A Lagrangean relaxation-based approach for routing and wavelength assignment in multigranularity optical WDM networks

Optical wavelength-division multiplexed (WDM) networks often include optical cross-connects with multigranularity switching capability, such as switching on a single lambda, a waveband, or an entire fiber basis. In addition, it has been shown that routing and wavelength assignment (RWA) in an arbitrary mesh WDM network is an NP-complete problem. In this paper, we propose an efficient approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve RWA in multigranularity WDM networks particularly with lambda and fiber switches. The task is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. The LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. With lower and upper bounds, we conduct a performance study on LRH with respect to accuracy and convergence speed under different parameter settings. We further draw comparisons between LRH and an existing practical approach via experiments over randomly generated and several well-known large sized networks. Numerical results demonstrate that LRH outperforms the existing approach in both accuracy and computational time complexity, particularly for larger sized networks.     

光网中路由与波长分配问题的一种新模型

路由与波长分配问题是波分复用光网中的一个关键问题.文章从经济学的角度出发提出了路由与波长分配问题的一种数学模型,并且进行了分析和仿真.结果表明,模型较大程度地反应了现实,对网络运营商而言很有参考价值.     

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.     

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.     

全光网静态路由选择和波长分配的分层图算法

文章提出一种将路由选择和波长分配结合起来的启发式的路由选择和波长分配(RWA)算法．通过这种新的分层图算法和限制光跳距的加权系数来优化全光网的静态路由选择和波长分配，使建立光连接时所需的波长数达到最少．最后对实际的ARPANet等5种光网络进行了计算机仿真，证明了本算法比以前的算法有更好的性能．     

A tabu search heuristic for the routing and wavelength assignment problem in optical networks

This letter proposes a tabu search heuristic for solving the routing and wavelength assignment (RWA) problem in optical WDM networks, considering the wavelength continuity constraint and a given set of connections to satisfy. For a number of available wavelengths on each link, this algorithm attempts to maximize the number of routed connections. The algorithm has been implemented and tested on NSFNET and EONNET networks and comparisons have been done with other algorithms in terms of the blocking rate. Generally, the results obtained with our tabu search heuristic are better than those provided by these algorithms.     

抗毁WDM网中支持QoS的选路和波长分配算法

该文首先探讨了抗毁WDM网中支持QoS的分层图模型,在此基础上提出一种抗毁WDM网中支持QoS的选路和波长分配算法。该算法根据上层业务不同的QoS要求,对其光路建立请求区别对待,以满足它们不同的阻塞率和恢复率要求。计算机仿真结果表明该算法既满足了上层业务不同的QoS要求,同时又充分利用了有限的网络资源,使全网的平均阻塞率降低。     

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.     

A tabu search heuristic for the routing and wavelength assignment problem in multigranular optical networks

This paper proposes a tabu search heuristic for solving the routing and wavelength assignment problem in multigranular optical networks, considering the wavelength-continuity constraint and a set of connections to satisfy. For a number of fibers per link, a number of wavebands per fiber, and a number of wavelengths per waveband, this algorithm attempts to minimize the total number of ports used in the network by efficiently grouping lightpaths into bands and fibers, and switching the whole bands and fibers. The algorithm has been implemented and tested on the NSFNET network, and comparisons have been made with the Balanced Path Routing and Heavy Traffic First (BPHT) algorithm in terms of number of ports. Generally, the results obtained with our tabu search heuristic are better than those provided by this algorithm.

Distributed dynamic grooming routing and wavelength assignment in WDM optical mesh networks

The bandwidth of a wavelength channel in WDM optical networks is very high compared to the user’s requirements for various applications. Therefore, there is a scope for better utilization of channel bandwidth by traffic grooming, in which several user’s channels are multiplexed for transmission over a single channel. Several research works have been reported on traffic grooming routing and wavelength assignment (GRWA) for static and dynamic traffic pattern under centralized environment. Distributed dynamic grooming routing and wavelength assignment (DDGRWA) is a new and quite unexplored area in WDM optical mesh networks. This article introduces the concept of distributed traffic grooming in WDM mesh networks which also includes virtual topology construction, reconfiguration, routing and wavelength assignment in the distributed environment assuming incoming traffic to be dynamic in nature. We have also presented simulation results of our algorithm on dynamically generated traffic under various network topologies.     

A new approach for routing and wavelength assignment for permanent and reliable wavelength paths in wide all-optical WDM networks

This article proposes a new approach for routing and wavelength assignment (RWA) for permanent and reliable wavelength paths (WP) in wide all-optical WDM networks with wavelength continuity constraint. Given a number of available wavelengths on each optical fiber, for each simple link failure of the network, we seek to maximize the number of satisfied requests for connections. This is known as RWAP problem. In our algorithm, called RWA with Minimum Loaded Link for Permanent and Reliable wavelength paths (MLL-PR), routing is based on the search for the optimal path while trying to minimize the maximum load on the links of the network in order to minimize the maximum link capacity and then minimize the number of dropped lightpaths after any link failure. The wavelength assignment is based on a graph coloring method using tabu-search. A series of experiments using two well-known networks (ARPANET and NSFNET) have been carried out in order to evaluate the performance of our approach, in terms of the number of blocked demands, for different failure scenarios. Generally, our results are better than those provided by the current solving approaches taken as reference.

