基于MPLS的快速重路由故障恢复综合模型

传统的多协议标签交换(MPLS)快速重路由故障恢复算法存在报文延迟、失序、故障修复时间过长等问题。为此,提出一种基于MPLS的快速重路由故障恢复综合模型,对LDP消息进行扩展、使用全局恢复机制和局部恢复机制相结合的综合策略,采用新型临时路径计算方法。仿真结果证明,该故障恢复综合模型可以降低丢包率,缩短故障恢复时间。     

面向共享风险链路组故障恢复的多路径路由生成算法

为了在IP层恢复网络共享风险链路组(SRLG)故障,提出一种基于改进人工蜂群算法的网络多路径路由生成算法.针对SRLG故障特点建立多路径路由生成模型,最后通过改进人工蜂群算法求解.仿真验证该方法不仅可以生成满足SRLG约束的备用路径,还可以增强故障恢复能力、降低算法复杂度、缩短重路由的平均路径长度.     

一种带宽前瞻式的应用层组播路由算法

流媒体直播是应用层组播技术的一个主要应用领域，对网络性能非常敏感，节点失效时快速恢复路由是一个核心问题。该文在几种常见的处理方法基础上，提出了一种带宽前瞻式的快速重建路由的方法。在节点离开或者发生故障之前就为其孩子节点计算备用路由，一旦节点离开，其孩子节点可以迅速找到并平滑地切换新的父节点，尽量选择服务能力较强的节点作为备用路由，从而增加树的稳定性。     

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.     

基于相交多路径的组播主动式恢复方案

提出了基于相交多路径的组播主动式恢复方案。该方案通过为树中节点提供备用父节点的方式,计算组播源到各个组成员的多条相交路径来代替不相交双树。相交多路径保证了构建成功率并为组播路由提供一定程度的保护。仿真结果表明,该方案构建的组播树以及故障恢复后组播树的代价均与现有方案相当,但是提供的故障恢复时间与现有方案相比显著缩短。     

无线Ad Hoc网络中可靠路由的研究

改进了ETX算法,提出了将动态ACK算法与改进的ETX算法相结合的新的链路状况监测算法,以便在选路时忽略质量不好的链路。建议了一种从中间节点开始恢复的备用路由机制以便在链路断时能快速恢复,取代了笔者之前提出的QDSR基于源节点的备用路由机制。NS2仿真实验结果表明,在节点移动速度较小的较大规模移动Ad Hoc网络中,改进后的算法明显减少了路由错误,并且减少了路由发生错误后重新找到一条路径所需要的平均时间。     

一种k跳回溯可信QoS重路由机制

在可信网络中,由于存在链路或节点失效,需要进行重路由。考虑到用户的服务质量QoS(Quality of Service)和可信需求且为了减少算法开销,提出了一种k跳回溯可信QoS重路由机制。该机制以k作为最大回溯跳数,从失效节点(或链路)的前一节点开始逐跳进行回溯选路,同时尽可能复用路径的原有链路。构建了网络模型和用户信任评估模型,并给出了用户需求描述、满意度计算方法和路径评判标准。仿真结果表明,该机制是可行和有效的,同现有机制相比,在满足用户需求的同时,提高了重路由成功率和用户满意度,并减少了重路由时间。     

一种高稳定性应用层组播树构建算法

提出一种基于节点在线时间期望的应用层组播树构建算法(MPOT)。根据路径的在线时间期望获得节点的插入位置,节点中断后利用组播节点在线时间的重尾现象,在恢复被迫中断节点时保留节点在线时间信息,构建高稳定性组播树。同时针对断裂恢复问题,提出带一阶预测的MPOT算法。模拟结果表明,2种算法构建的组播树均具有较高的稳定性。     

支持多故障恢复的MPLS快速重路由

分析了传统MPLS快速重路由应对多故障环境的不足,提出一种支持MPLS域并发多故障时快速恢复的重路由策略.通过有限洪泛故障信息,使本地修复的节点掌握有限范围内节点、链路的可用性信息,并通过建立主,从备份路径,保证MPLS层有效的恢复及较快的切换速度.理论分析及实验结果表明了该方法的可行性和有效性.     

