On Conflict-Free All-to-All Broadcast in One-Hop Optical Networks of Arbitrary Topologies

In this paper, we investigate the problem of all-to-all broadcast in optical networks, also known as gossiping. This problem is very important in the context of control plane design as it relates to status information dissemination. We present a routing and wavelength assignment (RWA) method to reduce the number of wavelengths such that the communication is conflict-free in a wavelength division multiplexing (WDM) optical environment without wavelength converters. Our approach utilizes the tap-and-continue capability of the optical nodes. The network topology is considered to be arbitrary as long as it is connected. Both cases of maximally and nonmaximally edge-connected graphs are studied. For the first case, we give a closed-form expression for the lower bound on the number of wavelengths, which is an elegant extension of the results in for concurrent broadcast trees in optical networks. Furthermore, we show how to achieve this bound. The second case is more involved and requires a specific procedure to achieve the minimum number of wavelengths. For this case, we provide an attractive method for the RWA algorithm that attempts to minimize the number of wavelengths. Our solution for this case is within a constant factor that is strictly less than 2 from the optimal solution. The proposed algorithm uses the concept of "cactus" representation of all minimum edge-cuts in a graph in a novel recursive approach.     

Dynamic Routing and Wavelength Assignment in Survivable WDM Networks

Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.     

Routing and wavelength assignment strategies in optical networks

We consider the routing and wavelength assignment (RWA) problem on wavelength division multiplexing (WDM) networks without wavelength conversion. When the physical network and required connections are given, RWA is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In WDM optical networks, there is need to maximize the number of connections established and to minimize the blocking probability using limited resources. This paper presents efficient RWA strategies, which minimizes the blocking probability. Simulation results show that the performance of the proposed strategies is much better than the existing strategy.     

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.     

Solving the routing and wavelength assignment problem in WDM networks for future planning - [Topics in optical communications]

In this article we define and analyze the routing and wavelength assignment problem by applying a virtual topology for both the optical network and the light paths. We introduce our developed algorithm to solve offline RWA problem. First the light path requests are constrained to repeated uniform distributed traffic. The reason is that this constraint permits us to study and analyze the behavior of the RWA problem. In addition, this constraint could be used as a benchmark to compare different algorithms. Then we relax the requests constraint to be non-uniform traffic. We show that the maximum number of assigned wavelengths depends on the number of traversed links, not on the shortest path length. Theorems are derived with proof to justify our algorithm. The effect of adding supplementary links to the WDM optical network is also explained to show how this approach could be used in the future planning for online operation. Finally, the result shows significant different in the number of wavelengths used compared to a recent backbone implemented network.     

On the routing and wavelength assignment in multifiber WDM networks

This paper addresses the problem of routing and wavelength assignment (RWA) in multifiber WDM networks with limited resources. Given a traffic matrix, the number of fibers per link, and the number of wavelengths a fiber can support, we seek to maximize the carried traffic of connections. We formulate the problem as an integer linear program (ILP), and show that the lightpaths selected by this formulation can indeed be established by properly configuring the optical switches. An upper bound on the carried traffic can be computed by solving the linear programming (LP)-relaxation of the ILP formulation. It is shown that this bound can be also computed exactly, and in polynomial-time, by solving a significantly simplified LP which considers only one wavelength. The bound can, thus, easily scale to an arbitrarily large number of wavelengths. Furthermore, we demonstrate that any instance of the RWA problem is also an instance of the more general maximum coverage problem. This allows us to take a greedy algorithm for maximum coverage and obtain an algorithm which provides solutions for the RWA problem that are guaranteed to be within a factor of (1-(1/e)) of the optimal solution. Each iteration of the greedy algorithm selects a set of lightpaths that realizes, using one wavelength, the maximum number of connection requests not previously realized. Computational results confirm the high efficiency of our proposed algorithm.     

