Transponder Tunability and Waveband Switching in Reconfigurable Optical Networks Open Access
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We investigate the blocking performance of all-optical reconfigurable networks with constraints on reconfiguration brought by Reconfigurable Optical Add/Drop Multiplexers (ROADMs) and tunable transponders. Considering a fully reconfigurable ROADM and limited tunable transponders at each ROADM port, we develop an analytical model to calculate call blocking probability in a network of arbitrary topology for two different models for transponder sharing within a node: Share-Per-Link and Share-Per-Node. In such a configuration, limited tunable transponders determine the set of wavelengths that can be added/dropped at a reconfigurable node. A lightpath can only be established if a transponder on both ends can tune to the same available wavelength along the route. We call this as wavelength termination constraint. The number of transponders (as many as ports) and the waveband size (the range of wavelengths over which a transponder is tunable) are the key parameters of the model assuming that wavebands are randomly assigned to transponders. We also present a heuristic algorithm for assigning wavebands to transponders at each node and modify the analytical model to approximate the performance of the algorithm. We present simulation results to validate our model and also show results for Share-Per-Link and Share-Per-Node models with various sets of parameters. We show that limited tunable transponders give the same performance with widely tunable transponders in terms of blocking. We also show that transponder wavelength/waveband assignment to limited tunable transponders is an important factor determining the blocking. We then show several algorithms for transponder wavelength/waveband assignment considering different kinds of traffic models (e.g., non-uniform traffic). With simulation results, we show that these algorithms improve the blocking performance of the network significantly. We then consider O-E-O conversions enabled in the network by the use of limited tunable transponders. Using two limited tunable transponders, first to drop a wavelength and then to add another wavelength at a node, a lightpath can be established on different wavelengths along its route. We call this technique multihopping. We develop several routing and wavelength assignment algorithms for fixed and alternate routing in order to find the nodes to do the O-E-O conversions if necessary. Using a graph model, these algorithms determine the best route on which the transponder and wavelength resources are the least exhausted. Finally, we investigate the waveband switching technique to reduce the switching costs of the network. In waveband switching, wavelengths are grouped and switched together as a waveband. We solve an optimization problem to find the minimum total number of wavebands required in a ring network. We show by numerical analysis that the sizes of switches can be reduced by a large amount using waveband switching compared to wavelength switching. Overall, this dissertation provides a detailed analysis on the performance of reconfigurable optical networks and investigates several design methods to improve the performance and reduce the cost.
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