基于强挂起弱预测机制的负载均衡模型研究

大数据时代的快速发展和大数据战略的明确提出,使得Web服务器集群将面临更加复杂和严峻的负载挑战。传统的负载均衡算法存在着明显的局限性。提出了一种基于强挂起弱预测机制的负载均衡模型,该模型利用强挂起机制和基于层次分析的三次指数平滑预测算法进行负载均衡动态调度。实验结果表明该模型在系统瞬时性能异常、高并发和重负载交互情况下的负载均衡效果优于传统负载均衡算法。     

基于预测的传感器网络副本自适应控制机制

最小跳数路由无线传感器网络具有自动倾向于路径最短、时延最小、能量最省的潜在优点,但已有机制尚不能保证这些优点的充分发挥.为充分发挥最小跳数路由无线传感器网络的潜在优势,在传统的最小跳数路由无线传感器网络数据汇聚机制的基础上,引入基于预测的自适应数据副本保证与抑制机制,形成MHR-DC网络模型.MHR-DC网络在基本不增加数据分组汇聚全程转发跳数的前提下,通过同跳节点代传以保证所有源生负载的高可靠传输、通过抑制数据分组的重复传送程度以提高网络能量效率、通过避开转发负载重的节点区域以达到负载均衡,优化网络综合性能指标,并增强网络时延最小的潜在优势.理论及仿真分析表明,该机制能保证网络数据传输的高可靠性和能量有效性以及优越的网络综合性能.     

增强型移动自主网络MAC层节能机制

在移动自组网中,节点通常采用能量有限的电池来供电,因此如何提高各个节点能量利用率,减少能耗,以延长网络的寿命,成为移动自组网协议中所有协议层的关键问题;为了节省能量,无限局域网标准IEEE802.11在分布式协调功能(DCF)的基础上定义了节能机制PSM,在对现有的802.11PSM协议进行分析和比较后提出一种自适应调整的节能机制EPSM;EPSM |改进了PSM在一个BI周期只能传送一个数据包的模式,大大减少传输延时,并采用中心节点交替苏醒的方式以延长中心节点的生存时间,达到节省能量的目的;通过仿真结果表明EPSM在减少传输时延、减少能耗以及提高节点生存时间等方面较PSM有了较大的提高.     

Crowds系统中基于递减转发概率的路长控制策略

Crowds匿名浏览系统中，基于固定的转发概率建立重路由路径用以在主机间转发用户请求，从而隐藏通信的发起者．在系统所采用的转发概率较大的情况下，产生的重路由路径过长，导致转发请求的延时以及系统中成员负载等性能开销过大．文中提出基于递减转发概率的路长控制策略，用以有效控制重路由路径长度，提高传输性能．首先证明在前趋攻击下，恶意成员攻破匿名保护所需的时间轮数，主要由系统中恶意成员数目所决定，受重路由路径长度的影响较小．基于该分析结果，提出了基于递减转发概率的路长控制策略．仿真结果表明，新策略能缩短重路由路径的长度，从而在保持系统匿名保护能力的前提下，有效提升系统的性能．     

一种网格环境下的动态负载均衡机制

负载均衡机制有利于提高广域分布式环境中资源共享和协同工作的效率。根据网格系统的特点,采用灰色预测方法,设计了一种动态资源负载均衡机制,给出了预测模型和实时预测策略以及基于该机制的负载均衡算法。该资源负载均衡机制具有以下特点：可在较小的开销下取得满意的负载均衡性能,具有网格环境下的可扩展性,能够适应网格资源动态变化的特性,解决资源发现过程中的负载均衡 问题。     

