Blocking Probability Research Based On Improved Layered-Graph Model In Optical Networks

With the development of information technology, especially Internet, the business carried by communications network gradually changes from WWW, Email to P2P, real-time video communications and so on. The fiber, which has great bandwidth and excellent transmission characteristics, is the best physical media of high-capacity, high-speed transmission. With the emergence of new business and explosive growth of data services, optical network is also facing more challenges, different size of business and bandwidth capacity of transmission channel are difficult to match, and the bandwidth and capacity requirements continue to grow rapidly. In dynamic wavelength routed optical networks, a series of lightpath requests from the source nodes to destination nodes arrive randomly and hold on a random time, due to unavailable network resources, some lightpath requests may be denied (blocked). The blocking probability is an important indicator to measure the network performance and the service quality.According to these issues, the paper has studied those problems of the blocking probability in optical networks based on layered graph model. The main work and innovative contributions of this paper can be summarized as:Firstly, this thesis introduces the basic principle of layered graph, and then study a layered graph model to evaluate the blocking probabilities in Wavelength routed optical networks without wavelength converters. This approach assumes fixed routing with First-Fit wavelength assignment. Fredericks and Hayward’s method, Sanders’s method and Rapp’s method are analyzed and compared to calculate the equivalent Poisson traffic. Secondly, we propose an improved layered graph model, which using the blocking probability matching method instead of the original moment matching method to calculate the equivalent Poisson traffic. The simulation results in tandem, ring and mesh network topology indicate that the improved approach is more accurate than previous works.At last we expand the layered graph model to bandwidth-variable optical networks. The mathematical models in two conditions of spectrum-continuity and spectrum-discontinuity are derived. The effect of the spectrum resources should or not be continuous to the blocking probabilities are also analyzed.