We describe a practical auditing approach designed to encourage fairness in peer-to-peer streaming. Auditing is employed to ensure that correct nodes are able to receive streams even in the presence of nodes that do not upload enough data (opportunistic nodes), and scales well when compared to previous solutions that rely on tit-for-tat style of data exchange. Auditing involves two roles: local and global. Untrusted local auditors run on all nodes in the system, and are responsible for collecting and maintaining accountable information regarding data sent and received by each node. Meanwhile, one or more trusted global auditors periodically sample the state of participating nodes, estimate whether the streaming quality is satisfactory, and decide whether any actions are required. We demonstrate through simulation that our approach can successfully detect and react to the presence of opportunistic nodes in streaming sessions. Furthermore, it incurs low network and computational overheads, which remain fixed as the system scales.

The use of Java for distributed systems and highavailable applications demands the validation of their fault tolerance mechanisms to avoid unexpected behavior during execution. We present an extension of FIONA (Fault Injector Oriented to Network Applications), a fault injection environment to experimentally validate the dependability of distributed Java applications. The main features of this extension are: its distributed architecture, which allows centralized configuration of multiple faults scenarios, and the support for a wider fault model associated with distributed systems, which includes network partitioning. For monitoring, FIONA supports the collection of log information and includes a helper application to integrate this information in a global log for post-mortem dependability analysis. FIONA is simple to operate, and we expect it will facilitate the conduction of validation experiments by application developers and testers.

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Peer-to-peer live streaming applications are becoming increasingly popular, and already reach millions of users worldwide. There are, however, many aspects in which these applications must evolve, among which video quality and security deserve particular attention. While the former is about to become a reality given recent advances in codecs and link bandwidth, the latter still presents great challenges. The decentralized nature of P2P live streaming systems makes them vulnerable to attacks, among which pollution is arguably the most harmful. Multimedia stream authentication allows the detection of polluted content and can help identifying malicious users, but its costs may be prohibitive. This paper presents an analytical evaluation of recent authentication mechanisms in light of their application in P2P live streaming. Its key contribution is to compare, unlike previous work, overheads and security of various signature amortization and light digital signature mechanisms for P2P live streaming of standard and high definition video. We demonstrate, contrary to previous work, that current authentication mechanisms do not scale in therms of quality, and are feasible in current hardware only with a favorable set of parameters. Our results justify the investigation of more efficient and adaptable approaches to the next generation of P2P streaming with secure, high definition video.

Due to their fundamental role in the design of faulttolerant distributed systems, consensus protocols have been widely studied. Most of the research in this area

Due to their fundamental role in the design of faulttolerant distributed systems, consensus protocols have been widely studied. Most of the research in this area