Multicast

Alongside the purpose-built multicast protocols, we released reference implementations of a resilient distributed hash table and of DHT-based multicast — NUPastry, NUScribe, and a work-in-progress NUSplitStream — together with the libraries and APIs the protocols were built on.

In a conventional multicast tree, bandwidth availability falls as you climb toward the root, so under load the links near the top become the bottleneck. FatNemo and FatScribe borrowed Leiserson’s fat-trees from parallel computing to widen the overlay where the traffic concentrates.

Application-level multicast has to deliver a stream over a network of participants who join, leave, and fail constantly. This project asked what structure survives that churn — producing Nemo, a resilient multicast protocol, its fat-tree successor FatNemo, DHT-based variants, and a series of comparative studies of how overlay designs actually behave under realistic conditions.