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.     

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。     

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.     

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。     

Path selection with preemption and re-routing control for multi-protocol label switching networks

Multi Protocol Label Switching (MPLS) networks enhance the services of conventional best-effort IP networks by providing end-to-end Quality of Service (QoS) guaranteed Label Switched Paths (LSP) between customer sites. The LSP has to be set up in advance before carrying the traffic. Contention for network resources may happen if many LSPs try to use a common network link with limited bandwidth. In this paper, we investigate the problem of providing services to high priority LSPs whereby existing LSPs with lower priority may be preempted. The consequent interruption of the services of preempted LSPs would detrimentally affect users’ perception on the QoS provided. Therefore, the preemption strategies may incorporate additional re-routing mechanisms to provide alternative paths for the LSPs which are to-be-preempted so that their services remain unaffected. A newly arrived high priority LSP in an MPLS network may find M possible paths between its source and destination. It may select the shortest path which may trigger preemption or choose a longer path which however utilizes more resources. We begin by formulating preemption strategies with global re-routing. Our investigations include the effects of routing of high priority LSPs on the shortest path and its alternative paths. We show that by persistently routing the high priority LSP on the shortest path, more preempted LSPs can be re-routed which would reduce the negative effects of preemption. However, as excessive re-routing may degrade the network performance as well, a re-routing control strategy is proposed to constrain the length of these re-routed paths. Finally, a decentralized preemption strategy with local re-routing is also presented to approximate the performance of the proposed strategy with significantly lower control overheads. Simulations show that with this approach, high priority LSPs can gain better access to network resources while simultaneously ensuring that, as compared to the existing preemption strategies, the network throughput and the ongoing connection services are not adversely affected.     

基于LSP路径拥塞的分布式流量工程算法

提出了一种MPLS网络并行路径间合理分配流量实现流量均衡的分布式流量工程算法DITB。该算法利用LER与LSR各自在统计网络状态信息方面的优势，通过引入3种消息实现彼此间网络状态信息的传送，由LER将整条路径的拥塞状况与单个链路的拥塞状况相结合，直接给出合理的流量均衡方案，达到流量工程的目的。通过仿真分析验证，该算法网络开销少、运算速度快、优化效果较为明显。     

一种快捷的MPLS网络负载均衡动态路由算法

针对MPLS网络引入了一种快捷的有带宽保证的负载均衡动态路由算法（FDRA）,该算法通过提出预期负载的概念和链路上的剩余容量来定义链路的成本,然后采用以链路成本为基础的最短路径算法选路,使得网络快捷地建立尽可能多的有带宽保证的路由,并且使这些路由均衡地通过网络。在与其他算法相比较中,该算法在业务请求拒绝率和重路由性能方面有更好的表现,特别是路由的建立时间快捷。     

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.     

TROP: A Novel Approximate Link-State Dissemination Framework For Dynamic Survivable Routing in MPLS Networks

In this paper, a novel approximate link-state dissemination framework, called TROP, is proposed for shared backup path protection (SBPP) in multiprotocol label switching (MPLS) networks. While performing dynamic explicit survivable routing in a distributed environment, link-state dissemination may cause a nontrivial signaling overhead in the process of exploring spare resource sharing among individual backup label switched paths (LSPs). Several previously reported studies have tackled this problem by initiating a compromise between the amount of dissemination and the achievable extent of resource sharing. The paper first summarizes the previously reported schemes into a compact and general link-state dissemination framework by way of singular value decomposition (SVD). To improve the accuracy of the matrix reconstruction and to eliminate the overestimation of the sharable spare capacity along each link, a novel SVD approach based on the min-plus algebra (also called tropical semirings) is introduced. Simulation results show that the proposed schemes can achieve a lower blocking probability than that by all the other counterpart schemes while taking the same complexity of link-state dissemination. This great advantage is gained at the expense of a longer computation time for solving a linear program (LP) in each dissemination cycle at the core nodes. We also consider the stale link-state phenomena that may cause imprecision in the routing information at the ingress nodes due to the delay in the periodic/event-driven link-state update message advertisement.     

基于MPLS网络的选播QoS路由算法

提出一种基于MPLS网络且保证QoS的选播路由算法。使用链路状态路由协议,找到一条从发出请求的客户到服务器方向上最小跳数的最优路径,该路径能满足选播服务带宽要求。使用度量为路径逆向(服务器到客户)上的链路带宽值,通过约束路由的标记分发协议,建立一条从服务器到客户方向的标记交换路径,并预留资源。仿真结果表明,在传输服务数据流时,该算法的时延及丢包率性能良好,能在一定程度上平衡服务器的负载。     

DORA: Efficient Routing for MPLS Traffic Engineering

This paper introduces DORA, a dynamic online routing algorithm for construction of bandwidth guaranteed paths in MPLS-enabled networks. The main objective of DORA is to place paths with reserved bandwidth evenly across the network in order to allow more future paths to be accepted into the network and to balance the traffic load. During path computation, the key operation in DORA is to avoid routing over links that (1) have high potential to be part of any other path, and (2) have low residual bandwidth available. Our simulation results based on unsuccessful path-setup ratio and successful path-reroutes upon link failure, show that DORA offers better performance than some sophisticated algorithms, while at the same time being less computationally expensive.     

