面向IP快速路径切换的OSPF冗余路径算法

在IP网络中,当某链路或者节点发生故障时,通过路由协议的收敛来绕开故障的链路或节点.对OSPF路由协议,这个时间至少为5秒,期间经过故障节点或链路的流量将会被丢弃,绝大多数的应用可以承受这种程度的延迟.但是,对延迟敏感的应用如VoIP而言,这种量级的延迟是很难为用户所接受的.基于现有的OSPF路由协议的最短路径树(SPT)算法,提出一种支持IP快速重路由的多冗余路径树计算算法.算法计算除最短路径外至少一条不相交无环备份路径,保证在最短路径的链路或节点故障时,通过快速切换到备份路径,以提高IP网络的故障收敛时间.     

基于SLA双链路负载分担与智能切换的链路安全仿真分析

为了解决实际工作中双链路间的互联互通问题,通信运营商之间新一轮的竞争逐渐由技术转向服务,由此服务提供商和消费者双方协商的服务等级协议SLA(Service Level Agreement,服务等级协议)受到越来越多人的关注,并且已经开始运用到各种场景,保证出口链路的高可用性和访问效率。SLA要发挥更大的作用,还需要进一步的研究和提高,结合多链路负载分担技术,比如电信和联通双链路双向流量按照预设的算法分担到不同的链路上,一旦某一条链路出现故障,能够智能切换到另一条可用链路上。这样便实现了链路负载分担和智能切换,从电信来的流量走电信线路回去,从联通来的流量走联通线路回去,当其中一条链路出现故障时,所有的流量从没有出现故障的线路走。     

基于自然连接度的无标度网络断边重连仿真

针对传统网络断边重连技术不能准确确定无标度网络故障位置,造成断边链路数据重构性能较差的问题,提出基于自然连接度的无标度网络下断边重连技术。将DeviceNet作为核心触发协议、CAN协议作为底层通信协议,构造Dramp流量控制策略;修正逻辑点带宽,捕获自然连接错误帧事件;在无标度网络链路两端建立源观测点,整合错误事件并去除掉观测位置信息,根据时间节点提取多维度源节点数据,完成关联故障定位,最后根据链路重构法及DNS域名解析,以链路负载为核心,重构传输链路完成断边重连。仿真结果表明,所提方法能够准确标定无标度网络故障位置,有效重连无标度断边网络。     

单向链路故障检测的研究

UDLD(UniDirectional Link Detection,单向链路检测)是一个Cisco私有的二层协议,用于监听利用光纤或双绞线连接的以太链路的物理配置,检测以太网交换机之间的单向链路故障,防止生成树引起的回环问题的发生。UDLD通过周期性地向对端端口发送UDLD报文,并接收解析对端端口发送的UDLD报文来进行单向链路的检测。UDLD需要链路两端设备都支持才能正常运行。当检测到单向链路故障时,UDLD会关闭相应接口并发送警告信息。     

多链路保接入无障碍——兆维推出CW-MLB系列产品

据统计,全球有1/4的企业遇到过接入线路故障的问题,平均总的故障时间是8小时,有24%的企业总的故障时间超过24小时。单链路接入方式暴露了更多的不足与缺陷,为了保证工作不受单一接入链路的影响,越来越多的企业开始考虑多链路负载均衡的可能性,为企业工作顺利地进行提供更良好的保障。所谓多链路负载均衡即是同时将多条接入线路(比如一条接ADSL,一条接专线)的带宽均衡分配给内网用户使用,从而达到解决比如一条链路出现问题,无法自动转到其他链路上;无法同时使用多条链路,并在一条链路流量大时自动分配其余流量到其他的链路上等等问题。五月…     

一种新型的多出口路由设计与实现

提出一种在多出口校园网环境下,如何解决出口瓶颈、流量负载均衡和对外设备访问的设计方案,方案基于HSRP、IP SLAs协议配合策略路由、地址翻译及智能DNS技术,充分发挥了CERNET和本地ISP的网络资源优势,实现了链路故障和拥塞时自动切换,提高了访问速度和链路的使用效率.     

