Abstract

Overlay networks have emerged as a powerful and highly flexible method for delivering content. We study how to optimize through-put of large, multipoint transfers across richly connected overlay networks, focusing on the question of what to put in each transmit-ted packet. We first make the case for transmitting encoded content in this scenario, arguing for the digital fountain approach which en-ables end-hosts to efficiently restitute the original content of size n from a subset of any n symbols from a large universe of encoded symbols. Such an approach affords reliability and a substantial de-gree of application-level flexibility, as it seamlessly tolerates packet loss, connection migration, and parallel transfers. However, since the sets of symbols acquired by peers are likely to overlap substan-tially, care must be taken to enable them to collaborate effectively. We provide a collection of useful algorithmic tools for efficient es-timation, summarization, and approximate reconciliation of sets of symbols between pairs of collaborating peers, all of which keep messaging complexity and computation to a minimum. Through simulations and experiments on a prototype implementation, we demonstrate the performance benefits of our informed content de-livery mechanisms and how they complement existing overlay net-work architectures.