一种WDM疏导网络动态组播路由算法

对无波长变换能力的波分复用（WDM）疏导网络中的组播路由和波长分配（MRWA）问题进行了研究，提出了动态组播流量疏导算法（DMTGA）。这种算法根据当前网络资源使用情况，结合流量疏导和负载均衡，对链路权重进行动态配置，构建满足组播业务请求带宽需求的组播树。在不同的网络负载下对算法进行仿真，对比分析了DMTGA对业务请求接入率、平均网络资源利用率和全网负载分布的影响。     

Virtual Source Based Multicast Routing in WDM Optical Networks

Wavelength-division multiplexed (WDM) networks using wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. Multicasting is the ability to transmit information from a single source node to multiple destination nodes and is becoming an important requirement in high-speed networks. As WDM technology matures and multicast applications become increasingly popular, supporting multicast routing at the WDM layer becomes an important and yet a challenging topic. This paper concerns with the problem of optical multicast routing in WDM networks. A few nodes in the network may have wavelength conversion and/or splitting capabilities. In this paper, a new multicast tree construction algorithm is proposed. This algorithm is based on a concept called virtual source. A virtual source is a node having both the splitting and wavelength conversion capabilities. By exploiting the presence of virtual source nodes, the proposed algorithm achieves improved performance. To further improve the performance, the algorithm assigns priorities to nodes based on their capabilities. The effectiveness of the proposed algorithm is verified through extensive simulation experiments.     

On Finding the Multicast Protection Tree Considering SRLG in WDM Optical Networks

In this letter, a new sharing mechanism, SRLG sharing, is proposed, which allows the links of the same shared risk link group (SRLG) in a primary light tree to share protections in WDM optical networks. In previous studies, how to share spare resources with SRLG constraints has not been studied in multicast optical networks. In this letter, considering SRLG sharing, we propose a novel algorithm –multicast with SRLG sharing (MSS)– to establish a protection light tree. Finally, the algorithm MSS and the algorithm multicast with no SRLG sharing (MNSS) are compared through a simulation to show that our new sharing scheme of SRLG sharing is more efficient than that of no SRLG sharing in terms of spare resource utilization and blocking probability.     

Dynamic Multicast Session Provisioning in WDM Optical Networks with Sparse Splitting Capability

In this work, we study dynamic provisioning of multicast sessions in a wavelength-routed sparse splitting capable WDM network with an arbitrary mesh topology where the network consists of nodes with full, partial, or no wavelength conversion capabilities and a node can be a tap-and-continue (TaC) node or a splitting and delivery (SaD) node. The objectives are to minimize the network resources in terms of wavelength-links used by each session and to reduce the multicast session blocking probability. The problem is to route the multicast session from each source to the members of every multicast session, and to assign an appropriate wavelength to each link used by the session. We propose an efficient online algorithm for dynamic multicast session provisioning. To evaluate the proposed algorithm, we apply the integer linear programming (ILP) optimization tool on a per multicast session basis to solve off-line the optimal routing and wavelength assignment given a multicast session and the current network topology as well as its residual network resource information. We formulate the per session multicast routing and wavelength assignment problem as an ILP. With this ILP formulation, the multicast session blocking probability or success probability can then be estimated based on solving a series of ILPs off-line. We have evaluated the effectiveness of the proposed online algorithm via simulation in terms of session blocking probability and network resources used by a session. Simulation results indicate that our proposed computationally efficient online algorithm performs well even when a fraction of the nodes are SaD nodes.     

Dynamic Routing in WDM Grooming Networks

Traffic grooming in optical networks has gained significant importance in recent years due to the prevailing sub-wavelength traffic requirement of end-users. In this paper, a methodology for dynamic routing of fractional-wavelength traffic in WDM grooming networks is developed. To evaluate the performance of routing algorithms, a new performance metric that reflects the network utilization is also proposed. The performances of shortest-widest path, widest-shortest path, and available shortest path routing algorithms are evaluated on a class of WDM grooming networks by considering traffic of different capacity requirements. The effect of dispersity routing, where higher capacity requests are broken into multiple unit capacity requests, is also investigated. The most interesting counter-intuitive result that is observed is that increasing the grooming capability in a network could result in degrading the performance of the widest-shortest path algorithm.     

