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Item type:Publication, Access status: with files , WDM network planning and management(2010); The rapid growth of Internet as well as bandwidth-intensive networking applications such as video-on-demand or multimedia conferencing, raise new challenges in network planning and management, and hence requires extensive new research in high-bandwidth transport networks, of which optical networks employing WDM technology is a promising candidate. Therefore, in this thesis, we study several issues related WDM networks. It includes 1.) network planning and optimization for WDM networks, 2.) wavelength converter placement and wavelength assignment in wavelength converting networks, 3.) design and 4.) reconfiguration of logical topologies for IP over WDM networks, and 5.) survivability for multi-layer WDM networks.Publicationtype: Doctoral Thesis839 859 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A Pricing Approach to Distributed Resource Allocation in IP and Peer-to-Peer Networks(2008); This work presents a novel decentralised approach for the resource allocation in Peer-to-Peer (P2P) networks. By decomposing a global optimisation problem distributed algorithms are derived and their efficiency, fairness and stability are shown. The model is based on resource pricing for TCP/IP. Therefore, also P2P over IP networks are studied as cross-layer optimisation problem.Publicationtype: Doctoral Thesis571 450 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Congestion pricing as scalable, efficient and stable congestion control for future IP networks(2005); This dissertation focuses on the design of more powerful distributed congestion control algorithms for TCP/IP networks by utilizing the theory of Congestion Pricing as a mathematical framework. Congestion Pricing, a strategy based on economics and optimization theory, leads to a social optimum for the entire network while Maintaining low queue sizes and, at the same time, high utilization. Using control theory, the stability of congestion control algorithms is further evaluated.Publicationtype: Doctoral Thesis590 478 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Methodology for Parameterisation of Large Scale Network Simulations(2003); Network providers are confronted with the optimisation or extension of existing networks. This leads to new challenges for simulation-based network dimensioning. The first challenge is the realistic simulation of the existing network, where topology information and traffic measurements have to be considered. The second challenge is to predict how changes of the existing network will affect its performance: link capacities, queue management algorithms etc. are subject to changes to adapt the network to changing traffic requirements. The best strategy for enhancing or extending the network under consideration can be found by comparing the resulting benefits and disadvantages between the existing network and new alternatives. The simulation of existing networks is an inverse problem: (i) the network description and some measurements are given from the network provider; (ii) the number and the behaviour of clients must be derived from the given parameters. Considering this problem was motivated by an industry project "ERNANI" funded by the "Deutsches Forschungsnetz" (DFN) and the German Telekom. The author proposes a new methodology to solve the inverse problem. First, an algorithm for the allocation of clients is proposed. This algorithm efficiently controls the average traffic intensity. Second, a method is developed for matching higher-order moments of the simulated traffic to measurements made in existing networks. Two higher moment parameters were selected, that are of major importance in network engineering: the coefficient of variation and the Hurst parameter. Realistic network simulations are characterised by high complexity because internal states of protocols must be stored for each connection. Therefore, memory requirements and simulation speed are major issues in such simulations. One solution for this problem is to reduce the number of clients by increasing the activity of each client in order to keep the traffic characteristics unchanged. To asses the applicability and performance of this solution, critical network parameters are estimated as a function of the number of clients. The parameters considered are: average link load, loss probability, coefficient of variation of the packet inter-arrival times, Hurst parameter and average end-to-end delay. It is shown in this work that the number of clients, as well as the required memory, could be reduced by a factor of 4-8 without significant impact on the studied parameters. Reducing the number of clients by a factor of 8 the simulation speed increased by approximately 33 %. This work represents a major step towards realistic modelling and simulation of existing networks. The simulation results based on the presented methodology are very promising. The successful increase of the simulation efficiency represents one step towards the realistic simulation of current and future multi-Gbit networks.Publicationtype: Doctoral Thesis889 690