· · · Institutional Repository

Growth and preferential attachment are the two ingredients of the scale-free network. Based on the Barabási-Albert scale-free model, we construct a more general model by replacing the linear preferential attachment with the nonlinear preferential attachment. We introduce different networks by controlling a parameter β which decides the preferential attachment of our model. We try to find the influence of β on the network structure and property. To study the influence, we investigate our model in three directions: topological characteristics, correlation of topological measures and attack vulnerability.

This thesis has two main topics. On the one hand it discusses how the robustness of a network can be increased as efficient as possible, where connectivity is treated as a robustness measure. On the other hand It treats capacity management of a network when it is still in its design phase. In particular, it shows how bandwidth management can be done on the network edges, while it also gives an implication to prioritize the vertices based on their relative importance. One of KPN's mobile core networks is treated as a case study.

As our dependency on communication increases so is the demand for protecting these communication lines. To provide failure-safe connections in optical networks, lightpaths can be protected. Protected lightpaths consist of a primary path and a backup path which are disjoint and ensure connection continuity in case of a single link failure. Optical networks consist of at least two layers, the optical layer and the physical layer. And although the primary and backup paths are disjoint in the optical layer, in the physical layer they may share the same fiber span or duct. These links are in the same Shared Risk Link Group (SRLG). If one link of a SRLG fails then all fail. Because of this, a single failure at the physical layer can causes multiple failures at the optical layer and protected paths could get disconnected if both paths have fibers in the broken fiber span. This thesis proposes an exact algorithm which finds the shortest SRLG-disjoint protected path in a network through an iterative approach.

Complex networks describe a wide range of systems and structures in the world. Any real network can be modeled as graph, expressed by an adjacency matrix or list. In many complex networks, when a graph of a certain type grows in size, its properties are expected to change. Each complex network presents specific topological features which characterize its individual properties and are influenced by the dynamics of processes executed on the network. The analysis of complex networks therefore relies on the use of measurements capable of expressing the most relevant topological features. Therefore, understanding and analyzing the properties of different sized graphs is a challenging topic in the research field. The objective of the thesis is to understand the evolving properties of growing networks. Therefore it focuses on comparison of topological metrics with different number of nodes and links. Growing graphs will be approached by two different schemes: preferential link attachment and random link attachment. Several common types of graph models are involved in the thesis. And we also consider different real-world network examples. With the analysis and comparison of numerical simulation results, we want to understand the changing tendency of topological metrics for evolving networks. In final, the thesis reveals different crucial factors affecting the evolving properties of growing network and concludes evolving properties based on both empirical and analytical results.

Offshore Communication Networks utilize multiple of communication technologies to eradicate any possibilities of failures, when the network is operational. Offshore Oil and Gas platforms and Wind parks (manned / unmanned) have strict and tight requirements for robust communication. Robustness of communication networks can be evaluated by the analysis of either transmission networks on the physical layer or by the network protocols and techniques run over the transmission network on higher layers. Offshore Oil and Gas facilities aim for continuous production to achieve the desired goals and a robust transmission network is very important to avoid production losses. In general, offshore transmission networks last for longer periods, which means transmission technologies must be robust with maximum availability against repair and replacement time and costs to evade interruptions, especially in catastrophic situations. But in reality a network can face multiple of problems, which can halt or interrupt communication for seconds, minutes, hours and in some cases days. In this thesis, the robustness of offshore transmission networks for Oil and Gas facilities is evaluated for normal and catastrophic situations to avoid maximum disruptions in communication by comparing three technologies (Optical, Microwave LOS, and Satellite communication) in terms of availability, repair and replacement time and costs, and by applying network graph theory to overcome technological differences. The results of the analysis show that the offshore transmission technologies have some predetermined trends, impacts and risks associated with different kind of manmade and natural hazards at different geographic locations, which can be prevented by applying network graph theory with a combination of transmission technologies for both normal as well as catastrophic situations. This thesis highlights the importance of robustness related to repair and replacement time and costs due to catastrophic calamities and will serve offshore industry to make an efficient decision while designing or extending transmission networks for offshore Oil and Gas facilities.