The growing trend of network virtualization results in a widespread adoption of virtual switches in virtualized environments. However, virtual switching is confronted with great performance challenges regarding packet...The growing trend of network virtualization results in a widespread adoption of virtual switches in virtualized environments. However, virtual switching is confronted with great performance challenges regarding packet classification especially in Open Flow-based software defined networks. This paper first takes an insight into packet classification in virtual Open Flow switching, and points out that its performance bottleneck is dominated by flow table traversals of multiple failed mask probing for each arrived packet. Then we are motivated to propose an efficient packet classification algorithm based on counting bloom filters. In particular, counting bloom filters are applied to predict the failures of flow table lookups with great possibilities, and bypass flow table traversals for failed mask probing. Finally, our proposed packet classification algorithm is evaluated with real network traffic traces by experiments. The experimental results indicate that our proposed algorithm outperforms the classical one in Open v Switch in terms of average search length, and contributes to promote virtual Open Flow switching performance.展开更多
This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these st...This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these strategies the inverter can realize secondary frequency regulation and voltage regulation. If the phase is near 0 or 2π a little disturbance may made the PLL output a big error, so a new PLL is proposed by this paper. A sine module is added in the PLL to avoid this error. In order to verify the strategy proposed by this paper a simulation model is built in Matlab/Simulink. The simulation results show that the control strategy can realize seamless switching.展开更多
This paper evaluates the performance of Internet Protocol Security (IPSec) based Multiprotocol Label Switching (MPLS) virtual private network (VPN) in a small to medium sized organization. The demand for security in d...This paper evaluates the performance of Internet Protocol Security (IPSec) based Multiprotocol Label Switching (MPLS) virtual private network (VPN) in a small to medium sized organization. The demand for security in data networks has been increasing owing to the high cyber attacks and potential risks associated with networks spread over distant geographical locations. The MPLS networks ride on the public network backbone that is porous and highly susceptible to attacks and so the need for reliable security mechanisms to be part of the deployment plan. The evaluation criteria concentrated on Voice over Internet Protocol (VoIP) and Video conferencing with keen interest in jitter, end to end delivery and general data flow. This study used both structured questionnaire and observation methods. The structured questionnaire was administered to a group of 70 VPN users in a company. This provided the study with precise responses. The observation method was used in data simulations using OPNET Version 14.5 Simulation software. The results show that the IPSec features increase the size of data packets by approximately 9.98% translating into approximately 90.02% effectiveness. The tests showed that the performance metrics are all well within the recommended standards. The IPSec Based MPLS Virtual private network is more stable and secure than one without IPSec.展开更多
随着网络技术的持续演进,为满足日益增长的通信需求,急需对油气自控网络进行升级。基于虚拟交换实例(Virtual Switching Instance,VSI)/虚拟扩展局域网(Virtual eXtensible Local Area Network,VXLAN)隧道通信技术,开展网际互连协议第4...随着网络技术的持续演进,为满足日益增长的通信需求,急需对油气自控网络进行升级。基于虚拟交换实例(Virtual Switching Instance,VSI)/虚拟扩展局域网(Virtual eXtensible Local Area Network,VXLAN)隧道通信技术,开展网际互连协议第4版/网际互连协议第6版(Internet Protocol Version 4/Internet Protocol Version 6,IPv6)双栈部署与效能评估相关研究。通过确立双栈架构的设计原则与目标,构建分层网络架构,实现VSI/VXLAN隧道与IPv4/IPv6双栈架构的深度融合,完成核心网络设备与接入层网络的双栈部署,并实施安全域划分。基于多维度效能评估指标体系,采集多测点、多负载条件下的性能数据,量化评估网络的安全防护能力。实验结果表明,该方案可显著提升油气自控网络在协议兼容性、传输效率与安全性方面的综合性能,为其数字化升级提供理论支撑与实践路径。展开更多
