美丽的平面

除了低频以外,平面喇叭在透明度、瞬态响应、空间感的塑造等方面,都是传统的锥形喇叭难以比拟的。     

地平面的分割

一个完整的地平面能减少电路板的EMI和串扰问题。在数模混合布板时,数字电路的同步开关噪声往往会影响敏感的模拟电路。分割的地平面能够提供高的噪声隔离度,但同时也会引起另外的一些EMI问题。本文就如何正确的分割地平面以及为什么这样分割进行了讨论,并给出了地分割的相应设计原则。     

平面上的抒情

不完全了解朱庆辰的人,只知道他是一位成功的企业家;了解他的人．知道他还是一位摄影爱好者：而真正了解他的人．却知道他是一位拿相机的诗人．是一位在平面上抒情的人。我就是这样看他的。之所以会有如此认识,并不是听信了某位权威的高谈阔论．而是朱庆辰的摄影作品告诉了我一个现实;我有了一个对手!因为我曾被狄源沧先生称赞为拿相机的诗人,并曾以此自诩！     

平面结环行器的优化设计

本文首先证明了用边界元分析结平面环行器的过程及程序的有效性和通用性。接着,优化处理了平面结环行器的有关参数,优化分两步,第一步是在结形状不变的情况下,用步长加速法优化圆结半径,耦合角及结外介质的介电常数;第二步是在第一步的基础上,用Powell方法优化结形状。最后给出了优化实例。     

平面扫描仪的选购

中国电脑市场的发展势头迅猛,扫描仪作为逐渐升温的输入设备,也有了长足的发展。当1998年全世界范围内扫描仪市场疲软的时候,国内扫描仪市场却有近90%的增幅。尽管这与国内扫描仪总量基数较低有关,但其日益增长的市场需求形势,强烈地吸引着世界各大扫描仪厂商。他们都想抓住即将到来的扫描仪需求旺盛时机,力求有新的突破。到现在,国内扫描仪市场上已有近三十家扫描仪厂商挤入,全球前五大扫描仪厂商更是毫不例外地争先抢占份额。各厂商争相使出杀手锏,展开一番龙争虎斗。置身于纷繁的扫描仪市场,你有没有因看花眼而无从选择？如何…     

平面聚光板

一种平面聚光板,由平面基板和反光镜片组成。反光镜片与平面基板呈不同的夹角,从而把光线反射到一点上,这种平面聚光板能代替抛物面太阳灶的作用。(中国专利号:97219211.5)(No.51)平面聚光板~~     

平面终端技术

本文对日益广泛采用的各种平面终端技术作用原理、设计方法及目前的发展水平作了较系统的介绍,并简要地比较了它们的优缺点、适用器件类型和击穿电压范围。     

Scalability of software defined network

With the development of software-defined networking (SDN),its scalability has become one of the most important issues of SDN.The features of SDN was studied which lead to its scalability problem when SDN was applied to large-scale network.The three main causes leading to scalability problem were discussed:control plane and data plane separation,logical centralized control and fine-grained flow control.Meanwhile,the studies which focus on the scalability of SDN from three aspects:scalability of performance,scalability of geographic and scalability of control was presented.Further,the studies on the performance evaluation of the scalability of SDN were introduced.Finally,the future work was discussed.     

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OpenFlow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OpenFlow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。     

Dynamic switch migration with noncooperative game towards control plane scalability in SDN

As software‐defined networking (SDN) is a logically centralized technology, the control plane scalability in SDN is increasingly important with the network scale increasing. Load balancing and maximizing resource utilization are very critical to the control plane in SDN, while switch migration is an effective approach to achieve these two performance metrics. However, switch migration is NP‐hard problem because it belongs to the problem of combinatorial optimization. To avoid the NP‐hard problem, we propose a switch migration scheme by adopting noncooperative game to improve the control plane scalability in SDN. First, we design a novel load balancing monitoring scheme to detect the load imbalance between controllers and trigger migrating switches. Then, we use noncooperative game among controllers to decide switch migration to get the maximizing overall profits. Last, we prove that our proposed approach can get Pareto optimality. Extensive simulations prove that our method is able to achieve a more scalable control plane with load balancing and maximizing resource utilization.     

基于可编程数据平面的南向协议研究

由于传统网络设备固化且依赖于物理基础设施,难以适应智能化网络的需求。为提高网络的智能化,开放网络的可编程能力,软件定义网络和可编程数据平面应运而生。文章介绍了软件定义网络、可编程数据平面,及其所对应的南向协议,包括OpenFlow协议及其所存在的问题,P4Runtime协议的优势。然后用Mininet软件搭建了网络仿真对P4Runtime的优势进行验证。仿真实验表明,在可编程数据平面协议无关的基础上,P4Runtime作为控制平面和数据平面之间的南向协议,提供了基于Python的交互式和脚本两种下流表方式,与SDN传统下流表方式相比具有更高的灵活性和扩展性,更易于管理人员对网络进行统一管理。为运营商、数据中心等应用场景提供了新的控制管理方案。     

ONVisor: Towards a scalable and flexible SDN‐based network virtualization platform on ONOS

