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.     

DWDM光传送网中选路和波长分配

本文综述了密集波分复用（DWDM）光传送网中选路和波长分配（RAW）研究领域的最新研究成果。分析比较了固定路由和备用路由下不同RAW算法的性能,还讨论了不同情况下采用波长变换对网络性能的改善。     

Routing and wavelength assignment with multigranularity traffic in optical networks

We propose a novel switching architecture of multigranularity optical cross-connects (MG-OXCs) for dealing with multigranularity traffic in the optical domain. MG-OXCs can cooperate with the generalized multiprotocol label switching (MPLS) control plane, which provides the advantages of cost reduction, better scalability in physical size, and unified traffic management. Detailed discussions are provided on the characteristics and implementation issues for the switching architecture. Based on the proposed MG-OXCs, two routing and wavelength assignment (RWA) with tunnel allocation algorithms are presented: dynamic tunnel allocation (DTA) and capacity-balanced static tunnel allocation (CB-STA). In the former, we use fixed alternate routing with k-shortest paths to inspect network resources along each alternate path for dynamically setting up lightpaths. For the latter, fiber and waveband tunnels are allocated into networks at the planning stage (or off-line) according to weighted network link-state (W-NLS). We will show that with the proposed algorithms, the RWA problem with tunnel allocation in the optical networks containing MG-OXCs can be solved effectively. Simulation is conducted on networks with different percentages of switching capacity and traffic load. The simulation results show that DTA is outperformed by CB-STA in the same network environment due to a well-disciplined approach for allocating tunnels with CB-STA.. We also find that the mix of the two approaches yields the best performance given the same network environment apparatus.     

Routing and wavelength assignment in optical networks from edgedisjoint path algorithms

Routing and wavelength assignment (RWA) problems in wavelength-routed optical networks are typically solved using a combination of integer programming and graph coloring. Such techniques are complex and make extensive use of heuristics. We explore an alternative solution technique in the well-known maximum edge disjoint paths (EDP) problem which can be naturally adapted to the RWA problem. Maximum EDP is NP-hard, but now it is known that simple greedy algorithms for it are as good as any of the more complex heuristic solutions. In this paper we investigate the performance of a simple greedy maximum edge disjoint paths algorithm applied to the RWA problem and compare it with a previously known solution method     

Routing and wavelength assignment in all-optical networks

Considers routing connections in a reconfigurable optical network using WDM. Each connection between a pair of nodes in the network is assigned a path through the network and a wavelength on that path, such that connections whose paths share a common link in the network are assigned different wavelengths. The authors derive an upper bound on the carried traffic of connections (or equivalently, a lower bound on the blocking probability) for any routing and wavelength assignment (RWA) algorithm in such a network. The bound scales with the number of wavelengths and is achieved asymptotically (when a large number of wavelengths is available) by a fixed RWA algorithm. The bound can be used as a metric against which the performance of different RWA algorithms can be compared for networks of moderate size. The authors illustrate this by comparing the performance of a simple shortest-path RWA (SP-RWA) algorithm via simulation relative to the bound. They also derive a similar bound for optical networks using dynamic wavelength converters, which are equivalent to circuit-switched telephone networks, and compare the two cases. Finally, they quantify the amount of wavelength reuse achievable in large networks using the SP-RWA via simulation as a function of the number of wavelengths, number of edges, and number of nodes for randomly constructed networks as well as de Bruijn networks. They also quantify the difference in wavelength reuse between two different optical node architectures     

Routing and wavelength assignment in all optical networks using differential evolution optimization