Minimizing the Number of Multicast Transmissions in Single-Hop WDM Networks

The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.     

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.     

WDM疏导网络中一种新的多播业务路由算法

研究了波分复用(WDM)网状网中动态多播业务量疏导,提出一种新的辅助疏导模型,其可以描述当前网络资源状况和节点分光特点,并动态更新.进而提出一种有效的多播业务量疏导启发式算法(MGA),将业务的多播选路和波长分配同时完成.仿真表明,该算法在波长连续性限制、网络波长和节点收发器数目有限的情况下,具有较低网络阻塞率.     

Scheduling Combined Unicast and Multicast Traffic in Broadcast WDM Networks

This paper studies the performance of various strategies for scheduling a combined load of unicast and multicast traffic in a broadcast WDM network. The performance measure of interest is schedule length, which directly affects both aggregate network throughput and average packet delay. Three different scheduling strategies are presented, namely: separate scheduling of unicast and multicast traffic, treating multicast traffic as a number of unicast messages, and treating unicast traffic as multicasts of size one. A lower bound on the schedule length for each strategy is first obtained. Subsequently, the strategies are compared against each other using extensive simulation experiments in order to establish the regions of operation, in terms of a number of relevant system parameters, for which each strategy performs best. Our main conclusions are as follows. Multicast traffic can be treated as unicast traffic, by replicating all multicast packets, under very limited circumstances. On the other hand, treating unicast traffic as a special case of multicast traffic with a group of size 1, produces short schedules in most cases. Alternatively, scheduling and transmitting each traffic component separately is also a good choice.     

A Novel Distributed Protocol for Path Selection in Dynamic Wavelength-Routed WDM Networks

This paper solves the problem of path selection for WDM mesh networks with a special focus on the implementation in middle-sized networks, such as metropolitan-area networks (MANs). A novel routing and signaling protocol, called asynchronous criticality avoidance (ACA), is proposed to improve the network performance. With the ACA protocol, a specific set of wavelength channels are defined as critical links between a node pair according to dynamic link-state. Criticality information is defined as the critical links and the associated information, which is coordinated and disseminated by each source node to every other source node as an inter-arrival critical coordination. Routing and wavelength assignment is performed along with the criticality avoidance mechanism, in which path selection process is devised to take the criticality information into consideration. Simulation is conducted in 22- and 30-node networks to examine the proposed approach. The simulation results show that the ACA protocol significantly outperforms the fixed-path least-congested (FPLC) and adaptive dynamic routing (ADR) schemes under the fixed alternate routing architecture.     

Performance of Adaptive Routing in Wavelength-Routed Networks with Wavelength Conversion Capability

This paper concerns itself with the performance of adaptive routing in wavelength-routed networks with wavelength conversion capability. Exploiting the concept of load balancing, we propose an adaptive weighted-shortest-cost-path (WSCP) routing strategy. The salient feature of WSCP is that it seeks the path that minimizes the resource cost while simultaneously maintaining the traffic load among the links as balanced as possible. In our simulation, we compare the blocking probability, average hops and link utilization of WSCP with traditional shortest-cost-path (SCP) strategy, fixed routing and alternate routing. The numerical results show that WSCP can enhance blocking performance and just lengthen hop distances a little longer. The improvement is more significant in denser networks or with more wavelengths. We also develop an analytical model to estimate blocking performance of WSCP and compare analyses with simulations. Because of the benefit from load balancing, the proposed WSCP strategy can be used as a path selection algorithm in traffic engineering.     

多光纤波分复用网动态路由和波长分配算法

本文研究了多光纤波分复用光互连网的动态路由和波长分配问题,提出了基于分层图模型的两种动态路由算法,LG-1和LG-2.这两种算法将路由和波长分配问题转换为如何在分层图中支持尽可能多的光路.这使得设计者可以同时考虑路由和波长分配子问题,从而取得了更好的效果.计算机仿真表明基于分层图的算法大大优于传统的固定路由和动态路由算法.     

