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Abstract:

Abstract — All of the advantages of application-layer overlay networks arise from two fundamental properties: (1) The network nodes in an overlay network, as opposed to lower-layer network elements such as routers and switches, are end systems and have capabilities far beyond basic operations of storing and forwarding; and (2) The overlay topology, residing above a densely connected IP-layer wide-area network, can be constructed and manipulated to suit one’s purposes. In this paper, we seek to significantly improve end-to-end throughput in application-layer multicast by taking full advantage of these unique characteristics. This objective is achieved with two novel insights. First, we depart from the conventional view that data can only be replicated and forwarded by overlay nodes. Rather, as end systems, these overlay nodes also have the full capability of encoding and decoding data at the message level using efficient linear codes. Second, we depart from traditional wisdom that the multicast topology from source to receivers needs to be a tree, and propose a novel and distributed algorithm to construct a 2-redundant multicast graph (a directed acyclic graph) as the multicast topology, on which network coding is applied. We design our algorithm such that the costs of link stress and stretch are explicitly considered as constraints and minimized. We extensively evaluate our algorithm by provable analytical and experimental results, which show that the introduction of 2-redundant multicast graph and network coding may indeed bring significant benefits, essentially doubling the end-toend throughput in most cases. Index Terms — Application-layer overlay networks, network coding, application-layer multicast.

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