Simplifying large-scale communication networks with weights and cycles

PhDA communication network is a complex network designed to transfer information from a source to a destination. One of the most important property in a communication network is the existence of alternative routes between a source and destination node. The robustness and resilience of a network are related to its path diversity (alternative routes). Describing all the components and interactions of a large communication network is not feasible. In this thesis we develop a new method, the deforestation algorithm, to simplify very large networks, and we called the simplified network the skeleton network. The method is general. It conserves the number of alternative paths between all the sources and destinations when doing the simplification and also it takes into consideration the properties of the nodes, and the links (capacity and direction). When simplifying very large networks, the skeleton networks can also be large, so it is desirable to split the skeleton network into different communities. In the thesis we introduce a community-detection method which works fast and efficient for the skeleton networks. Other property that can be easily extracted from the skeleton network is the cycle basis, which can suffice in describing the cycle structure of complex network. We have tested our algorithms on the Autonomous System (AS)l evel and Internet Protocol address (IPA)le vel of the Internet. And we also show that deforestation algorithm can be extended to take into consideration of traffic directions and traffic demand matrix when simplifying medium-scale networks. Commonly, the structure of large complex networks is characterised using statistical measures. These measures can give a good description of the network connectivity but they do not provide a practical way to explore the interaction between the dynamical process and network connectivity. The methods presented in this thesis are a first step to address this practical problem

Network-provider-independent overlays for resilience and quality of service.

PhDOverlay networks are viewed as one of the solutions addressing the inefficiency and slow evolution of the Internet and have been the subject of significant research. Most existing overlays providing resilience and/or Quality of Service (QoS) need cooperation among different network providers, but an inter-trust issue arises and cannot be easily solved. In this thesis, we mainly focus on network-provider-independent overlays and investigate their performance in providing two different types of service. Specifically, this thesis addresses the following problems: Provider-independent overlay architecture: A provider-independent overlay framework named Resilient Overlay for Mission-Critical Applications (ROMCA) is proposed. We elaborate its structure including component composition and functions and also provide several operational examples. Overlay topology construction for providing resilience service: We investigate the topology design problem of provider-independent overlays aiming to provide resilience service. To be more specific, based on the ROMCA framework, we formulate this problem mathematically and prove its NP-hardness. Three heuristics are proposed and extensive simulations are carried out to verify their effectiveness. Application mapping with resilience and QoS guarantees: Assuming application mapping is the targeted service for ROMCA, we formulate this problem as an Integer Linear Program (ILP). Moreover, a simple but effective heuristic is proposed to address this issue in a time-efficient manner. Simulations with both synthetic and real networks prove the superiority of both solutions over existing ones. Substrate topology information availability and the impact of its accuracy on overlay performance: Based on our survey that summarizes the methodologies available for inferring the selective substrate topology formed among a group of nodes through active probing, we find that such information is usually inaccurate and additional mechanisms are needed to secure a better inferred topology. Therefore, we examine the impact of inferred substrate topology accuracy on overlay performance given only inferred substrate topology information