Analytical Load Balancing Model in Distributed Open Flow Controller System

The Software Defined Network (SDN) is a concept based on a decoupling between the control plan and the data plan of a network. Thus, the network becomes programmable and can be coupled to the business applications of the users. The study that is discussed in this article looks at load planning and balancing in distributed controllers. To do this, a model and theoretical methods of performance evaluation related to appropriate software tools, to predict and control the quality of service offered to users is exposed. This paper exposed also a distributed architecture of controllers and then a module based on an adaptive load balancing algorithm that is fault tolerant and fluctuates controller loads. The experiments show a significant gain in efficiency of our solution.

HiLog:OpenHarmony的高性能日志系统

日志是计算机系统中记录事件状态信息的的重要载体,日志系统负责计算机系统的日志生成、收集和输出.OpenHarmony是新兴的、面向全设备、全场景的开源操作系统.在所述工作之前,包括日志系统在内OpenHarmony有许多关键子系统尚未构建,而OpenHarmony的开源特性使第三方开发者可以为其贡献核心代码.为了解决Open Harmony日志系统缺乏的问题,主要开展如下工作:(1)分析当今主流日志系统的技术架构和优缺点;(2)基于OpenHarmony操作系统的异构设备互联特性设计HiLog日志系统模型规范;(3)设计并实现第1个面向OpenHarmony的日志系统HiLog,并贡献到OpenHarmony主线;(4)对HiLog日志系统的关键指标进行测试和对比试验.实验数据表明,在基础性能方面,HiLog和Log的日志写入阶段吞吐量分别为1500 KB/s和700 KB/s,相比Android日志系统吞吐量提升114%;在日志持久化方面,HiLog可以3.5%的压缩率进行持久化,并且丢包率小于6‰,远低于Log.此外,HiLog还具备数据安全、流量控制等新型实用能力.

Utility Impact below Bridge or Culvert Soffit on Open Channel Flow

The background to this research was a flooding incident that occurred in Bridgend, Co. Donegal, Ireland in August 2017. While several properties were flooded, a flooding case study of a single dwelling house adjacent to the Bridgend River at Riverdale, Bunamayne, Co. Donegal, Ireland is used herein. For this study the flooded site shall be referred to as the “Hegarty property”. A structure in the form of a stone arched culvert is located directly adjacent to the two-storey detached dwelling house on the Hegarty Property. While the culvert is referred to locally as a bridge, within this research the word culvert will be used in connection with the structure. The culvert has a concrete surrounded utility (watermain) crossing at a gradient below the culvert soffit on the upstream face of the structure. The utility obstructed flow through the culvert and contributed to the flooding event. Given the implication of climate change and the increased probability of more extreme flooding events, it was decided to explore the case study to ascertain the factors that contribute to flooding events when utilities are positioned at culvert or bridge structures. This work was completed to assist undergraduate students, researchers, and local authorities in a relatively unknown area of flood causation.

Overbank Flow in a Multi-Staged Open Channel: Zonal and Overall Discharge Studies

An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the second stage floodplain, fractional contribution of the main channel and first stage floodplain under bankfull height plays a pivotal role in shear layer and momentum distribution. Therefore, a new mathematical model has been suggested for estimating the stage-discharge relationship for staged channels of more than one floodplain using the 1D technique of overall roughness correction. .

Effect of Mixed Vegetation of Different Heights on Open Channel Flows

Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .

Effect of Pre-Swirling Flow on Performance and Flow Fields in Semi-Opened Axial Fan

In this study, we tried to improve the performance by giving a pre-swirling flow to the radial inflow that occurred in the semi-opened axial fan. In addition, the flow fields of rotor outlet were clarified experimentally, and the effect of pre-swirling flow was considered. The experiment was carried out using a performance test wind tunnel with a square cross section of 880 mm. Three types of casings were prepared, in which the blade tip protruded 0%, 20%, and 40% of the meridional chord length. They were called R25, R15, and R05, respectively, in the casing bellmouth model code. Guide blades for generating a pre-swirling flow were installed on the vertical wall surface of the casing. In addition, a vertical wall was installed 60% upstream of the meridional chord length as an obstacle to prevent axial inflow. The velocity fields of the rotor outlet were measured using a hot-wire anemometer. From the results, the pre-swirling flow did not significantly affect the fan performance. When there was no obstacles wall upstream, there was a partial increase in efficiency, but the difference was not so large. When there was an obstacle wall upstream, the efficiency increased overall in the case of R15, but in the case of R05, the efficiency increased only in the low flow rate region, and conversely decreased in the high flow rate region. By observing the blade outlet flow fields when the performance was improved, it was confirmed that the influence of the tip leakage vortex was weakened.