An Ant-Based Approach for Dynamic RWA in Optical WDM Networks

In this paper, we propose a new ant-based algorithm for the dynamic routing and wavelength assignment (RWA) problem in optical WDM networks under the wavelength continuity constraint. Unlike conventional approaches, which usually require centralized global network information, our new RWA algorithm constructs the routing solution in a distributed manner by means of cooperative ants. To facilitate the ants’ foraging task, we adopt in our algorithm a probabilistic routing table structure for route selection. The new algorithm is highly adaptive in that it always keeps a suitable number of ants in the network to cooperatively explore the network states and continuously update the routing tables, so that the route for a connection request can be determined promptly by the current states of routing tables with only a small setup delay. Some new schemes for path scoring and path searching are also proposed to enhance the performance of our ant-based algorithm. Extensive simulation results upon three typical network topologies indicate that the proposed algorithm has a very good adaptability to traffic variations and it outperforms both the fixed routing algorithm and the promising fixed–alternate routing algorithm in terms of blocking probability. The ability to guarantee both a low blocking probability and a small setup delay makes the new ant-based routing algorithm very attractive for both the optical circuit switching networks and future optical burst switching networks     

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.     

Binary quadratic programming formulation for routing and wavelength assignment problem in all-optical WDM networks

Routing and wavelength assignment (RWA) is the most concern in wavelength routed optical networks. This paper proposes a novel binary quadratic programming (BQP) formulation for the static RWA problem in order to balance traffic load among a network links more fairly. Subsequently, a greedy heuristic algorithm namely variable-weight routing and wavelength assignment (VW-RWA) is proposed to solve the developed BQP problem. In this method, the weight of a link is proportional to the link congestion. Performance evaluation results for different practical network topologies show that our proposed algorithm can decrease the number of required wavelengths in the network, blocking rate and variance of used wavelengths in each link. Besides, it is shown that the number of required wavelengths to establish call requests for a given network topology can be reduced at lower cost compared to other heuristics.     

Multiple-Constraint-Aware RWA Algorithms Based on a Comprehensive Evaluation Model： Use in Wavelength-Switched Optical Networks

Because of explosive growth in Internet traffic and high complexity of heterogeneous networks,improving the routing and wavelength assignment (RWA) algorithm in underlying optical networks has become very important.Where there are multiple links between different the node pairs,a traditional wavelength-assignment algorithm may be invalid for a wavelength-switched optical networks (WSON) that has directional blocking constraints.Also,impairments in network nodes and subsequent degradation of optical signals may cause modulation failure in the optical network.In this paper,we propose an RWA algorithm based on a novel evaluation model for a WSON that has multiple constraints.The algorithm includes comprehensive evaluation model (CEM) and directional blocking constraint RWA based on CEM (DB-RWA).Diverse constraints are abstracted into various constraint conditions in order to better assign routing and wavelength.We propose using the novel CEM to optimize routing according to an assessed value of constraints on transmission performance.This eliminates the effects of physical transmission impairments in a WSON.DB-RWA based on CEM abstracts directional blocking conditions in multiple links between network nodes into directional blocking constraints.It also satisfies rigorous network specifications and provides flexibility,scalability,and first-fit rate for the backbone,especially in multiple links between WSON nodes.     

An algorithm for optimal assignment of a wavelength in a tree topology and its application in WDM networks

In this paper, we present a polynomial time algorithm that gives an optimal solution to the routing and wavelength assignment (RWA) problem in a tree topology. One of the major design issues in wavelength-division multiplexed networks is the assignment of the limited number of wavelengths among network stations so that greater capacity can be achieved. The problem of RWA is known to be NP-hard problem. Many researchers have tackled the problem of RWA with a number of efficient heuristic algorithms. This paper presents an algorithm that optimally assigns a single wavelength to maximize one-hop traffic in a tree topology. The algorithm uses dynamic programming and is shown to be optimal with a time complexity of O(N/sup 4/). We also propose a heuristic scheme to use our optimal algorithm for wavelength assignment in a general graph. The heuristic works on the tree subgraphs of a given graph and the remaining spare wavelengths can be assigned with an existing RWA policy.     