Different Algorithms for Normal and Protection Paths

Many network routing situations commonly require backup paths that satisfy various constraints on bandwidth, link or node selection, and ease of configuration. In this paper, we attempt to validate whether it is beneficial to have distinct algorithmic treatments of normal and backup path calculation, configuration, and maintenance. We present a modular suite of algorithms that enable us to manage normal and protection paths differently. In the process, we develop a simple extension of Minimum Interference Routing Algorithm for shared protection paths. We incorporate a distributed algorithm to separately calculate normal and backup paths in the network, using link state information, and present an evaluation of asynchronous dynamic reorganization of backup paths to reduce congestion in the network. Simulations demonstrate nontrivial quantitative reductions in blocking probabilities under certain conditions. We conclude that in order to choose an optimal algorithm for a protected QoS routing application, it is recommended to also consider a combination of two different algorithms for normal and backup paths.Rajarshi Gupta is a PhD candidate in Electrical Engineering and Computer Sciences at the University of California at Berkeley and will graduate in May 2005. Prior to this, he completed hisMS degree in 1999 at Berkeley and his BS degree in 1997 from the University of Maryland. From 1999 to 2003, Rajarshi worked with Extreme Networks as a Senior Designer, where he has been the author of 8 patents. He is interested in algorithms to ensure quality in networks–both wired and ad-hoc. This includes: analysis of network capacity; switching and scheduling mechanisms for efficient utilization of resources; and, routing algorithms to guarantee quality of service.Eric Chi received his MS degree in Electrical Engineering and Computer Sciences from the University of California at Berkeley in 2001 and his BAdegree in physics in 1999 from Rice University. Hiswork focused on distributed network capacity management.He hasworked on inventory restocking problems and protection path resource allocation in wired communication networks.Jean Walrand received the PhD degree from the Department of Electrical Engineering and Computer Sciences of the University of California at Berkeley where he is now Professor. His research interests include decision theory, stochastic processes, and communication networks. He is the author of An Introduction to Queueing Networks (Prentice Hall, 1988) and of Communication Networks: A First Course (2nd ed. McGraw-Hill, 1998) and coauthor of High-Performance Communication Networks (2nd ed, Morgan Kaufman, 2000). He is a Fellow of the Belgian American Education Foundation and of the IEEE and a recipient of the Lanchester Prize and of the Stephen O. Rice Prize.     

Routing demands with time-varying bandwidth profiles on a MPLS network

In this work we consider the problem of routing bandwidth-guaranteed flows with time-variable bandwidth profiles on a MPLS network. We assume that each demand is routed in an explicitly routed LSP, and the amount of bandwidth that must be reserved along the LSP varies during the day according to a piece-wise mask, which is known in advance. The time-of-day bandwidth profiles can be explicitly declared by the VPN customers in the SLA, or alternatively predicted by the ISP based on past measurements.In this framework, we propose a simple on-line algorithm for optimal selection of LSP paths. We also provide an ILP formulation for the associated off-line problem, and adopt it as a reference performance bound for the on-line algorithm.Additionally, we compare the performances of fixed and variable routing in presence of time-variable bandwidth profiles. The results presented here suggest that the a priori knowledge of the per-demand traffic profiles can be exploited to achieve a fixed routing configuration, which can be marginally improved by variable reconfigurations. We relate our findings with a couple of previous works that in different application contexts achieved similar results.     

MPLS VPN动态路径管理算法*

针对标签交换路径的设计与维护问题,提出基于故障恢复模型的MPLS VPN动态路径管理算法。该算法在备份路径设计准则的基础上,测试全连通MPLS VPN中备份路径可用性的条件,利用快速备份路径构造算法,在多故障发生时,自动地构造满足客户故障恢复需求的VPN路径,从而使VPN业务受干扰程度最小。     

A New Fast Backup Method for Bidirectional Multicast Traffic in MPLS Networks: Control Plane Procedures and Evaluation by Simulations

Bidirectional multicast mechanisms are used to support multi-point to multi-point (MP2MP) traffic such as video-conferencing. These mechanisms are deployed today in multi-protocol label switching (MPLS) networks using the connectionless mode in which traffic engineering (TE) features such as bandwidth reservation and fast reroute in case of link and/or node failure are not defined. Indeed, TE procedures are defined in MPLS for unicast and multicast point-to-multipoint (P2MP) traffic only. Hence, MP2MP traffic that requires TE procedures is carried out using a full mesh of P2P or P2MP paths. Similarly, a full mesh of P2P and P2MP backup paths should be predefined in order to fast reroute traffic in case of a node failure. This leads to a major scalability problem since MPLS TE paths incur heavy overhead burden on MPLS nodes (CPU and memory). In this paper, we emphasize on fast reroute procedures using MP2MP TE paths. In particular, we define the control plane procedures that should be established. In addition, we present a simulation study that demonstrates the scalability amelioration when using MP2MP TE paths for fast rerouting instead of full mesh P2P and/or P2MP paths.     

