傅里叶变换用于地下电缆故障检测(英文)

An analysis of underground power cables is performed using Fourier analysis with the objective of detecting fault and average life of the cables.Three types of cables are used in this experiment:a normal cable,a shorted cable, and a cable with holes.The impedance in each case is computed and Fourier transformation is applied so that the resulting impedance magnitude and impedance phase can be examined in the frequency domain.Various windowing techniques are applied to the experimental data to eliminate any interference.Fourier analysis is then applied to the impedance data calculated from both the sending end voltage and differential voltage.This analysis reveals differences in the frequency response of the three different types of a cable and can eventually be used as a measure for fault detection. Preliminary results reveal the differences in the frequency response.Accordingly,Fourier type methods can be effectively used as low cost and viable solutions to identify and detect faults in underground cables.

A subtree-based approach to failure detection and protection for multicast in SDN

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.