We propose a novel wavelength assignment algorithm that can establish lightpaths requiring the least wavelength conversions by chaining a minimum number of wavelength-continuous segments. Simulations show that our algorithm outperforms both first-fit and most-used schemes with large margins. Besides, moderate computational requirement and insignificant signaling overhead are also advantages of our algorithm.

In wavelength-routed optical networks, wavelength converters are considered as one of the most critical network resources because they can significantly reduce the blocking probability, but still remain quite expensive. Unfortunately, previous wavelength assignment algorithms have seldom considered their presence. Therefore, in this paper, we propose a novel dynamic algorithm that can minimize the number of wavelength translations. Our algorithm establishes lightpaths by connecting a minimum number of wavelength-continuous segments. We mathematically prove the correctness of our algorithm. Then, we carry out extensive performance evaluations over three typical topologies with full-range or limited-range converters to compare our proposed algorithm with first-fit and most-used algorithms. The simulations show that, to obtain similar blocking performance, our algorithm requires much fewer converters, or the same number of converters but with smaller conversion ranges. From another perspective, with the same conversion capacity, our algorithm can significantly improve the blocking performance. Our algorithm is also scalable due to its polynomial time complexity and insignificant local signaling overhead.

A CATV network which has a switched double star configuration, fiber to the home (FTTH) and full digital transmission has been tested to see the feasibility with one Head-End (HE), one Central Office (CO), one Distribution Center (DC), and 25 subscribers. Also POTS and NISDN services have been provided to 5 subscribers. Single mode optical fibers are fully deployed from a HE to subscribers. A PON with TDM/polling scheme has been implemented considering the economic issue. Also in the outside plant, we tried to use the existing facility including the in-house duct. This paper deals with the results of the trial and some issues on the operational view.

Atmospheric radio ducts can trap VHF/UHF radio waves and propagate them over long distances. 284.4625 MHz Japanese radio wave signal measurements show that the radio waves are propagated to Korea coastal regions when ground temperatures exceed 10C. This paper discusses the reasons for the existence of this critical temperature threshold.