Routing And Wavelength Assignment Algorithm Research Articles

An ant-based algorithm for distributed routing and wavelength assignment in dynamic optical networks

Future optical communication networks are expected to change radically during the next decade. To meet the demanded bandwidth requirements, more dynamism, scalability and automatism will need to be provided. This will also require addressing issues such as the design of highly distributed control plane systems and their associated algorithms to respond to network changes very rapidly. In this work, we propose the use of an ant colony optimization (ACO) algorithm to solve the intrinsic problem of the routing and wavelength assignment (RWA) on wavelength continuity constraint optical networks. The main advantage of the protocol is its distributed nature, which provides higher survivability to network failures or traffic congestion. The protocol has been applied to a specific type of future optical network based on the optical switching of bursts. It has been evaluated through extensive simulations with very promising results, particularly on highly congested scenarios where the load balancing capabilities of the protocol become especially efficient. Results on a partially meshed network like NSFNET show that the ant-based protocol outperforms other RWA algorithms under test in terms of blocking probability without worsening other metrics such as mean route length.

A New Proposal of an Efficient Algorithm for Routing and Wavelength Assignment in Optical Networks

The routing and wavelength assignment (RWA) algorithms used in optical networks are critical to achieve good network performance. However, despite several previous studies to optimize the RWA, which is classified as an NP-Hard, it seems that there is not, a priori, any solution that would lead to standardization of this process. This article presents the proposed RWA algorithm based on a Generic Objective Function (GOF) which aims to establish a base from which it is possible to develop a standard or multiple standards for optical networks. The GOF algorithm introduces the concept of implicit constraint, which guarantees a simple solution to a problem not as trivial as the RWA.

Analysis of Blocking Probability in Noise- and Cross-Talk-Impaired All-Optical Networks

In all-optical networks with no wavelength converters, signals are switched optically inside the nodes and therefore propagate over hundreds or thousands of kilometers with no electrical regeneration. Over such distances, physical impairments, such as intersymbol interference (ISI), amplifier noise, and leaks within nodes (cross-talk), accumulate and can lead to serious signal degradation, resulting in poor quality of transmission (QoT) as measured by signal bit-error rates. The role of routing and wavelength assignment (RWA) algorithms is to accommodate incoming calls in optical networks over a route and a wavelength. RWA algorithms block calls if a continuous wavelength from the source to the destination cannot be found (wavelength blocking) or when the QoT of the call is not acceptable (QoT blocking). Evaluating RWA algorithms via simulations is possible but time consuming, and hence analytical methods are needed. Wavelength blocking has been studied analytically in the past, but QoT blocking has never been analytically modeled to our knowledge. In this paper, we present an analytical method to evaluate blocking probability in all-optical networks, accounting for physical layer impairments. Our physical layer model includes ISI and noise, two static effects that only depend on the network topology, and also cross-talk, which depends on the network state. Simulations on three different topologies with various numbers of channels, representing small- to large-scale networks, show that our technique is suitable for quick and accurate dimensioning of all-optical networks: the accuracy of the blocking rates computed with the analytical method, taking only seconds or minutes to run, is the same as that of simulations, which take hours to run.

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.

Reducing the lightpath establishing time of FWM-aware dynamic RWA for wavelength-routed optical networks

A dynamic routing and wavelength allocation technique with an interplay between physical and network layer parameters encompassing Four-wave mixing (FWM) awareness and teletraffic performance of wavelength-routed optical networks has previously been proposed for a distributed approach. In this article, we present a fast computational algorithm for our routing and wavelength assignment (RWA) encompassing FWM-induced crosstalk. The objective is to minimize the time of establishing a dynamic lightpath. For this purpose, a precomputed matrix of FWM crosstalk products is used in an adapted version of the FWM-aware dynamic RWA algorithm. The approach is validated through simulations showing improvement up to 30–50% on the provisioning time of lightpaths for different network topologies compared to an online full computational scheme.