The routing and wavelength assignment (RWA) problem, known to be an NP-complete problem, seeks to optimally establish routes and adequate wavelengths for the requested connections according to an objective function. This paper presents the use of a novel approach based on a differential evolution (DE) algorithm to the RWA problem in wavelength-routed dense division multiplexing (DWDM) optical networks. The proposed DE-RWA algorithm is modeled to optimize not only the network wavelength requirement ( $ NWR $ , which is the minimum number of wavelengths needed to fulfill traffic demand) but also the average path length ( $ APL $ ). We present the impact of the control parameters of the DE algorithm on the improvement of system’s performance. Additionally, we present two strategies to improve the efficiency of the algorithm, knowing as the disjoint cut-set paths (DCS-P) algorithm and the use of a random mutation ( $ random -M$ ) parameter for DE. The proposed approach is evaluated for test bench optical networks with up to 40 nodes. Experiments show that the DE-RWA algorithm obtains results that equal the $ NWR $ lower bound for networks with and without wavelength conversion capability, whereas reduce the $ APL $ . The performance of the DE-based approach is compared against results obtained with the particle swarm optimization (PSO) and genetic algorithm (GA) models, showing that the DE-RWA outperform those algorithms. The presented DE-RWA model is simple to implement and could also be extended by adding other features such as impairment-aware, energy efficient, survivability among others in optical networks.     

Routing and wavelength assignment in WDM all-optical networks

A new mathematical formulation of the routing and wavelength assignment in wavelength division multiplexing (WDM) all-optical networks is proposed. Which yields tight linear programming lower bounds on the wavelength requirements both theoretically and computationally. An efficient procedure computing lower bounds is also presented together preliminary computational results.     

Routing and wavelength assignment vs. wavelength converter placement in all-optical networks

Blocking has been the key performance index in the design of an all-optical network. Existing research demonstrates that an effective routing and wavelength assignment strategy and a proper wavelength converter placement algorithm are the two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately in that the existing RWA algorithms have seldom considered the presence of wavelength conversion, while the wavelength converter placement algorithms have largely assumed that a static routing and random wavelength assignment algorithm is employed. The main objective of this article is to present some strong evidence that these two issues need to be considered jointly, and call for the reexamination of both RWA and wavelength converter placement.     

XGM波长变换器网络的路由波长分配算法研究

交叉增益调制(XGM,Cross-Gain Modulation),用于波长变换技术,可较简单地制成全光波长变换器。该文先用一个简单的近似模型分析了XGM波长变换器对路径阻塞率的影响,进而根据其本身固有的特点,设计了3种适合于XGM波长变换器网络的路由波长分配算法。通过在美国科学基金会骨干网络(NSFNET,National Science Foundation backbone network),和网孔型(Mesh-torus)网络中的仿真,从网络的阻塞率和公平性两个方面研究XGM波长变换器对网络性能的影响,同时比较了3种算法的性能。仿真结果表明,XGM波长变换器较无波长变换,可以在网络的阻塞率和公平性两个方面都得到较大的改善;3种算法中,FF/lowest算法在改善网络的阻塞率和公平性两个方面都是最优的。     

Routing and wavelength assignment algorithms based on equivalent networks

In this paper, a Wavelength Division Multiplexing （WDM） network model based on the equivalent networks is described, and wavelength-dependent equivalent arc, equivalent networks, equivalent multicast tree and some other terms are presented. Based on this model and relevant Routing and Wavelength Assignment （RWA） strategy, a unicast RWA algorithm and a multicast RWA algorithm are presented. The wavelength-dependent equivalent arc expresses the schedule of local RWA and the equivalent network expresses the whole topology of WDM optical networks, so the two algorithms are of the flexibility in RWA and the optimization of the whole problem. The theoretic analysis and simulation results show the two algorithms are of the stronger capability and the lower complexity than the other existing algorithms for RWA problem, and the complexity of the two algorithms are only related to the scale of the equivalent networks. Finally, we prove the two algorithms＇ feasibility and the one-by-one corresponding relation between the equivalent multicast tree and original multicast tree, and point out the superiorities and drawbacks of the two algorithms respectively.     

