Wenhai Wang

A new fault detection method for computer networks

Over the past few years, fault detection for computer networks has attracted extensive attentions for its importance in network management. Most existing fault detection methods are based on active probing techniques which can detect the occurrence of faults fast and precisely. But these methods suffer from the limitation of traffic overhead, especially in large scale networks. To relieve traffic overhead induced by active probing based methods, a new fault detection method, whose key is to divide the detection process into multiple stages, is proposed in this paper. During each stage, only a small region of the network is detected by using a small set of probes. Meanwhile, it also ensures that the entire network can be covered after multiple detection stages. This method can guarantee that the traffic used by probes during each detection stage is small sufficiently so that the network can operate without severe disturbance from probes. Several simulation results verify the effectiveness of the proposed method.

Performance Degradation Monitoring for Onboard Speed Sensors of Trains

Photoelectric speed sensors (PSSs), which are used for velocity measuring and positioning, are key components of train control systems. In real applications, the performance of PSSs may degrade, such as the decrease in the number of the output pulses, which is caused by the existence of jammed code tracks on the shading plates of PSSs. Considering this kind of performance degradation, this paper proposes an online performance-degradation-monitoring approach that can detect the existence of the jammed code tracks and estimate the number of them. Based on the results from the performance-degradation-monitoring approach, this paper also provides a compensation algorithm for the distorted speed readings resulting from the existence of the performance degradation. The results from the mathematical analysis and numerical examples verify the effectiveness of the proposed performance-degradation-monitoring approach for PSSs.

Remaining useful life prediction for non-stationary degradation processes with shocks

Predict the remaining useful life of devices in real time is important to maintenance management. This article addresses a remaining useful life predictive problem where the considered device suffers from non-stationary degradation with shocks. A novel degradation-shock system model subjected to a hidden degradation state is proposed to characterize the degradation process. To estimate the hidden system state, the Kalman filter is modified with optimal estimation. Then, based on Bayes’ theorem, a recursive algorithm is presented to estimate the unknown parameters of the model. With the proposed approach, the hidden state and unknown parameters can be updated at each sampling instant. Subsequently, the analytical solution for the remaining useful life is obtained, while the characteristics of the shocks as well as the uncertainties of the estimated system state are taken into account. Furthermore, the effectiveness of the proposed model is verified by a numerical simulation and a practical case study on a milling machine.

Data Transmission Reliability of a Two-source Single-sink Computer Network with a Common Arc

Abstract In a multi-state network (MSN), data can be transmitted through different paths. The previous literatures focus on the cases with arc-disjoint paths, but not the cases in which the paths have a common arc. In this work, we consider the case that two source nodes are sending data to the sink node through their own minimal paths (MP), where these two MPs possess a common arc in the computer network. Each source node generates a data sequence. The time intervals of the generated data are randomly distributed. Also, the amount of the data generated in different time instants are randomly distributed. These two variables can be obtained by the Monte-Carlo simulation method. As all the data are transmitted through a common arc, the data need to compete for the priority using the arc and conflictions may be caused. We consider the case that the two MPs are in connection and calculate the reliabilities of the data under their transmission time constraints. Simulation results reveal that the conflictions could prolong their transmission time and thus affect their reliabilities. This work may provide a cross-reference for managers to decide the amount of the data and the time intervals to get the ideal network reliabilities.

A New Rate-Based Active Queue Management Scheme over Wired-cum-Wireless Networks

With the development of wireless communication technologies, future networks will most likely be heterogeneous, consist of both wired and wireless links. However, current active queue management (AQM) schemes, which are originally designed for wired networks, could cause performance degradation of Transmission Control Protocol (TCP) flows over wired-cum-wireless networks. Thus, to deal with these problems, we propose a new rate-based AQM scheme (NRAQM). NRAQM scheme uses a new marking/dropping module and a timer updating module for packets dropping/marking and dropping/marking probability updating, which are different from other existing AQM schemes. The objectives of our proposed scheme are to stabilize networks with low end-to-end delay, and high link utilization regardless the dynamics of wired-cum-wireless networks conditions. Simulation results show that our proposed scheme outperforms the existing AQM schemes over wired-cum-wireless networks.