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.     

MPLS快速重路由多故障恢复算法的研究

传统的MPLS快速重路由技术在面对网络多故障的情况时有许多不足之处,为了更好的解决问题,提出一种新的MPLS快速重路由多故障恢复算法.算法采用Detour路径保护方式,对有不同备份路径经过的链路上的预留带宽资源进行共享管理,并为工作路径建立主、从备份路径.仿真实验结果显示,该算法能够有效减少备份路径上预留带宽资源消耗,对出现多故障的网络进行快速恢复.     

Multicast protection scheme in survivable WDM optical networks

The protection design is a key issue in survivable wavelength division multiplexing (WDM) optical networks. Most researches focused on protecting unicast traffic against the failure of a single network component such as a link or a node. In this paper, we investigate the protection scheme for multicast traffic in meshed WDM optical networks under dual-link failure consideration, and propose a novel protection algorithm called shared segment protection with reprovisioning (SSPR). Through dynamically adjusting link-cost according to the current network state, SSPR establishes a primary light-tree and corresponding link-disjoint backup segments for each multicast connection request. A backup segment can efficiently share wavelength capacity of its working tree or the common resource of other backup segments. Capacity reprovisioning establishes new segments for the vulnerable connections after a link failure and tolerates following link failures. The simulation results show that SSPR not only can make good use of wavelength resources and protect multicast sessions against any single-link failure, but also can greatly improve the traffic restorability in the event of dual-link breakdown.     

基于基本回路的MPLS网络重路由故障恢复机制

研究MPLS网络中的重路由故障恢复机制,提出一种新的计算备用路径的方法,将备用路径的计算分为预处理和在线计算2个过程,给出一种基于基本回路的重路由故障恢复机制(FC-R)。仿真分析表明,FC-R恢复时间较短,可以对抗节点故障或链路故障,大大缩短在线计算时间,减轻节点负担,能够得到性能较优的备用路径,进一步节省网络资源。     

一种保证NFV可靠性的最优备份拓扑生成方法

网络功能虚拟化（NFV）将服务功能链（SFC）映射到底层网络时,与传统的虚拟网络一样,会存在可靠性问题。本文针对NFV环境中的单链路故障,在考虑SFC拓扑设计和映射的基础上添加备份拓扑提高可靠性,再进一步简化备份拓扑,减少资源消耗。按照服务路径是否可分离,提出了两种最优备份拓扑的生成算法。仿真结果表明,最优备份拓扑在提高可靠性的基础上能够有效的减少备份带宽资源的消耗,提高资源利用率。     

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.     

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.     

A new approach for designing fault-tolerant WDM networks

In recent years, path protection has emerged as a widely accepted technique for designing survivable WDM networks. This approach is attractive, since it is able to provide bandwidth guarantees in the presence of link failures. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new approach for designing fault-tolerant WDM networks, based on the concept of survivable routing. Survivable routing of a logical topology ensures that the lightpaths are routed in such a way that a single link failure does not disconnect the network. When a topology is generated using our approach, it is guaranteed to have a survivable routing. We further ensure that the logical topology is able to handle the entire traffic demand after any single link failure. We first present an ILP that optimally designs a survivable logical topology, and then propose a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection.     

MPLS中的工作路由和后备路由确定算法

为提高网络资源的利用率,在基于Local故障恢复方案的前提下,提出了一种路由算法,这种算法在确定工作LSP的同时也确定好后备LSP,并使工作路由和后备路由带宽之和最小。     

Localized motion-based connectivity restoration algorithms for wireless sensor and actor networks

In wireless sensor and actor networks maintaining inter-actor connectivity is very important in mission-critical applications where actors have to quickly plan optimal coordinated response to detected events. Failure of one or multiple actors may partition the inter-actor network into disjoint segments, and thus hinders the network operation. Autonomous detection and rapid recovery procedures are highly desirable in such a case. This paper presents DCR, a novel distributed partitioning detection and connectivity restoration algorithm to tolerate the failure of actors. DCR proactively identifies actors that are critical to the network connectivity based on local topological information, and designates appropriate, preferably non-critical, backup nodes. Upon failure detection, the backup actor initiates a recovery process that may involve coordinated relocation of multiple actors. We also present an extended version of DCR, named RAM, to handle one possible case of a multi-actor failure. The proposed algorithms strive to avoid procrastination, localize the scope of recovery and minimize the movement overhead. Simulation results validate the performance of the proposed algorithms.     

Dynamic Path Management with Resilience Constraints under Multiple Link Failures in MPLS/GMPLS Networks

Most previous research on MPLS/GMPLS recovery management has focused on efficient routing or signaling methods from single failures. However, multiple simultaneous failures may occur in large-scale complex virtual paths of MPLS/GMPLS networks. In this paper, we present a dynamic MPLS/GMPLS path management strategy in which the path recovery mechanism can rapidly find an optimal backup path which satisfies the resilience constraints under multiple link failure occurrences. We derived the conditions to test the existence of resilience-guaranteed backup path, and developed a decomposition theorem and backup path construction algorithm for the fast restoration of resilience-guaranteed backup paths, for the primary path with an arbitrary configuration. Finally, simulation results are presented to evaluate the performance of the proposed approach.     

