As the operation of our fiber-optic backbone networks migrates from interconnected SONET rings to arbitrary mesh topology, traffic grooming on wavelength-division multiplexing (WDM) mesh networks becomes an extremely important research problem. To address this problem, we propose a new generic graph model for traffic grooming in heterogeneous WDM mesh networks. The novelty of our model is that, by only manipulating the edges of the auxiliary graph created by our model and the weights of these edges, our model can achieve various objectives using different grooming policies, while taking into account various constraints such as transceivers, wavelengths, wavelength-conversion capabilities, and grooming capabilities. Based on the auxiliary graph, we develop an integrated traffic-grooming algorithm (IGABAG) and an integrated grooming procedure (INGPROC) which jointly solve several traffic-grooming subproblems by simply applying the shortest-path computation method. Different grooming policies can be represented by different weight-assignment functions, and the performance of these grooming policies are compared under both nonblocking scenario and blocking scenario. The IGABAG can be applied to both static and dynamic traffic grooming. In static grooming, the traffic-selection scheme is key to achieving good network performance. We propose several traffic-selection schemes based on this model and we evaluate their performance for different network topologies.

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A novel generic graph model for traffic grooming in heterogeneous WDM mesh 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.

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

Sparse wavelength conversion and appropriate routing and wavelength assignment (RWA) algorithms are the two key factors in improving the blocking performance in wavelength-routed all-optical networks. It has been shown that the optimal placement of a limited number of wavelength converters in an arbitrary mesh network is an NP-complete problem. There have been various heuristic algorithms proposed in the literature, in which most of them assume that a static routing and random-wavelength assignment RWA algorithm is employed. However, the existing work shows that fixed-alternate routing and dynamic routing RWA algorithms can achieve much better blocking performance. Our study further demonstrates that the wavelength converter placement and RWA algorithms are closely related in the sense that a well-designed wavelength converter placement mechanism for a particular RWA algorithm might not work well with a different RWA algorithm. Therefore, the wavelength converter placement and the RWA have to be considered jointly. The objective of this paper is to investigate the wavelength converter placement problem under the fixed-alternate routing (FAR) algorithm and least-loaded routing (LLR) algorithm. Under the FAR algorithm, we propose a heuristic algorithm called minimum blocking probability first for wavelength converter placement. Under the LLR algorithm, we propose another heuristic algorithm called weighted maximum segment length. The objective of the converter placement algorithms is to minimize the overall blocking probability. Extensive simulation studies have been carried out over three typical mesh networks, including the 14-node NSFNET, 19-node EON, and 38-node CTNET. We observe that the proposed algorithms not only outperform existing wavelength converter placement algorithms by a large margin, but they also can achieve almost the same performance compared with full wavelength conversion under the same RWA algorithm.

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Wavelength converter placement under different RWA algorithms in wavelength-routed all-optical networks

Existing research demonstrated that an effective routing and wavelength assignment (RWA) scheme and a wavelength converter placement algorithm are the two primary vehicles for improving the blocking performance in a wavelength-routed all-optical network. However, these issues have largely been investigated separately, in particular, the RWA has seldom considered the existence of wavelength converters. In this paper, we argue perhaps for the first time, that an effective RWA algorithm needs to take into account the presence of wavelength conversion as the latter is usually done at much earlier stage during the capacity planning. We proceed to show that existing dynamic RWA algorithms largely fail in the presence of wavelength conversion. We then propose a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) RWA algorithm in conjunction with a simple heuristic wavelength converter placement algorithm called minimum blocking probability first (MBPF) that considers both the distribution of free wavelengths and the lengths of each route jointly. We further introduce an analytical model that can obtain the blocking performance of the proposed WLCR routing algorithm. Using both analysis and simulation, we carry out extensive numerical studies over the typical topologies including the ring, mesh-torus, and two mesh topologies, the 14-node NSFNET and the 19-node European Optical Network (EON); we compare the performance of proposed algorithm with a wide variety of existing routing algorithms including static routing, fixed-alternate routing and least-loaded routing algorithms. The results conclusively demonstrate that the proposed WLCR-FF algorithm can achieve much better blocking performance in the environment of sparse or/and full wavelength conversion.

/pdf/a-dynamic-rwa-algorithm-in-a-wavelength-routed-all-optical-2en80snxkp.pdf

A dynamic RWA algorithm in a wavelength-routed all-optical network with wavelength converters

We evaluate the performance of optical network designs using relatively few
				switch nodes at which wavelength conversion and electronic regeneration is possible.
				A simple heuristic for placing the fewest such nodes to reach a given blocking
				probability is based on the ranked frequency of shortest-path routes transiting each
				node. This strategy is found to be efficient in designing a translucent optical
				network with sparse electronic switch placement that performs very close in blocking
				to that of an opaque optical network. In addition, we apply a new two-dimensional
				Dijkstra algorithm for routing and wavelength assignment in the resultant
				translucent optical network. Simulation results indicate that a translucent optical
				network with sparse electronic switch placement based on the heuristic has much
				lower blocking than a fully transparent optical network when the constraint of the
				maximum transparent distance before regeneration is also considered. Moreover, when
				the switches are placed according to the heuristic, lightpath blocking can approach
				that of a fully opaque network with significantly fewer total electronic switches.
				In our results, lightpath blocking as low as that with the fully opaque network case
				was obtained with electronic switches selectively placed at approximately one node
				in three on average. The heuristic also performs well against random searching for
				an effective subset of electronic switch nodes and performs better than a prior
				optimal method that is based on a combinatorially exhaustive search and that is
				limited to assuming fixed shortest-path routing.

Sparse placement of electronic switching nodes for low blocking in translucent optical networks

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength converters play an important role in enhancing the fiber utilization and reducing the overall call blocking probability of the network. As the distortion of the optical signal increases with the increase in the range of wavelength conversion in optical wavelength converters, limited range wavelength conversion assumes importance. Placement of wavelength converters is a NP complete problem in an arbitrary mesh network. In this paper, we investigate heuristics for placing limited range wavelength converters in arbitrary mesh wavelength routed optical networks. The objective is to achieve near optimal placement of limited range wavelength converters resulting in reduced blocking probabilities and low distortion of the optical signal. The proposed heuristic is to place limited range wavelength converters at the most congested nodes, nodes which lie on the long lightpaths and nodes where conversion of the optical signals is significantly high. We observe that limited range converters at a few nodes can provide almost the entire improvement in the blocking probability as the full range wavelength converters placed at all the nodes. Congestion control in the network is brought about by dynamically adjusting the weights of the channels in the link thereby balancing the load and reducing the average delay of the traffic in the entire network. Simulations have been carried out on a 12-node ring network, 14-node NSFNET, 19-node European Optical Network (EON), 30-node INET network and the results agree with the analysis.

M. Shivakumar

Papers

A heuristic for placement of limited range wavelength converters in all-optical networks