Optimizing survivability of multi-state systems with multi-level protection by multi-processor genetic algorithm

In this paper we consider vulnerable systems which can have different states corresponding to different combinations of available elements composing the system. Each state can be characterized by a performance rate, which is the quantitative measure of a system's ability to perform its task. Both the impact of external factors (stress) and internal causes (failures) affect system survivability, which is determined as probability of meeting a given demand.In order to increase the survivability of the system, a multi-level protection is applied to its subsystems. This means that a subsystem and its inner level of protection are in their turn protected by the protection of an outer level. This double-protected subsystem has its outer protection and so forth. In such systems, the protected subsystems can be destroyed only if all of the levels of their protection are destroyed. Each level of protection can be destroyed only if all of the outer levels of protection are destroyed.We formulate the problem of finding the structure of series–parallel multi-state system (including choice of system elements, choice of structure of multi-level protection and choice of protection methods) in order to achieve a desired level of system survivability by the minimal cost. An algorithm based on the universal generating function method is used for determination of the system survivability. A multi-processor version of genetic algorithm is used as optimization tool in order to solve the structure optimization problem. An application example is presented to illustrate the procedure presented in this paper.     

On surviving dual-link failures in path protected optical WDM mesh networks

In this paper, we investigate the problem of enhancing dual-failure restorability in path protected mesh-restorable optical Wavelength Division Multiplexed (WDM) networks. Recent studies have demonstrated the need to survive simultaneous dual-link failures and have also provided solutions for handling such failures. A key finding of these early efforts is that designs providing complete (i.e. 100%) protection from all dual-failures need almost triple the spare capacity compared to a system that protects against all single-link failures. However, it has also been shown that systems designed for 100% single-link failure protection can provide reasonable protection from dual-link failures [M. Clouqueur, W. Grover, Mesh-restorable networks with 74 enhanced dual-failure restorability properties, in: Proc. SPIE OPTICOMM, Boston, MA, 2002, pp. 1-12]. Thus, the motivation for this work is to develop a hybrid mechanism that provides maximum (close to 100%) dual-failure restorability with minimum additional spare capacity.The system architecture considered is circuit-switched with dynamic arrival of sessions requests. We propose an adaptive mechanism, which we term active protection, that builds upon a proactive path protection model (that provides complete single-failure restorability), and adds dynamic segment-based restoration to combat dual-link failures. The objective is to optimize network survivability to dual-link failures while minimizing additional spare capacity needs. We also propose a heuristic constraint-based routing algorithm, which we term best-fit, that aids backup multiplexing among additional spare paths towards this goal. Our findings indicate that the proposed active protection scheme achieves close to complete (100%) dual-failure restorability with only a maximum of 3% wavelength-links needing two backups, even at high loads. Moreover, at moderate to high loads, our scheme attains close to 16% improvement over the base model that provides complete single-failure restorability. Also, the best-fit routing algorithm is found to significantly assist backup multiplexing, with around 15%-20% improvement over first-fit at all loads. The segment-based restoration algorithm reiterates the importance of utilizing wavelength converters in protection and is seen to provide around 15%-20% improvement over link restoration especially at moderate to high loads.     

网络可生存性研究进展

网络可生存性研究是对传统的安全概念和技术的突破,已经成为网络安全研究的新方向。该文首先分析了可生存性与传统安全概念的差异,通过对网络可生存性研究现状的分析和概括,总结出了可生存性定义要素、测定标准、实现技术及相关研究的一些共识。然后对国外可生存性研究的主要进展——可生存系统分析方法SSA进行了深入探讨,并分析了网络可生存性研究的发展趋势,最后对实现可生存性的两种不同方法进行了对比分析。     

开放的复杂巨系统Internet可存活性需求分析框架

传统的安全概念已不适应今天开放环境下的复杂信息系统。随着现代社会对Internet依赖性的增加,计算机网络系统的可存括性的需求成为亟待解决的问题。该文分析了Internet可存活性的重要性,提出了可存活性的需求框架,并使用HWMSE作为测试和评估网络系统可存活能力的方法,为提高巨型计算机网络的可存活性提供了有效的解决途径。     

