems

The increasing demand for wireless heterogeneous multimedia services presents a real challenge to mobile network operators. Even with the substantial increase in the supported bandwidth in emerging Broadband Wireless Access Systems (BWASs) such as 3.5G High Speed Downlink Packet Access (HSDPA) and the Worldwide Interoperability for Microwave Access (WiMAX), satisfying the bandwidth requirements of mobile users while increasing the revenues of network operators is still one of the major issues in these systems. Therefore, bandwidth provisioning will certainly play a decisive role in the success of such BWASs. In this paper, we propose a novel dynamic multiple-frame bandwidth provisioning scheme for BWASs. The proposed scheme spans multiple time frames and optimally allocates them to the different classes of traffic depending on their weights, the real-time bandwidth requirements of their users’ connections, their channel quality conditions and the expected obtained revenues. To maximize fairness and still maintain service differentiation between classes, we provide a unique formulation for dynamically computing the class weights. Simulation results are provided to show the potential and effectiveness of our scheme.     

基于多链路聚合的弱客户端数据传输模型

针对当前制约无线网络应用发展的无线低带宽和有线宽带速度的不对称现状,提出一种面向弱客户端的多链路聚合传输模型。采用通用的TCP/IP编程接口,可以有效地提高低带宽客户端数据传输的速率和稳定性,并具有良好的可靠性、可用性和负载均衡,从而尽可能地利用所有链路的带宽以达到最佳的传输速度。     

MANET下环境感知的服务可用性量化评估模型

移动Ad hoc网络(MANET)环境下,移动节点通过向其他节点提供服务是进行资源共享与能力协同的有效方式.但是由于 MANET环境的复杂性、链路的动态性和节点的异构性等特点,使得服务可用性时刻都在发生变化,且难以量化.通过对 MANET环境下服务运行环境和对影响服务可用性的节点、网络环境可用性的分析,提出了一个具有环境感知能力的服务可用性量化评估模型EQAM-SA,该模型由服务请求触发,实时获取服务运行参数、量化评估指标,并采用层次分析法和多属性综合评估法对服务的可用性进行量化评估.最后通过仿真实验验证了EQAM-SA的可行性和有效性.     

Exploring alternative spatial weights to detect crash hotspots

Identifying hotspots or crash clusters is an important problem for detecting high-risk locations at which vehicle accidents frequently occur. Several hotspot identification methods have been developed in the literature; however, there are often large differences between the spatial distributions of hotspots obtained by these methods, and spatial weights such as free flow travel times and congested flow travel times have not been fully examined as alternatives to the weight of distance. This paper compares the following commonly implemented network-based hotspot detection methods: Getis-Ord Gi*, Local Moran's I, KLINCS (K-function local indicators of network-constrained clusters), and KLINCS-IC (Inverse Cost) in order to provide insight into understanding the similarities and differences between selected hotspot detection methods when used with different spatial weights. This assessment is performed through using different spatial weights as part of the statistical analysis and comparing them to a prediction accuracy index. Moreover, a sensitivity analysis was conducted based on alternative spatial weights and different parameters to test the effect of bandwidth on the identified hotspots. The findings on the success of alternative spatial weights has a potential to improve the accuracy of the hotspot detection. Results indicate distinct differences in the spatial distributions of hotspots obtained through the considered methods that are based on alternative spatial weights. An interesting finding is that all alternative approaches (spatial weights and bandwidths) cluster when certain bandwidth values are exceeded. From a practical perspective, the CPAI results show that using network-constrained Local Moran's I statistics with a distance-based spatial weights may provide the most feasible approach while implementing safety-focused efforts.