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.     

一种时延约束下可靠性保证的服务功能链部署方法

针对网络功能虚拟化环境中底层网络物理节点随机失效导致网络服务中断问题,提出了一种兼顾网络服务可靠性和时延约束的服务功能链部署方法以保证网络服务的可靠性。首先提出一种相邻虚拟网络功能备份实例资源共享的备份机制和单路径与多路径混合的路由策略,然后对时延约束下服务功能链可靠性部署问题建立混合整数线性规划模型,并设计了基于K最短路径扩展的服务功能链部署算法。仿真结果表明,与现有方法相比,该方法降低了节点和带宽资源开销,并提高了网络服务请求接受率。     

面向SDN数据中心网络最大概率路径流量调度算法

随着数据中心网络规模的迅速增长,网络带宽利用率低下导致的网络拥塞问题日益突出,通过负载均衡提高数据中心网络链路带宽利用率和吞吐量成为了研究热点.如何结合流量特征、链路状态和应用需求进行流量的合理调度,是实现网络链路负载均衡的关键.针对数据中心突发性强、带宽占用率高的大象流调度问题,提出一种面向SDN数据中心网络最大概率路径流量调度算法,算法首先计算出满足待调度流带宽需求所有路径,然后计算流带宽与路径最小链路带宽之间的带宽比,结合所有路径的带宽比为每一条路径计算路径概率,最后利用概率机制选择路径.算法不仅考虑了流带宽需求和链路带宽使用情况,而且全局地考虑了流调度和链路带宽碎片问题.实验结果表明,最大概率路径调度算法能够有效地缓解网络拥塞,提高带宽利用率和吞吐量,减少网络延迟,从而提高数据中心的整体网络性能和服务质量.     

基于资源共享的MPLS组播网络中的路径恢复

MPLS组播网络能快速有效地传输数据,其中的路径恢复机制确保提供持续的网络服务。该文提出了一种基于资源共享的MPLS组播网络中的路径恢复方案,该方案在每条链路的入口处保存一个链路资源使用数据库,使用基于共享资源且提供带宽保证的备份路径计算方法来预先建立备份路径,能优化网络资源的利用并减少切换时延。     

基于业务类型的网络切片可靠性映射算法

网络切片是5G网络的基础架构技术,为在多个切片共享同一底层网络资源的同时保证切片的可靠性,提出一种区分业务类型的网络切片可靠性映射算法,解决底层网络链路故障、网络切片可靠性与资源利用率相互矛盾的问题。通过区分切片承载业务类型,对高可靠低时延切片请求的链路提前构建备份路径,并采用基于最大生成树链路的备份资源共享保护方法,对高带宽切片请求则采用基于链路可靠性的重映射算法恢复故障链路。仿真结果验证了该算法的有效性,与SVNE1+1和DPS-VNRA算法相比,其在切片成功运行率、长期收益开销比、物理链路利用率和故障恢复率方面均具有优势。     

基于分割模式的时间序列矢量符号化算法

针对符号化聚合近似算法(SAX)中时间序列必须等长分割的缺陷,提出一种基于分割模式的时间序列符号化算法(SMSAX)。利用三角阈值法对随机抽样的时间序列进行特征提取,计算时间序列最大压缩比,将其作为时间窗宽提取分割点,进而求出时间序列的分割模式。利用得到的分割模式对时间序列进行分割降维,通过均值和波动率对分割后的子序列进行向量符号化。根据时间序列特征对其进行不等长分割,并加入波动率消除奇异点的影响。实验结果表明,SMSAX能获得比SAX更精确的结果。     

一种基于QoS约束的kMUPP替换服务快速查找算法

动态服务组合运行过程中,当发生服务失效时,失效恢复机制通过切换到替换路径来保证整个服务正常执行。本文提出一种WSC_KUPB算法利用k-Shortest路径问题来研究最大效用路径问题,以自定义的服务质量效用函数为依据,选取有最大总效用的优化路径作为替换路径。实验表明,该算法能够在时间和可用性上很好地折衷。     

Comparison of recovery schemes to maximize restorable throughput in multicast networks

Multicast networks have many applications especially in real-time content delivery systems. For high-quality services, users do not expect to witness any interruption; thus, network link failure has to be handled gracefully. In unicast networks there are many approaches for dealing with link failures using backup paths. Recently, Cohen and Nakibly categorized these methods, provided linear programming formulations for optimizing network throughput under the assumption that the paths are splitable, and compared them experimentally. In this work, we take their approach and apply to the multicast failure recovery problem. We propose backup bandwidth allocation algorithms based on linear programs to maximize the throughput, and perform an experimental study on the performance of recovery schemes. We study many recovery schemes in multicast networks and propose a new recovery scheme that performs better than all other recovery scheme except the one that recomputed the whole multicast tree from scratch for each link failure.