WDM光网络的研究进展

波分复用技术（WDM）在主干传送网应用越来越普遍,WDM网络技术的研究也获得了迅速发展,综述了当前主干WDM网络的最新研究进展和发展趋势。     

A Scalable and Reliable Multicast Routing Protocol for Ad-hoc Wireless Networks

Multicasting is an essential service for ad-hoc wireless networks. In a multicasting environment with multiple senders, receivers or meeting members, traditional multicast routing protocols must pay great overhead for multiple multicast sessions. This work presents a scalable and reliable multicasting protocol for ad-hoc wireless networks. A virtual backbone is used as a shared structure for multiple sessions. A clustering scheme is used to reduce the routing path length. A novel scheme is developed to effectively multicast packets using forwarding gates. Furthermore, a lost packet recovery scheme is developed for reliable packet transmission. This scheme can be used to improve the reliability of traditional non-acknowledged multicasting approach. Experiments were conducted to evaluate the proposed multicasting scheme and the results demonstrate that our scheme outperforms other schemes in terms of packet delivery ratio, packet delivery time, control overhead, multicast efficiency, and cost effect. Furthermore, our approach is stable for networks with high mobility and the lost packet recovery scheme is cost-effective. Chyi-Ren Dow was born in 1962. He received the B.S. and M.S. degrees in information engineering from National Chiao Tung University, Taiwan, in 1984 and 1988, respectively, and the M.S. and Ph.D. degrees in computer science from the University of Pittsburgh, USA, in 1992 and 1994, respectively. Currently, he is a Professor in the Department of Information Engineering, Feng Chia University, Taiwan. His research interests include mobile computing, ad-hoc wireless networks, agent techniques, fault tolerance, and learning technology. Jyh-Horng Lin was born in 1975. He received the B.S. and M.S. degrees in information engineering from Feng Chia University, Taiwan, in 1998 and 2000, respectively. He is currently a candidate for the Ph.D. degree in the Department of Information Engineering, Feng Chia University, Taichung, Taiwan. His research interests include mobile computing and ad-hoc wireless networks. Kun-Tai Chen was born in 1978. He received the B.S. and M.S. degrees in information engineering from Feng Chia University, Taiwan, in 2000 and 2002, respectively. He is currently an engineer in the VIA technologies, Inc. Hsinchu branch, Taiwan. His research interests include mobile computing, ad-hoc wireless networks and video decoding. Sheng-Chang Chen was born in 1979. He received his B.S. degree and M.S. degree in information engineering from Feng Chia University, Taiwan, in 2001 and 2002. He is currently a Ph.D. degree in information engineering from Feng Chia University, Taiwan. His research interests include mobile computing, ad-hoc wireless network and fault tolerance technique. Shiow-Fen Hwang was born in 1963. She received her B.S., M.S. and Ph.D. degrees in Applied Mathematics from National Chiao Tung University, Taiwan, in 1985, 1987 and 1991, respectively. Currently, she is an Associate Professor in the Department of Information Engineering, Feng Chia University, Taiwan. Her research interests include interconnection networks, mobile computing, and computer algorithms.     

Impairment constraint multicasting in translucent WDM networks: architecture, network design and multicasting routing

The popularity of broadband streaming applications requires communication networks to support high-performance multicasting at the optical layer. Suffering from transmission impairments in multi-hop all-optical (transparent) WDM multicasting networks, the signal may be degraded beyond the receivable margin at some multicast destinations. To guarantee the signal quality, we introduce a translucent WDM multicasting network to regenerate the degraded signals at some switching nodes with electronic 3R (reamplification, reshaping and retiming) functionality. The translucent network is built by employing three kinds of multicasting capable switching architectures: (1) all-optical multicasting capable cross connect (oMC-OXC), (2) electronic switch and (3) translucent multicasting capable cross connect (tMC-OXC). Among them both the electronic switch and tMC-OXC are capable of electronic 3R regeneration. Furthermore, we propose a multicast-capable nodes placement algorithm based on regeneration weight, and two multicasting routing algorithms called nearest hub first and nearest on tree hub first to provide signal-quality guaranteed routes for the multicasting requests. The numerical simulation on two typical mesh networks shows that it is sufficient to equip 30% of the nodes or less with signal-regeneration capability to guarantee the signal quality.     