Routing and wavelength assignment in optical WDM networks with maximum quantity of edge disjoint paths

In the present paper, routing and wavelength assignment (RWA) in optical WDM networks is discussed. Previous techniques based on the combination of integer linear programming based lpsolver and graph coloring are complex and require extensive use of heuristics such as rounding heuristic which makes them slow and sometimes practically not reasonable. Another method employs the greedy approach in graph theory for obtaining available edge disjoint paths. Even though it is fast, it produces a solution for any connection request which is far from the optimal utilization of wavelengths. We propose a novel algorithm, which is based on the maximum flow to have the maximum quantity of edge disjoint paths. Here, we compare the offered method with previous edge disjoint paths algorithms applied to the RWA. Comprehensive computer simulation shows that the proposed method outperforms previous ones significantly in terms of running time. Furthermore, the new method shows compatible or better performance comparing to others in number of wavelengths used.The earlier version was published in ICCS 2004, Poland (Krakow). This research was supported by the Ministry of Information and Communication, Korea under the Information Technology Research Center support program supervised by the Institute of Information Technology Assessment, IITA-2005-(C1090-0501-0019).     

Routing and time-slot assignment in optical TDM networks

Optical time-division multiplexing (O-TDM) networks can provide a finer bandwidth granularity than wavelength-division multiplexing networks, and will play an important role in future all-optical networks. Since optical buffers are expensive, a small buffer size will be the characteristic of O-TDM systems. This paper analyzes the problem of routing and time-slot assignment in O-TDM networks. The results lead to the proposal of a Dijkstra-like shortest-path routing scheme that intends to maximize the performance of an optical network with a small number of optical buffers. Performance evaluation of the proposed scheme is also presented.     

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.     

On dynamic wavelength assignment in wavelength-convertible multi-granular optical networks

In this paper, we study the dynamic wavelength assignment problem in waveband-switched (WBS) networks composed of wavelength-convertible multi-granular OXCs (MGOXCs). With the aim to minimize the extra port consumption and utilize wavelength converters in an efficient manner, we propose a heuristic wavelength assignment algorithm named Least Weighted Configuration Cost (LWCC).WAPG, an algorithm proposed in previous literature, is compared with LWCC in both blocking performance and converter utilization. Numerical results show that LWCC offers more benefit in waveband grouping, which results in significant improvement in terms of blocking probability.     

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。     

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.     

The scheduling and wavelength assignment problem in optical WDM networks

We consider a scheduling problem, which we call the scheduling and wavelength assignment (SWA) problem, arising in optical networks that are based on the wavelength-division-multiplexing (WDM) technology. We prove that the SWA problem is NP-complete for both the preemptive and the nonpreemptive cases. Furthermore, we propose two efficient approximation algorithms. The first is for the preemptive case and is based on a natural decomposition of the problem to the classical multiprocessor scheduling and open-shop problems. For the nonpreemptive case, we prove that a naive implementation of list scheduling produces a schedule that can be m times far from the optimum, where m is the number of processors (equivalently, WDM channels). Finally, we give a more refined version of list scheduling and we prove it to be a 2-approximation algorithm for both the off-line and the on-line contexts.     

路由与波长分配的RWA算法应用于光通信网络

随着科学技术的不断发展,光通信网络成为了网络技术的主要发展趋势,逐渐在通信网络中发挥出显著作用.现阶段,光通信网络中的光网络主要采用基于密集波分复用技术组成,一旦波分数量增加,光网络中的路由选择与波长分配问题就难以解决.本文详细阐述了分层图模型的概念,提出波长可变光网络中的动态RWA算法,并在此基础上分析了动态RWA算法的数值模拟,以在提高波长资源利用率的同时,降低网络阻塞率.     

WDM光网络中的组播波长分配算法研究

组播是一种应用广泛的点到多点或多点到多点的通信方式,光层组播以其独特优势引起了人们的关注和重视.在综合分类的基础上,对光网络组播波长分配算法的最新研究进展进行了归纳和总结,并对今后需重点研究的方向进行了展望.