A framework for the characterization and analysis of software systems scalability

The term scalability appears frequently in computing literature, but it is a term that is poorly defined and poorly understood. It is an important attribute of computer systems that is frequently asserted but rarely validated in any meaningful, systematic way. The lack of a consistent, uniform and systematic treatment of scalability makes it difficult to identify and avoid scalability problems, clearly and objectively describe the scalability of software systems, evaluate claims of scalability, and compare claims from different sources. This thesis provides a definition of scalability and describes a systematic framework for the characterization and analysis of software systems scalability. The framework is comprised of a goal-oriented approach for describing, modeling and reasoning about scalability requirements, and an analysis technique that captures the dependency relationships that underlie typical notions of scalability. The framework is validated against a real-world data analysis system and is used to recast a number of examples taken from the computing literature and from industry in order to demonstrate its use across different application domains and system designs

Secure, Efficient and Privacy-aware Framework for Unstructured Peer-to-Peer Networks

Recently, the advances in Ubiquitous Computing networks and the increased computational power of network devices have led designers to create more flexible distributed network models using decentralised network management systems. Security, resilience and privacy issues within such distributed systems become more complicated while important tasks such as routing, service access and state management become increasingly challenging. Low-level protocols over ubiquitous decentralised systems, which provide autonomy to network nodes, have replaced the traditional client-server arrangements in centralised systems. Small World networks represent a model that addresses many existing challenges within Ubiquitous Computing networks. Therefore, it is imperative to study the properties of Small World networks to help understanding, modelling and improving the performance, usability and resiliency of Ubiquitous Computing networks. Using the network infrastructure and trusted relationships in the Small World networks, this work proposes a framework to enhance security, resilience and trust within scalable Peer-to-Peer (P2P) networks. The proposed framework consists of three major components namely network-aware topology construction, anonymous global communication using community trust, and efficient search and broadcasting based on granularity and pro-active membership management. We utilise the clustering co-efficient and conditional preferential attachment to propose a novel topology construction scheme that organises nodes into groups of trusted users to improve scalability. Network nodes communicate locally without advertising node identity at a global scale, which ensures user anonymity. The global communication is organised and facilitated by Service Centres to maintain security, privacy and integrity of member nodes. Service Centres are allocated using a novel leader election mechanism within unstructured scalable P2P networks. This allows providing fair and equitable access for existing and new nodes without having to make complex changes to the network topology. Moreover, the scale-free and clustering co-efficient characteristics of Small World networks help organising the network layout to maintain its balance in terms of the nodes distribution. Simulation results show that the proposed framework ensures better scalability and membership management in unstructured P2P networks, and improves the performance of the search and broadcasting in terms of the average shortest path and control overhead while maintaining user anonymity and system resiliency