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。     

基于分层路径计算单元与双矩阵博弈的多域光网络静态组播专用保护算法

在预先配置组播业务的多域光网络中,如何保证静态组播业务的生存性已成为广泛关注的问题。针对此问题,通过采用基于分层路径计算单元（PCE）架构的全局拓扑信息调度计算模型,利用双矩阵博弈来生成链路不相交的组播树和组播保护树,最后提出了一种基于分层PCE与双矩阵博弈的多域光网络静态组播专用保护算法,并给出了算法的具体示例。理论分析和实验结果表明,在一定的冗余资源配置下,该算法具有较低的时间复杂度,在优化组播工作树和组播保护树的资源分配结构的同时,可明显提高多域光网络静态组播业务的生存能力。     

A note on distributed multicast routing in point-to-point networks

The distributed algorithm for a multicast connection set-up, based on the ‘cheapest insertion’ heuristic, is reviewed. The multicast routing problem is translated into a Steiner tree problem in point-to-point networks where nodes have only a limited knowledge about the network. A solution is proposed in which the time complexity and the amount of information exchanged between network nodes are proportional to the number of members of the multicast group. The Steiner tree is constructed by means of a distributed table-passing algorithm. The analysis of the algorithm presented, backed up by simulation results, confirms its superiority over the algorithm based on ‘waving technique’.Scope and purposeMulticasting is a mechanism used in communication networks that allows distribution of information from a single source to multiple destinations. The problem of finding a multicast connection for a static group of communicating entities in connection-oriented point-to-point network can be formulated in graph theory as a minimum Steiner tree problem. Due to NP-completeness of the Steiner tree problem multicast, routing algorithms are based on heuristics. The diversity of network environments and the lack of centralised information about network topology require an effective distribution of the multicast routing algorithms among the network nodes. This article presents an alternative to the distributed algorithm proposed by Rugelj and Klavzar that implements the same heuristics for the construction of a minimum cost multicast connection in point-to-point networks. The present algorithm constitutes a substantial improvement over that previously proposed with regard to running time and the amount of the information exchanged between network nodes.     

QoS-driven multicast tree generation using Tabu search

Many multimedia communication applications require a source to transmit messages to multiple destinations subject to Quality-of-Service (QoS) delay constraint. The problem to be solved is to find a minimum cost multicast tree where each source to destination path is constrained by a delay bound. This problem has been proven to be NP-complete. In this paper, we present a Tabu Search (TS) algorithm to construct a minimum cost delay bounded multicast tree. The proposed algorithm is then compared with many existing multicast algorithms. Results show that on almost all test cases, TS algorithm exhibits more intelligent search of the solution subspace and is able to find better solutions than other reported multicast algorithms.     

基于暂态混沌神经网络的组播路由算法

讨论了高速包交换计算机网络中具有端到端时延的组播路由问题。首先给出了这类问题的网络模型及其数学描述，然后提出了基于暂态混沌神经网络的组播路由算法。实验结果表明，该算法能够快速有效地实现组播路由优化，并且计算性能及解的质量优于基于Hopfield神经网络的路由算法。     

A subtree-based approach to failure detection and protection for multicast in SDN

Software-defined networking (SDN) has received tremendous attention from both industry and academia. The centralized control plane in SDN has a global view of the network and can be used to provide more effective solutions for complex problems, such as traffic engineering. This study is motivated by recent advancement in SDN and increasing popularity of multicasting applications. We propose a technique to increase the resiliency of multicasting in SDN based on the subtree protection mechanism. Multicasting is a group communication technology, which uses the network infrastructure efficiently by sending the data only once from one or multiple sources to a group of receivers that share a common path. Multicasting applications, e.g., live video streaming and video conferencing, become popular, but they are delay-sensitive applications. Failures in an ongoing multicast session can cause packet losses and delay, which can significantly affect quality of service (QoS). In this study, we adapt a subtree-based technique to protect a multicast tree constructed for OpenFlow switches in SDN. The proposed algorithm can detect link or node failures from a multicast tree and then determines which part of the multicast tree requires changes in the flow table to recover from the failure. With a centralized controller in SDN, the backup paths can be created much more effectively in comparison to the signaling approach used in traditional multiprotocol label switching (MPLS) networks for backup paths, which makes the subtree-based protection mechanism feasible. We also implement a prototype of the algorithm in the POX controller and measure its performance by emulating failures in different tree topologies in Mininet.     