Fast setup of end-to-end paths for bandwidth constrained applications in an IP/MPLS–ATM integrated environment

Transport networks are currently being moved towards a model of high performance Internet Protocol/Multiprotocol Label Switching (IP/MPLS) routers interconnected through intelligent core networks. Currently, Asynchronous Transfer Mode (ATM) technology has been widely deployed in several network backbones along with the Private Network-to-Network Interface (PNNI) protocols as the control plane. In order to cope with the increasing Internet traffic demands in the current context, fast setup of end-to-end paths with the required Quality of Service (QoS) is necessary.This paper analyzes the case of two IP/MPLS networks interconnected through an ATM core network, assuming MPLS as the mechanism to provide Traffic Engineering in the IP networks, and a PNNI-based control plane in the core network. This paper aims to define a mechanism needed to set up a fast end-to-end QoS Label Switched Path (LSP) between two Label Switched Routers (LSRs) belonging to different IP/MPLS domains. First, the fast end-to-end setup is achieved by modifying the network backbone control plane. Second, two different aggregation schemes are proposed to summarize the QoS network state information to be transported through the ATM core network. Therefore, both the efficient aggregation schemes and the fast mechanism allow source routing to set up a path faster than the existing methods and to reduce the blocking probability using a summary of the available resource information.     

Reconfiguration for service and self-healing in ATM networks based on virtual paths

This paper presents a reconfiguration scheme resulting in capacity efficiency and fast restoration by utilizing the inherent benefits of Virtual Paths in ATM networks. The unified optimization of bandwidth reconfiguration is addressed so that switched ATM networks can support both service and survivability from a common pool of network spare capacity at a given time. The spare capacity is composed of idle bandwidth and freed up bandwidth from the switch pairs which have a surplus bandwidth. Fast restoration can be achieved by using the pre-optimized network spare bandwidth and preplanned backup Virtual Paths based on the link and node disjoint path routing scheme. The overall operation of the proposed self-healing strategy can be consolidated into distributed fault management functions at ATM layer based on Virtual Paths. The scheme enables a logical Virtual Paths ring protection switching in ATM networks.     

Backup path set selection in ad hoc wireless network using link expiration time

Topological changes in mobile ad hoc networks frequently render routing paths unusable. Such recurrent path failures have detrimental effects on quality of service. A suitable technique for eliminating this problem is to use multiple backup paths between the source and the destination in the network. Most of the proposed on-demand routing protocols however, build and rely on single route for each data session. Whenever there is a link disconnection on the active route, the routing protocol must perform a path recovery process. This paper proposes an effective and efficient protocol for backup and disjoint path set in an ad hoc wireless network. This protocol converges into a highly reliable path set very fast with no message exchange overhead. The paths selection according to this algorithm is beneficial for mobile ad hoc networks, since it produces a set of backup paths with much higher reliability. Simulations are conducted to evaluate the performance of our algorithm in terms of route numbers in the path set and its reliability. In order to acquire link reliability estimates, we use link expiration time (LET) between each two nodes.In another experiment, we save the LET of entire links in the ad hoc network during a specific time period, then use them as a data base for predicting the probability of proper operation of links.Links reliability obtains from LET. Prediction is done by using a multi-layer perceptron (MLP) network which is trained with error back-propagation error algorithm. Experimental results show that the MLP net can be a good choice to predict the reliability of the links between the mobile nodes with more accuracy.     

A novel path protection scheme for MPLS networks using multi-path routing

Multi-protocol label switching (MPLS) is an evolving network technology that is used to provide traffic engineering (TE) and high speed networking. Internet service providers, which support MPLS technology, are increasingly demanded to provide high quality of service (QoS) guarantees. One of the aspects of QoS is fault tolerance. It is defined as the property of a system to continue operating in the event of failure of some of its parts. Fault tolerance techniques are very useful to maintain the survivability of the network by recovering from failure within acceptable delay and minimum packet loss while efficiently utilizing network resources.In this paper, we propose a novel approach for fault tolerance in MPLS networks. Our approach uses a modified (k, n) threshold sharing scheme with multi-path routing. An IP packet entering MPLS network is partitioned into n MPLS packets, which are assigned to node/link disjoint LSPs across the MPLS network. Receiving MPLS packets from k out of n LSPs are sufficient to reconstruct the original IP packet. The approach introduces no packet loss and no recovery delay while requiring reasonable redundant bandwidth. In addition, it can easily handle single and multiple path failures.     

满足指定节点约束的路由算法

在MPLS或GMPLS网络中,路由算法常常需考虑节点约束条件(即用户可能指定一条端到端路径所必须经过的一些中途节点)。对链路代价值为整数的有向无回路网络,文章提出了一种伪多项式时间算法,用于计算满足指定节点约束的最小代价路径。对一般有向网络,文中给出了一种计算时间及空间上限可调的启发式算法。仿真实验结果表明,所给的启发式算法在网络规模变大时明显优于已知的算法。