机载自组网信道占用统计预测机制

在机载自组网随机竞争类MAC协议中,信道忙闲程度可以作为不同优先级分组接入信道的阈值,通过限制低优先级业务的接入,保证高优先级业务的QoS,从而克服重负载下分组盲目接入信道导致网络性能恶化的问题。提出一种信道占用统计预测机制,在对信道忙闲程度等级划分的基础上,采用滑动窗口机制、加权-马尔科夫链预测模型,通过统计信道负载的历史信息,将负载的多步预测值和真实值的差值作为当前时刻预测值的修正,以当前时刻信道负载的预测值判定信道忙闲,从而为不同优先级分组接入信道的阈值设置提供理论依据。仿真结果表明,该机制对信道负载的正确预测率在90%以上,能够为多优先级业务提供区分服务,并且可以明显改善随机竞争类协议在重负载下的性能。     

单收发器分布式多跳认知媒体接入控制协议优化设计

针对移动自组网（MANET）媒体接入控制（MAC）协议中存在的多收发器限制、信道负载失衡等问题,并兼顾多跳和控制开销等性能,提出一种单收发器多跳分布式认知MAC协议优化模型。首先基于功率节省模式（PSM）机制,利用通知传输指示消息（ATIM）窗口和DATA窗口时间分割实现认知MAC协议的信道感知和数据传输功能;其次对功率值非均匀量化和格雷编码,降低移动性导致的浮点型开销;然后设计了多跳分布式信道协作机制,以此为基础,重定义信道切换规则,确保信道之间负载均衡;最后对信道空出时间（CVT）、信道开启时间（COT）、吞吐量和信道负载时间进行仿真。结果表明,新协议无需多收发器支撑,各信道之间CVT、COT、负载时间差值分别降低了13 ms、20 ms和100 s,对应吞吐量提高了1.5%,实现了协议在收发器数、信道负载均衡、吞吐量和控制开销等性能方面的优化。     

Ad hoc网络中的简单跨层流控机制

为了提高Ad hoc网络中传输层协议的性能,基于跨层思想设计了一种简单可行的跨层流控机制。该机制结合网络层路由反馈、传输层协议和应用层速率自适应调节,通过跨层信息交互,应用层可根据网络层反馈的路由信息来调节业务的发送速率,将网络负载维持在合理的水平以最大化网络吞吐量。计算机模拟评价表明该机制能改善基于UDP和TCP的业务性能,在网络负载较低的情况下效果尤为明显。     

面向融合的电信业务平台中负载平衡算法实现

针对面向融合业务平台的系统特征,提出了一种新的负载平衡算法,该算法采用轻负载和重负载不同情况下的两阶段算法,轻负载的情况采用加权随机的算法以保证简单高效,重负载的情况采用基于负载更新的算法以保证负载均衡。在面向融合的电信业务平台上,对两阶段算法和随机、轮转算法进行了平均响应时间的测试对比,结果表明算法达到较好的性能。     

支持多类型业务的受限负载EDCA性能分析

无线局域网增强的分布式信道接入(EDCA)具有支持多类型业务的功能。为准确有效地分析EDCA机制的性能,提出一个考虑多类型业务的受限负载二维马尔可夫性能分析模型。该模型通过引入空闲、后回退等状态来精确刻画饱和与非饱和负载下系统的性能,并考虑EDCA重传次数、后碰撞过程等特征。仿真结果验证了模型的有效性,系统的最大吞吐量出现在非饱和负载情况下。     

基于虚拟令牌的自适应实时以太网络构建

CSMA/CD型Token Bus分别是总线网络中采用的竞争策略、无冲突策略的经典信道获取技术。前者在轻载荷下时延较小，却在重载荷下因信道仲裁开销过大使各项性能急剧变差，后者虽在重载荷下有相对确定的时延，但在轻载荷时却时延较大。该文引入一种自适应机制,使网络在轻载荷下运行CSMA/CD协议，而在重载荷下自动转换为Token Bus策略，并通过在应用层配置所编写的协议模块，使传统的非确定性以太网成为自适应实时以太网。     