基于距离成本能量有效的传感器网络路由协议

负载均衡和路径恢复给数据分发的大规模传感器网络带来了挑战。这些问题可以通过多路径和故障恢复路由能够部分得到解决。不幸的是现存的协议还不能满足大规模传感器网络的需求。文中提出了一种新的路由算法，DCEP。它通过计算节点间距离来建立传输路径。此协议不需要节点的位置信息。仿真表明此协议与DD、GPSR协议相比具有优异的表现。     

一种基于MPLS网络的快速故障恢复算法

现有的MPLS故障恢复方案存在不同的性能问题:Makam方案需要提前建立备份路径,浪费了大量网络资源;简单动态方案动态建立备份路径,资源利用率高,但是需要等待路由表收敛,恢复时间长,造成大量丢包.针对这些不足,提出了一种基于MPLS网络的快速故障恢复算法MBFR.MBFR算法在故障发生以后建立备份路径,但是不需要等待路由表收敛,只需根据PIL中信源树和当前故障信息就可以快速计算出备份路径,既不浪费网络资源,又缩小了恢复时间.仿真实验结果验证了MBFR算法的优越性.     

An efficient critical protection scheme for intra-domain routing using link characteristics

In recent years, there are substantial demands to reduce packet loss on the Internet. Among the proposed schemes, finding backup paths in advance is considered to be an effective method to reduce the reaction time. Very commonly, a backup path is chosen to be the most disjoint path from the primary path, or on the network level, a backup path is computed for each link (e.g., IPFRR). The validity of this straightforward choice is based on two things. The first thing is all the links may have the equal likelihood to fail; the second thing is, facing the high protection requirement today, it just looks weird to have links not protected or to share links between the primary and backup paths. Nevertheless, many studies have confirmed that the individual vulnerability of the links on the Internet is far from being equal. In addition, we have observed that full protection schemes (In this paper, full protection schemes means schemes (1) in which backup path is a most disjoint path from the primary path; or (2) which compute backup path for each link.) may introduce high cost (e.g., computation).In this paper, we argue that such approaches may not be cost-efficient and therefore propose a novel critical protection scheme based on link failure characteristics. Firstly, we analyze the link failure characteristics based on real world traces of CERNET2 (China Education and Research NETwork 2). The analysis results clearly show that the failure probabilities of the links in CERNET2 backbone are heavy-tailed, i.e., a small set of links causing most of the failures. Based on this observation, we find out two key parameters which strongly impact link criticality and propose a critical protection scheme for both single link failure situation and multi-link failure situation. We carefully analyze the implementation details and overhead for backup path schemes of the Internet today; the problem is formulated as an optimization problem to guarantee the routing performance and minimize the backup cost. This cost is special as it involves computational overhead. Based on this, we propose a novel Critical Protection Algorithm which is fast itself for both the single link failure and the multi-link failure versions. A comprehensive set of evaluations with randomly generated topologies, real world topologies and the real traces from CERNET2, shows that our scheme gains significant achievement over full protection in both single link failure situation and multi-link failure situation. It costs only about 30–60% of the full protection cost when the network relative availability increment is 90% of the full protection scheme.     

A backup path routing for guaranteeing bandwidth in mobile ad hoc networks for multimedia applications

This paper suggests a backup path routing scheme in ad hoc networks for multimedia applications. A data path is established in an on-demand manner when there is a need to send data. A primary and a backup path are created as a result of a route control message exchange process. Each control message has additional information for guaranteeing the service quality. A backup path is configured around the primary path in multi-hop wireless networks. After detecting a failure when sending data, a repairing procedure occurs near the failed node of the primary path. The proposed scheme exploits the route request and reply information exchanged between nodes to create a backup path. Proposed backup routing scheme uses a one-hop search method, and the rerouted path length is two-hop at maximum. The service quality as measured by the error rate and delay is considered when establishing and repairing a route by making an allowance for the required bandwidth. Simulation results show that the proposed backup path routing scheme has a better data delivery ratio and an improved end-to-end data delay while guaranteeing the requested bandwidth for multimedia application.     