传统硬件倒闸教学方法老旧,实验设备不足,导致一些学生只重视理论学习,缺乏动手能力。在新工科背景下,利用虚拟现实技术提高教学质量,提高学生实践能力,培养高质量电力方面的人才至关重要。本文基于虚拟现实技术的特点和实际教学案例,...传统硬件倒闸教学方法老旧,实验设备不足,导致一些学生只重视理论学习,缺乏动手能力。在新工科背景下,利用虚拟现实技术提高教学质量,提高学生实践能力,培养高质量电力方面的人才至关重要。本文基于虚拟现实技术的特点和实际教学案例,提出虚拟现实技术介入实验课程的概念,并通过Visual Studio Code设计实现一种虚拟倒闸作业系统。该系统能够下发倒闸任务,使培训人员在虚拟环境下直观学习、熟悉、模拟倒闸操作过程,引导学生在虚拟环境中实操,并实时判断操作行为,可用于培养新工科背景下的高质量实践型人才。展开更多
基金supported in part by National Natural Science Foundation of China(61272148,61572525,61502056,and 61602525)Hunan Provincial Natural Science Foundation of China(2015JJ3010)Scientific Research Fund of Hunan Provincial Education Department(15B009,14C0285)
文摘The growing trend of network virtualization results in a widespread adoption of virtual switches in virtualized environments. However, virtual switching is confronted with great performance challenges regarding packet classification especially in Open Flow-based software defined networks. This paper first takes an insight into packet classification in virtual Open Flow switching, and points out that its performance bottleneck is dominated by flow table traversals of multiple failed mask probing for each arrived packet. Then we are motivated to propose an efficient packet classification algorithm based on counting bloom filters. In particular, counting bloom filters are applied to predict the failures of flow table lookups with great possibilities, and bypass flow table traversals for failed mask probing. Finally, our proposed packet classification algorithm is evaluated with real network traffic traces by experiments. The experimental results indicate that our proposed algorithm outperforms the classical one in Open v Switch in terms of average search length, and contributes to promote virtual Open Flow switching performance.
文摘This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these strategies the inverter can realize secondary frequency regulation and voltage regulation. If the phase is near 0 or 2π a little disturbance may made the PLL output a big error, so a new PLL is proposed by this paper. A sine module is added in the PLL to avoid this error. In order to verify the strategy proposed by this paper a simulation model is built in Matlab/Simulink. The simulation results show that the control strategy can realize seamless switching.
文摘This paper evaluates the performance of Internet Protocol Security (IPSec) based Multiprotocol Label Switching (MPLS) virtual private network (VPN) in a small to medium sized organization. The demand for security in data networks has been increasing owing to the high cyber attacks and potential risks associated with networks spread over distant geographical locations. The MPLS networks ride on the public network backbone that is porous and highly susceptible to attacks and so the need for reliable security mechanisms to be part of the deployment plan. The evaluation criteria concentrated on Voice over Internet Protocol (VoIP) and Video conferencing with keen interest in jitter, end to end delivery and general data flow. This study used both structured questionnaire and observation methods. The structured questionnaire was administered to a group of 70 VPN users in a company. This provided the study with precise responses. The observation method was used in data simulations using OPNET Version 14.5 Simulation software. The results show that the IPSec features increase the size of data packets by approximately 9.98% translating into approximately 90.02% effectiveness. The tests showed that the performance metrics are all well within the recommended standards. The IPSec Based MPLS Virtual private network is more stable and secure than one without IPSec.
文摘随着网络技术的持续演进,为满足日益增长的通信需求,急需对油气自控网络进行升级。基于虚拟交换实例(Virtual Switching Instance,VSI)/虚拟扩展局域网(Virtual eXtensible Local Area Network,VXLAN)隧道通信技术,开展网际互连协议第4版/网际互连协议第6版(Internet Protocol Version 4/Internet Protocol Version 6,IPv6)双栈部署与效能评估相关研究。通过确立双栈架构的设计原则与目标,构建分层网络架构,实现VSI/VXLAN隧道与IPv4/IPv6双栈架构的深度融合,完成核心网络设备与接入层网络的双栈部署,并实施安全域划分。基于多维度效能评估指标体系,采集多测点、多负载条件下的性能数据,量化评估网络的安全防护能力。实验结果表明,该方案可显著提升油气自控网络在协议兼容性、传输效率与安全性方面的综合性能,为其数字化升级提供理论支撑与实践路径。
文摘传统硬件倒闸教学方法老旧,实验设备不足,导致一些学生只重视理论学习,缺乏动手能力。在新工科背景下,利用虚拟现实技术提高教学质量,提高学生实践能力,培养高质量电力方面的人才至关重要。本文基于虚拟现实技术的特点和实际教学案例,提出虚拟现实技术介入实验课程的概念,并通过Visual Studio Code设计实现一种虚拟倒闸作业系统。该系统能够下发倒闸任务,使培训人员在虚拟环境下直观学习、熟悉、模拟倒闸操作过程,引导学生在虚拟环境中实操,并实时判断操作行为,可用于培养新工科背景下的高质量实践型人才。