A survey on physical layer impairments aware routing and wavelength assignment algorithms in optical networks

Optical networks are moving from opaque and translucent architectures towards all-optical (transparent) architectures. In translucent architectures a small amount of regeneration (e.g. optical-electronic-optical conversion) is available in the network. The incorporation of the physical impairments in the routing and wavelength assignment (RWA) problem in transparent optical networks has recently received some attention from the research communities. This work compiles a comprehensive survey of the proposed algorithms that address this issue. The physical layer impairments and related classification in optical networks are initially presented followed by physical layer impairments (PLI) constrained and aware RWA algorithms. Algorithmic approach, current PLI-RWA proposals, impact of wavelength conversion on these algorithms, protection and resilience considerations, and proposed extensions to control planes are covered in this work. Further research topics are presented in this study.

On the performance of distributed lightpath provisioning with dynamic routing and wavelength assignment

Distributed lightpath provisioning in wavelength-division multiplexing (WDM) networks has gained wide research interests. In this article, we study the performance of distributed lightpath provisioning in WDM networks with dynamic routing and wavelength assignment (RWA). Specifically, we consider the case where routing of each lightpath is calculated based on globally flooded link-state information, and wavelength assignment is decided through local information exchanges. Simulation results show that such schemes steadily outperform those schemes with only global flooding or only local information exchanges. More significantly, the impacts of various factors on the proposed scheme, including RWA algorithm, network topology, number of wavelengths per fiber, global flooding interval, and traffic load, have been evaluated. Such evaluations help to achieve some insights useful for the future developments of efficient lightpath provisioning schemes.

Cross-layer adaptive routing and wavelength assignment in all-optical networks

In WDM all-optical networks where electrical regeneration is not available, physical impairments due to propagation in the fibers, amplifier noise, and leaks between channels and in the switches cannot be removed at the physical layer. These effects cause calls, especially between physically distant nodes, to be rejected because they cannot meet minimum Quality of Transmission (QoT) requirements, as measured by signal bit-error rates. It is possible to mitigate physical layer effects at the network layer using appropriate Routing and Wavelength Assignment (RWA) algorithms. We present new RWA algorithms which account for physical impairments in their design and increase QoT and fairness among users without sacrificing low blocking probabilities in metropolitan-sized networks. We also present RWA algorithms that can sharply decrease blocking probabilities in regional-sized networks using optional channel coding. All algorithms are evaluated through simulation in realistic scenarios and shown to successfully mitigate crosstalk effects and to perform better in terms of QoT and network access fairness than traditional algorithms.

Load balance RWA algorithm using statistical analysis in WDM mesh networks

This study investigates the routing and wavelength assignment (RWA) problem in all-optical wavelength division multiplexing (WDM) mesh networks. The RWA problems can be generally classified as static lightpath establishment (SLE) or dynamic lightpath establishment (DLE). Additionally, the Load Balance RWA (LBRWA) algorithm using the concept of root-mean-square (RMS) which is one of the statistical analysis methods is presented to solve the DLE problem in our study. The proposed algorithm evenly distributes the traffic loads between lightpaths in the RWA process. Simulation results indicate that the proposed algorithm has a lower blocking probability than the Least Loaded Routing algorithm (LLR) and the Maximum Channel Path Routing algorithm (MCPR).

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

The prediction-based routing in optical transport networks

In optical networks, the traditional routing problem is generally decoupled into two subproblems, the route selection and the wavelength assignment. Usual RWA (Routing and Wavelength Assignment) algorithms take the lightpath decision based on the network state information existing in those nodes caring about it. Unfortunately, this information might not be accurate enough so that the routing decisions could be incorrectly performed hence driving to a significant connection blocking increment. The mechanism proposed in this paper aims to optimize the network performance while reducing the signalling overhead required to keep updated network state information on all the network nodes. The novel idea introduced in the Prediction Based Routing allows lightpaths to be computed not according to the potentially inaccurate network state information but according to a prediction scheme. In this way, flooding update messages is not needed so that the signalling overhead is significantly reduced. After analyzing the PBR behaviour, we conclude that the PBR performs better than usual RWA algorithms (such as the Shortest-Path/Least-Loaded) in different scenarios of traffic loads and available resources.

