A socially aware caching mechanism for encounter networks

Managing community content in mobile communities is challenging, since informal groups may emerge spontaneously whenever opportunities exist. To deal with group dynamics, encounter based community support systems can be a solution. In encounter networks, peers exchange content whenever they physically meet, i.e., whenever peers are near to each other. To assure content availability within the community network, content needs to be replicated (cached) and continuously updated. A?well known drawback of this scheme is the fact that the resource usage can be quite high. In this paper we present new caching strategies based on sociological knowledge, aiming at improving the overall content quality. We derive mobility and connectivity aware cache policies and simulate their benefit for knowledge building with urban life simulations. Results show that context precision and recall can be greatly improved in comparison to traditional cache strategies applied in the majority of encounter networks.     

Distributed energy efficiency in future home environments

In this paper, a new architecture for sharing resources among home environments is proposed. Our approach goes far beyond traditional systems for distributed virtualization, like PlanetLab or grid computing, as it relies on complete decentralization in a peer-to-peer (P2P) like manner and, above all, aims at energy efficiency. Energy metrics are defined, which have to be optimized by the system. The system itself uses virtualization to transparently move tasks from one home to another to optimally utilize the existing computing power. We present an overview of our proposed architecture, consisting of a middleware interconnecting computers and routers in possibly millions of homes using P2P techniques. For demonstrating the potential energy saving of distributed applications, we present an analytical model for sharing downloads, which is verified by discrete event simulation. The model represents an optimistic case without P2P overhead and fairness. The model allows to assess the upper limit of the saving potential. An enhanced version of the simulation model also shows the effect of fairness. The fairer the system gets, the less efficient it is.     

Load-dependent energy saving in future home environments

Already hundreds of millions of PCs are found in homes, offering high computing capacity without being adequately utilized. This paper reveals the potential for energy saving in future home environments, which can be achieved by sharing resources, and concentrating 24/7 computation on a small number of PCs. We present three evaluation methods for assessing the expected performance. A?newly created prototype is able to interconnect an arbitrary number of homes by using the free P2P-library FreePastry. The prototype is able to carry out task virtualization by sending virtual machines (VMs) from one home to another, most VMs being of size around 4 MB. We present measurement results from the prototype. We then describe a general model for download sharing, and compare performance results from an analytical model to results obtained from a discrete event simulator. The simulation results demonstrate that it is possible to reach almost optimal energy efficiency for this scenario.     

Optimal server bandwidth for mobile video on demand

Multimedia services such as video-on-demand or Internet protocol television in mobile environments have established themselves in our daily lives, yet the obtained quality of service still leads to many open issues. One of them consists in minimizing the server bandwidth, and we recently proposed a novel patching scheme for transporting true video-on-demand called Hierarchical Patching, which minimizes the server bandwidth. In this paper, we present a new concept called Low Start, consisting of encoding the first part of a movie with a lower bitrate than the rest. In Hierarchical Patching, video parts at the beginning have a much higher probability to be transmitted than parts at the end. By using Low Start, we show that the overall server bandwidth can be drastically reduced. We furthermore investigate the impact of Low Start on the subjective quality of service as perceived by human observers, and show that, for mobile video, the optimal strategy is to encode a very short start time with a bandwidth as low as possible.     

Energy efficient peer-to-peer file sharing

This paper reveals the power saving potential of P2P file sharing in two cases; popular and unpopular files. For popular files, we derive, with regard to BitTorrent, an expression for the optimal time seeders should support leechers. For unpopular files, we extend an existing model by taking into account leechers?? power consumption dependent on the load. Leechers are assumed to build a temporary cluster within the P2P-overlay. We determine the required number of active leechers to cope with a given load and compare results from an analytical model to simulation. We demonstrate that it is possible to reach almost optimal energy efficiency for the download scenario by comparing the local case without cooperation with the distributed case where leechers cooperate.     

Serious storytelling – a first definition and review

Multimedia Tools and Applications - In human culture, storytelling is a long-established tradition. The reasons people tell stories are manifold: to entertain, to transfer knowledge between...