基于OpenFlow的SDN终端接入控制研究

为了解决基于Open Flow的SDN终端安全接入问题,通过对现有SDN中针对终端安全接入解决方案的深入研究,文章提出一种基于Open Flow的SDN终端接入控制系统。该系统将传统终端接入控制技术与基于Open Flow的SDN新型网络相结合,主要实现了SDN环境下的用户身份认证、终端安全状态评估、用户服务授权和Qo S控制等功能,并且对系统的安全性进行了详细分析。文章在Mininet中结合二次开发的RYU控制器进行网络仿真,完成了接入控制功能和通信时延性能的实验。实验结果表明,基于Open Flow的SDN终端接入控制系统具有灵活的接入控制安全策略,能够检测SDN中不安全终端接入带来的威胁,不仅实现了用户的身份认证,而且能够保证接入终端的安全,实现不同安全状态终端的访问授权。性能测试结果表明,基于Open Flow的SDN终端接入控制系统在身份认证时延、平台评估时延和通信时延等方面都能满足实际需要。

基于OpenFlow的SDN网络安全分析与研究

基于Open Flow的SDN技术将网络的数据平面和控制平面相分离,通过部署中央控制器来实现对网络的管控,为未来网络的发展提供了一种新的解决思路。然而,这种新型网络管控方法与传统网络在分布式控制平面上通过封闭网络设备进行管控的方法有着根本区别,因而在实现集中化管理的同时将引入新的管理和安全问题。文章首先介绍了其三层架构的自身缺陷和可能存在的安全问题,并从SDN架构的基础设施层、南向接口、控制层、北向接口和应用层等几个方面分别进行分析,总结出SDN不同层次存在安全问题的原因;随后,文章从认证机制、控制层的备份和恢复、网络异常识别和防御机制、应用隔离和权限管理等四个方面总结了当前的相关研究进展和研究思路,并提出了可行的解决方案;最后,对全文进行总结和展望。

基于OpenFlow网络的弹性服务质量保障方法

传统网络主要依靠固定的优先级标签机制为业务提供服务质量(QoS)保障。针对该方法没有考虑不同交换节点中负载差异性及无法及时应对网络中的拥塞与故障等问题,在OpenFlow网络中提出一种弹性QoS保障方法。对于新加入的业务流软件定义网络(SDN)控制器依据当前网络负载情况,通过空间排序快速搜索算法计算其在不同交换节点中的映射优先级,该算法可有效缩小搜索空间并得出近似最优解,所得结果在满足新加业务流端到端时延及带宽要求的同时,最低限度地影响系统其他业务流。通过仿真验证,在所提方法生效后,可使具有严格延迟指标要求业务流的保障精度大幅提升,并使业务流获得端到端的QoS保障。所提方法可应用于网络拥塞避免及网络故障自我修复等领域。

基于OpenFlow网络数据处理模型的研究

随着计算机网络的不断发展以及人们对网络性能要求的不断提高,现有网络很难满足人们的需要。Open Flow的出现能够很好地解决现有网络的不足,但存在网络会话识别效率不高,网络报文转发路径选择不佳等问题。针对匹配算法和路径转发进行了研究,提出了GODP(GPU Open Flow data processing)模型。该模型通过融合GPU计算与生物序列算法和机器学习方法,提出了GPTWF网络会话匹配算法和网络会话转发算法,有效提升了匹配效率,优化了网络环境。实验表明网络会话匹配算法加速比提升近290,网络会话转发算法使得链路丢包率低于5%,延时小于20 ms,网络会话丢包率和延时分别平均下降62.71%和73.88%。

openFlow/SDN控制器路由算法的研究

基于open Flow的SDN是新兴的网络技术,它将控制平面与数据平面分离,降低了网络管理的难度。首先介绍了SDN的思想及结构设计SDN控制器的架构,对SDN控制器路由算法进行分析,提出性能更好的算法方案,最后表明未来研究的方向。

基于OpenFlow的虚拟网实现研究

软件定义网络是一种数据和控制平面分离、软件可编程的新型网络架构及技术,控制平面使用以Open Flow为代表的协议对转发平面进行集中式控制。SDN架构的这些特点能很好地满足了云计算对虚拟网络的集中化、标准化、自动化的配置管理要求。针对传统虚拟网络技术支持云计算平台的不足,提出基于Open Flow的SDN技术设计虚拟网络的思路,论述了几种虚拟网络实现的原理与处理流程,并给出了模块化的软件设计及部分关键代码功能描述。

OpenFlow交换机协议一致性测试集模型研究

针对当前的Open Flow交换机协议测试技术的研究现状,介绍了两个Open Flow交换机协议一致性测试的测试集模型。

基于OpenFlow的发布/订阅系统的管理与安全

软件定义网络(Software Defined Network,SDN),是一种新型网络创新架构,其实现技术Open Flow通过将网络设备控制面与数据面分离开来,从而实现了网络流量的灵活控制,为核心网络及应用的创新提供了良好的平台。本文针对发布/订阅系统的数据时效性及安全上的问题,利用Open Flow这一具有集中管控能力的新型网络平台,实现了包括绘制全局拓扑图、管理设备信息、管理流量信息、管理用户订阅及策略信息在内的发布/订阅管理系统。在安全方面,通过对用户特征进行分析,使用数据挖掘算法查找可疑用户,找到后对其订阅限制的方式实现了对订阅攻击的有效防御。从而使得发布/订阅系统更加易于管理,更加安全和可靠。

Experimental study on influence of boundary on location of maximum velocity in open channel flows

The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.

