Distributed Dijkstra sparse placement routing algorithm for translucent optical networks

In this paper we study translucent optical networks as an alternative to fully transparent and fully opaque optical networks. In the former networks, a technique called sparse placement is used to overcome the lightpath blocking caused by the signal quality degradation, using much less regenerators, which must strategically be placed, in contrast to a fully opaque network. In this paper we propose a sparse placement algorithm based on two requirements. The first one is signal regeneration necessary to re-amplify, reshape, and retime the optical signals after some predefined transparent distance in order to successfully receive the signals at the destination node. The other is load balance of the traffic in the network aimed at efficient usage of the network capacity resources. We apply a distributed Dijkstra routing algorithm which dynamically changes weights of links during the process of locating regeneration capable nodes. We compare the performance of the proposed algorithm with commonly used sparse placement algorithms through simulation experiments. The benefits are such that load balancing of the network traffic is fully utilized, and with technological development it will be sufficient to equip up to 30% of nodes in the network with electronic regenerations in order to have the same performance as in an opaque network.

A New efficient dynamic MAC protocol for the delivery of multiple services over GPON

The Gigabit-capable passive optical network (GPON) has become an attractive and promising solution for the broadband access network. It is apparent that an efficient medium access control (MAC) protocol is crucial not only to catalyze the utilization of the upstream resources but also to support the GPON encapsulation method (GEM) for multiple services over GPON. A new approach for bandwidth reporting is developed to achieve dynamic awareness of both the changes of ONU queue status and the consequences of previous allocations. In addition, a novel balance transferring mechanism that enables a register and transfer process for successive allocation across multiple frames is presented. By incorporating the new schemes of bandwidth reporting process and the balance transferring mechanism into a frame-based scheduling procedure, an efficient dynamic bandwidth assignment MAC protocol is developed to support differentiated services over GPON. The performance of the new protocol is simulated and evaluated under a variety of traffic distributions. Simulated characteristics demonstrate a significantly improved network performance.

OSNR model to consider physical layer impairments in transparent optical networks

We propose a model that considers several physical impairments in all-optical networks based on optical signal-to-noise degradation. Our model considers the gain saturation effect and amplified spontaneous emission depletion in optical amplifiers, coherent crosstalk in optical switches, and four-wave mixing in transmission fibers. We apply our model to investigate the impact of different physical impairments on the performance of all-optical networks. The simulation results show the impact of each impairment on network performance in terms of blocking probability as a function of device parameters. We also apply the model as a metric for impairment-constraint routing in all-optical networks. We show that our proposed routing and wavelength assignment algorithm outperforms two common approaches.

Dynamic RWA with FWM-induced crosstalk awareness and modulation format conversion in wavelength-routed optical networks

The constraint of signal transmission quality and network resources utilization in transparent optical networks are herein addressed through a representative cost function based upon an impairment-constraint-base routing (ICBR) approach, taking into account link capacity utilization and the nonlinear physical effect, in the primary instance due to Four-Wave Mixing (FWM)-induced crosstalk. The FWM effect is considered one of the most severe physical impairments for the future photonic networks since the accumulation of FWM crosstalk may cause a fatal degradation in the teletraffic network performance. This paper presents an added functionality to the network model design based on all-optical modulation format conversion from conventional on-off keying (OOK) to quadrature phase-shift keying (QPSK) sending more data within the same bandwidth while minimizing the blocking probability. The joint effect of physical impairment (i.e., FWM-induced crosstalk) awareness and two different modulation formats is considered through numerical simulations. The proposed scheme is expected to realize an all-optical transparent interconnection between networks that employ diverse modulation formats. Results show that the proposed FWM-aware Routing and Wavelength Assignment (RWA) algorithm leads to a more realistic system performance while giving a significant improvement on the network performance.     

Autonomic failure prediction based on manifold learning for large-scale distributed systems

This article investigates autonomic failure prediction in large-scale distributed systems with nonlinear dimensionality reduction to automatically extract failure features.Most existing methods for failure prediction focus on building prediction models or heuristic rules by discovering failure patterns,but the process of feature extraction before failure patterns recognition is rarely considered due to the increasing complexity of modern distributed systems.In this work,a novel performance-centric approach to automate failure prediction is proposed based on manifold learning(ML).In addition,the ML algorithm named supervised locally linear embedding(SLLE)is applied to achieve feature extraction.To generalize the dimensionality reduction mapping,the nonlinear mapping approximation and optimization solution is also proposed.In experimental work a file transfer test bed with fault injection is developed which can gather multilevel performance metrics transparently.Based on the runtime monitoring of these metrics,the SLLE method can automatically predict more than 50% of the central processing unit(CPU)and memory failures,and around 70% of the network failure.     

静电危害及防护

为了避免静电在电子产品生产中的不良影响,在分析静电产生的原因及造成的危害的基础上,从导电体、绝缘体两个方面,有针对性地采取接地、静电屏蔽、离子中和等静电防护方法,有效地降低了电子产品的不良率及失效率,提高了电子部件质量。实践操作证明,静电对电子产品的损害可通过科学的操作方法、严格的管理制度消除。     

考虑储备期间失效的可修复备件需求模型

备件数量决定了装备维修能力和保障水平,能否科学地预测备件数量,取决于备件需求计算模型建立的准确性。在此根据备件维修性将备件分为可修复件和不可修复件,针对可修复件的备件需求问题,在考虑储备期间发生故障的前提下,利用备件可靠性框图方法,建立单可修复件、多可修复件的备件需求计算模型,解决了备件考虑储备期间故障的实际需求。结合工作环境的影响对模型中的故障率进行修正,使模型更贴近实际需求。     

水汽或结构对塑封电子器件可靠性的影响研究

传塑封装微电子器件在回流焊时的可靠性是微电子行业内最关心的问题之一。当一个具有不良可靠性的微电子器件通过红外回流焊接炉最终被焊接在印刷线路板上时,就会发生诸如裂纹、脱层、鼓胀等致命的缺陷。长期以来,＂水汽作用＂理论认为造成回流焊失效的原因是：处于潮湿环境中的封装材料-模制化合物从空气中吸收水汽,并且水汽沿着塑封体以及塑封体与引脚的界面向内扩散;当回流焊时在快速加热引起的热应力的作用下导致水汽膨胀而引起器件失效。于是回流焊前的预烘干就成为防止失效的重要手段。在多年的工作经历中遇到了＂预烘干＂也不能避免回流焊失效的一些生产案例,但是用＂结构强度＂的观点去改进结构的方法却十分有效。因此,认为＂水汽理论＂可能是人类认识上的一个＂误区＂,而决定传塑封装微电子器件回流焊可靠性的首要因素应是＂结构强度＂。     

高过载下军用电容的参数变化研究及失效分析

研究无线电引信中军用电容的高过载特性具有重要的意义,通过动态测试军用电容高过载下的特性,可以为系统地研究引信高过载特性提供可靠的依据。针对无线电引信中军用电容的工作环境,设计了军用电容在高过载条件下的动态测试试验方案并进行实验。最后,通过实验对高过载下军用电容的参数变化规律和失效模式进行了探讨,分析了电容参数变化及失效对引信的影响。     

基于知识推理的雷达装备故障预测专家系统

针对雷达装备常用的故障预测方法对故障检测人员和检测设备的依赖性大、要求高的弊端,建立了一个用于雷达装备故障预测的专家系统。论述了该系统的体系结构、系统功能、工作过程和结果的知识表示,实现了基于知识推理的雷达装备故障预测。