基于多条件约束的ASON动态组播路由算法

在将自动交换光网络(ASON)建模成着色多重图的基础上采用综合成本策略,设计了一种新的最小综合成本路径计算算法,并结合组播成员的动态变化特性提出一种满足多条件约束的动态组播路由(DMRMC)算法,使组播路由和波长分配在同一过程内完成,且尽可能使组播树的综合总成本最小,同时局部优化波长转换次数、分光次数和不同波长的使用数量。仿真实验表明,本文算法有效可行,与采用单成本策略的组播算法相比,其取得了更低的综合成本和更好的连接阻塞性能。     

Optimization of wavelength assignment for QoS multicast in WDMnetworks

This paper discusses quality-of-service (QoS) multicast in wavelength-division multiplexing (WDM) networks. Given a set of QoS multicast requests, we are to find a set of cost suboptimal QoS routing trees and assign wavelengths to them. The objective is to minimize the number of wavelengths in the system. This is a challenging issue. It involves not only optimal QoS multicast routing, but also optimal wavelength assignment. Existing methods consider channel setup in WDM networks in two separate steps: routing and wavelength assignment, which has limited power in minimizing the number of wavelengths. In this paper, we propose a new optimization method, which integrates routing and wavelength assignment in optimization of wavelengths. Two optimization algorithms are also proposed in minimizing the number of wavelengths. One algorithm minimizes the number of wavelengths through reducing the maximal link load in the system; while the other does it by trying to free out the least used wavelengths. Simulation results demonstrate that the proposed algorithms can produce suboptimal QoS routing trees and substantially save the number of wavelengths     

Virtual-node-based multicast routing and wavelength assignment in sparse-splitting optical networks

This paper investigates several problems associated with optical multicast routing and wavelength assignment in sparse-splitting optical networks for interactive real-time media distribution. Unfortunately, the constrained multicast routing with optimized wavelength assignment leads to NP-complete condition. Thus, in this paper, a virtual-node-based multicast routing algorithm is first proposed to satisfy the requirements of interactive real-time multicasting as well as the constraints from underlying optical networks. For the constructed multicast tree, we then associate an effective wavelength assignment algorithm. The experimental results show that the proposed algorithm combination performs well in terms of (1) the wavelength channel cost, (2) the maximum variation of inter-destination node delays, (3) the signal quality, and (4) the number of wavelength conversions.     

Multicast routing, load balancing, and wavelength assignment ontree of rings

There are two steps to establish a multicast connection in WDM networks: routing and wavelength assignment. The shortest path tree (SPT) and minimum spanning tree (MST) are the two widely used multicast routing methods. The SPT method minimizes the delay from the source to every destination along a routing tree, and the MST method is often used to minimize the network cost of the tree. Load balancing is an important objective in multicast routing, which minimizes the maximal link load in the system. The objective of wavelength assignment is to minimize the number of wavelengths used in the system. This paper analyzes the performance of the shortest path tree (SPT) and minimum spanning tree (MST) methods in the tree of ring networks, regarding the performance criteria such as the delay and network cost of the generated routing trees, load balancing, and the number of wavelengths required in the system. We prove that SPT and MST methods can not only produce routing trees with low network costs and short delays, but also have good competitive ratios for the load balancing problem (LBP) and wavelength assignment problem (WAP), respectively     

Multicast routing and wavelength assignment in multihop optical networks

This paper addresses multicast routing in circuit-switched multihop optical networks employing wavelength-division multiplexing. We consider a model in which multicast communication requests are made and released dynamically over time. A multicast connection is realized by constructing a multicast tree which distributes the message from the source node to all destination nodes such that the wavelengths used on each link and the receivers and transmitters used at each node are not used by existing circuits. We show that the problem of routing and wavelength assignment in this model is, in general, NP-complete. However, we also show that for any given multicast tree, the wavelength assignment problem can be solved in linear time.     

Multicast wavelength assignment with sparse wavelength converters to maximize the network capacity using ILP formulation in WDM mesh networks

In general, multicast routing and wavelength assignment (MC-RWA) can be subdivided in routing and wavelength assignment issues in wavelength-division multiplexing (WDM) mesh networks. Previous studies on WDM multicast have mainly focused on WDM multicast routing. The multicast wavelength assignment problem is studied in this paper. A unicast routing path can be established by a lightpath in an all-optical network. However, in the multicasting case, a multicast routing tree can be established by a single light-tree or several lightpaths, or a combination of several light-trees and lightpaths. We propose a wavelength assignment algorithm for finding an optimal combination of lightpaths and light-trees to construct a newly required multicast session. First of all, two cost functions are given to evaluate the establishing cost for each feasible wavelength, and then find a set of wavelengths that covers all destinations with the minimal cost using Integer Linear Programming (ILP) formulation. We focus on maximizing the total number of users served in a multicast session and the network capacity. The simulation results show that the proposed algorithm can improve system resource utilization and reduce the blocking probability compared with the First-Fit algorithm.This research was partially supported by the Grant of National Science Council, R.O.C. (NSC 94-2745-E-155-007-URD).     