WDM全光网自适应路由和波长分配算法

研究了无波长转换WDM全光网的路由和波长分配算法（RWA）。通过对已有算法的分析和比较,提出了一种自适应最小跳数路由算法（ADMH）。此算法以最小跳数路由为基础,同时考虑网络状态的变化,因而不仅能尽量少使用网络资源,也能使网络资源的分布保持均衡。计算机模拟仿真的结果表明,这种算法性能在各种网络参数条件下优于或等于已有算法。     

基于节点功能的WDM光网络分布式路由与波长分配算法

建立了一种具有节点功能区分的WDM多波长光网络模型,根据节点功能将其分为A、B两类,在此基础上提出了波长等价弧和等价网络等概念,并根据此类多波长光网络模型的节点和网络结构特点以及相应的选路和波长分配策略,提出了一种基于节点功能的多波长光网络分布式路由与波长分配算法——BONF算法,证明了算法的可行性,分析了算法的计算复杂度,比较了此算法与其它同类型算法的区别,指出了BONF算法的优点和不足。     

Ant colony optimization based load balancing routing and wavelength assignment for optical satellite networks

An ant colony optimization (ACO) based load balancing routing and wavelength assignment (RWA) algorithm (ALRWA) was put forward for the sake of achieving a fairy load balancing over the entire optical satellite networks. A multi-objective optimization model is established considering the characteristic of global traffic distribution. This not only employs the traffic intensity to modify the light path cost, but also monitors the wavelength utilization of optical inter-satellite links (ISLs). Then an ACO algorithm is utilized to solve this model, leading to finding an optimal light path for every connection request. The optimal light path has the minimum light path cost under satisfying the constraints of wavelength utilization, transmission delay and wavelength-continuity. Simulation results show that ALRWA performs well in blocking probability and realizes efficient load balancing. Meanwhile, the average transmission delay can meet the basic requirement of real-time business transmission.     

一种基于改进蚁群算法的光网络动态RWA机制

动态RWA(路由与波长分配)问题是智能光网络的核心问题.文章提出一种解决动态RWA问题的改进蚁群算法,在转移概率中加入了链路的空闲率作为约束条件,同时还引入了随机扰动防止搜索过早收敛于局部最优路径.仿真结果表明,改进算法与传统Dijkstra+ FF(首次命中)算法相比,可以显著降低阻塞率,提高资源利用率.     

Routing and wavelength assignment in optical networks

The problem of routing and wavelength assignment (RWA) is critically important for increasing the efficiency of wavelength-routed all-optical networks. Given the physical network structure and the required connections, the RWA problem is to select a suitable path and wavelength among the many possible choices for each connection so that no two paths sharing a link are assigned the same wavelength. In work to date, this problem has been formulated as a difficult integer programming problem that does not lend itself to efficient solution or insightful analysis. In this work, we propose several novel optimization problem formulations that offer the promise of radical improvements over the existing methods. We adopt a (quasi-)static view of the problem and propose new integer-linear programming formulations, which can be addressed with highly efficient linear (not integer) programming methods and yield optimal or near-optimal RWA policies. The fact that this is possible is surprising, and is the starting point for new and greatly improved methods for RWA. Aside from its intrinsic value, the quasi-static solution method can form the basis for suboptimal solution methods for the stochastic/dynamic settings.     

Dynamic routing and wavelength assignment in multi-granularity WDM networks

For the purpose of reducing the complexity and cost of optical large-scale cross-connect, wavelengths are grouped into wavebands or fiber to be switched as a single entity, which is called multi- granularity switching. However, it introduces more complexity into the routing and wavelength assignment problem. In this paper, we propose a novel graph model for describing the states of the multi-granularity switching WDM networks. Based on the model, the dynamic routing and wavelength assignment problems for multi-granularity traffic can be solved jointly, and different on-line wavelength grooming policies can be achieved simultaneously. By simulation, we compared the performance of our algorithms under different policy and different percent of fibers for fiber switching. The result proved that our algorithms yield better performance than those deal with the routing and wavelength assignment separately. This work was supported in part by NSFC Project No. 90104003, 60272023, 60372025 and National 863 project No. 2005AA122310.     

WDM网络中支持QoS的路由与波长分配算法

针对波分复用(wDM)网络中的路由与波长分配问题。提出了一种支持服务质量(QoS)的约束搜索算法。基于多目标规划模型,这种搜索算法可为网络各节点创建路由表,根据路由表信息求出非支配路径集合,从而一次性完成寻找路由和分配波长两项任务。仿真实例证明了该算法的有效性。     

WDM光网络中一种备用路由下支持优先级的波长分配算法

研究了WDM光网络中的动态业务下的波长分配问题,在无波长转换器的条件下提出了一种改进的动态门限算法.该算法不仅能保证高优先级请求有较低的阻塞率,同时还能优化低优先级请求的阻塞率,从而改善全网的平均阻塞率.此外,该算法利用负载均衡算法,能更加精确地描述波长分配对全网状态的影响,从而更加有效地利用了网络资源.计算机仿真结果证明了该算法的有效性.     

WDM光网中的一种邻域加权累积的波长分配策略

针对光核心传送网中单纤场景下的路由选择与波长分配（Routing and Wavelength Assignment,RWA）问题,提出了一种邻域加权累积的波长分配策略。在一条路径上为一个连接请求选择波长时,将网络的所有链路归入当前路径的不同邻域中,然后根据与路径之间的距离为不同邻域赋予不同的权重,进而对每个波长在全网中被占用的个数进行加权累积,最后选择累积值最大的可用波长建立连接。仿真结果表明,相对于现有的阻塞率最低的最大使用（Most-Used）波长分配策略,所提策略具有更低的阻塞率。