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.     

基于混合遗传算法的QoS多播路由算法

具有多QoS约束的多播路由问题具有NP完全的复杂度。基于延时、延时抖动、带宽、丢包率等QoS约束,描述了一种适应于研究QoS多播路由的网络模型,提出了基于遗传算法和禁忌搜索混合策略的具有多QoS约束的多播路由算法。该算法充分利用了遗传算法和禁忌搜索的优点。克服了遗传算法在求解多QoS约束多播路由问题中的爬山能力差以及不成熟收敛等问题。仿真实验结果表明,该算法为多QoS约束多播路由问题的求解提供了一种有效的新途径。     

A lexicographically fair allocation of discrete bandwidth for multirate multicast traffics

Fair bandwidth allocation is an important issue in the multicast network to serve each multicast traffic at a fair rate commensurate with the receiver's capabilities and the capacity of the path of the traffic. Lexicographically fair bandwidth layer allocation problem is considered and formulated as a nonlinear integer programming problem. A nonincreasing convex function of the bandwidth layers of the virtual sessions is employed to maximize the bandwidth of each virtual session from the smallest.To solve the fairness problem a genetic algorithm (GA) is developed based on the fitness function, ranking selection and the shift crossover. Outstanding performance is obtained by the proposed GA in various multicast networks. The effectiveness of the GA becomes more powerful as the network size increases.     

多媒体通信中带度约束的多播路由算法

随着多媒体业务的发展,多播技术应用日益广泛,多播路由是要寻找连接源节点和一组目的节点的一棵多播树,这个问题在数学上归结为Steiner树问题,它是一个NPC问题。在实际网络中,网络节点具备不同的多播能力,有些节点不支持多播,有些节点支持多播,但为了保证网络速度和节点负载平衡,支持多播的节点要限制其复制信息的数量,即节点的多播能力受限。在这种情况下,寻找多播树变得更加困难,该文用节点的约束来表示敏个节点具备的多播能力,节点多播能力受限情况下的多播路由问题被称为带度约束的多播路由问题,其仍是一个NPC问题。该文提出了一种求解带度的约束多播路由问题的双层遗传算法。算法的基本思想是最优多播树应是一棵满足度约束的最小生成树,因此问题的关键在于如何找到包括在最优生成树中的Steiner节点。遗传算法 采用二进制编码方式,内层算法用于求解满足度约束的最小生成树;外层算法进行全局搜索。该文将算法在稀疏图上进行实验,为了更好地模拟真实网络,稀疏图中每个节点具有不同的多播能力,并且多播目的节点数目相比于网络节点数要小。实验对算法进行了三方面比较：（1）解的质量;（2）计算时间;（3）算法的收敛性。实验结果表明,文中提出的遗传算法能够找到费用较小的多播树,但是当网络规模增大时,算法的求解时间也较长。     

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.     

基于混合遗传算法的多播路由多目标优化

互联网不断增长的多媒体应用引发人们研究如何满足这些应用的服务质量(QoS)约束.目前网络中多主机之间的多播通信一般需要严格的多个QoS保证,文中描述了一种适应于研究多播QoS路由多目标优化的网络模型,在此基础上提出了基于遗传算法和禁忌搜索混合策略的,具有多目标的多播路由QoS优化方法,以克服遗传算法的爬山能力差以及不成熟收敛等问题.此外还采用了改进的多播树编码方法及高效的遗传操作,同时还优化时延、丢包率和带宽利用率等不同的参数.实验结果表明,该算法为多播路由QoS多目标优化问题的求解提供了一种有效的新途径.     