PLR-based heuristic for backup path computation in MPLS networks

To ensure service continuity in networks, local protection pre-configuring the backup paths is preferred to global protection. Under the practical hypothesis of single physical failures in the network, the backup paths which protect against different logical failure risks (node, link and shared risk link group (SRLG)) cannot be active at the same time. Thus, sharing bandwidth between such backup paths is crucial to increase the bandwidth availability.In this article, we focus on the optimal on-line distributed computation of the bandwidth-guaranteed backup paths in MPLS networks. As the requests for connection establishment and release arrive dynamically without knowledge of future arrivals, we choose to use the on-line mode to avoid LSP reconfigurations. We also selected a distributed computation to offer scalability and decrease the LSP setup time. Finally, the optimization of bandwidth utilization can be achieved thanks to the flexibility of the path choice offered by MPLS and to the bandwidth sharing.For a good bandwidth sharing, the backup path computation entities (BPCEs) require the knowledge and maintenance of a great quantity of bandwidth information (e.g. non aggregated link information or per path information) which is undesirable in distributed environments. To get around this problem, we propose here a PLR (point of local repair)-based heuristic (PLRH) which aggregates and noticeably decreases the size of the bandwidth information advertised in the network while offering a high bandwidth sharing. PLRH permits an efficient computation of backup paths. It is scalable, easy to be deployed and balances equitably computations on the network nodes.Simulations show that with the transmission of a small quantity of aggregated information per link, the ratio of rejected backup paths is low and close to the optimum.     

备份航姿系统的磁传感器在线校准方法

磁航向角是备份航姿系统的重要输出参数,为提高测量性能,需对磁传感器进行误差标定。对于机载应用的磁传感器,地面标定方法需要耗费大量的时间且操作不便,在地表标定结果的适用性随距离标定的时间和使用空间位置的变化而降低。基于备份航姿系统的实际工作特点,提出一种在备份状态下利用飞机主惯导的姿态角信息对磁传感器误差进行在线校准的方案,设计了误差校准数据存储的数据结构,提出了校准数据对航向空间覆盖的充分性评价策略,最后利用无磁转台模拟环境,验证了某备份航姿系统的磁传感器在线校准方案的可行性和有效性。     

一种线性时间复杂度的高效路由保护方法

如何高效快速地应对网络中的故障是设计路由协议的基本要求和主要任务。由于动态路由协议在应对网络中的故障时,在协议动态收敛的过程中将会有大量的报文被丢弃。因此,目前路由器厂商普遍采用路由保护方法来克服网络故障,在众多的路由保护方法中,DC（downstream criterion）规则是一种被普遍认可的方法。然而,已有的实现 DC规则算法的时间复杂度普遍较高,并且复杂度随着网络节点平均度的增加而迅速增加。为了应对上述问题,提出一种线性时间复杂度的高效路由保护方案ERPLR（an efficient routing protection method with linear time complexity）,该方法首先提出了备份下一跳计算规则,然后在已有最短路径树的基础上,根据备份下一跳计算规则为所有的源目的节点对计算备份下一跳。在计算备份下一跳的过程中,每个节点和其邻居最多被访问一次,因此ERPLR的时间复杂度为O（V+E）。实验结果表明,与已有的实现DC规则相比较,ERPLR在故障保护率和路径拉伸度两个度量指标结果相似的情况下,在真实网络拓扑和模拟拓扑中,ERPLR分别降低了大约74.93%和78.91%的计算开销,该方法可以极大地降低DC规则的计算开销。     

