Disaster-aware service provisioning with manycasting in cloud networks

Cloud services delivered by high-capacity optical datacenter networks are subject to disasters which may cause large-area failures, leading to huge data loss. Survivable service provisioning is crucial to minimize the effects of network/datacenter failures and maintain critical services in case of a disaster. We propose a novel disaster-aware service-provisioning scheme that multiplexes service over multiple paths destined to multiple servers/datacenters with manycasting. Our scheme maintains some bandwidth (i.e., degraded service) after a disaster failure vs. no service at all. We formulate this problem into a mathematical model which turns out to be an Integer Linear Program (ILP), and we provide heuristic optimization approaches as ILP is intractable for large problem instances. Numerical examples show that exploiting manycasting by intelligently selecting destinations in a risk-aware manner for service provisioning offers high level of survivability against link and node failures that may be caused by disasters and post-disaster failures at no extra cost compared to the other survivable schemes.     

基于灾难预测多区域故障的虚拟光网络生存性映射

生存性虚拟光网络映射是提高光网络应对灾难故障的重要技术保障措施。为解决灾难性多区域故障导致弹性光网络的带宽容量损失问题,该文提出基于灾难预测故障模型的蚁群优化虚拟光网络映射 (DFM-ACO-VNM)算法。在该算法中,设计基于光节点资源和相邻链路的全局潜在故障概率的光节点排序映射准则,并设计启发式信息公式实现多区域故障下最小带宽容量损失的虚拟节点和虚拟链路协同映射。仿真结果表明,该文所提算法在多区域故障时能降低带宽容量损失,减少带宽阻塞率和提高频谱利用率。     

面向多节点故障的生存性虚拟网络映射方法

针对网络虚拟化环境中虚拟网络的生存性问题,提出一种面向多节点故障的生存性虚拟网络映射方法。该方法预先在物理网络中按比例留出备份资源并根据拓扑属性构造节点的候选集合,在发生节点故障后从故障节点的候选集合中选取重映射目标并动态分配预留的备用资源来恢复受到影响的虚拟网络,提高长期运营利润。仿真实验在多节点故障模型下从适用性、稳定性及性能方面验证了该方法的有效性。     

应对灾难风险的多虚拟机快速协同撤离机制研究

大规模灾难事件可能对通信网基础设施造成严重的威胁和破坏。针对大规模灾难风险下虚拟网的生存性问题,该文提出一种多虚拟机快速协同撤离(MRCE)机制。该机制采用后复制迁移技术实现虚拟机的在线迁移,通过基础迁移带宽的分配和升级,对属于同一虚拟网的多个风险虚拟机进行快速协同撤离,以减少单个虚拟网的撤离完成时长,降低损毁风险。仿真结果表明,该机制能在不同考察周期内获得较好的虚拟网撤离完成率和平均撤离完成时长。     

Dynamic recovery for survivable virtual network embedding

Network virtualization is a promising way to overcome the current ossification of the Intemet. It is essential challenge to find effective, efficient and robust embedding algorithms for recovering virtual network. The virtual network mapping algorithm based on integer programming which was proposed months ago. But it did consider the faults of physical network resources, which is so called survivable virtual network embedding （VNE） problem. Previous strategies for enabling survivability in network virtualization focused on providing protection for the physical network or enhancing the virtual networks by providing backup physical resources in advance, and treated all the physical failures as link failures. In the article, a dynamic recovery method is proposed to solve the survivable virtual network embedding problem based on the integer programming VNE algorithm. The dynamic recovery method doesn＇t need to backup physical resources and it makes more substrate resources which can be used in the embedding. The dynamic recovery process will be activated only when physical failures occur. Different algorithms are used to recovery node and link failures. Simulations show that the method helps to recover almost all of physical failures by finding the substitute nodes and paths, and its performance is very close to that of pure VNE method without considering physical failures.     