A weight-aware channel assignment algorithm for mobile multicast in wireless mesh networks

Wireless mesh networks (WMNs) are one of key technologies for next generation wireless networks. In this paper, we propose a heuristic channel assignment algorithm with weight awareness to support mobile multicast in WMNs. To enhance network throughput, our algorithm is based on the path forwarding weight to perform channel assignment. In addition to non-overlapping channels, partially-overlapping channels are also used in channel assignment. To fully exploit all available channels in channel assignment, we devise a new channel selection metric to consider the channel separation and the distance between nodes. In mobile multicast, the multicast tree structure cannot be fixed due to receiver (multicast member) mobility. The change of the multicast tree structure will result in channel re-assignment. The proposed algorithm is based on a critical-event driven manner to reduce the times of channel re-assignment as much as possible. Finally, we perform simulation experiments to show the effectiveness of the proposed channel assignment algorithm.     

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.     

Traffic distribution for end-to-end QoS routing with multicast multichannel services

With the development of multimedia group applications and multicasting demands, the construction of multicast routing tree satisfying Quality of Service (QoS) is more important. A multicast tree, which is constructed by existing multicast algorithms, suffers three major weaknesses: (1) it cannot be constructed by multichannel routing, transmitting a message using all available links, thus the data traffic cannot be preferably distributed; (2) it does not formulate duplication capacity; consequently, duplication capacity in each node cannot be optimally distributed; (3) it cannot change the number of links and nodes used optimally. In fact, it cannot employ and cover unused backup multichannel paths optimally. To overcome these weaknesses, this paper presents a polynomial time algorithm for distributed optimal multicast routing and Quality of Service (QoS) guarantees in networks with multichannel paths which is called Distributed Optimal Multicast Multichannel Routing Algorithm (DOMMR). The aim of this algorithm is: (1) to minimize End-to-End delay across the multichannel paths, (2) to minimize consumption of bandwidth by using all available links, and (3) to maximize data rate by formulating network resources. DOMMR is based on the Linear Programming Formulation (LPF) and presents an iterative optimal solution to obtain the best distributed routes for traffic demands between all edge nodes. Computational experiments and numerical simulation results will show that the proposed algorithm is more efficient than the existing methods. The simulation results are obtained by applying network simulation tools such as QSB, OpNet and MATLB to some samples of network. We then introduce a generalized problem, called the delay-constrained multicast multichannel routing problem, and show that this generalized problem can be solved in polynomial time.     

An improved scheme for self-healing in ATM networks

Broadband networks based on ATM technology can carry a large volume of data and can support diverse services like audio, video, and data uniformly. The reliability and availability levels provided by such networks should be very high. Self-healing is an elegant concept in this direction to provide highly reliable networks. A self-healing network can detect failures such as link/node failures and reroute the failed connections automatically using distributed control mechanisms. In this paper, we consider link and node failures including the VP terminating nodes unlike Kawamura and Tokizawa (Self-healing in ATM networks based on virtual path concept, IEEE Journal on Selected Areas in Communications 12 (1) (1994) 120–127). We present here an improved scheme for self-healing in ATM networks based on the concept of backup VPs. The problems we address are: (i) self-healing scheme; and (ii) backup VP routing. Two issues are addressed in the self-healing scheme: (i) backup VP activation protocol; and (ii) dynamic backup VP routing. We propose a new backup VP activation protocol which uses a VC packing strategy which allows the fast and prioritized restoration of critical VCs that were carried by failed VPs. We also propose a distributed dynamic backup VP routing algorithm which reduces the resource contention that may occur when multiple source–destination pairs contend for the routes simultaneously. The objective of the backup VP routing problem is to find a backup VP for each of the working VPs so that the cost of providing the backup is minimized. We propose a heuristic based solution for the backup VP routing problem using the concept of minimum cost shortest paths. We conducted simulation experiments to evaluate the performance of the proposed schemes. The results show that the proposed schemes are effective. Comparison of the results with those of the earlier schemes (R. Kawamura, I. Tokizawa, Self-healing in ATM networks based on virtual path concept, IEEE Journal on Selected Areas in Communications 12 (1) (1994) 120–127; C.J. Hou, Design of a fast restoration mechanism for virtual path-based ATM networks, Proceedings of IEEE INFOCOM’97, Kobe, Japan, April 1997) shows that the proposed schemes perform better.     