Routing Mechanisms Employing Adaptive Weight Functions for Shortest Path Routing in Optical WDM Networks

Optical dense wavelength division multiplexed (DWDM) networks are an attractive candidate for the next generation Internet and beyond. In this paper, we consider routing and wavelength assignment in a wide area wavelength routed backbone network that employs circuit-switching. When a session request is received by the network, the routing and wavelength assignment (RWA) task is to establish a lightpath between the source and destination. That is, determine a suitable path and assign a set of wavelengths for the links on this path. We consider a link state protocol approach and use Dijkstras shortest path algorithm, suitably modified for DWDM networks, for computing the shortest paths. In [1] we proposed WDM aware weight functions that included factors such as available wavelengths per link, total wavelengths per link. In this paper, we present new weight functions that exploit the strong correlation between blocking probability and number of hops involved in connection setup to increase the performance of the network. We also consider alternate path routing that computes the alternate paths based on WDM aware weight functions. The impact of the weight functions on the blocking probability and delay is studied through discrete event simulation. The system parameters varied include number of network nodes, wavelengths, degree of wavelength conversion, and load. The results show that the weight function that incorporates both hop count and available wavelength provides the best performance in terms of blocking probability.     

基于WDM网络的多播动态选路算法研究

提出了一个改进的稀疏分光器配置约束下的改进算法。在稀疏分光器配置约束下,多播路由不再是图论中”树”的形状,多播路由可能存在逻辑圈。现有的多播路由算法没有考虑这个特点,改进对此算法作了一下改进,通过仿真证明改进算法提高了网络性能。     

WDM光网络中基于链路的动态组播共享保护算法

针对WDM光网络中单链路失效的情况,提出了一种基于链路的保护动态组播业务的优化共享保护算法(Link-based optimized shared-protection algorithm for multicast sessions,LB-OSPM).该算法在对工作树任意光纤链路失效情况寻找保护路径时,允许组播内不同保护路径共享预留波长资源,同时通过引入预留波长使用情况矩阵和波长预留矩阵记录预留波长资源的使用情况,实现了不发生冲突的不同组播的保护链路间共享预留波长资源.研究采用欧洲光网络(European Optical Network,EON)的拓扑对不同波长资源配置和网络负载情况下LB-OSPM算法的网络连接阻塞率做了仿真.结果表明,通过引入共享机制,LB-OSPM算法在对单链路失效保证100％恢复率的同时可以获得更低的连接阻塞率,提高了波长资源利用效率.     

WDM格型光网络中的动态组播共享保护算法

该文针对WDM格型网络中单链路失效的情况,提出了一种保护动态组播业务的基于路径的优化共享保护(PB-OSPM)算法。该算法在基于最优路径对的共享不相交路径(OPP-SDP)算法的基础上,通过引入保护波长使用情况矩阵和波长预留矩阵记录预留波长资源的使用情况,允许不发生冲突的不同组播的保护路径间共享预留波长资源。研究采用欧洲光网络(EON)的拓扑对PB-OSPM算法和OPP-SDP算法在增性网络负载情况下的网络冗余度和同波长资源配置和网络负载情况下动态网络负载的网络连接阻塞率做了仿真。结果表明,相同条件下,PB-OSPM算法比OPP-SDP算法有更低的连接阻塞率。组播业务间波长资源的共享是提高波长资源利用率的有效方法。     

Priority-based Dynamic Lightpath Allocation for Survivable WDM Networks

In recent years, there has been considerable research interest in the design of survivable wavelength division multiplexing (WDM) networks. Many papers have proposed mixed-integer linear program (MILP) formulations as well as heuristics to optimally allocate lightpaths, using protection based schemes. Such schemes provide quick and guaranteed recovery, but do not use resources efficiently. About 50% of allocated resources remain idle, under fault-free conditions. If these “idle” resources were used for low-priority connections (which could be pre-empted if necessary), the resource utilization would improve significantly. This paper introduces two MILP formulations for priority-based dynamic lightpath allocation in survivable WDM networks. We define three different levels of service and allocate resources based on the requested service level. An important advantage of our approach is that while we can handle multiple levels of service, the traditional (single level) shared and dedicated path protection schemes can be treated simply as a special case of the proposed formulations. The first formulation solves the problem optimally, but is quite time consuming. The second formulation makes some simplifications, and is more efficient. The results demonstrate that our approach can significantly improve resource utilization and is feasible for practical sized networks, particularly under low- to medium-traffic load. For large networks and high traffic conditions, simpler heurtistic algorithms are more appropriate. In such cases, the proposed MILP formulation can be a useful tool to validate the performance of the heuristics.