Efficient routing and wavelength assignment for multicast in WDMnetworks

The next generation multimedia applications such as video conferencing and HDTV have raised tremendous challenges on the network design, both in bandwidth and service. As wavelength-division-multiplexing (WDM) networks have emerged as a promising candidate for future networks with large bandwidth, supporting efficient multicast in WDM networks becomes eminent. Different from the IP layer, the cost of multicast at the WDM layer involves not only bandwidth (wavelength) cost, but also wavelength conversion cost and light splitting cost. It is well known that the optimal multicast problem in WDM networks is NP-hard. In this paper, we develop an efficient approximation algorithm consisting of two separate but integrated steps: multicast routing and wavelength assignment. We prove that the problem of optimal wavelength assignment on a multicast tree is not NP-hard; in fact, an optimal wavelength assignment algorithm with complexity of O(NW) is presented. Simulation results have revealed that the optimal wavelength assignment beats greedy algorithms by a large margin in networks using many wavelengths on each link such as dense wavelength-division-multiplexing (DWDM) networks. Our proposed heuristic multicast routing algorithm takes into account both the cost of using wavelength on links and the cost of wavelength conversion. The resulting multicast tree is derived from the optimal lightpaths used for unicast     

Wavelength assignment for multicast in all-optical WDM networks with splitting constraints

Multicast is an important application in all-optical WDM networks. The wavelength assignment problem for WDM multicast is to assign a set of wavelengths to the links of a given multicast tree. In an all-optical WDM network without wavelength conversions, wavelength assignment is the key to guarantee the quality of service and to reduce communication costs. In this paper, we study wavelength assignment for WDM multicast with two criteria, to cover the maximum number of destinations, and to minimize the wavelength costs. The computational complexity of the problem is studied. Three heuristic algorithms are proposed and the worst-case approximation ratios for some heuristic algorithms are given. We also derive a lower bound of the minimum total wavelength cost and an upper bound of the maximum number of reached destinations. The efficiency of the proposed heuristic algorithms and the effectiveness of the derived bounds are verified by the simulation results.     

Avoidance of multicast incapable branching nodes for multicast routing in WDM networks

In this article we study the multicast routing problem in all-optical WDM networks under the spare light splitting constraint. To implement a multicast session, several light-trees may have to be used due to the limited fanouts of network nodes. Although many multicast routing algorithms have been proposed in order to reduce the total number of wavelength channels used (total cost) for a multicast session, the maximum number of wavelengths required in one fiber link (link stress) and the end-to-end delay are two parameters which are not always taken into consideration. It is known that the shortest path tree (SPT) results in the optimal end-to-end delay, but it can not be employed directly for multicast routing in sparse light splitting WDM networks. Hence, we propose a novel wavelength routing algorithm which tries to avoid the multicast incapable branching nodes (MIBs, branching nodes without splitting capability) in the shortest-path-based multicast tree to diminish the link stress. Good parts of the shortest-path-tree are retained by the algorithm to reduce the end-to-end delay. The algorithm consists of tree steps: (1) a DijkstraPro algorithm with priority assignment and node adoption is introduced to produce a SPT with up to 38% fewer MIB nodes in the NSF topology and 46% fewer MIB nodes in the USA Longhaul topology, (2) critical articulation and deepest branch heuristics are used to process the MIB nodes, (3) a distance-based light-tree reconnection algorithm is proposed to create the multicast light-trees. Extensive simulations demonstrate the algorithm’s efficiency in terms of link stress and end-to-end delay.     

