Underwater sensor networks are a very interesting case of wireless communication in extreme conditions. They exploit acoustic communication in the water and are nowadays used in surveillance and monitoring applications. These networks present very challenging aspects, such as low data rates and large delays, as well as the special propagation characteristics of the underwater medium. We propose an integer-linear programming approach to jointly optimize routing, link-scheduling and node placement in such a scenario. Accounting for these special aspects of underwater wireless communications leads to re-thinking traditional approaches; this results in original solutions, which highlight novel directions for further research in this area
All-optical networks with multiple fibers lead to several interesting optimization problems. In this paper, we consider the problem of minimizing the total number of fibers necessary to establish a given set of requests with a bounded number w of wavelengths, and the problem of maximizing the number of accepted requests for given fibers and bounded number w of wavelengths. We study both problems in undirected tree networks T = (V, E) and present approximation algorithms with ratio 1 + 4|E| log |V |/OPT and 4 for the former and with ratio 2.542 for the latter. Our results can be adapted to directed trees as well.
In all-optical networks with wavelength division multiplexing, every connection is routed along a certain path and assigned a wavelength such that no two connections use the same wavelength on the same link. For a given set P of paths (a routing), let χ(P) denote the minimum number of wavelengths in a valid wavelength assignment and let L(P) denote the maximum link load. We always have L(P) ≤ χ(P). Motivated by practical concerns, we consider routings containing only shortest paths. We give a complete characterization of undirected networks for which any set P of shortest paths admits a wavelength assignment with L(P) wavelengths. These are exactly the networks that do not benefit from the use of (expensive) wavelength converters if shortest-path routing is used. We also give an efficient algorithm for computing a wavelength assignment with L(P) wavelengths in these networks.
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