Network virtualization (NV) technologies have attracted a lot of attention as an essential solution for future networking infrastructure. The NV enables multiple tenants to share the same physical infrastructure and to create independent virtual networks (VNs) by decoupling the physical network in terms of topology, address, and control functions. One feasible way to realize full NV involves considering solutions based on the software‐defined networking (SDN) paradigm using its programmability. The SDN contributes many benefits to both network operations and management including programmability, agility, elasticity, and flexibility. There are several SDN‐based NV solutions; however, they suffered from a lack of scalability, high availability. Also, they have high latency between control and data plane because of proxy‐based architecture. In this thesis, we introduce a new NV platform, named Open Network Hypervisor (ONVisor). The design objectives include, among the features, (1) multitenancy, (2) scalability, (3) flexibility, (4) isolated VNs, and (5) VN federation. ONVisor was designed and implemented by extending Open Network Operating System, an open‐source SDN controller. The main features of ONVisor are (1) isolated control and data plane per VN, (2) support of distributed operations, (3) extensible translators, (4) on‐platform VN application development and execution, and (5) support of heterogenous SDN data‐plane implementations. Several experiments are conducted on various test scenarios in different test environments in terms of control and data plane performance compared to nonvirtualized SDN network. The results show that ONVisor can provide VNs a little bit lower control plane performance and similar data plane performance.     

Emulating Software Defined Network using Mininet-ns3-WIFI Integration for Wireless Networks

SDN enables a new networking paradigm probable to improve system efficiency where complex networks are easily managed and controlled. SDN allows network virtualization and advance programmability for customizing the behaviour of networking devices with user defined features even at run time. SDN separates network control and data planes. Intelligently controlled network management and operation, such that routing is eliminated from forwarding elements (switches) while shifting the routing logic in a centralized module named SDN Controller. Mininet is Linux based network emulator which is cost effective for implementing SDN having in built support of OpenFlow switches. This paper presents practical implementation of Mininet with ns-3 using Wi-Fi. Previous results reported in literature were limited upto 512 nodes in Mininet. Tests are conducted in Mininet by varying number of nodes in two distinct scenarios based on scalability and resource capabilities of the host system. We presented a low cost and reliable method allowing scalability with authenticity of results in real time environment. Simulation results show a marked improvement in time required for creating a topology designed for 3 nodes with powerful resources i.e. only 0.077 sec and 4.512 sec with limited resources, however with 2047 nodes required time is 1623.547 sec for powerful resources and 4615.115 sec with less capable resources respectively.

     

基于SDN的端到端无缝MPLS组网技术研究

针对MPLS技术在运营商应用中存在问题的分析,结合SDN思想和概念,将网络抽象为“网络转发”、“业务控制”和“运营支撑”三个平面,提出端到端无缝MPLS组网的解决方案。     

基于OpenFlow的SDN控制平面可扩展性综述

OpenFlow发展之初,主要是为了校园网络研究人员设计其创新网络架构提供真实的实验平台,形成一种新的网络构架SDN。随着其应用范围的增加,遇到的问题逐渐显现出来,尤其是可扩展性方面。文中介绍了OpenFlow的产生背景、特点及发展现状,以及几种较为典型的SDN控制器模型和控制平面框架,并对SDN可扩展性方面遇到的问题及解决方案进行了分析,并概述了其今后的发展方向。     

Stateful firewall‐enabled software‐defined network with distributed controllers: A network performance study

SummarySoftware‐defined network (SDN) is constructed by decoupling the control and data plane from the forwarding devices. The control plane operations are managed by centralized or distributed controllers, and the data plane operation is managed by respective forwarding devices. SDN provides an easy and efficient management solutions for software‐programmed consolidated middlebox in virtual machines. Additionally, SDN with centralized controller faces complications like scalability, network bottle neck, and single point failure. In this study, a stateful inspection firewall acts as a middlebox in distributed SDN‐controlled network. The controller is programmed with a failure detection and recovery mechanism to provide reliability and redundancy and enhance the overall performance of the network. The objective of stateful firewall on SDN architecture is to secure the network by monitoring the current connections and maintain its state information until the connection is active. In this paper, the performance of firewall‐enabled SDN with centralized and distributed controllers are measured, compared, and analyzed. The experiments are done using POX controller, and the results are verified by Mininet network emulation tool. The results show that the stateful firewall‐enabled SDN with distributed controller network improves the security, reliability, availability, and overall performance of the network. In the proposed SDN, average network throughput is improved by 43%, average network delay is reduced by 4%, average channel utilization is increased by 40%, average network overhead is reduced by 26%, and average network response time is reduced by 23%.     

VNF-Consensus: A virtual network function for maintaining a consistent distributed software-defined network control plane

Software-defined networks (SDN) usually rely on a centralized controller, which has limited availability and scalability by definition. Although a solution is to employ a distributed control plane, the main issue with this approach is how to maintain the consistency among multiple controllers. Consistency should be achieved with as low impact on network performance as possible and should be transparent for controllers, without requiring any change of the SDN protocols. In this work, we propose VNF-Consensus, a virtual network function that implements Paxos to ensure strong consistency among controllers of a distributed control plane. In our solution, controllers can perform their control plane activities without having to execute the expensive tasks required to keep consistency. Experimental results are presented showing the cost and benefits of the proposed solution, in particular in terms of low controller overhead.