光组播路由代价与波长使用量的联合优化方法

为解决光组播路由中组播中路由代价和波长资源消耗单一化造成的组播路树路由的代价过高问题,在分光节点约束条件下,提出了光组播路由代价与波长使用量联合优化的长路优先(LPF)方法和短路优先(SPF)方法。算法通过检查最小光组播树是否存在节点分光约束的问题,根据设置的波长使用代价控制因子,使LPF或SPF的路由代价和波长使用量最小。LPF方法首先选择组播树最长路径或新波长通道重路由受分光约束的目的节点,SPF方法先选择组播树中最短路径或新波长通道重路由受分光约束的目的节点,仿真结果表明,本文提出的两种联合优化方法都能实现路由代价较低和波长需求较少的目的。     

Optimal and heuristic algorithms for all‐optical group multicast in resource‐constrained WDM networks

Given a sparse‐splitting wavelength‐division multiplexing network with no wavelength converter, we study a group multicast problem that is how to transmit a number of multicast streams from the video server to multiple destinations simultaneously. To avoid the situation that the wavelengths are used up by the first few requests, one wavelength is available for each multicast request. Hence, some of destinations may not be included in the multicast trees because of the lack of wavelengths. Our goal is to construct a number of light trees with conflict‐free wavelengths for multiple requests so that the number of served clients is maximized. This problem is named as the revenue‐maximized and delay‐constrained group multicast routing problem. We first determine a set of multicast trees with the maximum number of served clients, then followed by the wavelength assignment to allocate the minimum number of wavelengths to the resulting trees. In this study, we propose two Integer Linear Programming ILP‐based algorithms for determining the optimal solutions for the light‐tree construction problem and the wavelength assignment problem, respectively. For large‐scale networks, two heuristics are introduced to solve the light‐tree construction problem approximately. A set of simulations are also provided for comparing performances of our algorithms against the other published methods. Copyright © 2016 John Wiley & Sons, Ltd.     

A multicast dynamic wavelength assignment algorithm based on matching degree

The wavelength assignment with multiple multicast requests in fixed routing WDM network is studied. A new multicast dynamic wavelength assignment algorithm is presented based on matching degree. First, the wavelength matching degree between available wavelengths and multicast routing trees is introduced into the algorithm. Then, the wave.length assignment is translated into the maximum weight matching in bipartite graph, and this matching problem is solved by using an extended Kuhn-Munkres algorithm. The simulation results prove that the overall optimal wavelength assignment scheme is obtained in polynomial time. At the same time, the proposed algorithm can reduce the connecting blocking probability and＂ improve the system resource utilization.     

New algorithms for multicast routing and wavelength assignment in multi-hop optical WDM networks

We study the problem of multicast routing and wavelength assignment (MC-RWA) in multi-hop optical WDM networks with respect to several target functions. Specially, we first study the MC-RWA problem under the target of minimize maximum hops, an efficient MC-RWA algorithm was proposed for that case. But for the objective of minimizing the total number of wavelength conversions, problem turns out to be NP-hard, we proposed a new approximation MC-RWA algorithm based on group Steiner tree. At last, combining the two objectives, a bi-factor approximation algorithm was introduced to minimize the both targets in the system simultaneously.     

Dynamic routing and wavelength assignment for limited-range wavelength conversion

We propose a dynamic routing and wavelength assignment algorithm in an all-optical network with limited-range wavelength conversions. For each randomly arrived request, the correlation of different wavelengths on different links in all possible routes is described by the wavelength weight in our algorithm. We try to assign wavelengths on each candidate route using a shortest-path algorithm based on the wavelength weight and choose the best as its route and wavelength assignment scheme. Numerical results obtained for NSFNET and a 12-node ring show that our algorithm can greatly reduce the blocking probability and the number of required conversions under uniform traffic or traffic dominated by larger hop routes.     

On the design of multi-wavelength copy interconnects with reduced complexity

A multi-wavelength copy interconnect is a switching network capable of replicating a signal arriving at the input on a specific wavelength to one or more outputs possibly on different wavelengths. Such an interconnect can be useful in building optical multicast switches for wavelength division multiplexing (WDM) networks. In this article, we investigate, for the first time, the problem of designing copy networks that can simultaneously multicast input signals to a set of outputs while changing the wavelength of the replica according to the required routing pattern. We propose a novel multi-wavelength crossbar (MWX) switch that can switch an input signal on a specific wavelength to two different output wavelengths. The proposed MWX is used as a building block to construct two classes of multi-log_2N copy networks, namely, baseline and Bene? interconnects. The design space of the proposed interconnect classes is characterized and their hardware complexity is analyzed. We show that the proposed interconnects are transparent to existing multicast routing algorithms, and present simple routing algorithms for routing of multicast requests over the proposed designs. Comparisons with existing designs confirm that the proposed interconnects require a smaller number of space switches and wavelength conversion processes as compared to most conventional copy networks. In particular, for a large number of wavelengths and for any number of fibers the proposed design requires 50% less switching elements as compared to best available designs.     