Dynamic RWA Based on the Combination of Mobile Agents Technique and Genetic Algorithms in WDM Networks with Sparse Wavelength Conversion

Genetic Algorithms (GA) provide an attractive approach to solving the challenging problem of dynamic routing and wavelength assignment (RWA) in optical Wavelength Division Multiplexing (WDM) networks, because they usually achieve a significantly low blocking probability. Available GA-based dynamic RWA algorithms were designed mainly for WDM networks with a wavelength continuity constraint, and they cannot be applied directly to WDM networks with wavelength conversion capability. Furthermore, the available GA-based dynamic RWA algorithms suffer from the problem of requiring a very time consuming process to generate the first population of routes for a request, which may results in a significantly large delay in path setup. In this paper, we study the dynamic RWA problem in WDM networks with sparse wavelength conversion and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and GA. By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously update the routing tables, the new hybrid algorithm can promptly determine the first population of routes for a new request based on the routing table of its source node, without requiring the time consuming process associated with current GA-based dynamic RWA algorithms. To achieve a good load balance in WDM networks with sparse wavelength conversion, we adopt in our hybrid algorithm a new reproduction scheme and a new fitness function that simultaneously takes into account the path length, number of free wavelengths, and wavelength conversion capability in route selection. Our new hybrid algorithm achieves a better load balance and results in a significantly lower blocking probability than does the Fixed-Alternate routing algorithm, both for optical networks with sparse and full-range wavelength converters and for optical networks with sparse and limited-range wavelength converters. This was verified by an extensive simulation study on the ns-2 network simulator and two typical network topologies. The ability to guarantee both a low blocking probability and a small setup delay makes the new hybrid dynamic RWA algorithm very attractive for current optical circuit switching networks and also for the next generation optical burst switching networks.

Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks

Blocking probability has been one of the key performance indexes in the design of wavelength-routed all-optical WDM networks. Existing research has demonstrated that an effective Routing and Wavelength Assignment (RWA) algorithm and wavelength conversion are two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately; in particular the existing RWA algorithms have seldom considered the presence of wavelength conversion. In this paper, we firstly demonstrate that the existing dynamic RWA algorithms do not work well in the presence of wavelength conversion as they usually only take into account the current traffic, and do not explicitly consider the route lengths. We then propose a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) algorithm that considers both the current traffic load and the route lengths jointly. We further introduce an analytical model that can evaluate the blocking performance for WLCR algorithm. We carry out extensive numerical studies over typical topologies including ring, mesh-torus, and the 14-node NSFNET; and compare the performance of WLCR-FF with a wide variety of existing routing algorithms including static routing, fixed-alternate routing and least-loaded routing. The results conclusively demonstrate that the proposed WLCR-FF algorithm can achieve much better blocking performance in the presence of sparse or/and full wavelength conversion.

A Routing and Wavelength Assignment Algorithm in Optical Burst Switching Networks

One-way resources reservation and distributed control scheme are two notable features of routing and wavelength assignment (RWA) in optical burst switching (OBS) networks. These two features make the initial routing of bursts, i.e., the selection of the routes and wavelengths at source nodes, dramatically influence the network performance, especially the networks with limited-range wavelength conversions (LWCs). In this paper, we present a RWA algorithm called pre-defined lightpath RWA (PL-RWA). In PL-RWA, initial routing of bursts is precisely designed to avoid wavelength contentions at intermediate nodes. At the network design stage, for each source-destination pair (s,d), a dedicated set of alternate lightpaths is predefined to guide the initial routing of the bursts of (s,d). The alternate lightpaths subject to the wavelength continuous constraint and are clash free. Source node s will pour the bursts destined for d into the alternate lightpaths predefined for (s,d) as many as possible. For the bursts that cannot be carried by the alternate lightpaths, the shortest path of (s,d) is selected as the route and wavelengths are assigned hop-by-hop in real time. Using alternate lightpaths, the randomness and uncertainty of one-way resources reservation under distributed control are diminished. The selection of alternate lightpaths is formulated as an integer programming (IP) and solved by a heuristic algorithm based on tabu search. Simulation results obtained for NSFNET show that our algorithm, which can greatly reduce not only burst loss probability but also the number of used wavelength conversions, has advantage over the current algorithms.

