Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjuncti...Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjunction with the generalized Ohm＇s law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.展开更多
Software-defined networking(SDN) has received tremendous attention from both industry and academia.The centralized control plane in SDN has a global view of the network and can be used to provide more effective soluti...Software-defined networking(SDN) has received tremendous attention from both industry and academia.The centralized control plane in SDN has a global view of the network and can be used to provide more effective solutions for complex problems,such as traffic engineering.This study is motivated by recent advancement in SDN and increasing popularity of multicasting applications.We propose a technique to increase the resiliency of multicasting in SDN based on the subtree protection mechanism.Multicasting is a group communication technology,which uses the network infrastructure efficiently by sending the data only once from one or multiple sources to a group of receivers that share a common path.Multicasting applications,e.g.,live video streaming and video conferencing,become popular,but they are delay-sensitive applications.Failures in an ongoing multicast session can cause packet losses and delay,which can significantly affect quality of service(Qo S).In this study,we adapt a subtree-based technique to protect a multicast tree constructed for Open Flow switches in SDN.The proposed algorithm can detect link or node failures from a multicast tree and then determines which part of the multicast tree requires changes in the flow table to recover from the failure.With a centralized controller in SDN,the backup paths can be created much more effectively in comparison to the signaling approach used in traditional multiprotocol label switching(MPLS) networks for backup paths,which makes the subtree-based protection mechanism feasible.We also implement a prototype of the algorithm in the POX controller and measure its performance by emulating failures in different tree topologies in Mininet.展开更多
基金National Natural Science Foundation of China(No.10376003)
文摘Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjunction with the generalized Ohm＇s law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.
文摘Software-defined networking(SDN) has received tremendous attention from both industry and academia.The centralized control plane in SDN has a global view of the network and can be used to provide more effective solutions for complex problems,such as traffic engineering.This study is motivated by recent advancement in SDN and increasing popularity of multicasting applications.We propose a technique to increase the resiliency of multicasting in SDN based on the subtree protection mechanism.Multicasting is a group communication technology,which uses the network infrastructure efficiently by sending the data only once from one or multiple sources to a group of receivers that share a common path.Multicasting applications,e.g.,live video streaming and video conferencing,become popular,but they are delay-sensitive applications.Failures in an ongoing multicast session can cause packet losses and delay,which can significantly affect quality of service(Qo S).In this study,we adapt a subtree-based technique to protect a multicast tree constructed for Open Flow switches in SDN.The proposed algorithm can detect link or node failures from a multicast tree and then determines which part of the multicast tree requires changes in the flow table to recover from the failure.With a centralized controller in SDN,the backup paths can be created much more effectively in comparison to the signaling approach used in traditional multiprotocol label switching(MPLS) networks for backup paths,which makes the subtree-based protection mechanism feasible.We also implement a prototype of the algorithm in the POX controller and measure its performance by emulating failures in different tree topologies in Mininet.