基于粒子群权值优化的网络可生存性增强方法

针对网络中发生频率最高的单链路瞬时故障,提出了一种应用粒子群算法优化链路权值来增强网络可生存性的方法。引入费用函数对利用率过高的链路赋以惩罚性的高费用来避免链路过载,以网络在无故障场景下最高链路费用与单链路故障场景下最高链路费用的加权和作为目标函数,建立了优化算法模型,并应用粒子群优化算法求解最优权值。实验结果表明,算法求得的权值可以使网络在故障条件下保持较低的链路利用率,避免了因流量转移而造成网络拥塞,增强了网络可生存性。     

探讨在路由器上配置OSPF路由协议

主要介绍链路状态路由协议的相关基本内容,并在Cisco路由器上配置链路状态路由协议OSPF。     

三维水声传感器网络中多径容错路由协议研究

针对三维水声传感器网络中因节点或链路故障导致的路由性能低下问题,提出一种多径容错路由协议。该协议通过为每个节点设计一种称为后备箱的数据结构,并利用节点的路由表和后备箱构造主后备链路和辅后备链路,以便在节点或链路发生故障的情况下修复路由路径,确保数据的正常传输。仿真结果表明,多径容错路由协议可以减小节点或链路故障对数据传输率和网络吞吐量的影响。     

基于ENSP的生成树协议原理仿真实验

生成树协议是二层网络设备重要的协议之一,但其工作过程较为抽象,在学习中很难领会其核心。文章从生成树的工作原理出发,用工程案例为引导,设计实验步骤,给出实验拓扑结构。利用ENSP软件仿真搭建实验环境,给出配置过程、配置命令,并进行数据流抓包分析验证。实践证明,学生通过该实验的学习,可以更好的理解二层交换网络生成树协议的功能,并高效地完成数据冗余链路配置及流量负载均衡。该仿真实验方法在通信网络实践课程教学中取得了较好的效果。     

相依网络中负载全局分配的级联故障模型

针对目前不同网络耦合成相依网络的研究不考虑相依边和负载的共同影响,提出一种同时考虑相依边和负载的相依网络级联故障模型。在级联故障中区分连接边和相依边对相依网络的不同作用,负载分配采用基于最短路径长度的可变负载全局分配原则,正常节点分配到的额外负载与距离故障节点的距离成反比关系,相依网络的子网选用IEEE118标准电网、小世界网络和随机图网络。相依网络的仿真结果表明,负载全局分配效应越小,网络抵制故障能力越强,负载故障对级联故障的贡献程度越小,不同耦合网络在特定的容忍系数下取得不同的平均故障迭代步数峰值;而负载全局分配效应较大时,网络崩溃或近似崩溃,平均故障迭代步数与容忍系数呈现近似单调递增关系。     

Using Network Fault Predictions to Enable IP Traffic Management

IP traffic management is important for the continued growth of the Internet. Several traffic management algorithms exist today. However, to enable these algorithms it is necessary to provide reliable alarms relating to network performance bottlenecks and failures. In this work we propose an algorithm to obtain reliable predictive alarms for network fault conditions. The algorithm is based on modeling network fault behavior. The algorithm has been successfully tested on two production networks. Predictive alarms were obtained for four different types of failures: file server failures, network access problems, protocol implementation errors, and runaway processes. The potential of using this model to do fault classification is also discussed. In addition, it is shown that the proposed algorithm performs better than the majority-vote scheme.     

Repairing multiple failures adaptively with erasure codes in distributed storage systems

Repairs of multiple failures in distributed storage systems have posed the challenges for erasure coding: how to minimize the repair time with the least extra repair network traffic cost. However, existing repair schemes designed for single failure suffer from the high network traffic cost due to the serial repairs for multiple failures. Repair schemes designed for multiple failures suffer from long repair time due to the centralized repair structure. In this paper, we propose a decentralized adaptive repair scheme, called DARS, to minimize the repair time with the least extra network traffic cost. Specially, we propose a three‐layer repair model to support the repairs for both the single and multiple failures. For low repair time, a bandwidth‐aware node selection technique is proposed to guide the selection of nodes, and a line‐structured data transmission technique is proposed to organize the data transmission between the providers and the newcomer. For the least extra network traffic cost, a core‐based data distribution technique is proposed to organize the data transmission between the coordinator and other newcomers, and an intersection provider adjustment technique is proposed to adaptively adjust the number of intersection providers. Moreover, we adopt the ‘lazy repair’ within a stripe to further reduce the repair network traffic cost. We implement and evaluate DARS on our raid distributed storage system under various parameter settings with 30 physical machines and 200 virtual machines. Experimental results confirm that DARS reduces the repair time by 29% and 55% on average compared with tree‐structured repair and CORE, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

具有通信约束的网络化控制系统容错控制研究

Implementing a control system over a communication network induces inevitable time delays that may degrade performance and even cause instability. One of the most effective ways to reduce the negative effect of delays on the performance of networked control system (NCS) is to reduce network traffic. In this paper, adjustable deadbands are explored as a solution to reduce network traffic in NCS. A method of fault-tolerant control of networked control system is presented, which takes into account system response as well as network traffic. The integrity design for a kind of NCS with sensor failures and actuator failures is analyzed based on robust fault-tolerant control theory and information scheduling. After detailed theoretical analysis, the paper also provides the simulation results, which further validate the proposed scheme.     

