Several peer-to-peer systems for live streaming have been recently deployed (e.g. CoolStreaming, PPLive, SopCast). These all rely on distributed, epidemic-style dissemination mechanisms. Despite their popularity, the fundamental performance trade-offs of such mechanisms are still poorly understood. In this paper we propose several results that contribute to the understanding of such trade-offs.

We consider the problem of broadcasting a live stream of data in an unstructured network. The broadcasting problem has been studied extensively for edge-capacitated networks. We give the first proof that whenever demand lambda + epsiv is feasible for epsiv > 0, a simple local-control algorithm is stable under demand lambda, and as a corollary a famous theorem of Edmonds. We then study the node-capacitated case and show a similar optimality result for the complete graph. We study through simulation the delay that users must wait in order to playback a video stream with a small number of skipped packets, and discuss the suitability of our algorithms for live video streaming.

We consider distributed algorithms for solving a range of problems in a framework for trust in large-scale distributed systems. The framework is based on the notion of trust structures; a set of 'trust-levels' with two distinct partial orderings. In the trust model, a global trust-state is defined as the least fixed-point of a collection of local policies of nodes in the network. We show that it is possible to compute the global trust-state using a simple, robust and totally asynchronous distributed-algorithm. We also consider a distributed notion of proof-carrying-requests as a means of approximating the least fixed-point, enabling sound reasoning about the global trust-state without computing the exact fixed-point. Our proof-carrying-request model is different than the notion of proof-of-compliance from traditional trust-management; in particular, all proofs are efficiently verifiable or easily rejected, but, in the worst case, may require as much communication as computing the actual trust-state itself