Network environment for testing peer-to-peer streaming applications

Peer-to-Peer (P2P) streaming applications are an emerging trend in content distribution. A reliable network environment was needed to test their capabilities and performance limits, which this thesis focused on. Furthermore, some experimental tests in the environment were performed with an application implemented in the Department of Communications Engineering (DCE) at Tampere University of Technology. For practical reasons, the testing environment was assembled in a teaching laboratory at DCE premises. The environment was built using a centralized architecture, where a Linux emulation node, WANemulator, generates realistic packet losses, delays, and jitters to the network. After an extensive literature survey an extension to the Iproute2’s Tc utility, NetEm, was chosen to be responsible of the network link emulation at the WANemulator. The peers are run inside VirtualBox images, which are used at the Linux computers to keep the laboratory still suitable for teaching purposes. In addition to the network emulation, Linux traffic controlling mechanisms were used both at the WANemulator and VirtualBox’s virtual machines to limit the traffic rates of the peers. When used together, emulation and rate limitation resemble to the statistical behaviour of the Internet quite closely. Virtualization overhead limited the maximum number of Virtual Machines (VMs) at each laboratory computer into two. Also, a peculiar feature in VirtualBox’s bridge implementation reduced the network capabilities of the VMs. However, the bottleneck in the environment is the centralized architecture, where all of the traffic is routed through the WANemulator. The environment was tested reliable with the chosen streamed content and 160 peers, but by tuning the parameters in WANemulator bigger overlays might be achievable. In addition, a distributed emulation should be possible with the environment, but it was not tested. The results from the experimental tests performed with the P2P streaming application proved the application to be functional in an environment that has mobile network conditions. The designed network environment is tested to work reliably, it enables reasonable scalability and provides better possibility to emulate the networking characteristics of the Internet, when compared to an ordinary local area network environment. /Kir1

Achieving Autonomic Computing through the Use of Variability Models at Run-time

Increasingly, software needs to dynamically adapt its behavior at run-time in response to changing conditions in the supporting computing infrastructure and in the surrounding physical environment. Adaptability is emerging as a necessary underlying capability, particularly for highly dynamic systems such as context-aware or ubiquitous systems. By automating tasks such as installation, adaptation, or healing, Autonomic Computing envisions computing environments that evolve without the need for human intervention. Even though there is a fair amount of work on architectures and their theoretical design, Autonomic Computing was criticised as being a \hype topic" because very little of it has been implemented fully. Furthermore, given that the autonomic system must change states at runtime and that some of those states may emerge and are much less deterministic, there is a great challenge to provide new guidelines, techniques and tools to help autonomic system development. This thesis shows that building up on the central ideas of Model Driven Development (Models as rst-order citizens) and Software Product Lines (Variability Management) can play a signi cant role as we move towards implementing the key self-management properties associated with autonomic computing. The presented approach encompass systems that are capable of modifying their own behavior with respect to changes in their operating environment, by using variability models as if they were the policies that drive the system's autonomic recon guration at runtime. Under a set of recon guration commands, the components that make up the architecture dynamically cooperate to change the con guration of the architecture to a new con guration. This work also provides the implementation of a Model-Based Recon guration Engine (MoRE) to blend the above ideas. Given a context event, MoRE queries the variability models to determine how the system should evolve, and then it provides the mechanisms for modifying the system.Cetina Englada, C. (2010). Achieving Autonomic Computing through the Use of Variability Models at Run-time [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/7484Palanci