Motivation and Approach

For streaming oriented applications, where timely data delivery is a key requirement, trees are generally considered the preferred overlay structure. However, when employed for bandwidth-demanding applications, such as video conferencing and multi-party games, basic trees are likely to be bandwidth constrained. Because bandwidth availability monotonically decreases as one ascends from the leaves, under high load, paths near the root tend to become the bottleneck and dominate delivery latencies. Once these links become heavily loaded or overloaded, packets start to be buffered or dropped.

We import the concept of fat-trees from parallel architectures into the realm of overlay networks to address the bandwidth constraints of conventional trees. We have implemented two novel protocols, FatNemo and FatScribe, that adopt the fat-tree approach for performance-centric and DHT-based overlay multicast systems. Through simulation and wide-area experimentation with these two and some alternative protocols, we have show that the proposed fat-tree approach for overlay multicast (i) lowers the forwarding responsibility of nodes, thus increasing system scalability to match the demands of high-bandwidth multicast applications; (ii) reduces the height of the forwarding tree, hence significantly shortening delivery latencies; and (iii) improves the system's robustness to node transiency by increasing path diversity in the overlay.





  • The Nixes Tool Set - A set of bash scripts to install, maintain, control and monitor applications on PlanetLab.

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