SDH/ATM双向自愈环的生存性定量分析方法

本文推导出了ＳＤＨ／ＡＴＭ双向自愈环在链路失效、节点失效及链球节点混合失效、节点失效及链路节点混合失效三种模型情况下的网络生存性函数,从导出的网络生存性函数可以方便地求出生存率的均值、最坏生存率、ｒ百分比生存率及零生存率等单个生存性测度。同时对导出的生存性函数结果进行了分析,结果表明本文的分析方法符合实际情况,是切实可行的,为分析和设计高生存性通信网络提出了统一的实现的方法。     

Restoration strategies for future networks

The prospect of broadband telecommunication networks loaded with massive quantities of information due to the wide range of services being supported stimulates extra concern for network survivability. As the effect of span or node failures could be drastic, rapid restoration strategies are imperative. This paper describes restoration techniques involving the control of digital crossconnect systems, and the exploitation of spare capacity which has been economically planned into the network. This represents a more extensive approach to survivability than straightforward protection switching, thus improving network reliability     

虚拟网络可生存的启发式可靠映射算法

针对虚拟网络可靠映射问题,引入虚拟网络可生存约束条件,确保在底层网络单节点失效情况下,被映射虚拟网络剩余部分仍保持连通,最大程度确保虚拟网络的完整性和服务的连续性。以最小化底层网络映射开销为目标函数,建立虚拟网络可靠映射的整数线性规划模型,提出一种虚拟网络可生存的启发式可靠映射算法RHM-SVN并进行求解。实验结果表明,该算法能够有效降低资源平均利用率,提高映射成功率、底层网络平均收益和虚拟网络恢复成功率。     

A framework for characterizing disaster-based network survivability

This paper formulates a general framework that includes and extends the existing definitions for network survivability. Based on this framework, network survivability is characterized by a survivability function rather than a single-value survivability measure, and various quantities of interest can be derived from the function. Examples are the expected survivability, the worst-case survivability, the r-percentile survivability, and the probability of zero survivability. The survivability function is especially useful for the study of large-scale disasters. For illustration, the authors derive the survivability function in closed form for a simple ring network under link failures. They also discuss the general procedure for finding survivability functions for complex networks, and show that the survivability function reveals useful information about a network. This framework provides a unified and practical approach to analyzing and designing highly survivable communications networks     

Backup reprovisioning with partial protection for disaster-survivable software-defined optical networks

As networks grow in size, large-scale failures caused by disasters may lead to huge data loss, especially in an optical network employing wavelength-division multiplexing (WDM). Providing 100 % protection against disasters would require massive and economically unsustainable bandwidth overprovisioning, as disasters are difficult to predict, statistically rare, and may create large-scale failures. Backup reprovisioning schemes are proposed to remedy this problem, but in case of a large-scale disaster, even the flexibility provided by backup reprovisioning may not be enough, given the sudden reduction in available network resource, i.e., resource crunch. To mitigate the adverse effects of resource crunch, an effective resource reallocation is possible by exploiting service heterogeneity, specifically degraded-service tolerance, which makes it possible to provide some level of service, e.g., reduced capacity, to connections that can tolerate degraded service, versus no service at all. Software-Defined Networking (SDN) is a promising approach to perform such dynamic changes (redistribution of network resources) as it simplifies network management via centralized control logic. By exploiting these new opportunities, we propose a Backup Reprovisioning with Partial Protection (BRPP) scheme supporting dedicated-path protection, where backup resources are reserved but not provisioned (as in shared-path protection), such that the amount of bandwidth reserved for backups as well as their routings are subject to dynamic changes, given the network state, to increase utilization. The performance of the proposed scheme is evaluated by means of SDN emulation using Mininet environment and OpenDaylight as the controller.     

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.     

SDH自愈环生存性定量分析

本文首先提出了网络生存性指标的概念,并对基于SDH自愈环拓扑结构的网络在灾害条件下的网络生存性进行了定量研究.文中分析了不同的业务分布条件对网络生存性指标的影响,以及灾害强度和网络生存性的关系.     

一种高生存性的光接入网结构

提出了一种新的双环加星型环的高生存性光接入网拓扑结构,并和现行各种光接入网拓扑结构的生存性进行了定量比较.在多故障情况下,具有比现行各种光接入网结构更高的生存率.随着故障数目的增加,其网络生存率均值下降缓慢,当故障数为6时,依然可以保持99.997%的高生存率均值,大大好于现行光接入网结构,说明该接入网结构能更好地满足用户对下一代光接入网生存性的要求.     

