In this paper we study translucent optical networks as an alternative to fully transparent and fully opaque optical networks. In the former networks, a technique called sparse placement is used to overcome the lightpath blocking caused by the signal quality degradation, using much less regenerators, which must strategically be placed, in contrast to a fully opaque network. In this paper we propose a sparse placement algorithm based on two requirements. The first one is signal regeneration necessary to re-amplify, reshape, and retime the optical signals after some predefined transparent distance in order to successfully receive the signals at the destination node. The other is load balance of the traffic in the network aimed at efficient usage of the network capacity resources. We apply a distributed Dijkstra routing algorithm which dynamically changes weights of links during the process of locating regeneration capable nodes. We compare the performance of the proposed algorithm with commonly used sparse placement algorithms through simulation experiments. The benefits are such that load balancing of the network traffic is fully utilized, and with technological development it will be sufficient to equip up to 30% of nodes in the network with electronic regenerations in order to have the same performance as in an opaque network.
In this article, we study the blocking probability in a wavelength division multiplexing (WDM) based asynchronous bufferless optical burst switched (OBS) network, equipped with a bank of wavelength converters. Our analysis encloses two wavelength reservation schemes JIT (just-intime) and JET (just-enough-time), and two-class data rate. The contribution of our work includes: (i) derivation of an accurate model for blocking probability of lower priority bursts in case of a non-preempted model; (ii) provision of the analytical model for blocking probability calculation in the OBS network, which includes these variables: two signaling schemes, partial wavelength conversion, two-class data, traffic intensity, cross-connect speed, number of wavelengths in WDM fiber, number of fibers in the node, number of wavelength converters, and number of nodes in the path; (iii) simulation results, which show that partial wavelength conversion provide quite satisfactory quality of service. We compare performance in a single OBS node, under various sets of parameter values. The OBS network shows great flexibility in terms of used multiclass data, and there is no dependence on the used higher layer protocol.
In this paper we examine ex ante electronic communications market analysis in the European Union's regulatory framework. We start with the analysis of relevant markets in accordance with the 1998 regulatory framework. Then we examine the 2002 regulatory framework through the definition of relevant markets, market analysis, SMP analysis, and adoption of measures for market regulation. We briefly compare the new 2007 regulatory framework with the previous ones. At the end we analyze some drawbacks of market analysis according to EU directives that have occurred in practice
We propose a new routing and wavelength assignment scheme that improves the blocking probability of WDM networks and offers a very good utilizat ion of the networks resources. This heuristic results in high quality of service, prioritization of the LAN networks and lower installat ion costs compared with the traditional RWA algorith ms applied in WDM networks. It is based on the distributed Dijkstra sparse placement routing algorithm, first-fit wavelength reservation and traffic mu ltip lexing. We apply load balancing and a sparse electronic switch placement algorithm during the process of finding the optimal lightpath in order to reduce the number of dropped lightpath sessions to zero, min imize the number of opaque nodes and maximize the utilization of the network.
Since the issue of finding optimal signal routes imposes itself as one of the main challenges within the framework of optimal networks, this paper aims at illustrating the development of a new, mixed-integer mathematical model for solving the static routing and wavelength assignment (RWA) problem in optical WDM networks and presents the comparison of results obtained by heuristics and CPLEX commercial software. The objective function of the mathematical model is to minimise the blocking probability by maximising the number of successfully connected lightpaths. In obtaining the results of simulations, two WDM networks with full wavelength conversion nodes were tested. The proposed heuristics are the Variable neighbourhood search (VNS) and Tabu search (TS). Firstly, we compare the results obtained by these two heuristics and CPLEX on a lowcomplexity WDM network, aiming to determine whether these heuristics may yield results which approximate optimal results. Secondly, having illustrated that the heuristics provide satisfactory results, we run these heuristics on a high-complexity WDM network. The results indicate minor differences in blocking probability and show that in majority cases, VNS spends ten times less CPU time as opposed to TS. In conclusion, we argue that VNS heuristic is appropriate for resolving this static RWA problem.
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