MulRoGA: A Multicast Routing Genetic Algorithm approach considering multiple objectives

We solve a multicast routing problem by means of a genetic algorithm (GA) without using multicast trees. The source-destination routes need to fulfill two conflicting objectives: maximization of the common links and minimization of the route sizes. The proposed GA can be characterized by its representation of network links and routes in a variable size multi-chromosome problem; local viability restrictions in order to generate the initial population and define variation operators; selection operators in order to choose the most promising individuals thus preserving diversity, and the fitness function in order to handle the conflicting multiple objectives. The proposed model is called a Multicast Routing Genetic Algorithm (MulRoGA). The model was tested on the 33-node European GéANT WAN network backbone and three other networks (66-node, 100-node and 200-node) randomly generated using the Waxman model on a network topology generator BRITE. On considering each network, a number of solutions were found for changes in the size and node members of the multicast groups, and the source node. The results of the MulRoGA operation suggest a consistent and robust performance in the various cases including comparisons with the methods of unicast shortest path routing, shortest path tree routing (SPT), and simulated annealing (SA) heuristic.     

Redundant multicast routing in multilayer networks with shared risk resource groups: Complexity,models and algorithms

This paper presents a redundant multicast routing problem in multilayer networks that arises from large-scale distribution of realtime multicast data (e.g., Internet TV, videocasting, online games, stock quotes). Since these multicast services commonly operate in multilayer networks, the communications paths need to be robust against a single router or link failure as well as multiple such failures due to shared risk link groups (SRLGs). The main challenge of this multicast is to ensure the service availability and reliability using a path protection scheme, which is to find a redundant path that is SRLG-disjoint (diverse) from each working path. The objective of this problem is, therefore, to find two redundant multicast trees, each from one of the two redundant sources to every destination, at a minimum total communication cost whereas two paths from the two sources to every destination are guaranteed to be SRLG-diverse (i.e., links in the same risk group are disjoint). In this paper, we present two new mathematical programming models, edge-based and path-based, for the redundant multicast routing problem with SRLG-diverse constraints. Because the number of paths in path-based model grows exponentially with the network size, it is impossible to enumerate all possible paths in real life networks. We develop three approaches (probabilistic, non-dominated and nearly non-dominated) to generate potentially good paths that may be included in the path-based model. This study is motivated by emerging applications of internet-protocol TV service, and we evaluate the proposed approaches using real life network topologies. Our empirical results suggest that both models perform very well, and the nearly non-dominated path approach outperforms all other path generation approaches.     

基于遗传算法的带宽-时延约束多播路由优化算法

随着许多多媒体在高速网络中的应用,多播路由问题成为越来越重要的课题。多播路由问题在计算机网络中是著名的Steiner树问题,同时也是NP完全问题。该文提出了一种基于遗传算法的多播路由优化算法,采用可变长度染色体(多播树)和基因(路径)应用于编码问题。该算法在满足带宽和时延约束条件下寻找代价最小的多播树。仿真实验证明该算法能快速找到最优解,收敛速度快,可靠性高,能够满足多媒体网络对实时性的要求。     

QoS multicast routing using a quantum-behaved particle swarm optimization algorithm

QoS multicast routing in networks is a very important research issue in networks and distributed systems. It is also a challenging and hard problem for high-performance networks of the next generation. Due to its NP-completeness, many heuristic methods have been employed to solve the problem. This paper proposes the modified quantum-behaved particle swarm optimization (QPSO) method for QoS multicast routing. In the proposed method, QoS multicast routing is converted into an integer programming problem with QoS constraints and is solved by the QPSO algorithm combined with loop deletion operation. The QPSO-based routing method, along with the routing algorithms based on particle swarm optimization (PSO) and genetic algorithm (GA), is tested on randomly generated network topologies for the purpose of performance evaluation. The simulation results show the efficiency of the proposed method on QoS the routing problem and its superiority to the methods based on PSO and GA.