信息系统生存性仿真模型研究

生存性是信息系统的重要特性之一,它建立在安全性、可靠性、可重用性等相关研究领域之上。该文首先分析了信息网络的生存性特点,提出了能反映信息系统生存性要素的仿真推演模型：在生存性研究中必须同时考虑网络攻击事件和应急修复过程对信息系统的生存性的影响,并分别给出了相应的系统状态转移矩阵的计算方法。最后,提出了研究信息网络生存性仿真的主要流程,并认为对信息系统生存性仿真测试结果的分析是调整和提高信息系统生存性的重要依据。     

On the hop-constrained survivable network design problem with reliable edges

In this paper, we study the hop-constrained survivable network design problem with reliable edges. Given a graph with non-negative edge costs and node pairs Q, the hop-constrained survivable network design problem consists of constructing a minimum cost set of edges so that the induced subgraph contains at least K edge-disjoint paths containing at most L edges between each pair in Q. In addition, we consider here a subset of reliable edges that are not subject to failure. We study two variants: a static problem where the reliability of edges is given, and an upgrading problem where edges can be upgraded to the reliable status at a given cost. We adapt for the two variants an extended formulation proposed in Botton, Fortz, Gouveia, Poss (2011) [1] for the case without reliable edges. As before, we use Benders decomposition to accelerate the solving process. Our computational results indicate that these two variants appear to be more difficult to solve than the original problem (without reliable edges). We conclude with an economical analysis which evaluates the incentive of using reliable edges in the network.     

鼠李糖乳杆菌的抑菌及其在大豆奶酪中性质研究

本文研究了Lactobacillus rhamnosus 6013在MRS培养基中，37℃厌氧培养48h的培养上清液对金黄色葡萄球菌、枯草杆菌、沙门氏菌有良好的抑菌作用.然后使用大豆奶酪细菌DH1、GH4结合该菌加入到豆奶中，在一定条件下制成细菌型发酵大豆奶酪.在发酵6h后，Lactobacillus rhamnosus 6013的活菌细胞数达10^8-10^9CFU/ml.在成熟30天后，pH值有轻微下降，该菌存活细胞数达10^7CFU/g，而DH1、GH4的活菌数分别为10^6，10^6CFU/g.当盐水中NaCl溶液浓度为2-4% （m/v），对Lactobacillus rhamnosus 6013存活影响很小.根据行业标准 SB/T 10170-93，评价了此大豆奶酪的外观、色泽、滋气味和组织状态等四个指标.以上结果表明潜在益生菌Lactobacillus rhamnosus 6013能耐受大豆奶酪的加工过程，而对大豆奶酪的发酵和口感没有负面的影响。     

基于GMPLS的光网络保护和恢复机制

通用MPLS(GMPLS)是MPLS向光网络扩展的必然产物，它提供了网络拓扑和资源发现以及连接配制等基本的功能。本文提出了基于GMPLS的网络故障恢复机制，包括其实现过程以及相关的信令消息。     

Survivability Performance Evaluation of WDM Networks with Wavelength Converters

Network Survivability is defined as the ability of a network to support the committed Quality of Services (QoS) continuously in the presence of different failure scenarios. Both availability and performance degradation of a system in presence of failure are integral components of survivability evaluation. Therefore, a composite model is presented for network survivability that includes system availability analysis to find out the cost due to system downtime, and system failure impact analysis to find out the transient performance degradation when failure occurs. A new analytical technique is presented to evaluate the excess loss due to failure (ELF) as the transient performance degradation when the system is operating in gracefully degraded states. Single and multiple link failures as well as node failures are considered. An algorithm is proposed to carry out the steady state availability analysis of a network even when the available paths between a pair of nodes are non-disjoint. A recursive generalized form of the availability algorithm when there are multiple paths available between a pair of nodes is presented. The availability model and the performance model are combined to construct a hierarchical model to evaluate the network survivability performance. Simulation results are used to validate the proposed model. A WDM network with wavelength conversion is considered as an example for this evaluation.     

WDM光网络的保护和恢复技术

文章概述了IP、SDH和WDM层网络的生存性技术,重点介绍了光传送网的光层生存性技术与光网络恢复技术,还对故障定位、多层生存性机制的协调等问题进行了简单介绍,最后给出了一个业务配置RWA算法与恢复RWA算法的实际方案。