Framework for waveband switching in multigranular optical networks: part I-multigranular cross-connect architectures

Optical networks using wavelength-division multiplexing (WDM) are the foremost solution to the ever-increasing traffic in the Internet backbone. Rapid advances in WDM technology will enable each fiber to carry hundreds or even a thousand wavelengths (using dense-WDM, or DWDM, and ultra-DWDM) of traffic. This, coupled with worldwide fiber deployment, will bring about a tremendous increase in the size of the optical cross-connects, i.e., the number of ports of the wavelength switching elements. Waveband switching (WBS), wherein wavelengths are grouped into bands and switched as a single entity, can reduce the cost and control complexity of switching nodes by minimizing the port count. This paper presents a detailed study on recent advances and open research issues in WBS networks. In this study, we investigate in detail the architecture for various WBS cross-connects and compare them in terms of the number of ports and complexity and also in terms of how flexible they are in adjusting to dynamic traffic. We outline various techniques for grouping wavelengths into bands for the purpose of WBS and show how traditional wavelength routing is different from waveband routing and why techniques developed for wavelength-routed networks (WRNs) cannot be simply applied to WBS networks. We also outline how traffic grooming of subwavelength traffic can be done in WBS networks. In part II of this study [Cao , submitted to J. Opt. Netw.], we study the effect of wavelength conversion on the performance of WBS networks with reconfigurable MG-OXCs. We present an algorithm for waveband grouping in wavelength-convertible networks and evaluate its performance. We also investigate issues related to survivability in WBS networks and show how waveband and wavelength conversion can be used to recover from failures in WBS networks

Routing and wavelength assignment in WDM optical networks

In this thesis, we focus on the routing and wavelength assignment problems in WDM all-optical networks. Since the general problem is difficult (NP-complete), we classify the problem into several models with different formulations. Our objectives are to analyze some subclasses of routing and wavelength assignment problems; to understand their special properties; to estimate algorithm bounds and performance; and, to design efficient heuristic algorithms. These goals are important because results that follow can help engineers design efficient network topologies and protocols, and eventually provide end-users with cost-effective high bandwidth.;We first study the off-line wavelength assignment problem in single fiber ring and tree networks: an optimal algorithm and an exact characterization of the optimal solution is given for binary and ternary tree topologies; an open problem based on path length restriction on trees, mentioned in the literature, is solved; and bounds are given for path-length and covering restrictions of the problem on ring networks. Then we consider multifiber optical networks, in which each link has several parallel fibers. We extend a stochastic model from the single-fiber case to the multifiber case and show that multifiber links can improve performance significantly. For some specific networks, such as ring and tree networks, we obtain some performance bounds. The bounds support our multifiber stochastic model conclusion. For practical importance, we also consider a WDM optical ring network architecture configuration problem as well as cost-effectiveness. We propose several WDM ring networks with limited fiber switching and limited wavelength conversion and these networks achieve almost optimal wavelength utilization. Attacking resource allocation within an WDM optical ring network to reduce overall equipment cost, we design a new algorithm and our simulation results indicate improvement of about 25%. This thesis also includes a new coloring problem partition-coloring and its applications.;In summary, the contributions in this thesis include several heuristic algorithms and theoretical tight upper bounds for both single fiber and multifiber all-optical networks. In particular, for ring networks we have proposed several network architectures to improve wavelength utilization and devised a new algorithm that combines routing and wavelength assignment to reduce hardware costs

A tabu search algorithm for sparse placement of wavelength converting nodes in optical networks

Cataloged from PDF version of article.All-optical Wavelength Division Multiplexing networks, providing extremely large bandwidths, are among the most promising solutions for the increasing need for high-speed data transport. In all-optical networks, data is transmitted solely in the optical domain along lightpaths from source to destination without being converted into the electronic form, and each lightpath is restricted to use the same wavelength on all the links along its path. This restriction is known as the wavelength continuity constraint. Optical wavelength conversion can increase the performance and capacity of optical networks by removing this restriction and relaxing the wavelength continuity constraint. However, optical wavelength conversion is a difficult and expensive technology. In this study, we analyze the problem of placing limited number of wavelength converting nodes in a multi- fiber network with static traffic demands. Optimum placement of wavelength converting nodes is an NP-complete problem. We propose a tabu search based heuristic algorithm for this problem. The objective of the algorithm is to achieve the performance of full wavelength conversion in terms of minimizing the total number of fibers used in the network by placing minimum number of wavelength converting nodes. Numerical results comparing the performance of the algorithm with the optimum solutions are presented. The proposed algorithm gives quite satisfactory results, it also has a relatively low computational complexity making it applicable to large scale networks.Şengezer, NamıkM.S

A heuristic for placement of limited range wavelength converters in all-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 [K.C. Lee, V.O.K. Li, IEEE J. Lightwave Technol. 11 (1993) 962-970] 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 optical signals is significantly high. We observe that limited range converters at 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), 28-node US long haul network, hypothetical 30-node INET network and the results agree with the analysis. (C) 2001 Elsevier Science B.V, All rights reserved

Resource allocation and scalability in dynamic wavelength-routed optical networks.

This thesis investigates the potential benefits of dynamic operation of wavelength-routed optical networks (WRONs) compared to the static approach. It is widely believed that dynamic operation of WRONs would overcome the inefficiencies of the static allocation in improving resource use. By rapidly allocating resources only when and where required, dynamic networks could potentially provide the same service that static networks but at decreased cost, very attractive to network operators. This hypothesis, however, has not been verified. It is therefore the focus of this thesis to investigate whether dynamic operation of WRONs can save significant number of wavelengths compared to the static approach whilst maintaining acceptable levels of delay and scalability. Firstly, the wavelength-routed optical-burst-switching (WR-OBS) network architecture is selected as the dynamic architecture to be studied, due to its feasibility of implementation and its improved network performance. Then, the wavelength requirements of dynamic WR-OBS are evaluated by means of novel analysis and simulation and compared to that of static networks for uniform and non-uniform traffic demand. It is shown that dynamic WR-OBS saves wavelengths with respect to the static approach only at low loads and especially for sparsely connected networks and that wavelength conversion is a key capability to significantly increase the benefits of dynamic operation. The mean delay introduced by dynamic operation of WR-OBS is then assessed. The results show that the extra delay is not significant as to violate end-to-end limits of time-sensitive applications. Finally, the limiting scalability of WR-OBS as a function of the lightpath allocation algorithm computational complexity is studied. The trade-off between the request processing time and blocking probability is investigated and a new low-blocking and scalable lightpath allocation algorithm which improves the mentioned trade-off is proposed. The presented algorithms and results can be used in the analysis and design of dynamic WRONs

TSCP: A tabu search algorithm for wavelength converting node placement in WDM optical networks

Sparse wavelength conversion can increase the performance of all-optical wavelength division multiplexing (WDM) networks signi cantly by relaxing the wavelength continuity constraint. In this paper, we study the wavelength converter placement problem in multi- ber networks with static traf c demands. We present a tabu search based heuristic algorithm. The objective of the algorithm is to satisfy all the traf c demands with the minimum total cost of bers achieved in the full conversion case, by placing minimum number of wavelength converting nodes. We also implement a greedy algorithm and compare the performances of these converter placement algorithms with the optimum solutions on a sample network. The Tabu search based algorithm achieves the optimum solution in 72% of the test cases and it increases the average number of wavelength converting nodes by less than 10% with respect to the optimum solution. The effect of the utilized routing scheme on the generated solutions and the correlation between the converter node locations and the amount of traf c passing through the nodes are also investigated. © 2005 IEEE