Power-saving mechanisms for energy efficient IEEE 802.16e/m

Efforts to reduce CO₂ emission regarded as a main reason of the green house effect are widely performed in Information and Communications Technology (ICT) industry. In particular, as fast growing mobile communications services consume more energy, there are wide efforts to increase energy efficiency in the area of Mobile Station (MS), radio Base Stations (BS), network controllers, and core networks. User's concern, however, is more focused on optimization of energy efficiency in MS with limited battery capacity, because MS consumes much energy for wide broadband data services in data-centric communications services with 4G technology rather than legacy voice-centric communications services.The key idea of power saving mechanism (PSM) in MS is to operate sleep-mode that the MS turns down main elements when there is no data to receive/transmit in order to save battery power. With legacy voice-centric communication services, traffic pattern is rather simple and well-known so that the sleep-mode of PSM is well operated. However, in 4G technology for various data-centric services power saving mechanism should be adaptive to changing traffic condition in order to achieve optimal energy efficiency. Thus, holistic perspective for power saving techniques is needed in consideration of characteristics of services and QoS constraints, multiple applications support, remained battery power, handover process, Multicast Broadcast Service (MBS) support, and so on.This paper surveys various power saving mechanisms proposed for IEEE 802.16e/m. We first present the basic operating mechanism of PSM and research issues for performance enhancement. Based on their limitations and potentials, we then review several proposals of PSM for IEEE 802.16m, an evolutional technology of IEEE 802.16e. It will be interesting for readers to observe that once PSM was standardized in IEEE 802.16e, many new ideas have been proposed to improve the performance of the original PSM, and some of them are survived and adopted to new standard technique in the advanced IEEE 802.16m.     

A scan restoration method for robust polar scan matching in dynamic environments

This paper addresses the problem of scan matching which is highly indispensable for mobile robot systems based on range sensors. Recently, polar scan matching (PSM) has been used in solving the problem because it is accurate and fast enough to be performed in real time. However, the performance of PSM degenerates when the portion of scan data from dynamic objects is excessively large. This paper proposes a scan restoration method to overcome this problem and improve the performance of PSM in dynamic environments. The proposed method restores the scan data from dynamic objects to appropriate scan data from static objects. First, whole scan data is segmented and classified as static and dynamic objects. Next, curvature functions are extracted from the classified segments and smoothed by interpolating the segments indicating dynamic obstacles. PSM with the proposed method was tested and evaluated in various real dynamic environments, which reveals that the proposed method can improve the performance of PSM in dynamic environments.     

Resource discovery and request-redirection for dynamic load sharing in multi-provider peering content delivery networks

A constellation of Content Delivery Networks (CDNs), termed as peering CDNs, endeavors to guarantee adequate delivery performance when the incoming request load is overwhelming for a single provider alone. Each user is served by an optimal Web server in terms of network cost, even under heavy load conditions. Before it could be comprehended, appropriate resource discovery and request-redirection mechanisms, coupled with an optimal server selection strategy, should be in place to perform the distribution of highly skewed loads. In this paper, we devise an effective load distribution strategy by adopting distributed resource discovery and dynamic request-redirection mechanisms, taking traffic load and network proximity into account. The load distribution strategy reacts to overload conditions, at a time instance, in any primary CDN server(s) and instantly distributes loads to the target servers, minimizing network cost and observing practical constraints. In this context, we exercise an asynchronous resource discovery protocol, reminiscent of the public/subscribe notion, and formulate the resulting redirection scheme. Extensive simulation analyses demonstrate the novelty of our approach. In particular, we show that our approach is effective to handle high load skews by preserving locality, and thus achieve service “responsiveness”. We also perform a sensitivity analysis to reveal that our redirection scheme outperforms other alternatives to handle peak loads.     

数据流QoS自适应框架调度算法的研究与实现

在数据流QoS自适应框架中,针对如何为具有截止期和重要性两个特征参数的流数据分派优先级,在讨论了了当前调度算法优缺点的基础上,提出了称为截止期-重要性优先DIF（deadline-importance first）的实时调度算法,并利用链表给出了算法的实现.实验结果表明,在所有负载条件下DIF算法相对于EDF（earliest deadline first）算法、HVF（highest value first）算法和CDF（criticalness-deadline first）算法,在性能方面具有明显改善,特别在系统过载的情况下,能够优雅地降级.     