Providing fault tolerance in wireless access networks

Research and development on network survivability has largely focused on public switched telecommunications networks and high-speed data networks with little attention on the survivability of wireless access networks supporting cellular and PCS communications. This article discusses the effects of failures and survivability issues in PCS networks with emphasis on the unique difficulties presented by user mobility and the wireless channel environment. A simulation model to study a variety of failure scenarios on a PCS network is described, and the results show that user mobility significantly worsens network performance after failures, as disconnected users move among adjacent cells and attempt to reconnect to the network. Thus, survivability strategies must be designed to contend with spatial as well as temporal network behavior. A multilayer framework for the study of PCS network survivability is presented. Metrics for quantifying network survivability are identified at each layer. Possible survivability strategies and restoration techniques for each layer in the framework are also discussed     

Using distributed topology update and preplanned configurations toachieve trunk network survivability

The authors present a new approach for trunk network survivability. This modular approach is intended for a telephone trunk network consisting of high-bandwidth fiber-optic links connected through reconfigurable digital cross-connect nodes. It works for both node and link failures. This approach comprises a distributed protocol with two parts. First, the surviving digital cross-connect nodes are caused to converge to an agreement on the topology (i.e., what is up and what is down). Second, based on the agreed topology and on a precomputed plan for that topology, the digital cross-connect nodes are reconfigured to restore as much call-carrying capacity as possible. The modularity of this approach comes from separating the problem of devising a distributed fault-tolerant protocol to determine what the failure is from the problem of designing a network reconfiguration for that failure     

A novel multi-link fault-tolerant algorithm for survivability in multi-domain optical networks

With the large-scale deployment of optical network equipments, the problems of separated domains management and the multi-domain-based survivability have become the primary challenge in new generation intelligent optical networks. Aimed at resisting multi-link failures in multi-domain optical networks (MDON), a heuristic multi-link fault-tolerant (MLFT) algorithm for survivability in MDON is proposed in this article, which applied Hamiltonian cycle protection and segment-shared protection to establish a novel survivability strategy for either intra-domain??s or inter-domain??s multiple links, respectively. Furthermore, a new virtual-link mapping scheme and link-cost formulas are presented to encourage the appropriate routing selection and load balancing, which can also contributed to better resource utilization ratio and blocking ratio. Simulation results show that MLFT realizes the multi-link fault-tolerant survivability at a lower cost with better performances in redundancy ratio, blocking ratio, and computation complexity.     

Designing reliable communication networks in a planned failure environment

A very important issue in many network applications is to provide protection against planned failures. In this paper we first define the concept of a planned failure and then analyze the cost implications in the design of a network for survivability (i.e. protection against planned failure), as against designing a network against random failures. We suggest a simple and systematic approach for designing survivable communication networks and also discuss briefly the consequences of availability of partial knowledge only.     

Physical impairments awareness based virtual network mapping strategy of elastic optical networks

As virtual networks services emerge increasingly with higher requirement of flexibility and robust, great complex challenges caused by physical-layer impairments are presented to the elastic optical networks(EON). Aimed to solve this problem, this paper proposes a physical impairment awareness based virtual network mapping stragegy of EON. The physical impairments awareness model is established, including both of linear factors and nonlinear ones. On this basis, this paper proposes a virtual network mapping strategy with detailed procedures, combined with node importance factors during the virtual network mapping procedure. Test results show that the proposed approach is able to reduce blocking rate and enhance services supporting ability of EON.     

光网络选路和波长分配研究

文章在叙述了光网络中选路和波长分配(RWA)要解决的基本问题后,对有关方面的近年研究作了综述,主要包括:虚拓扑重构、业务量疏导的RWA、多播RWA、抗毁网络的RWA.抗毁问题涉及WDM网络的抗毁选路、区分可靠性、网状网的快速恢复、多故障下的抗毁.     

Loopback recovery from double-link failures in optical mesh networks

Network survivability is a crucial requirement in high-speed optical networks. Typical approaches of providing survivability have considered the failure of a single component such as a link or a node. We motivate the need for considering double-link failures and present three loopback methods for handling such failures. In the first two methods, two edge-disjoint backup paths are computed for each link for rerouting traffic when a pair of links fails. These methods require the identification of the failed links before recovery can be completed. The third method requires the precomputation of a single backup path and does not require link identification before recovery. An algorithm that precomputes backup paths for links in order to tolerate double-link failures is then presented. Numerical results comparing the performance of our algorithm with other approaches suggest that it is possible to achieve almost 100% recovery from double-link failures with a moderate increase in backup capacity. A remarkable feature of our approach is that it is possible to trade off capacity for restorability by choosing a subset of double-link failures and designing backup paths using our algorithm for only those failure scenarios.