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Yatin Chawathe

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Abstract:
Scattercast: An Architecture for Internet Broadcast Distribution

Yatin Chawathe

Despite the phenomenal success of the world wide web, one class of Internet applications that has yet to be satisfactorily realized is that of Internet broadcasting--the distribution of Internet content from one or more sources to a large number of simultaneous receivers. The traditional solution for this problem, IP multicast, has met with limited success due to a number of factors including manageability, lack of robust inter-domain multicast routing, scalability, and heterogeneity. Hence, rather than relying on the existence of a globally deployed multicast backbone, we propose a new model for Internet broadcasting where we view multi-point delivery not as a network primitive but rather as an application-level infrastructure service. Our architecture relies on a collection of strategically placed network agents that collaboratively form an overlay network of unicast interconnections on top of which a source distributes data to its receivers. Clients locate a nearby agent and tap into the session via that agent. This model effectively partitions the client set into a number of small data groups interconnected by robust unicast links. We call this communication model scattercast and the network agents that are central to this model ScatterCast proXies or SCXs.

We address two key challenges that arise out of such an infrastructural approach. First, to form an efficient overlay network of SCXs, we developed a protocol called Gossamer that groups clients with SCXs and builds a distribution network composed of unicast connections across SCXs. Second, to allow applications to distribute data on top of this overlay in a manner that is optimized for the specific application and end-user environments, scattercast develops a highly flexible and application-aware transport framework that incorporates the semantics of the application data into the transport protocol. We believe that this approach of explicit application-level infrastructure embedded within the network is a new and promising direction for adaptive Internet applications such as network broadcasting. In the future, we expect to see a greater proliferation of such infrastructural elements that enhance the Internet's capabilities while at the same time co-existing with the core IP architecture.


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