A RWA Algorithm for Differentiated Services with QoS Guarantees in the Next Generation Internet based on DWDM Networks

A major challenge in next generation Internet (NGI) backbone networks based on dense-wavelength division multiplexing (DWDM) is the provision of guaranteed quality-of-service (QoS) for a wide variety of multimedia applications. This paper proposes a new routing algorithm called multi-wavelength minimum interference path routing (MW-MIPR) to provide more reliable QoS guarantees by consideration of the potential future network's congestion status. This improves wavelength utilization by choosing a route that does not interfere too much with potential future connection requests. Moreover, we introduce a differentiated routing and wavelength assignment (RWA) mechanism combined with recovery strategy and the proposed MW-MIPR algorithm based on the differentiated service model in the NGI. Simulation results show that the proposed MW-MIPR algorithm achieves a smaller blocking probability than dynamic routing (DR) that yields the best performance among previous RWA algorithms. And we prove that a differentiated RWA combined with a recovery capability together with the proposed routing scheme provides satisfied QoS assurance for each service class in terms of signal quality and survivability.

Adaptive Routing and Wavelength Assignment Algorithm for WDM Networks With Uniform and Non-Uniform Traffic Model

This letter studies routing and wavelength assignment (RWA) problem in wavelength-routed wavelength-division multiplexing networks with both uniform and nonuniform traffic model. Our research shows that the potential traffic load information is a crucial factor for routing algorithm design. Based on our analysis, an adaptive RWA algorithm is proposed. The simulation shows that the proposed algorithm performs much better than other adaptive RWA algorithms.

Routing and Wavelength Assignment in Multi-Segment WDM Optical Networks using Clustering Techniques

This paper studies the routing and wavelength assignment (RWA) problem in multi-segment optical networks. The notion of network segment is referred to any part of the network that requires special consideration of wavelength routing such as separate administrative domains in a large scale optical network, sub-networks run by various service providers, etc. In multi-segment optical networks, each segment has different resource availability or hardware characteristics. The differences between multi-segment optical networks and homogeneous optical networks are discussed. We then present a resource abstraction technique called blocking island and define a multi-segment blocking island graph (BIG) network model. Using a minimum splitting routing heuristic introduced in the context of the blocking island paradigm in conjunction with the multi-segment BIG model, we propose a general RWA algorithm that takes a combined view of the network resource to integrate routing, wavelength assignment and gateway selection in a single routing framework. In the simulation, we demonstrate the effectiveness of our proposed algorithm by comparing it with other state-of-the-art heuristics in this area.

Novel Adaptive Routing and Wavelength Assignment Algorithm for WDM Networks

This paper studies the routing and wavelength assignment (RWA) in wavelength-routed all optical Wavelength Division Multiplexing (WDM) networks. A conception named Link Multiplexing Degree is introduced in our research and a novel adaptive RWA algorithm named MinSum is proposed following our theory analysis. MinSum considers more network state information than other adaptive RWA algorithms while the calculation process is more reasonable. The simulation result shows that MinSum performs better than its counterparts and the network performance can be improved significantly by this novel algorithm.

Nature-Inspired Routing and Wavelength Assignment Algorithms for Optical Circuit-Switched Polymorphic Networks

Polymorphic optical networks simultaneously support several optical switching paradigms over a single physical network. In this way, they provide service differentiation at the optical layer by employing the most appropriate paradigm for each service. One type of such architecture is the optical circuit-switched polymorphic network (OCSPN), which combines optical circuit switching paradigms with different grades of dynamism. The performance of this network relies on the utilization of efficient routing and wavelength assignment (RWA) algorithms. In this article, we review the fundamentals of OCSPNs and present a set of efficient RWA algorithms based on ant colony optimization and genetic algorithms.

Routing and wavelength assignment of scheduled lightpath demands

We present algorithms that compute the routing and wavelength assignment (RWA) for scheduled lightpath demands in a wavelength-switching mesh network without wavelength conversion functionality. Scheduled lightpath demands are connection demands for which the setup and teardown times are known in advance. We formulate separately the routing problem and the wavelength assignment problem as spatio-temporal combinatorial optimization problems. For the former, we propose a branch and bound algorithm for exact resolution and an alternative tabu search algorithm for approximate resolution. A generalized graph coloring approach is used to solve the wavelength assignment problem. We compared the proposed algorithms to an RWA algorithm that sequentially computes the route and wavelength assignment for the scheduled lightpath demands.