Internet broadcasting--the simultaneous distribution of live content streams to a large audience--has a number of interesting applications ranging from real-time broadcasts of audio/video streams for online concerts or sporting events to efficient and reliable large-scale software distribution. We identify three fundamental requirements for scalable broadcasting services: an efficient infrastructure for large-scale broadcasting, an ability to adapt the infrastructure to suit the requirements of a wide range of applications, and ease of deployment of the infrastructure. Although solutions such as the network-layer IP multicast approach and a slew of overlay distribution networks exist today, none of these technologies satisfactorily address all of the above concerns.

In this paper, we argue that an application-customizable hybrid overlay is well-suited to meet these challenges. To this end, we propose an architecture called scattercast that relies on a network of strategically located agents called ScatterCast proXies or SCXs. These agents collaboratively provide the broadcast service for a session. Clients locate a nearby SCX and tap into the session via that SCX. Scattercast constructs a hybrid overlay network composed of unicast links between SCXs that interconnect locally-scoped multicast regions. Rather than define a single standardized service model for transmitting data on top of the overlay, scattercast builds a customizable transport framework that provides adaptability by leveraging application-defined semantics to drive the distribution of content. We demonstrate the ability of our architecture to provide efficient distribution via a set of simulation experiments. Finally, we present our experience with the adaptability of the framework by describing two applications, a real-time Internet radio and an online slide presentations tool, both of which we have built on top of a prototype implementation of the architecture.

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