基于Kubernetes应用的弹性伸缩策略

弹性伸缩是云计算的关键特征,它可以根据应用程序工作负载及时扩展计算资源以实现在高并发请求下应用的负载均衡.基于容器的微服务更应具有弹性伸缩功能从而在不同的工作负载条件下稳定运行.目前广泛使用的容器编排工具Kubernetes的弹性伸缩算法灵活性差,应对突发流量Pod会频繁进行扩展,并且扩展程度不能满足当前负载要求,会造成系统不稳定.针对这一问题,本文提出了一种自动缩放机制,将响应式扩展与弹性伸缩容忍度相结合,确保了系统的可靠性,大大提高了系统的灵活性,并具有很强的应用负载能力.实验测试表明,当系统面临大流量、高并发请求时,通过本文的方法实施弹性伸缩以后,失败请求率下降97.83%,保证了系统稳定性,能够很好的实现应用的负载均衡.     

基于MDA的UML模型转换技术——从顺序图到状态图

为了实现不同中间件平台之间的集成和互操作,OMG提出了一个标准的基于模型的体系结构:MDA。MDA将应用模型划分成与平台无关的模型(PIM)和与平台有关的模型(PSM),并定义了PIM和PSM之间的4种映射关系。该文主要对PIM到PIM之间的映射进行了研究。该映射实质上是PIM模型的精化,其主要方面是分析模型和设计模型之间的转换。MDA使用UML来描述各种模型。UML是一种可视化的通用的面向对象的建模语言。UML顺序图主要用于需求分析,而状态图在系统设计阶段起重要作用。该文介绍了一种从UML顺序图中合成状态图的方法,合成的过程基本上是自动完成的,只需要很少的用户交互,从而为PIM模型的精化提供有力的支持。     

Implementation and experimental performance evaluation of a hybrid interrupt-handling scheme

The performance of network hosts can be severely degraded when subjected to heavy traffic of today’s Gigabit networks. This degradation occurs as a result of the interrupt overhead associated with the high rate of packet arrivals. NAPI, a packet reception mechanism integrated into the latest version of Linux networking subsystem, was designed to improve Linux performance to suit today’s Gigabit traffic. NAPI is definitely a major step up from earlier reception mechanisms; however, NAPI has shortcomings and its performance can be further enhanced. A hybrid interrupt-handling scheme, which was recently proposed in Salah et al. [K. Salah, K. El-Badawi, F. Haidari, Performance Analysis and Comparison of Interrupt-Handling Schemes in Gigabit Networks, International Journal of Computer Communications, Elsevier, Amsterdam 30 (17) (2007) 3425–3441], can better improve the performance of Gigabit network hosts. The hybrid scheme switches between interrupt disabling–enabling (DE) and polling (NAPI). In this paper, we present and discuss major changes required to implement such a hybrid scheme in the latest version of Linux kernel 2.6.15. We prove experimentally that the hybrid scheme can significantly improve the performance of general-purpose network desktops or servers running network I/O-bound applications, when subjecting such network hosts to both light and heavy traffic load conditions. The performance is measured and analyzed in terms of throughput, packet loss, latency, and CPU availability.     

IEEE 802.11宽带无线局域网负载均衡优化研究*

在基于IEEE 802.11的宽带无线局域网中,随着终端STA的接入、移动和无线信道的时变性,各个接入点（AP）的负载将会产生差异,需要负载均衡优化机制平衡各个AP的差异,以达到网络资源的最大利用率。详细讨论了无线局域网中用到的几种负载均衡机制,分析了各自的优缺点,结合这些特点给出一种新的负载均衡机制。该机制能较准确地统计终端业务信息,降低切换失败风险,快速达到APs之间的负载均衡,优化提高网络整体性能。