Joint coverage and link utilization for fast IP local protection

To mitigate the impact of failures, many IP Fast Local Recovery (IPFLR) schemes have been proposed to reroute traffic in the events of failures. However, the existing IPFLR schemes either aimed to find the alternate backup routes to protect failures, or focused on balancing the traffic load routed on the backup routes. Furthermore, in Internet, flows are often managed by shortest path routing, and therefore purely determining the backup routing paths is not sufficient in protecting the error-prone networks. In this paper, we propose a Simulated Annealing based Load balancing and Protection (SALP) scheme to determine link weights for balancing link utilization in the non-failure state and simultaneously construct backup routing tables for protecting any single link failure in IP networks. In our proposed scheme, the two most significant issues, (1) load balancing and (2) coverage, are jointly considered to recover the network operation from single link failures. In the proposed scheme, upon a failure, only the nodes adjacent to a failure are activated to divert affected traffic to backup paths without disturbing regular traffic. Numerical results delineate that the proposed scheme achieves high coverage rate and load balancing at the expense of slightly increasing the entries of backup routing table.     

Backup reliability of stochastic imperfect-node computer networks subject to packet accuracy rate and time constraints

In a real-time computer network, arcs and nodes have multi-state capacity, lead time, and packet accuracy rate (PAR). Evaluating the reliability of a network whose nodes are imperfect is complex, because node failure results in the disablement of adjacent arcs. Such a network is named a stochastic imperfect-node computer network (SINCN). Under the strict assumption that each arc has a deterministic capacity, the quickest path problem is to find a path that sends a specific amount of data with minimum transmission time. Subject to both an assured PAR and time constraints, this paper proposes an efficient algorithm to evaluate the system reliability of an SINCN. Furthermore, a routing scheme is adopted to reinforce the system reliability. Accordingly, reliability based on the routing scheme is calculated. An application of our method on the Taiwan academic network is described to show its impact on the backup reliability for different routing schemes.     

Traffic recovery time constrained shared sub-path protection algorithm in survivable WDM networks

With the development of real-time applications, the traffic recovery time, which is defined as the duration between the failure occurrence on the working path and the interruptive traffic has been successfully switched to the backup path, has become the basic Quality-of-Service (QoS) requirement in survivable WDM networks. In this paper, we address the problem of shared sub-path protection with considering the constraint of traffic recovery time and propose a new heuristic algorithm called Traffic recovery time Constrained Shared Sub-Path Protection (TC_SSPP) to compute the working path and the Shared-Risk-Link-Group (SRLG)-disjoint backup sub-paths. The main target of our work is to improve the resource utilization ratio and reduce the blocking probability for dynamic network environment. By properly setting the delay parameter for each link and running the Delay Constrained Shortest Path Algorithm (DCSPA) to compute the backup sub-paths, TC_SSPP can effectively guarantee the traffic recovery time. Simulation results show that the proposed TC_SSPP can outperform the traditional algorithms.     

Using Shared Risk Link Groups to enhance backup path computation

To cope quickly with all types of failure risks (link, node and Shared Risk Link Group (SRLG)), each router detecting a failure on an outgoing interface activates locally all the backup paths protecting the primary paths which traverse the failed interface. With the observation that upon a SRLG failure, some active backup paths are inoperative and do not really participate to the recovery (since they do not receive any traffic flow), we propose a new algorithm (SRLG structure exploitation algorithm or SSEA) exploiting the SRLG structures to enhance the admission control and improve the protection rate.With our algorithm, more flexibility is provided for the backup path selection since a backup path which protects against the failure of a link belonging to a SRLG does not systematically bypass all the links of that SRLG. Moreover, our algorithm permits to save more bandwidth because it does not allocate the bandwidth for the inoperative backup paths even if they are activated.Simulations show that our algorithm SSEA decreases the ratio of rejected backup paths and, it reduces in distributed environments the average number of messages sent to manage the bandwidth information necessary for the backup path computation.