A Closed-Loop Control Traffic Engineering System for the Dynamic Load Balancing of Inter-AS Traffic

Inter-AS outbound traffic engineering (TE) is a set of techniques for controlling inter-AS traffic exiting an autonomous system (AS) by assigning the traffic to the best egress points (i.e. routers or links) from which the traffic is forwarded to adjacent ASes towards the destinations. In practice, changing network conditions such as inter-AS traffic demand variation, link failures and inter-AS routing changes occur dynamically. These changes can make fixed outbound TE solutions inadequate and may subsequently cause inter-AS links to become congested. In order to overcome this problem, we propose the deployment of a closed-loop control traffic engineering system that makes outbound traffic robust to inter-AS link failures and adaptive to changing network conditions. The objective is to keep the inter-AS link utilization balanced under unexpected events while reducing service disruptions and reconfiguration overheads. Our evaluation results show that the proposed system can successfully achieve better load balancing with less service disruption and re-configuration overhead in comparison to alternative approaches.     

Adaptive Pinning Synchronization of Complex Networks with Negative Weights and Its Application in Traffic Road Network

International Journal of Control, Automation and Systems - As local traffic congestion and uncertainty factors existing on roads may lead to cascading failures or even large area traffic network...     

The robustness of stability under link and node failures

In the area of communication systems, stability refers to the property of keeping the amount of traffic in the system always bounded over time. Different communication system models have been proposed in order to capture the unpredictable behavior of some users and applications. Among those proposed models the adversarial queueing theory (aqt) model turned out to be the most adequate to analyze an unpredictable network. Until now, most of the research done in this field did not consider the possibility of the adversary producing failures on the network structure. The adversarial models proposed in this work incorporate the possibility of dealing with node and link failures provoked by the adversary. Such failures produce temporal disruptions of the connectivity of the system and increase the collisions of packets in the intermediate hosts of the network, and thus the average traffic load. Under such a scenario, the network is required to be equipped with some mechanism for dealing with those collisions.In addition to proposing adversarial models for faulty systems we study the relation between the robustness of the stability of the system and the management of the queues affected by the failures. When the adversary produces link or node failures the queues associated to the corresponding links can be affected in many different ways depending on whether they can receive or serve packets, or rather that they cannot. In most of the cases, protocols and networks containing very simple topologies, which were known to be universally stable in the aqt model, turn out to be unstable under some of the newly proposed adversarial models. This shows that universal stability of networks is not a robust property in the presence of failures.     

Fast reroute from single link and single node failures for IP multicast

The rise in multicast implementations has seen with it an increased support for fast failure recovery from link and node failures. Most recovery mechanisms augment additional services to existing protocols causing excessive overhead, and these modifications are predominantly protocol-specific. In this paper, we develop a multicast failure recovery mechanism that constructs protocol independent fast reroute paths to recover from single link and single node failures. We observe that single link failure recovery in multicast networks is similar to recovering unicast traffic, and we use existing unicast recovery mechanisms for multicast traffic. We construct multicast protection trees that provide instantaneous failure recovery from single node failures. For a given node x, the multicast protection tree spans all its neighbors and does not include itself. Thus, when the node fails, the neighbors of the node are connected through the multicast protection tree instead of node x, and forward the traffic over the multicast protection tree for the duration of failure recovery. The multicast protection trees are constructed a priori, without the knowledge of the multicast traffic in the network. Based on simulations on three realistic network topologies, we observe that the multicast protection trees increase the routing table size only by 38% on average and the path length between any source–destination pair by 13% on average.     

IP/WDM网络的跨层控制系统设计

针对现有IP/WDM网络中IP层与光层在网络恢复阶段的协同控制问题,设计一种基于认知的跨层控制系统。该系统采用叠加网络技术,引入跨层协同机制,完成业务恢复集中控制及故障条件下IP层与光层资源的统一调度。通过加强层间业务信息、带宽资源使用信息、网络故障信息的共享与交互,解决了现有网络控制方式存在的上下层资源抢占和恢复震荡等问题,从而实现基于状态感知的网络故障恢复。性能评估结果表明,该系统能有效降低控制信令代价,提高中断业务的恢复速度,并且具有良好的网络生存性能。