Wavelength assignment with sparse wavelength conversion for optical multicast in WDM networks

This paper addresses the problem of multicast wavelength assignment for sparse wavelength conversion (MWA-SWC) in wavelength-routed wavelength-division-multiplexing (WDM) networks. It aims to optimally allocate the available wavelength for each link of the multicast tree, given a sparse wavelength conversion network and a multicast request. To our knowledge, little research work has been done to address this problem in literature.In this paper, we propose a new technique called MWA-SWC algorithm to solve the problem. The algorithm first maps the multicast tree from the sparse conversion case to the full conversion case by making use of a novel virtual link method to carry out the tree mapping. The method provides a forward mapping to generate an auxiliary tree as well as a reverse mapping to recover the original tree. Applying the auxiliary tree, we propose a dynamic programing algorithm for the wavelength assignment (WA) aiming to minimize the number of wavelength converters (NWC) required. Simulation results show that our new algorithm outperforms both random and greedy algorithms with regard to minimizing the NWC. Testing on various scenarios by varying the number of wavelength conversion nodes in the tree has confirmed the consistency of the performance. The primary use of the MWA-SWC algorithm is for static traffic. However, it can also serve as a baseline for dynamic heuristic algorithms. Typically, the MWA-SWC algorithm will provide great benefit when the number of available wavelengths on each link of the multicast tree is relatively large and the performance advantage is significant.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance assessment of multicast node placement for multicast routing in WDM networks with sparse light splitting

This article examines all-optical multicast routing for wavelength-routed optical networks with sparse Multicast Capable (MC) nodes in two phases. The first phase is MC node placement and use of a simple and straightforward Maximum Path Count First (MPCF) algorithm to obtain candidates for MC nodes. The second phase is multicast routing with MC-based schemes that minimizes the number of wavelength channels with minimum transmission delay as required by a given multicast session, in that a light-tree is first constructed to connect MC nodes in a multicast group by using two algorithms, namely, the Pre-computing Minimum Cost (PMC) tree algorithm and the Pre-computing Shortest Path (PSP) tree algorithm. System performance of the proposed MPCF MC node placement algorithm is compared with that of the Normalized Cuts (NC) MC node placement algorithm for both PMC and PSP multicast routing. Furthermore, simulation results compare PMC and PSP multicast routing based on MPCF and NC node placement with Re-route-to-Source (RTS), Re-route-to-Any (RTA), Member-First (MF), and Member-Only (MO) multicast routing based on a light forest for a given multicast session in terms of average number of wavelengths needed, average blocking probability, and mean maximum transmission delay.

Routing and wavelength assignment based on genetic algorithm

In this letter, the routing and wavelength assignment problem in all optical networks is considered. We improve the Max-RWA model presented by R. M. Krishnaswamy and K. N. Sivarajan (see ibid., vol.5, p.435-7, Oct. 2001) by introducing limited-range wavelength conversions. Considering transmission performance, we propose a new optimization objective, which is to establish the maximum number of connections with the least number of wavelength converters. The modified Max-RWA problem is formulated as a integer linear programming (ILP) problem, and then solved using a genetic algorithm. The extended layered-graph approach is used to assign routes and wavelengths when necessary, thus reducing the complexity of the genetic algorithm. Numerical results obtained for NSFNET are presented     

MC-BRM: A distributed RWA algorithm with minimum wavelength conversion

There are two strategies for solving Routing and Wavelength Assignment (RWA) in wavelength-routed networks: centralized and distributed. Centralized approaches are appropriate for small networks with light traffic, whereas distributed approaches are suitable for large networks with heavy traffic. Solving RWA problem in distributed algorithms can be generally divided into two phases: routing phase and wavelength assignment phase. Allocating a wavelength over a physical path for a connection request can be performed by one of two major strategies: Backward Reservation Method (BRM) and Forward Reservation Method (FRM). In this work, we assume that every node in the network can be equipped with a number of wavelength converters. Wavelength converters are usually chosen in a free policy. However, we propose a distributed algorithm, called Minimum-Conversion Backward Reservation Method (MC-BRM), that attempts to establish light-paths with minimum number of wavelength conversions. The MC-BRM algorithm can efficiently reduce the number of required wavelength conversions in the network. Besides improving blocking probability, MC-BRM can lead to better fairness in establishing light-paths with different number of hops. Finally, we make the worst case analysis for estimating wavelength conversion usages in individual nodes.