On the Tomography of Networks and Multicast Trees

In this paper we model the tomography of scale free networks by studying the structure of layers around an arbitrary network node. We find, both analytically and empirically, that the distance distribution of all nodes from a specific network node consists of two regimes. The first is characterized by rapid growth, and the second decays exponentially. We also show that the nodes degree distribution at each layer is a power law with an exponential cut-off. We obtain similar results for the layers surrounding the root of multicast trees cut from such networks, as well as the Internet. All of our results were obtained both analytically and on empirical Interenet data

The Emergency Direct Mobile App: Safety Message Dissemination over a Multi-Group Network of Smartphones using Wi-Fi Direct

Nowadays, the Wi-Fi Direct technology is supported by most of smartphones on the market, and provides a viable solution to guarantee opportunistic communication among group of devices in a 1-hop range. However, the current specifications of the standard do not support the inter-group communication, which constitutes a key requirement for content-delivery applications like the public safety ones. In this paper, we provide an in-depth analysis of the utilization of the Wi-Fi Direct technology for safety message dissemination over emergency and post-disaster scenarios. Three main contributions are provided. First, we show the experimental results of the Wi-Fi Direct technology on a test-bed composed of multiple heterogeneous smartphones, and we analyze the main factors affecting the system performance, like the network setup overhead, the communication range and the network throughput. Second, we investigate how to create multi-group Peer-to-Peer (P2P) networks by leveraging on the presence of P2P relay devices, which are in charge of offloading the data among different P2P groups, although being connected to only one P2P group at a time. An analytical model is proposed in order to derive the optimal group switching time which provides the best trade-off between the multihop delay and the delivery rate, by taking into account the buffer size of the P2P Group Owners (GO) devices. Finally, we describe the implementation of the network formation algorithm within the Emergency Direct mobile application, which allows the multi-hop dissemination of instantaneous and geo-localized alert messages among the smartphones located in the scenario of the emergency