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 Optical Networks Using Logical Link Representation and Efficient Bitwise Computation

In this paper, we propose and evaluate a new approach for implementing efficient routing and wavelength assignment (RWA) in wavelength division multiplexing (WDM) optical networks. In our method, the state of a fiber is given by the set of free wavelengths in this fiber and is efficiently represented as a compact bitmap. The state of a multiple-fiber link is also represented by a compact bitmap computed as the logical union of the individual bitmaps of the fibers in this link. Likewise, the state of a lightpath is represented by a similar bitmap computed as the logical intersection of the individual bitmaps of the links in this path. The count of the number of 1-valued bits in the bitmap of the route from source to destination is used as the primary reward function in route selection. A modified Dijkstra algorithm is developed for dynamic routing based on the bitmap representation. The algorithm uses bitwise logical operations and is quite efficient. A first-fit channel assignment algorithm is developed using a simple computation on the bitmap of the selected route. The resulting bitwise routing algorithm combines the benefits of least loaded routing algorithms and shortest path routing algorithms. Our extensive simulation tests have shown that the bitwise RWA approach has small storage overhead, is computationally fast, and reduces the network-wide blocking probability. The blocking performance of our RWA method compares very favorably with three routing methods: fixed alternate routing, shortest path using flooding, and Dijkstra’s algorithm using mathematical operations. Our simulation experiments have also evaluated the performance gain obtained when the network access stations are equipped with finite buffers to temporarily hold blocked connection requests.     

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.     

Computing approximate blocking probabilities for a class ofall-optical networks

We study a class of all-optical networks using wavelength-division multiplexing (WDM) and wavelength routing, in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: fixed routing and least loaded routing     

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.

一种稀疏分光配置约束下的WDM网络多播RWA算法

在波长路由WDM网络中,波长路由和波长分配是RWA算法提高光网络阻塞性能的两个重要阶段和关键技术。文章针对现有的稀疏分光配置约束下的光网络多播RWA算法复杂度高、代价高的问题,提出了一种新的稀疏分光器配置的RWA多播算法。该算法摒弃传统RWA算法在波长路由阶段就考虑稀疏分光约束能力的惯性思维,论文首次提出在波长分配阶段,才通过多播长转换器实现满足稀疏分光约束条件的分光能力传递。仿真结果表明,所提算法在平均代价和所需波长数目方面都获得了较优的性能。     

一种新型的动态路由和波长分配算法

本文讨论了WDM光网中，在动态业务流量和有限范围波长变换情况下的动态路由和波长分配（RWA）问题，基于Moone-Dijkstra算法，考虑到动态波长变换的可能和限制，提出了一种新型的、可实现动态最小代价路由和最佳虚波长通道的综合启发式算法（DMC－OVMP）。该算法对路由子问题和波长分配子问题既相互独立，又相互结合，优化了RWA，保证了网络信息传输的安全性。对中国教育和科研计算机网（CERNET）基于本算法进行了计算机仿真，实现了低的网络阻塞率。     

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.     

A Study of Path Protection in Large-Scale Optical Networks

We consider the problem of designing a network of optical cross-connects (OXCs) which provides end-to-end lightpath services to large numbers of client nodes, under the requirement that the network will survive any single-link failure. Our main objective is to quantify the additional resource requirements of implementing path protection schemes over a network with no survivability properties. To this end, we present heuristic routing and wavelength assignment algorithms for dedicated path protection and two variants of shared path protection, and integrate them into the physical and logical topology design framework we developed in an earlier study. We apply our heuristics to networks with up to 1000 client nodes, with a number of lightpaths that is an order of magnitude greater than the number of clients, and for a wide range of values for system parameters such as the number of wavelengths per fiber, the number of optical transceivers per client node, and the number of ports per OXC. Our results provide insight into the relative resource requirements of dedicated and shared path protection schemes. We also find that, using shared path protection schemes, it is possible to build cost-effective survivable networks that provide rich connectivity among client nodes with only a modest additional amount of resources over a network with no survivability properties.