Decoupled Delay and Bandwidth Centralized Queue-Based QoS Scheme in OpenFlow Networks

There are an increasing of scenarios that require the independent bandwidth and delay demands. For instance, in a data center, the interactive message would not occupy much bandwidth, but it requires the rigorous demands for the delay. However, the existing QoS approaches are mainly bandwidth based, which are inappropriate for these scenarios. Hence, we propose the decoupled scheme in the OpenFlow networks to provide the centralized differential bandwidth and delay control. We leverage the mature HTB to manage the bandwidth. And we design the Queue Delay Management Scheme (QDMS) for queuing delay arrangement, as well as the Comprehensive Parameters based Dijkstra Route algorithm (CPDR) for the propagation delay control. The evaluation results verify the decoupling effectiveness. And the decoupled scheme can reduce the delay for high priority flows.

Pore opening and binder flow during initial stage of thermal debinding in MIM

Pore opening and binder flow during the initial stage of thermal debinding in metal injection molded parts was investigated. Scaning electron microscopy(SEM) pictures of 316 L stainless steel parts using wax based binder show that small particles will move to the surface with the process of debinding. SEM pictures of different mass loss rate specimens indicate that initial pores will emerge when as little as 4% binder removes. During the initial stage of thermal debinding, vapor tension varies in different place due to the difference of curvature. Thus more binders will be removed in places with smaller cavity between metal powders, and in these places small openings emerge.

3-D hybrid LES-RANS model for simulation of open-channel T-diversion flows

The study of flow diversions in open channels plays an important practical role in the design and management of open-channel networks for irrigation or drainage. To accurately predict the mean flow and turbulence characteristics of open-channel dividing flows, a hybrid LES-RANS model, which combines the large eddy simulation （LES） model with the Reynolds-averaged Navier-Stokes （RANS） model, is proposed in the present study. The unsteady RANS model was used to simulate the upstream and downstream regions of a main channel, as well as the downstream region of a branch channel. The LES model was used to simulate the channel diversion region, where turbulent flow characteristics are complicated. Isotropic velocity fluctuations were added at the inflow interface of the LES region to trigger the generation of resolved turbulence. A method based on the virtual body force is proposed to impose Reynolds-averaged velocity fields near the outlet of the LES region in order to take downstream flow effects computed by the RANS model into account and dissipate the excessive turbulent fluctuations. This hybrid approach saves computational effort and makes it easier to properly specify inlet and outlet boundary conditions. Comparison between computational results and experimental data indicates that this relatively new modeling approach can accurately predict open-channel T-diversion flows.

Lateral Shear Layer and Its Velocity Distribution of Flow in Rectangular Open Channels

The lateral velocity distribution of flow in the shear layer of open channel is required to many problems in river and eco-environment engineering, e.g. distribution of pollutant dispersion, sediment transport and bank erosion, and aquatic habitat. It is not well understood about how the velocity varies laterally in the wall boundary layer. This paper gives an analytical solution of lateral velocity distribution in a rectangular open channel based on the depth-averaged momentum equation proposed by Shiono & Knight. The obtained lateral velocity distributions in the wall shear layer are related to the two hydraulic parameters of lateral eddy viscosity (λ) and depth-averaged secondary flow (Γ) for given roughened channels. Preliminary relationships between the above two parameters and the aspect ratio of channel, B/H, are obtained from two sets of experimental data. The lateral width (δ) of the shear layer was investigated and found to relate to the λ and the bed friction factor (f), as described by Equation (26). This study indicates that the lateral shear layer near the wall can be very wide (δ/H = 14.6) for the extreme case (λ = 0.6 and f = 0.01).

基于OpenFlow南向协议的SDN控制器性能测试方法及定量分析

随着软件定义网络(Software Defined Network,SDN)成为网络世界的新的范式转移,作为SDN网络的核心组件,控制器的性能得到了越来越多的关注。文章介绍了基于Open Flow 1.3这一南向协议的SDN控制器性能测试方法,并以某开源控制器为例,介绍测试结果的定量呈现方式和分析方法,为需要评估控制器性能的用户提供参考。